Term 1 Learning Objectives

Question 1

Explain the difference between anatomy and physiology.

Answer 1

Anatomy → structure of the body (at gross and fine (i.e., histologic) scales)

Physiology → study of function (i.e, how the dynamic processes of the body occur)

These are linked concepts; neither makes sense without the other!

Question 2

Use biological examples to illustrate key concepts in anatomy and physiology: structure/function, homeostasis, allostasis, and feedback.

Answer 2

• Structure determines function (e.g., space between bones indicates presence of muscles, tendons, ligaments and therefore motility)
• Homeostasis → ability to maintain a stable internal environment.
  
  • Requires a sensor/receptor to detect the change, a control centre to integrate the information, and an effector to ‘fix’ the problem)
• Allostasis → ability to adapt the set point (or behaviour) to meet different conditions (e.g., blood pressure set point changes based on activity; carb-loading by marathon runners = behavioural allostasis)
• Negative feedback loops → buffer changes - return variable to set point (e.g., blood glucose levels)
• Positive feedback loops → amplify changes - each cycle moves system further from initial stable point (e.g., blood clotting)

Question 3

Describe how curious features of our biology make (more) sense when considering development and evolution.

Answer 3

Bodies are products of development and evolution, both continuous processes.

For example, belly buttons only make sense if we consider development through time.

The recurrent laryngeal nerve is too long and only makes sense through consideration of the position of the larynx in modern and ancestral amphibians.

Evolution proceeds via natural and sexual selection, but it occurs within developmental constraints.

Question 4

Explain why the chemistry of water and of carbon are critical for biology using examples.

Answer 4

Water is the most important substance in the body because:

1. Water exists in different physical states at appropriate temperatures.
2. Lubrication → water reduces friction within joints and in body cavities, preventing injury
3. High heat capacity → helps maintain homeostasis
4. Solvent → water can dissolve many substances
5. Reactant and reaction medium → water is an ideal medium for biochemical reactions and sometimes participates as a reactant.
6. High surface tension → due to hydrogen-bonding between individual water molecules.

Carbon (with hydrogen) is a component of every organic compound → key molecule for life because:

1. Carbon can form four separate covalent bonds, enabling it to form rings, chains, and other extended structures.
2. Functional groups added to a carbon skeleton introduce different properties to the molecule.
3. Four types of carbon-containing (organic) molecules include:
   
   1. Carbohydrates
   2. Lipids
   3. Amino acids
   4. Nucleotides

Question 5

Compare and contrast the different ways that molecules and ions can move across cell membranes.

Answer 5

• Diffusion of water across a selectively permeable membrane down its concentration gradient = osmosis.
• Passive processes (no ATP required):
  
  • Diffusion
  • Carrier-mediated transport (carrier or channel proteins like aquaporin = facilitated diffusion)
• Active processes require ATP:
  
  • Vesicular transport → uses exocytosis or endocytosis to move molecules into/out of/ or through a cell
  • Primary carrier-mediated transport → uses energy from the decomposition of high energy compounds to move ions/molecules through ‘pump’ proteins against their concentration gradient.
  • Secondary carrier-mediated transport → ATP is consumed to generate a chemical gradient down which the target molecule can move; however, the energy is not used to directly move the molecule

Question 6

Describe how failure to regulate the cell life cycle can lead to tumours and cancers.

Answer 6

Cells, unless told otherwise, will continuously divide. A failure to tell a cell that they should remain in the ‘interphase stage’ (not dividing) would result in a cell that divides unchecked. Anytime a cell divides there is a possibility that they may acquire a mutation that disrupts their ability to control the rate of division (creating an abnormal cell) which is why cancer is most common in tissues where cell division happens rapidly and continuously (i.e., epithelium of the skin).

Benign neoplasms (a.k.a. tumour) → contained within one location and tend to grow slowly

Malignant neoplasms → grow rapidly and have the potential to invade and destroy nearby normal tissue, as well as spread throughout the body

Cancer occurs when neoplasms spread (= metastases)

Question 7

Describe the concentrations of sodium, potassium, chloride, and calcium across a cell membrane.

Answer 7

• [Sodium] → always higher outside cells
• [Chloride] → always higher outside cells
• [Potassium] → higher inside cells
• [Calcium] → higher outside cells

Question 8

Name the four main types of tissue and explain where in the body they are likely to be found.

Answer 8

The four main types of tissue are epithelial, connective, muscle, and nervous tissue.

• Epithelial → (1) Covers exposed surfaces, (2) lines internal passageways and chambers, and (3) forms secretory glands. Mucous membranes, integument (skin), surrounding organs. Will be found anywhere where a barrier to external space/environments are needed; for example, the skin creates a barrier between the environment that is external to the body versus that that is internal, and the surfaces of organs create barriers to environments that are external to the organs, for example the acidic environment of the abdominal cavity versus the internal space of the digestive organs.
• Connective → (1) Fills internal spaces, (2) provides structural support, and (3) stores energy. In tendons, ligaments, bones, blood, also ‘packing material’ of the body that is not an organ / muscle / nerve.
• Nervous → (1) Excitable tissue that (2) conducts electrical impulses, and (3) carries information. The nervous system is branching and reaches the majority of the body as it is what allows communication between different parts of the body, and also allows for the sensation of touch. Found in many places in the body including the integument, muscles, the brain and spinal cord, and organs.
• Muscle → (1) Excitable tissue that (2) contracts to produce movement and (3) includes skeletal muscle, cardiac muscle, and smooth muscle. It will be found in the arms, legs, abdomen, heart, amongst other places. Places where it wouldn’t be found would probably be the lumen of non-cardiac organs, and the epidermis.

Question 9

Compare and contrast the structure and general functions of different types of epithelial tissue, including glands.

Answer 9

Single layered epithelia are found in protected areas, whereas stratified epithelia are found in areas that have high physical and/or chemical stress. Similarly, epithelia with a greater apical surface compared to the lateral surface are more likely to be found in more protected areas, whereas epithelia with a smaller apical surface than lateral surface are likely to be found in areas with high physical and/or chemical stress.

• Epithelial structure: There are three different shapes that epithelial tissue comes in: squamous, cuboidal, and columnar. Additionally, each shape can be either stratified (with multiple cell layers), simple (with only one cell layer), or pseudostratified which consists of closely packed cells which appear to be arranged in layers but all of which in fact are attached to the basement membrane.
  
  • COLUMNAR: stratified or simple. can be found in the intestine; helps with absorption in the digestive, renal tracts; has cilia and microvilli.
  • CUBOIDAL: stratified or simple; found in the salivary glands, where it is stratified, as well as the kidney and pancreas (these are all compound gland sites, as well); helps with secretion and absorption.
  • SQUAMOUS: stratified or simple; found in the epidermis, where it is stratified; its form allows it to be tightly packed making a firm, linked barrier between outside and inside
  • PSEUDOSTRATIFIED COLUMNAR: found in the respiratory tract / trachea and helps filter air coming in and out; it is also contains cilia on its apical layer.
• Gland structure: Glands can either be simple (one duct), or compound (more than one duct). Examples of simple ducts are sweat glands, gastral glands, uterine glands, intestinal crypts. Examples of compound ducts are salivary glands, and pancreatic glands. Compound glands are normally found where high volumes are secreted.
  
  • Functions and types of glands:
    
    • EXOCRINE → specialized cells or groups of cells that secrete substances that reach the epithelial apical surface. Examples include sweat glands which help maintain thermal homeostasis, and sebaceous glands which lubricate surfaces of the body and keep moisture in while also forming a barrier against foreign substances
    • ENDOCRINE: secrete into the bloodstream and into the interstitial fluid. An example is the release of hormones within the body.
    • MEROCRINE: a mechanism by which a gland releases substances to external surfaces by exocytosis without actually destroying the gland cell (e.g., salivary galnds secrete mucin in vesicles)
    • APOCRINE: a mechanism of secretion whereby the gland releases chemicals to the external surface via the shedding of the apical surface and cytoplasm of the cell (e.g., milk production by mammary glands)
    • HOLOCRINE: a mechanism of secretion whereby the gland releases chemicals via the bursting (i.e., destruction) of the cell (e.g., sebum production by sebaceous glands)
    • GOBLET CELL: secretes mucin (forms mucous when mixed with water) to the internal passageways to protect internal epithelia; merocrine unicellular duct.

Question 10

Explain the basic definition of connective tissue and classify whether a tissue is a connective tissue or not based on a description.

Answer 10

Connective tissue is defined by the presence of extracellular protein fibres, and cells suspended within a ground substance. Types of connective tissue are diverse, but share the property of having relatively few cells that sit in or move through an extracellular matrix. All types of connective tissue are formed from mesenchyme, which is a loose embryonic tissue.

You can tell if something is or is not connective tissue based on a few descriptive factors. The obvious one is the relatively lower number of cells in connective tissue types; if you are looking at two microscopic images of tissue, connective tissue will be the one that has more ECF and fewer cells. Additionally, there will be a high number of protein fibres present in the matrix (either collagen, reticular, or elastic fibres).

Question 11

Compare and contrast the structure and general functions of different types of connective tissue.

Answer 11

There are three main types of connective tissue:

• CONNECTIVE TISSUE PROPER → tissue that has many types of cells and proteins. Either LOOSE, which creates a loose, open framework (reticular, adipose, or areolar), or DENSE where fibres are densely packed (elastic, regular, or irregular)
• FLUID → have distinctive cells that are suspended in a watery matrix with DISSOLVED proteins. Either BLOOD, which flows within the cardiovascular system, or LYMPH, which flows through the lymphatic system.
• SUPPORTIVE → has a LESS diverse cell population, and the matrix is much more densely packed (even more densely packed than dense connective tissue proper). Supportive tissue supports the placement of soft tissues / organs , holding things in place, and the position / weight of the body (skeletal system. It is made up of CARTILAGE which is a solid, rubbery matrix (includes hyaline, elastic, and fibro-cartilage), or BONE which is a solid, crystalline matrix.

How do connective tissue types COMPARE?

• All formed from mesenchyme, a loose and fluid embryonic tissue.
• All have an ECM, which is a nonliving substance made up of ground substance (flexible) and protein fibres which provide shape and structure.
• The presence of immature and mature cells of various types; -blasts. For example, fibroblasts, osteoblasts, and chondroblasts which are all immature, stem-type cells that secrete specific ground substances (chondroblasts for cartilage, osteoblasts for bone). The other end is the more mature cells, -cytes, like osteocyte, chondrocyte, etc, which maintain the health of the matrices which can sometimes revert back to their immature state if needed to create new ECM.
• The presence of macrophages

How do connective tissue types CONTRAST?

• Level of vascularization: for example, cartilage is avascular, whereas the dermis underlying the epidermis is heavily vascularized.
• Types of protein fibres vary in density and type
• The actual TYPES of immature and mature cells that create and maintain the ECM, as well as the types of fibres, and the amount of ground substance.
• Functions of the different types of connective tissue; supportive connective tissue in the form of bones supports the body weight, whereas loose adipose tissue provides padding and energy storage.

Question 12

Explain the difference between a tissue membrane and a fascia.

Answer 12

On the most basic level, membranes are physical barriers, and fasciae create internal compartments and divisions. That may sound quite similar in terms of function, but the two differ in both form and function.

• MEMBRANES are always formed from epithelial tissue + connective tissue, specifically areolar tissue (structure). They line or cover body surfaces to provide BARRIERS, which facilitate absorption, reduce friction, and provide protection from external environments (function)
• FASCIAE are connective tissue layers that are made up of connective tissue only. There are three types of fasciae; superficial (areolar and adipose), deep (dense irregular), and subserous (areolar) (structure). Fasciae does not facilitate absorption, but rather exists as a supportive packing material to create compartments when needed for structural purposes, or to provide form so that organs are held in place (other connective tissue types do this too) (function).

Question 13

Predict the consequences to the whole organism of a disruption of collagen synthesis.

Answer 13

Collagen aids in wound repair, dermis integrity, bone growth, bone matrix, outermost layers of blood vessels, amongst other functions in the body. Needless to say, it would be a big blow to the entire system if collagen synthesis was disrupted. Here are a few consequences that would occur:

• Skin thinning and dehydration; fine lines and wrinkles occur, elasticity of skin decreased (sagging), because collagen is the fibre that maintains much of the skin and provides its form
• Wounds would be slower to heal if less collagen was being synthesized, as collagen both triggers fibroblasts to the site of injury and also restores collagen to promote full skin regrowth and return the skin to its pre-wound rigidity and suppleness.
• Lots of other structures would also become weak, such as blood vessels and bones. The weakening would result from these structures having less connective tissue (in the form of collagen), which would reduce both their density and rigidity, make them more prone to breaks, etc.

To sum: collagen is important component of all sorts of connective tissues, so tissue would be prone to bruising as well. Barriers formed by epithelial and connective tissues could not be maintained due to lack of collagen production, so you would also be prone to infection because microorganisms could much more easily invade cells. Finally, the body would be a lot weaker due to loss of connective tissue holding muscles and joints together.

Question 14

Not all connective tissues have the same functions. Give examples of varying functions of connective tissues.

Answer 14

• Establish a structural framework for the body
  
  • Cartilage (flexible scaffolding)
  • Reticular (a web of tissue that supports soft organs)
  • Adipose (padding)
• Transport fluids and dissolved materials
  
  • Red blood cells and lymph
• Protect delicate organs
  
  • Reticular
• Support, surround, and interconnect other types of tissue
  
  • Reticular
• Store energy, especially in the form of triglycerides
  
  • Adipose
• Defend the body from invading microorganisms
  
  • White blood cells

Question 15

Explain at least four major functions of the integument and how these relate to the properties of the dermis, epidermis, and accessory structures.

Answer 15

Four major functions of the integument include: (1) regulation of thermal homeostasis, (2) providing a barrier against bacteria, viruses, and damage from the external environment, (3) fluid retention, and (4) the sensation of feeling.

• REGULATION OF THERMAL HOMEOSTASIS → relates to the eccrine and apocrine glands, which are accessory structures that begin in the dermis and move through the epidermis to release sweat to the external surface of the body. These glands promote evaporative cooling which helps regulate thermal homeostasis, however can also lead to dehydration in environmental conditions of heat with little access to water consumption. Additionally, hair follicles are an accessory structure that provide several functions including insulation.
• BARRIER AGAINST DAMAGE FROM EXTERNAL ENVIRONMENT → the stratified squamous epithelium that makes up the epidermis is tightly linked so it lets very little into the internal space of the body. The vascularization of the dermis allows for a quick response to any cuts or tears to the integument; the integument utilizes properties of fluid connective tissue (blood) such as the presence of macrophages to remove debris and other cells to prevent bacterial infection, as well as scab formation from blood platelets.
• FLUID RETENTION → the structure of the epithelial cells in the epidermis (squamous stratified) are tightly linked which prevents water from getting in or out, thereby keeping fluid inside your body. Additionally, sebaceous glands that release oil onto the surface of the skin and hair can provide a secondary barrier to keep fluid in, sort of like putting vaseline on something; it’s hard for water to move through it and evaporate.
• SENSATION OF FEELING → you are able to feel and sense your surroundings by touch / vibration from the external environment onto your skin. It is the part of your body that directly interacts with the external environment; thus, it is your gateway to the sensation of touch/feeling. This is supported in the integument by the innervation of the dermis; there are nerve endings throughout the dermis which respond to pressure and vibration and transport that sensory information to the brain, where it is communicated as sensation and a gateway to making sense of one’s environment.

Question 16

Explain the function of melanin and how melanocytes contribute to skin colour.

Answer 16

Melanin is a pigment that produces a darker skin tone (relative to baseline skin tone), and which is very important in protecting skin cells (keratinocytes) from sun damage. Under normal circumstances, sunlight has two important effects on skin cells: (1) it allows for the synthesis of Vitamin D (2) it can lead to damage to the DNA of the cell, which over time increases the likelihood of mutations that lead to uncontrolled cell division, resulting in neoplasms / cancer. This damage occurs because the UV photons are absorbed by DNA, which puts DNA into a higher, more reactive energy state, which is unable to be released safely and instead results in reactions with water and other DNA molecules (= damage). Contrastingly, when a skin cell is melanized it also absorbs UV photons from the sun, but it is able to SAFELY handle that energy by omitting it as heat. The downside of melanization is that it prevents the skin cell from absorbing and synthesizing vitamin D from the sun, which can lead to bodily consequences such as Rickets (not so much anymore, because vitamin D can be absorbed from food, and foods are now supplemented with Vitamin D).

Melanin gets into the cell this way → melanocytes in the dermis transfer portions of their cytoplasm, known as melanosomes, to keratinocytes in the upper epidermis. Melanosomes are packed with melanin. People with darker skin have MORE active melanocytes that produce MORE melanosomes MORE frequently to the keratinocytes. Additionally, different skin tones arise from different forms of the same pigment; people of Asian ancestry will have a different form of melanin than those from African history.

Question 17

Compare and contrast the processes of tissue repair in the dermis and epidermis.

Answer 17

DERMIS: repairs more slowly than epidermis, because it is forming new granulation tissue. Granulation tissue is a mixture of dividing mesenchymal cells, fibroblasts, and new blood vessels. Mast cell activation occurs in the dermis but not the epidermis; this is what results in the swelling around a new wound. Macrophages patrol the damaged areas, phagocytizing debris and pathogens. Extensive injuries result in the dermis repairing first. New capillaries form here

EPIDERMIS: repairs relatively more quickly via the proliferation of basal cells; the basal cells divide without daughter cells differentiating into keratinocytes, which allows for faster proliferation. The blood clot occurs here, restoring the integrity of the epidermis and restricting the entry of microorganisms in the area.

BOTH: Have a way to address pathogen and foreign body entrance to the body; dermis has macrophages, epidermis clots to form a scab and prevent entrance. Both dermis and epidermis are seeking to return skin to its pre-injury state, which is in a way homeostasis. Both responses involve the proliferation of cells in repair.

Question 18

Explain how skin and UV exposure are linked to Vitamin D and calcium homeostasis.

Answer 18

• Calcium and vitamin D are linked together in that vitamin D is converted to a hormone in the kidneys (= calcitriol) that is critical for calcium absorption. While calcium is not directly absorbed from UV exposure, calcium homeostasis DOES rely on UV exposure (in the absence of dietary vitamin D) as it cannot be absorbed without the hormone produced via vitamin D absorption.
• UV is absorbed in the spinosum and basale layers of the epidermis in the keratinocytes. UV interacts with a protein in the keratinocytes which results in an active form of vitamin D.

Question 19

Describe the effects of aging on the integument and analyze how this interacts with UV exposure.

Answer 19

Fewer melanocytes: melanocyte activity decreases and light skin people get very pale. When there’s less melanin in the skin, the integument becomes more sensitive to the UV rays because no melanin is present to absorb the harmful radiation. Sunburns are more likely. More UV absorption into the dermis = more DNA damage, DNA must be repaired, but DNA only has a limited amount of times it can repair itself successfully and accurately.

Thinning Epidermis: basal cell activity declines making skin thinner, which makes it more prone to injury and also decreases the skin’s metabolic abilities (it can’t make as much Vitamin D3 anymore)

Thinning Dermis: when the dermis thins it means there are less elastic fibres which weakens the structure of the integument causing wrinkles/sagging - most pronounced in areas that get the most sun

Question 20

Compare and contrast the role of skin in thermal and osmotic homeostasis.

Answer 20

There is a trade off between thermal and osmotic homeostasis in the skin, particularly in conditions where the external environment is warm/hot. This trade off exists because one of the skin’s roles in thermal homeostasis is in evaporative cooling; i.e., releasing the body’s heat as sweat, which cools the body by using energy to transform the sweat from a liquid to a vapour, cooling the surface of the body thereby cooling the body down. Contrastingly, another homeostatic pressure exists in hot environmental conditions as a result of evaporative cooling: dehydration. Osmotic regulation becomes more difficult when the body is losing water rapidly to cool down. A solution would be to increase water intake, as a form of behavioural homeostasis, to allow osmotic homeostasis and thermal homeostasis to regulate themselves simultaneously. If there is no water being consumed to encourage hydration, then osmotic homeostasis is preferred and evaporative cooling reduces, meaning you sweat less, feel hotter, but don’t pass out from lack of water. In COLD environmental circumstances, there is less of a trade off between thermal and osmotic homeostasis, because cold weather does not have a pressure on hydration (osmotic homeostasis), since the skin is not likely producing sweat. The skin also has a role in cold weather thermal homeostasis by having hair as insulation.

Comparisons: the skin controls both osmotic and thermal homeostasis by releasing (or not releasing) heat energy as sweat onto the surface of the skin. The goal in both cases is to maintain your body’s homeostasis.

Contrasting: the goal of maintaining one homeostasis makes the other homeostasis harder to obtain, and the regulation of either requires the sacrificing of the other, to some extent and dependent on conditions. (= trade off)

Question 21

Describe the five main anatomical components of the musculoskeletal system in terms of tissue type.

Answer 21

Bones, cartilage, ligaments, tendons, connective tissue

• Skeleton + muscles work together to support body weight & movement
  
  • Skeletal: support, protect tissues, store minerals, generates blood cells
  • Muscular: produce movement, support, generates heat
• Cartilage: supportive connective tissue w/ specialized support, found in surfaces between bones, ALSO in some non-bony cartilage (ears, nose)
• Ligaments: anchor BONES to bones
• Tendons: anchor MUSCLES to bones
  
  • BOTH = bands of fibrous, dense, regular, connective tissue -
• Bone: supportive connective tissue

Question 22

Compare and contrast the gross and fine anatomy of bone and cartilage with respect to structure and function.

Answer 22

Bone: the matrix in bone contains collagen (like cartilage) but also calcium salts, which makes it strong and relatively rigid. The matrix in bone is organized in concentric layers around blood vessels, in compact bone this is called osteons, in spongy bone it is called trabeculae. The medullary cavity (in the middle of the bone) contains bone marrow.

Bone cells:

• Osteogenic cells - undifferentiated bone cells - can become osteoblasts/osteocytes
• Osteoblasts - B for build, osteoblasts build new bone matrix
• Osteoclasts - C for chaos - osteoclasts destroy bone matrix - which releases calcium ions into the blood
• Osteocytes - bone cells within the matrix

Cartilage: cartilage is considered supporting connective tissue, provides flexible support for the body, and can be found between bones and also in some non-bony structures (like ears/nose). Cartilage is a solid rubbery matrix, and can be further subdivided into

• Hyaline cartilage - found between the tips of bones
• Elastic cartilage - support the ear + inner structures
• Fibrocartilage - dense and tough, found between vertebrae
• Chondrocytes (cartilage cells) are the only vascularized cells, and are found in the lacunae (holes in the matrix)
• Chondroitin sulfates combine with proteins to create proteoglycans, and form the matrix.

Bone and cartilage are grouped together because of the density/solidity of their extracellular matrix.

Question 23

Compare and contrast the different mechanisms of growth that occur in bone and cartilage, including when they can and cannot occur.

Answer 23

Bone Growth: bone in fetal growth → the first bones are formed by the ossification of the cartilage, which starts when blood vessels invade the cartilage, starting with long bones. Then the ossification creates concentric rings of bone around those blood vessels. First the ends (epiphysis) ossify, but the metaphysis (or shaft) remains cartilaginous, and grows via interstitial growth until puberty, which continues to elongate the shaft. Bone CANNOT grow anymore after puberty because the epiphyseal plate ossifies during puberty and creates a physical barricade to further elongation. (sesamoid bones are formed through the ossification of non-cartilaginous joints - patella is an ossified tendon)

Cartilage Growth: cartilage is the first thing to appear in a growing fetus. Both appositional (by adding new layers of tissues to the outside) and interstitial growth (growing from within) occur before birth. Interstitial growth occurs when the chondrocytes undergo division, then secrete additional matrix which creates physical distance between the chondrocytes, and the new matrix is formed. In appositional growth, cells differentiate into chondroblasts, which secrete new matrix and then mature into chondrocytes, adding new cells to the exterior.

Question 24

Explain the role of bone as a mineral reservoir and predict how bone cells will respond to changes in body calcium levels.

Answer 24

Bones are made of a collagen and calcium phosphate matrix which serve as a mineral reservoir, mainly for Calcium, that is regulated by hormones made by the parathyroid (PTH or parathyroid hormones) and the thyroid (calcitonin).

Calcium ions can be taken from the bloodstream and stored in the bones/ or removed from the bone matrix and put into the bloodstream in order to maintain homeostasis.

Balance between osteoblast and osteoclast activity maintains CA²⁺ homeostasis.

DECREASING BLOOD CA²⁺ LEVELS: parathyroid hormone is released and triggers increased osteoclast activity (it binds to osteoblasts and they release a hormone RANKL, that matures the osteoclasts so they can get to work). Increased osteoclast activity = more bone breakdown = more disposable Ca²⁺ ions to enter the bloodstream.

INCREASING CA²⁺ LEVELS: thyroid secretes calcitonin, which restricts osteoclast activity. Less osteoclast activity = less bone breakdown (balance between clasts and blasts is disrupted, so the osteoblasts are building more bone than osteoclasts are taking apart bone), so Ca²⁺ is turned into bone matrix, and removed from the bloodstream.

Question 25

Compare and contrast the processes and potential for repair in bone and cartilage.

Answer 25

BONE REPAIR: highly vascular 1. Blood clot is formed (fracture hematoma) 2. Osteogenic cells proliferate, newborn cells colonize the damaged area 3. First cartilage, then spongy bone appears 4. The ends (or cartilage and bone) reunite (usually within 2-4 weeks) 5. External colossus is visible, and it can take months-years for the spongy bone to reform into a compact bone. CARTILAGE REPAIR: avascular , rarely repairs itself in adulthood, and if/when it does it is only via appositional growth.

Question 26

Discuss the causes and treatments of osteoarthritis.

Answer 26

Osteoarthritis = caused by damage to articular cartilage (which we know can’t repair very well) a degenerative arthritis, the most common form, affecting mostly people 60+ as a result of cumulative wear and tear on joints or genetic factors affecting collagen formation. Treatment: a) regular exercise (more stress on the bones from the muscles pulling on them = more chances for the bones to rebuild) b) physical therapy (like massage of electrical stimulation TENS) c) anti-inflammatory drugs like aspirin d) last case scenario is artificial joints, which can restore mobility and relieve pain. Can last more than 15 years, but high impact activity is prohibited (jogging, running, playing sports)

Question 27

Explain the basic definition of muscle tissue and compare between its subtypes.

Answer 27

Muscle tissue is a tissue made from cells that are specialized to contract and produce movement/mechanical force. **Skeletal Muscle:** striated, voluntary and moves the body by pulling on bones. Also maintains body temp, provides stability in posture and body position, stores nutrients, guards body entrances and exits (sphincters) and supports soft tissue. **Cardiac Muscle:** striated, involuntary and found in the heart. Contractions allow blood to be pumped through blood vessels. **Smooth Muscle:** non-striated, involuntary, found in the walls of hollow organs like the digestive tract where it moves food and fluid along

Question 28

Describe the organization of skeletal muscle and the tissue types that is is made from.

Answer 28

From smallest to biggest: 1. Myofibrils (protein filament) bundled together create a muscle fiber, this is what is actually doing the contraction 2. Muscle fiber (myofiber) - contains multiple nuclei, surrounded by the endomysium 3. Endomysium - areolar connective tissue that surrounds each muscle fiber, contains capillaries, myosatellite cells (stem cells that repair damage) and axon of the neuron that controls the muscle fibers. 4. Many muscle fibers together = fascicle 5. Perimysium - fibrous layer that divides the fascicles from each other. Contains collagen and elastic fibers and also blood vessels and nerves that supply the muscle fibers within the fascicles 6. Many fascicles together = a muscle! Generally a fascicle is made up of 20-60 muscle fibers. 7. Epimysium - a dense layer of collagen that surrounds muscles to separate them from organs and surrounding tissue. Connected to deep fascia (dense connective tissue layer) 8. All muscles are surrounded by fascia.

Question 29

Contrast the features of a myofibre that make it unusual to the properties of most cells in the body.

Answer 29

\*\*Multiple nuclei\*\* - because they are developed through the fusion of myoblasts, the end product contains multiple nuclei. As many as 3000 per fiber! Myoblasts that don’t fuse into multinucleated myofibers become myosatellite cells (stem cells that repair damage) Significantly bigger than most other cells Plasma membrane in myofibers is called “SARCOLEMMA” and cell contains SARCOPLASM instead of cytoplasm

Question 30

Name the specialized parts of myofibers (including organelles and specializations of the cell membrane).

Answer 30

_myofiber_ - a muscle cell _sarcomere_- one full unit of a thin filament and a thick filament in a myofibre. (½ I-band + A band + ½ I-band) _sarcolemma_- the plasma membrane, the site that is closest to the NMJ and receives ACh binding, triggering sodium movement / depolarization _sarcoplasmic reticulum_ - like the cytoplasm but muscle specific, stores a bunch of calcium which it releases via the sodium binding to DHA protein which then moves the RYA (?) protein when sodium floods down from the t-tubules _myofibril_- the bundles of fibres that exist within a myofiber (20-100 per cell, i think) that are held by _endomysium_- a bundle as a unit is a fascicle. thin filament thick filament motor end plate neuromuscular junction nerve fibres blood vessels _myosatellite cells_ - stem cells that repair damaged muscle fibers (active in ‘bulking’) mitochondria

Question 31

Explain the role of neurotransmitters and membrane potential in muscle excitation and predict the effects of drugs that interfere with different stages.

Answer 31

Muscle excitation is reliant on a neuron releasing acetylcholine, a neurotransmitter, into the neuromuscular junction. The acetylcholine binds to nicotinamide channel proteins in the membrane of the skeletal muscle cell; these channels allow sodium to rush into the cell from the NMJ when a small increase in sodium ion membrane permeability leads to a set threshold of -55mV in neurons.

Question 32

Analyze why artificial stimulation is used to build and maintain muscles.

Answer 32

The electrical stimulation works at the level of the integument, sending an electrical pulse which simulates a nerve impulse that leads to muscle excitation. The muscle excitation will not be large enough to actually move a large muscle group, but it can work effectively for small contractions which do not strain other parts of the structure (like tendons and ligaments) which is great for injured athletes or bedridden individuals who do not want to add additional strain / weight strain onto fragile parts of their bodies, but that do want to preserve or even build their muscles. The small contractions that are coming via electrical impulse to the neurons which then fire an impulse to stimulate contraction can cause tiny tears in the muscle which must be repaired by the formation of new muscle fibres; this causes each piece of the torn muscle to join, repairing the muscle and in that making the muscle larger.

Question 33

Describe the arrangement of filaments in myofibril/sarcomere, and the key features of thin and thick filaments.

Answer 33

_M line:_ Connects the central portion of each thick filament _H band:_ lighter region on either side of M line, consists of thick filaments _A band_: The dark region of a sarcomere that contains thick filaments _I band_: The light region of a sarcomere that contains thin filaments (doesn’t overlap w/ thick filaments) _Z line:_ boundary between adjacent sarcomeres, consist of actin in which interconnect thin filaments of adjacent sarcomeres _Thin filaments_ look like a double helix and consist primarily of actin. Calcium binds to troponin, which causes tropomyosin to move away from the actin active site and allows myosin to interact with actin → begins contraction cycle _Thick filaments_ are primarily composed of myosin and a titin core

Question 34

Explain the steps of the contraction cycle, including the roles for calcium and ATP.

Answer 34

The transition from excitation to contraction begins when action potentials pass T-tubules, causing an electrical signal which triggers the release of calcium ions previously stored in the sarcoplasmic reticulum. The calcium then binds to troponin, causing tropomyosin to move away from the actin active site. Myosin is now able to bind to the actin active site, form a cross bridge, and complete a power stroke. The cross bridge cannot be broken until a new ATP molecule binds to the myosin neck.

Question 35

Analyze how the sliding filament model of sarcomere predicts different amounts of muscle tension depending on muscle length.

Answer 35

Basically, if there’s no overlap between the filaments (if the muscle is already totally extended), the muscle will only be able to contract and shorten the muscle a little bit because the maximum capacity of contraction. And same goes is the muscle is already fully contracted, (short) there’s no wiggle room for it to get even shorter.

Question 36

Explain what is occurring in each of the three phases of a muscle twitch, and why overlapping stimuli can summate to produce tetanic contraction.

Answer 36

Three phases of twitch stimuli: latent period, contraction, relaxation **LATENT PERIOD**; the amount of time the motor neuron takes to release ACh into the NMJ, as well as the time it takes for sodium to flood the cell and move down the t-tubules / sarcoplasmic reticulum **CONTRACTION**: steadily increases as more calcium floods in, exposing multiple binding sites for myosin heads to bind to, myosin binding to them, this process accounts for the steep but steady rise until peak contraction / force is reached. **RELAXATION**: Ca²⁺ is steadily removed from the sarcomere, which returns all exposed binding sites to being covered by troponin and tropomyosin. ATP continues to reposition the myosin neck. ‘peak relaxation’ (resting period) occurs when all active sites are blocked once more. Tetanic contraction occurs when ALL possible G-actin binding sites are exposed and bound to myosin heads; this is the highest point of contraction that cannot be superseded, the ceiling of contraction. If tetanic contraction is a plateau at the top of the graph, and an initial twitch is near the bottom, there is all of the space in between where a contraction can increase each twitch that occurs; this happens as more and more calcium is being released from the SR, exposing more binding sites and adding more “little men” to pull the rope.

Question 37

Define the term ‘motor unit’ and discuss how multiple motor units are recruited during synchronous and asynchronous recruitment.

Answer 37

Motor units refer to the motor neuron plus ALL of the muscle fibres that the motor neuron contacts - one motor neuron can contact up to 100 muscle fibres, but one muscle fibre can only have one corresponding motor unit. In synchronous recruitment, motor units are recruited by size; smaller units first, and then medium sized units, and then large units - large units take A LARGE stimulus in order to recruit and for the corresponding muscle fibres to contract. In asynchronous recruitment (pattern of firing motor neurons to prevent fatigue) when a muscle must sustain a contraction for minutes or more, motor units take turns being active and contracting, and then relaxing until its their turn again - this conserves stores of ATP and calcium so that no one motor neuron (/muscle fibre) runs out of stores and is unable to keep contracting, allowing the contraction to continue for a longer period of time.

Question 38

Describe how anatomical and physiological features can differ between different muscles and discuss how these affect tension generation.

Answer 38

Basically, three ‘size’ components matter where the largest has the most tension generation: motor neurons (more motor neurons active = more force and tension), more fascicles per myofiber, and more myofibrils per fascicle. Because the myofibrils are the location of the thin and thick filaments which are the base unit of a muscle contraction; each of these categories will increase in myofibril amount if the overall unit gets bigger, meaning that the overall contraction will increase. Hypertrophy → more myofibrils per myofiber , which is the only kind of growth that can occur in adults hyperplasia → more myofibers in general. Also, there are different arrangements of muscle fibres in a muscle group: parallel arrangement, or pennate arrangement. Parallel arrangement has shorter tendons that exist on each end, with all fascicles being parallel to the long end. Contrastingly, pennate muscles have longer tendons and fascicles are only parallel to the one end, so they can look different (unipennate, bipennate, or multipennate). This means that there are MORE muscle fibres pulling one tendon than in a parallel muscle; the pennate muscle will have shorter fibres but more force on that one tendon. More force in a pennate. Remember that the direction and amount of fibres on the individual tendon will both affect the overall tension.

Question 39

Explain how muscle shortening can occur at different speeds or reverse depending on the load of the muscle.

Answer 39

A muscle always has to contract with enough force to change the weight of itself, PLUS the weight of the load; this means that it will take a longer time for the muscle to shorten the heavier the weight is. Also, I suppose that it does take some time for the excitation contraction cycle to occur, so perhaps adding a bunch of latent periods together might take a longer time. A flex of a large muscle will take a lot of energy and activate many motor units so I suppose that would take some time to rally. Also, muscle shortening does not always happen, if there's a balance from gravity where the muscle simply does not want to extend but also not shorten, that is an isometric contraction. Eccentric contraction produces tension and gets longer but not as long as it would get if it wasn't doing any contraction at all. A good example is ‘braking’ so that you can be cushioned against the force of gravity as you ascend.

Question 40

Compare and contrast the different mechanisms skeletal muscles use to generate ATP when these mechanisms are used.

Answer 40

Muscles generate ATP aerobically or anaerobically by breaking down (catabolism) of glucose/glycogen, lipids or other organic molecules. Aerobic Metabolism: occurs in the mitochondria and requires a supply of oxygen, but can generate lots of ATP (\>30) from a single glucose molecule and can also metabolize fatty acids but requires more time. Anaerobic Metabolism: can occur in the cytosol and does not require an oxygen supply, it can only use glucose and generates less ATP per molecule of glucose, but can work very quickly and without oxygen. Phosphocreatine: can be used to very quickly convert ADP to ATP, but the stores of this molecule are really small and so it is used up very quickly. \*Trade off exists between how much ATP can be generated/with how quickly it can be obtained\* Resting Muscles use aerobic metabolism to build up a supply of ATP and also increase phosphocreatine levels and glycogen levels. Moderately active muscles can have ATP needs met by the slower pace of aerobic metabolism. At peak activity, muscles require additional support through glycolysis (anaerobic) or CP - both of which create waste products.

Question 41

Define the term ‘muscle fatigue’ and identify at least two physiological changes that contribute to it.

Answer 41

Muscle fatigue is when you use your muscles close to peak activity over and over and over again and they stop performing at the same rate; this affects both excitation and contraction in ways that are detailed below. Fatigue refers less to the below affects actually happening (specifically hydrogen running free in the cell), and more to homeostatic regulation that tells motor neurons not to contract, as that prevents actual damage to the bottom. What DOESN’T contribute to muscle fatigue is running out of ATP; this only happens when you die. everything else happens first! EXCITATION FATIGUE CONTRIBUTORS: - Potassium starts to build up outside of the cell here in the t-tubules where is is hard to diffuse away into the ECF; this affects the ability of the sarcoplasm to undergo more action potentials - Also, the depletion of ACh (neurotransmitter) from the motor neurons. You can run out of ACh temporarily and the motor neuron cannot perform its excitation stimulus because of this. CONTRACTION FATIGUE CONTRIBUTORS: Lactate and hydrogen ions build up in the cytoplasm; can affect how calcium interacts with tropomyosin which affects the formation of cross-bridges. - leaking of Ca²⁺ into the sarcoplasm; pump does not allow Ca²⁺ to get back into the SR…. affects like not being able to relax. Muscle Fatigue: a muscle is fatigued when it can no longer perform at the required level of activity. (when rapid ATP production affects the ability of the muscle to maintain the contraction cycle)

Question 42

Identify the key anatomical and physiological features that distinguish between Type I and Type II muscle fibres and analyze how these would contribute to performance differences and training effects.

Answer 42

Type 1 (slow twitch) Not as powerful, but fatigue resistant * more capillaries per muscle fibre = more oxygen supply * More mitochondria = more ability to produce ATP * Fewer Myofibrils = lower max tension * Maximum twitch develops slowly but it maintained longer (calcium+myosin pump) Type 2A (fast twitch) High force and rapid contraction, but fatigue easily * Fewer capillaries = less oxygen supply * More myofibrils = higher max tension * Less mitochondria = less efficient ATP production * Maximum twitch develops quickly, but is not maintained for long Type 2B: intermediate twitch, somewhere in between type 1 and type 2a. * Does not fatigue incredibly quickly, but also does not fire incredibly quickly.

Question 43

Describe the three anatomical divisions of the nervous system in terms of location and connectivity.

Answer 43

**_CNS - Central Nervous System, located in the brain and spinal cord_** * Processes information from the sensory neurons (found in PNS) integrates that info, then sends signals to the motor neurons (found in PNS) to respond PNS **_Peripheral Nervous System, located in all other nervous tissue_** * Detects stimuli from via sensory receptor neurons in peripheral tissue and translate the stimuli to action potentials that travel to the brain/spinal cord (CNS) * Respond to commands from the CNS through motor neurons that carry information from the CNS to peripheral tissues (muscles, organs etc) ENS **_Enteric Nervous System, located in the GI tract and mostly control digestion_** * Only partially connected to the CNS, but is capable of operating without intervention from the CNS, however information from the CNS can alter normal digestive function

Question 44

Explain the functions of the four compartments of a neuronal cell and classify a neuron based on the number and arrangement of its neurites.

Answer 44

**Neurons = information transfer (vs glial cells which play support roles), also neurons are highly polarized** * Cell Body: receives info and produces proteins * Dendrite: receive input/information from other cells * Axon: transmits action potentials to surrounding cells (also has key components to information transfer the axon hillock, initial segment) * Axon Terminal: convert electrical action potentials into chemical signals (neurotransmitters) * Can be characterized based on the arrangement of it’s neurites into: * Multipolar neurons: many dendrites and 1 axon (most common, most neurons are multipolar) * Bipolar neurons: 1 dendrite and 1 axon * Unipolar neurons: axon is only attached to the cell body in one spot (as opposed to the axon passing through the cell body giving it to different connection points with the soma) * Anaxonic neurites: rare, but have dendrites and axons that combine functions - sending and receiving information

Question 45

Explain the functions and key structure features of four different types of glia.

Answer 45

**Glial cells = support roles + neuron maintenance (vs neurons that carry info); the following 4 are the glial of the CNS.** _Ependymal Cells_: mainly produce, monitor and circulate CSF (cerebrospinal fluid) _Microglia_: mobile cells (like macrophages) that remove pathogens, waste and cellular debris through phagocytosis (engulfing it so it can be processed) and modify connections between neurons _Astrocytes/Satellite Cells_: maintain the BBB, also structural support, regulate dissolved ion/gas/nutrient content in interstitial fluid around neurons, and absorb and recycle neurotransmitters that aren’t reabsorbed/broken down at synapses _Myelinating cells (Oligodendrocytes and Schwann cells)_: structural framework and also produce myelin sheath.

Question 46

Compare and contrast the capacity of neurons in the CNS and PNS for repair.

Answer 46

**In both situations, if the cell body of a neuron dies, the whole neuron will die. But if an axon is damaged it has the capacity to regrow, IF it is an axon in the PNS.** PNS: contains different glial cells (Schwann Cells and Satellite cells) Because of the Schwann cells, PNS neurons are more easily repaired because the Schwann cells do not degenerate and instead they proliferate along where the axon used to be. Macrophages remove debris, and then the axon begins to regenerate and follows the ‘tunnel’ that has been created by the Schwann cells. If the axon reestablishes connection, then function can return to normal. CNS: nerve repair is much more limited because a) more axons are likely involved in the damage than in the PNS, b) astrocytes produce scar tissue that can prevent the axon from regrowing and connecting with itself c) (is it oligodendrocytes or astrocytes?) release chemicals that block axon growth

Question 47

Explain how a neuron's transmembrane potential arises from differences in ion concentrations and permeability, including the roles of ion channels and active transport proteins (e.g., pumps).

Answer 47

Transmembrane potential is caused by the separation of positive and negative charges by the plasma membrane. If all ions were equally permeable there would be no transmembrane potential, because the ions would naturally flow to equalize themselves within the solution. Generally the inside of a cell at rest is at -70 (70millivots less positive than the outside) Outside the cell (ECF) lots of Na⁺ and Cl^- ions (net positive charge) Inside the cell (ICF): lots of K+ and Protein- ions (net negative charge) Permeability: ions move through ion channels (because of their charge they are hydrophobic and can’t diffuse through the hydrophilic plasma membrane) so they move through ion channels/carrier proteins. Some of these channels are always open while others require a signal (whether it be ligand, mechanical, or electrically (voltage) stimulated) to tell them to open or close. Role of Ion Channels: allow for ions to pass through the plasma membrane and enter the cell, which can create a change in the membrane potential, a graded potential. Role of Pump/active transport pumps: stabilizes the neuron by bringing it back to its resting membrane potential, by sending 3Na⁺ ion out of the cell and bringing 2K⁺ back into the cell. This is important because the neuron is only ready to fire an action potential when ion distribution and membrane potential are at specific levels (most of the brains energy use is because of the pumps stabilizing neural membrane potentials).

Question 48

Predict the effects of changes to ion concentration or ion permeability on the transmembrane potential.

Answer 48

RMP is essentially the summation of all the equilibrium potentials, and since K⁺ has the greatest permeability, it would seem that the K⁺ equilibrium potential would contribute the greatest to the RMP

Question 49

List three different ways that ion channels can be gated and give an example of where you might find channels with each type of gating.

Answer 49

_Mechanically Gated_ - open in response to physical mechanical stimuli that physically distorts a neuron's membrane surface. Mechanical stimuli can be stretch, pressure, vibration - mostly found in special sense neurons. Example: cochlear hair cells _Voltage Gated_ - Open/close in response to changes in membrane potential, and are characteristic of excitable membranes - they are capable of generating and spreading action potential, and so are found along the axon of a neuron Example: _Chemically (or ligand) Gated_ - open when they bind to specific chemicals (or ligands), usually neurotransmitters. They are usually found along the cell body and dendrites of a neuron (where most synaptic communication occurs) Example: receptors that bind ACh at neuromuscular junctions are chemically gated.

Question 50

Define the following terms: graded potential, action potential, hyperpolarization, depolarization, repolarization.

Answer 50

_Graded Potential:_ changes in the membrane potential that cannot spread far from the site of stimulation. Any stimulus that opens a Gated Ion Channel will produce a graded potential. Graded potentials occur on the postsynaptic cell (dendrites and cell body) so it is usually a ligand gated ion channel binding a NT that creates a graded potential) _Action Potential:_ when a graded potential successfully reaches the threshold (usually around-55mV), voltage gated sodium channels are opened which causes a rush of sodium into the cell and ‘depolarizes’ (makes less negative, makes more positive), and sends the action potential (an electrical current) down the axon of the cell where it is transmitted to the next cell. _Hyperpolarization_: membrane potential gets more negative (moving further from zero, closer towards K⁺ equilibrium potential) - an increasingly (-) membrane potential is the result as K⁺ leaves the cytosol when K⁺ chemically gated ion channels are opened. _Depolarization_: any shift of the resting membrane potential towards a more positive value (resting MP is usually around -70mV, so to get more positive you are getting closer to 0) _Repolarization_: When a depolarized cell returns to equilibrium (chemical stimulus is removed and so the membrane returns to its normal resting potential as excess Na⁺ is transported out of the cytosol) a cell cannot respond when it is in the process of repolarizing (the neuron is in its absolute refractory period which means it cannot fire another AP no matter how strong it’s being stimulated - this prevents the AP from travelling backwards)

Question 51

Discuss at least three different factors that can alter the size and/or polarity of a graded potential.

Answer 51

Size of the stimulus: a bigger stimulus will result in a bigger graded potential Temporal Summation: a single synapse is stimulated repeatedly so before the first stimulus wears off, and the graded potential completely disappears, the addition of the 2nd or 3rd stimulus in that same location could reach a threshold. Spatial Summation: stimulus is in different locations but can overlap creating a bigger graded potential (imagine a bunch of boats driving around in a lake, those each represent the stimulus, the waves that each boat creates may overlap and the collision of their respective waves can create a bigger wave, which might be big enough to reach threshold) Action Potential have a set size, it does not change- all or nothing, however what can change in an AP is the frequency of stimulus (something really painful will generate a new AP one very quickly after the other, something less painful will generate an AP ‘once in a while)

Question 52

Explain how the different properties of voltage-gated sodium and voltage-gated potassium channels in an axon connect to the three different phases of an action potential, and to the action potential refractory period.

Answer 52

The 3 main phases of an action potential are depolarization, repolarization, and hyperpolarization Voltage gated sodium channels (VGIC) have 3 states - open, closed, inactivated. When the neuron is at rest, voltage gated ion channels are closed. When the threshold is reached, the VGIC opens, allows Na⁺ to rush in (because of its concentration gradient/the electrochemical gradient)- causing depolarization (step 1 in an action potential) Eventually, the amount of positively charged Na ions hyperpolarizes (step 2) the membrane, which triggers the sodium gated ion channels to be deactivated. Once the VGICs are closed, the refractory period begins because Na can no longer get into the cell, and the cell wants to get back to its resting membrane potential by using Na/K pumps to push the sodium in the cell back out of the cell) against its concentration gradient Voltage Gated potassium channels are also opened in response to the change in membrane potential, but open (and close) more slowly. This means that K⁺ flows out of the cell making it less positive, eventually negative. (Repolarization). The membrane is eventually hyperpolarized (more negative than it’s resting-70mv) which triggers the potassium gated ion channels to close. The Na/K pump restores it back to its normal resting membrane potential. Refractory period is necessary to prevent APs from travelling backward.

Question 53

Explain what happens to any graded potential as it spreads through a neuron, and why the same thing does not happen to an action potential.

Answer 53

Graded potentials degrade and decay with both time and distance from the site of stimulation. Graded potentials are generated when neurotransmitters bind to the ligand gated ion channels causing them to open. This creates a local change that CAN spread, but fades quickly & there are leak channels. This does not occur in action potentials because they rely on voltage gated ion channels, which once 1 is open, the depolarization spreads to adjacent sections, so creates a change that is not limited to the initial local point of depolarization

Question 54

Discuss how myelin can affect action potential conduction speed and the ATP usage of a neuron.

Answer 54

_Conduction Speed:_ Myelin sheaths are found on the axon of myelinated neurons (made by Schwann cells in the PNS and oligodendrocytes in the CNS) . The axon is responsible for transporting information in the form of electrical current. In myelinated neurons, the electrical current is ‘protected’ by the myelin sheath, which is resistant to electricity(does not conduct well) - less energy is lost when surrounded by a good insulator. Remember axons can be SUPER long! So you want the current to remain strong to reach your brain/spinal cord. Uses “saltatory propagation” which rely on the nodes (of Ranvier), which are gaps in the myelin, that contain voltage gated ion channels that essentially ‘boost’ the action potential, to reach the next node. Looks like it ‘jumps’ between the nodes. _Use of ATP_: metabolically ‘cheaper’ because the Na+/K+ pumps are only operating within the nodes of Ranvier, instead of all the way across the axon, so less ATP is required to make the pump do their pumping action.

Question 55

Describe the anatomy of an axon terminal and explain the role of voltage-gated calcium channels in neurotransmitter tissue.

Answer 55

Calcium channels at the end of the axon open (like NaGICs) once it gets positive enough, and Ca²⁺ flows into the cell at the terminal end. Axon terminal is part of the presynaptic neuron , and contains synaptic vesicles, which contain neurotransmitters. Calcium bonds to the proteins that are ‘docking’ the synaptic vesicles to the presynaptic membrane, which brings them closer to the membrane, and make the bilayer membrane creating a merge in membrane of the axon terminal and the synaptic vesicles - this allows for NTs to be released into the synaptic cleft (exocytosis). Then they bond on the postsynaptic membrane to ligand gated ion channels which generates a graded potential, and potentially an AP! Special anatomy: mitochondria for direct energy supply, and synaptic vesicles filled with neurotransmitters.

Question 56

Discuss how vesicles and neurotransmitters can be recycled at an axon terminal and predict the effects of interrupting these processes on the synapse.

Answer 56

NTs can passively diffuse out of the synapse, but it only works if the action potentials are being fried relatively infrequently. If the rate of NT release exceeds the rate of diffusion there are other ACTIVE methods for the NT’s to be removed from the synapse. The axon terminal has everything it needs (mostly proteins) to reform synaptic vesicles in its plasma membrane (once they have been emptied into the synaptic cleft) This process is called ‘synaptic endocytosis’ and is accelerated after period of axon stimulation. Enzymes that will break down the NT in the synapse into its components which are no longer able to stimulate the receptors. Active Re-uptake pumps take the NT back into the axon terminal for future use. Astrocytes (of the CNS) situate themselves near synaptic clefts and pump the NT out of the cleft into the astrocyte - where can be recycled and used again. - Interrupting this process is what lots of street drugs and also SSRIs (selective serotonin reuptake inhibitors) do → creates a synaptic cleft that is full of active, bindable, NTs, that can then bind to the postsynaptic ligand gated ion channels to create graded and/or action potentials / open more of the gates. - Great if you’re depressed because the serotonin released from the presynaptic cell remains in the synaptic cleft for longer, allowing it more opportunity to bring to the postsynaptic receptors generating happy action potentials

Question 57

Define or correctly apply the terms inhibitory and excitatory (post-synaptic potentials), temporal and spatial summation, and agonist and antagonist within the context of the nervous system.

Answer 57

Excitatory Post Synaptic Potential (EPSP): make a neuron more likely to fire an AP, by depolarizing the membrane, usually generated by the opening of Na channels Inhibitory Post Synaptic Potential (IPSP): make a neuron less likely to fire an AP, generated by the opening of channels permeable to K or Cl and often hyperpolarize the membrane. Agonist: a drug (something from outside the body) that mimics the action of an endogenous (something from inside the body) neurotransmitter Antagonists: a drug that blocks the activation of a neurotransmitter receptor Temporal Summation: stimulus is received multiple times in a row, before the first graded potential fully dissipates, can push the potential to threshold Spatial Summation: stimulated simultaneously in different locations, but the ‘overlap’ of GP can reach threshold and trigger an AP. \*an EPSP and an IPSP can cancel each other out if stimulated at the same time\*

Question 58

Define or correctly apply the terms: convergence, divergence, recurrence, and serial processing.

Answer 58

Convergence: several neurons synapse on one post-synaptic membrane Divergence: Is when one neuron sends info to multiple other neurons in a network Recurrence (textbook says reverberation) - when an axon loop back to the original point of stimulus, further stimulating the presynaptic neurons (like a positive feedback loop involving neurons) it will continue until synaptic fatigue or inhibitory stimuli break the cycle. Serial Processing: info is relayed neuron to neuron in a line. Occurs when sensory information is relayed from one part of the brain to another. \*neural pools are simply groups of interconnected neurons, the interaction of neural pools is called a neural circuit\*

Question 59

Describe and analyze the reflex arcs of simple spinal reflexes and predict the effects of different manipulations.

Answer 59

Simple Spinal Reflexes: begin at sensory receptor and end at motor neuron (peripheral effector) processing of the information occurs in the nuclei of the spinal cord (does not need to go to the brain to be processed) creates a rapid and automatic response - the reflex. Manipulating this (ie patella test), is detected by the sensory neuron and sent to the spinal cord where the motor neuron fires. If you knee doesn't jerk from the doctors examination, that's how you can know if something is wrong with you reflexes.

Question 60

Explain how non-neuronal structures (iris, lens, tympanum, and ossicles) allow light or sound to reach the sensory cells of the eye or ear.

Answer 60

iris = connective tissue, 2 layers of smooth muscle (2 circular layers with a gap in the middle, which is your pupil), so that the iris can contract in different ways. It either dilates the pupil in darkness, the outer layer contracts (causing the pupil to grow). Muscle of the iris gets smaller, pupil gets bigger. The other layer is the sphincter layer which contracts in bright light, making the pupil smaller. The iris manages the amount of light in the posterior chamber. lens = a cellular structure. The cells are transparent and firm, filled with crystallin which are almost completely transparent. Lens fits right below the pupil… it is connected to the ciliary body. The shape is convex, allowing it to bend and refract light. The ciliary body has a smooth muscle body, which can change the amount of tension that the fibres are putting on the lens, making it flatter or rounder. The amount of tension in the smooth muscle is called accommodation; this changes the focal length. Rounder lens = more refraction = focal point possible when object is CLOSE to you. If you want to focus on something far away, flatter = focal point is possible when the object is far away. Accommodation is the process of changing the shape of the lens to allow for changes in vision to match environmental needs. What is the lens doing vs what is the iris doing? depends on the situation.

Question 61

Describe the anatomical organization of the retina including the optic disc, fovea, the location of the photoreceptor layer and the distribution of the rods and cones.

Answer 61

The retina is part of the CNS; it grows during embryonic development outward from the rest of the diencephalon. It is where the neurons are! The other accessory structures exist to give physical / chemical / immune protection, whereas others help for the eye’s primary function (detecting, gathering, and organizing light). It is plastered along the surface of the vitreous chamber. * optic disc: many myelinated axons; there are multiple layers of neurons in the retina (3, 4, or 5,) all the axons leave through the optic disk; no photoreceptors here! this is the other round structure in the retina. * fovea centralis : this is inside the MACULA, which is one of two circular regions inside the retina. the fovea centralis is the point of central vision; most photoreceptors per unit area here! you want the light to come in directly to the macula from what you’re looking at * photoreceptor receptors: spread across the deep layer of the retina. Each of these will only respond to a corresponding light ray coming through a given location. They are like pixels, each responding to whether there is or isn’t light at a given spot. For light to get here, it has to go through more superficial layers of neurons that cannot respond to light at all. Photoreceptors are upside down and back to front in terms of the location they are tracking for light/no light. ○ receptor field: the space that a given photoreceptor tracks / responds to.

Question 62

Explain the transduction in photoreceptors in terms of neurotransmitter release and membrane potential before and after photons are absorbed.

Answer 62

Photoreceptors release neurotransmitters constantly in darkness; in the dark, sodium is continually coming in through internal ligand-gated channels. Ligand is there in dark; channel opens; constant depolarization from sodium rushing in; this results in constant neurotransmitter release IN THE DARK. When the light comes in, the retinal changes shape, which activates the opsin protein ‘transducin’, this cascade starts to destroy the inner ligand. Less concentration, receptors close, sodium no longer comes in, membrane is no longer depolarized so it instead becomes hyperpolarized. When it is hyperpolarized in the light, the neuron stops releasing neurotransmitters temporarily. For the particular opsin that absorbed the photon, it must wait until the photon is reset by some enzymes before it goes through the cycle again. There is a waiting period before the photon can respond, because it needs to reset its retinal first. Dark = neurotransmitter, depolarization Light = no more neurotransmitter, hyperpolarization.

Question 63

Compare and contrast the functional specializations of rods and cones and explain how the visual system discriminates colours.

Answer 63

Rods and cones are two different types of photoreceptors that have two different shapes. Both rods and cones contain opsin which are light-sensitive proteins. PHOTOTRANSDUCTION occurs here. It is an energetically intensive process. Photopigments = an opsin protein that combines with a photosensitive molecule called retinal. If a photon is absorbed by the structure, the retinal will change into a different conformation because its absorbed energy which then changes the structure of the entire protein around it, which starts off biochemical signaling, ● Retinal changes shape → changes opsin → neuron changes signalling…. RODS are super sensitive to light; you can detect a single photon in very much darkness in areas of the eye with a high concentration of rods. Are able to function even when there isn’t much light; they make changes to the neurotransmitter release . If there is a high amount of light, rods signal immediately and enter the rebuild period, taking awhile to get their retinal sorted out again. In other words, their opsins absorb light rapidly (called photobleaching), and are unable to respond to future photons. Rods use RHODOPSIN, which gives high sensitivity to blue-green photons. Rods show HIGH convergence to bipolar neurons (many rods [10-100] : synapse onto 1 bipolar neuron). Rods are more common than cones outside the macula / fovea; more likely to be found on the periphery. CONES are less sensitive; takes more light to initiate the cascade. Able to continue to signal even with bright light, does not get bleached out in the same way. Less convergence in cones, single cone with one per bipolar cell. Much higher density in the macula; especially in the fovea! They are the only photoreceptor in the fovea. There are three types of opsin proteins; an S, M, and L opsin (short, medium, and large wavelengths). S= purple/blue M= green L = red. If there are three different types of cones, you can detect whether you have a lot of one coloured light or a little of a different coloured light. If a person does not have cones, they would be colour blind, because rods only have one type of colour that they see (one opsin protein)... this is also why you cannot see colour in the dark, because cones do not activate from dim light. Your vision also is not high in its acuity, because rods have high convergence to bipolar neurons; it cannot narrow down where a stimulus is coming from in terms of photon detection, it can only say ‘ it was somewhere around here’ which can make lines blurry, etc. This is not the case with cones, because there is a 1-to-1 relationship between cones and neurons.

Question 64

Explain transduction in the inner hair cells in the cochlea in terms of ion channels, membrane potential, and neurotransmitter release.

Answer 64

hair cells cannot actually produce an action potential themselves, but it can depolarize to release neurotransmitters which can trigger an action potential in sensory neurons. when pressure waves cause movement of these hair cells the hair bends against the tectorial membrane triggering mechanically gated ion channels to open at the tip top of the hairs, allowing + into the hair depolarizing its membrane potential. then voltage gated Ca channels open at the base of the hair cell leading to neurotransmitter release onto the sensory nerve dendrite

Question 65

Explain how sound frequency (i.e., pitch) is encoded by different hair cells in the cochlea.

Answer 65

pitch is recognized in the basilar membrane of the cochlea. the reason we can decipher pitch is because the stiffness of the basilar membrane varies as it continues; it is thick and stiff at the oval window (for high freq) and loose at the cochlea apex (for low freq). this differentiation in stiffness means that different parts give stronger vibration resembling different frequencies. the larger the movement the more depolarization of the hair cell.

Question 66

Compare and contrast how information about the location of stimuli is encoded or computed in the visual and auditory systems.

Answer 66

The cochlea does not encode the location of sounds based on certain regions that are stimulated (like how the retina does). instead when the information is sent to the hindbrain the interneuron circuits there are able to detect differences in time and intensity between the two ears, and therefore puzzle together were the sound is coming from (as an example: say you are listening to a tv on your right hand side. this sound will hit your right ear before your left and you brain will realize that and tell you the sound is coming from the right)

Question 67

Identify key features that distinguish smooth muscle cells from striated muscle (e.g., structure, E-C coupling, innervation)

Answer 67

Smooth Muscle: - Small cells, one nuclei - No striations; actin filaments - found in internal walls of many organs, gastrointestinal tract, urethral tissue, - Excitation/Contraction coupling - both require calcium but, Striated Muscle: - very long cells with multiple nuclei - Striations; stripe pattern arising from - found attached to bones - Excitation/Contraction coupling - both require calcium but,

Question 68

Describe the anatomical differences that distinguish the ANS from the somatic nervous system, and the parasympathetic and sympathetic divisions from each other.

Answer 68

Sympathetic: fight or flight Parasympathetic: rest & digest This means that the sympathetic will do everything in its power to prepare the body to fight or flee (sending all disposable glucose to skeletal muscles, temporarily shutting down organ systems that wouldn’t be required in a fight/flight situations like urinary, digestive, reproductive, and activated ones that would be necessary for fighting/fleeing like respiratory, cardiovascular, muscular. Example: 1) By relaxing the smooth muscles of the digestive system, food is no longer being propelled through the digestive tract. 2) By relaxing the smooth muscles lining the respiratory tract, more air is able to enter the bloodstream to facilitate muscular activation in a fight/flight situation. Parasympathetic on the other hand is in charge of calming the body after the fight/flight stress response, and re engages the systems that were turned off - digestive, urinary etc - Example 1) by contracting the smooth muscles in the digestive system, food is passed through the stomach into the intestines, and propelled through the intestines to be eventually excreted.

Question 69

Understand the roles of the sympathetic and parasympathetic divisions and use this to predict their effects on target organs.

Question 70

Describe the key features of metabotropic receptor signalling and explain why the same receptor diversity means that the same neurotransmitter can have opposite effects on different effector cells.

Answer 70

* linked to intracellular proteins called G proteins, which initiate biochemical cascades to produce longer lasting responses, diverse biochemical effects in addition to membrane potential changes, and stimulatory or inhibitory responses.

Question 71

Predict the consequences of pharmacological manipulations of ANS pathways.

Question 72

Describe the typical pattern of connections between the ANS and the ENS and explain the differences between long and short visceral reflexes.

Question 73

Describe how the meninges, blood brain barrier, and cerebrospinal fluid provide specialized protection for the CNS.

Answer 73

CSF- cerebrospinal fluid is the fluid that exists between the skull bones and the Blood-Brain Barrier (BBB), helps provide cushioning / a barrier so that the brain isn’t wracking against hard bones, same as the BBB. Blood Brain Barrier: limits the movement of H₂0 and other hydrophilic molecules between the blood and the CNS, via tight junctions in the endothelial cells in the CNS. Glucose can pass through transport channels. Water passes through ‘leaky’ capillaries that contact ependymal cells (simple cuboidal cells lining the brain and spinal cord) Meninges: 3 specialized membranes that provide support and protection * Dura Mater - dense irregular connective tissue * Arachnoid Mater - elastic CT + simple squamous epithelium * Pia Mater - areolar CT + simple squamous epithelium

Question 74

Use information about the organization of the spinal cord and spinal nerves to make simple predictions about the location of spinal cord damage.

Answer 74

Spinal Cord Organization: CNS/Spinal cord tissue is divided into white and gray matter. ➢ White: composed almost entirely of myelinated axons, so it’s function is to carry information is split further into ○ Ascending White Matter : that sends information from the sensory neurons to the brain ○ Descending White Matter: sends information from the brain to the effectors/motor neurons ➢ Gray: mostly consists of glia, cell bodies, dendrites and axon terminals (everything that's not an axon) so it’s function is to integrate sensory and motor information Also, each segment of the spinal cord receives and sends out information to a specific body region/group of muscles for specific functions.

Question 75

Compare and contrast the principles of localization of function _and_ distributed processing in the nervous system using examples from the forebrain, especially the cortex.

Answer 75

* cerebrum * largest region of the brain * fissures - deep grooves that subdivide each cerebral hemisphere * gyri - folds in cerebral hemispheres that increase its surface area * sulci - shallow grooves in cerebral hemispheres that separate adjacent gyri * divided into left and right cerebral hemispheres * surfaces highly folded and covered by a superficial layer of gray matter, called the cerebral cortex * cerebral functions include conscious thought, memory storage and processing, sensory processing, and regulating skeletal muscle contractions * diencephalon * link between cerebral hemispheres and the rest of the CNS * thalamus - contains relay and processing centers for sensory information * hypothalamus - contains centers involved with emotions, autonomic function, and hormone production * cerebellum * second largest region of the brain * has only one tenth of the brain's volume but over one half of brain's neurons * functions include coordinating and modulating motor commands from the cerebral cortex * brainstem * midbrain - contains nuclei that process visual and auditory information and control reflexes triggered by these stimuli - also contains centers that help maintain consciousness * pons - connects cerebellum to brainstem and contains tracts and relay centers, as well as nuclei that function in somatic and visceral motor control * medulla oblongata - relays sensory information to other portions of the brainstem and to the thalamus * contains major centers that regulate autonomic functions, such as heart rate and blood pressure * Motor cortex * neurons of primary motor cortex direct voluntary movement by controlling somatic motor neurons in the brainstem and spinal cord * premotor cortex (somatic motor association area) coordinates learned movements * Gustatory cortex - receives information from taste receptors * Olfactory cortex - receives sensory information from the olfactory (smell) receptors * Auditory cortex * primary auditory cortex is responsible for monitoring auditory (sound) information * auditory association area monitors sensory activity in the auditory cortex and recognizes sounds such as spoken words * Sensory cortex neurons in the primary somato-sensory cortex receive somatic sensory information from receptors for touch, pressure, pain, vibration, or temperature * the somatosensory association area monitors activity in the primary somatosensory cortex - allows you to recognize a touch as light as a mosquito landing on your arm * Visual cortex * primary visual cortex receives information from the lateral geniculate bodies * visual association area monitors patterns of activity in the visual cortex and interprets results - when you see symbols c, a , r, your visual association area recognizes that they form the word car

Question 76

Explain how information about the environment or the body is represented in the brain.

Answer 76

Information about the environment is received by sensory neurons who generate a graded potential in response to any given environmental stimuli. If the graded potential is significant enough, an action potential is generated and travels along the axons to the brain/spinal cord where it is integrated. Then the brain/spinal cord may send out signals to motor neurons to respond appropriately.

Question 77

Describe what is measured in an EEG and how sleep or epileptic seizures can change an EEG reading.

Answer 77

EEG (electroencephalogram) recording of the electrical patterns (brain waves) generated by the activity of neurons through electrodes on the scalp. Can be used to detect brain abnormalities. What is measured? The patterns in the electrical field generated by neuronal activity. These brain waves can be divided into alpha, beta, theta, delta How does sleep change it? In different stages of a sleep cycle, the neuronal activity is different and therefore the brain waves present are also different. How does a seizure change it? A seizure is a temporary brain disorder accompanied by unusual sensation/abnormal movement/inappropriate behaviour. Accompanied by a change in the electrical pattern, starting in one spot in the cerebral cortex but can spread across the whole surface.

Question 78

# Define: Metabolism Basal Metabolic rate Nutrient pool

Answer 78

**Metabolism** → the sum of all chemical and physical changes that occur in body tissue (i.e., the processes that create ATP and those that spend ATP) **Basal Metabolic Rate** → an estimate of the number of calories (i.e., energy intake) the entire body requires to produce enough ATP to maintain all basic functions at rest. **Nutrient pool** → the nutrient resources available in the body that the body can utilize

Question 79

Explain (using specific examples) the difference between hormonal actions that directly affect metabolic rate, and the hormonal effects that affect metabolism by mobilizing the nutrient pool.

Answer 79

* Thyroid hormone receptors can directly regulate BMR by affecting mitochondrial function. * Some thyroid hormone receptors are found in the mitochondria, especially in skeletal muscle cells → when activated, these receptors upregulate mitochondrial activity, directly increasing ATP and heat production. * Several other hormones indirectly affect metabolism by mobilization of nutrients from different cellular stores * **Epinephrine and glucagon** → mobilize glucose and fatty acids from liver and adipose tissue * **Glucocorticoids and growth hormone** → mobilize fatty acids from adipose tissue and promote lipid uptake as well as gluconeogenesis → glucose-sparing effect - promot use of lipids for metabolism by most cells so that available glucose is saved for the CNS

Question 80

Describe and recognize key symptoms of thyroid hormone disruptions and connect these symptoms to different targets of thyroid hormones.

Answer 80

**Type I Diabetes mellitus** → destruction of insulin-secreting beta cells in the pancreas → insulin secretion is abolished or diminished → associated with ‘wasting’, high blood glucose. **Type II Diabetes mellitus** → insulin receptor insensitivity

Question 81

Analyze the effects of multiple hormones on the same regulated variable and classify them by the type of interactions.

Answer 81

* When different hormones produce changes in the same direction on a target variable, their effects can be purely additive, or synergistic (greater than the sum of the individual hormone effects). * Glucagon + epinephrine = **additive**; Glucagon + epinephrine + cortisol = **synergistic**

Question 82

Explain the roles of glucagon and insulin in maintaining normal blood glucose levels and how insulin secretion is regulated by blood glucose at a cellular level.

Answer 82

**Glucagon** → released by pancreatic alpha cells → stimulates gluconeogenesis and glyconenolysis in liver and release of glucose to plasma → increases blood glucose levels **Insulin** → released by pancreatic beta cells → stimulates glucose uptake by cells and glycogenesis in liver → decreases blood glucose levels * **Beta cells act as sensors for blood glucose level.** When blood glucose levels increase, the beta cells secrete insulin. * Insulin decreases blood glucose level and acts as a negative feedback loop to decrease secretion of insulin by the pancreatic beta cells. * Passive transport of glucose into beta cells is enhanced when blood glucose levels are high → leads to increased ATP production, which depolarizes cells. * **Beta cells at rest** → The K_ATP channel (= a passive transporter that only moves glucose according to the concentration gradient) is open, and the cell is at resting membrane potential. * When the potassium channel is open the voltage-gated calcium channels are closed and insulin remains in secretory vesicles inside the cytoplasm. * **Beta cell secretes insulin** → closure of K_ATP channels depolarizes the cell, triggering exocytosis of insulin. * When ATP levels are high, it binds the potassium channels and closes them so that the cell depolarizes and voltage-gated calcium channels open, resulting in secretion of insulin by exocytosis.

Question 83

Compare and contrast Type I and Type II diabetes mellitus in terms of their causes, symptoms, complications, and treatment.

Answer 83

_Type I_ * immune system destroys beta cells in the pancreas → no insulin secretion * wasting (because cells cannot access the nutrients have been digested and mobilized), high blood glucose, glucose in urine, is fatal in months if not treated * treated by constant, careful regiment of blood glucose monitoring and titrated insulin doses _Type II_ * insulin resistance * diabetic retinopathy, increased risk of heart attack, diabetic nephropathy and neuropathy, reduced blood flow to distal portions of limbs, damaged peripheral tissues * oral meds with various targets (increased insulin production, reduced liver glucose release, increased kidney glucose excretion, reduced intestinal glucose absorption) * ensure cholesterol levels are normal; maintain a healthy body weight; keep blood glucose within its recommended range; eat a balanced diet

Question 84

Explain the difference between stress and the stress response and describe how the nervous and endocrine systems are involved in triggering the stress response.

Answer 84

**Stress** → a situation that is *perceived* as a threat to homeostasis which produces the stress response **Stress response** → an allostatic response to try and preserve homeostasis before it's disrupted. * The **hypothalamus** produces sympathetic activation of the entire sympathetic nervous system, which includes epinephrine (adrenaline) release from the adrenal medulla, and activation of the HPA axis which leads to the secretion of ACTH from the pituitary which leads to secretion of cortisol and other glucocorticoids from glands in the adrenal cortex. * The amygdala is the ‘final decider’ about whether a situation is stressful or not, and whether a stress response occurs → once activated, the forebrain activates certain parts of the hypothalamus. * Two major hormonal pathways activated by the stress response: * Epinephrine → secreted by the adrenal medulla as part of sympathetic activation * Non-hormonal parts of the SNS are also activated * Cortisol → secreted from the adrenal cortex in response to HPA activation.

Question 85

Identify the three key phases of stress in the General Adaptation model, and the hormones or neural systems that are involved in each phase.

Answer 85

**Alarm phase** → starts within seconds and lasts for ~1 hour; result of sympathetic activation (all ganglia of the sympathetic division of the ANS become highly active simultaneously); results in: * Increased alertness by stimulation of the reticular activating system * disregard for danger; temporary insensitivity to pain stimuli * increased cardiovascular and respiratory activity centres of the pons and medulla oblongata → increases blood pressure, heart rate, breathing rate, and depth of respiration. * a general increase in muscle tone * mobilization of energy reserves **Resistance/recovery phase** → starts in ~1 hour and lasts for several hours due to the nature of gene expression response induced by cortisol; directed by hypothalamic neurons that release CRH onto the anterior pituitary; the hypothalamic releasing hormone (CRH) triggers the anterior pituitary cells to release a second regulatory hormone (ACTH) into the bloodstream, which stimulates the adrenal cortex to synthesize and secrete glucocorticoids like cortisol. * Glucose-sparing effects * Increase blood glucose concentration by gluconeogenesis (in the liver) * Lipolysis in adipocytes * enhanced lipid uptake by peripheral tissues * Suppresses immune system * Suppresses reproductive system * Alterations to memory and other cognitive functions * Long-term metabolic adjustments in the resistance phase: * Mobilization of remaining energy reserves; lipids from adipose; a.a. from skeletal muscle * conservation of glucose → peripheral tissues (except nervous) break down lipids to obtain energy * increased blood glucose → concentrations → liver synthesizes glucose from other carbohydrates, a.a., and lipids * conservation of salts and water, loss of potassium and hydrogen ions. **Exhaustion phase** → occurs under conditions of severe and prolonged stress (weeks to months); all metabolic reserves depleted; effects of stress hormones become counterproductive and lead to organ failure and death.

Question 86

Compare and contrast the endocrine and physiological features of the alarm phase and resistance/recovery phase of the stress response.

Answer 86

**_Endocrine_** **Alarm phase** → sympathetic activation results in secretion of epinephrine/adrenaline by the adrenal medulla, which acts on most cells in the body to prolong and intensify the sympathetic nervous system response to stress **Resistance/recovery phase** → HPA axis activation results in secretion of cortisol from the adrenal cortex, which has a glucose sparing effect, and also suppresses the immune and reproductive systems; the pancreas is also activated to secrete glucagon, which inhibits uptake of glucose by peripheral tissues; growth hormone secretion mobilizes energy reserves **_Physiological_** **Alarm phase** → sympathetic activation causes sweating, constricting of blood vessels, pupil dilation, increased cardiac output, inhibition of digestion and salivation, airway relaxation, etc. **Resistance/recovery phase** → conservation of salts and water, loss of potassium and hydrogen ions

Question 87

Predict the consequences of manipulations of adrenergic or glucocorticoid signalling for the physiological stress response.

Answer 87

_Adrenergic_ * Epinephrine secreted by adrenal medulla as part of sympathetic activation * Increases heart rate and blood pressure, increases breathing rate and blood glucose, decreases digestive and reproductive systems, liver converts glycogen to glucose. _Glucocorticoid_ * Cortisol is secreted from the adrenal cortex in response to activation of the HPA axis * Allows for protein catabolism in muscle and bone, gluconeogenesis in the liver, fat catabolism in adipose tissue, (=glucose sparing effects), diminished functions of immune system Questions from prof will take the following form: Always given: what the manipulation is (e.g. 'this drug is added which does [block/enhance] to blah blah blah protein'). Question: ask what will be the outcome. You would only have to predict what would happen for a defined manipulation, not remember all the ways that things can be manipulated.

Question 88

Explain what is meant by ‘chronic stress’ and discuss how hypercortisolaemia can disrupt the HPA axis, and the process of sympathetic activation.

Answer 88

* Chronic stress is distinct from the exhaustion phase of a severe stress response → it is not immediately life threatening, but does lead to alterations in the stress response → the same kind of stressor will produce a higher sympathetic stress response in a chronically stressed individual than a naively stressed one, and the parasympathetic nervous system will not rebound * Effects of chronic stress include: * Weight gain * Depression * Memory loss * Lack of concentration * Sleep disturbances * Susceptibility to infections * Irritable bowel syndrome * Thyroid imbalances * Infertility * Osteoporosis * Chronic stress affects neural tissues → especially the hippocampus * Prolonged exposure to glucocorticoids leads to a reduction in synapse numbers on hippocampal neurons → leads to disruption of HPA axis * The hippocampus has an important inhibitory effect on CRH-secreting neurons in the hypothalamus * The amygdala enhances CRH release * If the hippocampus is damaged/less active, there will be less inhibition on CRH-secreting neurons to balance excitatory signalling from the amygdala, which leads to more cortisol release (positive feedback)

Question 89

Define sex at the anatomical and chromosomal level and explain how these definitions differ.

Answer 89

**Chromosomal/Nuclear sex** → defined based on the presence of XX (female) or XY (male) chromosomes in somatic cells **Gonadal sex** → based on the type of internal genitalia present; females = ovaries; males = testes **Morphological sex** → based on the external genitalia; male = penis; scrotum; female = mons pubis; labia; clitoris

Question 90

Compare and contrast X and Y chromosomes.

Answer 90

**X-chromosome** → protein coding genes: 1000-2000; one of the two X chromosomes is permanently inactivated during development (= X chromosome inactivation), so the genetic material becomes tightly compacted and inaccessible to transcriptional or translational proteins (= Barr body: dense heterochromatic structure formed by XCI in XX females) **Y-chromosome** → protein coding genes: ~45; one of these genes is SRY, responsible for initiation male sex development While X and Y chromosomes are vastly different in size and genetic material, two regions of homology, known as **pseudoautosomal regions 1 and 2** exist and behave autosomally.

Question 91

Know how SRY gene expression influences hormone production and sex determination in the growing fetus.

Answer 91

* The SOX9 gene (i.e., testes determining factor) is triggered to be expressed if (and only if) SRY has been expressed at the right time and in the right amount. * In response to SOX9 expression in XY individuals, the primordial germ cells differentiate into sperm, and the supporting cells become Sertoli cells. * Sertoli cells secrete Anti-Müllerian hormone (AMH), which is responsible for degrading the Müllerian ducts. * On the other hand, primordial germ cells of the ovaries will develop into oocytes, and the supporting cell precursors develop into granulosa cells which do not secrete AMH. In the absence of AMH the Müllerian ducts do not degrade, but the Wolffian ducts do.

Question 92

Describe how testosterone and estrogen are produced, and the role they play in sex development.

Answer 92

* In response to testes development in XY individuals, the steroidogenic cell precursors develop into Leydig cells and produce androgens (i.e., testosterone). * Presence of androgens secreted within the developmental window in-utero causes the embryo to develop male external genitalia * The steroidogenic cell precursors develop into Follicular cells in the ovaries and produce estrogens. * The presence of estrogens secreted by the ovaries within the developmental window in-utero causes the embryo to develop female external genitalia

Question 93

Compare and contrast male and female postnatal sex development before and after the onset of puberty.

Answer 93

* Secondary sex development is initiated by increased production of gonadotropin releasing hormone within the hypothalamus. * GnRH then stimulates increased production of follicle stimulating hormone (FSH) and luteinizing hormone (LH) * Prior to puberty, these hormones act on the gonads and exhibit a negative feedback loop which inhibits their production. * At puberty, the negative feedback is removed and allows androgen production in the testes and estrogen production in the ovaries. * Responses to Testosterone in males: * facial hair * accelerated bone deposition and skeletal growth → closure of epiphyseal cartilage * increased muscle mass * sex drive initated * increased blood volume * growth of larynx and lengthening/thickening of vocal cords → deep voice * promotion of spermatogenesis * Response to estrogen in females * body hair in genital area * more rapid epiphyseal closure than in males (females are not as tall) * stimulated muscle growth (not to the same extent as in males) * female sex drive initiated * decreased plasma cholesterol levels * higher pitched voice due to no excessive growth of larynx and vocal cords * menstrual cycle onset

Question 94

Predict how chromosomal aneuploidy, gene mutation, and/or hormonal levels can influence sex development in intersex individuals.

Answer 94

* Klinefelter syndrome (47, XXY) → extra X chromosome * Characterized by tall stature with long limbs (re: SHOX gene dosage) and an increased risk for autism and ADHD * Influence on sex development: * testes do not develop → infertility * symptoms not apparent until puberty * androgen therapy is common * Turner syndrome (45, X0) → only one X chromosome * Short stature (re: SHOX gene dosage) and increased risk for thyroid disorder and ADHD * Influence on sex development: * Ovaries degenerate in early childhood - loss of estrogen and no secondary sex characteristics * Note: The SHOX gene is X-linked, escapes XCI and is involved in the growth of long bones * Androgen insensitivity → X linked recessive genetic condition; 46, XX or XY * Impairs testosterone activity and feminizes XY individuals * XX are carriers * Masculinizing congenital adrenal hyperplasia → autosomal recessive disorder; 46, XX * Increases androgen production * Impairs puberty and masculinizes XX individuals * XY not affected to same degree → consider as carriers

Question 95

Explain the roles of the three components (testes, ducts/glands, penis) of the male reproductive system, spermatogenesis, semen production, and sperm delivery.

Answer 95

**Ducts/glands →** contribute to maturation of sperm or secrete fluids to keep sperm viable **Urethra and penis** → responsible for depositing sperm in female reproductive tract **Testes** → makes the sperm

Question 96

Describe the organization of the testes and the penis including the tissue types present in each organ.

Answer 96

_Testes_ * scrotum (skin, muscle layers, and fascia) * membrane and fascia layers → tissues that allow the testes to move within the scrotum and keep the tubular lobes separated.

Question 97

Explain the steps of spermatogenesis including the support cells, and the time course and location when/where different stages occur.

Answer 97

* As the developing gametes progress from spermatogonium to spermatocyte, spermatid, and finally sperm, they move from the basal layer of the seminiferous tubule (within the testes) toward the lumen, while maintaining contact with the Sertoli cells which provide the developing sperm with chemical signals and nutrients. * Mitosis takes 16 days; Meiosis I completes within 24 days; Meiosis 2 occurs within hours; Spermiogenesis takes 24 days.

Question 98

Analyze trade-offs that arise from testicular anatomy and physiology (e.g., temperature and cell division)

Answer 98

* Mammalian testes are pushed out of the abdominopelvic cavity during embryonic development - but remain mobile in response to temperature (= cremaster contraction) * Benefit → sperm functions optimally at temperature cooler than internal body temperature * Cost → testes are vulnerable

Question 99

Describe the roles of the parasympathetic, sympathetic, and somatic nervous systems in the male sexual response.

Answer 99

**Parasympathetic** → innervate erectile tissue; during arousal, release nitric oxide as well as ACh, which relaxes smooth muscle (i.e., inhibition) allowing increased blood flow that fills the vascular spaces, causing erection **Sympathetic** → innervate the epididymis, vas deferens, and seminal vesicles; active during arousal, sperm and secretions are moved into urethra **Lumbosacral somatic motor neurons →** innervate the skeletal muscles at the base of the penis (i.e., the pelvic floor); during ejaculation, a spinal reflex produces rhythmic contractions, helping push semen out of the urethra.

Question 100

Explain the organization and regulation of the HPG axis for a typical male reproductive system, including pulsatile secretion pattern, sites of hormone action, and sources of negative feedback.

Answer 100

* **HPG axis** → involves releasing hormones of the hypothalamus, anterior pituitary and effector hormones of the gonads * LH → activates androgen synthesis and release from Leydig cells * FSH → activates Sertoli cells to promote spermatogenesis and also produce inhibin, a regulatory hormone * GnRH is released from the hypothalamus in a regular pulsatile manner → creates pulses of increased LH and FSH secretion from the anterior pituitary (~once every 2 hours) * Androgenic (testosterone) negative feedback occurs mostly at the level of the hypothalamus * Inhibin has a major role inhibitin secretion of gonadotropes from the anterior pituitary

Question 101

Explain the roles of the components of the female reproductive system in oogenesis and fertilization or pregnancy.

Answer 101

**Ovaries** → make the ova **Uterine tubes and uterus** → site of fertilization (tube) and site of embryonic foetal development (uterus) **Vagina and external genitalia** → responsible for receiving sperm (and pleasurable sensations associated with the sexual response)

Question 102

Describe the organization of the ovaries and uterus and explain the changes that occur in each organ over the ~28 day ovarian/uterine cycle.

Answer 102

**Ovary** → divided into cortical (oocytes develop here) and medullary (blood vessels enter here) regions

Question 103

Compare and contrast the processes of oogenesis and spermiogenesis as forms of gametogenesis, including the presence or absence of atresia over the lifespan.

Answer 103

**Ovary** → divided into cortical (oocytes develop here) and medullary (blood vessels enter here) regions * No direct connection between ovaries and uterine tubes * Atresia is loss of follicles and oocytes throughout reproductive lifespan. * During each ovarian cycle, multiple oocytes are activated but usually only one survives

Question 104

Explain the organization and regulation of the HPG axis for a typical female reproductive system, including changes in the pulsatile secretion over the ovarian cycle, sites of action for different hormones, and sources of negative feedback.

Answer 104

* LH is only secreted by gonadotropes when GnRH pulses are frequent and estrogen levels are high * Stimulates thecal cells to secrete androgens * FSH only requires GnRH stimulation for production and secretion * Stimulates granulosa cells to secrete aromatase, which converts the secreted androgens to estrogens; granulosa cells also secrete inhibin which provides direct negative feedback on the secretion of FSH from the pituitary * When estrogen levels are low → negative feedback on LH secretion * When estrogen levels rise (driven by FSH), they act synergistically with GnRH to enhance LH secretion → positive feedback * Progesterone (secreted by corpus luteum) has a primary role in negative feedback of GnRH secretion → when progesterone levels are high, GnRH release is very low

Question 105

Analyze how hormonal-based contraceptives affect the activity of the female HPG axis.

Answer 105

* Oral contraceptives rely on providing a constant **low** dose of estrogens and progesterones to prevent the spike in LH required for ovulation * Progesterone only pills act by thickening the cervical mucus to act as a barrier for sperm entry → not completely reliable * Combined Oral (CPOP)→ varying daily doses * Mini-pill (POP) → daily doses of progestins * Post-coital → very high dose of progesterones which block GnRH activity and prevent/delay ovulation

Question 106

Describe the roles of the autonomic and somatic nervous system in the typical female sexual response and compare this to their roles in the typical male sexual response.

Answer 106

**Both divisions of the ANS** → innervate erectile tissue in the clitoris and vagina (increases blood flow), and glands (leading to secretion of lubricating fluid Orgasm is associated with rhythmic activation of pelvic muscles (**somatic nervous system**) and smooth muscle in the uterus and vagina (**ANS**).

Question 107

Describe, compare, or contrast the processes occur in in the oocyte/zygote/morula/blastula during fertilization, cleavage, and implantation.

Answer 107

* After fertilization of the oocyte, the female and male genetic material mingle and form the zygote. * Cleavage begins immediately after the zygote is formed. * **Morula** → solid ball of cells (zygote undergoes repeated mitotic cell divisions without growing) * The cleavage stage ends when the morula becomes a blastocyst and hatches from the zona pellucida. * During implantation, trophoblast cells drive the erosion of the endometrial epithelium, lodging the blastocyst within the endometrium.

Question 108

Identify the three germ layers formed by gastrulation and briefly describe what this process is and when and where it occurs during pregnancy.

Answer 108

* Gastrulation follows implantation and creates three germ layers. * Ectoderm → forms head, epidermis, and nervous system * Mesoderm → forms skeleton, muscles, dermis, adipose, and connective tissue. * Endoderm → forms digestive system and parts of the urinary system.

Question 109

Describe the functions and origins of the placenta and explain the difference between the placenta and the umbilical cord.

Answer 109

* The placenta is connected to the foetus by the umbilical cord. It is (mostly) a foetal organ responsible for: * Nutrient and oxygen exchange * Removal of carbon dioxide and waste * Secretion of hormones into both bloodstreams.

Question 110

Name at least three hormones secreted by placental tissues, describe when their secretion is elevated, and explain their functions during pregnancy.

Answer 110

* Human chorionic gonadotropin (hCG) is secreted by the placental trophoblast very early in pregnancy; levels are highest during the first trimester; signals to the corpus luteum to survive; also promotes maternal immune tolerance of foetus * After the luteal-placental shift (i.e., the corpus luteum becomes the corpus albicans and stops all hormonal secretions); the placenta begins progesterone secretions, which maintains the endometrium; decreases uterine contractions allowing for better implantation and growth; maintains endometrium, inhibits labour, and active lactation * The placental trophopblast begins to synthesize estrogens as pregnancy progresses; plays a role in child birth and determining when the time is right by increasing prostaglandin production, and increasing myometrial activity to determine time of labour; increases blood flow to the baby; regulates receptors for other hormones * Relaxin → alters blood flow and promotes ligament loosening (i.e., loosening of the pubic symphysis to allow a larger gap between hip bones for pregnancy)

Question 111

Define the term ‘medical abortion’ and explain the role of mifepristone, the most commonly used drug for this procedure.

Answer 111

**Medical abortion** → taking a combination of medicines to end pregnancy by causing the uterine lining to shed **Mifepristone** → a steroid derivative that prevents progesterone from activating the progesterone receptor; leads to softening of the cervix and the disintegration of the endometrium, detaching both the placenta and the embryo

Question 112

Define the terms ‘organogenesis’ and ‘teratogen’ and explain why certain molecules or other factors can be teratogenic despite posing few or no risks to an adult.

Answer 112

Organogenesis → growth and maturation of organs during embryogenesis Teratogen → Molecules/factors that adversely alter embryonic development, including organogenesis.

Question 113

Identify and discuss the anatomical and physiological strains pregnancy places on the body.

Answer 113

_Anatomical_ * Restriction of lung expansion * Compression of digestive organs * Weight misaligned with body axis and skeleton * Bladder compressed * Pressure on rectum * Diastasis recti _Physiological_ * Late pregnancy is metabolically equivalent to running a marathon every day * Respiratory rate increases * Tidal volume imcreases * Maternal blood volume increases * Kidneys work faster (more urine produced) * Uterus expands * Hunger diminished due to compression on the stomach, however pregnant people need to eat more.

Question 114

Explain the changes that occur within the myometrial layer during late stages of pregnancy and how the myometrium produces labour contractions.

Answer 114

Organogenesis → growth and maturation of organs during embryogenesis Teratogen → Molecules/factors that adversely alter embryonic development, including organogenesis. * Roaccutane → anti-acne medication; a teratogen that can repress formation/growth of the forebrain → leads to anencephaly. * Thalidomide → anti-nausea medication; disrupts organ and limb formation → leads to still-births or phocomelia

Question 115

Analyze the roles of placental, foetal, and maternal factors in producing contractions and enhancing labour, and describe the three phases of successful labour.

Answer 115

* Labour is initiated by placental and foetal factors → signal cervix to soften * The foetal pituitary gland secretes oxytocin → myometrium begins to contract → pushes head toward cervix, stretches and dilates it → mechanosensory neurons trigger release of maternal oxytocin → leads to secretion of prostaglandins → drives increase in dilation of cervix → increased oxytoxin release → increased contractions of myometrium (i.e., a positive feedback cycle) * Dilation stage → uterine contractions become more frequent and intense, cervix dilates to ~10cm * Expulsion stage → uterine contractions may be supplemented with voluntary pelvic and abdominal contractions * Placental stage → continued uterine extractions dislodge placenta, which is then expelled

Question 116

Identify medical interventions that can be used to initiate or enhance labour or circumvent it.

Answer 116

* Manual ‘water-breaking’; rupture of membranes * Physical attempts to dilate the cervix * Direct application of prostaglandins to the cervix to help it begin to stretch and dilate. * Intravenous oxytocin is administered after regular uterine contractions → enhance contractions, not effective at initiating them.

Question 117

Compare and contrast the functions and composition of colostrum and breastmilk.

Answer 117

Colostrum → nutrient poor, rich in antibodies; provides immune protection for neonates who don't have a fully functioning immune system at birth. Breastmilk → contains relatively fewer immune molecules, but is nutrient rich (esp. fat and lactose)

Question 118

Explain the neurohormonal basis of lactation, including the distinct roles of anterior and posterior pituitary hormones.

Answer 118

* Contraction of myoepithelial tissue around milk ducts is part of a neurohormonal reflex that leads to milk ejection and stimulates further milk production * Hypothalamus secretes PIH → leads to release of prolactin from the anterior pituitary → milk secretion * Hypothalamus also stimulates release of oxytocin from the posterior pituitary → smooth muscle contraction → milk ejection * Mechanoreceptors in nipple, or the sound of a child's cry, stimulate higher brain centers which trigger hypothalamus to secrete PIH and stimulate the posterior pituitary