Test 1 study guide

Question 1

Identify the primary components of the skeletal system

Answer 1

Bones, cartilage, and connective tissue

Question 2

What are the major functions of the skeletal system?

Answer 2

Movement/mobility, support and protection, hempoeisis, and storage

Question 3

Describe the function of movement/mobility in the skeletal system

Answer 3

Bones form a system of levers that act as attachment sites for skeletal muscles allowing for mobility

Question 4

Describe the function of support and protection in the skeletal system

Answer 4

Bones create a structural framework for the body protecting many delicate tissues

Question 5

Describe the function of hemopoiesis in the skeletal system

Answer 5

Formed elements of the blood (RBCs, WBCs and platelet) develop in the red bone marrow of bones

Question 6

Describe the structural classification of bones and provide example of each type.

Answer 6

Long bone (ex. femur)
Greater in length than width
Flat bone (ex. frontal bone)
Flat, thin surface, may be curved
Irregular bone (ex. vertebrae)
Complex, elaborate shapes
Short bone (ex. tarsal bone)
Length nearly equal to width

Question 7

Describe the function of storage in the skeletal system

Answer 7

Mineral Storage: 99% of the body’s calcium and phosphate are stored in the bones
Lipid Storage: adipose tissue (fat) is stored in yellow bone marrow

Question 8

Compare the organic and inorganic components of the bone extracellular matrix.

Answer 8

Organic (1/3 matrix)
Provides Flexible Strength
Osteoid produced by osteoblasts * Ground substance consisting
largely of collagen, proteoglycans and glycoproteins arranged in a uniformed pattern
* Gives bone tensile strength by resisting stretching, contributes to bone flexibility
* Vitamin C required for collagen formation
Laid down first by osteoblasts
Inorganic (2/3 matrix)
Provides Weight Bearing Strength
Mineralized crystals (largely hydroxyapatite [Ca10(PO4)6(OH)2]) are deposited around collagen fibers of the osteoid resulting the mineralization/calcification of the bone matrix
* Hardened matrix accounts for relative rigidity of bones
* Vitamin D necessary for proper calcium absorption

Question 9

Identify each of the four bone cells and describe the function of each.

Answer 9

Osteoprogenitor Cells
* Derived from mesenchymal stem cells
* Differentiate into osteoblasts
Osteoblasts
* Synthesize and secrete osteoid (largely collagen) as part of mineralization
* Regulate osteoclast differentiation and activity
Osteocytes
* Mature cells enveloped by calcified osteoid
* Maintains matrix and responds to stress by
activating osteoblast and osteoclast activity
Osteoclasts
* Phagocytic, multinucleated cells that form by the fusion of bone marrow cells
* Digests and dissolves bone matrix through
resorption
* Proteolytic enzymes breaks down organic
material
* HCl dissolves inorganic material

Question 10

Compare the structural organization of compact and spongy bone tissues.

Answer 10

Compact Bone (Dense or cortical bone)
* Located at bone exterior
* Appears white, smooth, and solid
* Composed of osteons and lamellae
* Associated with both periosteum and
endosteum bone membranes
* Contains perforating foramen, Volkmann’s
and Central canals
Spongy Bone (Cancellous or trabecular bone)
* Located internal to compact bone
* Appears porous, with space between bone
tissue containing red bone marrow
* Composed of trabeculae
* Associated with endosteum bone
membrane

Question 11

Identify osteon, interstitial lamellae, external circumferential, and internal circumferential
lamellae structural regions within compact bone tissue.

Answer 11

Osteon
- Functional unit of compact bone composed of concentric lamellae and a central canal
Interstitial lamellae
-Compact bone remains of a partially resorbed osteon found between newer, complete osteons
External Circumferential lamellae
-Rings of compact bone that surround the entire outer compact bone surface; found immediately internal to bone periosteum
Internal circumferential Lamellae
-Rings of compact bone that line the inner edge of compact bone tissue; found adjacent to the endosteum

Question 12

Explain the organization of an osteon and the placement/interaction of osteocytes within an
osteon.

Answer 12

Each osteon contains multiple layers of concentric lamellae that surround a central canal
* Central canal contains blood vessels and nerves
Each lamellae is composed of inorganic crystals deposited between collagen fibers
* With in each individual concentric lamellae the collagen fibers are parallel
* Amongst each adjacent concentric lamellae the parallel collagen fibers are placed about 90 degrees from the collagen fibers in adjacent lamellae creating an alternating pattern among the concentric lamellae
* Osteoblasts that become surrounded by mineralized bone matrix develop into osteocytes
* Osteocytes are located between adjacent concentric lamellae
* The osteocyte cell body is housed in small open spaces called lacunae
* Cellular processes extend from the osteocyte cell body through thin, small spaces called canaliculi
* This allows for cells to communicate with each other where the cellular processes of each cell are joined through gap junctions

Question 13

Compare the structure and location of bone membranes associated with compact bone tissue.

Answer 13

• Osteoblasts that become surrounded by mineralized bone matrix develop into osteocytes
• Osteocytes are located between adjacent concentric lamellae
• The osteocyte cell body is housed in small open spaces called lacunae
• Cellular processes extend from the osteocyte cell body through thin, small spaces called canaliculi
• This allows for cells to communicate with each other where the cellular processes of each cell are joined through gap junctions

Question 14

Describe the function and location of a nutrient foramen, Volkmann’s and Central canals.

Answer 14

Nutrient Foramen
* Opening in the bone where vessels and nerves enter and exit
Perforating (Volkmann’s) Canal
* Carries blood vessels and nerves through compact bone, interconnecting the central canals of osteons
Central (Haversian) Canal
* Carry blood vessels and nerves through the center of individual osteons

Question 15

Describe the organization of trabeculae in spongy bone tissue including the associated bone
membrane.

Answer 15

• Forms an open lattice of narrow rods and plates of bones called trabeculae
• Spaces between trabeculae are filled with blood vessels and bone marrow
• Trabeculae composed of flattened layers of bone matrix called parallel lamellae
• Osteocytes housed in lacunae are located between lamellae
• Canaliculi (containing osteocyte cellular processes) radiate to adjacent osteocytes and to the outer surface of the trabeculae
• Outer surface of trabeculae covered by an incomplete endosteum

Question 16

Compare the anatomy of flat, irregular and short bone with the anatomy of a long bone.

Answer 16

• Central bone shaft that provides leverage and support
• Exterior consists of thick layer of compact bone covered by periosteum
• Interior composed of spongy bone bone
• Referred to as diploë in flat bone
• No medullary cavity is present, but bone marrow is found within spongy bone

Question 17

Compare the diaphysis, epiphyses, and metaphysis regions of a long bone.

Answer 17

Diaphysis
* Central bone shaft that provides leverage and support
* Exterior consists of thick layer of compact bone with thin spicules of spongy bone extending inward
* Contains a central medullary cavity (unique to long bones)
Epiphyses (Proximal & Distal)
* Enlarged surface ends( “knobs”) composed of a thin outer compact bone layer surrounding inner, bone marrow filled spongy bone
Metaphysis
* Region that widens and transfers the weight between the diaphysis and epiphysis
* Contains the cartilage containing epiphyseal plate, or growth plate, responsible for the lengthwise growth in bones
* Once growth ceases, bone tissue replaces all of the cartilage and the epiphyseal line (composed of a thin line of compact bone) remains

Question 18

Describe the function of the epiphyseal plate and differentiate between an epiphyseal plate and an epiphyseal line.

Answer 18

epiphyseal plate: contains cartilage; growth still occurring
epiphyseal line:
no cartilage present; growth ceased

Question 19

Identify the location and function of the medullary cavity.

Answer 19

Medullary cavity contains two types of highly vascularized
bone marrow – Red and Yellow
*Red Bone Marrow (myeloid tissue) is hemopoietic
* tissue containing highly active stem cells for the formed elements of blood
* All bone marrow is red at birth and is slowly converted to yellow as you age
* Red bone marrow located only in selected areas of adults, largely in regions of the of axial skeleton and a few areas of the appendicular skeleton including the proximal epiphyses of humerus and femur
Yellow Bone Marrow is composed largely of adipose (fat) tissue
* Retains the potential to convert back into red blood marrow under stress (i.e severe anemia)

Question 20

Compare and contrast the function and location of red and yellow bone marrow and describe how this changes throughout life.

Answer 20

Red Bone Marrow (myeloid tissue) is hemopoietic
tissue containing highly active stem cells for the formed elements of blood
* All bone marrow is red at birth and is slowly converted to yellow as you age
* Red bone marrow located only in selected areas of adults, largely in regions of the of axial skeleton and a few areas of the appendicular skeleton including the proximal epiphyses of humerus and femur
Yellow Bone Marrow is composed largely of adipose (fat) tissue
* Retains the potential to convert back into red blood marrow under stress (i.e severe anemia)

Question 21

Describe the locations of the periosteum and endosteum in long bones.

Answer 21

A double layer sheath that covers the outer surface of most bones
* Protects bone from surrounding
structures, anchors blood vessels and nerves, acts as attachment site for ligaments and tendons
* Missing in patella and joint surfaces of long bones covered by articular cartilage
Endosteum
An incomplete cellular layer containing osteoprogenitor cells, osteoblasts, and osteoclasts

Question 22

Describe the location and structure of the Perichondrium.

Answer 22

• Dense irregular connective composed mostly of collage fibers that covers cartilage surface and helps maintain its shape
• Most of the region contains fibroblasts but the deepest layer contains mesenchymal stem cells

Question 23

Describe the structural components of cartilage extracellular matrix.

Answer 23

• Avascular (mature tissue), gel-like protein matrix that includes collagen and aggrecan, a proteoglycan that allows it to absorb water
• Unlike bone, there is no calcium present in the extracellular matrix

Question 24

Identify the cartilage tissue cells and the function of each.

Answer 24

Mesenchymal Stem Cells
* Only found only in the deepest layers of the perichondrium
* Divides and forms chondroblasts
Chondrocyte
* Maintains the cartilage matrix * Found in individual lacunae
* Forms from a chondrobast
and may divide and create additional chondroblasts
Chondroblast
* Produces cartilage matrix
* Matures into chondrocytes
* Found in shared lacunae

Question 25

Describe the steps of appositional cartilage growth and identify the specific region where this
type of growth occurs.

Answer 25

• Growth occurs at the perichondrium and increases cartilage width
• Perichondrium surrounds cartilage in areas such as costal cartilage, between spinal vertebrae and nose; lacking in the articular cartilage of adults
• Mesenchymal stem cells divide and form chondroblasts
  Steps
  Mitotic activity occurs in mesenchymal stem cells within the deepest layers of the perichondrium forming chondroblasts.
  Chondroblasts each secrete cartilage matrix causing them to be pushed further and further apart.
  The chondroblasts mature into chondrocytes.

Question 26

Describe the steps of interstitial cartilage growth.

Answer 26

• Occurs when chondrocytes in the cartilage’s internal region divide forming chondroblasts
• Type of growth that occurs at the epiphyseal plate, allows for an increase in length
  Steps
  A chondrocyte within a lacuna begins to exhibit mitotic activity
  Cellular division of chondrocyte produces two new cells (chondroblasts) that occupy a single lacuna
  Each cell produces new cartilage matrix and begins to separate from its neighbor
  Previously secreted matrix matures, further separating individual cells in their own lacunae

Question 27

Identify the embryonic tissue that develop skeletal system structures form from.

Answer 27

• Mesenchyme tissue is the starting material for the skeletal system structures

Question 28

Identify the two different ways bones form and provide examples of bones that form each way.

Answer 28

Ossification occurs in two ways:
* Intramembranous: mesenchyme directly becomes bone
Ex-flat bones of skull, mandible and central part of the clavicle
* Endochondral: cartilage forms, then becomes bone
Ex-humerus, vertebrae, and ribs

Question 29

Explain the process of intramembranous ossification.

Answer 29

– Vascularized mesenchymal
membrane becomes ossified
Steps
Osteoid
1. Ossification centers form within thickened regions of mesenchyme
– Mesenchymal cells become
osteoprogenitor cells which differentiate into osteoblasts which secrete osteoid
2. Osteoid undergoes calcification forming the ossification center
- Calcification of matrix causes osteoblasts to become osteocytes
- Osteoblasts remain at the periphery, continuing to depositing osteoid, allowing for the expansion of the bone deposition
3.
Woven bone (primary bone) and bone membranes begin to form
– At first, woven bone is formed which is immature and poorly organized (lacking lamellae)
– Mesenchyme tissue condenses and forms the membranes
4.
Lamellar bone (secondary bone)
replaces woven bone
– Lamellar compact and lamellar spongy bone form
– Endosteum and periosteum fully developed

Question 30

Explain the process of endochondral ossification and how this relates to the anatomy of long bones.

Answer 30

1. Fetal hyaline cartilage model develops and perichondrium forms
   * Perichondrium develops into periosteum
2. Periosteal bone collar forms
   * Nutrient foramen starts to develop and interior cartilage breaks down due to mineralization
3. Primary ossification center forms
   * Periosteal bud blood vessel enters diaphysis
   * Cartilage in diaphysis ossifies and bone development extends in both directions toward epiphyses as bone replaces degenerating cartilage
4. Secondary ossification centers form in epiphyses
   * Cartilage in epiphyses calcifies, chondrocytes die
   * Blood vessels enter carrying osteoprogenitor cells which become osteoblasts active in forming woven bone
   * The woven bone in the diaphysis interior is removed by osteoclasts, forming the medullary cavity
   * Lengthwise growth occurs at epiphyseal plate until

Question 31

Compare woven and lamellar bone.

Answer 31

Lamellar bone only occurs through intramembranous ossification, woven bone only occurs in endochondral ossificiation

Question 32

Explain the process of endochondral bone growth, what region of the bone this occurs at, and the resulting impact of this type of growth on a bone.

Answer 32

Epiphyseal Plates
* Multiple epiphyseal plates may exist in a single bone
* Epiphyseal plates appear and fuse progressively at set ages
* These ages differ among males and females among specific regions with females typically closing at an earlier age
* Growth plate fusion on skeletal remains is used to determine age of death in forensics recognizing that the skeleton is sexually dimorphic and variations exist among populations

Question 33

Describe the five epiphyseal plate zones and their orientation in association with the diaphysis and epiphysis.

Answer 33

Zone of Resting Cartilage (closest to epiphysis)
Mature hyaline cartilage that secures epiphysis to epiphyseal plate
Zone of Proliferation
Chondrocytes undergo rapid mitotic division producing longitudinal columns of parallel, flattened lacunae
Zone of Hypertrophy
Chondrocytes cease to divide and begin to hypertrophy, walls of lacunae thin
Zone of Calcification
Minerals deposited between lacunae killing chondrocytes
Zone of Ossification (closest to diaphysis)
Lacunae walls break down, capillaries and osteoprogenitor cells enter as new bone matrix deposited on the calcified cartilage matrix

Question 34

Explain the process of appositional bone growth, what region of the bone this occurs at, and the resulting impact of this type of growth on a bone.

Answer 34

*Osteoblasts at periosteum deposit bone matrix in layers parallel to surface
*Osteoclasts at endosteum resorb bone matrix along medullary cavity at the diaphysis region to increase this area proportionally
Makes bones wider

Question 35

Compare the processes of deposition and reabsorption.

Answer 35

Deposition
* Adding Bone Tissue
* Process of bone matrix being added by osteoblasts
* Begins with secretion of osteoid by the osteoblasts, followed by the organized mineralization (calcification) of the matrix
Resorption
* Removing Bone Tissue
* Process of bone matrix being
broken down by osteoclasts
* Proteolytic enzymes secreted by osteoclasts chemically digest organic matrix components
* hydrochloric acid dissolves inorganic matrix producing freed calcium and phosphate ions which enter the blood

Question 36

Identify how the hormones TH, GH/IGF, sex hormones, glucocorticoids, and serotonin impact the skeletal system.

Answer 36

Thyroid hormone is necessary for the proper development of growth hormone (GH) which is essential to the formation and maintenance of the skeleton
* Thyroid hormone release is controlled by a negative feedback loop which includes interactions between the hypothalamus, pituitary gland, and thyroid gland
* Hypothalamus releases thyroid releasing hormone (TRH) which stimulates the pituitary gland to secrete thyroid stimulating hormone (TSH) which directly stimulates bone growth and indirectly stimulates bone growth through the secretion of thyroid hormone (TH; T3 & T4)
* During the development of the skeleton TH is necessary for the recruitment and maturation of both cartilage and bone cells
* TH Important regulator of normal bone growth, especially in childhood and stimulates bone growth and promotes synthesis of bone matrix by increasing the metabolic activity of the bone cells
* Growth Hormone released by the pituitary gland stimulates the production of insulin-like growth factor (i.e. IGF) in the liver
* Both GH and IGF enhance mineralization and increases bone density
* These hormones have a particularly potent effect on the cartilage within the epiphyseal plate region, stimulating elongation of the long bones
Sex hormones (i.e. estrogen and testosterone)
* Sex hormones levels dramatically increase at puberty with both having an especially strong impact at the epiphyseal plate by stimulating both cartilage and bone cells
* The growth rate of bone here is greater than that cartilage growth which initiates the closure of the epiphyseal plate, eventually leading to the formation of the epiphyseal line
* Postmenopausal women no longer produce significant amounts of estrogen and have an increased risk of osteoporosis
Glucocorticoids (ex. Cortisol)
* Steroid hormones released from the adrenal gland that
regulate blood glucose levels
* High levels cause increased bone loss and impair growth of the epiphyseal plate
* Glucocorticoids can be prescribed as anti-inflammatory medications (ex. Asthma treatment) so patients must be monitored since it could potentially have a negative impact on bone growth in children
Serotonin
* High levels of serotonin has a negative effect on osteoblast differentiation, may decrease bone density

Question 37

Explain how parathyroid hormone, calcitriol, and calcitonin function together to regulate blood calcium.

Answer 37

• Calcitriol stimulates the absorption of calcium from the small intestine into the blood
• Calcitriol formation in the kidney occurs more readily in the presence of Parathyroid Hormone
• Parathyroid hormone and calcitriol work synergistically to increase blood calcium levels
• Calcitriol stimulates absorption of calcium from small intestines into the blood
  Parathyroid hormone enhances the production of calcitriol. Both hormones working together to increase blood calcium levels.

Released in response to decreased blood calcium levels, stimulates bone resorption resulting in an increase in blood calcium levels

Calcitonin-Released by the thyroid in response to high blood calcium levels and in response to exercise; stimulates bone deposition resulting in a decrease in blood calcium levels

Question 38

Describe Wolff’s Law and explain its role in maintaining bone density.

Answer 38

Mechanical stress occurs in weight-bearing bone due to movement and exercise, required for proper bone remodeling
* skeletal contraction and gravitational forces biggest impact
* Stress detected by osteocytes which communicates to osteoblasts, triggering an increased synthesis of osteoid that adds to bone strength
* Removal of mechanical stress reduces collagen formation and causes demineralization
* Immobilization, microgravity environment (space) reduce bone mass
* Wolff’s Law states that bone in a healthy person or animal will adapt to the loads under which it is placed
* Internal bone architecture adapts as well as external

Question 39

Compare a simple and compound fracture and outline the steps of bone repair for a simple fracture.

Answer 39

• Simple fracture refers to a broken bone that doesn’t penetrate the skin
• Compound fracture occurs when one or more region of a bone pierces the skin
  Steps to healing
  1. A hematoma forms from broken blood vessels.
  2. A fibrocartilaginous (soft) callus forms as collagen fibers (from fibroblasts) and dense connective tissue (from chondroblasts) aggregate.
  3. A hard (bony) callus forms as adjacent osteoblasts produce bone tissue.
  4. The bone is remodeled.

Question 40

Identify the age at which bone density normally peaks and describe the effects of aging on the skeletal system.

Answer 40

Overall Impact
* Bone density peaks about 30 and decreases as you age
* Bones with larger portions of spongy bone are more susceptible causing a greater impact on vertebrae, mandible, and epiphyses
* Causes decrease in height, tooth loss, and fragile limbs
* Decrease in hormones (i.e. sex hormones) contribute to overall loss in mass
* Onset of menopause and subsequent loss of estrogen has a major impact on women increasing their risk of osteoporosis
Impact on Bone Composition
* Reduced tensile strength due to a decrease in osteoblast activity and therefore protein production
* Alters the ratio of organic/inorganic resulting in brittle bones with increased fracture risk
* Increased demineralization resulting in insufficient ossification and thinner, weaker bones (osteopenia)

Question 41

Compare the central and peripheral nervous system.

Answer 41

Central Nervous System Organs
* Covered by connective tissue
meninges
* Protected by skull and vertebrae
Brain
* Site of thoughts and intelligence
* Processes information received and sends messages back to the body
Spinal Cord
* Carries information between the brain and the body
* Musculoskeletal reflex center (i.e. knee jerk)
Peripheral Nervous System (PNS)
Peripheral Nervous System Structures
Nerves
* Bundled axons which carry signals to and from the CNS
* Extend from the brain or spinal cord
Ganglia
* Cluster of neuron cell bodies outside the CNS

Question 42

Compare a neuron and a nerve and describe where each is found (i.e. CNS only, PNS only, or both CNS & PNS).

Answer 42

Nerve: An organized, collective bundle of neuron axons that send signals throughout the PNS
All nervous tissue is composed of neurons and glial cells
* Neuron:
* Excitable cells
* Both the central nervous system (CNS) and peripheral nervous system (PNS) are made of nervous tissue
* Neurons are individual cells that send electrical signals while nerves, which are only found in the PNS, are organs composed of clusters of numerous neuron axons

Question 43

Describe the structural classification of neurons.

Answer 43

Multipolar Neuron
* Most common type of neuron
* Includes all motor neurons and most
interneurons
* Multiple processes extend directly from the
neuron cell body (soma)
* Typically has multiple dendrites and one axon
* Includes all motor neurons and most
interneurons
Bipolar neuron
* Limited locations, found in some special senses (e.g., retina of eye, olfactory epithelium in nose)
* Two processes extend directly from the cell body; one dendrite and one axon
Unipolar neuron
* Most sensory neurons
* Dendrites directly to peripheral process of axon; single
short process extends directly from the cell body and forms a “T” intersection with the two processes (peripheral and central) of the one long axon
Anaxonic neuron
* Interneurons
* Lacks an axon; processes are only dendrites that
extend from the cell body

Question 44

Describe the functional classification of neurons.

Answer 44

Sensory (Afferent) Neuron
* Receive somatic and visceral sensory input
* Conduct action potential signals to the CNS
* Most sensory neurons are unipolar with receptive region and cell body in PNS and axon end in CNS
Interneuron (Association Neuron)
* Receives signals from sensory neurons and sends signals to motor neurons
* Locate entirely in CNS
* Typically multipolar or anaxonic
neurons
Motor (Association) Neuron
* Conducts motor output from the CNS to effectors in the PNS
* Innervate both somatic (i.e. skeletal muscle) and autonomic effectors (i.e. smooth muscle)
* Multipolar neurons

Question 45

Compare electrical and chemical synapses.

Answer 45

Electrical synapse
*fastest
* Junction between two neurons that allows for the two-way transmission of electrical signals
* Presynaptic and postsynaptic neurons bound together by gap junctions
Chemical synapse
*most common type of synapse
* Presynaptic neuron’s axon terminal produces signal in the form of a neurotransmitter
* Postsynaptic neuron receives signal as neurotransmitter binds to receptors and causes a postsynaptic potential (either depolarization or hyper polarization)

Question 46

Define anterograde and retrograde axonal transport.

Answer 46

Anterograde transport:
Moves newly synthesized material toward synaptic knobs
Retrograde transport:
Moves used materials from axon for breakdown and recycling in cell body

Question 47

Compare fast and slow axonal transport

Answer 47

Fast axonal transport (approximately 400 mm/day)
Involves movement along microtubules, powered by motor proteins that split ATP
* Anterograde transport of vesicles, organelles, glycoproteins
* Retrograde transport of used vesicles, potentially harmful agents Slow axonal transport (approximately 0.1 - 3 mm/day)
Results from the flow of axoplasm
* Anterograde transport of enzymes, cytoskeletal components, new axoplasm

Question 48

Describe the anatomical (ex. Dendrites, axon) and functional regions (ex. Receptive, conductive) of a neuron.

Answer 48

Dendrites
* Short, unmyelinated processes branching off cell body
* Receive input and transfers these signals to cell body
Cell body (soma)
* Contains nucleus and organelles (ex. Nissl bodies)
* Receives signals and transfers them towards the axon hillock region
Axon
* Conducts action potentials from the axon hillock region to the axon terminal
* May be myelinated by neuroglial cells as shown (Neurolemmocytes in PNS; Oligodendrocytes in CNS)
* Neurotransmitters are released from the axon terminal (synaptic knob region) in response to action potentials reaching this area
Axon Hillock
* Contains the initial segment where summation of inputs occurs to determine if threshold is met
* If threshold is met an action potential is initiated in this region and conducted down the axon

Question 49

Compare pumps (ATPase), leak channels, chemically (ligand) gated channels, and voltage gated channels.

Answer 49

Chemically (Ligand) Gated Channels
Binding of neurotransmitters released from presynaptic neurons; production of graded potentials (may be excitatory or inhibitory)
Voltage Gated Channels
Summation of graded potentials; Initiation of action potential
Propagation of action potential
Action potential causes release of neurotransmitter
* Sodium leak channels are always open allowing sodium to move into the
neuron following its electrochemical gradient
* Potassium leak channels are always open allowing potassium to move out
of the neuron following its electrochemical gradient

Question 50

Identify a typical resting membrane potential value in a neuron and explain what contributes to this value.

Answer 50

Resting membrane potential (RMP): occurs along the entire membrane (all regions), -70 mV in most neurons
* An electrical charge difference across the membrane (intracellular and extracellular face) is maintained through leak channels and pump action, the inner face of
the membrane is negative compared to the outer face (extracellular) of the membrane giving the RMP a negative value
* K+ & Na+ Leak channels (movement along gradient) – located in all regions of the neuron
* Greater number of K+ leak channels, largest impact on RMP, more + charges moving from the intracellular fluid (ICF) to extracellular fluid (ECF)
* Na+/K+ pump (movement against the gradient) – located in all regions of the neuron
* Unequal movement of ions (3 positive charges out, 2 positive in)
* Maintains the concentration gradients for these ions
* In neurons, Na+/K+ pump can account for up to 75% energy expenses

Question 51

Compare depolarization and hyper polarization.

Answer 51

Depolarization:
Ion movement due to open receptors causes the inside to be relatively more positive (+)
Hyper-polarization:
Ion movement due to open receptors causes the inside to be relatively more negative (-)

Question 52

Explain what a graded potential is, where it occurs, and what type of channels are responsible for this potential.

Answer 52

• Graded potentials that change the membrane potential
• Rest in either depolarization or hyper polarization of the membrane

Question 53

Compare EPSP’ and IPSP’s, explain how each are generated, and identify each on a graph.

Answer 53

EPSP
1. Excitatory neurotransmitter is released from the synaptic knob of a presynaptic neuron and diffuses across the synaptic cleft
2. Neurotransmitter binds to a chemically gated cation channel causing them to open resulting in a net influx of sodium into the neuron
3. EPSP is established as the inner face of the plasma membrane becomes depolarized (more positive)
* Moving towards threshold
4. EPSP weakens as it moves from where it was initiated towards the initial segment where summation occurs
IPSP
1. Inhibitory neurotransmitter is released from the synaptic knob of a presynaptic neuron and diffuses across the synaptic cleft
2. Neurotransmitter binds to chemically gated K+ channels or chemically gated Cl– channels causing them to open allowing the specific ions to follow their gradient, resulting in the inner face of the membrane becoming more negative
* K+ (cation) moves out of the neuron (efflux)
* Cl- (anion) moves into the neuron (influx)
3. IPSP is established as the inner face of the plasma membrane becomes hyper polarized (more negative)
* Moving further away from
threshold
4. IPSP weakens as it moves from where it was initiated towards the initial segment where summation occurs

Question 54

Compare temporal and spatial summation.

Answer 54

Temporal summation: The same presynaptic neuron initiates postsynaptic potentials rapidly within a narrow period of time.
Spatial summation: Different presynaptic neurons initiate postsynaptic potentials within a narrow period of time.

Question 55

Identify where in a neuron an action potential is initiated and identify which type of channels are responsible for conducting an action potential.

Answer 55

Action Potentials
* Action potentials occur in axons due to the opening of voltage-gated channels
* K + and Na+ voltage gated channels are closed during the resting membrane potential,
opening in response to reaching threshold (-55 mV)
* K + voltage gated channels have one gate and two states (open or closed)
* Na+ voltage gated channels have two gates, activation and inactivation gates,
allowing for three different receptor states (resting, activation, and inactivation)
* Once an action potential is initiated it must go through three sequential phases; 1.
depolarization, 2. repolarization, 3. hyperpolarization

Question 56

Describe the three states of a voltage-gated sodium channel.

Answer 56

• Na+ voltage-gated channels have two gates, activation and inactivation gates
• At resting state (resting membrane potential) the inactivation gate is open, but the activation gate is closed preventing sodium from moving through the channel
• Reaching threshold initiates the opening of the inactivation gate while the activation gate remains open (activation state), allowing for sodium to move into the axon (influx) making the inner face of the membrane more positive
• The channel remains in the activation state for a short period of time before the
  inactivation gate closes (inactivation state) preventing the movement of sodium through the channel
• The channel remains closed as it resets back to the resting state

Question 57

Describe the phases of an action potential and identify these on a graph.

Answer 57

Action Potential initiated and depolarization
* Sodium from adjacent axon regions depolarizes the membrane, allowing it to reach threshold (-55 mV)
* Voltage-gated sodium channels open in response to threshold (activation state); sodium influx makes the inside more positive, continuing to depolarize the membrane resulting in a reversal of polarity (+ mV), peaking at about +30 mV when the inactivation gate closes
* Voltage-gated potassium channels remain closed during this period
Repolarization:
* Sodium Voltage Gated Channels closed (inactivation state)
* Potassium Voltage Gated Channel Open
* Potassium efflux causes a return to resting membrane potential (-70 mV)
Hyperpolarization:
* Voltage-Gated Sodium Channels closed (Resting State)
* Voltage-Gated Potassium Channel closing, but slowly, allowing for additional potassium to efflux resulting in the hyperpolarization of the membrane (peaking at about -80 mV)
* Resting membrane potential (and normal ionic concentration) is reestablished by the sodium/potassium pump and membrane returns to normal resting levels (-70 mV)

Question 58

Describe the significance of the absolute refractory period and compare this with the relative refractory period.

Answer 58

Absolute Refractory Period
No stimulus can initiate action potential
* Voltage gated Na+
channels are NOT in resting state
* Either open int theactivation) or closed (inactivated)
* Ensures that action potential moves in one direction only (towards synaptic knob)
Relative Refractory Period
* The Na+ voltage gated channel has returned to its resting state during the hyperpolarization phase
* This means that this channel is capable of responding (becoming activated) if threshold is met
* Another action potential is possible, but requires a stronger than normal stimulus since the membrane is more negative (ex. -80 mV) than the resting membrane potential (ex. -70 mV) since it takes a stronger signal to reach threshold
* The Na+ voltage gated channel has returned to its resting state during hyperpolarization so it can respond, but returned to resting state, but membrane still hyperpolarized

Question 59

Compare the location and physiology of graded and action potentials in a neuron.

Answer 59

See slide #33

Question 60

Describe the process of myelination and where on the neuron this occurs.

Answer 60

Myelination
1. Neurolemmocyte starts to wrap around a portion of an axon.
2. Neurolemmocyte cytoplasm and plasma membrane begin to form consecutive layers around the axon as wrapping continues.
3. The overlapping inner layers of the neurolemmocyte plasma membrane form the myelin sheath.
4. Eventually, the neurolemmocyte cytoplasm and nucleus are pushed to the periphery of the cell as the myelin sheath is formed.

Question 61

Compare continuous and saltatory conduction.

Answer 61

Continuous Conduction
Continuous conduction occurs as action potentials travel down the entire axon of unmyelinated axons
Each adjacent region of the axon undergoes all phases of the action potential (depolarization, repolarization, hyperpolarization) sequentially
Action potentials are unidirectional, traveling from the axon hillock region of the neuron (where they originated from) towards the synaptic knob region of the neuron due to the absolute refractory period
* Sodium influx that occurs at one region stimulates depolarization of the next region down the line (anterograde) where the sodium voltage gated channels were in the resting state
Saltatory Conduction
* Saltatory conduction only occurs in myelinated axons
* In saltatory conduction action potentials occur specifically in the unmyelinated regions (neurofibril nodes) where a large number of voltage-gated Na+ and K+ channels are present
* The myelinated regions (covered by neurolemmocytes in PNS) are insulated areas where a very limited number of voltage gated Na+ and K+ channels are present
* Sodium entering the axoplasm of the myelinated regions diffuses through the axoplasm until it stimulates threshold at the voltage gated channels present on the adjacent neurofibril node
* The reduced areas that undergo action potentials (neurofibril nodes) along the axon in saltatory conduction allows these signals to travel faster than continuous conduction where the action potentials must travel down the entire length of the axon membrane

Question 62

Explain the role of calcium in neurotransmitter release.

Answer 62

Calcium pumps present, but not shown, maintain the calcium gradient