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MCAT Biology > Muscle, Bone, And Skin > Flashcards

Muscle, Bone, And Skin Flashcards

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1
Q

Three types of muscle tissue

A
  1. Skeletal muscle
  2. Cardiac muscle
  3. Smooth muscle
    Types of muscle differ in structure, function, and nervous system innervation, but have properties in common
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2
Q

How does a muscle generate force?

A

By contracting its cells

Mechanism of muscle contraction differs between three types of muscles

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3
Q

Major functions of muscle

A
  1. Body movement
  2. Stabilization of body position
  3. Movement of substances through the body
  4. Generating heat to maintain body temperature
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4
Q

Skeletal Muscle

A

Type of striated muscle that controls voluntary movements
Consciously controlled to produce specific desired movements
Innervated by the somatic system
Moves the body and allows running and lifting weights, thermoregulation, and movement of fluids in the cardiovascular and lymphatic systems
Connects one bone to another via a tendon (Tendon muscle to bone)

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5
Q

Tendon

A

Connective tissues attaching muscle to bone

Fibrous, allowing them to store elastic potential energy

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6
Q

Ligament

A

Connective tissue attaching bone to bone

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7
Q

How does a muscle create movement at a joint?

A

Muscle stretches across a join to create movement
Origin of muscle is usually its attachment on the larger bone closer to the midpoint of the body (remains relatively stationary)
Insertion: Attachment at other end of muscle, on smaller bone farther from midpoint
- moves relative to larger bone as muscle contracts
Exact placement of origin and insertion of muscle determines how it moves a joint, and how much force, or torque a muscle contraction can make

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8
Q

How do muscle agonist and antagonists work together to move?

A

Muscle whose contraction is primarily responsible for movement is called agonist, antagonist muscle stretches in response to agonist’s contraction and opposes movement so that motion is smooth and controlled
E.g. biceps and triceps function antagonistically
Muscle movements can also involve synergistic muscles
Synergistic: assists agonist by stabilizing origin bone or by positioning insertion bone during movement
Agonist, antagonistic, and synergistic muscles perform movement and maintenance of posture

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9
Q

What other function does the contraction of skeletal muscle help with?

A

Peripheral circulatory assistance
Contraction of skeletal muscles help squeeze blood and lymph through respective vessels, aiding circulation
Thermoregulation
Contraction of skeletal muscle produces large amounts of heat
Shivering reflex: rapid contraction, or shaking, of skeletal muscle to warm the body
- Controlled by the hypothalamus upon stimulation by receptors in the skin and spinal cord
When necessary, energy stored as glycogen can be metabolized and used to power muscle contraction that provide heat to body

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10
Q

How are most skeletal muscles class three levers?

A

Force applied by contraction of the muscle (via muscular attachment) is between the fulcrum (joint) and the load (part of body that moves)
Use more force to perform a given amount of work than would be used if there were no lever at all
Greater force than mg is required to lift a mass m
Shorter lever arm reduces bulk of body and increases range and control of movement

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11
Q

Sarcomere

A

Smallest functional unit of contractile apparatus in skeletal muscle
composed of many strands of two kinds of protein filaments
Thick filaments: made of myosin
Several long myosin molecules wrap around each other to form one thick filament
Globular heads, myosin heads protrude along both ends of thick filament
Thin filaments: made of globular protein actin
Attached to actin are proteins troponin and tropomyosin (participate in mechanism of contraction)
Myosin and actin filaments overlap and slide past each other when muscles contract and relax

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12
Q

Z line

A

Separates one sarcomere from the next

This is the location where actin filaments attach

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13
Q

I band

A

Area containing actin only (including the Z line, so contains part of two sarcomeres)
From the end of one myosin filament to the end of another

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14
Q

H zone

A

Area containing only myosin
Excludes the areas with actin
Changes with contraction

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15
Q

A band

A

Area where myosin is present, including where it overlaps with actin
Includes the H zone

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16
Q

M line

A

Midline of the myosin fibers in a sarcomere

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17
Q

Myofibril

A

Sarcomeres are positioned end to end to form a myofibril
Each myofibril is surrounded by specialized endoplasmic reticulum of the muscle cell, the sarcoplasmic reticulum
Lodged between myofibrils are many mitochondria to create supplies of ATP required for muscle contraction
Modified cellular plasma membrane called sarcolemma wraps several myofibrils together to form muscle cell (AKA myocyte, or muscle fiber)

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18
Q

Sarcoplasmic reticulum

A

Specialized endoplasmic reticulum of the muscle cell

Lumen of sarcoplasmic reticulum is filled with Ca2+ ions

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19
Q

Fasciculus

A

Many muscle fibers/ cells are further bound together to form fasciculus
Many fasciculi make up a single muscle

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20
Q

What is the heirarchical organization of the muscle?

A

Sarcomeres, smallest functional unit, line up end to end to form myofibrils, which are wrapped together by the sarcolemma to form a muscle cell
Many muscle cells bound together to form a fasciculus and many fasciculi form a muscle

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21
Q

How does the nervous system control the contraction of a skeletal muscle?

A

Motor neuron in the somatic nervous system attaches to a muscle cell at a motor end plate, forming a neuromuscular junction
Motor end plate is region of highly excitable muscle, while neuromuscular junction is synapse between motor neuron and motor end plate
Action potential of neuron releases Acetylcholine into synaptic cleft, activating ion channels in sarcolemma of muscle cell and creating action potential that propagates along sarcolemma
AP moves deep into muscle cell, via small infoldings of sarcolemma called T-tubules, which facilitate uniform contraction of muscle by allowing rapid spread of APs
AP spread to sarcoplasmic reticulum, causing release of Ca2+ around sarcomere, which allows myosin and actin fibers to slide past each other, starting a contraction

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22
Q

Sliding filament model

A

Myosin and actin work together by sliding alongside each other to create contractile force of skeletal muscle
Process of contraction requires the expenditure of energy in the form of ATP
Each myosin head crawls along the actin in a 5 stage cycle

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23
Q

What is the 5 stage cycle of the sliding filament model?

A
  1. In rest, myosin heads in high-energy “cocked” position w/ P & ADP group attached. Tropomyosin covers active sites on actin, heads can’t bind to actin
  2. SNS increases Ca2+ levels in sarcomere, troponin changes configuration and pulls back tropomyosin, exposing active site. Myosin heads bind to actin, cross-bridges
  3. Myosin heads expels P & ADP, bends into low energy position and drags actin. Called power stroke, causes shortening of sarcomere (contraction)
  4. New ATP attaches to myosin head and release from active site. Active site covered by tropomyosin
  5. ATP splits into P & ADP, and energy used to recock head into higher energy position. Cycle repeated many times to form contraction w/ Ca2+ actively pumped back into sarcoplasmic reticulum at end of each cycle
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24
Q

How many muscle fibers are innervated by a single neuron?

A

2-2000 fibers
Neuron and muscle fibers that it innervates are called a motor unit
Motor units are independent of each other
Force of contracting muscle depends on the number and size of active motor units, as well as frequency of APs in each neuron of motor unit
Smaller units are activated firstk and larger motor units are recruited as needed
- result is smooth increase in force generated by muscle

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25
Q

Motor Units

A

Muscle fibers that are innervated together
Muscles requiring intricate movements, like those in the finger have small motor units
Muscles requiring greater force and less finesse have larger motor units

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26
Q

Muscle Fatigue

A

Can result from nervous or metabolic causes
After sustained use of same motor unit, nerve supplying the unit can become temporarily unable to supply signals necessary to continue frequent, high intensity contraction of the muscle
Metabolic fatigue can result from depletion of energy stores within the muscle or decreased sensitivity to effects of calcium in contracting muscle due to buildup of waste products from metabolism

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27
Q

What happens when oxygen demands of metabolism exceed body’s supply of oxygen?

A

Muscle cells can switch from citric acid cycle and oxidative phosphorylation to anaerobic glycolysis to produce ATP
Result is excess of lactic acid, which is later metabolized by body when O2 is avail
Oxygen debt: need for increased oxygen after exercise in order to metabolize excess lactic acid

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28
Q

What are the types of skeletal muscle fibers?

A 
Type I (slow twitch or slow oxidative): slow contractile velocity, low amount of force, slow to fatigue and can be employed for long periods
Type II (fast twitch) divided into two sub categories type IIa (fast oxidative( and type IIb (fast glycolytic): type IIa fast contractile velocity, resistant to fatigue, but not as resistant as type I, type IIb have rapid contractile velocity, generate great force, but fatigue quickly
Differ in contractile velocity, maximum force production, and resistance to fatigue
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29
Q

Type I muscle fibers

A

Appear red, contain large amounts of myoglobin, O2 storing protein similar to hemoglobin. Have large numbers of mitochondria, so efficiently use O2 to generate ATP
Relatively slow contractile velocity, produce low amount of force
Have advantage that they are slow to fatigue and can be employed for long periods of time due to mitochondria and high myoglobin content
O2 and ATP necessary for long periods

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30
Q

Type IIa muscle fibers

A

Red, so have myoglobin stores
Have fast contractile velocity, resistant to fatigue, but not as resistant as type I
Have long-term anaerobic activity

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31
Q

Type IIb muscle fibers

A

Appear white due to low myoglobin content
Contract rapidly and can generate a lot of force, but fatigue quickly
Contain large amounts of glycogen
Have short-term anaerobic activity

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32
Q

How do muscles in the body differ in terms of compositions of different muscle fiber types?

A

Most muscles in body have mixture of fiber types
Ratio of mixture depends on contraction requirements of muscle and genetics of individual
Relative amounts of fiber types may influence a person’s natural aptitude for activities
Large amounts of type I fibers are found in postural muscles
Large amounts of type IIA found in upper legs, large amounts of type IIB fibers found in upper arms

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33
Q

Hypertrophy

A

Increase in muscle cell diameter and change in muscle conformation due to repeated forceful, repetitive contractions
Adult human skeletal muscle does not usually undergo mitosis to create new muscle cells
Number of changes occur over time to meet need for increased strength; increased diameter of muscle fibers, increased numbers of sarcomeres and mitochondria, and lengthened sarcomeres

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34
Q

Cardiac Muscle

A

Tissue that human heart is composed mainly of, involuntary nervous stimulation
Specialized, electrically-excitable tissue, which permits propagation of electrical signals that cause the heart to beat normally
Cardiac muscle is striated, which means it is composed of sarcomeres
Each cardiac muscle cell contains only one nucleus, while skeletal muscle cells are multi-nucleated
Cardiac muscle forms a net that contracts on itself like a squeezing fist

35
Q

Intercalated discs

A

Separate cardiac muscle cells
Areas that contain gap junctions that allow an action potential to spread from one cardiac cell to next via electrical synapses
Synchronize contraction of groups of cardiac muscle cells
Coordination of contraction controls efficient pumping of blood through chambers of heart

36
Q

Why do cardiac muscle cells have numerous large mitochondria?

A

Heart must beat continuously for entire length of human life

Provide constant supply of ATP

37
Q

Where is nervous system control over cardiac muscle?

A

Involuntary, so innervated by autonomic nervous system
Cardiac muscle is self-excitatory and modulates own rhythm through SA and AV node
However, input from autonomic nervous system can affect contraction frequency and thus heart rate
Sympathetic innervation increases heart rate, parasympathetic innervation via vagus nerve decreases heart rate

38
Q

How does cardiac muscle grow?

A

Hypertrophy, just like skeletal muscle

No actual mitosis

39
Q

Cardiac Muscle action potential

A

Exhibits a plateau after depolarization, created by slow voltage-gated Ca2+ channels which allow calcium to enter and maintain inside of membrane at positive potential difference
Repolarization of cardiac muscle is slower and more frequent than skeletal muscle
Plateau lengthens time of contraction, preventing new APs from starting in middle of previous contraction
Without calcium, heart would beat far too quickly to serve as functional pump
Gives heart enough time to refill with blood and prevents tetanus (sustained contraction) that can occur in skeletal muscle

40
Q

Smooth Muscle

A

Composes muscular layer of internal organs and blood vessels
Contain only one nucleus, and contract involuntarily which means innervation from the autonomic nervous system
Contain thick and thin filaments that aren’t organized into sarcomeres, also contain intermediate filaments
Groups of spindle-shaped cells grouped in irregular bundles, uni-nucleated

41
Q

Intermediate filaments

A

Filaments present in smooth muscle which are attached to dense bodies spread throughout the cell
Dense bodies: serve similar function to Z-lines of striated muscle
When thin and thick filaments contract, cause intermediate filaments to pull dense bodies together (smooth muscle cells shrink length-wise during contraction)

42
Q

What are the two types of smooth muscle?

A
  1. Single-unit or visceral, most common
    Connected by gap junctions that spread AP from single neuron through large group of cells, allowing cells to contract as single unit
    - Electrical synapses via gap junctions allow for faster signal transmission than chemical, simultaneous contraction
    - Small arteries / veins, stomach, intestines, uterus, and urinary bladder
  2. Multi-unit
    - Each fiber directly attached to neuron, can contract independently from other fibers
    - Large arteries, bronchioles, pili muscles attached to hair follicles, and iris
43
Q

What are some signals that smooth muscle may contract or relax in response to?

A

Neural signals, hormones, changes in pH, O2, and CO2 levels, temperature, and ion concentration

44
Q

Is the vagus nerve part of the parasympathetic or sympathetic nervous system?

A

Parasympathetic

45
Q

If the heart is innervated by the vagus nerve, what effect will this have on heart rate?

A

Heart rate will slow, because vagus nerve is parasympathetic and excitation of parasympathetic nervous system inhibits heart rate

46
Q

Bone

A

Living connective tissue in the body

Contains four types of cells surrounded by extensive calcium/protein matrix composed of inorganic minerals and proteins

47
Q

Functions of bone

A

Support soft tissue, protection of internal organs, assistance in body movement, mineral (calcium) storage, blood cell production, and energy storage in form of adipose cells in bone marrow

48
Q

Four types of cells in bone tissue

A
  1. Osteoprogenitor (osteogenic) cells differentiate into osteoblasts
  2. Osteoblasts secrete collagen and organic compounds. Incapable of mitosis, releases matrix materials around themselves, become enveloped by matrix and differentiate into osteocytes
  3. Osteocytes: incapable of mitosis, exchange nutrients and waste materials with blood. Osteoblast that has become trapped within bone cavity (lacuna)
  4. Osteoclasts: resorb bone matrix, releasing minerals black into the blood, thought to develop from white blood cells called monocytes
49
Q

General structure of bones

A

Typical long bones have a long shaft (diaphysis)
Two ends, each composed of metaphysis and epiphysis
Sheet of cartilage between epiphysis and metaphysis is called epiphyseal plate, where long bones grow in length when stimulated by growth hormone (GH) during childhood/adolescence

50
Q

Two main types of bone structure

A
  1. Spongy bone: trabecular or cancellous bone, contains red bone marrow, site of red blood cell development
  2. Compact bone: cortical bone surrounds a hollow area inside the diaphysis known as medullary cavity, holds yellow bone marrow. Yellow bone marrow contains adipose cells for fat storage
51
Q

Bone Remodeling

A

Osteoclasts burrow tunnels through old compact bone
Followed by osteoblasts which lay down new bone matrix onto tunnel walls, forming concentric rings, called lamillae
Leave open spaces in center of lamellae known as Haversian canals

52
Q

Osteon

A

Entire system of lamellae and Haversian canal is called an osteon or Haverisan system
Haversian canals and spaces allow for communication and nutrient exchange
- Contain blood and lymph vessels
- Connected by cross canals called Volkmann’s canals

53
Q

How do osteocytes that are trapped in lacuna exchange nutrients?

A

Spaces known as canalicculi

54
Q

How is remodeling subject to endocrine control?

A

Parathyroid hormone helps regulate Ca2+ levels in bloodstream by influencing bone
High levels of parathyroid hormone signal osteoclasts to resorb bone to release Ca2+
Vitamin D helps restore Ca2+ stores in bone by promoting Ca2+ absorption through digestive system
Calcitonin released by C cells of thyroid stimulates osteoblasts to store excess Ca2+

55
Q

How does bone help regulate mineral content of blood?

A

Osteoclasts release calcium into blood, osteoblasts use calcium and take from blood
Calcium salts are only slightly soluble, so most calcium in blood is bound by proteins or phosphates (HPO42-)
Too much free calcium in blood causes membranes to be hypo-excitable, leading to fatigue and memory loss, too little results in cramps and convulsions
Ca2+ levels are maintained to generate large conc. Gradient w/ high Ca2+ out of cells and low Ca2+ in cytosol

56
Q

How is most of the body’s Ca2+ stored?

A

In bone matrix as the mineral hydroxy-apatite [Ca10(PO4)6(OH)2]
Contributes to strength of bones
Collagen fibers give bone great tensile strength (stretch)
Hydroxyapatite crystals lie alongside collagen fibers, giving bone great compressive strength
Some Ca2+ stored in form of slightly soluble calcium salts like CaHPO4- which buffer plasma Ca2+ levels
Bone is reservoir to store excess Ca2+ and HPO42-

57
Q

Specialized bone types

A
  1. Long: have shaft that is curved for strength
    - Composed of compact and spongy bone
    - Leg, arm, finger, and toe
  2. Short: often roughly cuboidal in shape
    - ankle, wrist
  3. Flat: provide organ protection and large areas for muscle attachment
    - skull, sternum, ribs, and shoulder blades
  4. Irregular: irregular shape and variable amounts of compact and spongy bone
    - e.g. ossicles of ear
58
Q

Cartilage

A

Flexible, resilient connective tissue
Composed primarily of collagen, great tensile strength
Has no blood vessels or nerves except in its outside membrane

59
Q

What is the function of cartilage?

A

Gives shape and structure to various body parts (ears)

Serves important functions of providing cushion, connection, and elasticity to joints of body

60
Q

What are the three types of cartilage?

A
  1. Hyaline: reduces friction, absorbs shock in joints, most common
  2. Fibrocartilage
  3. Elastic
61
Q

Joints

A

Locations where bones connect in ways that allow for varying amounts of movement, depending on type

62
Q

Hyaline Cartilage

A

Semi-rigid connective tissue composed of many chondrocytes
Cells synthesize an extracellular matrix of proteoglycans, collagen, and water that keeps them apart from each other in spaces known as lacunae
Strong, but compressible due to high water content
Reduces friction between bones in kee joint as they move against each other

63
Q

Fibrous Joints

A

Occur betweent wo bones held closely and tightly together by fibrous connective tissue
Permits extremely minimal movement
Maintains fixed relationship between two bones
E.g. teeth with mandible, skull bones after childhood

64
Q

Cartilaginous joints

A

Allow little movement
Occur between two bones tightly connected by cartilage, such as ribs and sternum, or pubic symphysis in pelvis
Slight flexibility of cartilaginous joints allows them to absorb some energy and can help in event of trauma

65
Q

Synovial joints

A

Wide range of movement possible, bones not bound directly by intervening cartilage
Separated by a capsule filled with synovial fluid, which provides lubrication and nourishment to cartilage
Synovial fluid contains phagocytotic cells that remove microbes and particles
E.g. shoulder and knee

66
Q

Skin

A

Largest organ in the body with a wide variety of functions that contribute to homeostasis
Has specific immune cells and unique patterns of innervation that help protect the body from pathogens
Transmits information about environmental surroundings to rest of body

67
Q

Functions of the skin

A
  1. Thermoregulation
  2. Protection
  3. Environmental sensory input
  4. Osmoregulation
  5. Immunity
  6. Blood reservoir
  7. Vitamin D synthesis
68
Q

How does the skin help regulate body temperature (thermoregulation)?

A

Heat from blood can be dissipated by endothermic evaporation of sweat, but most is dissipated by radiation (only effective if body temp > room temp)
Vasodilation: more blood directed to surface capillaries for greater heat loss
vasoconstriction: blood shunted away from capillaries of skin to reduce heat loss
Thermoregulation through sweating, vasoconstriction, and vasodilation is under influence of hormonal control
Hairs can erect via SNS stim of associated muscles, insulating warm air next to skin
Skin has warmth and cold receptors

69
Q

How is the skin protection for the body?

A

Skin is a physical barrier to abrasion, pathogenic organisms, many chemicals, and ultraviolet radiation

70
Q

How does the skin receive environmental sensory input?

A

Skin gathers information from environment through many types of sensory receptors including thermoreceptors, mechanoreceptors, nociceptors

71
Q

How does the skin participate in osmoregulation?

A

Skin is relatively impermeable to water, protecting against dehydration
Some water and salts are excreted through skin via diffusion
Excretion and sweating are ways that skin contributes to osmoregulation, keeping conc. Of solutes in body fluids at appropriate level

72
Q

How does the skin contribute to the immune system?

A

Skin is one of the first lines of defense by preventing pathogenic organisms from entering the body via a physical barrier (innate immune system)
Also has specialized cells of epidermis that are components of immune system

73
Q

How is the skin a blood reservoir?

A

Vessels in the dermis hold up to 10% of blood of resting adult

74
Q

How does the skin participate in Vitamin D synthesis?

A

UV radiation activates molecule in skin that is precursor to vitamin D
Activated molecule modified by enzymes in liver and kidneys to produce vitamin D

75
Q

What are the two principal parts of the skin?

A
  1. Superficial epidermis
  2. Deeper dermis
    Beneath both layers is subcutaneous tissue called superficial fascia or hypodermis
    - Important heat insulator for body (fat layer), maintains normal core temps of body on cold days
76
Q

What is the primary purpose of the epidermis?

A

Protection from the environment

Avascular epithelial tissue (no blood vessels)

77
Q

Four major cell types of epidermis

A
  1. Keratinocytes: 90% of epidermis, contain melanin, produce protein keratin (waterproofing)
  2. Melanocytes: transfer melanin to keratinocytes
  3. Langerhans cells: interact with helper T cells of immune system
  4. Merkel cells: attach to sensory neurons and function in sensation of touch
78
Q

Four layers of epidermis

A 
Stratum basale (SB), fourth from top layer, contains Merkel and stem cells
Stratum spinosum (SS), third from top layer
Stratum granulosum (SG), second from top layer
Stratum corneum (SC), top layer
Exposure to friction or pressure stimulates a fifth layer, causing thickened skin forming a protective callus
79
Q

How does skin move from deepest layers of epidermis to top over time?

A

Skin cells must be continually replaced with constant exposure to environment
Stem cells continually divide to give rise to keratinocytes and other new replacement skin cells
Keratinocytes once produced are pushed to top layer of epidermis, accumulating keratin and dying, losing cytoplasm, nucleus, and other organelles
At outermost layer of skin, cells slough off body
Process of keratinization, from birth of cell to sloughing off- 2-4 weeks
Outermost layer of cell has 24-30 layers of flat, dead cells

80
Q

Dermis

A

Connective tissue derived from mesodermal cells
Embedded with blood vessels, nerves, glands, and hair follicles
Collagen and elastic fibers in dermis provide skin with strength, extensibility, and elasticity
Sensors for touch: nociceptors, mechanoreceptors, and thermoceptors

81
Q

Hair

A

Column of keratinized cells held tightly together and plays a role in tactile sensation and thermoregulation
Hair follicles are embedded in the dermis
Arrector pili muscles that surround base of hair follicles allow them to become erect, trapping air close to skin to help maintain body heat
As new cells added to base, hair grows

82
Q

Nails

A

Keratinized cells

Provide physical protection for skin

83
Q

Glands in dermis

A

Sebaceous (oil) gland: associated with hair follicle, empties oil direclty into follicle and onto skin
Sweat glands:
(1) Eccrine sweat glands: found over entire surface of skin and produce sweat in response to heat
(2) Apocrine sweat glands: congregated in certain regions of dermis, produce an acrid-smelling sweat in response to stress

MCAT Biology (14 decks)

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