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Applied Physiology > Skeletal muscle structure and function > Flashcards

Skeletal muscle structure and function Flashcards

1
Q

what is the function/contractile unit of muscle?

A

sarcomere
-from 1 Z-disc to another Z-disc

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2
Q

describe the thin filament

A

Actin
-double stranded actin helix
-tropomyosin covering
-troponin

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3
Q

Tropomyosin

A

binds on the actin to cover the myosin binding sites

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4
Q

Troponin

A

keeps the tropomyoisin in place
three types
-troponin T
-troponin C
-troponin I

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5
Q

Troponin T

A

anchors the trimer to tropomyosin

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6
Q

troponin C

A

binds Ca allowing for the contraction

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7
Q

Troponin I

A

inhibits the interaction between actin and myosin when intracellular Ca is low

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8
Q

describe the thick filament

A

myosin
-motors generating force
-myosin head the binds to actin
-hinge connects myosin to the tail

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9
Q

titin

A

-giant protein that maintains the sacromere structure
-provides passive tension when relaxed muscle is stretched

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10
Q

H-zone

A

space between the actin
-this is what shortens during a contraction

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11
Q

I-band

A

from one end of myosin to another
-only actin is found here

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12
Q

A-band

A

end of myosin to the the end of the same myosin with the M-line in the middle
-only myosin
-does not shorten during contraction

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13
Q

m-line

A

the middle of a sarcomere

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14
Q

Describe the steps of excitation of the muscle cell

A
  1. nerve impulse arrives at NMJ
  2. Action potential from neuron causes Ca to enter and stimulate the release of acetylcholine to be released
  3. AcH binds to receptors on the motor endplate producing an endplate potential that will depolarize the muscle cell
  4. The depolarization goes down the T-tubules which are a part of the sacroplasmic reticulum that will release Ca++ into the cell
    -Ca is released from the lateral sac/terminal cisternae (part of the SR)
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15
Q

Describe the steps of contraction

A
  1. Ca++ binds to troponin C and causes a position change in the tropomyosin releasing the myosin binding sites
  2. Myosin will bind to actin and initiates the release of energy that was stored within the myosin
  3. the myosin head will preform the power stroke drawing the actin into the M-line
  4. the attachment of a new ATP will cause detachment of the actin and myosin
  5. ATP is hydrolyzed so that the myosin will have energy for cocking/attaching to the next actin molecule
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16
Q

What causes Ca channels in SR to open

A

voltage sensors

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17
Q

describe relaxtion after a contraction

A

-Ca++ - Aptase of the SR uptake the Ca back into the lateral sacs
- most stored Ca is in the lateral sacs weakly bound to a protein calsequestrin

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18
Q

temporal summation

A

one motor neuron firing/stimulating a muscle fiber many times

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19
Q

Spatial summation

A

more than one motor neuron stimualting a muslce fiber at one

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20
Q

twitch

A

complete cycle of contraction and relaxation in 1 muscle cell

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21
Q

tetanic contraction

A

a sustained contraction

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22
Q

What is a motor unit

A

1 motor neuron and all the fibers it innervates

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23
Q

small motor untis

A

-less muscle fibers
-more specific movement
-fine motor skills

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24
Q

Large motor units

A

-more muscle fibers
-postural muscles
-gross motor control

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25
Q

type 1 fibers

A

-slow fibers
-high amount of mitochondria
-high resistance to fatigue
-aerobic energy system
-low ATPase activity (glycolytic enzymes)
-low Vmax (speed of shortening)
-high efficiency (use of energy)
-Moderate specific tension

26
Q

type 2a

A

-fast fibers
-high/moderate amount of mitochondria
-high/moderate resistance to fatigue
-aerobic/anaerobic energy system
-high ATPase activity (glycolytic enzymes)
-high Vmax (speed of shortening)
-moderate efficiency (use of energy)
-high specific tension

27
Q

Type 2x

A

-fast fibers
-low amount of mitochondria
-low resistance to fatigue
-anaerobic energy system
-highest ATPase activity (glycolytic enzymes)
-highest Vmax (speed of shortening)
-low efficiency (use of energy)
-high specific tension

28
Q

what are the biochemical properties of muscle that are important for muscle function

A
  1. oxidative capacity: # mitochondria, capillaries, amount of myoglobin (the ability of use O2)
  2. type of myosin isoform: differnet forms myosin and ATPase activity
  3. abundance of contractile proteins within the fiber: size; large fibers have more actin/myosin which can generate more force
29
Q

Isometric contraction

A

fixed length = joint doesn’t move

30
Q

isotonic contraction

A

fixed load ]
-concentric
-eccentric

31
Q

preload-

A

load before any contraction (a resting force from gravity and position of sacromere)
passive tension: at rest there is a certain amount of tension from the proteins

32
Q

active tension

A

load is added= muscles has to develop more tension to hold it there

33
Q

length-tension relationship under isometric condtions

A

-muscle can generate more force at a specific range (not at either end range)
-preload/active length tension

34
Q

Afterload

A

-resistance a muscle must overcome
speed and force relationship; there is an optimal speed to generate a force

35
Q

force-velocity relationship under isotonic conditions

A

speed of shortening decreases as total load increases

36
Q

what is muscle fatigue

A

reduction in muscle power output

37
Q

What causes muscle fatigue

A

-central vs peripheral
-intensity varible

38
Q

What is central vs peripheral causes of muscle fatigue

A

central: motivation and alpha motor neurons (comes from the central NS)

peripheral: causes that occur in the muscle; has to do with intensity
-high intensity= result of metabolic phosphate, H+, and free radicals that prevent the binding of Ca++ to troponin
-moderate intensity= free radicals and depletion of glycogen (energy)

39
Q

What causes muscle cramps/what resolves them

A
  1. dehydration/electrolyte balance- would not cause an isolated cramp (not well supported)
  2. CNS changes: motor neurons are firing a lot and can cause a change in firing from GTO (prevent tension and allows relaxation) and the muscle spindles (increase excitability can cause a decrease GTO activity and increase Spindle activity and CNS cannot respond)
  3. stretching resolves the cramp
40
Q

Describe the phases of muscle twitch: Latent period

A

-first 5-10 millisecond where the electrical impulse and Ca++ is released but not quite enough yet to result in a full contraction

41
Q

Describe the phases of muscle twitch: contraction

A

the fibers are overlapping and myosin is preforming the power stroke

42
Q

Describe the phases of muscle twitch: relaxation

A

Ca++ is being removed and stored back into the lateral sacs
ACh is being broken down and recycled

43
Q

What factors influence the regulation of contraction force

A

-number and type of motor units recruited (also how effectively can you recruit them)
-initial muscle length (where is the muscle at)
-natural of neural stimulation (are you expecting it)
-contractile history: PAP (post activation potentiation (warming up allows more efficient muscles action)

44
Q

What is the relationship between force and velocity

A

the less force/load on the muscle the higher the velocity of contraction

45
Q

What is the hierarchy of control of movement and what they do?

A
  1. association cortex and basal ganglion: refine, plan movement
  2. primary motor cortex and cerebellum: determine the sequence of commands (coordinate different movements at different times)
  3. Spinal cord Neuronal circuits: lowest level of control such as a reflex
46
Q

UMN

A

Upper motor neurons that come from the brain/some come from the brainstem and control the LMN

47
Q

LMN

A

lower motor neurons
come from the spinal cord and some come from the brain stem
also called alpha motor neurons
synapse with muscles

48
Q

Spinal interneurons

A

between sensory and motor neurons or between motor and motor
found in the spinal cord

49
Q

Sensory neurons

A

-go through the DCML
-cell bodies found in the DRG

50
Q

muscle/joint proprioceptors

A

where you are in space

51
Q

What types of descending motor tract pathways are there

A

-lateral pathways: the tract runs in the lateral SC
-Ventromedial pathways that originate in the brainstem

52
Q

what are examples of lateral pathways (descending motor tracts)

A

corticospinal
rubrospinal

53
Q

corticospinal

A

fibers from motor cortex
-crosses at medulla pyramids
-under voluntary control

54
Q

rubrospinal

A

-originates in the red nucleus of midbrain
-under involuntary control

55
Q

What are examples of ventromedial pathways

A
  1. vestibulospinal
  2. tectospinal
  3. reticulospinal
56
Q

vestibulospinal

A

balance and extension
connected to vestibular and control head and neck position

57
Q

tectospinal

A

directs head and eyes

58
Q

reticulospinal

A

fine control of posture

59
Q

where is the primary motor cortex and what is it supplied by?

A

-precentral gyrus
-middle cerebral artery (face and UE)
-anterior cerebral artery (LE movements)

60
Q

Where is the Basal ganglion and what are its compnents?

A

-forebrain, deep cerebral nuclei that initiates movement

Components:
-striatum (caudate nucleus and putamen)
-Globus pallidus
-subthalamic nucleus
substantia nigra

61
Q

What are the main areas of cortical control of motor function

A

-primary motor cortex
-basal ganglia
-cerebellum

62
Q

Where do the
1. Lateal corticospinal tract,
2. rubrospinal tract
and
3. tectospinal tract
decussate

A
  1. pyramids of the medulla
  2. ventral tegmental
  3. ventral tegmental

Applied Physiology (15 decks)

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