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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
type 1 fibers
-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
type 2a
-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
Type 2x
-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
what are the biochemical properties of muscle that are important for muscle function
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
Isometric contraction
fixed length = joint doesn't move
30
isotonic contraction
fixed load ] -concentric -eccentric
31
preload-
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
active tension
load is added= muscles has to develop more tension to hold it there
33
length-tension relationship under isometric condtions
-muscle can generate more force at a specific range (not at either end range) -preload/active length tension
34
Afterload
-resistance a muscle must overcome speed and force relationship; there is an optimal speed to generate a force
35
force-velocity relationship under isotonic conditions
speed of shortening decreases as total load increases
36
what is muscle fatigue
reduction in muscle power output
37
What causes muscle fatigue
-central vs peripheral -intensity varible
38
What is central vs peripheral causes of muscle fatigue
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
What causes muscle cramps/what resolves them
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
Describe the phases of muscle twitch: Latent period
-first 5-10 millisecond where the electrical impulse and Ca++ is released but not quite enough yet to result in a full contraction
41
Describe the phases of muscle twitch: contraction
the fibers are overlapping and myosin is preforming the power stroke
42
Describe the phases of muscle twitch: relaxation
Ca++ is being removed and stored back into the lateral sacs ACh is being broken down and recycled
43
What factors influence the regulation of contraction force
-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
What is the relationship between force and velocity
the less force/load on the muscle the higher the velocity of contraction
45
What is the hierarchy of control of movement and what they do?
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
UMN
Upper motor neurons that come from the brain/some come from the brainstem and control the LMN
47
LMN
lower motor neurons come from the spinal cord and some come from the brain stem also called alpha motor neurons synapse with muscles
48
Spinal interneurons
between sensory and motor neurons or between motor and motor found in the spinal cord
49
Sensory neurons
-go through the DCML -cell bodies found in the DRG
50
muscle/joint proprioceptors
where you are in space
51
What types of descending motor tract pathways are there
-lateral pathways: the tract runs in the lateral SC -Ventromedial pathways that originate in the brainstem
52
what are examples of lateral pathways (descending motor tracts)
corticospinal rubrospinal
53
corticospinal
fibers from motor cortex -crosses at medulla pyramids -under voluntary control
54
rubrospinal
-originates in the red nucleus of midbrain -under involuntary control
55
What are examples of ventromedial pathways
1. vestibulospinal 2. tectospinal 3. reticulospinal
56
vestibulospinal
balance and extension connected to vestibular and control head and neck position
57
tectospinal
directs head and eyes
58
reticulospinal
fine control of posture
59
where is the primary motor cortex and what is it supplied by?
-precentral gyrus -middle cerebral artery (face and UE) -anterior cerebral artery (LE movements)
60
Where is the Basal ganglion and what are its compnents?
-forebrain, deep cerebral nuclei that initiates movement Components: -striatum (caudate nucleus and putamen) -Globus pallidus -subthalamic nucleus substantia nigra
61
What are the main areas of cortical control of motor function
-primary motor cortex -basal ganglia -cerebellum
62
Where do the 1. Lateal corticospinal tract, 2. rubrospinal tract and 3. tectospinal tract decussate
1. pyramids of the medulla 2. ventral tegmental 3. ventral tegmental

Applied Physiology (15 decks)

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