Lesson 2/3 Flashcards by Catherine McDowell

corticobulbar tract vs corticospinal tract

corticobular connects motor cortex to brain stem and controls motor for head, neck, and face. corticospinal controls motor for the rest of the body

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a motor unit consists of…

one motor neuron and all the muscle fibers it innervates

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a motor neuron determines _________

fiber types and only one fiber type per motor unit

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explain the events at the NMJ and how an AP occurs

1 - AP reaches the terminal
2 - voltage gated Ca channels open
3 - Ca enters axon terminal
4 - ACh released into cleft
5 - ACh binds to postsynaptic recepts. Na+ enters muscle cell and K- exits cell following concentration gradient. membrane is now less negative so AP occurs
6 - ACh diffuses away or is broken up by acetylcholinesterase
7 - choline is reabsorbed by the axon for recycling

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what protein allows the vesicle to dock to the cell membrane

SNARE/SM protein complex

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what cell traps ACh in the synaptic cleft

kranocyte

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ACh receptor is a ________- and therefore needs an ACh to dock on both sides to open

dimer

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what type of Ach receptor do we only see in babies or denervated muscle? what is it replaced by when we are healthy adults?

gamma
epsilon

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Acetylcholinesterase breaks down ACh and makes…

acetate
choline (recycled back into cell)
H+ ion

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What starts excitation contraction coupling

1 - ACH released from axon terminal of a motor neuron and binds to receptors in the motor end plate. this binding elicits an end-plate potential, which triggers an action potential in the muscle cell.

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What happens next?

2 - action potential propagates along the sarcolemma and down the T tubules.

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2 - action potential propagates along the sarcolemma and down the T tubules.

What happens next?

3 - action potential triggers Ca+ release from SR

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3 - action potential triggers Ca+ release from SR

What happens next?

4 - Ca+ binds to troponin C, exposing myosin binding sites

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4 - Ca+ binds to troponin C, exposing myosin binding sites

What happens next?

5 - crossbridge cycle begins (muscle contracts)

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5 - crossbridge cycle begins (muscle contracts)

What happens next

6 - Ca+ is actively transported back into lumen of SR following the action potential

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6 - Ca+ is actively transported back into lumen of SR following the action potential

What happens next

7 - tropomyosin blocks myosin-binding sites (muscle fiber relaxes)

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What is the steric hindrance model

Tropomyosin blocks the myosin binding site on actin until calcium binds to troponin C

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How is force produced

crossbridge

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What is the rate limiting step in the cross bridge cycle?

how fast ATP can be hydrolyzed by myosin

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How does the cross bridge cycle begin?

1 - Tight binding between actin and myosin in the rigor state

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1 - Tight binding between actin and myosin in the rigor state

What happens next

2 - ATP binds to myosin. Myosin disassociates from actin

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2 - ATP binds to myosin. Myosin disassociates from actin

What happens next?

3 - myosin hydrolyzes ATP. ADP + Pi remain attached to myosin head

What happens next

4 - energy of hydrolyzing ATP cocks myosin head and weakly binds to new actin molecule

What happens next

5 - release of Pi initiates power stroke

5 - release of Pi initiates power stroke What happens next

6 - myosin head releases ADP and returns to rigor state

isotonic means

constant tension

isokinetic means

constant velocity

concentric means

shortening

eccentric means

lengthening

isometric means

constant length

Po = ________ velocity and ______ load

zero max

Vmax = _______- velocity and _______ load

max zero

isometric force _____ Po

concentric force _____ Po

eccentric force ________- Po

is Vmax or force changing as a result of strength training on a force velocity curve

force moves to the right with strength training

What is the strength of a muscle contraction influenced by?

- size of muscle - # and size of motor units recruited - # and size of fibers within motor unit - total amount of contractile protein - amount of force per individual actin-myosin (crossbridge) interactions - fraction of crossbridges bound and producing force

What is a motor unit

one motor neuron and all the fibers innervated by that neuron

explain all or nothing principle

one AP induces all fibers within that motor unit to contract

all fibers within a motor unit are the ______ type

same

_______ motor units for fine motor skills, _______ motor units for gross skills

small large

motor units are recruited via the _______

size principle

what is the skeletal muscle recruitment order according to the size principle

1, 2a, 2x

gross motor = _______ innervation ratio fine motor = _______ innervation ratio

low large

what is the optimal overlap measurement for sarcomeres

2.2-2.25um

what does the length tension curve illustrate?

there is an optimal amount of overlap between sarcomeres

power = _______ x ______

force x velocity

peak power occurs at ______ of Po and about ________ of Vmax

30-40% 30%

relaxed muscle is elastic, force is required to stretch it. this is ___________

passive tension

_________ contributes to passive tension

connective tissue

________ provides passive elasticity

titin

what happens with AP is successful?

fusion of twitches to make tetanus

what are some velocity parameters to measure muscle twitches

- contraction time (CT) - relaxation time (RT) - one half RT (1/2 RT)

what does the one half RT parameter measure?

the efficiency of SERCA