Lecture 2 - Functional properties of skeletal muscle 2 Flashcards Preview

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Flashcards in Lecture 2 - Functional properties of skeletal muscle 2 Deck (20):
1

What gives us the capability to vary the strength of contraction?

the varying number f Motor units recruited at any time

Varying the frequency of contraction of individual MUs

2

What is the physiology of Fast-fatigueable (FF) MU type?

Type IIX

fast contracting
relax very qucikly
repeated stimulation produces force quickly but will fatigue


ely on glycolysis
poor capillarisation

3

What is the physiology of S (slow) MU type?

Type I

rely upon oxidation
rich capillarisation

slow contraction, slow relaxation

fatigue - can sustain force over time, more resistant to fatigue

4

What is the physiology of Fast- fatigue resistant (FR) MU type?

Type IIA

rely on both types of metabolism

properties lie in the middle of the FF and S types

5

What are the fastest contracting fibres in humans?

Type IIX

6

A given level of excitatory input will produce more depolarisation of the ______ axons becasue of their ...

A given level of excitatory input will produce more depolarisation of the smallest axons becasue of their smaller membrane areas

First axons to fire will be those of the smallest MUs

7

Any task recruits the slow MUs first, then as the task intensity increases...

Larger MUs

8

What do muscle spindles sense?

the lengths of the muscle fibres during contraction

9

Golgi tendon organs are..

designed to sense the forces developed by the fibre

10

The centres of the intrafusal fibres are not ______but their ends do contain fibres that contract when stimulated by ____-motor neurons

The centres of the intrafusal fibres are not contractile but their ends do contain fibres that contract when stimulated by gamma-motor neurons

11

extrafusal ("ordinary") muscle fibres are innervated by..

alpha-motor neurons

12

The sensory neurons that wrap around the centre of the spindle are ...

tonically active

they fire A.Ps when the muscle is at resting length

these signals travel to the spinal cod where the afferent spindle synapses with the alpha-MN

13

The alpha-MN create tonic excitation and contraction in the extrafusal fibres associated with the muscle spindle meaning...

even at "rest" a muscle maintains a certain degree of tension or tone

14

How is spindle length maintained during contraction?

Gamma-motor neurons innervate the ends of the intrafusal fibres which then contract

maintaining stretch on the sensory nerve endings, counteracts the release of tension on the spindle

Therefore, when the extrafusal fibres shorten during contraction, the intrafusal fibres remain stretched and continue to monitor tension in the muscle

15

What does activation of Golgi tendon organ (GTO) cause?

inhibition of a-MN and decreases muscle contraction

slows muscle contraction as the force of contraction increases

16

GTOs prevent...

excessive contraction that might injure the muscle

17

What is a myotatic unit?

collection of pathways controlling a single joint

18

what is an example of a monosynaptic stretch reflex?

knee jerk reflex

involvesonly two neurons: sensory from the muscle spindle and the somatic MN to the muscle

19

What is the reciprocal inhibition in the knee jerk reflex?

relaxation of the hanstrings

There is branching of the sensroy neuron as it enters the SC - one colateral activates the MN innervating the quads, the other synapses with and inhibitory interneuron which then inhbitirs the MN controlling the hamstring muscle

20

What are flexion reflexes?

polysynaptic reflexes that cause limbs to be pulled away from painfuls timuli

rely on divergent pathways in the SC

the afferent nociceptor activates several excitatory interneurons