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Y2 MSK > Physiology > Flashcards

Physiology Flashcards

1
Q

Physiological functions of skeletal muscles

A 
Maintain posture 
Purposeful movement in relation to the external environment 
Respiratory movement 
Heat production 
Contribution to whole body metabolism
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2
Q

Describe the three muscle types with regards to action and striations

A

Skeletal - striated, voluntary
Cardiac - striated, involuntary
Smooth - non-striated, involuntary

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3
Q

What causes a striated appearance under a microscope?

A

Alternating myosin thick (dark) and actin thin (light) filaments within the muscle

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4
Q

What type of innervation applies to each muscle type?

A

Skeletal - somatic

Cardiac and smooth - autonomic

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5
Q

What are the main differences between skeletal and cardiac muscle?

A 
Initiation - neurogenic vs. myogenic 
Motor units vs no motor units
NMJ vs gap junctions 
Ca++ from SR vs ECF + SR 
Motor unit recruitment and summation vs Frank-Starling
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6
Q

What is the neurotransmitter at the NMJ?

A

ACh

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7
Q

What is the definition of a motor unit?

A

A single alpha motor neuron and all of the skeletal muscle fibres it innervates

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8
Q

What differences are there in motor units with regards to function?

A

No. of fibres within unit - fine actions have fewer fibres e.g. external eye, facial expression, hand muscles.

Precision vs Power

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9
Q

What is the functional unit of skeletal muscle?

A

Sarcomere

NB: sarcomeres –> myofibrils –> fibres

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10
Q

Function of Tendons

A

attachment of muscle to bone - lever systems

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11
Q

What is a myofibril?

A

Specialised contractile intracellular structures, containing alternating thick (myosin) and thin (actin) filaments arranged into sarcomeres

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12
Q

What makes up the boundaries of a sarcomere?

A

Z lines - connect the thin filaments of two adjoining sarcomeres

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13
Q

What are the 4 zones of a sarcomere?

A

A band - entire span of thick filaments, including where thin overlap at ends
H zone - lighter area in the middle of the A band where the thin filaments do not reach
M line - middle of A band and H zone
I band - remaining portion of thin filaments not overlapping any thick

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14
Q

Is ATP required for contraction or relaxation (sliding filaments)?

A

Both

Contraction - to power cross bridges
Relaxation - releases cross bridges and pumps Ca++ back into SR

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15
Q

Define Excitation Contraction Coupling

A

the process whereby the surface action potential results in the activation of contractile structures of the muscle fibre

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16
Q

What triggers the release of Ca++ from the lateral sacs of the SR?

A

The spread of the surface action potential down the transverse T-tubules

NB - t tubules are extensions of the surface membrane which stretch into the fibre

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17
Q

How does calcium switch on cross bridge formation?

A

Ca++ binds with troponin, pulling the troponin-tropomyosin complex aside to expose the cross bridge binding site

18
Q

Two primary factors influencing the gradation of skeletal muscle tension -

A

No. of fibres in the muscle - motor unit recruitment allows for stronger contraction

The tension developed by each contracting fibre - depends on the frequency pf stimulation, the summation of contraction, the length of muscle fibres and the thickness of muscle fibres.

19
Q

Which physiological mechanism helps prevent muscle fatigue?

A

During submaximal contractions, asynchronous motor unit recruitment prevents muscle fatigue

20
Q

In skeletal muscle, summation of contraction can occur through repetitive fast stimulation (AP) -T/F?

A

True

21
Q

Define summation

A

If a muscle fibre is restimulated before it has fully relaxed, the second “twitch” is added on top of the first = summation

22
Q

Define tetanus

A

Maximum sustained contraction due to rapid fire stimulation with no opportunity to relax

MB - remember that cardiac muscle cannot be tetanised due to refractory period

23
Q

What is the optimal length and how does this effect contraction?

A

Optimum length is the point of optimal overlap of thick filament and thin filament cross bridging sites. This allows for maximal tetanic contraction to be achieved.

In the body, resting length is roughly optimal.

24
Q

How does the contractile component result in the movement of the limb?

A

Skeletal muscle tension id transmitted to the bone via the stretching and tightening of the elastic component (connective tissue/tendon)

25
Q

What are the two types of skeletal muscle contraction?

A

Isotonic - body movements etc, constant tension as length changes
Isometric - supporting fixed objects and posture, constant length

26
Q

What are the main differences between types of skeletal muscle fibre?

A

ATP synthesis pathways
Resistance to fatigue
Activity of myosin ATPase (determining speed of contraction via energy available for cross bridge cycling)

27
Q

What metabolic pathways supply ATP in the muscle fibre?

A

Immediate - transfer of phosphate from creatine phosphate to ADP
Aerobic - Ox Phos
Anaerobic - glycolysis

28
Q

3 types of skeletal muscle fibre

A

Slow Oxidative type I - slow twitch fibres
Fast oxidative type IIa - intermediate twitch
Fast glycolytic type IIx - fast twitch

29
Q

Main uses of the three muscle fibre types

A

Slow oxidative - prolonged low work aerobic activity e.g. walking, maintain posture

Fast oxidative - prolonged activity with moderate work e.g. jogging

Fast glycolytic - anaerobic, short term high intensity e.g. jump

30
Q

Reflex action (def)

A

a stereotyped response to a specific stimulus

31
Q

Give an example of a monosynaptic spinal reflex

A

The stretch reflex

32
Q

How does the stretch reflex occur?

A 
Negative feedback resisting passive change in length, resulting in maintenance of optimal length 
sensory receptor (muscle spindle) is activated by muscle stretch, increasing firing in the afferent neurons.

These in turn synapse with alpha motor neurons (efferent limb) in spinal cord to innervate stretched muscle.

33
Q

What spinal segment and peripheral nerves are involved in each reflex initiated by rubber hammer?

A 
Knee - L3,4 - femoral 
Ankle - S1,2 - tibial 
Biceps - C5,6 - musculocutaneous 
Brachioradialis - C5,6 - radial 
Triceps - C6,7 - radial
34
Q

What are muscle spindles?

A

Sensory receptors for stretch reflex - a collection of specialised fibres, called intrafusal fibres (ordinary fibres = extrafusal), with sensory nerve endings called annulospiral fibres.

35
Q

What makes up the efferent motor supply of muscle spindles?

A

gamma motor neurons - adjust tension to maintain sensitivity during shortening

36
Q

What might impair skeletal muscle function?

A

Intrinsic muscle disease
Disease of NMJ
Disease of lower motor neurons
Disruption of input to motor nerves

37
Q

List types of myopathies which may cause intrinsic muscle disease

A 
Congenital e.g. muscular dystrophy, myotonia 
Inflammatory e.g. polymyositis 
Non-inflammatory e.g. fibromyalgia 
Endocrine e.g. Cushings, thyroid disease
Toxic e.g. alcohol, statins
38
Q

Symptoms of muscle disease

A

Muscle weakness
Delayed relaxation after voluntary contraction (myotonia)
Muscle pain (myalgia)
Muscle stiffness

39
Q

Ix for neuromuscular disease

A 
EMG 
Nerve conduction studies (determine functional integrity) 
Muscles enzymes (CK)
Inflammatory markers (CRP, PV)
Muscle biopsy
40
Q

What is EMG?

A

Electromyography - records the frequency and amplitude of muscle fibres APs to help differentiate between primary muscle disease and neurological disease - non-diagnostic

Y2 MSK (5 decks)

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