Physiology

Question 1

Physiological functions of skeletal muscles

Answer 1

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

Question 2

Describe the three muscle types with regards to action and striations

Answer 2

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

Question 3

What causes a striated appearance under a microscope?

Answer 3

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

Question 4

What type of innervation applies to each muscle type?

Answer 4

Skeletal - somatic

Cardiac and smooth - autonomic

Question 5

What are the main differences between skeletal and cardiac muscle?

Answer 5

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

Question 6

What is the neurotransmitter at the NMJ?

Answer 6

ACh

Question 7

What is the definition of a motor unit?

Answer 7

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

Question 8

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

Answer 8

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

Precision vs Power

Question 9

What is the functional unit of skeletal muscle?

Answer 9

Sarcomere

NB: sarcomeres –> myofibrils –> fibres

Question 10

Function of Tendons

Answer 10

attachment of muscle to bone - lever systems

Question 11

What is a myofibril?

Answer 11

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

Question 12

What makes up the boundaries of a sarcomere?

Answer 12

Z lines - connect the thin filaments of two adjoining sarcomeres

Question 13

What are the 4 zones of a sarcomere?

Answer 13

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

Question 14

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

Answer 14

Both

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

Question 15

Define Excitation Contraction Coupling

Answer 15

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

Question 16

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

Answer 16

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

Question 17

How does calcium switch on cross bridge formation?

Answer 17

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

Question 18

Two primary factors influencing the gradation of skeletal muscle tension -

Answer 18

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.

Question 19

Which physiological mechanism helps prevent muscle fatigue?

Answer 19

During submaximal contractions, asynchronous motor unit recruitment prevents muscle fatigue

Question 20

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

Answer 20

True

Question 21

Define summation

Answer 21

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

Question 22

Define tetanus

Answer 22

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

Question 23

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

Answer 23

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.

Question 24

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

Answer 24

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

Question 25

What are the two types of skeletal muscle contraction?

Answer 25

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

Question 26

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

Answer 26

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

Question 27

What metabolic pathways supply ATP in the muscle fibre?

Answer 27

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

Question 28

3 types of skeletal muscle fibre

Answer 28

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

Question 29

Main uses of the three muscle fibre types

Answer 29

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

Question 30

Reflex action (def)

Answer 30

a stereotyped response to a specific stimulus

Question 31

Give an example of a monosynaptic spinal reflex

Answer 31

The stretch reflex

Question 32

How does the stretch reflex occur?

Answer 32

``` 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.

Question 33

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

Answer 33

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

Question 34

What are muscle spindles?

Answer 34

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

Question 35

What makes up the efferent motor supply of muscle spindles?

Answer 35

gamma motor neurons - adjust tension to maintain sensitivity during shortening

Question 36

What might impair skeletal muscle function?

Answer 36

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

Question 37

List types of myopathies which may cause intrinsic muscle disease

Answer 37

``` 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 ```

Question 38

Symptoms of muscle disease

Answer 38

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

Question 39

Ix for neuromuscular disease

Answer 39

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

Question 40

What is EMG?

Answer 40

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