Muscle physiology

Question 1

Skeletal muscle is innervated by the somatic/autonomic nervous system

Answer 1

Somatic

Question 2

Smooth and cardiac muscle are innervated by the somatic/autonomic nervous system

Answer 2

Autonomic

Question 3

What is a motor unit?

Answer 3

One alpha motor neurone and all the muscle fibres it supplies

Question 4

What is the correlation between precision control and motor unit size?

Answer 4

the more precise control the movement requires, the less muscle fibres are involved in the motor unit

Question 5

Where has the largest ratio of neurones to muscle fibres in a motor unit in the human body?

Answer 5

The extraoccular muscles
Neurones:fibres = 1:3
Contrast with gastrocnemius
neurones:fibres = 1:1000-2000

Question 6

What is the correlation between strength of muscle and motor unit size?

Answer 6

the more power (with less precision) required, the more muscle fibres are supplied by a single neurone.

Question 7

Each muscle fibre is formed from many cells - true/false

Answer 7

False - each muscle fibre is a single cell

Question 8

Each muscle fibre is formed from myofibrils - true/false

Answer 8

True

Question 9

Myofibrils are the smallest contractile unit of a muscle - true/false

Answer 9

False

Question 10

Sarcomeres are the smallest functional contractile units of skeletal muscle - true/false

Answer 10

True

Question 11

Skeletal muscle usually attaches to the skeleton via _____ to give a lever system

Answer 11

Tendons

Question 12

A myofibril contains alternating bands of thick ______ filaments and thin ______ filaments

Answer 12

Myosin

Actin

Question 13

The A-band contains many/few myosin filaments with many/few actin filament

Answer 13

Many

Few

Question 14

The H-zone is a region within the _____ ______ that appears slightly lighter

Answer 14

A-band

Question 15

The H-zone contains only myosin/actin filaments

Answer 15

Myosin

Question 16

The I-band consists of thin actin filaments and/without thick myosin filaments

Answer 16

Without thick filaments

Question 17

The H-zone shortens in contraction, the A-zone remains the same/shortens and the I-zone stays the same - true/false

Answer 17

False
H-zone shortens
A-zone remains the same
I-zone shortens 
Entire sarcomere shortens

Question 18

ATP is required for both contraction and relaxation of smooth muscle. True/False

Answer 18

True

Question 19

Ca2+ ions are required to allow ATP to bind to myosin heads. True/false

Answer 19

False - Ca2+ is required to allow cross bridge formation

Question 20

How does Ca2+ affect muscle contraction

Answer 20

Ca2+ affects muscle contraction as it displaces the troponin-tropomyosin complex and exposes the myosin cross-bridge binding sites on the actin filaments

Question 21

What are the two factors affecting the production of tension in a muscle?

Answer 21

Number of muscle fibres contracting

tension developed by each contracting fibre

Question 22

In skeletal muscle the duration of the AP is much shorter/longer than the twitch.

Answer 22

Shorter

Question 23

A shorter AP than a twitch means that your muscles can repeatedly contract to give the same amount of force. True/false

Answer 23

False - muscle repeatedly contracting gives an increased force - summation of twitches

Question 24

What is tetanus?

Answer 24

Tetanus is when the muscle fibres are repeatedly stimulated to contract with no relaxation between stimuli and a maximum sustained contraction is generated

Question 25

Cardiac muscle cannot be tetanized. True/false

Answer 25

true

Question 26

Why can cardiac muscle not be tetanized?

Answer 26

Its relatively long refractory period prevents overstimulation

Question 27

Tension within a contracting muscle increases/decreases with increasing frequency of the muscle stimulation

Answer 27

Tension within a contracting muscle increases with increasing frequency of the muscle stimulation

Question 28

Give the relationship between length of fibre and contraction tension

Answer 28

Maximum contraction is achieved when the muscle fibre is at its optimum length before onset of contraction

Question 29

Why does optimal length give maximum contraction?

Answer 29

the optimal length is the point at which the most actin binding sites and myosin cross bridges overlap.

Question 30

How does a stretched fibre affect the strength of the contraction?

Answer 30

There is less/insufficient overlap of actin binding sites and myosin cross bridges and so contraction is less/doesnt occur

Question 31

How does a shortened fibre affect the strength of the contraction?

Answer 31

there is plenty of overlap but the muscle cannot shorten much further and so contraction is decreased

Question 32

In the body a resting muscle is approximately its optimal length - true/false

Answer 32

True

Question 33

Skeletal muscle tension, resulting from cross bridge cycling, is transferred to bone via dilation and relaxation of tendons and muscle connective tissues - true/false

Answer 33

False - transferred via the stretching and tightening of connective tissues and tendons

Question 34

There are two types of muscle contraction - name them

Answer 34

Isotonic and isometric

Question 35

What is isotonic contraction?

Answer 35

Contraction where muscle tension remains constant but muscle length changes

Question 36

What is isometric contraction?

Answer 36

Muscle tension develops across the muscle but fibre length remains constant.

Question 37

Give TWO examples of when an isotonic contraction is used

Answer 37

(1) For body movements | (2) for moving objects

Question 38

Give TWO examples of when an isometric contraction is used

Answer 38

(1) supporting objects in a fixed position | (2) maintaining body posture e.g. while walking

Question 39

What is the relationship between load and the velocity at which muscles shorten?

Answer 39

the bigger the load, the slower the muscle shortens

Question 40

What is a congenital myopathy?

Answer 40

A condition, present at birth, which shows microscopic histological changes leading to reduced contractility of muscles

Question 41

Apart from congenital myopathy, name three (of four) other causes of intrinsic muscle diseases

Answer 41

Acquired myopathy e.g. polymyositis Endocrine myopathy e.g. Cushing's Syndrome, thyroid disease Toxic myopathy e.g. from alcohol or statins Chronic degeneration of contractile elements e.g. Muscular dystrophy

Question 42

What is a reflex?

Answer 42

A stereotyped response to a specific stimulus

Question 43

What is the simplest form of co-ordinated movement?

Answer 43

A reflex

Question 44

Why are the neural pathways of reflexes important?

Answer 44

They allow for localising lesions in the motor system.

Question 45

Where are pathways responsible for reflexes located?

Answer 45

At various levels along the motor system

Question 46

What is the simplest example of a monosynaptic spinal reflex?

Answer 46

The stretch reflex.

Question 47

Stretch reflexes are a positive feedback mechanism by which the muscle resists the passive change in muscle length to maintain optimum length - true/false

Answer 47

False - stretch reflex is a NEGATIVE feedback mechanism by which the muscle resists the passive change in muscle length to maintain optimal length.

Question 48

The stretch reflex helps to maintain posture while standing/walking (choose one)

Answer 48

Walking

Question 49

The sensory receptor in the stretch reflex is ________ activated by ________

Answer 49

The sensory receptor in the stretch reflex is muscle spindle activated by muscle stretch

Question 50

Stretching the muscle increases/decreases firing in the afferent/efferent neurones.

Answer 50

Increases and afferent

Question 51

Afferent neurones in the stretch reflex synapse in the ____ ____ with alpha/beta/gamma ______ neurones.

Answer 51

Afferent neurones in the stretch reflex synapse in the Spinal cord with alpha/beta/gamma motor neurones.

Question 52

Activation of the stretch reflex results in contraction/relaxation of the stretched muscle

Answer 52

Contraction

Question 53

In the stretch reflex, contraction/relaxation of antagonist muscles happens simultaneously with contraction/relaxation of the stretched muscle

Answer 53

relaxation of the antagonist | Contraction of the stretched muscle

Question 54

Fibres in muscle spindles are known as extrafusal/intrafusal fibres. Fibres not part of muscle spindles are known as extrafusal/intrafusal fibres

Answer 54

Intrafusal fibres - muscle spindle | Extrafusal fibres - not muscle spindles

Question 55

Muscle spindles are found within the ________ of the muscle and run parallel/anti-parallel/perpendicular to the muscle fibres

Answer 55

Within the belly of the muscle and run parallel to the muscle fibres

Question 56

Muscle spindles have sensory nerve endings known as ________

Answer 56

Annulospiral fibres

Question 57

Discharge from annulospiral fibres decreases when muscle is stretched - true/false

Answer 57

False - discharge from annulospiral fibres increases when muscle is stretched.

Question 58

the afferent/efferent neurone supplying the muscle spindle is the alpha/beta/gamma motor neurone

Answer 58

efferent - gamma neurone

Question 59

What is the function of the gamma motor neurone?

Answer 59

It adjusts the tension in the spindle to maintain sensitivity to stretch when the muscle is contracting.