Physiology 2

Question 1

what does gradation of skeletal muscle tension depend on?

Answer 1

number of fibres contracting in the muscle

tension developed by each contracting fibre

Question 2

what contributes to the number of muscle fibres contracting?

Answer 2

motor unit structure

motor unit recruitment

Question 3

how is muscle fatigue prevented in submaximal contraction?

Answer 3

asynchronous motor unit recruitment

Question 4

what contributes to the tension developed by each fibre?

Answer 4

frequency of stimulation
summation of contractions
length of fibre at onset of contraction
thickness of fibre

Question 5

describe 3 types of twitching?

Answer 5

single twitch (not useful, weak)
twitch summation
Tetanus (smooth, sustained contraction)

Question 6

how does twitching differ in cardiac muscle?

Answer 6

tetanus cannot occur in cardiac muscle due to the long refractory period, so another AP cannot act until muscle is relaxed

Question 7

how does frequency of stimulation affect tension developed by skeletal muscle?

Answer 7

increased frequency = increased tension

Question 8

when does maximal tetanic contraction occur?

Answer 8

when muscle is at optimum length (Lo)under resting conditions (not shortened or too stretched)
means optimum overlap between actin and myosin so most cross bridges can form

Question 9

why is stretched muscle not effective?

Answer 9

actin and myosin don’t overlap so corss bridges cant form between them as they cant reach

Question 10

is the resting length of a skeletal muscle the same as its optimal length?

Answer 10

yes

Question 11

what are the 2 types of skeletal muscle contraction?

Answer 11

isotonic

isometric

Question 12

what is isotonic contraction?

Answer 12

muscle tension remains constant as the muscle length changes

• body movements
• moving objects

Question 13

what is isometric contraction?

Answer 13

muscle tension changes as muscle length stays constant

• supporting objects in fixed positions
• maintaining body posture

Question 14

how is muscle tension transmitted to bone?

Answer 14

via elastic component of muscle

Question 15

how does load affect velocity of muscle shortening?

Answer 15

larger load (heavier object) = slower velocity of shortening

Question 16

what are the main differences between diiferent types of skeletal muscle fibres?

Answer 16

• enzymatic pathways for ATP synthesis (some produce more than others)
• the resistance to fatigue (amount of ATP synthesis dependant)
• activity of myosin ATPase (determines speed at which ATP is broken down and energy made available - speed of contraction)

Question 17

are all muscle fibres in a whole muscle the same?

Answer 17

no

usually the same in one motor unit

Question 18

what is the main method of ATP production in skeletal muscle?

Answer 18

oxidative phosphorylation - main source when oxygen present

anaerobic glycolysis - main source when lacking in oxygen

transfer of high energy phosphate from creatine phosphate to ADP (immediate source)

Question 19

what are the 3 types of skeletal muscle fibres?

Answer 19

slow oxidative (type 1)
fast oxidative (type 2a)
fast glycolytic (type 2x)

Question 20

type 1?

Answer 20

used for prolonged, low work aerobic activities (maintaining posture, walking)

• low myosin ATPase activity
• high oxidative phosphorylation
• low anaerobic glycolysis

Question 21

type 2a?

Answer 21

use both aerobic and anaerobic metabolism
useful for prolonged relatively moderate work activities (jogging)
- high myosin ATPase activity
- high oxidative phosphorylation
- intermediate anaerobic glycolysis

Question 22

type 2x?

Answer 22

use anaerobic metabolism and are mainly used for short term, high intensity activity (jumping)

• high myosin ATPase activity
• low oxidative phosphorylation
• high anaerobic glycolysis

Question 23

what inputs motor neurons?

Answer 23

brain and variety of other receptors
- e.g withdrawal reflex
can be excitatory or inhibitory

Question 24

what is a reflex?

Answer 24

stereotyped response to as specific stimulus

simplest form of coordinated movement

Question 25

how can reflexes be used clinically?

Answer 25

can show where lesions/problems are in the motor system

Question 26

what is the simplest monosynaptic spinal reflex?

Answer 26

stretch reflex

Question 27

what is the stretch reflex?

Answer 27

negative feedback system that resists passive change in muscle length to maintain optimal resting length

Question 28

what is activated in the stretch reflex?

Answer 28

muscle spindles (specialised sensory receptor muscle fibres)

Question 29

how does a stretch reflex occur?

Answer 29

stretching of the muscle spindle increases firing in the afferent neurons afferent neurons synapse in spinal cord with alpha motor neurons that innervate stretched muscle of efferent limb results in contraction of stretched muscle

Question 30

what are muscle spindles/ordinary fibres also known as?

Answer 30

``` spindles = intrafusal ordinary = extrafusal ```

Question 31

where are muscle spindles found?

Answer 31

within belly of muscles and run parallel to ordinary fibres | have sensort nerve endings known as annulospiral fibres

Question 32

what nerves supply muscle spindles and what do they do?

Answer 32

efferent motor neurons known as gamma motor neurons adjust the level of tension in the muscle spindles to maintain their sensitivity to stretch when the muscle shortens during contraction

Question 33

what can cause impairment of skeletal muscle function?

Answer 33

intrinsic disease of muscle disease of NMJ disease of lower motor neurons disruption of input to motor nerves (upper motor neuron disease)

Question 34

2 general types of intrinsic muscle disease?

Answer 34

genetic myopathies | acquired myopathies

Question 35

describe 3 types of genetic myopathies

Answer 35

``` congenital myopathies chronic degredation (muscular dystrophy) abnormalities in muscle membrane ion channels (myotonia) ```

Question 36

describe 4 acquired myopathies

Answer 36

inflammatory - polymyositis non-inflammatory - fibromyalgia endocrine - cushings, thyroid toxic - alcohol, statins

Question 37

what are 4 symptoms of muscle disease?

Answer 37

muscle weakness delayed relaxation (myotonia) muscle pain (myalgia) muscle stiffness

Question 38

give 4 investigations used for neuromuscular disease?

Answer 38

``` electromyography (EMG) Nerve conduction studies Muscle enzymes (CK) inflammatory markers (CRP) Muscle biopsy ```

Question 39

what is single twitch?

Answer 39

muscle fibre is restimulated after it has completely relaxed | useless

Question 40

what is a twitch summation?

Answer 40

muscle fibre is restimulated before it has completely relaxed stronger than single

Question 41

what is tetanus?

Answer 41

muscle fibre is stimulated so rapidly that is doesn't have an opportunity to relax at all maximal sustained contraction

Question 42

how is the contractile component of skeletal muscle transmitted to bone?

Answer 42

via the stretching and tightening of muscle connective tissue and tendon (elastic component)

Question 43

how can the stretch reflex be elicited?

Answer 43

tapping the muscle tendon with a hammer this rapidly stretches the muscle resulting in contraction - e.g knee jerk

Question 44

what does knee jerk test?

Answer 44

femoral nerve | L3 and L4

Question 45

what does ankle jerk test>

Answer 45

tibial nerve | S1 and S2

Question 46

what does biceps jerk test?

Answer 46

musculocutaneous nerve | C5-C6

Question 47

what does triceps jerk test?

Answer 47

radial nerve | C6-C7

Question 48

what does brachioradialis test?

Answer 48

radial nerve | C5-C6

Question 49

do muscle spindles contribute to overall strength of muscle contraction?

Answer 49

no

Question 50

how does electromyography work?

Answer 50

records frequency and amplitude of muscle fibres action potentials can differentiate between primary and secondary muscle disease