Physiology: Skeletal Muscle 2

Question 1

what effect will more motor units have on the strength of contraction

Answer 1

greater strength

Question 2

how is a stronger contraction achieved

Answer 2

stimulation of more motor unitrs (recruitment)

Question 3

what is the purpose of asynchonrous motor unit recruitment

Answer 3

occurs during submaximal contractions to help prevent muscle fatigue

Question 4

what 4 things does muscle tension depend on

Answer 4

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

Question 5

define twitch summation

Answer 5

muscle fibre restimulated before it has completely relaxed, the second twitch is adding on to the first one resulting in summation

Question 6

what is a tetanic contraction

Answer 6

muscle fibre is stimulated so rapidly that it doesnt have the chance to relax between the stimuli, and a maximal sustained contraction occurs - known as tetanus

Question 7

why can cardiac muscle not be tetanised

Answer 7

due to refractory period

Question 8

describe the relation between tension developed in skeletal muscle and frequency of stimulation

Answer 8

as frequency of stimulation inc tension developed by skeletal muscle inc

Question 9

what is skeletal muscles optimum length for maximal tetanic contraction

Answer 9

resting condition - optimal overlap between actin and myosin

Question 10

define isotonic contraction

Answer 10

muscle tension remains constant and muscle length changes

Question 11

define isometric contraction

Answer 11

muscle tension develops at constant muscle length

Question 12

how is tension transmitted to bone

Answer 12

via elastic components of muscle

Question 13

give an example of when isometric contraction used

Answer 13

maintaining body posture

Question 14

give an example of when isotonic contraction used

Answer 14

moving object (flexing)

Question 15

describe the relation ship between velocity of muscle shortening and load

Answer 15

the velocity of shortening decreases as the load increases

Question 16

at maximum load what happens to shortening

Answer 16

0 velocity of shortening (cant move) - isometric contraction

Question 17

muscles that can do what are more resistant to fatigue

Answer 17

have a greater capacity to synthesise ATP

Question 18

what determines the speed of contraction

Answer 18

activity of myosin ATPase - determines speed at which energy is made available for cross bridge recycling

Question 19

what are the 3 metabolic pathways that supply ATP in the muscle fibre

Answer 19

transfer of high energy phosphate from creatinine phosphate to ADP oxidative phosphorylation (O2 present) glycolysis (O2 not present)

Question 20

name the types of fibres

Answer 20

I - slow oxidative

IIa - fast oxidative

IIx - fast glycolytic (white)

Question 21

what are the I fibres used for

Answer 21

prolonged low work aerobic activities eg walking

Question 22

what are the IIa fibres used for

Answer 22

aerobic and anaerobic metabolism - prolonged moderate work eg jogging

Question 23

what are IIx fibres used for

Answer 23

anaerobic metabolism - short term high intensity activities eg jumping

Question 24

what type of reflex is the stretch reflex

Answer 24

• monosynaptic
• negative feedback that resists passive change in muscle length to maintain optimal resting length of muscle

Question 25

what is the sensory receptor for the stretch reflex

Answer 25

muscle spindle - activated my muscle stretch

Question 26

describe the stretch reflex

Answer 26

• negative feedback that resists passive change in muscle length to maintain optimal resting length of muscle, helps to maintain posture when walking eg
• muscle spindle activated by muscle stretch increases firing in afferent neurones
• synapse with the spinal cord with alpha motor neurones (efferent)
• contraction of stretched muscle

Question 27

how can the stretch reflex be ellicited

Answer 27

tapping muscle eg patellar tendon, this rapidly stretches the muscle

Question 28

what are muscle spindles known as

Answer 28

intrafusal fibres

Question 29

what are ordinary muscle fibres referred to as

Answer 29

extrafusal fibres

Question 30

how do muscle spindles run in relation to ordinary muscle fibres

Answer 30

parallel within belly of muscles

Question 31

what are muscle spindles sensory nerve endings known as

Answer 31

annulospiral fibres

Question 32

what are muscle spindles

Answer 32

sensory receptors for stretch reflex

Question 33

what happens to the muscle spindles when the muscle is stretched

Answer 33

the discharge from the sensory endings (annulospiral fibres) is increased

Question 34

what are the efferent neurones that supply muscle spindles

Answer 34

gamma motor neurones - own efferent motor nerve neurones

Question 35

what do the gamma motor neurones do

Answer 35

adjust the level of muscle tension in the spindles to maintain their sensitivity when the muscle shortens during contraction

Question 36

does the contraction of intrafusal fibres contribute to overall strength of muscle contraction

Answer 36

no

Question 37

what does a electromyography do

Answer 37

detect the presence of muscular activity - record frequency and amplitude of muscle fibres action potentials

Question 38

what is the use of EMG

Answer 38

differentiate primary muscle disease from muscle weakness caused by neurological disease

Question 39

knee jerk spinal segments

Answer 39

Question 40

ankle jerk

Answer 40

S1 and 2, tibial nerve

Question 41

biceps jerk

Answer 41

C5-6, musculocutaenous nerve

Question 42

brachioradialis

Answer 42

C5-6, radial nerve

Question 43

triceps jerk

Answer 43

C6-7 - radial nerve