1- skeletal physiology 2

Question 1

what is motor unit recruitment?

Answer 1

when more than 1 motor unit is stimulated to make stronger contraction

Question 2

how does asynchronous motor units recruitment help prevent fatigue?

Answer 2

Asynchronous motor unit recruitment involves different motor units activating at different times during submaximal contractions. This allows some muscle fibers to rest while others are active, distributing the workload and reducing overall muscle fatigue.

Question 3

what does level of tension developed by each contracting muscle fibre depend on? (like general factors)

Answer 3

• frequency of stimulation
• summation of contractions
• length of muscle fibre(optimum overlap)
• thickness of muscle fibre

Question 4

describe twitch summation in skeletal muscle fibres?

Answer 4

it’s basically the idea that skeletal muscle keeps being stimulated just before 1st stimulation is over (the twitch is the movement of muscle), receives 2nd stimulation before it had time to completely relax

tension developed increases with increasing frequency of stimulation

Question 5

what is maximal tetanic contraction?

Answer 5

= highest possible force by muscle causing continuous contraction without any relaxation

(achieved when muscle at optimal length before onset of contraction)

Question 6

what are 2 types of skeletal muscle contraction?

Answer 6

1. isotonic contraction
2. isometric contraction

Question 7

what is isotonic contraction?

Answer 7

type of contraction where muscle tension remains constant as muscle length changes

used for = body movements and moving objects

Question 8

what is isometric contraction?

Answer 8

type of contraction where muscle tension develops at constant muscle length

used for = supporting objects in fixed position and maintaining body posture

Question 9

what are main differences between skeletal muscle fibres?

Answer 9

1. enzymatic pathways for ATP synthesis
2. resistance to fatigue (muscle fibres with greater capacity to synthesise ATP are more resistant to fatigue)
3. activity of myosin ATPase (determines speed at which energy made available = speed of contraction)

Question 10

what are 3 ways ATP made?

Answer 10

1. creatine phosphate to make ATP. transfer of high energy phosphate tp ADP
2. oxidative phosphorylation (major way)
3. glycolysis (way for anaerobic metabolism)

Question 11

what are 3 types of skeletal muscle fibres?

Answer 11

1. slow oxidative (type I, slow twitch)
2. fast oxidative (type IIa, intermediate twitch)
3. fast glycolytic (type IIx, fast twitch)

Question 12

when are Slow oxidative type I fibres used? why?

Answer 12

mainly for prolonged relatively low work aerobic activities e.g. maintenance of posture, walking

• because they have myosin ATPase activity low so slow speed and resistance to fatigue high since mitochondria so low energy for long time

Question 13

what are Fast oxidative (Type IIa) fibres used for? why?

Answer 13

use both aerobic and anaerobic metabolism and are useful in prolonged relatively moderate work activities e.g. jogging

• since some good myosin ATP-ase activity and some mitochondria

Question 14

what are Fast glycolytic (Type IIx) fibres used for? why?

Answer 14

use anaerobic metabolism and are mainly used for short-term high intensity activities e.g. jumping

• they have lots of myosin ATPase so high energy used but not much mitochondria so tired easily

Question 15

what is stretch reflex?

Answer 15

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

Question 16

give basic pathway of stretch reflex?

Answer 16

• sensory receptors is muscle spindle and activated by muscle stretch
• stretching muscle spindle increases firing in afferent neurons
• afferent neurons synapse in spinal cord with alpha motor neuron (efferent) that innervate stretched muscle

= activation of reflex results in contraction of stretched muscle

Question 17

what are muscle spindles?

Answer 17

they’re collection of specialised muscle fibres for stretch reflex - they have sensory nerve endings known as annulospiral fibres

• they have efferent nerve supply called gamma motor neurons

Question 18

what are intrafusal and extrafusal fibres?

Answer 18

intrafusal = muscle spindles sensory receptors in stretch reflex
extrafusal = ordinary muscle fibres

Question 19

where are muscle spindles found?

Answer 19

in belly of muscles and run parallel to ordinary muscle fibres

Question 20

what can impairment of skeletal muscle be caused by?

Answer 20

1. intrinsic disease of muscle
2. disease of NMJ
3. disease of lower motor neurons which supply muscle
4. disruption of input to motor nerves