Sports science - skeletal muscle + innervation

Question 1

What are the main functions of skeletal muscle?

Answer 1

• movement
• posture
• storing and moving substances
• generating heat

Question 2

State the gross muscle anatomy in order

Answer 2

• force produced by the muscle
• force is transmitted to the skeleton via the tendon
• movement occurs OR joint is stabilised OR posture is maintained

Question 3

What is the thin filament in skeletal muscle known as?

Answer 3

actin

Question 4

What is the thick filament in skeletal muscle known as?

Answer 4

myosin

Question 5

What are myofibrils made up of?

Answer 5

thin and thick filament (actin and myosin)

Question 6

How many myosin molecules are there per thick filament?

Answer 6

300

Question 7

What are the two subunits of mysoin?

Answer 7

S1 - globular head
S2 - flexible region and tail

Question 8

What are the 3 structural proteins?

Answer 8

• titin
• nebulin
• desmin

Question 9

What does titin do?

Answer 9

helps return to resting state

Question 10

What does nebulin and desmin do?

Answer 10

scaffolding for the sarcomere

Question 11

What is the evidence for the sliding filament mechanism?

Answer 11

• I band becomes narrower
• sarcomere shortens/ Z lines move closer together
• H zone becomes narrower

Question 12

What are the 3 proteins used in the sliding filament mechanism?

Answer 12

• myosin
• actin
• tropomyosin

Question 13

What does the sarcoplasmic reticulum do?

Answer 13

• regulates intracellular levels
• stores calcium and releases on stimulation to allow contraction

Question 14

Process of the cross bridge cycle

Answer 14

• action potential arrives at sarcoplasmic reticulum
• calcium ions then released from the sarcoplasmic reticulum
• calcium binds to troponin
• causing tropomyosin to change shape, exposing binding sites on the actin filament
• hydrolysis of ATP changes the angle of the myosin head, forming a cross bridge
• pi released from the myosin head changes the angle of the myosin head, causing a powerstroke
• myosin head then picks up another ATP and bond with actin is released
• repeats until Ca+ or ATP levels drops

Question 15

What type of muscle contraction generates the most force?

Answer 15

eccentric

Question 16

Why is force during shortening less than isometric force?

Answer 16

the faster the movement the less time myosin heads have to attach to binding sites

Question 17

Why is force during lengthening greater than isometric contraction?

Answer 17

• compliant portion of myosin stretched further than during isometric force
• forcible detachment of myosin heads with stretch

Question 18

What are the 3 types of muscle fibres?

Answer 18

• type 1
• type 2A
• type 2X

Question 19

What type of cell is a motor neurone?

Answer 19

single nerve cell

Question 20

What is a motor unit?

Answer 20

a single motor neuron and all of the fibres it innervates

Question 21

How many fibres are there per motor unit during gross movements?

Answer 21

2000-3000

Question 22

How many fibres are there per motor unit during fine movements?

Answer 22

2 OR 3

Question 23

List the structures of a motor neurone

Answer 23

• cell body
• myelin sheath
• axon
• dendrites
• nodes of ranvier
• terminal branches of axon
• shwann cells

Question 24

Process at the neuromuscular junction

Answer 24

• action potential arrives at the pre synaptic neuron
• axon terminal depolarised
• influx of calcium ions then enter the axon terminal
• encourages the release of acetylcholine into the synaptic cleft
• acetylcholine then interacts with the sodium ion channels on the post synaptic membrane
• sodium ion channels open and an influx of sodium causes depolarisation at the post synaptic neuron
• as the charge of the muscle cell membrane increases, voltage gated calcium channels open and there is a calcium influx
• the increase in charge also stimulates calcium release from the sarcoplasmic reticulum
• when the action potential ceases, the acetylcholine re-enters the neuron as choline and acetic acid

Question 25

Define efferent neurones

Answer 25

neurons that send impulses from the central nervous system to your limbs and organs E.G muscles

Question 26

Define afferent neurones

Answer 26

neurons that carry nerve impulses from sensory receptors or sense organs towards the central nervous system

Question 27

What does a golgi tendon organ (GTO) do?

Answer 27

• senses tension in the tendon when the muscle contracts
• has an inhibitive (negative) afferent neuron
• when excessively large forces are generated, feedback from GTO causes activation of muscle to decrease - PROTECTIVE

Question 28

Passage of an action potential at the nodes of ranvier

Answer 28

• at rest more sodium ions (Na+) outside than inside the axon
• action potential then arrives so sodium channels open
• Na+ enters the axon
• increased Na+ within the axon causes the exposed parts of the axon between the myelin sheaths to DEPOLARISE
• Na+ gates close (30mV)
• when membrane potential reaches +30mV potassium (K) gates open
• K+ leaves the axon and the inside of the axon becomes less positive REPOLARISATION

Question 29

What happens within depolarisation?

Answer 29

• sodium gates open
• inside of axon becomes more positive
• so sodium gates close

Question 30

What happens within repolarisation?

Answer 30

• potassium gates open
• inside of the axon becomes less positive
• potassium gates close

Question 31

At what membrane potential do potassium gates close?

Answer 31

-90mV