Sports science - skeletal muscle + innervation Flashcards
What are the main functions of skeletal muscle?
- movement
- posture
- storing and moving substances
- generating heat
State the gross muscle anatomy in order
- force produced by the muscle
- force is transmitted to the skeleton via the tendon
- movement occurs OR joint is stabilised OR posture is maintained
What is the thin filament in skeletal muscle known as?
actin
What is the thick filament in skeletal muscle known as?
myosin
What are myofibrils made up of?
thin and thick filament (actin and myosin)
How many myosin molecules are there per thick filament?
300
What are the two subunits of mysoin?
S1 - globular head
S2 - flexible region and tail
What are the 3 structural proteins?
- titin
- nebulin
- desmin
What does titin do?
helps return to resting state
What does nebulin and desmin do?
scaffolding for the sarcomere
What is the evidence for the sliding filament mechanism?
- I band becomes narrower
- sarcomere shortens/ Z lines move closer together
- H zone becomes narrower
What are the 3 proteins used in the sliding filament mechanism?
- myosin
- actin
- tropomyosin
What does the sarcoplasmic reticulum do?
- regulates intracellular levels
- stores calcium and releases on stimulation to allow contraction
Process of the cross bridge cycle
- 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
What type of muscle contraction generates the most force?
eccentric
Why is force during shortening less than isometric force?
the faster the movement the less time myosin heads have to attach to binding sites
Why is force during lengthening greater than isometric contraction?
- compliant portion of myosin stretched further than during isometric force
- forcible detachment of myosin heads with stretch
What are the 3 types of muscle fibres?
- type 1
- type 2A
- type 2X
What type of cell is a motor neurone?
single nerve cell
What is a motor unit?
a single motor neuron and all of the fibres it innervates
How many fibres are there per motor unit during gross movements?
2000-3000
How many fibres are there per motor unit during fine movements?
2 OR 3
List the structures of a motor neurone
- cell body
- myelin sheath
- axon
- dendrites
- nodes of ranvier
- terminal branches of axon
- shwann cells
Process at the neuromuscular junction
- 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
