Muscle

Question 1

4 main functions of skeletal muscle?

Answer 1

Movement
Thermoregulation
Metabolism
Endocrinology

Question 2

4 main features of skeletal muscle?

Answer 2

Excitable
Contractile
Extensible
Elastic

Question 3

Describe the epimysium

Answer 3

Meaning upon / on top of muscle, is a fibrous tissue envelope that surrounds skeletal muscle. It is a layer of dense irregular connective tissue which ensheaths the entire muscle and protects muscles from friction against other muscles and bones.

Question 4

Describe the perimysium

Answer 4

Meaning around muscle, is the sheath of connective tissue surrounding a bundle of muscle fibres.

Question 5

Describe the endomysium

Answer 5

Meaning within the muscle, is a wispy layer of areolar connective tissue that ensheaths each individual myocyte (muscle fiber, or muscle cell)

Question 6

Name the elements of a sarcomere

Answer 6

Thin filament (actin)
Thick filament (Myosin)
Z disks
M line
Titin filament

Question 7

What is excitation contraction coupling?

Answer 7

The process of which an action potential is generated in the sarcolemma due to the influx of sodium into the sarcolemma due to the ligand gated sodium channels in the synaptic cleft
(Excitation)
This action potential propagates through the T tubules, triggering the release of calcium into the sarcomere
Triggering the contraction of the myosin heads to the myosin binding sites on the actin filament
(Contraction)

Question 8

Another name for motor end plate?

Answer 8

Neuromuscular junction

Question 9

Run through the processes between an action potential in a motor neuron and an action potential in a muscle cell

Answer 9

1. Action potential triggers voltage gated Ca+ channels based on presynaptic terminal. Influx of Ca+ into neuron
2. Ca+ binds to synaptic vesicles containing ACh
3. Commands vesicle to secrete ACh into synaptic cleft
4. ACh binds to ligand gated Na+ channel in cleft
5. Influx of Na+ triggers action potential to propagate

ACh unbinds to the ligand channel
Binds to acetylcholinesterase
Broken down into choline + acetic acid
Diffuses back into motor neuron
ACh reforms, diffuses into vesicles

Question 10

Explain cross bridge cycling

Answer 10

Ca+ released from sarcoplasmic reticulum binds to Troponin
This binding moves the tropomyosin in a way that reveals the myosin binding sites
The myosin heads, currently with ADP+P bind to the myosin binding sites (cross bridge formed)
Myosin cross-bridge then turn towards centre of sarcomere (power stroke)
They then release the ADP+P
Binding with ATP causes myosin to release from actin filament
Then hydrolyze ATP to be ‘primed’ again in resting position

Question 11

What is the power stroke?

Answer 11

The rotation of the myosin cross bridge towards centre of sarcomere (contraction)

Question 12

What is a cross-bridge?

Answer 12

The result of myosin binding to actin filament

Question 13

Summarise the Length-tension relationship

Answer 13

The ability of a muscle
to produce force is a
function of the muscle’s
length whilst
contracting

Maximal force occurs at mid-range contraction

Reduced sarcomere length = less chance for filaments to slide over each other (reduced force)
Increased sarcomere length = more opportunities for filaments to slide over each other generating force
Over extension = less filaments capable of sliding over each other

Question 14

Summarise force summation

Answer 14

Under load, motor units are recruited from smallest to largest. In practice, this means that slow-twitch, low-force, fatigue-resistant muscle fibers are activated before fast-twitch, high-force, less fatigue-resistant muscle fibers