Muscle Physiology

Question 1

What are the 3 types of muscle cells

Answer 1

Skeletal
Smooth
Cardiac

Question 2

What are the characteristics of skeletal muscle

Answer 2

Multi-nucleated
Long, unbranched fibres
Voluntary contraction
Striated
Transverse tubules
Sarcoplasmic reticulum

Question 3

What are characteristics of smooth muscle

Answer 3

Uninucleated
Unbranched fibres
Involuntary contraction
Unstriated

Question 4

What are the characteristics of cardiac muscle

Answer 4

Branched fibres
Intercalated discs
Purkinje fibres
Faintly striated
Inherent rhythm

Question 5

What is a muscle fascicule

Answer 5

Bundle of muscle fibres

Question 6

What is a myofibril

Answer 6

Bundle of interconnected protein filaments of striated muscles

Question 7

What filaments are found in the myofibrils

Answer 7

Thick filaments - myosin
Thin filaments - actin

Question 8

What is the contractile functional unit of the myofibril

Answer 8

The sarcomere

Question 9

What are a bands

Answer 9

Dark bands that contain thick filaments myosin

Question 10

What are i bands

Answer 10

Light bands that contain only thin filaments actin

Question 11

Where are i bands found

Answer 11

Between 2 thick filaments

Question 12

What are z discs

Answer 12

The area that transverse i bands that mark the point of connection between two actin filaments

Question 13

What is an m line

Answer 13

Middle of the sarcomere containing protein myomesin

Question 14

What is the h zone

Answer 14

Area between the m line and the z disc
Only contains myosin

Question 15

What is the main function of a myofibril

Answer 15

Produce a muscular contraction

Question 16

Where is a muscular contraction induced from

Answer 16

The neuromuscular junction

Question 17

What is the neurotransmitter involved in muscle contractions

Answer 17

Acetylecholine

Question 18

What helps to regulate the muscle contraction

Answer 18

2 proteins
Troponin and tropomyosin

Question 19

What is crucial to be present in a muscle contraction

Answer 19

Calcium

Question 20

How is calcium regulated within the muscle cell

Answer 20

The sarcoplasmic reticulum

Question 21

Where can you find endomysium

Answer 21

Surrounding individual muscle fibres

Question 22

Where can you find perimysium

Answer 22

Surrounding a bundle of muscle fibres forming a fascicle

Question 23

Where can you find epimysium

Answer 23

Surrounding the entire muscle

Question 24

What are the 3 types of skeletal muscle

Answer 24

Type I - slow oxidative
Type IIa - fast oxidative
Type IIx - fast glycolytic

Question 25

Describe the fibre size, contraction speed, force generated, susceptibility to fatigue, type of metabolism and role of Type I skeletal muscle fibres

Answer 25

Fibre size - small
Contraction speed - slow
Force generated - low
Susceptibility to fatigue - low
Type of metabolism - oxidative so high mitochondrial content
Role - low intensity, high duration eg postural muscles

Question 26

Describe the fibre size, contraction speed, force generated, susceptibility to fatigue, type of metabolism and role of Type IIa skeletal muscle fibres

Answer 26

Fibre size - large
Contraction speed - fast
Force generated - high
Susceptibility to fatigue - medium
Type of metabolism - primarily oxidative but can switch to glycolysis
Role - short high intensity

Question 27

Describe the fibre size, contraction speed, force generated, susceptibility to fatigue, type of metabolism and role of Type IIx skeletal muscle fibres

Answer 27

Fibre size - very large
Contraction speed - very fast
Force generated - very high
Susceptibility to fatigue - high
Type of metabolism - Anaerobic glycolysis
Role - very short maximal intensity

Question 28

What are skeletal muscles innervated by

Answer 28

Alpha-motor neurons

Question 29

What is a neuromuscular junction

Answer 29

Specialised synapse which connects a alpha-motor neuron and a skeletal muscle fibre

Question 30

What triggers a skeletal muscle contraction

Answer 30

An action potential arriving at the neuromuscular junction causing the opening of voltage gated calcium channels

Question 31

What does the increase in intracelluar calcium cause

Answer 31

Cause vesicles containing acetylecholine to be released into the synaptic cleft

Question 32

What does acetylecholine in the synaptic cleft trigger

Answer 32

It activates the nicotinic ACh receptors in the muscle fibre plasma membrane

Question 33

When the ligand ion channels in the muscle fibre plasma membrane are active what does this cause

Answer 33

Influx of sodium ions and depolarisation of the muscle fibre membrane potential which activates voltage sensitive sodium channels resulting in a action potential in the muscle fibre

Question 34

How does the membrane of the muscle fibre repolarise

Answer 34

Acetylecholine is rapidly broken down in the cleft by Acetylecholinesterase which terminates the signal and allows for repolarisation

Question 35

Describe the process of excitation contraction coupling

Answer 35

Action potential is generated and it travels along the sarcolemma and Down the t-tubule to depolarise the membrane

Depolarisation triggers voltage gated l-type calcium channels which allows calcium to enter the cell

Calcium influx leads to activation of ryanodine receptors located in the sarcoplasmic reticulum allowing for calcium to flow into the cytoplasm increasing the concentration more

Calcium binds to troponin-c which reveals a binding site on actin for the myosin head through a conformational change

Binding results in ATP hydrolysis providing energy for actin and myosin to slide past each other and shorten the sarcomere length initiating muscle contraction

Question 36

How does relaxation of the muscle fibre occur

Answer 36

Calcium is pumped back into the sarcoplasmic reticulum to reverses the conformational change removing the binding site and so restoring the sarcomere length