Muscle tissues

Question 1

Function of muscle tissues

Answer 1

To generate force through contraction, enabling movement.

Question 2

3 types of muscle tissue

Answer 2

• skeletal muscle
• smooth muscle
• cardiac muscle

Question 3

Properties of muscle

Answer 3

Muscle has contractibility, excitability, extensibility and elasticity.

Question 4

Skeletal muscle

Answer 4

• under voluntary control of the somatic nervous system (SNS)
• specialised for rapid, forceful contraction under short duration
• striated due to arrangement of contractile myofibrils in repeating sarcomere units
• myocytes are large elongated muscle fibres
• myocytes have multiple periperally positioned nuclei

Question 5

Smooth muscle

Answer 5

• under involuntary control of the autonomic nervous system (ANS)
• specialised for continuous contractions of relatively low force
• non-striated due to criss-cross arrangement of contractile myofibrils, anchored to dense bodies
• myocytes are small, spindle shaped cells connected by gap junctions
• myocytes have one central nucleus

Question 6

Cardiac muscle

Answer 6

• involuntary contraction arises from the muscle tissue itself (myogenic)
• rate and force of contraction is regulated by the autonomic nervous system (ANS)
• produces strong, continuous contractions
• striated
• cells are branching, and joined by intercalated disks for rapid spread of contractile stimuli
• cardiomyocytes typically contain one or two central nuclei

Question 7

Organisation of skeletal muscle

Answer 7

Endomysium is connective tissue surrounding individual muscle fibres. Perimysium is loose collagenous connective tissue surrounding bundles of muscle fibres, called fascicles. Epimysium is dense collagenous connective tissue surrounding all the fascicles and neurovascular bundle of a muscular unit.

Question 8

Sarcomere

Answer 8

The repeating unit of a muscle fibre, consisting of:

• Light (I) band= thin actin filaments only
• Dark (A) band= both thin actin and thick myosin filaments

Question 9

Muscle cell organelles

Answer 9

Sarcoplasm=the cytoplasm of muscle cells.
Sarcolemma= the plasma membrane surrounding muscle cells.
Sarcoplasmic reticulum= acts as a calcium reservoir.

Question 10

T-tubule system

Answer 10

A specialised system formed by the invagination of the sarcolemma, surrounding and forming an internal network within the myofibril. Allows the uniform, instant depolarisation of the entire muscle fibre for fast and even contraction.

Question 11

Neuromuscular junction

Answer 11

The interface between a motor neurone and a muscle cell, formed of a pre- and post-synaptic membrane. Vesicles contain a neurotransmitter (ACh).

Question 12

3 types of muscle fibres

Answer 12

• type I (slow twitch)
• type IIA (fast/intermediate twitch)
• type IIB (fast twitch)

Question 13

Type I muscle fibres

Answer 13

• lots of mitochondria and myoglobin
• smaller diameter, rich blood supply
• aerobic respiration
• fibres maintain continuous contraction
• for muscles used all the time

Question 14

Type IIA muscle fibres

Answer 14

• some mitochondria and myoglobin

- both aerobic and anaerobic respiration

Question 15

Type IIB muscle fibres

Answer 15

• little mitochondria and myoglobin
• contracts more rapidly due to faster myosin
• relies on glycolysis of glycogen and anaerobic respiration
• for intense but sporadic contraction

Question 16

Intercalated disks

Answer 16

• contain gap junctions, desmosomes and adhering junctions
• allow rapid spread of contractile stimuli
• create physical and electrical connections
• connect cardiomyocytes

Question 17

Satellite cell

Answer 17

Involved in the maintenance, repair and regeneration of skeletal muscle cells.

Question 18

Nerve entry point

Answer 18

Where the nerve enters the muscle, typically situated halfway between its origin and insertion. The muscle shortens at its centre first, pulling in both directions and allowing even contraction.

Question 19

Sliding filament theory

Answer 19

1) An AP is transmitted across the NMJ, depolarising the sarcolemma, which causes an efflux of Ca2+ from the sarcoplasmic reticulum.
2) Ca2+ binds to troponin, causing tropomyosin filaments to release actin.
3) Actin binding sites are exposed, freeing them for cross-bridge formation with myosin.
4) Hydrolysis of ATP breaks cross bridges, allowing the myosin filaments to ‘row’ along.