15.7: Structure of skeletal muscle

Question 1

Muscles

Answer 1

Effector organs that respond to nervous stimulation by contracting and so bring about movement.

Question 2

Three types of muscle

Answer 2

smooth, cardiac and skeletal

Question 3

Cardiac muscle

Answer 3

In the heart

Question 4

Smooth muscle

Answer 4

In the walls of blood vessels and the gut

Question 5

Skeletal muscle

Answer 5

Makes up the bulk of the body in vertebrates, attached to the bone, under conscious control.

Question 6

Which types of muscle aren’t under conscious control

Answer 6

cardiac and smooth

Question 7

Myofibrils

Answer 7

Tiny muscle fibres that make up individual muscle and are extremely powerful collectively.

Question 8

Sarcoplasm

Answer 8

Nuclei and cytoplasm which are shared by muscle fibres.

Question 9

Muscle fibres made from

Answer 9

separate muscle cells fused together

Question 10

Where is the sarcoplasm mostly found

Answer 10

around the circumference of the fibre and contains large conc.s of mitochondria and ER

Question 11

Myofibrils are made up of two types of protein filament

Answer 11

actin, myosin

Question 12

Actin

Answer 12

Thinner and consists of two strands twisted around one another

Question 13

Myosin

Answer 13

Thicker and consists of long rod shaped tails with bulbous heads that project to the side

Question 14

Why do mircofibrils appear striped

Answer 14

due to alternating light and dark coloured bands

Question 15

Light bands

Answer 15

I bands,

appear lighter because the thick and thin filaments don’t overlap in this region

Question 16

Dark bands

Answer 16

A bands,

appear darker because the thick and the thin filaments overlap in this region

Question 17

H-zone

Answer 17

A lighter-coloured region at the centre of each A-band.

Question 18

Z-line

Answer 18

A line at the centre of each I band.

Question 19

Sacromere

Answer 19

Distance between adjacent z-lines. When a muscle contracts, sacromeres shorten and the pattern of bands changes.

Question 20

Tropomyosin

Answer 20

An important protein found in muscle, which forms a fibrous strand around the actin filament.

Question 21

Two types of muscle fibre

Answer 21

Slow twitch and fast twitch

Question 22

Slow-twitch muscle fibres

Answer 22

Contract more slowly than fast-twitch and provide less powerful contractions but over a longer period of time. Adapted to endurance work and for aerobic respiration to avoid lactic acid build up.

Question 23

Fast-twitch muscle fibres

Answer 23

Contract more rapidly and produce powerful contractions but only for a short period. Adapted to intense exercise.

Question 24

Adaptations of fast-twitch muscles

4

Answer 24

• Thicker and more myosin filaments
• High conc. of glycogen
• High conc. of enzymes involved in anaerobic respiration which provides ATP rapidly
• store of phosphocreatine, so provide energy for muscular contractions

Question 25

Phosphocreatine

Answer 25

A molecule that rapidly generate ATP from ADP in anaerobic conditions and so provides for muscular contractions.
(A store in fast-twitch muscle fibres)

Question 26

Neuromuscular junctions

Answer 26

Point where a motor neurone meets a skeletal muscle fibre (many junctions along a muscle)

Question 27

Motor unit

Answer 27

All muscle fibres supplied by a single unit act together as a single functional unit.

Question 28

Motor unit

Role in muscle exertion

Answer 28

Gives control over the force the muscle exerts, the intensity of the force needed- number of units stimulated.

Question 29

What happens when a nerve impulse is received at the neuromuscular junction?

Answer 29

Synaptic vesicles fuse with the presynaptic membrane and release their acetylcholine.
Acetylcholine then diffuses to the postsynaptic membrane and alters its permeability to Na+ ions which enter rapidly and depolarise the membrane.

Question 30

At neuromuscular junction how it ensured the muscle isn’t overstimulated?

Answer 30

Acetylcholine is broken down by acteylcholinesterase to ethanoic acid and choline which then diffuse back into the neurone, where energy from mitochondria recombine acetylcholine.

Question 31

Similarities between neuromuscular junctions and a synapse?

4

Answer 31

• have neurotransmitters that are transported by diffusion
• have receptors that cause an influx of Na+ ions when bonded to neurotransmitter
• use a Na-K pump to repolarise the axon
• use enzymes to break down the neurotransmitter

Question 32

Difference between neuromuscular junction and a cholinergic synapse
Excitatory/inhibitory?

Answer 32

neuromuscular junction: only excitatory

cholinergic synapse: excitatory or inhibitory

Question 33

Difference between neuromuscular junction and a cholinergic synapse
Neurones involved

Answer 33

neuromuscular junction: only motor

cholinergic synapse: motor, sensory and intermediate may be involved

Question 34

Difference between neuromuscular junction and a cholinergic synapse
What does it link?

Answer 34

neuromuscular junction: neurones-muscles

cholinergic synapse: neurones-neurones or neurones- other effector organs

Question 35

Difference between neuromuscular junction and a cholinergic synapse
Involvement with action potentials

Answer 35

neuromuscular junction:
Action potential ends here
cholinergic synapse: new action potential may be produced on postsynaptic neurone

Question 36

Difference between neuromuscular junction and a cholinergic synapse
Where does acetylcholine bind to receptors on?

Answer 36

neuromuscular junction: binds to receptors on membrane of muscle fibre
cholinergic synapse:
Binds to receptors on membrane of postsynaptic neurone