Muscle Control

Question 1

What are the subdivisions of the nervous system?

Answer 1

• Topographical subdivisions
• Functional subdivisions
• Directional subdivisions

Question 2

What is included in the topographical subdivisions?

Answer 2

• central NS - brain and spinal cord
• peripheral NS - cranial and spinal nerves

Question 3

What’s included in functional subdivisions?

Answer 3

• somatic (voluntary)
• visceral (involuntary) also includes the sympathetic and parasympathetic subdivisions

Question 4

What’s included in the directional subdivisions?

Answer 4

• Afferent = towards brain and spinal cord
• Efferent = away from the brain and spinal cord

Question 5

what is a neuron?

Answer 5

• A type of nerve cell that transmits information quickly

Question 6

What do dendrites do?

Answer 6

-Synapse with other neurones to receive information

Question 7

What does and axon do?

Answer 7

• axon rapidly conduct action potential to distant site
• myelination enhances conduction speed

Question 8

What is a motor neuron?

Answer 8

• Efferent nerve cell transmitting information from CNS to muscle to elicit contraction
• they are excitatory

Question 9

Complete the sentence … each skeletal muscle fibre is innervated by …

Answer 9

• one motor neurone
• but each neurone can innervate few or many fibres

Question 10

Skeletal muscle requires innervation from what to contract?

Answer 10

• motor neurons

Question 11

The pattern of muscle contraction (strength, speed, duration) is determined by what?

Answer 11

• the pattern of activity in motor neurons

Question 12

what is a motor unit?

Answer 12

• A motor neurone plus all the muscle fibres it innervates

Question 13

Ratio of neurone to muscle fibres depends on what?

Answer 13

• the muscle function

Question 14

If a muscle has fine control and low force what size motor unit would it have?

Answer 14

• small motor unit

Question 15

If a muscle has less control and a large force what size motor unit would it have

Answer 15

• large motor units

Question 16

What can muscle force be controlled by?

Answer 16

• number of motor units recruited
• altering pattern of activity within a motor unit

Question 17

What is a neuromuscular junction?

Answer 17

• A specialised chemical synapse between motor neurone and muscle

Question 18

Synaptic vesicles contain what neurotransmitter? and what does it do?

Answer 18

• acetylcholine which enforces one-way messaging

Question 19

why is the sarcolemma folded at the neuromuscular junction

Answer 19

• to increase surface area

Question 20

How do we ensure that there is only one action potential per nerve?

Answer 20

• Acetylcholinesterase rapidly degrades Ach left in the cleft

Question 21

How can you detect muscle action potentials?

Answer 21

• electromyography can be used to detect electrical activity in muscles

Question 22

What is the function of T-tubules?

Answer 22

• T-tubules conduct an action potential deep into the muscle fibre
• T-tubules surrounded by sarcoplasmic reticulum

Question 23

What is the function of the sarcoplasmic reticulum?

Answer 23

• Store of calcium ions

Question 24

What are coupled receptors?

Answer 24

• voltage-sensitive proteins in the T-tubules which are linked to calcium channels in the sarcoplasmic reticulum

Question 25

What is the name for the calcium ion channels in the sarcoplasmic reticulum?

Answer 25

- Ryanodine receptors

Question 26

What causes Ryanodine receptors to open?

Answer 26

- when an action potential arrives at a ryanodine receptor, it causes a change in shape of the voltage sensor meaning that protein channels open and calcium ions move from the sarcoplasmic reticulum into the cytosol

Question 27

What happens after muscle control?

Answer 27

calcium ions in the cytosol are pumped back into the sarcoplasmic reticulum ( the pump required ATP). This stops contraction.

Question 28

Increasing the frequency of nerve impulses means what?

Answer 28

- contraction force doesn't have time to fully subside before a new action potential arrives - greater force can be developed - more stretching of elastic components in muscle

Question 29

If action potentials are frequent enough muscles will undergo what?

Answer 29

- tetanic contraction

Question 30

What is tetanic contraction?

Answer 30

- Sustained, constant high force - useful - normal contraction type for most skeletal muscles

Question 31

How does depolarisation of the postsynaptic membrane result in muscle contraction?

Answer 31

- The sarcolemma has thin, tube-like extensions into the cell (T-tubules), surrounding Z-discs of myofibrils * T-tubules conduct AP deep into muscle fibre * Sarcoplasmic reticulum expanded and well-developed near to T-tubules * AP travel in T-tubule stimulates Ca2+ release from SR