skeletal muscle as target for nervous system control

Question 1

What is the neuromuscular junction (NMJ)?

Answer 1

• A specialised synapse between a motor neuron and a skeletal muscle fibre. It is the site of transmission of AP from nerve to muscle.

Question 2

What are the post-synaptic events leading to the initiation of APs?

Answer 2

1. Arrival of AP at NMJ
2. Release of ACH
3. Binding of ACH to receptors
4. Depolarization
5. Activation of sodium voltage gated channels
6. Propagation of AP along sarcolemma

Question 3

What is the wave of excitation?

Answer 3

• Propagation of AP along the membrane of a. neuron/ muscle cell

Question 4

What is E-C coupling?

Answer 4

• Process by which electrical signal arrives at the contractile machinery for contraction.

Question 5

What are main steps of E-C coupling?

Answer 5

1. AP travels along sarcolemma
2. AP travels down the T-tubules
3. SR releases calcium via channels
4. Calcium ions bind to troponin
5. Tropomyosin exposes active myosin binding sites on the actin
6. Myosin binds to actin
7. ATP binds to myosin- providing energy

Question 6

What components are found in the SR?

Answer 6

• T-tubules
• Calcium pumps

Question 7

What is contractile machinery?

Answer 7

• Components within the muscle cells that are involved in muscle contraction

Question 8

What is the role of the myofibril with the SR and how does it relate to contraction?

Answer 8

• They are responsible for controlling muscle contraction are relaxation. There are different bands of densities along the length of the myofibril. Each band is known as a disc. Discs from Z-Z are known as the unit of sarcomere which is the smallest functional contractile unit.

Question 9

What is the cross bridge cycle?

Answer 9

describes interaction of myosin head group and actin.

Question 10

What are motor units?

Answer 10

movements are made and smoothed out by motor units. Large motor units can be recruited when lifting a piano e.g.

Question 11

How do you improve smoothness of motor actions?

Answer 11

Frequency coding, recruitment of motor units with larger cells.

Question 12

What are the steps of rigorous mortis (death)?

Answer 12

1. ATP stops
2. SR calcium pumps stop
3. Actin/ troponin complex is activated
4. No ATP is available for cross bridge detachment
5. Muscles stiffen
6. Only enzymatic breakdown of proteins can reverse this

Question 13

What are the factors of muscle ageing (sarcoponia)?

Answer 13

1. Myosin production
2. mitochondrial malfunction
3. Motor axon atrophy
4. Atrophy of muscle fibres

Question 14

Ipsilateral Vs contralateral

Answer 14

Ipsilateral= same side of body
Contralateral= opposite side of body

Question 15

What are the five components of the reflex arc?

Answer 15

1. Receptor
2. Sensory neuron
3. Integration centre
4. Motor neuron
5. Effector