Neuromuscular and spinal cord

Question 1

Synapses

Answer 1

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Question 2

The neuromuscular junction

Answer 2

-Specialised synapse between the motor neuron and the motor end plate on the muscle fibre cell membrane

Question 3

Activation of the neuromuscular junction

Answer 3

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Question 4

The alpha motor neuron

Answer 4

• lower motor neurons of the brainstem motor nuclei and the ventral horn of the spinal cord
• innervate the extrafusal muscle fibres of the skeletal muscles
• activation causes skeletal muscle contraction (voluntary)
• the motor neuron pool contains all alpha motor neurons innervating a single muscle

Question 5

The motor unit

Answer 5

• single motor neuron together with all the muscle fibres that it innervates (one motor neuron activity and multiple muscle fibres)
• smallest functional unit with which to produce force
• stimulation of one motor unit causes contraction of all muscle fibres in that unit
• humans have ~420,000 motor neurons and 250 million skeletal muscle fibres
• each motor neuron supplies ~600 muscle fibres on average

Question 6

Type I (types of motor unit, slow, S)

Answer 6

• smallest diameter cell bodies
• small dendritic trees
• thinnest axons
• slowest conduction velocity

Question 7

Type IIA (types of motor unit, fast, fatigue resistant, FR0

Answer 7

• larger diameter cell bodies than type I
• larger dendritic trees
• thicker axons
• faster conduction velocity

Question 8

Type IIB (types of motor unit, fast, fatiguable, FF)

Answer 8

• larger diameter cell bodies
• larger dendritic trees
• thicker axons
• faster conduction velocity

Question 9

Mechanisms by which the brain regulates muscle force produced by a single muscle

Answer 9

• Recruitment

- Rate coding

Question 10

Recruitment

Answer 10

• motor units are not randomly recruited, instead governed by the ‘size principle’)
• smaller units are recruited first (generally slow twitch units)
• as more force is required, more units are recruited
• allows fine control, under which low force levels are required

Question 11

Rate coding

Answer 11

• a motor unit can fire at a range of frequencies with slow units firing at a lower frequency
• as the firing rate increases, the force produced by the unit increases
• summation occurs when units fire at frequency too fast to allow muscle relaxation between arriving action potentials

Question 12

Neurotrophic factors

Answer 12

• type of growth factor
• prevent neuronal death
• promote growth of neurones after injury

Question 13

Reflex

Answer 13

• An automated and often inborn response to a stimulus that involves a nerve impulse passing inward from a receptor to a nerve centre and then outward to an effector (muscle or gland) without reaching the level of the consciousness
• no higher control of action in reflexes so perform action unconsciously

Question 14

The effect of neurotrophic factors

Answer 14

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Question 15

The reflex arc

Answer 15

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Question 16

The monosynaptic reflex

Answer 16

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Question 17

The Hoffman reflex

Answer 17

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Question 18

Polysynaptic reflexes

Answer 18

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Question 19

Supraspinal control of reflexes

Answer 19

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Question 20

Hyper-reflexia

Answer 20

-overactive or over-responsive reflexes

Question 21

Hypo-reflexia

Answer 21

• below normal or absent reflexes

- mostly associated with lower motor neuron lesions

Question 22

Transmission across synapses

Answer 22

• input alters membrane potential of the post synaptic neuron in one of two directions
• membrane potential can be made less negative (ie: brought closer to threshold for firing)->excitatory post synaptic potential
• membrane potential can be made more negative (ie: brought further away from threshold for firing)->inhibitory post synaptic potentials

Question 23

Babinksi sign (hyper-reflexia)

Answer 23

• tests for upper motor neuron dysfunction
• stimulus applied on lateral aspect of foot and along the balls of the toes
• if dysfunction is present, the big toe flexes and the smaller toes fan out