NEURO: MOTOR CONTROL Flashcards Preview

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Flashcards in NEURO: MOTOR CONTROL Deck (44)
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1

how is a skeletal muscle attached to bone?

by tendons

2

what is a skeletal muscle comprised of?

several fasciculi
fasciculi are comprised of several muscle fibres which are made of myofibrils - contain actin and myosin

3

what is a motor unit?

an alpha motor neuron and all the extrafusal skeletal muscle fibres it innervates

4

where are the muscle fibres in a single motor unit located?

they are all in the same muscle - may be spread out

5

what is the relationship between the number of muscle fibres and variation of movement?

less muscle fibres = greater variation of movement
eg fingertips

6

what is the effect of more motor neurons firing?

more power is produced

7

what do more laterally located alpha motor neurons control?

more distal muscles

8

what do more medially located alpha motor neurons control?

more proximal muscles

9

what is muscle tone?

the degree of contraction of a muscle or proportion of motor units that are active at any one time

10

what does high muscle tone feel like?

firm or rigid
it resists passive stretch

11

what does low muscle tone feel like?

soft or flaccid
it offers little resistance to passive stretch

12

how does alpha motor neurons contribute to resistance to muscle stretch when relaxed?

it does not make a significant contribution

13

how does alpha motor neurons contribute to resistance to muscle stretch when alert?

there is more activation of alpha motor neurons occur and muscle tone increases

14

what is the motor end plate?

the region of the muscle fibre plasma membranes directly under the axon terminal

15

what is the neuromuscular junction?

it is the junction of an axon terminal with the motor end plate

16

what is an end plate potential (EPP)?

it is comparable to EPSPs but is larger than a single EPSP
occurs at neuromuscular junctions

17

what is an end plate potential in comparison to an EPSP?

a single EPP is larger than a single EPSP as the neurotransmitter is released over a larger surface area- therefore more ion channels open

18

how are action potentials propagated at a neuromuscular junction?

the action potential is propagated over the surface of the muscle fibre and into the T-tubules to spread throughout the muscle
the neuromuscular junction is typically located in the middle of a muscle fibre so action potentials are propagated in both directions

19

what happens at a neuromuscular junction?

1. action potential in motor neuron arrives at the axon terminal and depolarises into axon terminal
2. voltage gated Ca2+ channels open and Ca2+ diffuse into axon terminal
3. Ca2+ binds to proteins that allow ACh vesicles to fuse with neuronal plasma membrane
4. ACh diffuses to motor end plate and binds to cholinergic nicotinic receptors
5. this opens ion channel in receptor protein resulting in more Na+ moving in than K+ moving out - an EPP is produced

20

are neuromuscular junctions excitatory or inhibitory?

they are all excitatory only

21

which neurotransmitter is present in neuromuscular junctions?

acetylcholine

22

what are upper motor neurons?

they are neurons whose cell boy originates in the cerebral cortex or brainstem and terminates within the brainstem or spinal cord
they exert their effects via lower motor neurons

23

which neurotransmitter is typically involved in upper motor neurons?

glutamate

24

what happens if there is damage to an upper motor neuron?

it causes weakness or paralysis of movement for the group of muscles it innervates

25

what are the signs of upper motor neuron damage?

- hypertonia - high muscle tone
- hyperreflexia - brisk reflexes
- spasticity - muscle is tight
- positive babinski sign
- clonus - muscle suddenly stretched and stays there

26

what is the positive babinski sin?

the large toe extends (instead of flexes) in response to a blunt object stroked on the plantar surface

27

what is a common cause of upper motor neuron damage?

a stroke - when it affects the cerebral cortex of internal capsule

28

what are lower motor neurons?

multipolar neurons which connect with upper motor neurons and the skeletal muscle it innervates
the cell body lies within the ventral horn of the spinal cord or the brainstem motor nuclei

29

how many muscle fibres can be innervated by one lower motor neurm?

one lower motor neuron can innervate several muscle fibres but a single muscle fibre is innervated by only on LMN

30

where are alpha motor neurons found?

the cell bodies originate in laminae VIII and IX of the ventral horn - they are somatotopically organised