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Anatomy & Physiology > Motor Nervous System > Flashcards

Motor Nervous System Flashcards

1
Q

What are the different types of muscle in the motor NS?

A 
Smooth muscle
Cardiac muscle (Striated)
Skeletal muscle (Striated)
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2
Q

Describe cardiac muscle?

A
  • Striated
  • Small
  • Branched cells
  • Central nucleus (1-5)
  • Contains INTERCALATED DISCS that allow myocytes, in the cardiac muscle, to be connected to one another
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3
Q

Where is the location of the cardiac muscle?

A

Heart

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4
Q

Describe the innervation of the cardiac muscle?

A

Innervated by AUTONOMIC nerves that alter the rate of contraction of the myocytes.
The myocytes contract due to the self-contractile pacemaker cells.

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5
Q

What is the function of the cardiac muscle?

A

1) Circulation of the blood

2) Maintains the blood pressure

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6
Q

Describe the smooth muscle?

A
  • Non-striated
  • Small
  • Spindle shaped cells with tapered end
  • Only 1 centrally located nucleus
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7
Q

Where is smooth muscle located?

A

The walls of:

1) Blood vessels
2) Respiratory tract
3) Cardiovascular tract
4) Digestive tract
5) Reproductive tract
6) Hollow bones

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8
Q

Describe the innervation of the cardiac muscle?

A

1) The smooth muscle in the digestive tract walls is self-contractile
2) Anywhere else is innervated by autonomic nerve fibres for the contraction of smooth muscle

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9
Q

What is the function of smooth muscle?

A

1) Movements of food
2) Controls the diameter of airways and blood vessels
3) Reproductive tract secretions.

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10
Q

Describe the skeletal muscle?

A
  • Striated
  • Very long
  • Multi-nucleated (100’s) - that are located near the plasma membrane
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11
Q

Where is skeletal muscle located?

A

Associated with bones and connective tissue (throughout the body)

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12
Q

Describe the innervation of skeletal muscle?

A

Innervated with SOMATIC nerve fibres

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13
Q

What are the 6 functions of skeletal muscle?

A

1) Movement
2) Stabilisation of the skeleton
3) Makes Sphincters (guard entry and exit of substances)
4) Protects internal organs
5) Nutrient reserve
6) Generates heat

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14
Q

What are the 2 ends of a skeletal muscle called?

A

1) Origin (Fixed-end of the skeletal muscle attached to the bone via a tendon)
2) Insertion (Moveable end of the skeletal muscle attached to the bone via a tendon)

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15
Q

What are the 4 types of skeletal muscle?

A

1) Synergist muscle
2) Antagonist muscle
3) Prime move (agonist muscle)
4) Fixator

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16
Q

What is the synergist muscle?

A

Skeletal muscles that work together or move in the same direction

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17
Q

What are antagonist muscles?

A

Skeletal muscles that move in the opposite direction to the prime mover

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18
Q

What is the prime mover?

A

(agonist) The skeletal muscle that is the MAIN muscle that is moving in order for the body to carry out a particular movement.

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19
Q

What is the fixator muscle?

A

The skeletal muscles that stabilises the origin of the prime mover. In order for a particular movement to be carried out.

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20
Q

Give 2 examples of skeletal muscle pairs (prime mover and antagonist) =

A 
Biceps = flexes the the forearm (prime mover)
Triceps = extends the forearm (antagonist)
Hamstrings = flexes the leg (prime mover)
Quadriceps = extend the leg (antagonist)
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21
Q

Describe the arrangement of the muscle?

A

1) Muscle
2) Many fasicles
3) Fasicle
4) Many muscle fibers
5) Muscle fiber (muscle cell)
6) Many myofibril
7) Myofibril
8) Many myofilaments (actin and myosin)

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22
Q

What are the 3 tissues (mysiums) in the muscle arrangement?

A

1) Endomysium
2) Perimysium
3) Endomysium

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23
Q

Where is the location of the endomysium?

A

Surrounds the entire muscle. Inside the endomysium are all the fasicles.

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24
Q

Where is the location of the perimysium?

A

Surrounds all the fasicles in the muscle

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25
Q

Where is the location of the endomysium?

A

Contained within the fasicles and surrounds the myofibrils inside the fasicle.

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26
Q

What is the motor unit?

A

Basic unit of contraction

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27
Q

What does the motor unit consist of?

A

1) Motor nerve fibre
2) Its cell body in the anterior grey column of the spinal cord
3) Its axon will branch off to form the motor end plates
4) 1 motor end plat per 1 myofibril
5) The myofibril and motor end plate = neuromuscular junction

28
Q

How does the amount of muscle fibers per motor unit differ between extraocular and limb muscles?

A

Extraocular muscles: (for fine control) Few muscle fibres per motor unit

Limb muscles: (for coarse control) Many muscle fibres per motor unit

29
Q

What are the different types of skeletal muscle fibers?

A

1) Type 1
2) Type 2
3) Type 3

30
Q

What 4 properties cause these skeletal muscle fibers to differ?

A

1) Metabolism
2) Endurance
3) Contractile properties
4) Force generated by the muscle fibres

31
Q

Describe 4 properties of Type 1 skeletal muscle fibre?

A

1) Metabolism = aerobic
2) Endurance = high
3) Contractile properties = slow myosin/slow contraction
4) Force generated by the muscle fibres = low

32
Q

Describe 4 properties of Type 2a skeletal muscle fibre?

A

1) Metabolism = mixed
2) Endurance = medium
3) Contractile properties = fast myosin/fast contraction
4) Force generated by the muscle fibres = medium

33
Q

Describe 4 properties of Type 2b skeletal muscle fibre?

A

1) Metabolism = anaerobic
2) Endurance = low
3) Contractile properties = fast myosin/fast contraction
4) Force generated by the muscle fibres = high

34
Q

Which type of skeletal muscle fibers are best for sprint and which type is best for marathon?

A

Sprint - Type 2b

Marathon - Type 1

35
Q

How are the types of skeletal muscle fibres given these different properties?

A

Each skeletal muscle fibre type will only ever be innervated by 1 particular motor nerve fibre.
(1 motor nerve fibre per 1 skeletal muscle fibre)

36
Q

What special thing happens to a particular motor nerve fibre that innervates a particular type of skeletal muscle fibre (if a neuropathy has occurred)?

A

Another motor nerve fibre will extend branches onto the type of skeletal muscle fibre that the neuropathy motor nerve fibre was once supplying.
This skeletal muscle fibre will now have he properties that the motor nerve fibre causes rather than their previous properties.

37
Q

Definition of myopathy

A

A disease in the MUSCLE FIBRE which causes the muscle fibre’s characteristics to change. It is caused by congenital or acquired

38
Q

Give a example of a myopathy?

A

MUSCULAR DYSTROPHY

39
Q

What is muscular dystrophy associated with?

A

It is associated with the ‘X’ chromosome and affects ONLY BOYS.

40
Q

What is the problem in muscular dystrophy?

A

The skeletal muscle fibres degenerate.

41
Q

What causes the skeletal muscle fibres to degenerate in muscular dystrophy?

A

1) The gene that codes for DYSTROPHIN is missing.
2) Dystrophin normally anchors the actin myofilaments
3) Without the actin filaments being anchored, when the myosin heads attach and slide past the actin - friction will occur.
4) The muscle fibres degenerate

42
Q

When are boys affected by muscular dystrophy?

A

In the first few years of life - normal functioning of the muscle fibres
In adolescents - can’t walk

43
Q

How can the force of contraction be altered in a motor unit?

A

By altering the frequency of action potentials that occur down the motor nerve fibres supplying the muscle fibre.
High frequency - the muscle has TETANIC contractions (has no time to relax)
Low frequency - the muscle has time to relax and therefore causing muscle twitching.

44
Q

Inputs and outputs to/from the motor nerve fibre:

A

Inputs: Descending paths from the brain, sensory inputs from the spinal cord, inter-neurones in the spinal cord
Outputs: Neuro-muscular junction

45
Q

What are muscle spindles?

A

Sensory STRETCH receptors in muscles that detect a change in muscle LENGTH

46
Q

How is the role of muscle spindles related to stretch related to the contraction of the muscle?

A

1) When a muscle stretches (due to a weight pulling on it) the spindle inside the muscle stretches too.
2) This stimulates the MECHANO-SENSITIVE RECEPTORS to fire an action potential.
3) This causes the muscle to CONTRACT - so that less damage is down to the muscle due to it being stretched..

47
Q

Name 2 examples of reflexes:

A

1) Tendon Jerk Reflex

2) Normal withdrawal (flexor) Reflex

48
Q

Describe the neurone pathway for the tendon jerk reflex?

A

1) Spindles detect the muscle has been stretch (with the reflex hammer).
2) The afferent sensory (myelinated) neurone sends information to the spinal cord (in the lumbar region)
3) One synapse
4) Lower motor efferent (myelinated) neurones send information to the muscle fibre
5) Contraction of the muscle fibre - knew jerk

49
Q

What occurs during the natural withdrawal (flexor) reflex that is essential to cause the prime mover muscle to flex?

A

RECIPROCAL INHIBITION

50
Q

What is the importance of reciprocal inhibition?

A

It causes the antagonist muscle to relax so that the prime mover muscle (agonist - the one that flexes) to contract - in order to carry out the reflex.

51
Q

How does reciprocal inhibition occur?

A

1) Inhibitory interneurones (in the spinal cord) inhibit alpha motor neurones.
2) These alpha motor neurones are connected to the antagonist muscle.
3) If they have been inhibited, they won’t be able to cause the antagonist muscle to contract (therefore it can only relax).
4) This allows the prime mover (agonist) to contract, in order to flex and cause the reflex.

52
Q

What type of reflex is important during the normal withdrawal (flexor) reflex (e.g. when one leg steps on a pin):

A

Crossed-extensor reflex

53
Q

What occurs during the crossed-extensor reflex and why is it important?

A

1) The extend neurone innervating the extensor muscle (the limb that hasn’t stepped on the pin - the opposite limb) is activated, by an interneurone, in order to extend.
2) And the flex neurone innervating the extensor muscle is inhibited.
This importance of this is so the opposite limb can support the extra load as the other limp has flexed.

54
Q

What 4 parts of the CNS are involved in planning, initiating and regulating skeletal muscle movements:

A

1) Motor areas of the cerebral cortex
2) Basal Ganglia (acts as a relay neurone - to control muscle tone in order to control co-ordinated and slow muscle movements)
3) Cerebellum (involuntary controls voluntary skeletal muscle for balance and posture)
4) Spinal cord nerves (reflexes)

55
Q

What are the 2 efferent pathways coming from the brain, travel in the spinal cord and control skeletal muscle movements?

A

1) Lateral pathway

2) Ventromedial pathway

56
Q

Where do the efferent neurones travelling in the lateral pathway of the SC come from?

A

Motor area of the cerebral cortex

57
Q

Where do the efferent neurones travelling in the ventromedial pathway of the SC come from?

A

The cerebellum

58
Q

Where are the pre-synaptic terminals located?

A

At the end of axon branches extending from the motor nerve fibre (in the neuro-muscular junction).

59
Q

Where are the synaptic vesicles located in the pre-synaptic terminals?

A

In the active zones (above the junctional folds)

60
Q

Which neurotransmitter is released from the vesicles in the pre-synaptic terminal, at the neuro-muscular junction, in order to initiate the muscle contraction?

A

acetylcholine

61
Q

Where are the acetylcholine receptors found in the neuromuscular junction?

A

In the junctional folds

62
Q

What does ‘EXCITATION-CONTRACTION COUPLING’ mean?

A

The coupling of the release of acetylcholine and the contraction of the muscle.

63
Q

What happens during excitation-coupling contraction?

A

1) Acetylcholine is released from the pre-synaptic terminal.
2) Acetylcholine binds to the acetylcholine receptors in the junctional fold.
3) Sodium influx in the muscle cell.
4) Threshold is reached.
5) Voltage-gated sodium channels open - action potenial occurs.
6) This action potential causes voltage-gated calcium channels to open in the T-tubules. Calcium influx from extracellular fluid.
7) This causes the sarcoplasmic reticulum to release calcium.
8) High intracellular calcium causes muscle contraction

64
Q

What are the 4 things which allow the excitation-contraction coupling to occur almost simultaneously?

A

1) Sarcolemma (cell membrane of the muscle cell) that contains holes - that make up the T-tubules (extracellular is connected with intracellular)
2) Sarcoplasmic reticulum (surrounds the myofibrils) - store calcium
3) The calcium channels in the T-tubules are continuous with the calcium channels in the sacroplasmic reticulum
4) When an action potential is stimulated in the muscle cell - calcium is influxed from many sources (T-tubules and sarcoplasmic reticulum).

65
Q

What is special about acetylcholinesterase that breaks down acetylcholine?

A

It has the fastest catalytic rate known enzyme

66
Q

What 2 things are essential for the sliding filament theory to occur?

A

1) ATP

2) Calcium

67
Q

What are the stages of the sliding filament theory?

A

1) At rest - troponin proteins cover the binding sites on the actin filaments.
2) When an action potential occurs in the muscle cell, calcium (from the extracellular fluid through the T-tubule calcium channales and sarcoplasmic reticulum) bind to the troponin molecules.
3) Calcium causes the troponin molecules to expose the binding sites.
4) Myosin heads bind to the actin bind sites to form a cross-bridge
5) The myosin head pivot and the myosin filament moves upwards (requires ATP).
6) The myosin heads will detach from the actin binding sites (when calcium is no longer present - as the action potential in the muscle cell has stopped) - this requires ATP.

Anatomy & Physiology (16 decks)

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