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PMP 101 - Health, Disease And The Patient > Nervous System: Divisions, Function + Muscle Contraction (w4) > Flashcards

Nervous System: Divisions, Function + Muscle Contraction (w4) Flashcards

1
Q

What does the somatic nervous system control ?

A

It controls the movement of skeletal muscles.

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2
Q

What two divisions are in the autonomic nervous system ?

A
  • parasympathetic division
    -sympathetic division
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3
Q

What are the two control centres is the brain (cortex) ?

A
  • Somatosensory cortex
  • Motor cortex
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4
Q

What do ascending tracts do ?

A

They relay information from the spinal cord to the sensory cortex.

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5
Q

What do descending tracts do ?

A

They relay information from the motor cortex to the spinal cord.

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6
Q

What are sensory neurones, and what do they do ?

A

They are myelinated neurones which relay information to the spinal cord and the brain.
They sense touch, stretch and pain.

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7
Q

What are motor neurones and what do they do ?

A

They are multipolar and myelinated neurones which relay nerve impulses from the spine to trigger contraction of the skeletal muscle.

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8
Q

What is a unipolar neurone ?

A

A neurone which has a cell body at dorsal root ganglion.
For example; Sensory neurone

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9
Q

What makes up a neuromuscular junction (NMJ) ?

A

A synapse somatic motor neurone and a muscle fibre.

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10
Q

What neurotransmitter is at the skeletal muscle neuromuscular junctions ?

A

Acetylcholine

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11
Q

What is the motor end plate (MEP) and what do you find here ?

A

The MEP is the post synaptic membrane and you find the chollinergic receptors.

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12
Q

Describe the function of skeletal (striated) muscle and how it is connected to bones ?

A
  • It enables the movement of limbs and other parts of the skeleton and is connected to bone via tendons (origin) or via tendons (insertion).
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13
Q

Describe the function of cardiac (striated) muscle ?

A

Cardiac muscle is the pump in the circulation system (heart). It has intrinsic pacemaker activity and is myotonic.

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14
Q

Where is smooth muscle found ?

A

Around many hollow internal organs.

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15
Q

What is the cytoplasm of a muscle fibre called ?

A

Sarcoplasm

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16
Q

List the 4 key proteins involved in contraction;

A
  • Myosin
  • Actin
  • Troponin
  • Tropomyosin
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17
Q

What makes up a single thick filament ?

A

Many myosin molecules

18
Q

Which is the thick filament and which is the thin filament ?

A

Thick filament = myosin
Think filament = actin

19
Q

What is the A band ?

A

The length of the myosin filament.

20
Q

Describe the 4 main steps to the cross bridge cycle;

A

1) ATP binds to Myosin causing it to release the actin.
2) Myosin the hydrolyses ATP. This energy released from the ATP rotates the myosin head to the cocked position where it weakly binds to the actin.
3) The power stroke then begins when the tropomyosin moves off the binding site.
4) Myosin then releases ADP at the end of the power stroke.
-ADP released = the myosin head is tightly bound to the actin (rigor state) the cycle is ready to begin once more as a new ATP molecule binds to myosin.

21
Q

What does it mean when tight binding is in rigor state ?

A

It’s when there is tight binding between the myosin head and the actin.

22
Q

What does an action potential trigger the release of ?

A

Calcium ions

23
Q

What are the 4 main events which occur at the neuromuscular junction ?

A

1) resting state
2) AP ( action potential ) arrival - cause release of Ach and depolarisation of pre-synapse.
3) Depolarisation of MEP -wave of depolarisation passes down the fibre causing the pre-synapse to re-polarised.
4) Contraction of muscle - MEP repolarises and muscle fibre depolarises (contraction)

Muscle fibre then repolarises and process repeats.

24
Q

Which portion of the nervous system is considered involuntary ?

A

Autonomic nervous system

25
Q

What are the two binding sites of the myosin head ?

A

-actin
-ATP

26
Q

Where do the calcium ions bind to ?

A

They bind to the troponin and shift the position of the tropomyosin.

27
Q

Where is the neurotransmitter acetylcholine formed ?

A

In the synaptic terminal

28
Q

What is the activity at the neuromuscular junction described as ?

A

Acetylcholinergic

29
Q

Describe the process of ACh at the neuromuscular junction …

A
  • ACh is formed in the synaptic terminal.
  • It is generated by ChAT.
  • It is then packaged into vesicles.
  • Calcium entry causes fusion of the synaptic vesicles.
  • ACh is then released into the synaptic cleft.
  • Some of it binds to the nicotinic ACh receptors.
  • the rest is broken down by Ach - esterase.
  • choline molecules are then taken up.
30
Q

How does Botox inhibit vesicular fusion ?

A

It alters proteins required for vesicular fusion with the presynaptic membrane.

31
Q

What are the medical uses of Botox ?

A

-Severe muscular spasms - Blepharospasm
-Children with cerebral palsy, motor neuron disease
-Speech deficits following throat cancer

Botulinum toxicity still occurs from preserved foods – bacterial exotoxin
How many poisons work eg snake venom - bungarotoxin

32
Q

What is a motor unit ?

A

A motor unit is 1 motor neurone and its muscle fibres.

33
Q

What is recruitment of force dependant on ?

A

The number of active muscle fibres, muscles are made up of many motor units.

34
Q

What does gradation of force depend on ?

A

The recruitment of motor units.

35
Q

What is the all or nothing principle ?

A

The skeletal muscle fibre/motor unit either operates or it does not.

36
Q

Describe threshold in relation to creating a response …

A

If the threshold stimulus for a nerve is reaches and the threshold for muscle contraction is reached, the muscle fibre will contract, otherwise it will not.

37
Q

Describe recruitment in terms of muscle contraction …

A

The greater the force of contraction needed, the more motor units are required, each motor unit operated in the all or nothing principle.

38
Q

Why is a steady supply of ATP needed for skeletal ,suckle contraction ?

A
  • contraction (cross bridge forming and release)
  • relaxation (pump Ca2+)
  • Restoring of Na+ and K+ levels after action potential occurs.
39
Q

List the sources of ATP in skeletal muscle contraction ?

A
  • Phosphocreatine - A source of ATP
  • Carbohydrates ( aerobic metabolism - producing 30 ATP per glucose molecule) ( anaerobic glycolysis - glucose metabolised to lactate/lactic acid with a yield of only 2 ATP per glucose)
40
Q

List some similarities of smooth muscle and skeletal muscle …

A
  • Both have actin - myosin cross bridges with sliding filaments.
  • Both have muscle contraction (cross bridge movements) initiated by an increase in free cytosolic Ca2+.
41
Q

List some differences of smooth muscle and skeletal muscle …

A
  • layers of smooth muscle may run in several directions.
  • smooth muscle contracts and relaxes much more slowly.
  • smooth muscle needs less energy to generate the same amount of force.
  • smooth muscle is controlled by the autonomic nervous system.
  • in smooth muscles, there is no troponin in the actin filaments, instead it uses calmodulin.
  • in skeletal muscle the target for calcium is actin whereas in smooth muscle the target for calcium is myosin.
42
Q

Describe smooth muscle contraction …

A

-External Ca2+ ions enters cell (opened calcium channels in the sarcolemma released from SR)
-Bind to calmodulin
-Ca2+ / calmodulin complex then activates an enzyme called myosin (light chain) kinase (MLCK)
-MLCK in turn, activates the myosin heads by phosphorylating them (converting ATP to ADP and Pi, with the Pi attaching to the head)
-The heads can then attach to actin-binding sites and pull on the thin filaments. Causes fibre to contract
-Muscle contraction continues until ATP-dependent calcium pumps actively transport Ca2+ out of the cell.
(Low concentration of calcium remains to maintain muscle tone.-Important around blood vessels.)

PMP 101 - Health, Disease And The Patient (35 decks)

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