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Biomedicine (Semester II) > 13. Nervous System I > Flashcards

13. Nervous System I Flashcards

1
Q

Nervous System: definition

A

Network of fibres throughout the body that co-ordinate a diverse range of voluntary and involuntary actions

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2
Q

How does the nervous system co-ordinate actions?

A

By transmitting signals between parts of the body

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3
Q

How does the nervous system maintain homeostasis?

A

Works with the endocrine system

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4
Q

Divisions of the nervous system

A
  1. Central Nervous System (CNS)

2. Peripheral Nervous System (PNS)

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5
Q

Which areas of the body are covered by the central nervous system (CNS)?

A

Brain

Spinal cord

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6
Q

Which areas of the body are covered by the peripheral nervous system (PNS)?

A

Peripheral nerves (any that aren’t in the CNS)

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7
Q

What are the functions of the nervous system?

A
  1. Sensory
  2. Integration
  3. Motor
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8
Q

Describe the sensory function of the nervous system

A

Detects internal and external environmental changes through proprioception, sensation or touch

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9
Q

Which neurons carry out the sensory function?

A

Sensory neurons

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10
Q

Describe the integration function of the nervous system

A

Processes sensory information by analysing, storing and making decisions

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11
Q

Where is the integration function mainly carried out?

A

In the brain

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12
Q

Which neurons carry out the integration function?

A

Interneurons

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13
Q

Describe the motor function of the nervous system

A

Produces a response to sensory information to effect change

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14
Q

Which neurons carry out the motor function?

A

Motor neurons

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15
Q

What are the subdivisions within the peripheral nervous system?

A
  1. Somatic nervous system

2. Autonomic nervous system

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16
Q

What does the spinal cord do?

A

Connects the brain and peripheral nervous system

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17
Q

What does the peripheral nervous system do?

A

Carries messages to and from the CNS

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18
Q

What does the somatic nervous system do?

A

Controls voluntary muscles (skeletal)

Transmits sensory information to the CNS

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19
Q

What does the autonomic nervous system do?

A

Controls involuntary body functions

Works automatically to maintain homeostasis

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20
Q

What are the subdivisions within the autonomic nervous system?

A
  1. Sympathetic nervous system

2. Parasympathetic nervous system

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21
Q

What does the hypothalamus do?

A

It’s the control centre over autonomic motor neurons in organs, glands, cardiac and smooth muscles

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22
Q

Regions covered by the sympathetic nervous system

A

Thoraco-lumbar

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23
Q

Regions covered by the parasympathetic nervous system

A

Cranio-sacral

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24
Q

What happens to the pupils in the ANS?

A

SNS: dilation
PNS: constriction

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25
Q

What happens to the lungs in the ANS?

A

SNS: bronchodilation
PNS: bronchoconstriction

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26
Q

What happens to the heart in the ANS?

A

SNS: HR and blood pressure increases
PNS: HR and blood pressure decreases

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27
Q

What happens in the GIT in the ANS?

A

SNS: decreased motility and secretions
PNS: increased motility and secretions

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28
Q

What happens in the liver in the ANS?

A

SNS: conversion of glycogen to glucose
PNS: glycogen synthesis

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29
Q

What happens with the adrenal glands in the ANS?

A

SNS: releases adrenaline
PNS: nothing

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30
Q

What is the enteric nervous system?

A

Brain of the GIT

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31
Q

How many neurons does the GIT contain?

A

Around 100 million

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32
Q

What regulates the enteric nervous system?

A

Autonomic nervous system

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33
Q

What do sensory neurons do in the enteric nervous system?

A

Monitor chemical changes in the GIT (via chemo-receptors) and stretching of its walls

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34
Q

What do motor neurons do in the enteric nervous system?

A

Govern motility and secretions of the GIT and associated glands

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35
Q

What do interneurons do in the enteric nervous system?

A

Connect the myenteric and submucosal plexuses

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36
Q

What are the cells that make up nervous tissue?

A
  1. Neurons

2. Neuroglia (glial cells)

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37
Q

What do neurons do?

A

Process and transmit information

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38
Q

What qualities do neurons have?

A

They’re electrically excitable

Ability to create a nerve impulse/action potential

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39
Q

What do glial cells do?

A

Surround neurons and hold them in place
Supply neurons with nutrients and oxygen
Destroy pathogens and remove dead neurons

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40
Q

How many types of glial cells are there? And where can they be found?

A

4x in CNS

2x in PNS

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41
Q

What percentage of brain volume is made up of glial cells?

A

90%

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42
Q

What is a nerve?

A

A bundle of one or more neurons

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43
Q

What is a stimulus?

A

Anything that can create an action potential

Can be internal or external

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44
Q

Components of a neuron

A
  1. Cell body
  2. Dendrites
  3. Axon
  4. Myelin sheath
  5. Nodes of Ranvier
  6. Terminal endings
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45
Q

What is the cell body of a neuron?

A

Nucleus

Organelles

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46
Q

What is grey matter?

A

Mostly cell bodies
Dendrites
Unmyelinated axons

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47
Q

What is white matter?

A

Mostly myelinated axons

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48
Q

What are nuclei?

A

Clusters of cell bodies in the CNS

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49
Q

What are ganglia?

A

Clusters of cell bodies in the PNS

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50
Q

What are dendrites?

A

The receiving portion of the cell

They communicate with other dendrites

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51
Q

What is an axon?

A

Long, cylindrical projections that carry nerve impulses away from the cell body towards another neuron

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52
Q

How long are axons?

A 
<1mm in CNS up to...
Approx 1m (sciatic nerve)
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53
Q

What is the axolemma?

A

Membrane covering the axon

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54
Q

What is the axon terminal?

A

The end of an axon

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55
Q

What are tracts?

A

Bundles of axons in the CNS

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56
Q

What are nerves?

A

Bundles of axons in the PNS

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57
Q

Can axons regenerate if injured?

A

Yes, at a rate of 1-2mm per day

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58
Q

What is the myelin sheath?

A

A multi-layered lipid and protein covering around the axons

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59
Q

What does the myelin sheath do?

A

Electrically insulates the axon
Increases the speed of nerve conduction
Participates in axon regeneration

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60
Q

How and when is the myelin sheath formed?

A

Formed by glial cells in the embryo
Continue through childhood
Peak in adolescence

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61
Q

What are nodes of Ranvier?

A

Gaps in the myelin sheath

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62
Q

What is needed for the production of myelin?

A

Vit B12

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63
Q

What qualities do glial cells have?

A

Non-excitatory
Smaller than neurons but 50x more prevalent
Can multiply and divide

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64
Q

What do glial cells do after a trauma?

A

Fill spaces left by damaged neurons

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65
Q

What are the glial cells found in the CNS?

A

Astrocytes
Oligodendrocytes
Microglia
Ependymal cells

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66
Q

What are astrocytes?

A

Star-shaped and most numerous/largest glial cells in CNS
Hold neurons to their blood supply
Contribute to blood-brain barrier

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67
Q

What are oligodendrocytes?

A

Glial cells that myelinate axons in the CNS

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68
Q

What are microglia?

A

Phagocytic immune cells in brain
Multiply with damage
Derived from monocytes

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69
Q

What are ependymal cells?

A

Epithelial cells which line the walls of the four ventricles of the cerebrum and central canal of the spinal cord

Produce cerebrospinal fluid (CSF)
Beat their cilia to circulate CSF

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70
Q

What are the glial cells found in the PNS?

A

Schwann cells

Satellite cells

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71
Q

What are Schwann cells?

A

Glial cells that produce myelin around the axons of neurons in the PNS

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72
Q

When are most myelination and dendrite connections completed by?

A

Age of 3

73
Q

What can malnutrition in infancy cause?

A

Irreversible nerve damage

74
Q

What are satellite cells?

A

Provide structural support to cell bodies in the PNS

Exchange substances

75
Q

What are the two types of electrical signal in a neuron?

A
  1. Graded potential

2. Action potential

76
Q

Describe graded potential

A 
Short distance communication
Occurs in the dendrites and cell body
Amplitude proportional to strength of stimulus
No threshold
Longer duration
77
Q

Describe action potential

A 
Long distance communication
Occurs along axon
All or nothing
Has threshold
Shorter duration
78
Q

How are graded and action potentials facilitated?

A
  1. Specific ion channels open and close when stimulated

2. Electrical difference across the cell membrane (resting potential)

79
Q

What are ion channels?

A

Transport channels for ions

Created by transmembrane proteins within the neuron membranes

80
Q

How do ion channels work?

A

When they open, they allow specific ions to move through the membrane across a concentration gradient e.g. Na+ channels let Na+ ion through

81
Q

When do ion channels open?

A

In response to a stimulus

82
Q

What stimuli can cause an ion channel to open?

A

Changes in:

  1. Voltage
  2. Chemicals (hormones)
  3. Mechanical pressure
83
Q

What is resting potential?

A

Electrical difference between the interior and exterior of the cell membrane

84
Q

How many millivolts is resting potential?

A

Approx. 70mV

85
Q

What makes up the interior of a cell during resting potential?

A

Interior = negative ions build up

K+ and large negatively-charged proteins and phosphates that can’t leave the cell

86
Q

What makes up the exterior of a cell during resting potential?

A

Exterior = positive ions build up

Na+ and Cl-

87
Q

What does the sodium-potassium pump do?

A

Pumps 3x Na+ out for every 2x K+ it pumps back in

During refractory period after repolarisation

88
Q

What makes the sodium-potassium pump work?

A

ATP

89
Q

What is an action potential?

A

The formation of a nerve impulse down the axon

90
Q

What are the two stages of an action potential?

A
  1. Depolarisation

2. Repolarisation

91
Q

What is depolarisation?

A

The negative membrane potential (-70mV) reverses and becomes positive, reaching +30mV

92
Q

What is repolarisation?

A

When the cell membrane is restored to -70mV

93
Q

What is depolarisation triggered by?

A

Stimulation to a nerve ending

94
Q

What happens during depolarisation?

A
  1. Nerve ending is stimulated
  2. Na+ channels open allowing Na+ to flood INTO the cell up to about +30mV
  3. A positive charge builds up inside the cell
95
Q

What is the threshold value that depolarisation must meet in order to generate an action potential?

A

-55mV

96
Q

What happens during repolarisation?

A
  1. K+ channels open much more slowly, so just as the Na+ channels are closing, the K+ channels open
  2. This allows K+ to flood OUT of the cell, restoring the membrane potential to -70mV
97
Q

What is the refractory period?

A

Period after repolarisation in which a nerve can’t generate another action potential as Na+ and K+ are on the wrong sides of the membrane

98
Q

What happens during the refractory period?

A

Sodium-potassium pump pumps 3x Na+ back out and 2x K+ back into the cell to restore resting potential

99
Q

What is the absolute refractory period?

A

Where even a strong impulse can’t generate an action potential

100
Q

What is the relative refractory period?

A

Where a larger than normal stimulus is needed to generate an action potential

101
Q

What is conduction?

A

The movement of a nerve impulse along the axon of a neuron

102
Q

What is an unmyelinated axon?

A

Where there’s no sheath around the nerve

103
Q

How does depolarisation work in an unmyelinated axon?

A

Continuous, step by step conduction away from the cell body down the axon

104
Q

What is myelin?

A

An insulator

Prevents ionic currents crossing the cell membrane

105
Q

How does depolarisation work in a myelinated axon?

A

High concentration of Na+ gates in the nodes of Ranvier (unmyelinated)
These cause the currents to appear to jump from node to node - saltatory conduction

106
Q

Describe continuous conduction

A
  1. Unmyelinated
  2. Step by step depolarisation
  3. Slower
  4. Less energy efficient
107
Q

Describe saltatory conduction

A
  1. Myelinated
  2. Leaps of depolarisation
  3. Faster
  4. More energy efficient (less ATP needed for Na-K pumps)
108
Q

What causes action potentials to conduct more slowly?

A

Lower temperatures

109
Q

How do local anaesthetics work?

A

Block Na+ gates, preventing them from opening
This stops an action potential from being formed
Nerve can’t transmit a pain message

110
Q

What are synapses?

A

The gaps between neurons

111
Q

What are the ends of axon terminals called?

A

Synaptic end bulbs

112
Q

What is the space between the synaptic end bulb and the post-synaptic neuron called?

A

Synaptic cleft

113
Q

What is the synaptic cleft filled with?

A

Interstitial fluid

114
Q

What are neurotransmitters?

A

Chemical messengers that carry the nerve impulse across the synaptic cleft

115
Q

Where are neurotransmitters stored?

A

In synaptic vesicles

116
Q

What effects can neurotransmitters have on the post-synaptic neuron?

A

Excitatory or inhibitory

117
Q

What do excitatory neurotransmitters do?

A

Pass on the action potential by causing depolarisation of the post-synaptic neuron

Open the Na+ ion channels

Inner membrane becomes more positive

118
Q

What do inhibitory neurotransmitters do?

A

Stop the action potential by causing hyperpolarisation of the post-synaptic neuron

Open the K+ ion channels

Inner membrane becomes more negative

119
Q

How does a synapse transmit a signal?

A
  1. Action potential arrives at the synaptic end bulb
  2. Depolarisation begins causing calcium channels to open, sending calcium to the synaptic end bulb
  3. Increase in Ca causes synaptic vesicles to release neurotransmitters into the synaptic cleft
  4. The neurotransmitters diffuse across the synapse and bind to receptors on the post-synaptic neuron
  5. This opens the ion channels, generating an action potential
120
Q

How many neurotransmitters have been identified?

A

More than 100

121
Q

What are the different types of neurotransmitters?

A
  1. Amino acids - glutamate, GABA
  2. Monoamines - dopamine, serotonin
  3. Neuropeptides - endorphins
  4. Unique molecules - acetylcholine
122
Q

What is glutamate?

A

An excitatory neurotransmitter in the CNS

123
Q

What role does glutamate play in the CNS?

A

Memory and learning

124
Q

What is GABA?

A

An inhibitory neurotransmitter in the brain

Produced from glutamate

125
Q

What is glutamate produced from?

A

The amino acid glutamine

126
Q

What is needed to convert glutamate to GABA?

A

Vit B6

127
Q

What is the function of GABA?

A

Preventing neural overactivity

128
Q

What is serotonin?

A

Other name = 5-Hydroxytryptamine (5-HTP)

Produced from amino acid tryptophan

129
Q

Where is 95% of serotonin produced?

A

In the digestive tract (enteric nervous system)

130
Q

Where is the remaining 5% of serotonin located?

A

In the CNS

131
Q

What is the function of serotonin?

A 
Intestinal motility
Epithelial cell secretion
Attention
Sleep regulation
Pain regulation
132
Q

Which enzyme removes serotonin from a synapse?

A

Monoamine oxidase (MAO)

133
Q

Where is dopamine located?

A

Several areas of the brain, including the substantia nigra

134
Q

From which substance is dopamine synthesised from?

A

The amino acid tyrosine

135
Q

What is the function of dopamine?

A 
Movement
Reward mechanisms (sugars, cigarettes, alcohol)
Regulating muscle tone
Cognition
Emotion
136
Q

Which hormone does dopamine inhibit?

A

Prolactin

137
Q

How is dopamine removed from a synapse?

A

Reuptake

Degradation by enzymes MAO and COMT (catechol-oxygen-methyl transferase)

138
Q

Which pathology is associated with dopamine depletion?

A

Parkinson’s disease

139
Q

What type of neurotransmitters are adrenaline and noradrenaline?

A

Monoamine

140
Q

What are adrenaline and noradrenaline produced from?

A

Tryosine

141
Q

What is the primary function of adrenaline and noradrenaline?

A

Excitatory neurotransmitter

Also hormones

142
Q

Where are adrenaline and noradrenaline located?

A

Sympathetic NS
Motor neurons
Brain
Adrenal medulla

143
Q

How are adrenaline and noradrenaline removed from the synapses?

A

Reuptake

Degradation by enzymes MAO and COMT (catechol-oxygen-methyl transferase)

144
Q

What is MAO?

A

Monoamine oxidase (enzyme)

145
Q

What is COMT?

A

Catechol-oxygen-methyl transferase (enzyme)

146
Q

What are neuropeptides?

A

Small proteins acting as neurotransmitters and hormones

147
Q

Common types of neuropeptides

A

Endorphins
Enkephalins
Dynorphins
Substance P

148
Q

What is the function of neuropeptides?

A

Act as neuromodulators - exerting regulatory effects on synaptic receptors

149
Q

What is special about enkephalins, endorphins and dynorphins?

A

They are opioids (natural analgesics)

Released after exercise

150
Q

What is the function of substance P?

A

Enhances the feeling of pain

151
Q

What is acetylcholine?

A

Excitatory neurotransmitter (but inhibitory in vagus nerve)

152
Q

Where is acetylcholine located?

A

Parasympathetic NS
CNS
Neuromuscular junction

153
Q

What is the function of acetylcholine?

A

Muscle contraction

Cognition

154
Q

How is acetylcholine removed?

A

Degraded by the enzyme acetylcholinesterase

155
Q

Which pathologies are associated with acetylcholine?

A

AZD

156
Q

What is nitric oxide?

A

Excitatory neurotransmitter

157
Q

What is nitric oxide formed from?

A

Arginine

158
Q

What is the function of nitric oxide?

A

Vasodilation

159
Q

What is the pharmacological use of nitric oxide?

A

Angina (GTN spray)

Viagra enhances NO

160
Q

Where is MAO located?

A

Neurons

Astrocytes

161
Q

What is the function of MAO?

A

Breakdown of monoamines:

Serotonin
Adrenaline
Noradrenaline
Dopamine

162
Q

What is the function of COMT?

A

Catalyses the breakdown of:
Adrenaline
Noradrenaline
Dopamine

163
Q

Which herb inhibits MAO?

A

St John’s Wort

164
Q

Which type of action potential does touch excite?

A

Graded potential

165
Q

Which nerve endings does touch excite?

A

Sensory nerve endings

166
Q

What happens when touch triggers a graded potential?

A
  1. The graded potential triggers the axon of a sensory neuron to form an action potential
  2. This action potential travels into the CNS
  3. Neurotransmitters are released at synapses
167
Q

Where is touch interpreted?

A

In the primary somatosensory area of the brain

168
Q

What do spinal nerves do?

A

Carry impulses to and from the spinal cord

169
Q

How many spinal nerves are there?

A

31 pairs

170
Q

How is a spinal nerve named?

A

Based on the spinal level it originates from e.g. L5

171
Q

What do combined spinal nerves become?

A

Peripheral nerves

172
Q

What happens if a spinal nerve is injured e.g. disc prolapse, bone spur, tumour?

A

It can cause pain and altered sensation e.g. numbness/tingling in the associated distribution

173
Q

What is an associated distribution also known as?

A

Dermatome

174
Q

Can neurons in the peripheral nervous system regenerate?

A

Only if Schwann cells and the cell body are intact, and there’s no scar tissue

175
Q

Can neurons in the central nervous system regenerate?

A

No

176
Q

What inhibits neuron regeneration in the CNS?

A

Oligodendrocytes and astrocytes

177
Q

What happens as neurons can’t regenerate?

A

Scar tissue is formed instead

Debris clean up is slow as no macrophages

178
Q

What happens if there is a disruption to nerve supply?

A

Could interfere with the health of the tissue structure the nerves supply

179
Q

What can disrupt nerve health?

A

Stress
Anxiety
Depression

Biomedicine (Semester II) (20 decks)

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