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BioMed S2 > 13. Nervous System I > Flashcards

13. Nervous System I Flashcards

1
Q

Nervous System: definition

A

Network of fibres throughout the body that co-ordinates 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
‘Perception’

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12
Q

Which neurons carry out the integration function?

A

Interneurons

Act as connectors within the nervous system

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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

Somatic nervous system
(‘body’/voluntary)

Autonomic nervous system (‘automatic’/involuntary)

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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

Conveys sensory information to the CNS
Controls voluntary muscles (skeletal)

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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

Sympathetic nervous system
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

Sympathetic nervous system is innervated from where ?
Giving rise to which term ?

A

The thoracic and lumbar spine
Thoraco-lumbar

The nerves are just anterior to the vertebrae

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23
Q

Parasympathetic nervous system innervation is from where ?
Giving rise to what term ?

A

Vagus nerve (brainstem)
Sacrum
Cranio-sacral

Therapeutic effects of cranial-sacral touch

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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 (glycogenolysis)
PNS: glycogen synthesis (glycogenesis)

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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

Neurons
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 (have an ability to create an action potential)
They transmit electrical signals
They transmit information

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39
Q

What do glial cells do?

A
  • Surround neurons and hold them in place
  • Neurons would not function without glial cells
  • Supply neurons with nutrients and oxygen
  • Destroy pathogens and remove dead neurons

Glial = ‘glue’

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40
Q

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

A

SIX
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 contained in 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
Whitish colour of myelin is responsible for the name

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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 neurons

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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
2 sensory tracts ‘going up’
1 motor tract ‘going down’

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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 most axons

Can have up to 100 layers

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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

Can be affected by malnourishment in early years

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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

Vitamin B12

Essential co-factor

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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 (unlike neurons)

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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 glial cells
Most numerous/largest glial cells in CNS
Hold neurons to their blood supply
Contribute to blood-brain barrier (wrap around blood vessels)

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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 (CNS)
Mobile in the brain
Multiply with damage
Derived from monocytes

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69
Q

What are ependymal cells?

A

Epithelial glial cells in CNS which line the walls of :
* 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

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73
Q

What can malnutrition in infancy cause?

A

Irreversible nerve damage

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74
Q

What are satellite cells?

A

Provide structural support to cell bodies in the PNS
Exchange substances

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75
Q

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

A

Graded potential
Action potential

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76
Q

Describe graded potential

A

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

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77
Q

Describe action potential

A

Long distance communication
Occurs along axon of a neuron
‘All or nothing’
Has threshold*
Shorter duration

*Stimulus must reach a certain point before signal is sent

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78
Q

How are graded and action potentials facilitated?

A

Specific ion channels open and close when stimulated
Existance of ‘resting potential’ (electrical difference across the cell membrane)

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79
Q

What are ion channels?

A

Transport channels for ions

Created by transmembrane proteins within the neuron cell membrane

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80
Q

How do ion channels work?

A

When they open, they allow specific ions to move through the membrane across a concentration gradient.
Passive transport (either simple or facilitated diffusion)

Eg. The Sodium ion channel is specific for NA+ ions

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81
Q

When do ion channels open?

A

In response to a stimulus

For an action potential the stimulus must reach the threshold

82
Q

What stimuli can cause an ion channel to open?

A

Changes in:

  • Voltage
  • Chemicals (hormones)
  • Mechanical pressure
83
Q

Describe resting potential

A

Electrical difference* between the interior and exterior of the cell membrane
The potential to generate an electrical signal

*This creates an electrochemical gradient across the membrane

84
Q

How many millivolts is resting potential?

A

Approx. -70mV

Note minus 70mV

85
Q

What does the sodium-potassium pump do?

A

During refractory period after repolarisation, pumps 3 Na+ out for every 2 K+ it pumps back in

86
Q

What makes the sodium-potassium pump work?

A

ATP

Required as Na-K pump is an active transport process

87
Q

What is the definition of an action potential?

A

The formation of a nerve impulse down the axon

88
Q

What are the two stages of an action potential?

A
  1. Depolarisation
  2. Repolarisation
89
Q

What is depolarisation?

A

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

90
Q

What is repolarisation?

A

When the cell membrane is restored to -70mV

91
Q

What is depolarisation triggered by?

A

Stimulation of sensory nerve ending.

92
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
93
Q

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

94
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
95
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

refactory = resistant to stimulus

96
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

97
Q

What is the absolute refractory period?

A

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

98
Q

What is the relative refractory period?

A

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

99
Q

What is conduction (in the nervous system)?

A

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

100
Q

What is an unmyelinated axon?

A

Where there’s no myelin sheath around the axon

101
Q

How does depolarisation work in an unmyelinated axon?

A

Via continuous conduction:
Depolarization of one section of the membrane causes the adjacent section to depolarize, step-by-step propagation of the action potential.
Relatively slower process than conduction in a myelinated axon

102
Q

What is the function of myelin?

A

Electrically insulates the axon
Increases the speed of nerve conduction.

103
Q

How does conduction work in a myelinated axon?

A

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

104
Q

Describe continuous conduction

A
  1. Unmyelinated
  2. Step by step depolarisation
  3. Slower
  4. Less energy efficient
105
Q

Describe saltatory conduction

A
  1. Myelinated
  2. ‘Leaps’ of depolarisation
  3. Faster
  4. More energy efficient (less ATP needed for Na-K pumps)
106
Q

What causes action potentials to conduct more slowly?

A

Lower temperatures

107
Q

How do *local *anaesthetics work?

A

Block Na+ channels, preventing them from opening
This stops an action potential from being formed
Nerve inhibited from transmitting the pain message

108
Q

What are synapses?

A

The gaps between neurons
Or between neurons and muscles

109
Q

What are the ends of axon terminals called?

A

Synaptic end bulbs

110
Q

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

A

Synaptic cleft

111
Q

What is the synaptic cleft filled with?

A

Interstitial fluid

112
Q

What are neurotransmitters?

A

Chemical messengers that carry the nerve impulse across the synaptic cleft

113
Q

Where are neurotransmitters stored?

A

In synaptic vesicles

114
Q

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

A

Excitatory or inhibitory

115
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

116
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

117
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 exocytosis of synaptic vesicles (releasing 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
118
Q

How many neurotransmitters have been identified?

A

More than 100

119
Q

What are the different types of neurotransmitters?

A
  • Amino acids - glutamate, GABA
  • Monoamines - dopamine, serotonin
  • Neuropeptides - endorphins, substance P
  • Unique molecules - acetylcholine, nitric oxide
120
Q

What is glutamate?

A

An excitatory neurotransmitter in the CNS

121
Q

What role does glutamate play in the CNS?

A

Memory and learning

122
Q

What is GABA*?

*Gamma Aminobutyric Acid

A

An inhibitory neurotransmitter in the brain
Produced from glutamate

123
Q

What is glutamate produced from?

A

The amino acid glutamine

124
Q

What is needed to convert glutamate to GABA?

Gamma Aminobutyric Acid

A

Vitamin B6

125
Q

What is the function of GABA?

Gamma Aminobutyric Acid

A

Preventing neural overactivity

126
Q

What is the chemical name for serotonin?

A

5-Hydroxytryptamine
(5-HTP)

Produced from amino acid tryptophan

127
Q

Where is 95% of serotonin produced?

A

In the digestive tract (enteric nervous system)

128
Q

Where is the remaining 5% of serotonin located?

A

In the CNS

129
Q

What is the function of serotonin in the GIT?

A

Intestinal motility
Epithelial cell secretion

130
Q

Which enzyme removes serotonin from a synapse?

A

Monoamine oxidase (MAO)

131
Q

Where is dopamine located?

A

Several areas of the brain, including the substantia nigra

132
Q

From which substance is dopamine synthesised from?

A

The amino acid tyrosine

133
Q

What is the function of dopamine?

A

Movement
Reward mechanisms
Regulating muscle tone
Cognition
Emotion

134
Q

Which hormone does dopamine inhibit?

135
Q

How is dopamine removed from a synapse?

A

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

136
Q

Which pathology is associated with dopamine depletion?

A

Parkinson’s disease

137
Q

What type of neurotransmitters are adrenaline and noradrenaline?

138
Q

What are adrenaline and noradrenaline produced from?

139
Q

What is the primary function of adrenaline and noradrenaline?

A

Excitatory neurotransmitters

Also hormones

140
Q

Where are adrenaline and noradrenaline located?

A

Sympathetic NS
Motor neurons
Brain
Adrenal medulla

141
Q

How are adrenaline and noradrenaline removed from the synapses?

A

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

142
Q

What is MAO?

A

Monoamine oxidase (enzyme)

143
Q

What is COMT?

A

Catechol-oxygen-methyl transferase (enzyme)

144
Q

What are neuropeptides?

A

Small proteins acting as neurotransmitters and hormones

145
Q

Common types of neuropeptides

A

Endorphins
Enkephalins
Dynorphins
Substance P

146
Q

What is the function of neuropeptides?

A

Act as neuromodulators - exerting regulatory effects on synaptic receptors

147
Q

What is special about enkephalins, endorphins and dynorphins?

A

They are opioids (natural analgesics)

Released after exercise

148
Q

What is the function of substance P?

A

Enhances the feeling of pain

149
Q

What is acetylcholine?

A

Excitatory neurotransmitter (but inhibitory in vagus nerve)

150
Q

Where is acetylcholine located?

A

Parasympathetic NS
CNS
Neuromuscular junction

151
Q

What are the roles of the NT acetylcholine?

A

Muscle contraction (NMJ)
Cognition (memory retrieval)

152
Q

How is acetylcholine removed?

A

Degraded by the enzyme acetylcholinesterase

153
Q

Which pathology is associated with acetylcholine?

A

Alzheimer’s disease
90% are deficient in ACh

154
Q

What is nitric oxide?

A

Excitatory neurotransmitter

155
Q

What is nitric oxide formed from?

156
Q

What is the function of nitric oxide?

A

Vasodilation

157
Q

What is the pharmacological use of nitric oxide?

A

Angina (GTN spray)
Viagra enhances NO

158
Q

Where is MAO* found?

*Monoamine oxidase

A

Neurons
Astrocytes (glial)

159
Q

What is the function of MAO?

A

Breakdown of monoamines:
Serotonin
Dopamine
Adrenaline
Noradrenaline

160
Q

What is the function of COMT?

Catechol-O-methyl transferase

A

Catalyses the breakdown of:
Adrenaline
Noradrenaline
Dopamine

161
Q

Which herb inhibits MAO?

A

St John’s Wort

162
Q

Which type of potential does touch excite?

A

Graded potential

163
Q

Which nerve endings does touch excite?

A

Sensory nerve endings
(Meissner’s corpuscles)

164
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 spinal tracts
  3. Neurotransmitters are released at synapses
165
Q

Where does perception of touch take place?

A

In the primary somatosensory* area of the brain

*Part of the sensory cortex of the brain

166
Q

What do spinal nerves do?

A

Carry impulses to and from the spinal cord

167
Q

How many spinal nerves are there?

168
Q

How is a spinal nerve named?

A

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

169
Q

What do combined spinal nerves become?

A

Peripheral nerves
(with given names, such as sciatic nerve)

170
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 dermatome (the area of skin it supplies)

171
Q

Can neurons in the PNS regenerate?

A

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

172
Q

Can neurons in the CNS regenerate?

173
Q

What cells produce scar tissue in the CNS?

A

Astrocytes

174
Q

What happens as neurons can’t regenerate?

A

Scar tissue is formed instead
Debris clean up is slow as no macrophages

175
Q

What happens if there is a disruption to nerve supply?

A

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

176
Q

What can disrupt nerve health?

A

Stress
Anxiety
Depression

177
Q

What is proprioception?

A

The awareness of our body’s position in space
Relies on sight, inner ear and constant messages from feet!

Affected by diabetic neuropathy, and B12 deficiency (myelin sheath)

178
Q

What is the reflex arc?

A

A neural pathway that allows for the rapid and involuntary response to a stimulus without conscious thought or decision-making involvement.
Interneurons in the spinal cord act as the integration centres

179
Q

How is the ANS involved with energy use?

A

SNS - arouses body to expend energy
PNS - calms body to conserve and maintain energy

180
Q

What is the biggest nerve in the PNS?

A

Vagus nerve
AKA ‘the wandering nerve’

181
Q

What activities involve the vagus nerve

A

Promotes mechanical and chemical digestions (releasing enzymes and acids)

182
Q

What is somato-viseral reflex ?
|Verbal, not on slides

A

A bi-directional reflex arc that connects sensory stimuli from the somatic region to produce responses in the visceral region, and vice versa.

183
Q

What is a gliomas ?

A

Type of brain tumor that originates from glial cells

After trauma, glia fill spaces left by damaged neurons

184
Q

What is the effect of heavy metals on astrocytes ?

A

Damages the projections which weakens the blood-brain barrier

185
Q

What is the purpose of the myelin sheath ?

A
  • insulates the axon
  • increases the speed of nerve impulse conduction
  • participates in axon regeneration
186
Q

What is polarity ?

A

A difference in electrical charge

187
Q

What are the key ion channels ?

A

Sodium (Na+) channels
Potassium (K+) channels

188
Q

What creates the resting potential ?

A

A build up of negative ions on the inside
of the cell membrane, relative to the
extracellular fluid which contains more
positive ions

189
Q

What causes the potential difference between the interior and exterior of the axon?

A

Higher number of NA+ ions surrounding the axon (which contains a lower number of K+ ions and negatively charged protein molecules)
Therefore the inside of the axon is more negatively charged compared to the outside.

190
Q

What does it mean for a cell to be polarised ?

A

The cell membrane exhibits a membrane potential
The cell is ‘charged’
It has the capacity to conduct an electrical signal

191
Q

How are electricity and electrical fields related to healthy tissues ?

A
  • Electrical flow means there is an electromagnetic field present
  • External and internal factors can disrupt this field and therefore disrupt the electrical flow (energy flow)
  • Disruption to the flow would interfere with the health of the tissue it supplies (and vice versa)
192
Q

Describe an action potential

A

A series of events which reverses the
membrane potential and then restores it to its resting state.

193
Q

Why is an action potential ‘all or nothing’

A

Because once triggered there is no reduction in the signal as it travels

194
Q

What happens to neurotransmitters following a nerve implulse ?

A

The neurotransmitters need to be inactivated and removed for the process to be able to start again.
This can occur by
* diffusion,
* enzymes breakdown (e.g. MAO)
* re-absorption.

195
Q

Fill in the blanks

196
Q

What is the effect of diazepam* on the CNS ?

*Valium

A

Enhances GABA to reduce neural over-activity

197
Q

What is the function of serotonin (outside of GIT)?

A

Attention
Sleep regulation
Pain regulation

198
Q

What is the effect of stress or poor diet on serotonin levels ?

A

Production and availabiltity is reduced
Reuptake is inhibited

199
Q

What are the functions of the amino acid tyrosine

A
  • Precursor to
  • Dopamine
  • Adrenaline
  • Noradrenaline
  • Building block for T3 and T4 (thyroid hormones)
  • Precursor to melanin
200
Q

What are the side effects of botox?

Not on slides

A

Works by blocking Ach in muscles
This can reduce physical capacity for mimicry (shown to reduce empathy!)

201
Q

What is a dermatome ?

A

The distribution of skin innervated by a spinal nerve

derm = skin / tome = segment

202
Q

What is neuroplasticity ?

Lecture verbal not on slide

A

The possibility to build a new neural pathway in the brain despite physical damage.
Learning through repeated actions

BioMed S2 (34 decks)

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