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
2
Q
How does the nervous system co-ordinate actions?
A
By transmitting signals between parts of the body
3
Q
How does the nervous system maintain homeostasis?
A
Works with the endocrine system
4
Q
Divisions of the nervous system
A
- Central Nervous System (CNS)
2. Peripheral Nervous System (PNS)
5
Q
Which areas of the body are covered by the central nervous system (CNS)?
A
Brain
Spinal cord
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)
7
Q
What are the functions of the nervous system?
A
- Sensory
- Integration
- Motor
8
Q
Describe the sensory function of the nervous system
A
Detects internal and external environmental changes through proprioception, sensation or touch
9
Q
Which neurons carry out the sensory function?
A
Sensory neurons
10
Q
Describe the integration function of the nervous system
A
Processes sensory information by analysing, storing and making decisions
11
Q
Where is the integration function mainly carried out?
A
In the brain
12
Q
Which neurons carry out the integration function?
A
Interneurons
13
Q
Describe the motor function of the nervous system
A
Produces a response to sensory information to effect change
14
Q
Which neurons carry out the motor function?
A
Motor neurons
15
Q
What are the subdivisions within the peripheral nervous system?
A
- Somatic nervous system
2. Autonomic nervous system
16
Q
What does the spinal cord do?
A
Connects the brain and peripheral nervous system
17
Q
What does the peripheral nervous system do?
A
Carries messages to and from the CNS
18
Q
What does the somatic nervous system do?
A
Controls voluntary muscles (skeletal)
Transmits sensory information to the CNS
19
Q
What does the autonomic nervous system do?
A
Controls involuntary body functions
Works automatically to maintain homeostasis
20
Q
What are the subdivisions within the autonomic nervous system?
A
- Sympathetic nervous system
2. Parasympathetic nervous system
21
Q
What does the hypothalamus do?
A
It’s the control centre over autonomic motor neurons in organs, glands, cardiac and smooth muscles
22
Q
Regions covered by the sympathetic nervous system
A
Thoraco-lumbar
23
Q
Regions covered by the parasympathetic nervous system
A
Cranio-sacral
24
Q
What happens to the pupils in the ANS?
A
SNS: dilation
PNS: constriction
25
What happens to the lungs in the ANS?
SNS: bronchodilation
PNS: bronchoconstriction
26
What happens to the heart in the ANS?
SNS: HR and blood pressure increases
PNS: HR and blood pressure decreases
27
What happens in the GIT in the ANS?
SNS: decreased motility and secretions
PNS: increased motility and secretions
28
What happens in the liver in the ANS?
SNS: conversion of glycogen to glucose
PNS: glycogen synthesis
29
What happens with the adrenal glands in the ANS?
SNS: releases adrenaline
PNS: nothing
30
What is the enteric nervous system?
Brain of the GIT
31
How many neurons does the GIT contain?
Around 100 million
32
What regulates the enteric nervous system?
Autonomic nervous system
33
What do sensory neurons do in the enteric nervous system?
Monitor chemical changes in the GIT (via chemo-receptors) and stretching of its walls
34
What do motor neurons do in the enteric nervous system?
Govern motility and secretions of the GIT and associated glands
35
What do interneurons do in the enteric nervous system?
Connect the myenteric and submucosal plexuses
36
What are the cells that make up nervous tissue?
1. Neurons
| 2. Neuroglia (glial cells)
37
What do neurons do?
Process and transmit information
38
What qualities do neurons have?
They're electrically excitable
| Ability to create a nerve impulse/action potential
39
What do glial cells do?
Surround neurons and hold them in place
Supply neurons with nutrients and oxygen
Destroy pathogens and remove dead neurons
40
How many types of glial cells are there? And where can they be found?
4x in CNS
| 2x in PNS
41
What percentage of brain volume is made up of glial cells?
90%
42
What is a nerve?
A bundle of one or more neurons
43
What is a stimulus?
Anything that can create an action potential
| Can be internal or external
44
Components of a neuron
1. Cell body
2. Dendrites
3. Axon
4. Myelin sheath
5. Nodes of Ranvier
6. Terminal endings
45
What is the cell body of a neuron?
Nucleus
| Organelles
46
What is grey matter?
Mostly cell bodies
Dendrites
Unmyelinated axons
47
What is white matter?
Mostly myelinated axons
48
What are nuclei?
Clusters of cell bodies in the CNS
49
What are ganglia?
Clusters of cell bodies in the PNS
50
What are dendrites?
The receiving portion of the cell
| They communicate with other dendrites
51
What is an axon?
Long, cylindrical projections that carry nerve impulses away from the cell body towards another neuron
52
How long are axons?
```
<1mm in CNS up to...
Approx 1m (sciatic nerve)
```
53
What is the axolemma?
Membrane covering the axon
54
What is the axon terminal?
The end of an axon
55
What are tracts?
Bundles of axons in the CNS
56
What are nerves?
Bundles of axons in the PNS
57
Can axons regenerate if injured?
Yes, at a rate of 1-2mm per day
58
What is the myelin sheath?
A multi-layered lipid and protein covering around the axons
59
What does the myelin sheath do?
Electrically insulates the axon
Increases the speed of nerve conduction
Participates in axon regeneration
60
How and when is the myelin sheath formed?
Formed by glial cells in the embryo
Continue through childhood
Peak in adolescence
61
What are nodes of Ranvier?
Gaps in the myelin sheath
62
What is needed for the production of myelin?
Vit B12
63
What qualities do glial cells have?
Non-excitatory
Smaller than neurons but 50x more prevalent
Can multiply and divide
64
What do glial cells do after a trauma?
Fill spaces left by damaged neurons
65
What are the glial cells found in the CNS?
Astrocytes
Oligodendrocytes
Microglia
Ependymal cells
66
What are astrocytes?
Star-shaped and most numerous/largest glial cells in CNS
Hold neurons to their blood supply
Contribute to blood-brain barrier
67
What are oligodendrocytes?
Glial cells that myelinate axons in the CNS
68
What are microglia?
Phagocytic immune cells in brain
Multiply with damage
Derived from monocytes
69
What are ependymal cells?
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
70
What are the glial cells found in the PNS?
Schwann cells
| Satellite cells
71
What are Schwann cells?
Glial cells that produce myelin around the axons of neurons in the PNS
72
When are most myelination and dendrite connections completed by?
Age of 3
73
What can malnutrition in infancy cause?
Irreversible nerve damage
74
What are satellite cells?
Provide structural support to cell bodies in the PNS
| Exchange substances
75
What are the two types of electrical signal in a neuron?
1. Graded potential
| 2. Action potential
76
Describe graded potential
```
Short distance communication
Occurs in the dendrites and cell body
Amplitude proportional to strength of stimulus
No threshold
Longer duration
```
77
Describe action potential
```
Long distance communication
Occurs along axon
All or nothing
Has threshold
Shorter duration
```
78
How are graded and action potentials facilitated?
1. Specific ion channels open and close when stimulated
| 2. Electrical difference across the cell membrane (resting potential)
79
What are ion channels?
Transport channels for ions
| Created by transmembrane proteins within the neuron membranes
80
How do ion channels work?
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
When do ion channels open?
In response to a stimulus
82
What stimuli can cause an ion channel to open?
Changes in:
1. Voltage
2. Chemicals (hormones)
3. Mechanical pressure
83
What is resting potential?
Electrical difference between the interior and exterior of the cell membrane
84
How many millivolts is resting potential?
Approx. 70mV
85
What makes up the interior of a cell during resting potential?
Interior = negative ions build up
| K+ and large negatively-charged proteins and phosphates that can't leave the cell
86
What makes up the exterior of a cell during resting potential?
Exterior = positive ions build up
| Na+ and Cl-
87
What does the sodium-potassium pump do?
Pumps 3x Na+ out for every 2x K+ it pumps back in
| During refractory period after repolarisation
88
What makes the sodium-potassium pump work?
ATP
89
What is an action potential?
The formation of a nerve impulse down the axon
90
What are the two stages of an action potential?
1. Depolarisation
| 2. Repolarisation
91
What is depolarisation?
The negative membrane potential (-70mV) reverses and becomes positive, reaching +30mV
92
What is repolarisation?
When the cell membrane is restored to -70mV
93
What is depolarisation triggered by?
Stimulation to a nerve ending
94
What happens during depolarisation?
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
What is the threshold value that depolarisation must meet in order to generate an action potential?
-55mV
96
What happens during repolarisation?
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
What is the refractory period?
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
What happens during the refractory period?
Sodium-potassium pump pumps 3x Na+ back out and 2x K+ back into the cell to restore resting potential
99
What is the absolute refractory period?
Where even a strong impulse can't generate an action potential
100
What is the relative refractory period?
Where a larger than normal stimulus is needed to generate an action potential
101
What is conduction?
The movement of a nerve impulse along the axon of a neuron
102
What is an unmyelinated axon?
Where there's no sheath around the nerve
103
How does depolarisation work in an unmyelinated axon?
Continuous, step by step conduction away from the cell body down the axon
104
What is myelin?
An insulator
| Prevents ionic currents crossing the cell membrane
105
How does depolarisation work in a myelinated axon?
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
Describe continuous conduction
1. Unmyelinated
2. Step by step depolarisation
3. Slower
4. Less energy efficient
107
Describe saltatory conduction
1. Myelinated
2. Leaps of depolarisation
3. Faster
4. More energy efficient (less ATP needed for Na-K pumps)
108
What causes action potentials to conduct more slowly?
Lower temperatures
109
How do local anaesthetics work?
Block Na+ gates, preventing them from opening
This stops an action potential from being formed
Nerve can't transmit a pain message
110
What are synapses?
The gaps between neurons
111
What are the ends of axon terminals called?
Synaptic end bulbs
112
What is the space between the synaptic end bulb and the post-synaptic neuron called?
Synaptic cleft
113
What is the synaptic cleft filled with?
Interstitial fluid
114
What are neurotransmitters?
Chemical messengers that carry the nerve impulse across the synaptic cleft
115
Where are neurotransmitters stored?
In synaptic vesicles
116
What effects can neurotransmitters have on the post-synaptic neuron?
Excitatory or inhibitory
117
What do excitatory neurotransmitters do?
Pass on the action potential by causing depolarisation of the post-synaptic neuron
Open the Na+ ion channels
Inner membrane becomes more positive
118
What do inhibitory neurotransmitters do?
Stop the action potential by causing hyperpolarisation of the post-synaptic neuron
Open the K+ ion channels
Inner membrane becomes more negative
119
How does a synapse transmit a signal?
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
How many neurotransmitters have been identified?
More than 100
121
What are the different types of neurotransmitters?
1. Amino acids - glutamate, GABA
2. Monoamines - dopamine, serotonin
3. Neuropeptides - endorphins
4. Unique molecules - acetylcholine
122
What is glutamate?
An excitatory neurotransmitter in the CNS
123
What role does glutamate play in the CNS?
Memory and learning
124
What is GABA?
An inhibitory neurotransmitter in the brain
| Produced from glutamate
125
What is glutamate produced from?
The amino acid glutamine
126
What is needed to convert glutamate to GABA?
Vit B6
127
What is the function of GABA?
Preventing neural overactivity
128
What is serotonin?
Other name = 5-Hydroxytryptamine (5-HTP)
| Produced from amino acid tryptophan
129
Where is 95% of serotonin produced?
In the digestive tract (enteric nervous system)
130
Where is the remaining 5% of serotonin located?
In the CNS
131
What is the function of serotonin?
```
Intestinal motility
Epithelial cell secretion
Attention
Sleep regulation
Pain regulation
```
132
Which enzyme removes serotonin from a synapse?
Monoamine oxidase (MAO)
133
Where is dopamine located?
Several areas of the brain, including the substantia nigra
134
From which substance is dopamine synthesised from?
The amino acid tyrosine
135
What is the function of dopamine?
```
Movement
Reward mechanisms (sugars, cigarettes, alcohol)
Regulating muscle tone
Cognition
Emotion
```
136
Which hormone does dopamine inhibit?
Prolactin
137
How is dopamine removed from a synapse?
Reuptake
| Degradation by enzymes MAO and COMT (catechol-oxygen-methyl transferase)
138
Which pathology is associated with dopamine depletion?
Parkinson's disease
139
What type of neurotransmitters are adrenaline and noradrenaline?
Monoamine
140
What are adrenaline and noradrenaline produced from?
Tryosine
141
What is the primary function of adrenaline and noradrenaline?
Excitatory neurotransmitter
| Also hormones
142
Where are adrenaline and noradrenaline located?
Sympathetic NS
Motor neurons
Brain
Adrenal medulla
143
How are adrenaline and noradrenaline removed from the synapses?
Reuptake
| Degradation by enzymes MAO and COMT (catechol-oxygen-methyl transferase)
144
What is MAO?
Monoamine oxidase (enzyme)
145
What is COMT?
Catechol-oxygen-methyl transferase (enzyme)
146
What are neuropeptides?
Small proteins acting as neurotransmitters and hormones
147
Common types of neuropeptides
Endorphins
Enkephalins
Dynorphins
Substance P
148
What is the function of neuropeptides?
Act as neuromodulators - exerting regulatory effects on synaptic receptors
149
What is special about enkephalins, endorphins and dynorphins?
They are opioids (natural analgesics)
| Released after exercise
150
What is the function of substance P?
Enhances the feeling of pain
151
What is acetylcholine?
Excitatory neurotransmitter (but inhibitory in vagus nerve)
152
Where is acetylcholine located?
Parasympathetic NS
CNS
Neuromuscular junction
153
What is the function of acetylcholine?
Muscle contraction
| Cognition
154
How is acetylcholine removed?
Degraded by the enzyme acetylcholinesterase
155
Which pathologies are associated with acetylcholine?
AZD
156
What is nitric oxide?
Excitatory neurotransmitter
157
What is nitric oxide formed from?
Arginine
158
What is the function of nitric oxide?
Vasodilation
159
What is the pharmacological use of nitric oxide?
Angina (GTN spray)
| Viagra enhances NO
160
Where is MAO located?
Neurons
| Astrocytes
161
What is the function of MAO?
Breakdown of monoamines:
Serotonin
Adrenaline
Noradrenaline
Dopamine
162
What is the function of COMT?
Catalyses the breakdown of:
Adrenaline
Noradrenaline
Dopamine
163
Which herb inhibits MAO?
St John's Wort
164
Which type of action potential does touch excite?
Graded potential
165
Which nerve endings does touch excite?
Sensory nerve endings
166
What happens when touch triggers a graded potential?
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
Where is touch interpreted?
In the primary somatosensory area of the brain
168
What do spinal nerves do?
Carry impulses to and from the spinal cord
169
How many spinal nerves are there?
31 pairs
170
How is a spinal nerve named?
Based on the spinal level it originates from e.g. L5
171
What do combined spinal nerves become?
Peripheral nerves
172
What happens if a spinal nerve is injured e.g. disc prolapse, bone spur, tumour?
It can cause pain and altered sensation e.g. numbness/tingling in the associated distribution
173
What is an associated distribution also known as?
Dermatome
174
Can neurons in the peripheral nervous system regenerate?
Only if Schwann cells and the cell body are intact, and there's no scar tissue
175
Can neurons in the central nervous system regenerate?
No
176
What inhibits neuron regeneration in the CNS?
Oligodendrocytes and astrocytes
177
What happens as neurons can't regenerate?
Scar tissue is formed instead
| Debris clean up is slow as no macrophages
178
What happens if there is a disruption to nerve supply?
Could interfere with the health of the tissue structure the nerves supply
179
What can disrupt nerve health?
Stress
Anxiety
Depression
