13. Nervous System I Flashcards
(202 cards)
1
Q
Nervous System: definition
A
Network of fibres throughout the body that co-ordinates 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)
- 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
‘Perception’
12
Q
Which neurons carry out the integration function?
A
Interneurons
Act as connectors within the nervous system
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
(‘body’/voluntary)
Autonomic nervous system (‘automatic’/involuntary)
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
Conveys sensory information to the CNS
Controls voluntary muscles (skeletal)
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
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
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
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
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 (glycogenolysis)
PNS: glycogen synthesis (glycogenesis)
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?
Neurons
Neuroglia (glial cells)
37
What do neurons do?
Process and transmit information
38
What qualities do neurons have?
They're electrically excitable (have an ability to create an action potential)
They transmit electrical signals
They transmit information
39
What do glial cells do?
* 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'
40
How many types of glial cells are there? And where can they be found?
SIX
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 contained in 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
Whitish colour of myelin is responsible for the name
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 neurons
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
2 sensory tracts 'going up'
1 motor tract 'going down'
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 most axons
| Can have up to 100 layers
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
| Can be affected by malnourishment in early years
61
What are nodes of Ranvier?
Gaps in the myelin sheath
62
What is needed for the production of myelin?
Vitamin B12
| Essential co-factor
63
What qualities do glial cells have?
Non-excitatory
Smaller than neurons but 50x more prevalent
Can multiply and divide (unlike neurons)
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 glial cells
Most numerous/largest glial cells in CNS
Hold neurons to their blood supply
Contribute to **blood-brain barrier** (wrap around blood vessels)
67
What are oligodendrocytes?
Glial cells that myelinate axons in the CNS
68
What are microglia?
**Phagocytic** immune cells in brain (CNS)
Mobile in the brain
Multiply with damage
Derived from monocytes
69
What are ependymal cells?
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
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?
Graded potential
Action potential
76
Describe graded potential
Short distance communication
Occurs in the dendrites and cell body of the neuron
Amplitude proportional to strength of stimulus
No threshold
Longer duration
77
Describe action potential
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
78
How are graded and action potentials facilitated?
Specific ion channels open and close when stimulated
Existance of 'resting potential' (electrical difference across the cell membrane)
79
What are ion channels?
Transport channels for ions
| Created by transmembrane proteins within the neuron cell membrane
80
How do ion channels work?
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
81
When do ion channels open?
In response to a stimulus
| For an action potential the stimulus must reach the threshold
82
What stimuli can cause an ion channel to open?
Changes in:
* Voltage
* Chemicals (hormones)
* Mechanical pressure
83
Describe resting potential
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
How many millivolts is resting potential?
Approx. **-**70mV
| Note *minus* 70mV
85
What does the sodium-potassium pump do?
During refractory period after repolarisation, pumps 3 **Na+** out for every 2 **K+** it pumps back in
86
What makes the sodium-potassium pump work?
ATP
| Required as Na-K pump is an active transport process
87
What is the definition of an action potential?
The formation of a nerve impulse down the axon
88
What are the two stages of an action potential?
1. Depolarisation
2. Repolarisation
89
What is depolarisation?
The negative membrane potential (-70mV) reverses and becomes positive, reaching +30mV
90
What is repolarisation?
When the cell membrane is restored to -70mV
91
What is depolarisation triggered by?
Stimulation of sensory nerve ending.
92
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
93
What is the threshold value that depolarisation must meet in order to generate an action potential?
-55mV
94
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
95
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
| refactory = resistant to stimulus
96
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
97
What is the absolute refractory period?
Where even a strong stimulus can't generate an action potential
98
What is the relative refractory period?
Where a larger than normal stimulus is needed to generate an action potential
99
What is conduction (in the nervous system)?
The movement of a nerve impulse along the axon of a neuron
100
What is an unmyelinated axon?
Where there's no myelin sheath around the axon
101
How does depolarisation work in an unmyelinated axon?
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
What is the function of myelin?
Electrically insulates the axon
Increases the speed of nerve conduction.
103
How does conduction work in a myelinated axon?
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
Describe continuous conduction
1. Unmyelinated
2. Step by step depolarisation
3. Slower
4. Less energy efficient
105
Describe saltatory conduction
1. Myelinated
2. 'Leaps' of depolarisation
3. Faster
4. More energy efficient (less ATP needed for Na-K pumps)
106
What causes action potentials to conduct more slowly?
Lower temperatures
107
How do *local *anaesthetics work?
Block Na+ channels, preventing them from opening
This stops an action potential from being formed
Nerve inhibited from transmitting the pain message
108
What are synapses?
The gaps between neurons
Or between neurons and muscles
109
What are the ends of axon terminals called?
Synaptic end bulbs
110
What is the space between the synaptic end bulb and the post-synaptic neuron called?
Synaptic cleft
111
What is the synaptic cleft filled with?
Interstitial fluid
112
What are neurotransmitters?
Chemical messengers that carry the nerve impulse across the synaptic cleft
113
Where are neurotransmitters stored?
In synaptic vesicles
114
What effects can neurotransmitters have on the post-synaptic neuron?
Excitatory or inhibitory
115
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
116
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
117
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 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
How many neurotransmitters have been identified?
More than 100
119
What are the different types of neurotransmitters?
* Amino acids - glutamate, GABA
* Monoamines - dopamine, serotonin
* Neuropeptides - endorphins, substance P
* Unique molecules - acetylcholine, nitric oxide
120
What is glutamate?
An excitatory neurotransmitter in the CNS
121
What role does glutamate play in the CNS?
Memory and learning
122
What is GABA*?
| *Gamma Aminobutyric Acid
An inhibitory neurotransmitter in the brain
Produced from glutamate
123
What is glutamate produced from?
The amino acid glutamine
124
What is needed to convert glutamate to GABA?
| Gamma Aminobutyric Acid
Vitamin B6
125
What is the function of GABA?
| Gamma Aminobutyric Acid
Preventing neural overactivity
126
What is the chemical name for serotonin?
5-Hydroxytryptamine
(5-HTP)
| Produced from amino acid tryptophan
127
Where is 95% of serotonin produced?
In the digestive tract (enteric nervous system)
128
Where is the remaining 5% of serotonin located?
In the CNS
129
What is the function of serotonin in the GIT?
Intestinal motility
Epithelial cell secretion
130
Which enzyme removes serotonin from a synapse?
Monoamine oxidase (MAO)
131
Where is dopamine located?
Several areas of the brain, including the substantia nigra
132
From which substance is dopamine synthesised from?
The amino acid tyrosine
133
What is the function of dopamine?
Movement
Reward mechanisms
Regulating muscle tone
Cognition
Emotion
134
Which hormone does dopamine inhibit?
Prolactin
135
How is dopamine removed from a synapse?
Reuptake
Degradation by enzymes MAO and COMT (catechol-oxygen-methyl transferase)
136
Which pathology is associated with dopamine depletion?
Parkinson's disease
137
What type of neurotransmitters are adrenaline and noradrenaline?
Monoamine
138
What are adrenaline and noradrenaline produced from?
Tryosine
139
What is the primary function of adrenaline and noradrenaline?
Excitatory neurotransmitters
| Also hormones
140
Where are adrenaline and noradrenaline located?
Sympathetic NS
Motor neurons
Brain
Adrenal medulla
141
How are adrenaline and noradrenaline removed from the synapses?
Reuptake
Degradation by enzymes MAO (monoamine oxidase) and COMT (catechol-oxygen-methyl transferase
142
What is MAO?
Monoamine oxidase (enzyme)
143
What is COMT?
Catechol-oxygen-methyl transferase (enzyme)
144
What are neuropeptides?
Small proteins acting as neurotransmitters and hormones
145
Common types of neuropeptides
Endorphins
Enkephalins
Dynorphins
Substance P
146
What is the function of neuropeptides?
Act as neuromodulators - exerting regulatory effects on synaptic receptors
147
What is special about enkephalins, endorphins and dynorphins?
They are opioids (natural analgesics)
| Released after exercise
148
What is the function of substance P?
Enhances the feeling of pain
149
What is acetylcholine?
Excitatory neurotransmitter (but inhibitory in vagus nerve)
150
Where is acetylcholine located?
Parasympathetic NS
CNS
Neuromuscular junction
151
What are the roles of the NT acetylcholine?
Muscle contraction (NMJ)
Cognition (memory retrieval)
152
How is acetylcholine removed?
Degraded by the enzyme acetylcholinesterase
153
Which pathology is associated with acetylcholine?
Alzheimer's disease
90% are deficient in ACh
154
What is nitric oxide?
Excitatory neurotransmitter
155
What is nitric oxide formed from?
Arginine
156
What is the function of nitric oxide?
Vasodilation
157
What is the pharmacological use of nitric oxide?
Angina (GTN spray)
Viagra enhances NO
158
Where is MAO* found?
| *Monoamine oxidase
Neurons
Astrocytes (glial)
159
What is the function of MAO?
Breakdown of monoamines:
Serotonin
Dopamine
Adrenaline
Noradrenaline
160
What is the function of COMT?
| Catechol-O-methyl transferase
Catalyses the breakdown of:
Adrenaline
Noradrenaline
Dopamine
161
Which herb inhibits MAO?
St John's Wort
162
Which type of potential does touch excite?
Graded potential
163
Which nerve endings does touch excite?
Sensory nerve endings
(Meissner's corpuscles)
164
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 spinal tracts
3. Neurotransmitters are released at synapses
165
Where does perception of touch take place?
In the primary somatosensory* area of the brain
| *Part of the sensory cortex of the brain
166
What do spinal nerves do?
Carry impulses to and from the spinal cord
167
How many spinal nerves are there?
31 pairs
168
How is a spinal nerve named?
Based on the spinal level it originates from e.g. L5
169
What do combined spinal nerves become?
Peripheral nerves
(with given names, such as sciatic nerve)
170
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 dermatome (the area of skin it supplies)
171
Can neurons in the PNS regenerate?
Only if Schwann cells and the cell body are intact, and there's no scar tissue
172
Can neurons in the CNS regenerate?
No
173
What cells produce scar tissue in the CNS?
Astrocytes
174
What happens as neurons can't regenerate?
Scar tissue is formed instead
Debris clean up is slow as no macrophages
175
What happens if there is a disruption to nerve supply?
Could interfere with the health of the tissue structure that the nerves supply
176
What can disrupt nerve health?
Stress
Anxiety
Depression
177
What is proprioception?
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
What is the reflex arc?
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
How is the ANS involved with energy use?
SNS - arouses body to expend energy
PNS - calms body to conserve and maintain energy
180
What is the biggest nerve in the PNS?
Vagus nerve
AKA 'the wandering nerve'
181
What activities involve the vagus nerve
Promotes mechanical and chemical digestions (releasing enzymes and acids)
182
What is somato-viseral reflex ?
|Verbal, not on slides
A bi-directional reflex arc that connects sensory stimuli from the somatic region to produce responses in the visceral region, and vice versa.
183
What is a gliomas ?
Type of brain tumor that originates from glial cells
| After trauma, glia fill spaces left by damaged neurons
184
What is the effect of heavy metals on astrocytes ?
Damages the projections which weakens the blood-brain barrier
185
What is the purpose of the myelin sheath ?
* insulates the axon
* increases the speed of nerve impulse conduction
* participates in axon regeneration
186
What is polarity ?
A difference in electrical charge
187
What are the key ion channels ?
Sodium (Na+) channels
Potassium (K+) channels
188
What creates the resting potential ?
A build up of negative ions on the inside
of the cell membrane, relative to the
extracellular fluid which contains more
positive ions
189
What causes the potential difference between the interior and exterior of the axon?
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
What does it mean for a cell to be polarised ?
The cell membrane exhibits a membrane potential
The cell is 'charged'
It has the capacity to conduct an electrical signal
191
How are electricity and electrical fields related to healthy tissues ?
* 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
Describe an action potential
A series of events which reverses the
membrane potential and then restores it to its resting state.
193
Why is an action potential 'all or nothing'
Because once triggered there is no reduction in the signal as it travels
194
What happens to neurotransmitters following a nerve implulse ?
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
# Fill in the blanks
196
What is the effect of diazepam* on the CNS ?
| *Valium
Enhances GABA to reduce neural over-activity
197
What is the function of serotonin (outside of GIT)?
Attention
Sleep regulation
Pain regulation
198
What is the effect of stress or poor diet on serotonin levels ?
Production and availabiltity is reduced
Reuptake is inhibited
199
What are the functions of the amino acid tyrosine
* Precursor to
- Dopamine
- Adrenaline
- Noradrenaline
* Building block for T3 and T4 (thyroid hormones)
* Precursor to melanin
200
What are the side effects of botox?
## Footnote
Not on slides
Works by blocking Ach in muscles
This can reduce physical capacity for mimicry (shown to reduce empathy!)
201
What is a dermatome ?
The distribution of skin innervated by a spinal nerve
| derm = skin / tome = segment
202
What is neuroplasticity ?
## Footnote
Lecture verbal not on slide
The possibility to build a new neural pathway in the brain despite physical damage.
Learning through repeated actions
