Neuro (summary sheets) Flashcards
(388 cards)
1
Q
What does white matter contain?
A
Myelinated axons
2
Q
What does grey matter contain?
A
Cell bodies and no myelin sheaths
3
Q
What is the function of oligodendrocytes?
A
Myelinate axons in the brain (CNS)
4
Q
What is the function of Schwann cells?
A
Myelinate axons in the rest of the body (PNS)
5
Q
What is a tract (brain)?
A
Location of pathway e.g. spinothalamic tract
6
Q
What is a commissure (brain)?
A
Tract connecting one hemisphere to the other, tracts that cross the midline
7
Q
What is the lemnisci (brain)?
A
Narrow strip of fibres
8
Q
What is the funiculi (brain)?
A
Rope or chord
9
Q
What is a fasiculi (brain)?
A
Bundle e.g. gracile fasiculus
10
Q
What is a capsule (brain)?
A
Sheet of white matter fibres that border a nucleus of grey matter
11
Q
What is a column (brain)?
A
Longitudinally running fibres separates by other structures e.g. dorsal column
12
Q
What is the cortex (brain)?
A
Laminated grey matter on outside of the brain e.g. motor cortex
13
Q
What are the nuclei (brain)?
A
Collection of nerve cell bodies within the CNS e.g. arcuate nucleus (in the thalamus, arises from the diencephalon)
14
Q
What are the ganglia (brain)?
A
Collection of nerve cell bodies outside the CNS i.e. in the PNS e.g. dorsal root ganglia (derived from neural crest cells) AND some inside CNS that have a capsule e.g. basal ganglia
15
Q
What are afferents (brain)?
A
Axons taking information towards the CNS e.g. sensory fibres
16
Q
What are efferents (brain)?
A
Axons taking information to another site from the CNS e.g. motor fibres
17
Q
What are reticular (brain)?
A
‘Netlike’ where grey & white matter mix e.g. reticular formation of brainstem
18
Q
How are axons gathered?
A
Into tracts
19
Q
Define rostral
A
Towards the nose (anterior)
20
Q
Define caudal
A
Towards tail (posterior)
21
Q
Define dorsal (brainstem/cord)
A
Posterior
22
Q
Define ventral (brainstem/cord)
A
Anterior
23
Q
Define dorsal (cerebrum)
A
Superior
24
Q
Define ventral (cerebrum)
A
Inferior
25
Define sulci (brain)
Grooves
26
Define gyri (brain)
Ridges
27
What is the function of the frontal lobe of the brain?
- Voluntary movement on opposite side of body
| - Intellectual functioning, thought processes, reasoning and memory
28
What does the frontal lobe of dominant hemisphere control?
- Speech (Broca's area)
| - Writing (if right handed, left side is dominant)
29
What does Broca's area do?
Controls speech
30
What is the function of the parietal lobe of the brain?
Receives and interprets sensation (proprioception)
31
What is the function of the temporal lobe of the brain?
- Understanding spoken word (Wernicke's area)
| - Memory & emotion
32
What does Wernicke's area do?
Understanding spoken word
33
What is the function of the occipital lobe of the brain?
Understanding visual images and meaning of written words
34
What underlies the cortex of the brain?
The white matter
35
Where are grey matter structures found in the body?
- Deep in the white matter
| - Surround ventricles
36
What is the general function of the thalamus?
Relay centre direction inputs to cortical areas
37
What is the general function of the hypothalamus?
Links endocrine system to brain and involved in homeostasis
38
What is the general function and structure of the basal ganglia
- Caudate nucleus, putamen & globus pallidus
| - Motor control, cognition & non-motor behaviour
39
What is the striatum of the basal ganglia?
The caudate nucleus and putamen
40
What is the lentiform nucleus of the basal ganglia?
Globus pallidus and putamen
41
What is the function of the cerebellum?
Coordination of voluntary motor movement, balance, equilibrium and muscle tone
42
What is the structure of the cerebellum?
Lies over the dorsal surface of the brain stem and attached to it by 3 peduncles
43
Which peduncle joins the cerebellum and the midbrain?
Superior
44
Which peduncle joins the cerebellum and the pons?
Middle
45
Which peduncle joins the cerebellum and the medulla?
Inferior
46
How is the cerebellum separated from the dorsal brainstem?
By the 4th ventricle, which forms part of its roof
47
What is the cerebellum made of?
Folded cortex, white matter and deep inner nuclei
48
What does a cerebellar injury result in?
Movements which are slow and uncoordinated
49
What are the functions of the brainstem?
- Special senses
- Sensory & motor for head & neck via cranial nerves
- Autonomic regulation of the body
- Regulates consciousness
50
What is the pathway between the brain and spinal cord?
Brainstem
51
What are 3 components of the brainstem?
Midbrain, pons and medulla oblongata
52
What are the two components of the mid-brain?
Tectum (superior & inferior colliculi) and cerebral peduncle (tegmentum & crus cerebri)
53
What structure surrounds the cerebral aqueduct?
The midbrain
54
What bridges the brainstem to the cerebellum?
Pons
55
What is the medulla oblongata continuous with?
The spinal cord
56
What are the two types of specialised cell in the CNS?
- Nerve cell or neurones
| - Neuroglia (astrocytes, oligodendrocytes & microglia)
57
What is gastrulation?
Single layer blastula developing into a triple-laminar disc (gastrula)
58
Define neuraltion
The process of formation of the embryonic nervous system
59
What is the process of neuraltion?
- Ectoderm thicks to form the neural plate in the 3rd week
- Undergoes mitosis to form the mid-line groove (neural goove)
- This deepens and detaches to form the neural tube
- The presumptive neural crest cells run dorso-laterally along the neural groove
60
What cells do the neural crest cells develop to form?
- Sensory (dorsal root) ganglia of the spinal cord and cranial nerves V,VII, IX &X
- Schwann cells
- Pigment cells
- Adrenal medulla
- Bony skull
- Meninges
- Dermis
61
What does the rostral part of the neural tube form in an adult?
The brain (CNS), grows faster than the caudal portion
62
What does the caudal part of the neural tube form in an adult?
The spinal cord
63
What are the 3 primary brain vesicles present by the 5th week of embryonic development?
- Prosencephalon (forebrain)
- Mesencephalon (midbrain)
- Rhombencephalon (hindbrain)
64
What are the secondary brain vesicles which are present by the 7th week of embryonic development?
- Prosencephalon —> Telencephalon & Diencephalon
- Mesencephalon —>
Mesencephalon
- Rhombencephalon —>
Metencephalon & Myelencephalon
65
What does the telencephalon give rise to in the mature brain?
Cerebral hemisphere & lateral ventricles
66
What does the diencephalon give rise to in the mature brain?
Thalamus, hypothalamus & third ventricle
67
What does the mesencephalon give rise to in the mature brain?
Midbrain (colliculi) & aqueduct
68
What does the metencephalon give rise to in the mature brain?
Cerebellum, pons and upper part of 4th ventricle
69
What does the myelencephalon give rise to in the mature brain?
Medulla oblongata & lower part of 4th ventricle
70
When does the neural tube usually close?
At the end of the 4th week
71
What is spina bifida?
Failure of the tube to close in the spinal cord
72
What is anencephalus?
Failure of the tube to close in the cephalic region (brain)
73
What may cause spinal cord abnormalities?
Faulty induction or environmental factors, which act on the neuroepithelial cells
74
When is the eye formed in embryo?
3 weeks
75
When is there cerebral expansion and commissures in embryo?
10 weeks
76
When are the basic structures of the brain established in embryo?
3 months
77
When does myelination occur in embryo?
5 months
78
When has the lobes cerebrum formed in embryo?
7 months
79
When has the gyri and sulci formed in embryo?
9 months
80
When do abnormalities to the CNS tend to occur?
Dependent on time of infection - generally 2nd trimester
81
What are the basic functions of the brainstem?
- Basic vital functions (breathing & heart rate)
| - Delivers basic responses
82
What is the corpus callous?
A huge fibre bundle that connect the left and right hemispheres together
83
Which part of the brain delivers much more complex responses?
The cerebral cortex
84
What percentage of the basic cerebellum contains neurones?
70% - very high percent
85
Which part of the brain does the most complex tasks?
The cerebellum
86
How do all sensorimotor, cognitive and motivational/effect structures connect to the cerebellum?
By re-entrant loops
87
Where does the basic cerebellum receive input from?
The motor cortex, brain stem nuclei and sensory receptors
88
Which part of the brain modulates upper motor neurones?
Basic cerebellum
89
What is the structure of the cortex like?
Very uniform over its entire surface
90
What may damage to the cerebellum do?
Makes many movements inaccurate, slow & uncoordinated
91
Which part of the brain makes sure movement commands are done properly?
The cerebellum - other parts can issue the commands but its the cerebellum which ensures it's done properly
92
Where in the brain is responsible for fine coordinated voluntary movement?
Cerebellum
93
What are the main components of the basal ganglia?
- Dorsal striatum (caudate nucleus & putamen)
- Ventral striatum (nucleus accumbens & olfactory tubercle)
- Globus pallidus (internal and external segment)
- Ventral pallidum
- Substantia nigra
- Subthalamic nucleus
94
What makes up the dorsal striatum?
Caudate nucleus & putamen
95
What makes up the ventral striatum?
Nucleus accumbens and olfactory tubercle
96
What makes up the globus pallidus?
Internal and external segment
97
How does the basal ganglia connect to inputs of the brain?
By recurrent loops
98
What does the basal ganglia do in the sense of the competing systems in the brain?
Selects which one to do out of:
- Emotions
- Cognitions
- Sensorimotor
99
What are the outputs of the basal ganglia like?
Inhibitory & tonically active (slow & continuous)
100
What is the function of the hippocampus?
- Critical for episodic memory
- Essential for the construction of mental images
- Vital role in short term memory
- Important for spatial memory & navigation
101
What is the hippocampus part of?
The limbic system
102
What is anterograde tract tracing?
Transport from neuronal cells bodies to axon terminals
103
What is retrograde tract tracing?
Transport from axonal terminals to neuronal cell bodies
104
How can an increase in neural activity be detected by lumbar puncture?
- Results in the increase in the release of neurotransmitter
- More breakdown product
- Detected in CSF by lumbar puncture
105
How can an increase in neural activity be detected by imaging techniques?
- More active regions require more oxygen
- So require more blood
- Imaging can detect haemodynamic changes
106
What can a EEG detect?
Gives an indication of regional brain activity underlying electrodes
107
What is the basic cellular unit of the nervous system?
Neurones
108
How can neurones be adapted?
They are specialised for different functions
109
What are the basic components of all neurones?
- Dendrites
- Cell body/soma
- Axon
- Presynaptic terminal
110
What are the functions of the neurones?
- Receive information via dendrites which transmit to the cell body (soma)
- Transmit information via axons and action potentials are propagated from the axon hillock
111
What are neurones stained with H&E?
- Haemotoxylin stains the nuclei acids blue
| - Eosin satins the proteins red
112
What can stain myelin?
Luxor fast blue (LFB)
113
What can stain RER in the neurones?
Cresol violet (CV)
114
Define neural plasticity
The basis of learning and memory
115
What is an early marker of Alzheimer's?
The loss of dendritic spines
116
What are the three functional classes that neurones can be divided into?
- Afferent (sensory)
- Efferent (motor)
- Interneurons (within the CNS)
117
What forms the nerves of the PNS?
Groups of afferent and efferent neurone axons together with connective tissue and blood vessels
118
What is a nerve fibre?
A single axon
119
What is a nerve?
A bundle of axons (fibres) bound together by connective tissue
120
Where do afferent neurones convey information to?
From the tissues to organs TOWARDS the CNS
121
What do afferent neurones have at their peripheral ends?
Furthest from the CNS, afferent neurones have sensory receptors
122
What happens at the ends of afferent neurones?
The sensory receptors respond to various physical or chemical changes in their environment by generating electrical signals in the neurone
123
How do the axons of the afferent neurones divide?
- The peripheral process begins where the dendritic branches converge from the receptor ends
- The central process enters the CNS to form junctions with other neurones
124
What is the only part of the afferent neurone which enters the CNS?
The central process. The cell body & long axon (peripheral process) are outside the CNS
125
Where do efferent neurones convey information to?
Away from the CNS to effector cells such as muscle, gland or other cell types
126
Which part of efferent neurones are present within the CNS?
- Cell bodies and dendrites are within the CNS
| - The axons extend out to the periphery
127
What is the function of interneurones?
Connect neurones within the CNS - form the majority of neurones
128
Which parts of the interneurones lie within the CNS?
They lie entirely within the CNS
129
What do sheaths of myelin usually consist of?
20-200 layers of highly modified plasma membrane wrapped around the axon by a nearby supporting cell
130
What does the myelin compromise of?
70% lipid & 30% protein
131
What are the myelin-forming cells of the CNS?
Oligodendrocytes - each one of these may branch to form meylin on as many as 40 axons
132
What are the myelin-forming cells of the PNS?
Schwann cells - they form individual myelin sheaths surrounding segments at regular intervals along the axons
133
What are nodes of Ranvier?
The spaces between adjacent sections of myelin where the axons' plasma membrane is exposed to extracellular fluid
134
What is a function of myelin?
Increases the speed of conduction along the axons
135
Where are myelinated axons usually found?
In the somatic nerves - they are thicker
136
Where are unmyelinated axons usually found?
In the post-ganglionic autonomic fibres, fine sensory fibres, olfactory neurones and interneurones
137
What are the two cell types in the CNS?
Neurones and glial cells
138
What is the function of glial cells?
Surround the cell body, axon and dendrites of the neurones and provide them with physical and metabolic support
139
What are the 5 types of glial cells?
- Oligodendrocytes
- Schwann cells
- Astrocytes
- Microglia
- Ependymal cells
140
What is the function of oligodendrocytes?
- Glial cells of the CNS
- Myelinating cells for rapid nerve conduction
- Provides metabolic support for axons and transports metabolic products directly into axons
- Myelinate multiple axons
141
What is the function of Schwann cells?
- Glial cells of the PNS
- Myelinating cells
- Myelinate single axons
142
What is the function of astrocytes?
Help regulate the composition of the extracellular fluid in the CNS by removing K ions and neurotransmitters around synapses
143
What is the astrocytes function with glutamate?
Astrocytes take it up, covert it into glutamine and release it, then neurones can take it up ad convert it back to glutamate for reuse
144
What is the astrocytes function with the formation of tight junctions?
- They stimulate this between the walls of the capillaries found in the CNS - this forms the blood-brain barrier
- This is done by foot processes closely applied around capillaries
145
How do astrocytes sustain the neurones metabolically?
By providing glucose and removing ammonia
146
What is the structure of astrocytes?
Star-like cells
147
What are the most numerous glial cells in the CNS?
Astrocytes
148
Where are protoplasmic astrocytes found?
In grey matter
149
Where are fibrous astrocytes found?
In white matter
150
What are radial glia?
Crucial in guiding developing neurones - these are only developmental and aren't found in the adult brain
151
What are Muller glia?
Specialised radial glia of the retina
152
What are Bergmann glia?
Found in the cerebellum, support Purkinje cell dendrites and synapses
153
What is the structure of microglia?
Specialised macrophage-like cells that perform immune functions in the CNS
154
What are microglia derived from?
Progenitors that migrate into the CNS from the periphery
155
Which glial cell is proliferative at injury?
Microglia
156
What is the structure of microglia in the cortical grey matter?
They are more ramified (branched)
157
Which glial cell is phagocytotic?
Microglia
158
Which glial cells contributes to synaptic plasticity?
Microglia
159
Where are ependymal cells found?
Line the fluid-filled cavities within the brain (ventricles) and spinal cord
160
What is the structure of ependymal cells?
Have cilia, microvilli and desmosomes
161
What are the functions of the ependymal cells?
- Regulate the production and flow of CSF
| - Provides a barrier between CSF and brain
162
What is the blood-brain barrier formed by?
Endothelial cells, pericytes and astrocytes
163
What are pericytes?
Contractile cells that wrap around the endothelial cells of capillaries and venules
164
What are the features of the blood-brain barrier?
- Endothelial tight junctions
- Astrocyte end feet
- Pericytes
- Continuous basement membrane (lacks fenestrations)
- Requires specific transported for glucose, essential ions etc.
165
What are circumventrular organs?
Parts of the brain which lack the blood-brain barrier e.g. posterior pituitary
166
Why may some parts of the brain lack the blood-brain barrier?
Need to be in contact with the blood for a sensory role to monitor
167
Where does the CSF circulate?
- In the subarachnoid space (around the brain and spinal cord)
- Within the ventricles
168
What is the main function of CSF?
Offers protection by cushioning brain from gentle movements
169
What are the four ventricles of the brain?
- Lateral (paired)
- III
- IV
170
How do ventricles and subarachnoid spaces connect?
Via cisterns
171
What is the normal volume of CSF?
120ml
172
What is the appearance/structure of CSF?
A clear, colourless liquid which contains: protein, urea, glucose & salts
173
Where is CSF mainly produced?
By the ependymal cells in the choroid plexuses of the lateral ventricles
174
What is the choroid plexus formed from and what does it form around?
- Formed from modified ependymal cells
| - They from around a network of capillaries, large surface area
175
How is CSF absorbed?
By arachnoid granulations (villi) e.g. in the superior sagittal sinus
176
What is hydrocephalus and what is it caused by?
- Abnormal accumulation of CSF in ventricular system
| - Often due to a blocked cerebral aqueduct
177
What does hydrocephalus cause in adults?
Leads to a build up of pressure which can damage brain tissue as skull is hard in adults
178
What is the resting membrane potential?
When the inside of the cell of the neurone is negatively charged compared to the outside
179
What is the typical resting potential?
-70mV
180
How is the resting membrane potential met?
- The Na/K ATPase pump in the membrane develop conc. gradients by pumping 3 Na out for every 2 K in (by active transport)
- Na is concentrated outside axon while K is inside
- Very few Na gated channels are open, meaning small diffusion of Na back in
- However, leak K channels are open, resulting in K diffusing out the axon, making inside more negative than outside
181
What is the process of the changes in action potential?
- A neurotransmitter binds to specific ligand-gated ion channels, on post synaptic membrane, Na ions enter neurone
- This inflow allows the inside of the neurone to become more +ve - initial depolarisation
- This stimulates the opening of some voltage-gated Na channels, resulting in further entry & depolarisation
- When the membrane reaches the critical threshold potential, depolarisation becomes a +ve feedback loop of Na entry
- At around 30mV, the channels are closed and the influx stops
- The K diffuses out the neurone by voltage gated K channels down a conc. gradient, causing repolarisation
- Once it reaches a -ve potential, it causes the channels to close
182
What is the critical threshold potential?
Around -55mV
183
When does an absolute refractory period occur?
During the period when the voltage-gated Na+ channels are either already open or have proceeded to their inactivated state after during the first action potential
184
What follows the absolute refractory period?
The relative refractory period
185
What happens in the relative refractory period?
Where a second action potential can be produced - but only if the stimulus strength is considerably greater than usual
186
What is the purpose of the refractory period?
- Limit the number of action potentials an excitable membrane can produce in a given period of time
- They allow action potentials to be separated so that individual electrical signals are able to pass down the axon
187
What causes current to flow in the neurone membrane?
- The generation of an action potential at particular segment on the neurone
- This is due to the difference in potential between the dopalirsed membrane and adjacent segements at resting potential
188
What does the propagation speeds along a membrane depend on?
- Fibre diameter
| - Myelination
189
How does the fibre diameter determine the speed of transport along the membrane?
The larger the diameter, the faster the action potential propagates
190
How does myelination determine the speed of transport along the membrane?
Increases propagation speeds, as action potentials only occur at the nodes of Ranvier
191
What is saltatory conduction?
When action potentials appear to jump from one node to the next as they propagate along a myelinated fibre
192
What is a synapse?
An anatomically specialised junction between two neurones at which the electrical activity in a presynaptic neurone influences the electrical activity of a post synaptic neurone
193
What happens at an excitatory synapse?
The membrane potential of a postsynaptic neurone is brought closer to threshold
194
What happens at an inhibitory synapse?
The membrane potential of a postsynaptic neurone is either driven further from threshold or stabilised at its resting potential
195
What are the two types of synapse?
Electrical and chemical
196
How are the presynaptic and postsynaptic cells joined in an electrical synapse?
By gap junctions
197
How does conduction occur in a electrical synapse?
- Local currents arriving from action potentials flow directly across the junction through the connecting channels
- This depolarises the membrane of the second neurone to threshold
198
Is the communication at electrical synapses quick?
Extremely rapid
199
Which synapses allow for synchronised transmission?
Electrical
200
Where are electrical synapses found?
In brainstem neurones e.g. breathing & hypothalamus, hormone secretion
201
How are the presynaptic and postsynaptic neurones joined in a chemical synapse?
Joined by the synaptic cleft
202
How is direct propagation prevented in a chemical synapse?
By the synaptic cleft
203
How does the presynaptic vesicle look like as it has received an action potential?
Ends in a slight swelling at the axon terminal, which holds the synaptic vesicles
204
How are signals transmitted across the synaptic cleft in a chemical synapse?
By a chemical messenger - neurotransmitter - which is released by the presynaptic axon terminal
205
What is a cotransmitter?
When there is more than one neurotransmitter simultaneously released from an axon
206
What are chemical synapses covered by and why is this important?
- Covered by astrocytes (glial cells)
| - Essential for the reuptake of excess neurotransmitter
207
What is the process of neurotransmitter release?
- Ca ion channels open when an action potential reaches the pre-synaptic terminal
• Ca ions cause vesicles to move to release sites and fuse with the presynaptic cell membrane and discharge their contents
• Neurotransmitter diffuses across the synaptic cleft and attaches to receptor sites on the post-synaptic membrane
208
What does a higher concentration of neurotransmitter release mean?
The more likely there will be binding to receptor and thus action potential propagation
209
What are the 5 processes of synaptic transmission?
- Manufacture
- Storage
- Release
- Interact with post-synaptic receptors
- Inactivation
210
On what system do drugs of the brain work on?
The 5 processes of synaptic transmission
211
What is the neurotransmitter used in the brain & neuromuscular junction?
Acetylcholine
212
What are the 2 main acetylcholine receptors?
Muscarinic & nicotinic
213
What happens once acetylcholine has been bound to the post-synaptic receptor?
- The enzyme, acetylcholine esterase, breaks it down into choline & acetyl
- The choline can then be reabsorbed by the presynaptic neurone to make more acetylcholine
214
What is the effect when neurotransmitters bind to excitatory channels?
Depolarisation will occur - many Na leave and few K enter
215
What is the effect when neurotransmitters bind the inhibitory channels?
Hyperpolarisation will occur - many K leave OR many Cl enter
216
What happens once a neurotransmitter has bound?
Results in propagation of action potentials (if excitatory)
217
What is temporal summation?
Input signals arrive from the sam presynaptic cell at different times. These summate since there are a greater number of open ion channels and thus a greater flow of positive ions
218
What is spatial summation?
Where two inputs occur at different locations in the postsynaptic neurone
219
What is the function of spatial and temporal summation?
Increases the inward flow of +ve ions and bring the postsynaptic membrane to threshold so action potentials are initiated
220
When are unbound neurotransmitters removed from the synaptic cleft?
- They are actively transported back into the presynaptic axon terminal or by near glial cells
- Diffuse away from receptor site
- Are enzymatically transformed into inactive substances, some are transported back into the presynaptic neurone for reuse
221
What are fast neurotransmitters?
Short lasting effects, tend to be involved in rapid communication
222
Give 3 examples of fast neurotransmitters
- Acetylcholine
- Glutamate (excitatory)
- GABA (inhibitory)
223
What are neuromodulators?
- Cause change in synaptic membrane that last longer times
| - Associated with slower events such as learning, development, motivational states
224
Give 3 examples of neuromodulators
- Dopamine
- Noradrenaline
- Serotonin
225
How do local anaesthetics work?
- Interput axonal transmission
| - They block sodium channels preventing neurones from depolarising - no action potential
226
What is the major neurotransmitter of the PNS at the neuromuscular junction?
Acetylcholine (also used in brain & spinal cord)
227
What are cholinergic neurones?
Neurones which release ACh
228
What is acetylcholine synthesise from?
Choline (common nutrient in food) & acetyl choline A, stored in synaptic vesicles
229
What is the function of acetylcholinesterase?
Rapidly destroys ACh, releasing choline & acetate. The choline is transported back to the presynaptic neurone to be reused
230
What are the two general types of ACh receptors?
Nicotinic & muscarinic
231
What is the receptor in a nicotinic receptor?
An ion channel
232
What do nicotinic receptors respond too?
ACh & nicotine
233
Where are nicotinic receptors found?
The neuromuscular junction
234
Why are nicotinic receptors important in the brain?
They are important in cognitive functions and behaviour
235
Why are tobacco products so addictive?
Due to the presence of nicotinic receptors on presynaptic terminals in reward pathways of the brain
236
What do muscarinic receptors respond too?
ACh and the mushroom poison muscarine
237
Where are muscarinic receptors present?
In the brain and at junctions where a major division of the PNS innervates peripheral glands & organs
238
Where is noradrenaline the main neurotransmitter?
In the peripheral heart and central nervous systems
239
How is noradrenaline affected by antidepressants?
- Blocks the reuptake of noradrenaline
| - Increases the amount of noradrenaline by inhibiting the enzyme which breaks it down
240
How do stimulates affect noradrenaline?
Increases release and blocks uptake
241
Which neurotransmitter is important in the basal ganglia?
Dopamine
242
How is dopamine affected by antipsychotic drugs?
Blocks receptor so other neurotransmitter can't activate receptor
243
How is dopamine affected by stimulants?
Increases release and blocks reuptake
244
How is dopamine affected by anti-parkinsons drugs?
Increases dopamine manufacture
245
What is the effect of serotonin?
Has an excitatory effect on pathways that mediate sensations
246
How is serotonin affected by antidepressants?
Results in an increase in conc. of synaptic serotonin
247
How is serotonin affected by ecstasy?
Neurotoxic - destroys the terminal of axons
248
What is the main excitatory neurotransmitter?
Glutamate
249
What is the main inhibitory neurotransmitter?
GABA
250
What is the normal hearing range?
20 - 20,000 Hz
251
What is the function of the outer ear?
Helps collect sound
252
What is the function of the middle ear?
Transmission of sound
253
What is the function of the inner ear?
The conversion of sound into neural impulses
254
How is sound transmitted in the external ear?
- Enters through the pinna/auricle (exterior of ear)
- Enters ear via external auditory canal
- Makes its way through the canal to the tympanic membrane
- As air molecules push against the membrane, it causes the tympanic membrane to vibrate at the same frequency
255
What can help amplify and direct sound in the outer ear?
The shape of the pinna and external auditory canal
256
What is the pattern of vibration of the tympanic membrane at different frequencies?
- Vibrates slowly to low frequency sounds
| - Vibrates very rapidly to high frequency sounds
257
What marks the end of the external ear and marks the start of the middle ear?
The tympanic membrane
258
What is the middle ear?
An air-filled cavity in the temporal bone of the skull
259
What is sensation of the middle ear provided by?
The glossopharyngeal nerve (CN9)
260
What are the pressures in the external auditory canal and middle ear canal?
Normally equal to atmospheric pressure
261
How is the middle ear exposed to atmospheric pressure?
By the Eustachian tube
262
How is the middle ear connected to the pharynx?
By the Eustachian tube
263
How does the Eustachian tube open into the pharynx?
Through a slit-like opening which is normally closed
264
What causes the opening of the Eustachian tube into the pharynx to open?
Muscle movements e.g. swallowing, yawning or sneezing
265
What causes a difference in pressure between the middle and external ear?
Changes in altitude
266
What happens once the pressure outside the ear and in the external auditory meatus change?
- The middle ear initially remains constant as the Eustachian tube is closed
- The constant pressure can stretch the tympanic membrane to stretch
267
How can the pain of the tympanic membrane due to pressure changes be relived?
- By yawning/swallowing
- Allows the opening of the Eustachian tube
- Allows pressure in the middle ear to equilibrate with the external atmospheric pressure
268
How are the vibrations of the tympanic membrane transmitted to the inner ear?
Through a moveable chain of three bones (ossicles)
269
What is the order of the ossicles which the vibrations have to travel through?
Malleus, incus and stapes
270
What is the joint between the ossicle bones?
Synovial
271
What are the functions of the ossicles?
To couple the total vibrations of the tympanic membrane to the oval window
272
What is the oval window?
A membrane covered opening between the middle and inner ear
273
Why is it useful that the oval window is much smaller than the tympanic membrane?
To ensure a greater force per area, which is needed to adequately transmit the sound energy through the fluid filled cochlea
274
How can the amount of energy transmitted to the inner ear be lessened?
By the contraction of two small muscles of the middle ear (the tensor tympani and stapedius)
275
Which nerve innervates the contraction of tensor tympani?
The mandibular branch of trigeminal nerve (CN5)
276
Which nerve innervates the contraction of stapedius?
Facial nerve (CN7)
277
Where does the tensor tympani muscle attach to?
The malleus
278
What does contraction of tensor tympani do?
Dampens the movement of malleus
279
What does the stapedius attach to?
The stapes
280
What do tensor tympani and stapedius reflexively act to and why?
- Continuous loud noise
| - To protect the delicate receptor apparatus in the inner ear
281
What can't the sensory tympani and stapedius protect against?
Sudden intermittent loud sounds
282
What is the inner ear?
The cochlea
283
What is the organ of hearing?
Cochlea
284
What is the cochlea?
A spiral-shaped, fluid filled space in the temporal bone
285
How is the cochlea divided?
Almost completely lengthwise by a membranous tube (cochlear duct)
286
Where are the sensory receptors of the auditory system found?
The cochlear duct of the cochlea
287
What is the cochlea duct filled with?
Endolymph - a compartment of extracellular fluid containing high K and low Na
288
What is the structure of endolymph similar to?
Intracellular fluid
289
What is either side of the cochlear duct filled with?
Perilymph
290
What is the structure of perilymph similar to?
Cerebrospinal fluid (CSF)
291
Where is the Scala vestibuli located?
- Above the cochlear duct
- Begins at the oval ducts
- Forms the entrance to the inner ear from the oval window
292
Where is the Scala tympani located?
- Below the cochlear duct
| - Connects to the middle ear via a second-membrane covered opening, the round window
293
At which point do the Scala vestibuli. and tympani become continuous?
At the far end of the cochlear duct (the helicotrema)
294
What do sound waves from the external acoustic channel cause the tympanic membrane to do?
Move in and out which in turn is transmitted to ossicles, which transmit this to the oval window
295
What do the sound waves at the oval window cause?
Causes the oval window to move in and out of the Scala vestibuli. This movement causes waves of pressure at the Scala vestibuli
296
What do the waves of pressure in the Scala vestibuli cause?
- They are transmitted across the cochlear duct with some being transmitted toward the helicotrema
- Goes into the Scala tympani where pressure is relieved by the movements of the membrane of the round window
297
What is the side of the cochlear duct closest to the Scala tympani formed by and what sits in it?
- Formed by the basilar membrane
| - Organ of corti sits inside it
298
What does the organ of Corti contain?
- The ear's sensitive receptor cells
| - Pressure difference across the duct membrane to vibrate
299
What is the structure of the base of the basilar membrane of the ear and why is this significant?
- Is narrow & stiff
| - Sensitive to high frequencies
300
What is the structure of the apex of the basilar membrane of the ear and why is this important?
- Is wider & less stiff
| - Sensitive to low frequencies
301
What are the hair cells of the organ of corti?
The receptor cells of the organ of corti
302
What are the functions of tue hair cells of the organ of Corti?
They are mechanoreceptors which have hair-like stereo-cilia protruding from one end
303
What can damage the sterocilia of hair cells?
Antibiotics
304
What is the anatomical groups of the hair cells of the Organ of Corti?
- A single row of inner hair cells
| - 4-5 rows of outer hair cells
305
Where do the stereocilia of the inner hair cells extend into and what are their functions?
- The endolymph fluid
| - They convert pressure waves caused by the movement of fluid in the cochlear duct into receptor potentials
306
Where do the stereocilia of the outer hair cells extend into and what are their functions?
- Embedded in the overlying tectorial membrane
| - Mechanically alter its movement to sharpen frequency tuning at each point along the basilar membrane
307
What is the tectorial membrane and what is its function?
- It overlies the organ of Corti in the ear
- As the pressure waves displace the basilar membrane, the hair cells move in relation to the stationary tectorial membrane resulting in the bending of the stereocilia
308
What happens when the stereo cilia bends towards the tallest member of the bundle?
- Fibrous connections pull open the mechanically gated K+ channels
- Results in an influx of K+ from the surrounding endolymph
- Depolarises the membranes
309
What happens after the membrane which holds the stereocilia (hair cell) is depolarised?
- Triggers the opening of voltage-gated Ca ions
| - Triggers the release of neurotransmitter
310
What happens when the stereocilia are bent in the opposite way to 'usual'?
This closes the channels (K) which allows the cell to rapidly repolarise
311
What is the neurotransmitter of the hair cells?
- Glutamate
| - This binds to and activates protein-binding sites on the terminals of the afferent neurones
312
What happens as the sound waves vibrate the basilar membrane?
- The stereocilia are bent back and forth
- The membrane potential of the hair cells rapidly oscillates
- Bursts of glutamate are released on the afferent neurones
313
What do the bursts of glutamate from the sound waves vibrating on the basilar membrane do?
- Generation of action potentials in the neurones
| - The axons join the cochlear branch of the vestibulocochlear nerve (CN8)
314
What does a greater energy (loudness) of a sound wave cause?
A greater frequency of action potentials generated in the afferent nerve fibres
315
Why do each hair cell respond to a limited range of sound frequencies?
- Due to its position on the basilar membrane
| - One particular frequency stimulates it the most strongly
316
Where do cochlear nerve fibres make dendritic contact with the hair cells of the organ of Corti?
- Within the cochlear duct
| - The cell bodies of these fibres lie within the cochlea and are collectively called the spiral ganglion
317
What are the spiral ganglion?
The cell bodies of the cochlear nerve which lie within the cochlea
318
At what level does the cochlear nerve join the brainstem?
At the level of the rostral medulla
319
What happens to the fibre of the cochlear nerve once they have met the rostral medulla?
- They bifurcate (split into 2)
| - End in the dorsal and ventral cochlear nuclei
320
Where do the dorsal and ventral cochlear nuclei lie close too?
The inferior cerebellar peduncle
321
What happens to the cochlear nerve fibres after the cochlear nuclei?
- The second-order neurones ascend into the pons
| - The fibres travel to the superior olivary nucleus
322
Where does the superior olivary nucleus travel to?
- Fibres leave the brainstem in the vestibulocochlear nerve and end in the organ of corti
- Some also travel to the inferior colliculus of the midbrain
323
What is the function of the fibres of the superior olivary nucleus in the ear?
- Have an inhibitor function
- Adjust transmission of auditory information through the cochlear nerve by mediating contractions of the tensor tympani and stapedius in response to loud noises
324
What happens to the superior olivary nucleus fibres once they are in the inferior colliculus of the midbrain?
The inferior brachium (nerve fibre) carries the auditory information to the medial geniculate body of the thalamus
325
Where do the nerve fibres of the superior olivary nucleus travel to from the medial geniculate body of the thalamus?
- Travel through the internal capsule
| - Goes to the primary auditory cortex of the temporal lobe
326
Where is the primary auditory cortex located?
Situated on the dorsal surface of the superior temporal gyrus
327
What is the region of the temporal lobe which surrounds the primary auditory cortex?
Wernicke's area
328
What is the function of Wernicke's area?
- Where auditory information is interpreted and understood
| - Also important in the processing of language in the brain
329
Where is Wernicke's area located?
The superior temporal lobe
330
What will happen in a patient if Wernicke's area is damaged?
- Unable to understand questions
| - Speech will be incomprehensible
331
Summarise the path of the cochlear branch of the vestibulocochlear nerve (CN8)
- Cochlear nuclei
- Superior olivary nucleus
- Inferior colliculus
- Medial geniculate body - via the inferior brachium (nerve)
- Primary auditory cortex, in Wernicke's area
332
Which parts of the colliculus and geniculate body are used for auditory information?
- Inferior colliculus
- Medial geniculate body
- I'MAuditory (way to remember)
333
Which parts of the colliculus and geniculate body are used for auditory information?
- Superior colliculus
| - Lateral geniculate body
334
What is the simplified pathway of chords tympani (branch of facial nerve CN7)?
Conveys taste information from the tongue and runs through the middle ear to carry taste messages to the brain
335
How does inflammation of the facial nerve (CN7) potentially cause pain behind the ear?
It exits the cranial cavity into the internal acoustic meatus behind the cochlea
336
What type of cell can also be found in the vestibular apparatus of the inner ear?
Hair cells
337
What is the vestibular apparatus?
A connected series of endolymph-filled membranous tubes that also connect with the cochlear duct
338
What is the function of the hair cells in the vestibular apparatus of the inner ear?
Detect changes in the motion and position of the head by a stereocilia transaction mechanism
339
What does the vestibule apparatus consist of?
- Three membranous semicircular canals
| - Two sack-like swellings (utricle & saccule)
340
Where does the vestibule apparatus lie?
In the temporal bone on the side of the head
341
What is the function of the semi-circular canals?
- Detect angular acceleration during the rotation of the head along three perpendicular axes
342
When do the semicircular canals detect angular acceleration?
- When nodding the head up and down
- Shaking the head from side to side
- Tipping the head so the the ear touches the shoulder
343
What do the receptor cells of the semicircular canals contain?
Stereocilia
344
Where are the stereocilia encapsulated in the semicircular canals?
- Within the capula, a gelatinous mass
| - This extends across the lumen of each semicircular canal at the ampulla
345
Wha happens to the semicircular canal when the head moves?
- The attached bodies of the hair cells all move with it
346
What happens to the endolymph (fluid) filling the duct when the head moves?
- It is not attached to the skull
| - Due to inertia (staying in the same place), remains in its original position
347
What happens to the ampulla when the head moves and what does this cause?
- The moving ampulla is pushed against the stationary fluid
- This causes bending of the stereocilia
- This causes an alteration in the rate of release of glutamate from the hair cells
348
What happens to glutamate after it is released from the hair cells after the movement of the head?
- Crosses the synapse and activates neurones associated with the hair cells
- This initiates the propagation of action potential towards the brain
349
What determines the direction the stereocilia are bent and which hair cells are stimulated?
The speed and magnitude of rotational head movements
350
What can vary the glutamate release from the hair cells compared to at rest?
- At rest glutamate is released
- An increase in release occurs if there is bending of the stereocilia towards the largest hair
- A decrease in release occurs if there is being of the stereocilia away from the largest hair
351
How are hair cells of the ear depolarised?
- Has one direction of maximum neurotransmitter release
- When stereocilia are bent in that direction, the receptor cell depolarises
- When the stereocilia are bent in the opposite direction, the cell hyperpolarises
352
What happens to endolymph when the head continuously rotates at a steady velocity?
- The endolymph begins to move at the same rate at the rest of the head
- Stereocilia slowly return to resting position
- Hair cells are only stimulated during acceleration or deceleration
353
What are the otolithic organs?
The utricle and saccule
354
What is the function of the utricle and saccule?
Provide information about linear acceleration of the head, and about the changes in head position in relation to gravity
355
What is the position of the hair cells in the utricle and what do they respond to?
- Point nearly straight up when standing
- Respond when the head is tipped away from the horizontal plane
- Also respond to linear accelerations in the horizontal plane
356
What is the position of the hair cells of the saccule and what do they respond to?
- Project at right angles to those of the utricle
- They respond when moving away from lying to a standing position
- They also respond to vertical accelerations (e.g. jumping on trampoline)
357
What are stereocilia projecting from the hair cells covered by?
A gelatinous substance in which tiny stones (otoliths) are embedded
358
Where do the stereocilia project in the vestibular system?
The otolithic membrane
359
What are otoliths?
Calcium carbonate crystals which make the gelatinous substance heavier than that of the surrounding endolymph
360
What response does the gelatinous otolithic material do in response to a change in position?
- Moves according to the forces of gravity
- Pulls against the hair cells so that the stereocilia on the hair cells bend
- The receptor cells are stimulated
- The action potential is propagated via the vestibular nerve (branch of vestibulocochlear nerve - CN8)
361
What are the uses of vestibular information?
- Control of eye muscles so if head moves, the eyes can remain fixed
- Reflex mechanisms of maintaining upright posture and balance
- Conscious awareness of the position & acceleration of the body (proprioception)
362
What is proprioception?
- Conscious awareness of the position
- Acceleration of the body
- Perception of the space surrounding the body
- Memory of spatial information
363
Where do the central processes of the vestibular fibres mostly end?
In the vestibular nuclei of the rostral medulla
364
What are the three coats of the eye?
- Outer
- Middle (uvea)
- Inner
365
What are present in the outer layers of the eye?
Cornea & sclera
366
What are the two main functions of the cornea?
- Transmission of light
| - Refraction
367
Name two things that the cornea must be
- Transparent
| - Have a smooth spherical surface
368
What is significant of the dehydrate endothelium of the cornea?
Doesn't repair
369
What is the innermost layer of the cornea?
Dehydrate endothelium
370
What is the function of the dehydrate endothelium of the cornea?
Maintain corneal clarity by plumping water out (since water molecules alter the regular spacing between collagen fibres & cause opacity)
371
What is significant about the surface epithelium of the cornea?
Capable of repair - many layers that slough off and are constantly regenerated
372
What is the outer layer of the eye (and cornea)?
The surface epithelium
373
What is the sclera of the eye?
Forms the white capsule around the eye, except at its anterior surface where it is specialised into the clear cornea
374
What is the function of the sclera?
- Offers protection; formed of a tough outer layer of collagen
- Serves as an insertion point for the external muscles of the eye
375
Which part of the eye is a continuation of the dura matter and cornea?
The sclera
376
What does the middle (uvea) of the eye consist of?
- Iris
- Ciliary body
- Choroid
377
Which part of the eye is a specialised section of choroid?
Iris
378
What is the function of the iris?
Contains & controls the size of the pupil - which lets light in
379
What makes the pupil smaller and what system does so?
- Sphincter muscles (circular fibres)
| - Parasympathetic
380
What makes the pupil larger and what system does so?
- Dilator muscles (radial fibres)
| - Sympathetic
381
Which part of the eye is coloured?
Iris
382
What is the epithelium of the ciliary body of the eye and what does it produce?
- Glandular epithelium
| - Produces aqueous humour & nutrients for cornea/lens
383
What is aqueous humour?
- Mainly water and electrolytes
- Located in the anterior chamber
- Important in maintaining intraocular pressure
384
What is the ciliary body made of?
Smooth muscle
385
What is the function of the ciliary body?
Controls accommodation; the adjustment of the lens in the eye so that clear images of objects at different distances are formed on the retina
386
Where does the ciliary body receive innervation from?
The parasympathetic system
387
What is the choroid important for?
The nutrition of the outer retina (photoreceptors)
388
What are the components of the inner of the eye?
- Retina
| - Tear film
