Neuro Flashcards
1
Q
What is the difference between white and grey matter?
A
White matter contains myelinated axons, grey matter contains cell bodies and no myelin sheaths
2
Q
What is the function of oligodendrocytes?
A
Myelinating axons in the brain
3
Q
Define tracts
A
Location of a pathway
4
Q
Define funiculi
A
Rope or cord
5
Q
Define fasiculi
A
Bundle
6
Q
Define capsule
A
Sheet of white matter fibres that border a nucleus of grey matter
7
Q
Define Column
A
Longitudinally running fibres seperated by other structures
8
Q
Define cortex
A
Laminated grey matter on the outside of the brain
9
Q
Define Nuclei
A
Collection of nerve bodies within the CNS
10
Q
Define Ganglia
A
Collection of nerve cell bodies outside the CNS
11
Q
Define afferents
A
Axons taking information towards the CNS
12
Q
Define efferents
A
Axons taking information to another site from the CNS
13
Q
Define reticular
A
‘Netlike’, where grey and white matter mix
14
Q
Define ipsilateral
A
On the same side
15
Q
Define contralateral
A
On the opposite side
16
Q
Define rostral
A
Towards the nose (Anterior)
17
Q
Define caudal
A
Towards tail (posterior)
18
Q
What are sulci?
A
Grooves
19
Q
What are gyri?
A
Ridges
20
Q
What are the functions of the frontal lobe?
A
Voluntary movement on opposite side of the body. Frontal lobe of dominant hemisphere controls speech (Broca’s area), and writing.
Intellectual functioning, thought processes, reasoning and memory
21
Q
What are the functions of the parietal lobe?
A
Recieves and interprets sensations, including pain, touch, pressure, size and shape, and body-part awareness (proprioception)
22
Q
What are the functions of the temporal lobe?
A
Understanding the spoken word (wernicke’s- understanding), sounds as well as memory and emotion
23
Q
What are the functions of the occipital lobe?
A
Understanding visual images and meaning of written words
24
Q
What are some of the grey matter structures?
A
Thalamus, hypothalamus, and basal ganglia
25
What is the role of the thalamus?
Relay centre direction inputs to cortical areas
26
What is the role of the hypothalamus?
Links endocrine system to brain and involved in homeostasis
27
What is the striatum made of?
Caudate and putamen
28
What are the basal ganglia?
Caudate nucleus, putamen and globus pallidus
29
What is the lentiform nucleus made of?
Globus and putamen
30
What is the role of the basal ganglia?
Motor control, cognition and non-motor behaviour
31
What is the role of the cerebellum?
Co-ordinates movement and balance
32
How is the cerebellum attached to the brain stem?
Via three peduncles- midbrain, pons, medulla
33
How is the cerebellum seperated from the dorsal brainstem?
Via the 4th ventricle which forms part of its roof
34
What is the cerebeullum made up of?
Folded cortex, white matter and deep inner nuclei
35
What do cerebellar injuries result in?
Movements that are slow and uncoordinated
36
What is asynergia?
The loss of coordination of motor movement
37
What is an intention tremor?
Movement tremors
38
What is hypotonia?
Weak muscles
39
What is nystagmus?
Abnormal eye movement
40
What are the functions of the brainstem?
```
Special senses
Sensory and motor for head and neck via cranial nerves
Autonomic regulation of the body
Regulates consciousness
Pathway between brain and spinal cord
```
41
What is the mid brain formed from?
```
Tectum (superior and inferior colliculi)
Cerebral peduncle (tegmentum and crus cerebri)
```
42
What does the mid-brain surround?
The cerebral aqueduct
43
What are the two types of specialised cell found in the CNS?
Neurones (many types e.g. pyramidal, stellate, golgi, purkinje)
Neuroglia (astrocytes, olgiodendrocytes and microglia)
44
What is the corpus callosum?
A huge fibre bundle that connects the left and right hemispheres together
45
What percentage of cells in the cerebellum are neurones?
70%
46
What are the roles of the cerebellum?
All sensorimotor, cognitive and motivational/effective structures connect to the cerebellum via re-entrant loops
Recieves input from motor cortex, brain stem nuclei and sensory receptors
Modulates upper motor neurones
Responsible for fine coordinated voluntary movement
47
What can damage to the cerebellum do to movement?
Make it inaccurate, slow and uncoordinated
48
What are the main components of the basal ganglia?
Dorsal striatum- caudate nucleus and putamen
Ventral striatum- nucleus accumbens and olfactory tubercle
Globus pallidus- internal and external segment
Ventral pallidum
Substantia nigra
Subthalamic nucleus
49
What are the competing systems in the brain?
Emotions
Cognitions
Sensorimotor
50
Which area of the brain selects which of the competing systems should be used?
The basal ganglia
51
How is the basal ganglia connected to inputs of the brain?
Via recurrent loops
52
What are the outputs of the basal ganglia like?
Inhibitory and tonically active (slow and continuous)
53
What system is the hippocampus part of?
The limbic system
54
What are the roles of the hippocampus?
Episodic memory
Construction of mental images
Short term memory
Spatial memory and navigation
55
What is anterograde?
Transport from neuronal cell bodies to axon terminals
56
What is retrograde?
Transport from axonal terminals to neuronal cell bodies
57
What are class A experiments?
Diagnosis
Some behavioural, physiological or pharmacological variable is manipulated and the consequent effects on brain activity/ structure are measured
58
What are the issues with class A experiments?
No adequate controls to ensure that the observed changes are produced only by the specific manipulation
Are measured changes in brain specific to the claimed region
59
What are type B experiments?
Treatment
Some aspect of the brain structure (lesion) or activity (stimulation/inhibition) is manipulated and the consequent effect on behaviour/physiology/endocrinology is measured
60
What are the issues with type B experiments?
Are the effects of the brain manipulation specific to the claimed changes
Is the brain manipulation specific to the intended neural structures
61
What does EEG stand for?
Electroencephalogram
62
How does an EEG detect brain activity?
It gives an indication of regional brain activity underlying electrodes. It is sensitive to activity in the temporal regions but less sensitive to those in spatial regions. EEG is good at detecting signs of epilepsy
63
How does a lumbar puncture detect brain activity?
Increases in neural activity results in the increase in the release of neurotransmitters and their associated breakdown products. This can be detected in the CSF via a lumbar puncture
64
What are the basic components of all neurons?
Dendrites
Cell body/soma
Axon
Presynaptic terminal
65
How do neurons stain under H&E?
The haemotoxylin stains the nucleic acids blue and the eosin stains the proteins red
66
What can be used to stain myelin?
Luxor fast blue
67
What can be used to stain nissI?
Cresol violet
68
What is the early marker of Alzheimers'?
The loss of dendritic spines
69
What are the three functional classes of neurons?
Afferent (sensory), efferent (motor) and interneurons (within the CNS)
70
What neurons are the nerves of the PNS formed from?
Groups of afferent and efferent neurone axons together with connective tissue and blood vessels
71
In which direction do afferent neurons convey information?
From tissues and organs towards the CNS
72
Where are afferent neuron's sensory receptors found?
At their peripheral ends (fartherst from the CNS)
73
How do the sensory receptors of afferent neurons work?
They respond to various physical or chemical changes in their environment by generating electrical signals in the neurone
74
What are the two branches of the afferent axon?
The peripheral process and the central process
75
Where does the peripheral process begin?
Where the dendritic branches converge from the receptor endings
76
Where does the central process run?
It enters the CNS to form junctions with other neurons
77
In which direction do efferent neurons convey information?
Away from the CNS to effector cells such as muscle gland or other cell types
78
Where are cell bodies and dendrites of efferent neurons found?
Within the CNS
79
Where are the axons of the efferent neurons found?
Extending out towards the periphery
80
What is the role of the interneurons?
To connect neurons within the CNS
81
Where are the interneurons found?
Within the CNS
82
What is a myelin sheath?
20 to 200 layers of highly modified plasma membrane wrapped around the axon by a nearby supporting cell
83
What are olgiodendrocytes?
Myelin forming cells in the brain and spinal cord
84
What are schwann cells?
Cells in the PNS that form individual myelin sheaths surrounding 1 to 1.5mm long segments at regular intervals along the axons
85
What are node of Ranviers?
The spaces between adjacent sections of myelin where the axons plasma membrane is exposed to extracellular fluid.
86
Where are myelinated axons normally found?
Somatic nerves I.E. in fast sensory/motor systems
87
Where are unmyelinated axons normally found?
Post-ganglionic autonomic fibres, fine sensory fibres, olfactory neurones and interneurons
88
What are the roles of glial cells?
Surrounding the soma, axon, and dendrites of neurones and providing them with physical and metabolic support
89
What are the types of glial cell?
```
Olgiodendrocytes
Schwann Cells
Astrocytes
Microglia
Ependymal cells
```
90
How many axons can one olgiodendrocyte myelinate?
Up to 40
91
How many axons can one schwann cell myelinate?
1
92
What are the specific roles of astrocytes?
Help regulate the composition of the extracellular fluid in the CNS by removing K+ ions and neurotransmitters around synapses
Take up glutamate then convert it to glutamine and release it, then neurones can take it up and convert it back to glutamate for reuse.
Stimulate the formation of tight junctions between the cells that make up walls of capillaries found in the CNS- this forms the blood-brain barrier which is a more selective filter for exchanged substances that is present between the blood and most other tissues
Sustain the neurones metabolically e.g. by providing glucose and removing ammonia
93
What shape are astrocytes?
Star-like
94
What are the most numerous glial cells in the CNS?
Astrocytes
95
What are the specific types of astrocytes?
Radial glia
Muller glia
Bergmann glia
96
What is the role of radial glia?
Guiding developing nerones (these cells are developmental and not found in the adult brain)
97
What are muller glia?
Specialised radial glia of the retina
98
What are bergmann glia?
Specialised cells found in the cerebellum. Support purkinje cell dendrites and synapses
99
What are microglia?
Specialised macrophage-like cells that perform immune functions in the CNS
100
How do microglia appear in the cortical grey matter?
More ramified
101
What are the roles of microglia?
Proloferate at sites of injury (phagocytic)
Migrate to sites of damage
Phagocytose debris/microbes
Contribute to synaptic plasticity
102
How can microglia be negative?
Can be too sensitive, causing excess inflammation and destruction of dendritic spines
103
What are ependymal cells?
Line fluid-filled cavities within the brain and spinal cord that regulate the production and flow of cerebrospinal fluid. Provides a barrier between CSF and brain,
104
What are the properties of ependymal cells?
Cilia, microvilli and desmosomes
105
Is epilepsy a disease of the neurones, glia or both?
Neuron
106
Is motor neurone disease a disease of the neurones, glia or both?
Neuron and glia
107
Is depression a disease of the neurones, glia or both?
Neuron and glia
108
Is Alzheimers disease a disease of the neurones, glia or both?
Neuron and glia
109
Is Multiple Sclerosis a disease of the neurones, glia or both?
Neurones and glia (olgiodendrocytes are attacked)
110
What is the blood rain barrier formed by?
Endothelial cells, pericytes and astrocytes
111
What are the features of the blood brain barrier?
Endothelial tight junctions
Astrocyte end feet
Pericytes
Continuous basement membrane, not fenestrated
Requires specific transporters for glucose, essential ions etc.
112
What are circumventrular organs?
Parts of the brain that lack a blood-brain barrier
113
What are the four ventricles?
Lateral (paired)
III
IV
114
Where does cerebrospinal fluid circulate?
Subarachnoid space
115
How do the ventricles and subarachnoid spaces connect?
Cisterns
116
What does the CSF contain?
Protein, urea, glucose and salts
117
Where is the CSF produced?
Ependymal cells in the choroid plexuses of the lateral ventricles
118
What is the choroid plexus formed from?
Modified ependymal cells formed around a network of capillaires with a large surface area
119
How is CSF absorbed?
Via arachnoid granulations (villi)
120
What is hydrocephalus?
An abnormal accumulation of CSF in the ventricular system, often due to a blocked cerebral aqueduct. This leads to a build up of pressure which can damage brain tissue, In children with soft skull, the pressure will cause the osul to bulge and look abnormal as well as damaging the brain.
121
What is the resting membrane potential?
Under resting conditions, all cells have a potential difference across their plasma membranes, with the inside of the cell negatively charged with respect to the outside. It varies from -40 to -90 mV, with typically being -70mV.
122
How many Na+ ions are pumped per K+ ions by the Na+/K+ATPase pumps?
3Na+ out of the neurone for every 2K+ that are pumped in
123
Why does the neural membrane have a higher permeability to K+ than to Na+?
Voltage gated Na+ and K+ channels are closed, but K+ leak channels are open
124
What causes the initial depolarization during an action potential?
A neurotransmitter binds to a specific ligand-gated ion channel on the post synaptic membrane, so Na+ are allowed to enter the neurone. The inflow of Na+ results in the inside of the neurone being slightly more positive.
125
How are voltage-gated Na+ channels stimulated to open?
Inital depolarization by inflow of Na+ (positive feedback loop)
126
What is the average critical threshold potential?
-55mV
127
When are the voltage-gated Na+ channels inactivated during generation of an action potential?
At +30mV
128
How is the membrane repolarized during an action potentials?
The 'sluggish' voltage-gated K+ channels open in a delayed response to their initial depolarization. This results in K+ defusing out of the neurone, down their concentration gradient, causing the neurone to rapidly repolarize back to its resting potential.
129
What stimulates the voltage gated K+ channels to close during repolarization?
The return of the neurone to a negative potential (however due to their sluggish nature they do this slowly)
130
What is the absolute refractory period?
The period when the voltage-gated Na+ channels are either open or have proceeded to their inactivated state during the first action potential. A second stimulus, no matter how string, will not produce a second action potential.
131
What is the relative refractory period?
The interval whereby a second action potential can be produced- but only if the stimulus strength is considerably greater than usual.
132
What factors can alter the propagation speed?
Fibre diameter
| Myelination
133
How does fibre diameter alter propagation speed?
The larger the fibre diameter, the faster the action potential propagates, since a larger fibre offers less internal resistance to local current meaning adjacent regions of the membrane are able to reach threshold faster
134
How does myelination increase propagation speeds?
There is less "leakage" of charge across the myelin, meaning a local current can spread farther along an axon. Also the concentration of Na+ channels in the myelinated region is low, therefore, action potentials only occur at the nodes of Ranvier, where the myelin coating is interrupted and the concentration of voltage-gated Na+ channels is high.
135
What is saltatory conduction?
When action potentials appear to jump from one node to the next as they propagate along a myelinated fibre
136
What is multiple sclerosis?
The degeneration of myelin and development of scar tissue which in turn disrupts and eventually blocks neurotransmission along myelinated axons
137
What are the symptoms of multiple sclerosis?
```
Uncontrolled eye movements
Slurred speech
Partial/complete paralysis
Tremor
Loss of co-ordination
Weakness
Sensory numbness, prickling, pain
```
138
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
139
Where is a membrane potential of a post synaptic neurone brought closer to the threshold?
Excitatory synapse
140
Where is a membrane potential of a post synaptic neurone driven down further from the threshold or stabilised?
Inhibitory synapse
141
What are the two types of synapse?
Electrical and chemical
142
Where are electical synapses found?
In brainstem neurons e.g. breathing, and hypothalamus e.g. hormone secretion
143
How are the plasma membranes of pre and post synaptic cells joined in electrical synapses?
Gap junctions
144
What are the properties of electrical synapses?
Rapid communication between cells
Allow for synchronised transmission
Gap junctions
145
How are the membranes of pre and post synaptic cells joined in chemical synapses?
Synaptic cleft
146
What is the role of the synaptic cleft?
Preventing direct propagation of the current from the presynaptic neurone to the post synaptic cell
147
What is a contransmitter?
The second neurotransmitter that is relelased from an axon
148
What stimulates a calcium ion channel to open?
When an action potential reaches the pre-synaptic terminal
149
Describe how an action potential can result in a neurotransmitter attaching onto the next cells post synaptic membrane
Calcium ion channels open when an action potential reaches the pre-synaptic terminal. Calcium ions cause vesicles to move to release sites and fuse with the presynaptic cell membrane and discharge their neurotransmitter contents. The neurotransmitter then diffuses across the synaptic cleft and attaches to receptor sites on the post-synaptic membrane.
150
What are the 5 processes of synaptic transmission?
1. Manufacture- intracellular biochemical processes
2. Storage- Vesicles
3. Release- Acton Potential
4. Interact with post-synaptic receptors- diffusion across synapse
5. Inactivation- break-down or re-uptake
151
What are the two main acetylcholine receptors?
Muscarinic and nicotinic
152
What is acetylcholine broken down into by acetylcholine esterase?
Choline and acetyl
153
What happens when neurotransmitters are released from a presynaptic neuron?
A fraction of them bind to receptors on the postsynaptic neurone. These receptors can take the form of transmitter-gated ion channels. These channels are sensitive to specific neurotransmitters.
154
Which synaptic channel type causes depolarisation?
Excitatory channels (excitory post-synaptic potential (EPSP))- Many Na+ leave and a few K+ enter
155
Which synaptic channel causes hyperpolarisation?
Inhibitory channels (inhibitory post-synaptic potential (IPSP)) Many K+ leave or many Cl- enter
156
What are the two types of summation?
Temporal and spatial
157
What is temporal summation?
Input signals arrive from the same presynaptic cell at different times. The potentials summate since there are a greater number of open ion channels and thus a greater flow of positive ions into the cell
158
What is spatial summation?
Where two inputs occur at different locations in the post synaptic neurone
159
What is the reason for summation?
To make sure that the threshold is reached so that an action potential is initiated
160
What causes unbound neurotransmitters to be removed from the synaptic cleft?
1. They are actively transported back into the presynaptic axon terminal or in some cases by nearby glial cells
2. They diffuse away from the receptor site
3. Are enzymatically transformed into inactive substances, some are transported back into the presynaptic neurone for reuse
161
What are common fast neurotransmitters?
Acetylcholine
Glutamate (excitatory)
GABA (inhibitory)
162
What are the properties of fast neurotransmitters?
Short lasting effects, tend to be involved in rapid communication
163
What are the properties of neuromodulators?
Cause change in synaptic membrane that last for longer time e.g. minutes, hours or even days, include alterations in enzyme activity or influences DNA transcription in protein synthesis. Associated with slower events such as learning, development, motivational states etc.
164
What are examples of neuromodulators?
Dopamine
Noradrenalin
Serotonin
165
What are the most common local anaesthetics?
Procaine and lignocaine
166
How do local anaesthetics work?
They interrupt axonal neurotransmission. They do this by blocking sodium channels thereby preventing the neurones from depolarising meaning theshold isn't met and thus no action potential is developed to be propagated. This results in pain relief since pain isn't transmitted. Local anaesthetics can diffuse through mucus membranes easily thus sometimes can act on muscles too.
167
What is the major neurotransmitter of the PNS at the neuromuscular junction?
Acetyl Choline
168
What are cholinergic neurons?
Neurones that release ACh
169
What is acetylcholine synthesised from?
Choline (common nutrient in food) and acetyl choenzyme A in the cytoplasm of synaptic terminals and stored in synaptic vesicles
170
Where is acetylcholinesterase locates and what is its role?
Located on the post synaptic and presynaptic membranes and rapidly destroys ACh, realising choline and acetate
171
What are the two general types of ACh receptors?
Nicotinic receptors
| Muscarinic receptors
172
Describe nicotinic receptors
These respond to ACh and nicotine. They contain an ion-channel and are found in the neuromuscular junction. Nicotine receptors in the brain are important in cognitive functions and behaviour. The presence of nicotinic receptors on presynaptic terminals in reward pathways of the brain explains why tobacco products are so addictive.
173
Describe muscarinic receptors
These respond to ACh and also the mushroom poison muscarine. These receptors couple with G proteins, which in turn then alter the activity of a number of different enzymes and ion channels. These receptors are present in the brain and at junctions where a major division of the PNS innervates peripheral glands and organs
174
Describe how sarin causes paralysis
Sarin inhibits the action of acetylcholinesterase thereby causing a buildup of ACh in the synaptic cleft resulting in overstimulation of postsynaptic ACh receptors, initially causing uncontrolled muscle contractions but eventually leading to receptor desensitation and paralysis
175
Where is noradrenaline found?
In the peripheral heart and central nervous systems
176
What is noradrenaline affected by?
Antidepressant drugs: impramine
Antidepressant drugs: Monamine oxidase inhibitor
Stimulants: Amphetamine
177
How does imipramine affect noradrenaline?
Blocks the reuptake of noradrenaline. Theraputic effect is only seen after 3-5 weeks as the blockage of reuptake does not cause a theraputic effect, instead its the brains response to it that does
178
How does monamine oxidase inhibitor affect noradrenaline?
It increases the amount of noradrenaline by inhibiting the enzyme monoamine oxidase which is the enzyme used to break down noradrenaline
179
How does amphetamine affect noradrenaline?
Increases release and blocks reuptake
180
Where is dopamine found?
In the basal ganglia
181
How is dopamine affected?
Antipshychotic drugs: such as chloropromazine which is an antagonist
Stimulants: amphetamine/cocaine
Antiparkinsons drug: L-DOPA
182
How do anti-psychotic drugs affect dopamine?
Blocks receptor so other neurotransmitter cannot activate receptor
183
How do stimulants affect dopamine?
Increases release and blocks reuptake
184
How do anti-parkinsons drugs affect dopamine?
Increases dopamine manufacture
185
What is the role of serotonin?
Has an excitatory effect on pathways that mediate sensations
186
What is serotonin affected by?
Antidepressant drug: Prozac
| Ecstasy
187
How does prozac affect serotonin?
Selective serotonin reuptake inhibitor (SSRI), resulting in an increase in the concentration of synaptic serotonin
188
How does ecstasy affect serotonin?
Neurotoxic to serotonin neurones, destroy in the terminal of axons
189
What is the role of glutamate?
The main excitatory neurotransmitter
190
What is the role of GABA?
The main inhibitory neurotransmitter
191
What causes parkinsons?
Degradation/death of dopaminergic neurones
192
What is L-DOPA?
A precursor for dopamine
193
How can L-DOPA help for parkinsons?
It is able to cross the blood brain barrier. It is then taken up by serotonin neurones and converted and released as dopamine due to the fact that serotonin neurones contain the same enzyme needed to convert L-DOPA to dopamine as the dopaminergic neurones have
194
What is the normal hearing range?
20-20000 Hz
195
When is the ear most sensitive?
1000-4000 Hz
196
What are the roles of the outer, middle and inner ear?
Outer ear helps collect sound
Middle ear is for the transmission of sound
Inner ear is for the conversion of sound into neural impulses
197
What is the route of sound through the external ear?
Pinna (or auricle)
External auditory canal/ meatus
Tympanic membrane
198
How does the sound in the tympanic membrane cause sound waves?
The air molecules push against the membrane, causing the tympanic membrane to vibrate at the same frequency as the sound wave. The membrane vibrates slowly to low frequency sounds and very rapidly to high frequency sounds.
199
Where is the middle-ear?
An air filled cavity in the temporal bone
200
What innervates the middle-ear?
The glossopharyngeal nerve CN IX
201
How is the middle ear exposed to atmospheric pressure?
Via the eustachian tube which connects the middle ear to the pharynx
202
What causes the slit-like opening where the eustachian tube opens into the pharynx to open?
When muscle movements result in the opening of the tube during swallowing, yawning or sneezing
203
What are the ossicles?
The malleus, the incus, the stapes
204
How do vibrations transmit from the tympanic membrane into the inner ear?
The tympanic membrane moves in and out which in turn is transmitted to the ossicles which in turn transmit this movement to the oval window. The oval window moves in and out of the scala vestibuli, creating waves of pressure here.
205
What are the two small muscles in the middle ear, and their innervations?
```
Tensor tympani (mandibular branch
of trigeminal CN5) and stapedius (CN7- facial)
```
206
What are the roles of the two small muscles in the middle ear?
They lesson the amount of energy transmitted to the inner ear via contraction
207
What is the attachment of the tensor tympani?
The malleus
208
What is the attachment of the stapedius?
The stapes
209
What stimulates the actions of the small middle ear muscles?
Reflexively contract to continuous loud noise to protect the delicate receptor apparatus of the inner ear
210
What is the name of the inner ear?
The cochlea
211
Describe the cochlea
A spiral shaped, fluid filled space in the temporal bone. It is almost completely divided lengthwise by a membranous tibe called the cochlear duct- which contains the sensory receptors of the auditory system
212
What is the fluid inside the cochlea?
Endolymph- a compartment of extracellular fluid containing a high concentration of K+ and a low concentration of Na+
213
What is found in the compartments either side of the cochlear?
Perilymph- which is similar in composition to the cerebrospinal fluid
214
Where is the scala vestibuli found?
Above the cochlear duct, and it begins at the oval window.
215
Where is the scale tympani found?
Below the cochlear duct, connecting to the middle ear via a second-membrane covered opening, the round window
216
Where is the organ of corti?
Sitting upon the basilar membrane
217
What is contained within the organ of corti?
The ears sesnitive receptor cells
218
Describe the basilar membrane?
Narrow and stiff at the base thus sensitive to high frequencies
Wider and less stiff at the apex thus sensitive to low frequencies
219
What is a hair cell?
A receptor cell of the organ of Corti. These cells are mechanoreceptors that have hairlike stereo-cilia protruding from one end
220
How can some antibiotics damage the organ of corti?
They can damage the stereocilia of the hair cells
221
What are the two anatomically separate groups of hair cells?
A single row of inner hair cells and 4-5 rows of outer hair cells
222
What is the role of the sterocilia of inner hair cells?
They extend into the endolymph fluid and convert pressure waves caused by the movement of fluid in the cochlear duct into receptor potentials
223
What is the role of the sterocilia of outer hair cells?
They are embedded in the overlying tectorial membrane and mechanically alter its movement to sharpen frequency tuning at each point along the basilar membrane
224
Where is the tectorial membrane?
Overlying the organ of corti
225
How does the bending of the stereocilia towards the tallest membrane trigger neurotransmitter release?
When the stereocilia bend towards the tallest member of the bundle, fibrous connections called TIP links pull open the mechanically gated K+ channels, resulting in an influx of K+ from the surrounding endolymph thereby depolarising the membrane. This change in voltage triggers the opening of voltage-gated Ca2+ channels near the base of the cell, which in turn triggers neurotransmitter release.
226
How does the bending of the hair cell away from the tallest membrane trigger repolarization?
The bending slackens the tip links, thereby closing the channels and allowing the cell to rapidly repolarize
227
What is the neurotransmitter released from hair cell?
Glutamate
228
How does the release of glutamate from a hair cell generate an action potential?
It binds to and activates protein-binding sites on the terminals of the afferent neurones. This results in the generation of action potentials in the neurons.
229
What nerve do the action potentials generated by the hair cells travel down?
The cochlear branch of the vestibulocochlear nerve (CN VIII)
230
What is the spiral ganglion?
The cell bodies of the cochlear nerve fibres and organ of corti, which lie within the cochlea
231
At what level does the cochlear nerve join the brainstem?
The level of the rostral medulla
232
Where does the bifurcations of the cochlear nerve end?
In the dorsal and ventral cochlear nuclei, which lie close to the inferior cerebellar peduncle
