Neuro Flashcards
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 myelinates axons in the CNS and PNS?
A
CNS: oligodendrocytes
PNS: schwann cells
4
Q
what is a tract?
A
location of a pathway
5
Q
what is a commissure?
A
tract connecting one hemisphere to the other - tracts that cross the midline
6
Q
what is a lemnisci?
A
narrow strip of fibres
7
Q
what is a funiculi?
A
rope or cord
8
Q
what is a fasiculi?
A
bundle e.g. gracile fasiculus
9
Q
what is a capsule?
A
sheet of white matter fibres that border a nucleus of grey matter
10
Q
what is a column?
A
longitudinally running fibres separated by other structures e.g. dorsal column
11
Q
what is a cortex?
A
laminated grey matter on outside of brain e.g. motor cortex
12
Q
what are nuclei?
A
collection of nerve cell bodies within the CNS
13
Q
what are ganglia?
A
collection of nerve cell bodies the CNS (e.g. dorsal root ganglia in PNS) and some inside the CNS with a capsule e.g. basal ganglia
14
Q
what are afferents?
A
axons taking information towards the CNS e.g. sensory fibres
15
Q
what are efferents?
A
axons taking information to another site from the CNS e.g. motor fibres
16
Q
what is reticular?
A
netlike, where grey and white matter mix e.g. reticular formation of brainstem
17
Q
what is the coronal plane?
A
vertical/frontal - parallel with coronal suture of skull
18
Q
what is the horizontal plane?
A
transverse, cuts body in half unequally
19
Q
what is the sagittal plane?
A
cuts down nose, parallel with sagittal suture
20
Q
what is ipsilateral/contralateral?
A
ipsilateral: same side
contralateral: opposite side
21
Q
what is medial/median?
A
medial: towards midline
median: at midline
22
Q
what is lateral?
A
away from midline
23
Q
what is rostral/caudal?
A
rostral: towards nose (anterior)
caudal: towards tail (posterior)
24
Q
what is dorsal/ventral in brainstem and cord?
A
dorsal: posterior
ventral: anterior
25
what is dorsal/ventral in cerebrum?
dorsal: superior
ventral: inferior
26
what are sulci?
grooves
27
what are gyri?
ridges
28
what is the function of the frontal lobe?
voluntary movement on opposite side of body
frontal lobe of dominant hemisphere controls speech (Broca's area) and writing (if right handed, then left hemisphere is dominant etc)
intellectual functioning, thought processes, reasoning and memory
29
what is the function of the parietal lobe?
receives and interprets sensations, including pain, touch, pressure, size, shape and body-part awareness (proprioception)
30
what is the function of the temporal lobe?
understanding the spoken word, sounds and memory/emotion
31
what is the function of the occipital lobe?
understanding visual images and meaning of written words
32
what underlies the cortex?
white matter
33
where are grey matter structures located in the brain?
deep in white matter, surround ventricles
34
what grey matter structures are in the brain?
thalamus, hypothalamus, basal ganglia
35
what is the function of the thalamus?
relay centre direction inputs to cortical areas
36
what is the function of the hypothalamus?
links endocrine system to brain and involved in homeostasis
37
what does the basal ganglia consist of? what is its function?
caudate nucleus, putamen and globus pallidus
motor control, cognition and non-motor behaviour
38
what is the striatum?
caudate and putamen
39
what is the lentiform nucleus?
globus and putamen
40
what is the cerebellum? what is its function?
coordinates voluntary movement and balance, equilibrium and muscle tone
41
what is the structure of the cerebellum?
lies over dorsal surface of brains stem, attached to it by 3 peduncles
separated from dorsal brainstem by 4th ventricle which forms part of its roof
folded cortex, white matter and deep inner nuclei
42
how is the cerebellum attached to the brainstem? which side is it attached to?
dorsal
superior peduncle: midbrain
middle peduncle: pons
inferior peduncle: medulla
43
how is the cerebellum separated from the dorsal brainstem?
4th ventricle - forms part of its roof
44
what do cerebellar injuries lead to?
slow and uncoordinated movement
asynergia, intention tremor, hypotonia, nystagmus
45
what is asynergia?
loss of coordination of motor movement
46
what is intention tremor?
movement tremors
47
what is hypotonia?
weak muscles
48
what is nystagmus?
abnormal eye movements
49
what are the functions of the brainstem?
special senses, sensory/motor for head and neck via CNs, autonomic regulation of the body, regulates consciousness, pathway between brain and spinal cord
50
what does the midbrain consist of?
```
tectum (superior and inferior colliculi)
cerebral peduncle (tegmentum and crus cerebri)
```
surrounds cerebral aqueduct?
51
what does the midbrain surround?
cerebral aqueduct
52
what cell types does the CNS contain?
nerve cell/neurones: pyramidal, stellate, Golgi, Purkinje
neuroglia: astrocytes, oligodendrocytes, microglia
53
where does fertilisation occur?
uterine tube
54
what are the first clump of cells after fertilisation
morula
16 cells
55
what does the morula develop into?
blastocyst (more than 16 cells) with hole in the middle called blastocele
56
what is gastrulation?
single layer blastula developing into trilaminar disc (gastrula)
57
what is a gastrula?
trilaminar disc
58
what is neurulation?
process of formation of the embryonic nervous system
59
what happens in neurulation?
ectoderm thickens in midline to form neural plate in third week of development
ectoderm undergoes differential mitosis to cause formation of midline groove (neural groove
groove deepens and eventually detaches from the overlying ectoderm to form the neural tube
60
how is the neural plate formed?
ectoderm thickens in the midline to form the neural plate in 3rd week
61
how is the neural groove formed?
ectoderm undergoes differential mitosis
62
what lies lateral to the neural plate?
presumptive neural crest cells which run dorso-laterally along neural groove
63
how do presumptive neural crest cells run?
dorsolaterally along neural groove
64
what do neural crest cells develop into?
sensory (dorsal root) ganglia of spinal cord and CNs V, VII, IX, X
Schwann cells
pigment cells
adrenal medulla
bony skull
meninges
dermis
a lot of the head and neck
65
development of the brain and spinal cord
rostral portion of neural tube develops into brain (CNS)
caudal portion of the neural tube develops into the spinal cord
66
what does the central cavity within the spinal cord develop into?
central canal of spinal cord and ventricles of the brain
67
what happens in the 5th week of embryonic development?
three primary brain vesicles can be identified
68
when can primary brain vesicles be identified?
5th week
69
what are the 3 primary brain vesicles?
prosencephalon (forebrain)
mesencephalon (midbrain)
rhombencephalon (hindbrain)
70
how do secondary brain vesicles form? when?
further differentiation
7th week
71
what does the prosencephalon differentiate into?
telencephalon and diencephalon
72
what does the mesencephalon differentiate into?
mesencephalon
73
what does the rhombencephalon differentiate into?
metencephalon and myelencephalon
74
what does the telencephalon give rise to?
cerebral hemisphere and lateral ventricles
75
what does the diencephalon give rise to?
thalamus, hypothalamus, third ventricle
76
what does the mesencephalon give rise to?
midbrain (colliculi) and aqueduct
77
what does the metencephalon give rise to?
cerebellum, pons and upper part of 4th ventricle
78
what does the myelencephalon give rise to?
medulla oblongata and lower part of 4th ventricle
79
what does the central cavity of the brain develop into?
forming system of chambers (ventricles) which contain CSF
80
when does the neural tube usually close?
end of 4th week
81
what is spina bifida?
failure of the tube to close in the spinal cord
82
what is anencephalus?
failure of the tube to close in the cephalic region (brain)
83
why may the neural tube fail to close?
due to faulty induction or environmental teratogens (any agent that can disturb the development of the embryo) acting on neuroepithelial cells
84
developmental milestones at 3 weeks, 10 weeks, 3, 5, 7 and 9 months
3 weeks: eye formation
10 weeks: cerebral expansion and commissures
3 months: basic structures established
5 months: myelination has begun
7 months: lobes of cerebrum have formed
9 months: gyri and sulci formed
85
what are abnormalities to the CNS dependent on?
time of infection
86
what are critical periods?
6th week: eye malformation, e.g. cataracts
9th week: deafness can occur e.g. malformation of organ of Corti
5th to 10th week: cardiac malformation
87
when do CNS disorders generally occur?
2nd trimester
88
when does the risk of CNS disorders fall? why?
after 16 weeks
most structures have already developed
89
development of sensation
innervation of dermal skin, dorsal root ganglion connecting to spinal cord, C-fibre connection, organised thalamus, retinal inputs, myelination, connections from thalamus to cortex
90
when is the dermal skin innervated?
28 weeks
91
when does the dorsal root ganglion connect to the spinal cord?
from 8 weeks
non-noxious (no pain detected)
92
when is there C-fibre connection?
from 19+ weeks
noxious (painful) stimuli
93
when is the thalamus organised?
from 8+ weeks
94
when do retinal inputs arrive?
14-16 weeks
95
when does myelination occur?
from 25 weeks
96
when does the thalamus connect to the cortex?
from 24 weeks
97
what is the function of the brain stem?
basic vital functions
98
what is the corpus callosum?
fibre bundle connecting left and right hemispheres together
99
how many neurons does the cerebellum have?
70% neurones
100
how do structures connect to the cerebellum?
all sensorimotor, cognitive and motivational/effective structures connect to cerebellum via re-entrant loops
101
where does the cerebellum receive input from?
motor cortex, brain stem nuclei, sensory receptors
102
what is the output of the cerebellum?
modulates UMNs
103
skill development of the cerebellum
always working, predicting the consequences and correcting actions so they can be improved if there's error
104
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
105
how does the basal ganglia connect to inputs of the brain?
by recurrent loops
106
competing systems in the brain and what the basal ganglia does with them
emotions, cognitions, sensorimotor
selects which one to do
107
what are the outputs of the basal ganglia?
inhibitory and tonically active (slow and continuous)
108
what are the functions of the hippocampus?
episodic memory
essential for the construction of mental images
vital role in STM
important for spatial memory and navigation
109
what is the hippocampus part of?
limbic system
110
what is anterograde tract tracing?
transport from neuronal cell bodies to axon terminals
111
what is retrograde tract tracing?
transport from axonal terminals to neuronal cell bodies
112
how do neurones project?
not A -> B, but A -> B -> C -> D
113
what are class A experiments?
diagnosis
some behavioural, physiological or pharmacological variable is manipulated and consequent effects on brain activity/structure are measured
114
critical evaluation of class A experiments
diagnosis
are there adequate controls to ensure that observed changes are produced only by claimed behavioural/physiological/pharmalogical manipulations?
are measured changes specific to claimed regions in brain?
115
what are type B experiments?
treatment
some aspect of brain structure (lesion) or activity (stimulation/inhibition) is manipulated and effects on behaviour/physiology/endocrinology is measured
116
critical evaluation of type B experiments
are effects of brain manipulation to claimed changes?
is used brain manipulation specific to intended neural structures?
117
basis of detection of brain activity
increases in activity -> increase in release of neurotransmitters and breakdown products (CSF via lumbar puncture)
active regions need more O2/blood (haemodynamic changes detected by modern imaging)
118
what does EEG do?
electroencephalogram
regional brain activity underlying electrodes
signs of epilepsy
(overexcitation of neurons -> cell death)
119
what are EEGs sensitive/insensitive to?
sensitive to activity in temporal regions, less to spatial regions
120
components of neurones
dendrites, cell body/soma, axon, presynaptic terminal
121
how do neurons receive and transmit information?
receive info via dendrites, transmit to soma
transmit info via axons and action potentials are propagated from the axon hillock
122
neurons stained by H&E
haemotoxylin stains nucleic acids blue
eosin stains proteins red
123
what stains myelin?
luxor fast blue (LFB)
124
what stains Nissl (RER)?
cresol violet (CV)
125
what is neural plasticity?
basis of learning and memory
ability of the brain to change throughout an individual's life
126
what is an early marker of Alzheimers?
loss of dendritic spines
127
functional classes of neurons
afferent (sensory), efferent (motor), interneurons (within CNS)
128
what forms the nerves of the PNS?
groups of afferent and efferent neurone axons together with connective tissue and blood vessels
129
what is a nerve fibre?
single axon
130
what is a nerve?
bundle of axons (fibres) bound together by connective tissue
131
what do afferent neurons do?
convey information from tissues and organs towards the CNS
132
structure of afferent neurons
sensory receptors at peripheral ends (farthest from CNS)
axon divides after leaving cell body
133
what do sensory receptors do? where are they located?
at peripheral ends of afferent neurons
respond to various physical/chemical changes in their environment by generating electrical signals in neurone
134
what does the axon of an afferent neuron divide into?
peripheral process begins where dendritic branches converge from receptor endings - long
central process enters CNS to form junctions with other neurons - shorter
135
are afferent process inside or outside of the CNS?
cell body and peripheral process are outside the CNS/in PNS
a part of the central process enters CNS
136
what do efferent neurons do?
convey information away from CNS to effector cells, e.g. muscle, gland, etc
137
are efferent neurons inside or outside of the CNS?
cell bodies and dendrites are within the CNS, axons extend out to periphery
138
what do interneurons do? where do they lie?
connect neurons within CNS - form majority of neurons
lie entirely within CNS
139
what is myelin?
20-200 layers of highly modified plasma membrane wrapped around axon by nearby supporting cell
highly compacted - 70% lipid and 30% protein
140
what are the myelin-forming cells in the CNS?
oligodendrocytes - can branch to form myelin on up to 40 axons
141
what are the myelin-forming cells in the PNS?
Schwann cells - form individual myelin sheaths surrounding 1-1.5 mm long segments at regular intervals along axons
142
what are nodes of Ranvier?
spaces between adjacent sections of myelin where axon's plasma membrane is exposed to ECF
143
what does myelin do?
increases speed of conduction along axons
144
what are features of myelinated axons?
thicker
found in mostly somatic nerves e.g. fast sensory/motor systems, muscle and spinal systems
145
what are features of unmyelinated axons?
thinner
post-ganglionic autonomic fibres, fine sensory fibres, olfactory neurones and interneurons - where speed is not of the essence e.g. hypothalamus
146
what do glial cells do?
surround soma, axon, dendrites of neurones and provide them with physical and metabolic support
147
function of oligodendrocytes
myelinating multiple axons
insulates axon segments, enabling rapid nerve conduction
metabolic support - transport metabolic products directly into axons
148
functions of astrocytes
regulate composition of ECF in CNS by removing K+ ions and neurotransmitters (e.g. glutamate)
take up glutamate and convert it to glutamine and release it, then neurons can take it up and convert back to glutamate for reuse
BBB
sustain neurones metabolically - provide glucose and remove ammonia
149
what are astrocytes in the grey matter called?
protoplasmic
150
what are astrocytes in the white matter called?
fibrous
151
what are specific types of astrocytes?
radial glia, Mueller glia and Bergmann glia
152
what are radial glia?
guide developing neurones
only developmental, not found in adult brain
153
what are Mueller glia?
specialised radial glia of the retina
154
what are Bergmann glia?
found in cerebellum
support purkinje cell dendrites and synapses
155
what are microglia? what are they derived from?
specialised macrophage-like cells that perform immune functions in the CNS
derived from progenitors that migrate into the CNS from the periphery
156
what do microglia do?
proliferate at sites of injury (phagocytic)
phagocytose debris/microbes
contribute to synaptic plasticity - can eat unwanted dendritic spines
157
what are microglia like in the cortical grey matter?
more ramified (branched)
158
when can be microglia be bad?
being too sensitive and causing excessive inflammation and destruction of dendritic spines
159
what are ependymal cells? what do they do?
line fluid filled cavities within brain (ventricles) and spinal cord
regulate production and flow of CSF
cilia, microvilli, desmosomes
provide barrier between CSF and brain
160
diseases of neurons, glia or both?
```
epilepsy
MND
depression
Alzheimers
MS
```
epilepsy: neurone
MND: neurons and glia
depression: neurons and glia
Alzheimers: neurons and glia
MS: neurons and glia (oligodendrocytes attacked)
161
what is attacked in MS?
oligodendrocytes
162
what forms the BBB?
endothelial cells, pericytes, astrocytes
163
what are pericytes?
contractile cells that wrap around the endothelial cells of capillaries and venules
164
what are the features of the BBB?
endothelial tight junctions
astrocyte end feed
pericytes
continuous BM (lacks fenestrations)
requires specific transporters for glucose, essential ions etc
165
what are circumventricular organs?
parts of brain that lack the BBB
need to be in contact with blood for sensory role to monitor
posterior pituitary
166
what is CSF?
clear, colourless liquid containing protein, urea, glucose and salts
167
where does CSF circulate?
through subarachnoid space (around brain and spinal cord) and within ventricles
offers protection by cushioning brain from gentle movements
168
what connects ventricles and subarachnoid spaces?
cisterns
169
what is the volume of CSF?
120mls
170
what is CSF produced by?
ependymal cells in choroid plexuses of lateral ventricles
171
what is the choroid plexus?
formed from modified ependymal cells
| around a network of capillaries, large SA
172
how is CSF absorbed?
via arachnoid granulations (VILLI) e.g. in superior sagittal sinus
173
what is hydrocephalus?
abnormal accumulation of CSF in ventricular system
often due to blocked cerebral aqueduct
174
what does hydrocephalus lead to?
build up of pressure which can damage brain tissue as skull is hard in adults
in children with soft skulls, the pressure causes the skull to bulge and look abnormal, and damage the brain
175
what is the resting membrane potential?
all cells under resting conditions have a potential difference across their plasma membranes, with the inside of the cell negatively charged with respect to the outside
176
what is the magnitude/typical resting potential?
- 40 to -90mV
| typical: -70mV
177
how is the concentration gradient established?
Na+/K+ ATPase pumps in neurone membrane develop conc. gradients by pumping 3 Na+ ions out of neurone for every 2 K+ ions that are pumped in, against their concentration gradients, via active transport
Na+ ions concentrated outside, K+ ions inside
178
what channels are open in a resting membrane potential?
very few Na+ voltage gated channels - few Na+ ions can diffuse back into the axon
K+ voltage gated channels closed
leak K+ channels are open, increasing membrane permeability -> K+ ions diffusing out of axon down conc. gradient
179
what makes Na+ ions able to enter the neurone?
when a neurotransmitter binds to a specific ligand-gated ion channel on the post synaptic membrane
180
what is initial depolarisation?
inflow of Na+ ions results in the inside of the neurone to become slightly more positive
181
what does the initial depolarisation stimulate?
opening of some voltage-gated Na+ channels, leading to further entry of Na+ ions into the neurone and further depolarisation
182
what does further depolarisation lead to?
when the membrane reaches critical threshold potential (-55mV), depolarisation becomes a positive feedback loop
183
what is the critical threshold potential? what does it lead to?
-55mV
positive feedback loop - Na+ entry causes depolarisation, which opens more voltage-gated Na+ channels, which leads to more depolarisation etc
184
what is reverse polarisation? what does it lead to?
+30mV
voltage-gated Na+ channels are inactivated and Na+ influx stops
185
what opens in a delayed response to the initial depolarisation? what does this lead to?
sluggish voltage-gated K+ channels
K+ diffuses out of the neurone, down the concentration gradient, causing rapid repolarisation
186
what causes rapid repolarisation?
delayed opening of the sluggish voltage gated K+ channels in response to initial depolarisation
187
what causes hyperpolarisation?
return of the neurone to negative potential causes voltage gated K+ channels to close, but slowly
membanes permeability to K+ remains above resting levels -> continued outflow, more negative than -70mV
188
when is the resting membrane restored?
when voltage-gated K+ channels finally close
189
what is the absolute refractory period? when does it occur?
a second stimulus, no matter how strong, won't produce a second action potential
voltage-gated Na+ channels are already open or have proceeded to their inactivated state after during the first potential
190
what is the relative refractory period?
interval where a second action potential can be produced following the absolute refractory period, only if stimulus strength is greater than usual
lasts until membrane returns to the resting potential
191
what is the function of the refractory periods?
limit the number of action potentials an excitable membrane can produce in a given period of time
separate action potentials so individual signals can pass down the axon
192
what causes a current to flow? what does it do?
generation of an action potential at a particular segment on the neurone membrane
difference in potential between depolarised membrane and adjacent segments at resting potential
depolarises adjacent membrane, causing voltage-gated Na+ channels to open
193
what causes action potential propagation along the membrane?
new action potential generates local currents of its own
depolarise region adjacent to it
etc
194
why can't the impulse travel backwards?
propagation travels in the direction of the region of membrane that has recently been active
adjacent membrane behind potential is in its absolute refractory period - can't depolarise
195
what does propagation along a membrane depend on?
fibre diameter and myelination
196
how does fibre diameter affect propagation speeds?
larger the fibre diameter, the faster the action potential propagates, as a larger fibre offers less internal resistance to local current - adjacent regions are able to reach threshold faster
197
how does myelination affect propagation speeds?
increases it
less leakage of charge across the myelin - local current can spread farther along axon
conc. of Na+ channels in myelinated region is low - action potentials can only occur at nodes of Ranvier (high conc. of Na+ channels)
198
what is saltatory conduction?
action potentials appear to jump from one node to the next as they propagate along a myelinated fibre
faster than in non-myelinated fibres of same axon diameter
199
how do conduction velocities vary?
0.5m/s in small-diameter fibres to 100m/s in large-diameter myelinated fibres
200
what is axonal transmission?
transmission of information from point A to B
201
what is MS?
most common disease of nervous system in young adults
autoimmune
degeneration of myelin an development of scar tissue which disrupts and eventually blocks neurotransmission along myelinated axons
202
what are the symptoms of MS?
uncontrolled eye movements - seeing double
slurred speech
partial/complete paralysis
tremor
loss of coordination
weakness
sensory numbness, prickling, pain
203
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 postsynaptic neurone
204
what is an excitatory synapse?
membrane potential of a postsynaptic neuron is brought closer to threshold (depolarised)
205
what is an inhibitory synapse?
membrane potential of a postsynaptic neuron is either driven further from threshold (hyperpolarised) or stabilised at its resting potential
206
what happens if the membrane of a postsynaptic neuron reaches threshold?
generate action potentials that are propagated along its axon to terminal branches which influence the excitability of other cells
207
what types of synapses are there?
electrical and chemical (majority)
208
what is the structure of electrical synapses?
plasma membranes of presynaptic and postsynaptic cells are joined by gap junctions
allow local currents from arriving action potentials to flow directly across the junction
209
what is the speed of conduction in electrical synapses?
extremely rapid
synchronised transmission
210
where are electrical synapses found?
brainstem neurons e.g. breathing and hypothalamus and hormone secretion
211
what is the structure of a chemical synapse?
plasma membranes of neurons are joined by the synaptic cleft
212
what is the axon terminal?
axon of the presynaptic neurone ends in a slight swelling which holds the synaptic vesicles containing neurotransmitter molecules
213
what is the synaptic cleft? what does it do?
separates the presynaptic and postsynaptic neurons and prevents direct propagation of the current
214
how are signals transmitted across the synaptic cleft?
chemical messenger (neurotransmitter)
more than one may be simultaneously released
215
what is a cotransmitter?
more than one neurotransmitter may be simultaneously released from an axon
216
what are synapses covered by? what do they do?
astrocytes (glial cell) - reuptake of excess neurotransmitter
217
what happens in the process of neurotransmitter release?
calcium ion channels open when an action potential reaches the presynaptic terminal
calcium ions cause vesicles to move to release sites and fuse with cell membrane and discharge their contents
218
what role do calcium ions have in neurotransmitter release?
calcium ions cause vesicles to move to release sites and fuse with cell membrane and discharge contents
219
what happens when an action potential reaches a presynaptic terminal?
calcium ion channels open
220
what are the 5 processes of synaptic transmission?
manufacture - intracellular biochemical processes
storage - vesicles
release - action potential
interaction with post-synaptic receptors - diffusion across synapse
inactivation - breakdown or reuptake
221
what is an example of the processes involved in synaptic transmission?
acetylcholine
222
where is acetylcholine used?
brain and neuromuscular junction
223
what are the main acetylcholine receptors?
muscarinic and nicotinic
224
breakdown/reabsorption of acetylcholine
once bound to the postsynaptic receptor, the enzyme acetylcholine esterase breaks it down into choline and acetyl
choline is reabsorbed to be recycled
225
what enzyme breaks down acetylcholine in the synaptic cleft?
acetylcholine esterase
226
what are receptors on the postsynaptic neurone called?
transmitter-gated ion channels
227
?are transmitter-gated ion channels sensitive to?
specific neurotransmitters
228
what happens in an EPSP?
many Na+ leave and a few K+ enter
229
what happens in an IPSP?
many K+ leave or many Cl- enter
230
what are the two means of combined effects?
temporal or spatial summation
231
what is temporal summation?
input signals arrive from same presynaptic cell at different times
potentials summate as there are a greater number of open ion channels, thus a greater flow of positive ions into the cell
232
what is spatial summation?
two inputs occur at different locations in the postsynaptic neuron
233
when are unbound neurotransmitters removed from the synaptic cleft?
actively transported back into the presynaptic axon terminal or by nearby glial cells
diffuse away from receptor site
enzymatically transformed into inactive substances - some reused
234
what are fast neurotransmitters?
short lasting effects, tend to be involved in rapid communication
235
what are examples of fast neurotransmitters?
acetylcholine, glutamate (excitatory), GABA (inhibitory)
236
what are neuromodulators? what do they do?
cause change in synaptic membrane that lasts for longer times
alterations in enzyme activity or influences DNA transcription in protein synthesis
slower events e.g. learning, development, motivational states
237
what are examples of neuromodulators?
dopamine, noradrenaline/norepinephrine, serotonin
238
what are the most common local anaesthetics?
procaine and lignocaine
239
how do local anaesthetics work?
interrupting axonal neurotransmission
blocking sodium channels -> preventing neurons from depolarising, so threshold isn't met -> no action potential is developed to be propagated
240
what effect do local anaesthetics produce?
pain relief as pain isn't transmitted
241
what can local anaesthetics diffuse through? what does this mean?
mucus membranes
act on muscles
242
what is acetylcholine?
major neurotransmitter of the PNS at the neuromuscular junction
also used in brain and spinal cord
243
what are neurons that release ACh called?
cholinergic neurons
244
synthesis and storage of ACh
synthesised from choline (common nutrient in food) and acetyl coenzyme A in cytoplasm of synaptic terminals and stored in synaptic vesicles
245
what stops activation of ACh receptors?
conc. decreases due to enzyme acetylcholinesterase
246
where is acetylcholinesterase? what does it do?
postsynaptic and presynaptic membranes
rapidly destroys ACh, releasing choline and acetate
247
what are 2 general types of ACh receptor?
nicotinic and muscarinic
248
what are nicotinic receptors?
respond to ACh and nicotine
contains ion channel
249
where are nicotinic receptors found?
neuromuscular junction and brain
250
what are the functions of nicotinic receptors?
ones in brain are important in cognitive functions and behaviour
one cholinergic system using them plays role in attention, learning and memory by reinforcing the ability to detect and respond to meaningful stimuli
on presynaptic terminals in reward pathways - tobacco products are addictive
251
what are muscarinic receptors?
respond to ACh and mushroom poison muscarine
252
what do muscarinic receptors do?
couple with G proteins, which alter the activity of different enzymes and ion channels
253
where are muscarinic receptors present? give examples?
brain
junctions where a major division of the PNS innervates peripheral glands and organs
salivary glands, heart and lungs (bronchoconstriction M3)
254
what do cigarettes contain?
nicotine (agonists) - interact and open receptor
255
what does sarin do? what does this lead to?
inhibits the action of acetylcholinesterase
buildup of ACh in synaptic cleft -> overstimulation of postsynaptic ACh receptors
initially, uncontrolled muscle contractions
eventually, receptor desensitisation and paralysis
256
where is noradrenaline found?
transmitter in the peripheral heart and CNS
257
what is noradrenaline affected by?
```
antidepressant drugs (imipramine and monamine oxidase)
amphetamine (stimulant)
```
258
how does imipramine affect noradrenaline?
blocks reuptake of noradrenaline
therapeutic effect only seen after 3-5 weeks
blockage of reuptake doesn't cause therapeutic effect, but brain's response to it does
259
how does monoamine oxidase inhibitor affect noradrenaline?
increases amount of noradrenaline by inhibiting enzyme monoamine oxidase which breaks down noradrenaline
260
what causes the breakdown of noradrenaline?
monoamine oxidase enzyme
261
how does amphetamine affect noradrenaline?
stimulant
increases release and blocks reuptake
262
where is dopamine found?
basal ganglia
263
what is dopamine affected by?
antipsychotic drugs, stimulants, anti-parkinsons drug
264
how do antipsychotics affect dopamine?
e.g. chlorpromazine
antagonist - blocks receptor so other neurotransmitter can't activate it
265
how do stimulants affect dopamine?
amphetamine/cocaine
increases release and blocks reuptake
266
how do anti-parkinsons drugs affect dopamine?
L-DOPA increases dopamine manufacture
267
what is serotonin?
excitatory effect on pathways that mediate sensations
268
what is serotonin affected by?
antidepressants, ecstasy
269
how do antidepressant drugs affect serotonin?
e.g. Prozac/Zoloft/sertraline
Selective Serotonin Reuptake Inhibitor
increase in conc. of synaptic serotonin
270
how does ecstasy affect serotonin?
neurotoxic to serotonin neurons
destroy terminal of axons
271
what is glutamate?
main excitatory neurotransmitter
272
what is GABA?
main inhibitory neurotransmitter
273
what happens in Parkinsons? what is L-DOPA?
degradation/death of dopaminergic neurons
precursor for dopamine
274
what happens when L-DOPA is given to patients?
able to cross BBB
taken up by serotonin neurones and converted and released as dopamine - serotonin neurons have same enzyme needed to convert L-DOPA to dopamine as the dopaminergic ones have
275
what is the interaction between L-DOPA and serotonin neurones?
taken up by them, then converted and released as dopamine as they share the enzyme needed to convert L-DOPA to dopamine
276
what is the human hearing range?
20 to 20000 Hz
277
at what is the ear most sensitive?
1000 - 4000 Hz
278
what are the functions of the outer, middle and inner ear?
outer: collect sound
middle: transmission of sound
inner: conversion of sound into neural impulses
279
how does sound enter the ear?
through pinna/auricle (exterior part of ear)
then via the external auditory canal/meatus
280
what do features of the points of entry of sound into the ear do?
shape of pinna and external auditory canal/meatus help amplify and direct the sound
281
what does the sound reach when travelling though the canal? what does it do?
to tympanic membrane (eardrum)
as air molecules push against the membrane, it causes the tympanic membrane to vibrate at same frequency as sound wave
282
vibration of tympanic membrane
slowly to low frequency sounds
rapidly to high frequency sounds
283
what marks the end of the external ear and the start of the middle ear?
tympanic membrane (ear drum)
284
what is the ear drum?
tympanic membrane
285
what is the middle ear?
an air filled cavity in the temporal bone of the skull
286
what provides the sensation of the middle ear?
glossopharyngeal nerve (CNIX)
287
what are the normal pressures in the external auditory canal and middle ear cavity?
normally equal to atmospheric pressure
288
how is the middle ear exposed to atmospheric pressure?
via the eustachian tube (auditory tube) - connects the middle ear to the pharynx
289
what is the eustachian tube?
connects middle ear to the pharynx - opens into pharynx through a slit-like opening which is normally closed
exposes the middle ear to atmospheric pressure
290
when is the opening of the eustachian tube into the pharynx opened/closed?
normally closed
muscle movements e.g. swallowing, yawning or sneezing -> opening of tube
291
when does a difference in pressure between the middle and external ear occur?
changes in altitude
292
what can cause pain in the ear? how can it be relieved?
constant pressure in the middle ear -> stretching tympanic membrane
yawning/swallowing -> opening of eustachian tube -> pressure in middle ear equilibrates with external atmospheric pressure
293
how are the vibrations of the tympanic membrane transmitted to the inner ear?
moveable chain of three bones - ossicles
294
what are ossicles?
smallest bones in the body
malleus, incus, stapes
synovial joints between them
295
what do ossicles do?
transmit vibrations from the tympanic membrane into the inner ear
act as a piston - couple the vibrations of tympanic membrane to oval window
296
what is the oval window?
a membrane covered opening between the middle and inner ear
total force of a sound wave applied to tympanic membrane is completely transferred
297
what is a feature of the oval window that makes it effective for its function?
much smaller than membrane
force per area is much greater - adequately transmits sound energy through fluid filled cochlea
298
how can the amount of energy transmitted to the inner ear be lessened?
contraction of 2 small muscles in inner ear - tensor tympani and stapedius
299
what muscles lessen the amount of energy transmitted to the inner ear?
tensor tympani and stapedius
300
what is the tensor tympani? what is its innervation?
small muscle in inner ear
attaches to malleus, contraction dampens the bones movement
mandibular division of trigeminal nerve (V3)
301
what bone does the tensor tympani attach to?
malleus
contraction -> dampening its movement
302
what is the stapedius? what is its innervation?
small muscle in inner ear
attaches to stapedius, contraction dampens bones movement
facial nerve (VII)
303
what bone does the stapedius attach to?
stapes
contraction -> dampening its movement
304
what is the function of the tensor tympani and stapedius muscles?
act reflexively to continuous loud noise to protect delicate receptor apparatus in inner ear
can't protect inner ear from sudden intermittent loud sounds
305
what is the inner ear?
cochlea
306
what is the cochlea?
inner ear, organ of hearing
spiral shaped, fluid filled space in the temporal bone
307
how many times does the cochlea spiral?
2.5 - 2.75 times
308
how is the cochlea divided?
almost completely divided lengthwise by membranous tube (cochlea duct)
309
what is the cochlea duct? what does it contain?
membranous tube
contains sensory receptors of the auditory system
endolymph - compartment of ECF containing high conc. of K+ and low conc. of Na+
310
what is endolymph?
compartment of ECF containing high conc. of K+ and low conc. of Na+
found in cochlea duct
311
what is on either sides of the cochlea duct?
compartments filled with perilymph - similar in composition to CSF
scala vestibuli and scala tympani
312
what is perilymph?
similar in composition to CSF
in scala vestibuli and tympani
313
what is the scala vestibuli?
above the cochlear duct
begins at oval window
entrance to inner ear from the oval window
314
what is the scala tympani?
below cochlear duct
connects to middle ear via round window
315
what is the helicotrema?
where the scala vestibuli and tympani are continuous, at the far end of the cochlear duct
316
where are the scala vestibuli and tympani continuous?
at the helicotrema, at the far end of the cochlear duct
317
how does the oval window transmit sound waves?
they receive input from the ossicles
moves in and out of the scala vestibuli, creating waves of pressure
transmitted toward the helicotrema and into the scala tympani where pressure is relieved by movements of the membrane of the round window
318
what is the side of the cochlear duct closes to the scala tympani formed by?
basilar membrane
319
what sits on the basilar membrane in the inner ear?
organ of corti
320
what is the organ of corti?
contains sensitive receptor cells
pressure difference across the duct causes the basilar membrane to vibrate
321
what is the basilar membrane sensitive to?
base: narrow and stiff - high frequencies
apex: wider and less stiff - low frequencies
322
what are the receptor cells of the organ of Corti? what are they called?
hair cells
mechanoreceptors with hairlike stereocilia protruding from one end
323
what are the groups of hair cells?
2 anatomically separate
single row of inner hair cells
4-5 rows of outer hair cells
324
where do the stereocilia lie? what do they do?
extend into endolymph fluid and convert pressure waves caused by movement of fluid in cochlear duct into receptor potentials
embedded in overlying tectorial membrane - mechanically alter its movement to sharpen frequency tuning at each point on basilar membrae
325
what leads to bending of the stereocilia?
pressure waves displace basilar membrane - hair cells move in relation to the stationary tectorial membrane
326
what causes the membrane of hair cells on organ of Corti to depolarise?
stereocilia bend towards tallest member of bundle -> TIP LINKS pull open mechanically gated K+ channels -> influx of K+ from endolymph
327
what are TIP LINKS? what do they do?
fibrous connections
when stereocilia bend towards tallest member in bundle, tip links pull open mechanically gated K+ channels -> flow in from endolymph
depolarises membranes
328
what does the influx of K+ from endolymph lead to?
change in voltage triggers opening of voltage-gated Ca2+ channels near base of cell -> triggers neurotransmitter release
329
what happens when tip links slack?
bending hair cells in opposite direction
closes K+ channels and cell rapidly depolarises
330
what is the neurotransmitter released from the hair cells of organ of Corti? what does it do?
glutamate - binds to and activates protein binding sites on terminals of afferent neurones
331
what happens as sound waves vibrate basilar membrane?
stereocilia bend back and forth, membrane potential rapidly oscillates and bursts of glutamate are released onto afferent neurons
332
what makes up the cochlear branch of the vestibulocochlear nerve (VIII)?
axons from afferent neurons
333
where does the cochlear nerve join the brainstem?
at the level of the rostral medulla
334
what happens to the cochlear nerve after it joins the brainstem?
fibres bifurcate and end in the dorsal and ventral cochlear nuclei (close to inferior cerebellar peduncle)
335
where are the dorsal and ventral cochlear nuclei?
close to inferior cerebellar peduncle
336
what happens from the cochlear nuclei?
second-order neurons ascend into the pons where fibres travel to superior olivary nucleus
337
what happens in the superior olivary nucleus?
has fibres that leave the brainstem in the vestibulocochlear nerve and end in the organ of Corti - inhibitory function
adjust transmission of auditory info through cochlear nerve by mediating contractions of tensor tympani to loud noises
338
where do fibres travel from the superior olivary nucleus?
inferior colliculus of the midbrain
339
what happens from the inferior colliculus of the midbrain in the auditory pathway?
inferior brachium (nerve fibre carries auditory information to medial geniculate body of the thalamus
340
what happens from the medial geniculate body in the auditory pathway?
fibres travel through the internal capsule to the primary auditory cortex of the temporal lobe
341
where is the primary auditory cortex located?
temporal lobe - dorsal surface of the superior temporal gyrus
342
what is the overall neural auditory pathway?
cochlear nerve -> brainstem at rostral medulla -> bifurcation, end in dorsal and ventral cochlear nuclei -> superior olivary nucleus -> inferior colliculus (midbrain) -> medial geniculate body (via inferior brachium) -> internal capsule -> primary auditory cortex (Wernicke's area)
343
where is the medial geniculate body?
thalamus
344
where is the inferior colliculus?
midbrain
345
what does the inferior brachium do?
nerve - transmits auditory info from inferior colliculus to medial geniculate body
346
what is Wernicke's area? what does it do?
region of the temporal lobe surrounding the primary auditory cortex
auditory information is interpreted and understood
superior temporal lobe
processing language in the brain
347
what is Wernicke's aphasia?
patient can't understand questions and speech will be incomprehensible
348
what is involved in the visual pathway?
superior colliculus
lateral geniculate body
349
what is the chorda tympani? what does it do?
branch of facial nerve (CNVII)
taste information from tongue
runs through middle ear to carry taste messages to brain
350
what is Bell's palsy?
acute unilateral inflammation of the facial nerve - pain behind ear (chorda tympani and facial nerve in internal acoustic meatus)
paralysis of facial muscles and failure to close eye
351
where does the facial nerve exit the cranial cavity?
internal acoustic meatus behind the cochlea - inflammation may result in pain behind ear
352
what is the vestibular apparatus?
connected series of endolymph filled, membranous tubes that also connect with the cochlear duct
353
what does the vestibular apparatus consist of?
3 membranous semicircular canals and 2 saclike swellings - utricle and saccule
lie in temporal bone on either side of head
354
what do the hair cells in the vestibular apparatus detect?
changes in motion and position of the head by stereocilia transaction mechanism
355
what do semicircular canals detect?
angular acceleration during rotation of the head along 3 perpendicular axes
activated when nodding head up and down, shaking from side to side and tipping head so ear touches the shoulder
356
what is the structure of the stereocilia in the receptor cells of the semicircular canals?
encapsulated within a gelatinous mass (capula)
capula extends across lumen of each semicircular canal at the ampulla (slight bulge in wall of each duct)
357
how are signals about the movement of the head sent to the brain?
semicircular canal and attached bodies of hair cells move with head when moving
endolymph - not attached to skull. remains in position (inertia)
moving ampulla pushed against stationary fluid -> bending of stereocilia and alteration in rate of release of glutamate from hair cells
glutamate crosses synapse and activates neurones associated w/ hair cells, initiating propagation of action potential towards brain
358
what determines the direction in which stereocilia are bent in?
speed and magnitude of rotational head movements
359
stereocilia in the semicircular canals and neurotransmitter release
each hair cell receptor has one direction of maximum neurotransmitter release
stereocilia bent in this direction -> receptor cell depolarises
other direction -> hyperpolarises
360
what happens when the head continuously rotates at a steady velocity?
duct fluid begins to move at same rate as rest of the head
stereocilia return to resting position
hair cells only stimulated by acceleration/deceleration
361
what are hair cells stimulated by?
acceleration/deceleration
362
what does damage to the semicircular canals of one side lead to?
nystagmus
363
what is nystagmus?
rapid, jerky, back and forth movement of eyes
slow phase towards damaged side and rapid reset away from damaged side
364
what else can cause nystagmus?
pouring ice cold water into external auditory meatus -> convection currents in semicircular canals
