1
Q
What are the two major cellular building blocks of the CNS?
A
- Neurons
- Glial cells
2
Q
Where do neurons originate from?
A
Neural stem cells
3
Q
How many neurons are there in the brain?
A
100 billion
4
Q
What percentage of all brain cells do neurons make up?
A
10%
5
Q
What is the role of neurons?
A
o Role- cause action potentials to be generated, which is essential for communication (basis for memory, learning…)
6
Q
What is the typical size of neurons?
A
5 microns to 100 microns
7
Q
What are the main parts of neurons and what parts of the brain do they make up/ what is their role?
A
o Composition
Cell body- soma
• Grey matter
Dendrites- synaptic processes from soma that receive input from other neurons
Axon- projects information from soma
• White Matter due to axonal myelination from oligodendrocytes
8
Q
When do neurons proliferate?
A
Neuronal proliferation (generation of neuroblasts) in first 5 months of pregnancy
9
Q
When do neurons differentiate?
A
Neuronal differentiation in 4-9 months of pregnancy
10
Q
Are neuronal connections only formed prenatally or can they be formed postnatally?
A
Neuronal connections continue to form postnatally
11
Q
What glial cells are there?
A
o Astrocytes
o Oligodendrocytes
o Microglia
o Ependymal cells
12
Q
Where do astrocytes originate from?
A
Origin- neural stem cells but late differentiation
13
Q
Where do oligodendrocytes originate from?
A
Origin- neural stem cells but late differentiation
14
Q
Where do microglia originate from?
A
Origin- derive from external bone marrow
15
Q
Where do ependymal cells originate from?
A
Origin- neural stem cells but late differentiation
16
Q
What are the overarching functions of astrocytes?
A
Functions- • Homeostatic functions • Structural support • Contribute to blood brain barrier • Response to injury
17
Q
What is the function of oligodendrocytes?
A
Functions-
• Myelination of axons which allows speed of action potential along axons to be increased
• Occurs postnatally
18
Q
What are the functions of microglia?
A
- Resident immune cells of CNS
- Phagocytosis
- Response to injury
19
Q
What is the difference between activated microglia and homeostatic microglia?
A
o Activated microglia- thick processes and becomes amoeboid
o Homeostatic microglia- thin processes
20
Q
What are the functions of ependymal cells?
A
Functions-
• Line ventricles
• Responsible for choroid plexus growth
• Produce CSF
21
Q
What are the origins of dorsal/ventral organisation of sensory and motor systems?
A
o Patterns of differentiation
Midline mesoderm (and later the notochord which sits at midline of neural groove and is positioned ventrally) produces a signalling molecule called Sonic Hedgehog (SHH) which causes neuroblasts in close proximity to mesoderm to become motor neurons
Ectoderm next to the neural plate produces an opposing signalling molecule Bone Morphogenetic Proteins (BMPs) which causes neuroblasts to differentiate into sensory neurons
22
Q
Describe the origin of the alar/basal organisation in the spinal cord
A
o Functional organisation
Different gradients of signalling molecules establish a functional organisation which persists in adult spinal cord
Alar (dorsal) derivatives become sensory neurons, whilst basal (ventral) derivatives become motor
23
Q
What genes are responsible for determining rhombomere functioning and cranial nerve distribution in these rhombomeres?
A
• Hox genes are responsible for determining function of rhombomeres (parts of rhombencephalon) and which cranial nerve type will be expressed at each rhombomere level
o At each rhombomere level, there is a different set of genes being expressed
24
Q
What is hox gene expression in rhombomere rostrocaudal organisation determined by? Describe the gradient in rhombomere terms
A
Hox gene expression is determined by gradient of FGF8 and Retinoic Acid
• High Retinoic Acid concentration at rhombomere 8 (caudal)
• High FGF8 concentration at rhombomere 1 (rostral)
25
How many layers of cells are there within developing embryo, and what are they?
o Within developing embryo, there are three layers-
Ectoderm- outer layer of cells
• Nervous system develops from the ectoderm
Endoderm- innermost layer of cells
Mesoderm- middle layer of cells
26
Describe a timeline of the general development of the brain
* 3rd Week- Formation of neural groove and beginning of nervous system development
* 4th week- Primary neurulation and formation of the primary vesicles
* 5th -6th week- The secondary vesicles
* 6th- 12th week- Shaping the telencephalon
* 2nd month to 4th month- Formation of temporal and frontal lobes
* 37 days to 50 days- Cavity of the neural tube becomes ventricular system
* 31 weeks onwards- Progressive development of cortical convolutions (sulci and gyri)
* Continued growth of telencephalon
27
Describe a general outline of the development of CNS
Ectoderm-> thickens to form neural plate->folds and fuses to form neural tube-> divides into prosencephalon, mesencephalon, rhombencephalon and spinal cord
Prosencephalon divides into telecenphalon (which divides into cerebral cortex and basal ganglia) and diencephalon (which divides into retina, thalamus and hypothalamus)
Mesencephalon becomes midbrain
Rhombencephalon divides into metencephalon (which becomes the pons and cerebellum) and myelencephalon (which becomes the medulla)
Spinal cord divides into alar plate (which becomes the dorsal horn) and the basal plate (which becomes the ventral horn)
28
Describe in general terms the development of the PNS
Neural crest cells migrate to become DRG, Shwann cells, melanocytes, enteric ganglia, sympathetic ganglia
29
Describe how the neural groove is formed
o Midline mesoderm releases signalling molecules (noggin and chordin) which lead to thickening of the overlying ectoderm to form the neural plate
o Neural plates then folds inwards to form the neural groove
30
Once the neural groove is formed, how does primary neurulation and formation of the primary vesicles occur? Include a timeline. What happens directly after primary neurulation?
o Neural groove further folds inwards and gets deeper and deeper (day 20)
Between the ectoderm border and the neural groove is the neural crest
o Primary neurulation- Neural tube closes (begins on day 21 and finishes on day 26)
o Groups of cells from the neural crest are left behind and separate from neural tube – developed neural crest is INDEPENDENT of neural tube
Form dorsal root ganglia
Form autonomic ganglia
Form adrenal medulla
o Closure of neural tube results in ectoderm continuation overlying the neural tube (which will form the skin)- neural tube detaches from overlying ectoderm
31
What nervous system does the neural groove become?
CNS
32
What nervous system does the neural crest become?
PNS
33
When does the rostral end of the neural tube close during primary neurulation and what will it become?
o Primary neurulation- Neural tube closes (begins on day 21 and finishes on day 26)
Rostral end- where the brain will form
• Rostral end of neural tube closes on day 24
34
What structural features form as the rostral end of the neural tube closes?
```
o Primary vesicles-
Prosencephalon
Mesencephalon
Rhombencephalon
o Curvature-
Cervical flexure
• Between spinal cord and rhombencephalon
• Disappears in the adult brain
Cephalic flexure
• Between rhombencephalon and mesencephalon
• Persists in adult brain
```
35
When does the caudal end of the neural tube close and what will it become?
Caudal end- where the spinal cord will form
| • Caudal end of neural tube closes on day 26
36
What can happen if there is a failure to close the rostral end of the neural tube?
• Failure of rostral end of neural tube to close is a fatal developmental defect which will result in death of embryo
37
What can happen if there is a failure to close the caudal end of the neural tube?
• Failure of the caudal end of the neural tube to close results in spina bifida
38
Describe the 3 different types of spina bifida and their characteristics
o Spina bifida occulta- most mild form of spina bifida.
Where vertebrae surrounding the spinal cord are not fully developed
o Meningocele- more severe form of spina bifida.
Meninges is outside vertebral canal and sitting close to skin in sac-like structure
o Myelomeningocele – most severe form of spina bifida.
Spinal cord and meninges outside vertebral canal and sitting in sac-like structure
Leads to loss of control in lower limbs and bowel movements
Caused by vitamin D12 deficiency
39
How is the 4th ventricle formed? Describe the motor/sensory organisation and structure around the 4th ventricle
Neural tube spreads apart to form diamond-shaped cavity with a thin membrane roof (pontine flexure)- 4th ventricle
At level of pons, motor neurons are medial and sensory neurons are lateral
Dorsal/ventral orientation in the spinal cord becomes medial/lateral in the brain stem
• All basal structures stay medially (motor neurons)
• All alar structures move laterally (sensory neurons)
Sulcus limitans persists as an important boundary between sensory and motor neurons
• Sits between alar and basal plates
40
Describe how the telencephalon begins to be shaped and the involvment of the diencephalon in this shaping
• 6th- 12th week- Shaping the telencephalon
o Rostral tip of the neural tube forms a thin membrane- lamina terminalis
Lamina terminalis is the origin of the corpus callosum
o The basal part of the telencephalon thickens to form the pre-cursor of the basal ganglia- basal ganglia then folds back on the diencephalon
o The diencephalon thickens to form the thalamus and hypothalamus, separated by a sulcus
o By the end of the 12th week, the diencephalon and telencephalon have fused
41
Describe how the temporal and frontal lobes are formed
• 2nd month to 4th month- Formation of temporal and frontal lobes
o Starts growth in temporal and frontal direction at 2nd month
o Each cerebral hemisphere assumes the shape of a great arc around the insula
o Parts of the hemisphere originally dorsal to the insula get pushed around into the temporal lobe
42
When does neuronal proliferation peak?
5 weeks to 5 months
43
Where does neuronal proliferation occur?
Occurs in the ventricular zone
44
How does the cleavage plane off neuroblasts during neuronal proliferation change as development progresses? What are the consequences of this change?
o Cleavage plane importance
During early development, there is vertical cleavage in neuroblast cells
• Both daughter cells can go on to replicate themselves
• Large capacity for developing new neuroblasts
During late development (after 5 months), there is horizontal cleavage of neuroblast cells
• Only one daughter cell can divide again
• The other cell will migrate to its final destination in the nervous system
• Lower capacity to proliferate
45
How does the cleavage plane during cell division determine neuroblast cell during development? What are the consequences of this?
Cleavage plane during cell division determines neuroblast fate due to signalling molecule positioning
• Signalling molecules and effects
o Notch signalling molecule- away from ventricular surface at top
Cell migrates away to final destination and stops division
o Numb signalling molecule- close to ventricular surface at bottom
Cell continues to dive
• Horizontal cleavage- one daughter cell gets notch, one gets numb
• Vertical cleavage- both daughter cells get both notch and numb
o Numb is inhibitory to notch, and hence the daughter cells continue to divide
46
Describe how the 6 layered cerebral cortex is developed and the cells used to help this process
o Inside-out development of 6 layered cerebral cortex
Radial glial cells- provide scaffold on which cortex is built and guides migration of neuroblasts along their thin fibres
Neuroblasts migrate from ventricular surface along radial glia and cross the subplate to arrive in the cortical plate (first cells become layer VI neurons)
• Innermost layers form first
47
When does differentiation of astrocytes peak?
At birth
48
When does differentiation of oligodendrocytes peak?
Postnatal and throughout adulthood
49
Describe what differentiation into a specific phenotype is based on
o All differentiation into specific phenotype is based on signalling molecules which reside in anatomical location where it finishes its migration path
50
Which arteries does the brain blood supply come from?
The internal carotid artery (2/3) and vertebral arteries (1/3)
51
Which arteries can you see in the lateral view of the brain?
o Internal carotid artery system
Middle cerebral arteries and their branches
Anterior cerebral arteries and their branches
52
Which arteries can you see in the medial view of the brain?
o Vertebral arteries system
Posterior inferior cerebellar arteries
Anterior inferior cerebellar arteries
Superior Cerebellar arteries
Posterior cerebral arteries and their branches
Anterior and posterior spinal arteries
53
What are the main dural sinuses?
```
• Superficial and deep cerebral veins drain into the dural sinuses:
o Superior sagittal sinus
o Inferior sagittal sinus
o Cavernous sinus
o Sphenoparietal sinus
o Basilar sinus
o Straight sinus
o Great cerebral vein
o Transverse sinus
o Confluence of sinuses
o Superior and inferior petrosal sinuses
o Sigmoid sinus and drainage
```
54
Is the brain hollow? True or False?
• The brain is hollow
55
Where did the lateral ventricles develop from?
• Lateral ventricles developed from telencephalon
56
What forms the walls of the third ventricle?
• Thalamus and Hypothalamus form walls of third ventricle
57
Where is the 3rd ventricle located?
Diencephalon
58
What does the diencephalon consist of?
```
Thalamus
Hypothalamus
Epithalamus
Subthalamus
Retina
```
59
Describe what surrounds the 4th ventricle
• 4th ventricle is surrounded by brainstem (include mesencephalon) and cerebellum
60
Describe the CSF pathway
Choroid plexus->lateral ventricle Interventricular foramen-> 3rd ventricle -> cerebral
aqueduct -> 4th ventricle- > median and lateral apertures -> cerebellomedullary cistern-> pontine cistern OR superior cistern ->interpeduncular cistern-> cistern of the lateral cerebral fossa-> arachnoid granulations of
superior sagittal sinus
61
What is the structure of the blood brain barrier?
o Non-fenestrated capillaries with tight junctions surrounded by basement membrane formed by an insoluble protein secreted by pericyte, whose structural and functional character is maintained by surrounding adjacent astrocyte foot processes
62
What maintains the blood brain barrier?
Astrocytes secrete molecules which maintains non-fenestrated morphology
63
What forms a neurovascular unit?
o Neurons, astrocytes and brain capillaries may form a neurovascular unit
64
What iss the role of the blood brain barrier?
• The role of the blood brain barrier is to protect the brain from neuroactive and neurotoxic substances
o Neuroactive compounds (amino acids, bioamines, neuropeptides, drugs…) have to be kept out of the brain
o Neurotoxic compounds (such as cytokines) have to be kept out of the brain
• Desirable substances (such as oxygen, glucose) must be allowed to enter and leave
65
Why do neuroactive compounds need to be kept out of the brain
Neuroactive compounds interact with receptors and could activate/inhibit neurons haphazardly- this is why they need to be kept out
66
Why do neurotoxic compounds need to be kept out of the brain?
Neurotoxic compounds can overexcite cells and can trigger process that leads to death of neurons, or can be toxic to neurons specifically
67
How can the blood brain barrier get damaged by and why?
• The blood brain barrier can be damaged or altered by:
o High blood pressure for a very long time-> capillaries can be mechanically damaged and broken
o Infections (thought that inflammatory response can accidently change and damage the blood brain barrier)
o Specific compounds (N-Acetyl-aspartyl-glutamate, quinolinic acid, hormones, vascular endothelial growth factor)
o In brain tumours (due to abnormal, non-functioning astrocytes pushing out normal astrocytes)
o In multiple sclerosis (inflammatory disease which can cause breakdown in BBB)
o Brain oedema (stroke, head injury can cause permanent loss of neurons)
68
Why do some parts of the brain have a naturally low blood brain barrier and where are these parts?
• Even in healthy organisms, some parts of the brain have a naturally low blood brain barrier (circumventricular organs: organum vasculosum of lamina terminalis, area posterema)
o These areas are permeable to certain compounds as they monitor blood content through their receptors and alarm brain if something toxic is detected
69
What is De Vivo disease?
• De Vivo disease: glucose transport (via GLUT1) is compromised, patients tend to have serious problems such as mental retardation
70
How can compounds cross the blood brain barrier? Give examples
o They can dissolve in the lipid component of BBB (Such as caffeine, nicotine or ethanol)
More lipophilic compounds pass more easily across the blood brain barrier (BBB)
Some lipid soluble undesirables can get through
Large molecules (proteins) do not normally get through but sometimes they do (like viruses)
Molecules that have a high oil-water partition coefficient (dissolve more readily in oil than water (lipophilic vs hydrophilic) dissolve more easily through the Blood Brain Barrier
o They are actively transported
Phenylalanine, D-Glucose, L-DOPA and essential amino acids (which contain aromatic groups not synthesised naturally by mammals) are actively transported across the blood brain barrier
Fast process
Different transporter used for each molecule
o If via cerebrospinal fluid which is taken up by brain
Hormones and vitamins
Route via CSF is slower than the active transport
71
How can you modify drugs to cross the blood brain barrier
o Making them more lipophilic (e.g. by adding an aromatic component (lipophilic moiety to the molecule to make it less charged))
Such treatment may change chemical or pharmacological characteristics of the compounds- increases specificity
o Synthesizing prodrug compounds with little or no pharmalogical activity but readily crossing the blood brain barrier, then converting to active compounds
E.g. heroin which, when reaching the blood brain barrier, is converted into morphine which can have a dramatic effect
o High intensity focused ultrasound (except it opens blood brain barrier for everything)
But if it can be focused, then can introduce drug into small part of the brain
72
What is the first sense active in newborns?
Olfaction
73
How is olfaction stimulated?
o Stimulation through ingestion of odorants with respiratory movements
74
Are we born with inbuilt codes of olfaction or are they learned?
o Born with inbuilt codes of olfaction
75
Do different smells activate the same or different brain regions?
different smells activate different brain regions
76
What is the sense with the most direct route to the brain system in which affect (feeling) is generated?
• Olfaction is the sense with the most direct route to brain system in which affect is generated
o Affect- feeling state
o Smell is tightly coupled to emotional experience of the world and creation of emotional memory
77
What are the uses of olfaction and the olfactory system?
* Location of food, mate and danger
* Drives behavioural state changes
* Alters sensory responsiveness
* Can itself be altered by behavioural state and mood
78
What types of neurons are olfactory receptors?
Bipolar projection neurons
79
How many olfactory receptors are there per nostril
6 million
80
On what type of epithelium do olfactory receptors reside on?
o Sit in pseudostratified columnar epithelium
81
Are olfactory receptors able to regenerate? If so, when?
o Able to regenerate after 10 days
82
What is on the end of the olfactory knob?
o Possess rigid cilia (3-50 per cell) on end of olfactory knob and axonal endings
83
What is the purpose of olfactory cilia?
Cilia increase surface area with which odorant can react with sensory receptor
84
How many receptor proteins are on cilia in humans and what is the consequence of this?
About 500-1000s receptor proteins on cilia in humans- means that humans have the ability to detect several thousand chemical structures
85
Why does each individual cell respond slightly differently to different constellations of odor?
Each cell has only one receptor protein, which responds to a wide range of odorants depending on its chemical composition
• Receptor bind specific chemical elements of an odorant
o Means that each cell will respond slightly differently to different constellations of odor
• Individual receptor cells respond to odorants with one specific structure
86
Where do olfactory axons pass through from the nose to the brain? Do they pass singularly or are they grouped?
o 10-100 cell axons penetrate each space in the cribriform plate of the ethmoid bone
87
Are olfactory receptor cell axons myelinated or unmyelinated?
Unmyelinated- transmission speed is slow
88
Where are olfactory receptors located?
o Olfactory receptors are located in the nasal cavity
Located in the olfactory mucosa but can also be found as low as the inferior turbinate and in the retronasal region as well
89
Why are olfactory receptors isolated from each other?
Receptors are isolated from each other so electrical discharge does not get distorted by their neighbours
90
What is the role of Bownmans glands in the olfactory system?
• Bowmans glands constantly secrete mucus in mucosa to allow for odorants to be better detected and for detoxification and degradation of odorants
91
Describe the role of olfactory receptors in the retronasal region?
• Those in the retronasal region would be important for detection of flavours
92
What are the components of olfactory mucosa and why?
```
• Mucosa contains many different chemicals to protect brain from harmful components
o Glycoproteins
o Free ionic salts
o Fluid
o Antibodies
```
93
Describe how odorants can generate an action potential in the olfactory system
o Olfactory receptors mechanism
In the mucous layer
• Odorants get dissolved on cilia surface- move from air phase to aqueous phase
• Odorants bind to receptors found on ciliated structures
In the cell and intracellular fluid
When receptors are bound, a G protein coupled intracellular signalling pathway (including adenylate cyclase and then cAMP) is activated
This allows cation channels to open to allow the influx of both sodium and calcium into the cell, generating the action potential
94
What is the purpose of the turbinates/nasal conchae in the olfactory system?
• Bones of internal nasal structure are called the turbinates/ nasal conchae
o These bones make the air swirl around, which makes sure that any odorant in the air that is breathed in gets maximum exposure to the receptor cell layer in the uppermost portion of the nasal cavity
95
Where is the olfactory bulb?
o Found on ventral part of frontal lobes
| o Encased by pia mater and arachnoid mater
96
What are the origins of the olfactory bulb?
o Derived from telencephalon
97
What does the olfactory bulb comprise of?
```
o Comprises of:
Neurons
Afferent
Efferent nerve fibres
Interneurons
Microglia
Astrocytes
Blood vessels
```
98
Where is the location of the first synapse in the olfactory pathway?
Olfactory bulb
99
How many layers does the olfactory bulb have and what are they?
```
o Six concentric cellular layers
1st layer- olfactory nerve layer
2nd layer- Glomerular layer
3rd layer- external plexiform layer
4th layer- mitral cell layer
5th layer- internal plexiform layer
6th layer- granule cell layer
```
100
In what layer of the olfactory bulb do receptor cells synapse?
• Receptor cells synapse in glomerular layer
101
What is the glomerulus made of? Does it recieve inputs from singular or multiple olfactory receptors?
o Glomerulus- formed from incoming axons of CNI and the primary dendrite of the mitral cells
• Axons from similar receptor cells converge in common glomeruli
o Each glomerulus structure receives inputs from multiple olfactory receptors
102
What cells output from the olfactory bulb?
• Main output cells are mitral cells and tufted cells regulated by glomeruli
103
What cells do apical dendrites of mitral cells and tufted cells receive signals from? What is the use of these signals?
o Apical dendrites of mitral cells and tufted cells receive signals from:
Olfactory receptor cells (in the glomeruli)
Interneurons in the glomerular layer and the granule cell layer
• Lateral inhibition- interneurons can amplify or turn down signals coming into olfactory system-> selection of interesting smells
Incoming nerve fibres from the brain which contain a number of neurotransmitters, including dopamine, acetylcholine, noradrenaline and GABA which tune olfactory bulb in order to amplify signals from smells the brain is currently interested in
104
Which olfactory bulb layer is the biggest layer?
Granule cell layer (1/2 volume of the bulb)
105
What is the role of the olfactory bulb?
o Olfactory bulb is first stage in decoding the various patterns of synaptic input associated with different odorants- mitral cell axons then protect to olfactory cortex via olfactory tract
106
What are the primary olfactory regions?
```
o Anterior olfactory nucleus
o Olfactory tubercle
o Piriform cortex
o Pre-piriform cortex
o Peri-amygdaloid cortex
o Entorhinal cortex
o Amygdala
```
107
What are the secondary olfactory regions?
```
• Secondary olfactory regions (get input from primary olfactory regions)
o Hippocampus
o Hypothalamus
o Thalamus
o Orbitofrontal cortex
o Cerebellum
```
108
Where is the anterior olfactory nucleus located?
Located behind the olfactory bulb
109
Where does the anterior olfactory nucleus project to?
Projects contralaterally into the olfactory bulb and the primary olfactory regions (via the anterior commissure)
Projects ipsilaterally into primary olfactory regions (olfactory tubercle and anterior perforated substance)
110
What is the role of the anterior olfactory nucleus?
Thought to regulate olfactory function ((phylogenetically old system- dichotomous behavioural response: whether something needs to be approached or avoided)
111
What input does the olfactory tubercle recieve?
Receives a massive dopaminergic input from ventral tegmental area and substantia nigra, in addition to odorant information
112
What is the role of the olfactory tubercle?
Critic for odor guided behaviours, but not sense of smell
| • Required for prediction of what will happen based on past experience with smell which will drive behaviour
113
What does the olfactory tubercle project to ?
Projects to medio-dorsal thalamus, which projects onto insular and orbital frontal cortex
• Medio-dorsal thalamic recipient areas encode context and emotional experiences associated with smell
114
What does the piriform cortex include?
```
Includes the:
• Olfactory tract
• The uncus
• Cortical amygdala
• Anterior part of the parahippocampal gyrus
```
115
What is the role of the piriform cortex for olfaction?
For emotional memory formation in which smell plays a big part
Piriform cortex has anterior and posterior sub-regions
• Anterior= chemical detection
o Intensity
o Particular chemical quality
• Posterior= odor categorisation
116
What does the piriform cortex project to in the olfactory system?
Piriform cortex also projects into other primary olfactory regions including entorhinal cortex, amygdala, anterior olfactory nucleus
Also projects into secondary olfactory region mediodorsal thalamus
117
How are odors represented in the pre-piriform cortex and the peri-amygdaloid cortex?
In broad patches
118
What does the entorhinal cortex project to in the olfactory system and what is the role of each of these projections?
Entorhinal cortex projects to hippocampus, insular cortex, orbital frontal cortex, hypothalamus and amygdala (via the uncinate fasciculus)
• Hippocampus- memory
• Insular cortex and orbital frontal cortex- smell memory driven behavioural selection
• Hypothalamus- defensive behaviours
119
Where is the septal nuclei located?
Located below the rostrum of the corpus callosum/anterior to lamina terminalis
120
What do septal nuclei project to in the olfactory system?
Projects to hypothalamus and older parts of the limbic system
121
What is the role of the septal nuclei in the olfactory system?
Not thought to play a role in sense of smell rather in guiding behaviours related to reward and reinforcement (phylogenetically old system)
122
What does the anterior perforated substance recieve input from in the olfactory system?
o Anterior perforated substance
Cells in the anterior perforated substance form part of the olfactory nucleus/tubercle
In addition to direct mitral cell collaterals it receives input from the anterior olfactory nucleus, amygdala and temporal cortex
123
What does the anterior perforated substance project to in the olfactory system and what is the consequence of this?
This area ultimately projects to the stria medullaris into the habenular nuclei and medial forebrain bundle
• Habenular nucleus- where depressive like behaviours might be
124
Describe the olfactory pathway
1. Sensory receptors in nasal mucosa detect chemical odorant
2. Send signal through axon
3. Axons pierce cribriform plate
4. Fibres make contact with olfactory bulb
5. Information goes to olfactory tract, which then moves posteriorly and splits into two divisions: the medial tract and the lateral tract
6. Sends signals to other cortical structures (primary olfactory regions) which send signals to secondary olfactory regions
a. Does not have obligatory thalamic relay
125
Describe the medial olfactory tract
i. Medial fibres of the tract synapse the anterior olfactory nucleus and the septal area. Some fibres project to the contralateral olfactory bulb via the anterior commissure
1. Primitive olfactory system
126
Describe the lateral olfactory tracts
b. Lateral olfactory tract
i. Lateral fibres synapse on third-order neurons in the olfactory tubercle
ii. Lateral fibres synapse on third-order neurons in the olfactory cortex/primary olfactory cortical regions (pre-piriform cortex, piriform cortex, peri-amygdaloid cortex and entorhinal cortex) directly
1. New olfactory system
2. Majority of fibres
iii. Lateral fires synapse on neurons in mediodorsal thalamus
1. Newest olfactory system
127
What are the components of the olfactory system?
* Olfactory receptors
* Bones of internal nasal structure are called the turbinates/ nasal conchae
* Olfactory bulb
* Primary olfactory regions
* Secondary olfactory regions (get input from primary olfactory regions)
128
What are the two types of MRI scans and what are they the most useful for?
• Two types of MRI scans
o T1 scan
Regional brain volume and cortical thickness exploration advantage
o T2 scan
T2 images are slightly more sensitive than T1 images to myelin destruction or edema
Better for detection of brain pathologies
129
What is the colour of CSF in T1-weighted scans?
Dark
130
What is the colour of white matter in T1-weighted scans?
Light
131
What is the colour of cortex in T1-weighted scans?
Grey
132
What is the colour of fat in T1-weighted scans?
Bright
133
What is the colour of inflammation in T1-weighted scans?
Dark
134
What is the colour of CSF in T2-weighted scans?
Bright
135
What is the colour of white matter in T2-weighted scans?
Dark grey
136
What is the colour of cortex in T2-weighted scans?
Light grey
137
What is the colour of fat in T2-weighted scans?
Light
138
What is the colour of inflammation in T2-weighted scans?
Bright
139
How is an MRI image produced?
o Each atom contains protons which are positively charged and spinning around an axis
o This spinning charge creates a small magnetic field
o An MRI machine is effectively a large magnet so that when an individual is placed inside the magnet, their magnetic protons line up along the longitudinal axis with the MRI magnetic field
o A short strong electromagnetic pulse (radiofrequency pulse) is applied to disturb the spinning protons- this results in less of them spinning in the same axis as the MRI magnetic field and more spinning in a transverse plane
o Once the radiofrequency pulse is turned off, the protons return to their original direction along the MRI magnetic field- longitudinal magnetization gradually increases until it reaches the same point where it was before the radiofrequency pulse
140
What is T1 time in an MRI image?
The rate of the return of protons to their original direction along the MRI magnetic field is called the longitudinal relaxation time or T1 time
141
What is T2 time in an MRI image?
The rate of decrease of the transverse relaxation is called the transverse relaxation time or T2 time
142
Are T1 time and T2 time dependent or independent on each other?
The T1 and T2 relaxation times are different and are independent processes
143
What properties of the brain does MRI depend on?
• Principles of MRI
o Different tissues have different T1 and T2 relaxation times
o Water has a high T1 and T2 relaxation time whereas fat has lower T1 and T2 relaxation times
o By applying a series of radiofrequency pulses the MRI can distinguish between different tissues that have different relaxation rates
144
Which combination of scan times and field strengths make the best collection of MRI scans?
• Result collection of scans
o Taking multiple images and averaging them produces greater contrast between gray matter and white matter
o Even higher spatial resolution and grey/white differentiation is possible with longer scan times and higher field strengths
145
Describe the components of the sensory apparatus (tongue)
o Soft palate (Cranial nerve VII)
o Epiglottis and epiglottal papillae (Cranial nerve X)
o Papillae
Cirumvallate papillae (Cranial nerve IX)
Foliate papillae (Cranial nerve IX and VII)
Fungiform papillae (Cranial nerve VII)
Contain taste buds in walls
146
Describe the structure of taste buds
• Buds are comprised of a number of different sensory cells, which have a common opening (small pore known as the taste pore)
147
Do taste buds regenerate? When and from what?
• These cells are regenerated over days- derived from cells in the basal lamina of the tissue
148
Through what fibres do taste buds relay information to the CNS?
• They are sensory cells that make synaptic contact with afferent fibre which will send information to CNS (unlike gustatory receptors, which have their own axon)
149
Do different taste buds respond to all chemicals in the same way or in a different way? How does this work?
• Different taste bud cells only respond to a particular kind(s) of certain chemicals- the gustatory afferent axon they synapse with reflects this, as fibre discharges only to chemical that cell responds to
o Fidelity of transmission- when the cell detects a particular chemical, its associated fibre will fire only to that chemical (labelled line code)
150
How is saltiness detected?
o Amyloride-sensitive sodium channel in cell membrane (epithelial sodium channel) activates
o Membrane depolarised and voltage gated sodium and calcium channels open
o Calcium enters cell
o Neurotransmitter released onto sensory fibres
o Depolarisation in postsynaptic nerve fibre
o Tight synaptic coupling and high fidelity- will not activate other adjacent cells not responsive to saltiness
151
How is sourness detected?
o Membrane depolarised by action of hydrogen ions by hydrogen ions entering through amiloride sensitive sodium channels and hydrogen ions inhibiting potassium channels
o Membrane depolarised and voltage gated sodium and calcium channels open
o Calcium enters cell
o Neurotransmitter released on to sensory fibres
o Depolarisation
152
How is bitter, sweet or umami detected?
o Specialised G-protein coupled receptors which activate phospholipase C
o Phospholipase C activates IP3
o Calcium released from intracellular stores
o Triggers voltage gated sodium and calcium channels to open
o Transmitter released onto sensory afferent fibres
o Depolarisation
153
What are the bitter receptors?
Bitter receptors: T2 receptors
| • Can have different conformations in membrane
154
What are the sweet receptors?
Sweet receptors: T1R2 receptors and T1R3 receptors
| • Have to be both bound simultaneously by sugary substances to transduce experience of sweetness
155
What are the umami receptors?
Umami receptors: T1R1 receptors and T1R3 receptors
156
How will cells respond to taste sensations?
• Cells will respond to taste sensations as a function of the representation of the basic tastes within that tastant – compound sensations
157
Describe the taste pathway up until the structure that is the origin of all mar taste pathways in the brain
• Taste fibres enter the brain in the brainstem
o Cranial nerves attached to papillae/cavity enter as a visceral sensory nerve into the lateral aspect of the open medulla and synapse in the nucleus of the tractus solatarius (NTS)
NTS- origin of all major taste pathways in the brain
158
From the NTS, describe the conscious perception pathway for all the different cranial nerves responsible
For Cranial nerves VII and IX: Nucleus of Tractus Solatarius-> travel ipsilaterally to caudal ventroposteriormedial nucleus of the thalamus-> primary gustatory cortex (insula cortex)
For Cranial nerve X (vagus): Nucleus of Tractus Solatarius->via the parabrachial nucleus-> travel ipsilaterally to caudal ventroposteriormedial nucleus of the thalamus-> primary gustatory cortex (insula cortex)
159
Where is the parabrachial nucleus and what input does it receive?
• Parabrachial nucleus-> found at the junction of the pons and midbrain
o Taste input from back of mouth (because of innervation from CNX)
160
What input does the ventroposteriormedial nucleus of the thalamus recieve in addition to taste?
• Ventroposteriormedial nucleus of the thalamus is also the sensory nucleus for the trigeminal nerve (somatosensation from head)
161
Where is taste perception thought to be encoded?
In the insular cortex
162
Describe the pathway responsible for evoking reflexive motor behaviours in response to taste (from the NTS)
Nucleus of Tractus Solatarius -> medullary reticular formation
• Medullary reticular formation: salivatory nuclei, orofacial motorneurons, trigeminal complex (facial sensation and motor output to mastication muscle)
163
What are examples of reflexive motor behaviours evoked in response to taste? Do these responses change over time?
• Taste reflexes
o Tastes also evoke reflexive motor behaviours, for example changes in facial expression and tongue movements that are interpreted as hedonic or aversive states
For babies and mammals-
• Gaping- for aversive tastes
• Stick tongue out to increase surface area- for good tastes
When increase experience of these tastes, responses are elaborated to include the ventral tegmental area and the nucleus accumbens
• Used to shape our attraction to food tastes
164
Describe the taste pathway responsible for emotional memory around taste experience (from NTS)
Nucleus of Tractus Solatarius-> (parabrachial nucleus for cranial nerve X) -> hypothalamus/amygdala
• Emotional memory around chemical experience
• Taste affect-> amygdala and hypothalamus pathway
• Taste reflex-> only hypothalamus pathway
165
What is the pathway that triggers copious salivation in response to taste (from NTS)
To trigger copious salivation, nucleus of the solitary tract-> thalamus-> hypothalamus->salivatory nucleus of the medulla for parasympathetic salivation (VII and IX)
166
Which structure can trigger the retching reflex in response to taste?
Nucleus of the solitary tract
167
What are the primary afferent taste fibres, where are their cell bodies found in and what part of the sensory apparatus of taste are they responsible for innervating?
o Primary afferent taste fibres are found in
Facial nerve (cell body in genicular ganglion)
• Receives chemosensory information from mucosa of palate and rostral 2/3rd of tongue
Glossopharyngeal nerve (cell body in inferior glossopharyngeal ganglion)
• Receives chemosensory information from caudal 1/3rd of tongue and rostral pharynx
Vagus nerve (cell body in inferior vagal ganglion)
• Receives chemosensory information from caudal pharynx and larynx
168
Where do the primary afferent taste fibres converge?
o Converge on caudal brainstem
169
What transduces the chilli/pepper taste?
o Trigeminal nerve- transduces “chilli” or “pepper” taste due to heat detected as somatosensory component of taste experience
170
Where do all primary afferent taste fibres project to?
o All primary afferent taste fibres project to the rostral 2/3rds nucleus of the solitary tract (NTS)
171
Are the taste pathways conserved or different in different mammals?
• Anatomical tracing studies confirm in other species that this is a restricted view of the pathways involved in taste perception-> all species have about same pathway for chemical sensation in nervous system and have same reflexive reactions to tastes
172
Where do smell and taste inputs converge and why?
• Convergence in discrete set of regions of CNS of smell and taste- where decisions about behaviours based on past states is occurring
o Cingulate gyrus
Pleasant/unpleasant experiences and emotional responses to them
o Orbitofrontal cortex
Select appropriate behaviours
o Insula
Area responsible for emotional responses
Maximal activity in anterior cingulate and insular cortex reflects congruent stimuli- stronger activation than for individual stimuli
• Prewired for stimuli that would present stronger activation together- expectation of stimuli that would occur together
173
Describe why an aversive experience may cause a loss of appetite
• Most of the taste experience in humans involves learning about taste
o Aversive experiences that are associated with specific foods/eating can lead to negative associations
People can lose desire to eat as consequence of mislearning of the association between side effects of particular treatment and the need to eat
174
What circuitry is essential to learning about food safety and what can happen if this circuitry is inhibited? Why may this be?
Ability to learn about food safety depends critically on acetylcholine
Blocking glutamatergic circuits means inability to learn about aversive stimuli but ability to learn about safe foods
This may be because cortex has both input about sensation (due to conscious gustatory ciruit) and emotion of taste (due to bidirectional connection to amygdala)
175
Describe how learning about the safety of a new food occurs and what happens if the new stimulus is aversive
• Cortex also gets input from nucleus basalis magnocellularis
o Massive cholinergic nucleus in base of forebrain
o Floods insula cortex with acetylcholine when new situations arise
Allows novel taste experience to be coded as safe or unsafe
o The acetylcholine binds to muscarinic receptors
o Activation of muscarinic receptor phosphorylates the NMDA receptors which unblocks the NMDA receptors, making it available for glutamate
o If experience that you had eating the new taste stimulus is bad, it releases glutamate from the basal lateral amygdala-> binds to free NMDA receptor-> potential for producing a new memory becomes cemented as a change in function of the neuron saying that the previous expectation that something you eat is safe is now a signal that it is unsafe
176
What are the periphery structures of the visual system?
```
• Periphery structures (still part of the CNS)
o Retina
o Optic nerve
o Optic chiasma
o Optic tract
```
177
Where does the retina come from?
Diencephalon
178
Describe the layers of the retina and the cells in these layers
```
Layers (from top to bottom)- light travels from the ganglion cells to the photoreceptors, while action potentials travel from photoreceptors to ganglion cells
• Ganglion cells
o Magnocellular
o Parvocellular
• Amacrine cells-interneurons
• Bipolar cells-interneurons
• Horizontal cells-interneurons
• Photoreceptors- receptive to light
o Cones
o Rods
• Pigment epithelium
```
179
What function do retinal ganglion cells serve?
these cells are the only ones that have axons projecting out of the retina into the optic nerve
180
What function do magnocellular cells serve?
Transmit/activated by information about motion
181
What function do parvocellular cells serve?
Transmit/activated by information about colour and form
182
What function do retinal amacrine cells and horizontal cells serve?
o Dampen down excessive visual input
183
What function do retinal bipolar cells serve?
o Connect photoreceptors to ganglion cells
184
What is the difference between rods and cones?
```
o Cones
Pick up different types of colours
Day vision
o Rods
Receptive to light
Night vision
```
185
What is the role of photoreceptors?
receptive to light
186
What is the role of the pigment epithelium?
o Absorbs any scattered light
o Phagocytes
Clears shed disks from photoreceptors as a result of transduction
187
What is the optic disk?
• Acts as a blind spot
| o Where all axons of ganglion cells collect and form the optic nerve
188
What does the central retina consist of?
* Fovea centralis- where photoreceptors are in the central retina
* Macula lutea- mountain of ganglion cells
189
Why is the fovea centralis so crucial for detailed vision?
o Light hits the photoreceptors directly
o Detail is increased
o Faithful transmission- one photoreceptor talks to one ganglion cell
Transmit accuracy
190
Where is the central retina located?
• Temporal to optic disk
191
Where is the nasotemporal division in the retina located?
• The nasotemporal division is at the fovea centralis
192
Why is our periphery vision not very accurate?
• One photoreceptor for 100000 ganglion cells
| o Each ganglion cell gets details for many photoreceptors so detail is not as great
193
What is macular degeneration and how does it occur?
• Macular degeneration: loss of vision from central retina
o Pigment epithelium undergoes degeneration first
o Photoreceptors die due to unfavourable environment
o Late stage- ganglion cells may degenerate
194
What is detached in retinal detachments?
• Retinal detachments
o Dislodged retina
o Detachments of pigment epithelium and photoreceptors
195
What is the difference between the optic nerve and the optic tract?
o Optic nerve
Contains fibres from one eye
o Optic tract
Contains fibres from both eyes
196
Describe what occurs in the optic chiasma in terms of decussations
Some fibres cross to the other side and others don’t
• Nasal fibres (medial side)- fibres decussate (contralateral)
• Temporal retina- fibres do not decussate (ipsilateral)
197
When there is blindness in one eye, is it a prechiasmatic issue or a postchiasmatic issue?
Prechiasmatic issue
198
When there is blindness in both eyes, is it a prechiasmatic issue or a postchiasmatic one?
Postchiasmatic issue
199
What are the central structures of the visual system?
```
o Hypothalamus
o Brainstem
Visual reflexes
o Thalamus
Main visual input that it projects to the cortex
o Optic radiation
o Cortex
```
200
What is the function of the conscious visual pathway?
Conscious vision
| Topography
201
What is the function of the lateral geniculate nucleus in the visual pathway? How does it perform this function?
• Organises ganglion cell axons in terms of function in different laminae (parvocellular or magnocellular regions)
• Organises ganglion cell axons in terms of topography and location in laminae (central or peripheral retina regions)- each laminae is about ½ a retina
• Organises ganglion cell axons in terms of eye location (lateral) in different alternating laminae (ipsilateral or contralateral regions)
o Each laminae driven by one or other eye- motion and colour have their own laminae as they come in from different eyes
202
What are the main structures in the conscious visual pathway?
Lateral geniculate nucleus of the thalamus
| Primary visual cortex (V1)
203
In what part of the lateral geniculate nucleus is the inferior retina mapped?
Lateral part of the lateral geniculate nucleus
204
In what part of the lateral geniculate nucleus is the superior retina mapped?
Medial part of the lateral geniculate nucleus
205
In what part of the lateral geniculate nucleus is the central retina mapped?
Caudal part of the lateral geniculate nucleus
206
In what part of the lateral geniculate nucleus is the peripheral retina mapped?
Rostral part of the lateral geniculate nucleus
207
Where is the inferior retina mapped in V1?
Inferior bank V1
208
Where is the superior retina mapped in V1?
Superior bank V1
209
Where is the central retina mapped in V1?
Caudal V1
210
Where is the peripheral retina mapped in V1?
Rostral V1
211
What defines the primary visual cortex?
• Layer IV- band of Gennari (banks of calcarine sulcus)
212
What is the link between the primary visual cortex and the lateral geniculate nucleus?
• Faithful input from the lateral geniculate nucleus according to topography, function and laterality
213
What are the structures in the unconscious and reflex visual pathway?
```
Suprachiasmatic nucleus
Pretectum
Superior colliculus
Pulvinar
Secondary visual cortex (V2-V5)
```
214
What is the role of the suprachiasmatic nucleus in the visual system and how does it achieve this role?
* Projects to pineal gland-> which releases melatonin
| * Circadian rhythms
215
What is the role of the pretectum in the visual system and how does it achieve this role?
* Projects to Endiger Westphal nucleus -> projects to sphincter pupillae of the iris
* Pupil constriction-both eyes constrict
216
What is the role of the superior colliculus in the visual system
• Visual reflex
o Avoidance
o Attention
217
What is the role of the pulvinar in the visual system and how does it achieve this role?
• Higher order
o Attention
Directs attention-> tells superior colliculus to track object
Parietal cortex helps focus attention
o Recognition
Integrate vision, somatosensation and audition
218
Which cortex(es) are responsible for visual orientation?
o V2 and V3
219
Which cortex(es) are responsible for visual colour?
V4
220
Which cortex(es) are responsible for motion?
V5
Where magnocellular pathway ends
People with V5 lesions do not appreciate motion
221
Where do the secondary visual cortices get their inputs from?
• Gets input from V1
o Conscious vision, topography, blindsight
o Residual vision- get appreciation but not conscious of it
222
What are structures/pathway of the auditory system?
• Ear (periphery)-> Cochlear nuclei (medulla) -> Superior olive (medulla/pons)-> Inferior colliculus (midbrain)-> Medial geniculate nucleus of the thalamus ->Primary auditory cortex-> Secondary auditory cortex
223
What structures is the ear composed of ?
```
o External ear
o Middle ear
Ear drum/tympanic membrane
Auditory ossicles
o Inner ear
Fluid-filled sac
Organ of corti (hair cells)
Cochlea (and cochlear nerve)
```
224
Describe how sound comes in to the ear to the occurence of electrical transduction
o Process-
Sound waves come in
Cause vibration of tympanic membrane
Results in intensified movement of ossicle which changes movement of fluid in inner ear
Organ of Corci respond to fluid movement and change mechanical movement into electrical impulse which passes down the cochlear nerve
225
How are noises transducted as loud/soft?
• The more movement in the hair cells, the louder the noise, the greater the impulse down the cochlear nerve
226
What is the cochlear nuclei made of (cells/nuclei)?
```
• Cochlear nuclei (medulla)
o Heterogenous nuclei
Fusiform cells
Bushy cells
Octopus cells
o Two nuclei
Dorsal nucleus
Ventral nucleus
```
227
What is the function of the cochlear nuclei?
o Enhance/preserve timing-enhance intensity information
228
What does the dorsal nucleus of the cochlear nuclei project to? How?
Dorsal nucleus-> inferior colliculus
| • Via lateral lemniscus
229
What does the ventral nucleus of the cochlear nuclei project to? How?
Ventral nucleus-> lateral and medial superior olive
• Both contralateral and ipsilateral superior olives
o Point where contralateral and ipsilateral fibres cross is called the trapezoid body
230
Describe the composition of the superior olive and what roles they play in sound processing
o Two nuclei
Lateral superior olive- intensity of sound
Medial superior olive- time difference of sound
o Sound localisation- bilateral (compares sound properties between two ears)
231
Describe the composition of the inferior colliculus
o Three nuclei:
Central
Dorsal
External
232
Describe the role of the inferior colliculus in sound processing
o Nexus, convergence of lots of different types of input
Integrates different inputs
Filter/discriminates against sounds/ dampens down noises treated as unimportant
Auditory motor reflex (startle)
• Descending projections to neck and body
233
Describe the role of the medial geniculate nucleus of the thalamus in sound processing
o Relays to cortex
| o Organises all auditory inputs into a form that the cortex likes
234
Describe the composition of the medial geniculate nucleus of the thalamus
o Three nuclei:
Ventral
Medial
Dorsal
235
Describe the location and function of the primary auditory cortex
• Primary auditory cortex
o Superior temporal gyrus on transverse gyrus Heschl
Area doubled on the right compared to left
o Appreciation of location/frequency of sound
o Conscious apprectiation
236
Describe the location and function of the secondary auditory cortex
• Secondary auditory cortex
o Superior temporal gyrus: plenum temporale
On left side, plenum temporale much larger than right
o Relate/understand the sound
Connection with parietal cortex-> recognition of sound: put sound in context of life
237
How does sharpening of a sound occur? Describe the pathway
• Descending projections
o Olivochochlear bundle -> from olive to cochlea
Cerebral cortex can send downward projection to request subcortical structures to sharpen the sound
• Dampens down areas of the system that are not particularly active-> dampens down surrounds and hence enhances interesting sound
Once input from cortex, olive outputs to cochlear
• Cochlear silences regions of organs of corti upon request
238
What is the human hearing range?
• 20Hz- 20000 Hz: human range
239
What affects the human hearing range?
o Diminishes with age, particularly high frequency
o Bacterial infections can knock out hair cells
o Loud noises can damage hair cells with time
240
How is every auditory structure mapped?
• Every auditory structure is mapped by frequency- tonotopic map (from high to low)
241
How is the cochlea tonotopically mapped?
o High frequencies at base of cochlea, low frequencies at tail of cochlea
242
How is the primary auditory cortex tonotopically mapped?
o Rostral cortex- low frequencies
| o Caudal cortex- high frequencies
243
Describe how different sound qualities is extracted from sounds with the same frequency?
• Cochlear fibres can have specific frequencies they respond to optimally
o Will synapse with range of nerve cells in cochlear nucleus
o All cochlear nerve cells extract information from the specific fibre
o Map frequencies-
Isofrequency strips- Different cells extract different qualities from same frequency
• All stimulated by particular frequency
• All have 5-10 cells extracting information from frequency-specific fibre
244
How is the information processed in the auditory system?
• Two main functional pathways
o Two parallel pathways- evident clearly from inferior colliculus onwards
Processed independently in parallel
245
What are the two main functional parallel pathways of the auditory system?
o Core
| o Belt
246
Describe the function and pathway of the core sound pathway
```
Key sound characteristics
• Frequency
• Intensity
• Timing
Starts at central inferior colliculus-> ventral nucleus of medial geniculate nucleus-> terminates in transerve gyrus of heschel (A1)
```
247
Describe the function and pathway of the belt sound pathway
```
Associative and integrative
• Mixing with different modalities
o Audition
o Somatosensory
o Visceral
o Emotional
Dorsal/external nucleus of the inferior colliculus-> medial/dorsal nucleus of medial geniculate nucleus-> planum temporale (A2)
```
248
How are sounds localised?
• Sounds are localised in two ways:
o Intensity- is it louder in one ear?
o Time- which ear does it reach first?
249
What is the role of superior olive in sound localisation? Give details.
• Superior olive key player-binaural
o Compares inputs from both ears (azimuth/horizontal plane)
o Lateral superior olive- compares intensity
o Medial superior olive- compares timing
o Sound shadow at back of head- delays process and intensity of binaural detection
250
What are the three main types of deafness? Describe them
• Types of deafness
o Three main ones
Conductive: external/middle ear damage
Sensorineural: inner ear neural damage/ organ of corci
• Organ of corci never replaced
Pure word/comprehension deafness: cortex (Wernicke aphasia/dysphasia) damage
251
When does the main decussations in auditory pathways occcur?
o Side of deafness- lots of decussation of auditory pathways (starting from superior olive up)
252
What structure damage causes unilateral deafness?
Unilateral
• Middle/external ear
• Cochlea/cochlear nerve
253
What structure damage causes bilateral deafness?
Bilateral
• Central brainstem (after cochlear nuclei)
• Cortex
NEUR3905
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