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NEUR3905 > Weeks 1 to 3 > Flashcards

Weeks 1 to 3 Flashcards

1
Q

What are the two major cellular building blocks of the CNS?

A
  • Neurons

- Glial cells

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2
Q

Where do neurons originate from?

A

Neural stem cells

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3
Q

How many neurons are there in the brain?

A

100 billion

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4
Q

What percentage of all brain cells do neurons make up?

A

10%

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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…)

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6
Q

What is the typical size of neurons?

A

5 microns to 100 microns

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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

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8
Q

When do neurons proliferate?

A

 Neuronal proliferation (generation of neuroblasts) in first 5 months of pregnancy

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9
Q

When do neurons differentiate?

A

 Neuronal differentiation in 4-9 months of pregnancy

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10
Q

Are neuronal connections only formed prenatally or can they be formed postnatally?

A

 Neuronal connections continue to form postnatally

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11
Q

What glial cells are there?

A

o Astrocytes
o Oligodendrocytes
o Microglia
o Ependymal cells

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12
Q

Where do astrocytes originate from?

A

 Origin- neural stem cells but late differentiation

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13
Q

Where do oligodendrocytes originate from?

A

 Origin- neural stem cells but late differentiation

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14
Q

Where do microglia originate from?

A

 Origin- derive from external bone marrow

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15
Q

Where do ependymal cells originate from?

A

 Origin- neural stem cells but late differentiation

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16
Q

What are the overarching functions of astrocytes?

A 
	Functions-
•	Homeostatic functions
•	Structural support
•	Contribute to blood brain barrier
•	Response to injury
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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

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18
Q

What are the functions of microglia?

A
  • Resident immune cells of CNS
  • Phagocytosis
  • Response to injury
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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

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20
Q

What are the functions of ependymal cells?

A

 Functions-
• Line ventricles
• Responsible for choroid plexus growth
• Produce CSF

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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

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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

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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

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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)

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25
Q

How many layers of cells are there within developing embryo, and what are they?

A

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

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26
Q

Describe a timeline of the general development of the brain

A
  • 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
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27
Q

Describe a general outline of the development of CNS

A

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)

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28
Q

Describe in general terms the development of the PNS

A

Neural crest cells migrate to become DRG, Shwann cells, melanocytes, enteric ganglia, sympathetic ganglia

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29
Q

Describe how the neural groove is formed

A

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

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30
Q

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?

A

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

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31
Q

What nervous system does the neural groove become?

A

CNS

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32
Q

What nervous system does the neural crest become?

A

PNS

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33
Q

When does the rostral end of the neural tube close during primary neurulation and what will it become?

A

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

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34
Q

What structural features form as the rostral end of the neural tube closes?

A 
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
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35
Q

When does the caudal end of the neural tube close and what will it become?

A

 Caudal end- where the spinal cord will form

• Caudal end of neural tube closes on day 26

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36
Q

What can happen if there is a failure to close the rostral end of the neural tube?

A

• Failure of rostral end of neural tube to close is a fatal developmental defect which will result in death of embryo

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37
Q

What can happen if there is a failure to close the caudal end of the neural tube?

A

• Failure of the caudal end of the neural tube to close results in spina bifida

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38
Q

Describe the 3 different types of spina bifida and their characteristics

A

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

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39
Q

How is the 4th ventricle formed? Describe the motor/sensory organisation and structure around the 4th ventricle

A

 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

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40
Q

Describe how the telencephalon begins to be shaped and the involvment of the diencephalon in this shaping

A

• 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

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41
Q

Describe how the temporal and frontal lobes are formed

A

• 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

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42
Q

When does neuronal proliferation peak?

A

5 weeks to 5 months

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43
Q

Where does neuronal proliferation occur?

A

Occurs in the ventricular zone

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44
Q

How does the cleavage plane off neuroblasts during neuronal proliferation change as development progresses? What are the consequences of this change?

A

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

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45
Q

How does the cleavage plane during cell division determine neuroblast cell during development? What are the consequences of this?

A

 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

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46
Q

Describe how the 6 layered cerebral cortex is developed and the cells used to help this process

A

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

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47
Q

When does differentiation of astrocytes peak?

A

At birth

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48
Q

When does differentiation of oligodendrocytes peak?

A

Postnatal and throughout adulthood

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49
Q

Describe what differentiation into a specific phenotype is based on

A

o All differentiation into specific phenotype is based on signalling molecules which reside in anatomical location where it finishes its migration path

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50
Q

Which arteries does the brain blood supply come from?

A

The internal carotid artery (2/3) and vertebral arteries (1/3)

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51
Q

Which arteries can you see in the lateral view of the brain?

A

o Internal carotid artery system
 Middle cerebral arteries and their branches
 Anterior cerebral arteries and their branches

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52
Q

Which arteries can you see in the medial view of the brain?

A

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

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53
Q

What are the main dural sinuses?

A 
•	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
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54
Q

Is the brain hollow? True or False?

A

• The brain is hollow

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55
Q

Where did the lateral ventricles develop from?

A

• Lateral ventricles developed from telencephalon

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56
Q

What forms the walls of the third ventricle?

A

• Thalamus and Hypothalamus form walls of third ventricle

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57
Q

Where is the 3rd ventricle located?

A

Diencephalon

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58
Q

What does the diencephalon consist of?

A 
	Thalamus
	Hypothalamus
	Epithalamus
	Subthalamus 
	Retina
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59
Q

Describe what surrounds the 4th ventricle

A

• 4th ventricle is surrounded by brainstem (include mesencephalon) and cerebellum

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60
Q

Describe the CSF pathway

A

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

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61
Q

What is the structure of the blood brain barrier?

A

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

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62
Q

What maintains the blood brain barrier?

A

 Astrocytes secrete molecules which maintains non-fenestrated morphology

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63
Q

What forms a neurovascular unit?

A

o Neurons, astrocytes and brain capillaries may form a neurovascular unit

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64
Q

What iss the role of the blood brain barrier?

A

• 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

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65
Q

Why do neuroactive compounds need to be kept out of the brain

A

 Neuroactive compounds interact with receptors and could activate/inhibit neurons haphazardly- this is why they need to be kept out

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66
Q

Why do neurotoxic compounds need to be kept out of the brain?

A

 Neurotoxic compounds can overexcite cells and can trigger process that leads to death of neurons, or can be toxic to neurons specifically

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67
Q

How can the blood brain barrier get damaged by and why?

A

• 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)

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68
Q

Why do some parts of the brain have a naturally low blood brain barrier and where are these parts?

A

• 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

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69
Q

What is De Vivo disease?

A

• De Vivo disease: glucose transport (via GLUT1) is compromised, patients tend to have serious problems such as mental retardation

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70
Q

How can compounds cross the blood brain barrier? Give examples

A

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

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71
Q

How can you modify drugs to cross the blood brain barrier

A

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

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72
Q

What is the first sense active in newborns?

A

Olfaction

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73
Q

How is olfaction stimulated?

A

o Stimulation through ingestion of odorants with respiratory movements

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74
Q

Are we born with inbuilt codes of olfaction or are they learned?

A

o Born with inbuilt codes of olfaction

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75
Q

Do different smells activate the same or different brain regions?

A

different smells activate different brain regions

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76
Q

What is the sense with the most direct route to the brain system in which affect (feeling) is generated?

A

• 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

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77
Q

What are the uses of olfaction and the olfactory system?

A
  • Location of food, mate and danger
  • Drives behavioural state changes
  • Alters sensory responsiveness
  • Can itself be altered by behavioural state and mood
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78
Q

What types of neurons are olfactory receptors?

A

Bipolar projection neurons

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79
Q

How many olfactory receptors are there per nostril

A

6 million

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80
Q

On what type of epithelium do olfactory receptors reside on?

A

o Sit in pseudostratified columnar epithelium

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81
Q

Are olfactory receptors able to regenerate? If so, when?

A

o Able to regenerate after 10 days

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82
Q

What is on the end of the olfactory knob?

A

o Possess rigid cilia (3-50 per cell) on end of olfactory knob and axonal endings

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83
Q

What is the purpose of olfactory cilia?

A

 Cilia increase surface area with which odorant can react with sensory receptor

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84
Q

How many receptor proteins are on cilia in humans and what is the consequence of this?

A

 About 500-1000s receptor proteins on cilia in humans- means that humans have the ability to detect several thousand chemical structures

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85
Q

Why does each individual cell respond slightly differently to different constellations of odor?

A

 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

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86
Q

Where do olfactory axons pass through from the nose to the brain? Do they pass singularly or are they grouped?

A

o 10-100 cell axons penetrate each space in the cribriform plate of the ethmoid bone

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87
Q

Are olfactory receptor cell axons myelinated or unmyelinated?

A

Unmyelinated- transmission speed is slow

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88
Q

Where are olfactory receptors located?

A

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

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89
Q

Why are olfactory receptors isolated from each other?

A

 Receptors are isolated from each other so electrical discharge does not get distorted by their neighbours

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90
Q

What is the role of Bownmans glands in the olfactory system?

A

• Bowmans glands constantly secrete mucus in mucosa to allow for odorants to be better detected and for detoxification and degradation of odorants

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91
Q

Describe the role of olfactory receptors in the retronasal region?

A

• Those in the retronasal region would be important for detection of flavours

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92
Q

What are the components of olfactory mucosa and why?

A 
•	Mucosa contains many different chemicals to protect brain from harmful components 
o	Glycoproteins 
o	Free ionic salts
o	Fluid
o	Antibodies
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93
Q

Describe how odorants can generate an action potential in the olfactory system

A

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

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94
Q

What is the purpose of the turbinates/nasal conchae in the olfactory system?

A

• 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

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95
Q

Where is the olfactory bulb?

A

o Found on ventral part of frontal lobes

o Encased by pia mater and arachnoid mater

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96
Q

What are the origins of the olfactory bulb?

A

o Derived from telencephalon

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97
Q

What does the olfactory bulb comprise of?

A 
o	Comprises of: 
	Neurons
	Afferent
	Efferent nerve fibres
	Interneurons 
	Microglia
	Astrocytes 
	Blood vessels
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98
Q

Where is the location of the first synapse in the olfactory pathway?

A

Olfactory bulb

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99
Q

How many layers does the olfactory bulb have and what are they?

A 
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
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100
Q

In what layer of the olfactory bulb do receptor cells synapse?

A

• Receptor cells synapse in glomerular layer

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101
Q

What is the glomerulus made of? Does it recieve inputs from singular or multiple olfactory receptors?

A

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

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102
Q

What cells output from the olfactory bulb?

A

• Main output cells are mitral cells and tufted cells regulated by glomeruli

103
Q

What cells do apical dendrites of mitral cells and tufted cells receive signals from? What is the use of these signals?

A

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
Q

Which olfactory bulb layer is the biggest layer?

A

Granule cell layer (1/2 volume of the bulb)

105
Q

What is the role of the olfactory bulb?

A

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
Q

What are the primary olfactory regions?

A 
o	Anterior olfactory nucleus 
o	Olfactory tubercle
o	Piriform cortex
o	Pre-piriform cortex 
o	Peri-amygdaloid cortex
o	Entorhinal cortex 
o	Amygdala
107
Q

What are the secondary olfactory regions?

A 
•	Secondary olfactory regions (get input from primary olfactory regions)
o	Hippocampus 
o	Hypothalamus
o	Thalamus
o	Orbitofrontal cortex
o	Cerebellum
108
Q

Where is the anterior olfactory nucleus located?

A

 Located behind the olfactory bulb

109
Q

Where does the anterior olfactory nucleus project to?

A

 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
Q

What is the role of the anterior olfactory nucleus?

A

 Thought to regulate olfactory function ((phylogenetically old system- dichotomous behavioural response: whether something needs to be approached or avoided)

111
Q

What input does the olfactory tubercle recieve?

A

 Receives a massive dopaminergic input from ventral tegmental area and substantia nigra, in addition to odorant information

112
Q

What is the role of the olfactory tubercle?

A

 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
Q

What does the olfactory tubercle project to ?

A

 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
Q

What does the piriform cortex include?

A 
	Includes the:
•	Olfactory tract
•	The uncus 
•	Cortical amygdala
•	Anterior part of the parahippocampal gyrus
115
Q

What is the role of the piriform cortex for olfaction?

A

 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
Q

What does the piriform cortex project to in the olfactory system?

A

 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
Q

How are odors represented in the pre-piriform cortex and the peri-amygdaloid cortex?

A

In broad patches

118
Q

What does the entorhinal cortex project to in the olfactory system and what is the role of each of these projections?

A

 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
Q

Where is the septal nuclei located?

A

 Located below the rostrum of the corpus callosum/anterior to lamina terminalis

120
Q

What do septal nuclei project to in the olfactory system?

A

 Projects to hypothalamus and older parts of the limbic system

121
Q

What is the role of the septal nuclei in the olfactory system?

A

 Not thought to play a role in sense of smell rather in guiding behaviours related to reward and reinforcement (phylogenetically old system)

122
Q

What does the anterior perforated substance recieve input from in the olfactory system?

A

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
Q

What does the anterior perforated substance project to in the olfactory system and what is the consequence of this?

A

 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
Q

Describe the olfactory pathway

A
  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
Q

Describe the medial olfactory tract

A

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
Q

Describe the lateral olfactory tracts

A

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
Q

What are the components of the olfactory system?

A
  • 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
Q

What are the two types of MRI scans and what are they the most useful for?

A

• 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
Q

What is the colour of CSF in T1-weighted scans?

A

Dark

130
Q

What is the colour of white matter in T1-weighted scans?

A

Light

131
Q

What is the colour of cortex in T1-weighted scans?

A

Grey

132
Q

What is the colour of fat in T1-weighted scans?

A

Bright

133
Q

What is the colour of inflammation in T1-weighted scans?

A

Dark

134
Q

What is the colour of CSF in T2-weighted scans?

A

Bright

135
Q

What is the colour of white matter in T2-weighted scans?

A

Dark grey

136
Q

What is the colour of cortex in T2-weighted scans?

A

Light grey

137
Q

What is the colour of fat in T2-weighted scans?

A

Light

138
Q

What is the colour of inflammation in T2-weighted scans?

A

Bright

139
Q

How is an MRI image produced?

A

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
Q

What is T1 time in an MRI image?

A

 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
Q

What is T2 time in an MRI image?

A

 The rate of decrease of the transverse relaxation is called the transverse relaxation time or T2 time

142
Q

Are T1 time and T2 time dependent or independent on each other?

A

 The T1 and T2 relaxation times are different and are independent processes

143
Q

What properties of the brain does MRI depend on?

A

• 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
Q

Which combination of scan times and field strengths make the best collection of MRI scans?

A

• 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
Q

Describe the components of the sensory apparatus (tongue)

A

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
Q

Describe the structure of taste buds

A

• Buds are comprised of a number of different sensory cells, which have a common opening (small pore known as the taste pore)

147
Q

Do taste buds regenerate? When and from what?

A

• These cells are regenerated over days- derived from cells in the basal lamina of the tissue

148
Q

Through what fibres do taste buds relay information to the CNS?

A

• 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
Q

Do different taste buds respond to all chemicals in the same way or in a different way? How does this work?

A

• 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
Q

How is saltiness detected?

A

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
Q

How is sourness detected?

A

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
Q

How is bitter, sweet or umami detected?

A

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
Q

What are the bitter receptors?

A

 Bitter receptors: T2 receptors

• Can have different conformations in membrane

154
Q

What are the sweet receptors?

A

 Sweet receptors: T1R2 receptors and T1R3 receptors

• Have to be both bound simultaneously by sugary substances to transduce experience of sweetness

155
Q

What are the umami receptors?

A

 Umami receptors: T1R1 receptors and T1R3 receptors

156
Q

How will cells respond to taste sensations?

A

• Cells will respond to taste sensations as a function of the representation of the basic tastes within that tastant – compound sensations

157
Q

Describe the taste pathway up until the structure that is the origin of all mar taste pathways in the brain

A

• 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
Q

From the NTS, describe the conscious perception pathway for all the different cranial nerves responsible

A

 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
Q

Where is the parabrachial nucleus and what input does it receive?

A

• Parabrachial nucleus-> found at the junction of the pons and midbrain
o Taste input from back of mouth (because of innervation from CNX)

160
Q

What input does the ventroposteriormedial nucleus of the thalamus recieve in addition to taste?

A

• Ventroposteriormedial nucleus of the thalamus is also the sensory nucleus for the trigeminal nerve (somatosensation from head)

161
Q

Where is taste perception thought to be encoded?

A

In the insular cortex

162
Q

Describe the pathway responsible for evoking reflexive motor behaviours in response to taste (from the NTS)

A

 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
Q

What are examples of reflexive motor behaviours evoked in response to taste? Do these responses change over time?

A

• 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
Q

Describe the taste pathway responsible for emotional memory around taste experience (from NTS)

A

 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
Q

What is the pathway that triggers copious salivation in response to taste (from NTS)

A

 To trigger copious salivation, nucleus of the solitary tract-> thalamus-> hypothalamus->salivatory nucleus of the medulla for parasympathetic salivation (VII and IX)

166
Q

Which structure can trigger the retching reflex in response to taste?

A

Nucleus of the solitary tract

167
Q

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?

A

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
Q

Where do the primary afferent taste fibres converge?

A

o Converge on caudal brainstem

169
Q

What transduces the chilli/pepper taste?

A

o Trigeminal nerve- transduces “chilli” or “pepper” taste due to heat detected as somatosensory component of taste experience

170
Q

Where do all primary afferent taste fibres project to?

A

o All primary afferent taste fibres project to the rostral 2/3rds nucleus of the solitary tract (NTS)

171
Q

Are the taste pathways conserved or different in different mammals?

A

• 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
Q

Where do smell and taste inputs converge and why?

A

• 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
Q

Describe why an aversive experience may cause a loss of appetite

A

• 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
Q

What circuitry is essential to learning about food safety and what can happen if this circuitry is inhibited? Why may this be?

A

 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
Q

Describe how learning about the safety of a new food occurs and what happens if the new stimulus is aversive

A

• 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
Q

What are the periphery structures of the visual system?

A 
•	Periphery structures (still part of the CNS)
o	Retina 
o	Optic nerve
o	Optic chiasma
o	Optic tract
177
Q

Where does the retina come from?

A

Diencephalon

178
Q

Describe the layers of the retina and the cells in these layers

A 
	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
Q

What function do retinal ganglion cells serve?

A

these cells are the only ones that have axons projecting out of the retina into the optic nerve

180
Q

What function do magnocellular cells serve?

A

 Transmit/activated by information about motion

181
Q

What function do parvocellular cells serve?

A

 Transmit/activated by information about colour and form

182
Q

What function do retinal amacrine cells and horizontal cells serve?

A

o Dampen down excessive visual input

183
Q

What function do retinal bipolar cells serve?

A

o Connect photoreceptors to ganglion cells

184
Q

What is the difference between rods and cones?

A 
o	Cones 
	Pick up different types of colours
	Day vision
o	Rods
	Receptive to light
	Night vision
185
Q

What is the role of photoreceptors?

A

receptive to light

186
Q

What is the role of the pigment epithelium?

A

o Absorbs any scattered light
o Phagocytes
 Clears shed disks from photoreceptors as a result of transduction

187
Q

What is the optic disk?

A

• Acts as a blind spot

o Where all axons of ganglion cells collect and form the optic nerve

188
Q

What does the central retina consist of?

A
  • Fovea centralis- where photoreceptors are in the central retina
  • Macula lutea- mountain of ganglion cells
189
Q

Why is the fovea centralis so crucial for detailed vision?

A

o Light hits the photoreceptors directly
o Detail is increased
o Faithful transmission- one photoreceptor talks to one ganglion cell
 Transmit accuracy

190
Q

Where is the central retina located?

A

• Temporal to optic disk

191
Q

Where is the nasotemporal division in the retina located?

A

• The nasotemporal division is at the fovea centralis

192
Q

Why is our periphery vision not very accurate?

A

• One photoreceptor for 100000 ganglion cells

o Each ganglion cell gets details for many photoreceptors so detail is not as great

193
Q

What is macular degeneration and how does it occur?

A

• 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
Q

What is detached in retinal detachments?

A

• Retinal detachments
o Dislodged retina
o Detachments of pigment epithelium and photoreceptors

195
Q

What is the difference between the optic nerve and the optic tract?

A

o Optic nerve
 Contains fibres from one eye
o Optic tract
 Contains fibres from both eyes

196
Q

Describe what occurs in the optic chiasma in terms of decussations

A

 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
Q

When there is blindness in one eye, is it a prechiasmatic issue or a postchiasmatic issue?

A

Prechiasmatic issue

198
Q

When there is blindness in both eyes, is it a prechiasmatic issue or a postchiasmatic one?

A

Postchiasmatic issue

199
Q

What are the central structures of the visual system?

A 
o	Hypothalamus
o	Brainstem
	Visual reflexes
o	Thalamus
	Main visual input that it projects to the cortex 
o	Optic radiation 
o	Cortex
200
Q

What is the function of the conscious visual pathway?

A

 Conscious vision

 Topography

201
Q

What is the function of the lateral geniculate nucleus in the visual pathway? How does it perform this function?

A

• 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
Q

What are the main structures in the conscious visual pathway?

A

 Lateral geniculate nucleus of the thalamus

 Primary visual cortex (V1)

203
Q

In what part of the lateral geniculate nucleus is the inferior retina mapped?

A

Lateral part of the lateral geniculate nucleus

204
Q

In what part of the lateral geniculate nucleus is the superior retina mapped?

A

Medial part of the lateral geniculate nucleus

205
Q

In what part of the lateral geniculate nucleus is the central retina mapped?

A

Caudal part of the lateral geniculate nucleus

206
Q

In what part of the lateral geniculate nucleus is the peripheral retina mapped?

A

Rostral part of the lateral geniculate nucleus

207
Q

Where is the inferior retina mapped in V1?

A

Inferior bank V1

208
Q

Where is the superior retina mapped in V1?

A

Superior bank V1

209
Q

Where is the central retina mapped in V1?

A

Caudal V1

210
Q

Where is the peripheral retina mapped in V1?

A

Rostral V1

211
Q

What defines the primary visual cortex?

A

• Layer IV- band of Gennari (banks of calcarine sulcus)

212
Q

What is the link between the primary visual cortex and the lateral geniculate nucleus?

A

• Faithful input from the lateral geniculate nucleus according to topography, function and laterality

213
Q

What are the structures in the unconscious and reflex visual pathway?

A 
	Suprachiasmatic nucleus
	Pretectum 
	Superior colliculus
	Pulvinar
	Secondary visual cortex (V2-V5)
214
Q

What is the role of the suprachiasmatic nucleus in the visual system and how does it achieve this role?

A
  • Projects to pineal gland-> which releases melatonin

* Circadian rhythms

215
Q

What is the role of the pretectum in the visual system and how does it achieve this role?

A
  • Projects to Endiger Westphal nucleus -> projects to sphincter pupillae of the iris
  • Pupil constriction-both eyes constrict
216
Q

What is the role of the superior colliculus in the visual system

A

• Visual reflex
o Avoidance
o Attention

217
Q

What is the role of the pulvinar in the visual system and how does it achieve this role?

A

• 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
Q

Which cortex(es) are responsible for visual orientation?

A

o V2 and V3

219
Q

Which cortex(es) are responsible for visual colour?

A

V4

220
Q

Which cortex(es) are responsible for motion?

A

V5
 Where magnocellular pathway ends
 People with V5 lesions do not appreciate motion

221
Q

Where do the secondary visual cortices get their inputs from?

A

• Gets input from V1
o Conscious vision, topography, blindsight
o Residual vision- get appreciation but not conscious of it

222
Q

What are structures/pathway of the auditory system?

A

• 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
Q

What structures is the ear composed of ?

A 
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
Q

Describe how sound comes in to the ear to the occurence of electrical transduction

A

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
Q

How are noises transducted as loud/soft?

A

• The more movement in the hair cells, the louder the noise, the greater the impulse down the cochlear nerve

226
Q

What is the cochlear nuclei made of (cells/nuclei)?

A 
•	Cochlear nuclei (medulla)	
o	Heterogenous nuclei 
	Fusiform cells
	Bushy cells
	Octopus cells 
o	Two nuclei
	Dorsal nucleus
	Ventral nucleus
227
Q

What is the function of the cochlear nuclei?

A

o Enhance/preserve timing-enhance intensity information

228
Q

What does the dorsal nucleus of the cochlear nuclei project to? How?

A

 Dorsal nucleus-> inferior colliculus

• Via lateral lemniscus

229
Q

What does the ventral nucleus of the cochlear nuclei project to? How?

A

 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
Q

Describe the composition of the superior olive and what roles they play in sound processing

A

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
Q

Describe the composition of the inferior colliculus

A

o Three nuclei:
 Central
 Dorsal
 External

232
Q

Describe the role of the inferior colliculus in sound processing

A

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
Q

Describe the role of the medial geniculate nucleus of the thalamus in sound processing

A

o Relays to cortex

o Organises all auditory inputs into a form that the cortex likes

234
Q

Describe the composition of the medial geniculate nucleus of the thalamus

A

o Three nuclei:
 Ventral
 Medial
 Dorsal

235
Q

Describe the location and function of the primary auditory cortex

A

• 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
Q

Describe the location and function of the secondary auditory cortex

A

• 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
Q

How does sharpening of a sound occur? Describe the pathway

A

• 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
Q

What is the human hearing range?

A

• 20Hz- 20000 Hz: human range

239
Q

What affects the human hearing range?

A

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
Q

How is every auditory structure mapped?

A

• Every auditory structure is mapped by frequency- tonotopic map (from high to low)

241
Q

How is the cochlea tonotopically mapped?

A

o High frequencies at base of cochlea, low frequencies at tail of cochlea

242
Q

How is the primary auditory cortex tonotopically mapped?

A

o Rostral cortex- low frequencies

o Caudal cortex- high frequencies

243
Q

Describe how different sound qualities is extracted from sounds with the same frequency?

A

• 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
Q

How is the information processed in the auditory system?

A

• Two main functional pathways
o Two parallel pathways- evident clearly from inferior colliculus onwards
 Processed independently in parallel

245
Q

What are the two main functional parallel pathways of the auditory system?

A

o Core

o Belt

246
Q

Describe the function and pathway of the core sound pathway

A 
	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
Q

Describe the function and pathway of the belt sound pathway

A 
	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
Q

How are sounds localised?

A

• Sounds are localised in two ways:
o Intensity- is it louder in one ear?
o Time- which ear does it reach first?

249
Q

What is the role of superior olive in sound localisation? Give details.

A

• 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
Q

What are the three main types of deafness? Describe them

A

• 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
Q

When does the main decussations in auditory pathways occcur?

A

o Side of deafness- lots of decussation of auditory pathways (starting from superior olive up)

252
Q

What structure damage causes unilateral deafness?

A

 Unilateral
• Middle/external ear
• Cochlea/cochlear nerve

253
Q

What structure damage causes bilateral deafness?

A

 Bilateral
• Central brainstem (after cochlear nuclei)
• Cortex

NEUR3905 (5 decks)

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