Practical 2 - Special senses

Question 1

can olfactory pathways be traced on the surface of the brain?

Answer 1

ventral surfcae of the brain

Question 2

where do olfactory pathways begin?

Answer 2

olfactory bulbs (which receive olfactory nerve input), the olfactory tracts and some olfactory areas of cortex (the uncus/ pyriform cortex and anterior perforated substance)

aparently

Question 3

visual information pathway?

Answer 3

optic nerves

chiasm and tracts

lateral geniculate body of the thalamus

via the optic radiation to primary visual cortex in the occipital lobe.

Question 4

optic nerves, chiasm and tracts (seen on the _______ brain surface) to the lateral geniculate body of the thalamus (seen on the ______ prosection

Answer 4

optic nerves, chiasm and tracts (seen on the ventral brain surface) to the lateral geniculate body of the thalamus (seen on the brainstem prosection

Question 5

Auditory processing begins in the …

Answer 5

uditory processing begins in the brainstem

Question 6

Eye movements are controlled via the ____ _____and the oculogyric nuclei of cranial nerves…….

Answer 6

Eye movements are controlled via the superior colliculi and the oculogyric nuclei of cranial nerves III, IV and VI.

Question 7

what co-ordinates eye and head movements.

Answer 7

The medial longitudinal fasciculus co-ordinates eye and head movements.

Question 8

describe the auditory pathway

Answer 8

1. vestibular cochlear nerve bifurcates
   
   1. one branch to dorsal cochlear nucleus
   2. one branch to ventral cochlear nucleus
2. fibres fom both these (ipsilateral and contralateral) go to superior olivary nucleus
3. fibres from sup. olivary nucleus + cochlear nucleus form lateral lemniscus
4. lateral lemniscus ascends through pons to tectum of midbrain - terminates in inferior colliculus
5. fibres from inferior colliculus innervate medial geniculate body of thalamus
6. gives off auditory radiation to auditory cortex of temporal lobe

Question 9

Fibres of the vestibulocochlear nerve reach the brainstem at the ……… and bifurcate

Answer 9

Fibres of the vestibulocochlear nerve reach the brainstem at the cerebellopontine angle and bifurcate

Question 10

Both dorsal ventral cochlear nuclei lie on the what….

Answer 10

Both nuclei lie on the dorsolateral surface of the medulla

Question 11

where do the superior olivary nuclei lie?

Answer 11

lie close to the medial lemniscus in the pons

Question 12

where is the first site for binaural interaction

Answer 12

Fibres reach the superior olivary nuclei from both the ipsilateral and contralateral cochlear nuclei, so it is the first site for binaural interaction.

Question 13

what is the lateral lemniscus

Answer 13

Fibres from the superior olivary nuclei, as well as some fibres from the cochlear nuclei, which bypass the superior olivary nuclei, form the main ascending auditory pathway, the lateral lemniscus

Question 14

describe the path of teh lateral lemniscus

Answer 14

ascends through the pons and, on reaching the tectum of the midbrain, terminates in the inferior colliculus

Question 15

the auditory radiation traverses what to the auditory cortex of the temporal lobe.

Answer 15

the auditory radiation traverses the internal capsule to the auditory cortex of the temporal lobe.

Question 16

Answer 16

Question 17

Dorsal surface of the thalamus, brainstem and floor of the fourth ventricle after removal of the cerebellum

Answer 17

Question 18

upper medulla

Answer 18

Question 19

what are the 4 vestibular nuclei?

Answer 19

There are four vestibular nuclei (superior, inferior, lateral and medial)

Question 20

The superior vestibular nucleus projects to the …

Answer 20

The superior nucleus projects to the thalamus.

Question 21

Section through lower midbrain (level of the inferior colliculus)

Answer 21

Question 22

Section through upper midbrain (level of the superior colliculus)

Answer 22

Question 23

what are subcortical structures?

Answer 23

Subcortical structures are a group of diverse neural formations deep within the brain which include the diencephalon, pituitary gland, limbic structures and the basal ganglia. They are involved in complex activities such as memory, emotion, pleasure and hormone production.

Question 24

describe the olfactory pathway

Answer 24

1. olfactory nerves enter the cranium through the cribriform plate of the ethmoid bone and synapse in the olfactory bulb
2. Second order fibres leave the olfactory bulb in the olfactory tract and project via the olfactory stria to various regions of the olfactory and limbic cortex, including the uncus/ pyriform cortex and the olfactory tubercle underlying the anterior perforated substance, which is the site of entry for striate arteries supplying the internal capsule and striatum (susceptible to stroke).
3. The amygdala and entorhinal cortex receive inputs from the pyriform cortex and further projections from these regions include the hypothalamus and brainstem reticular formation, which generate endocrine and autonomic responses to olfactory experience.
4. The olfactory tubercle projects on to the thalamus with further projections to the insula and the orbitofrontal cortex which underlie olfactory perception.

tough card

Question 25

base of the brain showing olfactory structures.

Answer 25

Note that the parahippocampal gyrus is made up of the pyriform cortex and the entorhinal cortex. Although structure in this region varies considerably between individuals, most brains have a clear uncus and parahippocampal gyrus.

Question 26

describe the visual pathway

Answer 26

1. optic nerve 2. optic chiasm 3. optic tract 4. lateral geniculate nucleus (LGN) of the thalamus 5. Second order fibres from the LGN pass around the lateral ventricle in the optic radiation and terminate in the primary visual cortex of the occipital lobe

Question 27

lateral geniculate nucleus (LGN) of the thalamus (found.....

Answer 27

lateral geniculate nucleus (LGN) of the thalamus (found **lateral to the medial geniculate nucleus**

Question 28

what is the stria of Gennari

Answer 28

Even to the naked eye a section of this cortex is often distinguishable by a white strip that runs through the grey matter, parallel to the surface. This is called the stria of Gennari, and is due to the dense axonal input from the thalamus to layer IV of visual cortex.

Question 29

Visual pathways and visual field defects

Answer 29

Question 30

which nerves innervate the eye

Answer 30

Motor neurons innervating the eye muscles are located in the three motor nuclei of the 3rd (oculomotor), 4th (trochlear) and 6th (abducens) cranial nerves

Question 31

where are the oculogyric nuclei located

Answer 31

near the midline at distinctive levels in the brain stem

Question 32

You should be able to identify the position of the oculomotor nucleus in sections of the upper mid brain

Answer 32

write that down

Question 33

do other brain regions control eye activity\>

Answer 33

Several brain regions, including the vestibular nuclei and the superior colliculus influence and co-ordinate activity in these (oculogyric) motor nuclei, thereby controlling eye movements

Question 34

what is the medial longitudinal fasciculus

Answer 34

The medial longitudinal fasciculus (MLF) is a bundle of fibres on either side of the midline, which extends throughout the brainstem and continues caudally into the upper cervical segments of the spinal cord. The MLF connects vestibular nuclei to the motor nuclei controlling eye movements (for vestibuloocular movements) and the superior colliculus to the cervical motor neurons in the upper spinal cord controlling head movement. The MLF therefore co-ordinates tracking movements of the eyes and head.

Question 35

what is the MLF commonly affected in\>

Answer 35

multiple sclerosis leading to nystagmus, diplopia and defects in gaze control

Question 36

what initiates eye movements

Answer 36

Eye movements are initiated by eye fields in the cerebral cortex These project to the superior colliculus, which embodies a retinotopic map of visual space Gaze centres in the reticular formation of the pons translate position into appropriate motor commands to the three oculogyric nuclei. These commands are carried in the MLF.

Question 37

Overview of circuitry involved in generating eye movements (saccades)

Answer 37

Question 38

Subcortical information usually reaches the cerebral cortex via ...

Answer 38

Subcortical information usually reaches the cerebral cortex via the thalamus

Question 39

how is the thalamus divided into nuclei?

Answer 39

The grey matter of the thalamus is divided into a series of functionally distinct nuclei by layers of white matter

Question 40

The white matter divides the thalamus into _ major groups

Answer 40

The white matter divides the thalamus into 3 major groups

Question 41

3 major thalamus groups

Answer 41

medial, ventral and anterior nuclear groups

Question 42

what does the ventral thalamic nuclei group do?

Answer 42

contain the **ascending somatosensory relays** (the ventro- posterior part: Vp), and the relays from cerebellum and basal ganglia to primary motor cortex (via the ventrolateral part; Vl) and motor association areas (premotor cortex and supplementary motor areas - via the ventro-anterior nuclei; Va)

Question 43

the lateral and medial geniculate nuclei (LGN & MGN), relays for ..

Answer 43

the lateral and medial geniculate nuclei (LGN & MGN), relays for vision and hearing, respectively

Question 44

The anterior group of thalamic nuclei (A) projects to the ,....... what? and is important for what probably?

Answer 44

The anterior group of thalamic nuclei (A) projects to the cingulate gyrus and is probably important for perception of internal emotional state, although this is not fully understood.

Question 45

A major input to the anterior nucleus is from the.... which are important for what?\>

Answer 45

A major input to the anterior nucleus is from the mammillary bodies of the hypothalamus (Practical 6), which are important for the formation of declarative memory.

Question 46

The two largest nuclei of the thalamus are?

Answer 46

The two largest nuclei of the thalamus – the medial nuclei (MD) and the pulvinar (Pul)

Question 47

cortico-thalamo-cortical relays - what are they?

Answer 47

medial nuclei (MD) and the pulvinar (Pul) receive most input from the cerebral cortex itself, and project to areas of association cortex, which do not have a simply defined unimodal input, but instead have inputs from many other areas

Question 48

medial nuclei (MD) and the pulvinar (Pul) - whats the associated cortex?

Answer 48

There are two huge regions of association cortex: * the pre-frontal cortex, anterior to the motor areas of cerebral cortex, much of which receives input from the medial nuclei; * the temporal- parietal-occipital association cortex, much of which receives input from the pulvinar

Question 49

why arent medial nuclei and pulvinar well understood?

Answer 49

Since humans have large areas of association cortex, the medial nuclei and pulvinar are very large in humans, and since they cannot be studied in animals, their function is poorly understood.

Question 50

Picture of thalmus nuclei

Answer 50

Question 51

do humans have large areas of assocaited cortex?

Answer 51

yes

Question 52

how many layers are there in cerebral cortex?

Answer 52

6 layers - stacked

Question 53

Layer 4 of the cortex receives input from wherer?

Answer 53

thalamus

Question 54

layer 5 outputes to where?

Answer 54

the major output layer to subcortical structures ## Footnote (e.g. the pyramidal cell layer in motor cortex that forms the corticospinal tract).

Question 55

Layer VI of the cortex does what? layer 2 and 3 do what?

Answer 55

Layer VI sends feedback to the thalamus whilst layers II and III project to other cortical areas

Question 56

describe Layer 1

Answer 56

outer layer, lying immediately under the cortical surface is the molecular layer (layer I); it contains fibres running parallel to the cortical surface but very few neurons (therefore is not visible with the Golgi or Nissl stain).

Question 57

describe layer 2

Answer 57

The outer granular layer (layer II) is characterised by the presence of small rounded neurons.

Question 58

layer 3 - describe

Answer 58

Immediately below it is another layer that looks quite different; this is the outer pyramidal layer (layer III), and contains triangular-shaped "pyramidal" neurons (output neurons)

Question 59

describe layer 4

Answer 59

the inner granular layer (layer IV; neurons receiving input)

Question 60

describe layer 5

Answer 60

inner pyramidal layer (layer V; output neurons).

Question 61

describe layer 6

Answer 61

Finally, a thin innermost layer with some scattered cells in it - the multiform layer (layer VI).

Question 62

desxcribe how cortical organisation in the primary sensory cortex is not usual

Answer 62

Since this area receives major thalamic inputs, the major input layer (layer IV) is correspondingly well developed, and the "output" layers reduced. Note the thickness of the granular layer IV, which is particularly well developed in human primary visual cortex (V1), where the afferent fibres from the lateral geniculate nucleus form a conspicuous horizontal streak of white matter, the stria of Gennari, which can be seen in brain slices by eye.

Question 63

describe how cortical organisation is unusual in the primary motor cortex

Answer 63

This area has an enlarged layer V, with giant pyramidal output neurons, but relatively few granule cells in layer IV.

Question 64

describe how cortical organisation is in association cortex

Answer 64

for now be aware that it lacks anatomic specialisation in any particular layer. It is sometimes described as ‘homotypic’.

Question 65

T or F ## Footnote certain evolutionarily primitive parts of the cortex do not have 6 layers of cortex

Answer 65

T ## Footnote certain evolutionarily primitive parts of the cortex do not have 6 layers of cortex

Question 66

Note that certain evolutionarily primitive parts of the cortex do not have 6 layers of cortex, such as the hippocampus (\_ layers) and parahippocampal gyrus and cingulate gyrus (\_\_\_\_ layers)

Answer 66

Note that certain evolutionarily primitive parts of the cortex do not have 6 layers of cortex, such as the hippocampus (3 layers) and parahippocampal gyrus and cingulate gyrus (4-5 layers)

Question 67

Older 3 layered cortex is known as _______ or \_\_\_\_\_\_\_\_\_, and intermediate 4-5 layered cortex is known as \_\_\_\_\_\_\_\_

Answer 67

Older 3 layered cortex is known as palaeocortex or allocortex, and intermediate 4-5 layered cortex is known as juxtallocortex

Question 68

The 6 layers of the cerebral neocortex, using different staining methods: A, Golgi stain (entire cells); B, Nissl stain (nucleic acids); C, Weigart stain (myelinated axons)

Answer 68

Question 69

Overview of connections of the different cortical layers

Answer 69

Question 70

describe auditory processing disorders?

Answer 70

* apparatus of the ear is functional * but CNS deficits make auditory processing difficult * genetic and environmental (e.g. infection or injury) causes * Different aspects of hearing can be affected, including sound **recognition** and sound **localisation**. *

Question 71

a unilateral lesion in the pathway rarely causes a major impairment in hearing. why?

Answer 71

The auditory pathway is both crossed and uncrossed above the level of the cochlear nuclei, so a unilateral lesion in the pathway rarely causes a major impairment in hearing

Question 72

T or F ## Footnote Visual field defects can be important indicators of brain dysfunction

Answer 72

T

Question 73

olfactor deficits occur due to

Answer 73

* aging * clinical conditions (eg alzheimers)

Question 74

give some examples of olfactors deficits

Answer 74

* **anosmia** (inability to detect odours), * **hyposmia** (decreased ability to detect odours), * **dysosmia** (poor identification of odour, e.g. phantosmia, or perception of smell in the absence of an odorant and agnosia, where odours can be detected but not distinguished).

Question 75

The MLF is commonly affected in ..... leading to?

Answer 75

The MLF is commonly affected in multiple sclerosis leading to nystagmus, diplopia and defects in gaze control.

Question 76

what is Retrosigmoid craniotomy

Answer 76

is a classical surgical approach that involves removing and replacing the bone (craniotomy). It is sited posterior to the sigmoid sinus and inferior to the transverse sinus. It allows access to the lateral cerebellum and cerebellopontine angle, where cranial nerves VII and VIII emerge. It is used, for example, when removing an ependymoma, a type of tumour that arises from the ependymal cells that line the ventricles. It is one of the most common tumours in childhood, where it usually arises in the vicinity of the 4th ventricle. If they are removed completely at surgery, often the tumour does not recur and no further therapy is required.

Question 77

fat

Answer 77

mamba