Practical 2 - Special senses Flashcards
can olfactory pathways be traced on the surface of the brain?
ventral surfcae of the brain
where do olfactory pathways begin?
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
visual information pathway?
optic nerves
chiasm and tracts
lateral geniculate body of the thalamus
via the optic radiation to primary visual cortex in the occipital lobe.
optic nerves, chiasm and tracts (seen on the _______ brain surface) to the lateral geniculate body of the thalamus (seen on the ______ prosection
optic nerves, chiasm and tracts (seen on the ventral brain surface) to the lateral geniculate body of the thalamus (seen on the brainstem prosection
Auditory processing begins in the …
uditory processing begins in the brainstem
Eye movements are controlled via the ____ _____and the oculogyric nuclei of cranial nerves…….
Eye movements are controlled via the superior colliculi and the oculogyric nuclei of cranial nerves III, IV and VI.
what co-ordinates eye and head movements.
The medial longitudinal fasciculus co-ordinates eye and head movements.
describe the auditory pathway
- vestibular cochlear nerve bifurcates
- one branch to dorsal cochlear nucleus
- one branch to ventral cochlear nucleus
- fibres fom both these (ipsilateral and contralateral) go to superior olivary nucleus
- fibres from sup. olivary nucleus + cochlear nucleus form lateral lemniscus
- lateral lemniscus ascends through pons to tectum of midbrain - terminates in inferior colliculus
- fibres from inferior colliculus innervate medial geniculate body of thalamus
- gives off auditory radiation to auditory cortex of temporal lobe
Fibres of the vestibulocochlear nerve reach the brainstem at the ……… and bifurcate
Fibres of the vestibulocochlear nerve reach the brainstem at the cerebellopontine angle and bifurcate
Both dorsal ventral cochlear nuclei lie on the what….
Both nuclei lie on the dorsolateral surface of the medulla
where do the superior olivary nuclei lie?
lie close to the medial lemniscus in the pons
where is the first site for binaural interaction
Fibres reach the superior olivary nuclei from both the ipsilateral and contralateral cochlear nuclei, so it is the first site for binaural interaction.
what is the lateral lemniscus
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
describe the path of teh lateral lemniscus
ascends through the pons and, on reaching the tectum of the midbrain, terminates in the inferior colliculus
the auditory radiation traverses what to the auditory cortex of the temporal lobe.
the auditory radiation traverses the internal capsule to the auditory cortex of the temporal lobe.
Dorsal surface of the thalamus, brainstem and floor of the fourth ventricle after removal of the cerebellum
upper medulla
what are the 4 vestibular nuclei?
There are four vestibular nuclei (superior, inferior, lateral and medial)
The superior vestibular nucleus projects to the …
The superior nucleus projects to the thalamus.
Section through lower midbrain (level of the inferior colliculus)
Section through upper midbrain (level of the superior colliculus)
what are subcortical structures?
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.
describe the olfactory pathway
- olfactory nerves enter the cranium through the cribriform plate of the ethmoid bone and synapse in the olfactory bulb
- 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).
- 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.
- The olfactory tubercle projects on to the thalamus with further projections to the insula and the orbitofrontal cortex which underlie olfactory perception.
tough card
base of the brain showing olfactory structures.
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.
describe the visual pathway
- optic nerve
- optic chiasm
- optic tract
- lateral geniculate nucleus (LGN) of the thalamus
- 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
lateral geniculate nucleus (LGN) of the thalamus (found…..
lateral geniculate nucleus (LGN) of the thalamus (found lateral to the medial geniculate nucleus
what is the stria of Gennari
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.
Visual pathways and visual field defects
which nerves innervate the eye
Motor neurons innervating the eye muscles are located in the three motor nuclei of the 3rd (oculomotor), 4th (trochlear) and 6th (abducens) cranial nerves
where are the oculogyric nuclei located
near the midline at distinctive levels in the brain stem
You should be able to identify the position of the oculomotor nucleus in sections of the upper mid brain
write that down
do other brain regions control eye activity>
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
what is the medial longitudinal fasciculus
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.
what is the MLF commonly affected in>
multiple sclerosis leading to nystagmus, diplopia and defects in gaze control
what initiates eye movements
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.
Overview of circuitry involved in generating eye movements (saccades)
Subcortical information usually reaches the cerebral cortex via …
Subcortical information usually reaches the cerebral cortex via the thalamus
how is the thalamus divided into nuclei?
The grey matter of the thalamus is divided into a series of functionally distinct nuclei by layers of white matter
The white matter divides the thalamus into _ major groups
The white matter divides the thalamus into 3 major groups
3 major thalamus groups
medial, ventral and anterior nuclear groups
what does the ventral thalamic nuclei group do?
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)
the lateral and medial geniculate nuclei (LGN & MGN), relays for ..
the lateral and medial geniculate nuclei (LGN & MGN), relays for vision and hearing, respectively
The anterior group of thalamic nuclei (A) projects to the ,……. what? and is important for what probably?
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.
A major input to the anterior nucleus is from the…. which are important for what?>
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.
The two largest nuclei of the thalamus are?
The two largest nuclei of the thalamus – the medial nuclei (MD) and the pulvinar (Pul)
cortico-thalamo-cortical relays - what are they?
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
medial nuclei (MD) and the pulvinar (Pul) - whats the associated cortex?
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
why arent medial nuclei and pulvinar well understood?
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.
Picture of thalmus nuclei
do humans have large areas of assocaited cortex?
yes
how many layers are there in cerebral cortex?
6 layers - stacked
Layer 4 of the cortex receives input from wherer?
thalamus
layer 5 outputes to where?
the major output layer to subcortical structures
(e.g. the pyramidal cell layer in motor cortex that forms the corticospinal tract).
Layer VI of the cortex does what?
layer 2 and 3 do what?
Layer VI sends feedback to the thalamus whilst layers II and III project to other cortical areas
describe Layer 1
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).
describe layer 2
The outer granular layer (layer II) is characterised by the presence of small rounded neurons.
layer 3 - describe
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)
describe layer 4
the inner granular layer (layer IV; neurons receiving input)
describe layer 5
inner pyramidal layer (layer V; output neurons).
describe layer 6
Finally, a thin innermost layer with some scattered cells in it - the multiform layer (layer VI).
desxcribe how cortical organisation in the primary sensory cortex is not usual
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.
describe how cortical organisation is unusual in the primary motor cortex
This area has an enlarged layer V, with giant pyramidal output neurons, but relatively few granule cells in layer IV.
describe how cortical organisation is in association cortex
for now be aware that it lacks anatomic specialisation in any particular layer. It is sometimes described as ‘homotypic’.
T or F
certain evolutionarily primitive parts of the cortex do not have 6 layers of cortex
T
certain evolutionarily primitive parts of the cortex do not have 6 layers of cortex
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)
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)
Older 3 layered cortex is known as _______ or _________, and intermediate 4-5 layered cortex is known as ________
Older 3 layered cortex is known as palaeocortex or allocortex, and intermediate 4-5 layered cortex is known as juxtallocortex
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)
Overview of connections of the different cortical layers
describe auditory processing disorders?
- 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.
*
a unilateral lesion in the pathway rarely causes a major impairment in hearing.
why?
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
T or F
Visual field defects can be important indicators of brain dysfunction
T
olfactor deficits occur due to
- aging
- clinical conditions (eg alzheimers)
give some examples of olfactors deficits
- 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).
The MLF is commonly affected in …..
leading to?
The MLF is commonly affected in multiple sclerosis leading to nystagmus, diplopia and defects in gaze control.
what is Retrosigmoid craniotomy
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.
fat
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