Neuroanatomy Flashcards
Describe the ascending auditory pathway to the dorsal cochlear and ventral cochlear nuclie
vestibulocochlear
nerve reaches the brainstem at the cerebellopontine angle and bifurcates: i) one branch ends in
the dorsal cochlear nucleus,
ii) the other in the ventral cochlear nucleus
Where are the ventral and dorsal cochlear nuclei
on the dorsolateral surface of the medulla
What is the ascending auditory pathway from the cochlear nuclei
fibres relay in the superior olivary nuclei
fibres reach the SON from both the ipsilateral and contralateral cochlear nuclei so this is the first site for binaural interaction
Where is the SON
close to the medial meniscus in the pons
How are the SON and ION related
they are not - SON is in the pons, involved in hearing, while the functionally unrelated inferior olivary nucleus is on the medulla and is involved in motor control
What forms the main ascending auditory pathway
What is this known as
fibres from the SON combining with fibres from the cochlear nuclei which bypassed the SON
the lateral lemniscus
What is the route of the main ascending auditory pathway to the MGN
What happens after the MGN
ascends through the pons and, on reaching the tectum of the midbrain, terminates in the inferior colliculus
fibres then pass to the medial geniculate nucleus in the thalamus
MGN gives the auditory radiation which traverses the internal capsule to the auditory complex of the temporal lobe
What is the result of a unilateral lesion to the auditory pathway above the cochlear nuclei
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.
Briefly list the steps in the ascending auditory pathway
vestibulocochlear nerve -> cerebellopontine angle -> bifurcation either ventral or dorsal cochlear nucleus -> SON-> SON fibres and direct fibres from cochlear nuclei combine to form lateral lemniscus -> inferior colliculus-> MGN-> auditory radiation-> auditory cortex of temporal lobe
what are the vestibular nuclei
four vestibular nuclei (superior, inferior, lateral and medial)
What do you need to know about the vestibular nuclei (2)
don’t need to identify them individually,
note that the lateral (Deiter’s) nucleus is made up of large neurons and gives rise to the descending lateral vestibulospinal tract, (important in balance)
The superior nucleus projects to the thalamus.
What are the second order fibres in the olfactory pathway
axons of the mitral cells
Describe the olfactory pathway to the projections from the olfactory tract
olfactory nerve fibres enter the cranium through the cribriform plate of the ethmoid bone and synapse in the olfactory bulb
Second order fibres leave olfactory bulb as olfactory tract and project via olfactory stria to pyriform cortex (uncus) and olfactory tubercle
What is the entry for striate arteries supplying internal capsule and striatum
What olfactory structure underlies it
what is this region susceptible to
anterior perforated substance
olfactory tubercle
stroke
Where does the pyriform cortex project to
what is next in the pathway and what do these structures do
amygdala and entorhinal cortex
these project to the hypothalamus and brainstem reticular
formation, which generate endocrine and autonomic responses to olfactory experience
Where does the olfactory tubercle project to? what is the subsequent pathway
thalamus with further projections to the insula and the
orbitofrontal cortex which underlie olfactory perception
What are the optic nerve fibres
axons of retinal ganglion cells
Describe the visual pathway up to the LGN
Optic fibres enter through optic foramen and fibres from the nasal retina decussate in the optic chiasm
optic tract leaves the chiasm to wrap around the midbrain. Main projection from here is to LGN in thalamus.
some tract projections to the pretectal region, suprachiasmatic nucleus, and a large projection to superior colliculus
What are the destinations of the projections from the optic tract other than the LGN
What is the role of each
pretectal
region in the rostral midbrain (pupil response),
the suprachiasmatic nucleus (circadian
rhythms)
a large projection to the superior colliculus (visual
reflex centre; is not involved in the
direct transmission of sensory
information.)
Where do visual fibres from the LGN head?
N pass around the
lateral ventricle in the optic radiation and terminate in the primary visual cortex of the
occipital lobe
How can you distinguish the primary visual cortex
e by a white strip that runs through the grey matter, parallel to the surface - the stria of Gennari, and is due to the dense axonal input from the thalamus to layer IV of visual cortex
Where are the motor neurons innervating the eye muscle located
in the three motor nuclei of the 3rd
(oculomotor), 4th (trochlear) and 6th (abducens) cranial nerves
“oculogyric” nuclei are located near the midline at distinctive levels in the brain stem
Which brain regions influence the oculogyric nuclei
vestibular nuclei and the superior colliculus
What is the medial longitudinal fasiculus
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.
What does the MLF connect? Therefore what is its function
connects vestibular nuclei to the motor nuclei controlling eye movements (for vestibulo-ocular
movements) and the superior colliculus to the cervical motor neurons in the upper spinal
cord controlling head movement.
co-ordinates tracking movements of the eyes and head
What causes nystagmus in MS
what else does this cause
the disease attacks MLF
damage to the MLF also causes diplopia and defects in gaze control
How are eye movements initiated
What is the pathway from here
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
How does subcortical information usually reach the cerebral cortex
via the thalamus
How is the thalamus divided
grey matter is divided into nuclei by layers of white matter:
3 major groups (medial, ventral and anterior nuclear groups)
What does the anterior thalamic nuclear group contain (3)
the ascending somatosensory relays (the ventroposterior part: Vp),
the relays from cerebellum and basal ganglia to primary motor cortex (via the ventrolateral part; Vl)
motor association areas (premotor cortex and supplementary motor areas - via the ventro-anterior nuclei; Va)
What are posterior to the Vp, Vl, and Va parts of the thalamus
LGN
MGN
Where does the anterior thalamic nuclear group project
to the cingulate gyrus and is probably important for perception of internal emotional state
Name a major input to the anterior nucleus of the thalamus
what are they important for
the mammillary bodies of the
hypothalamus, which are important for the formation of declarative memory.
What are the 2 largest nuclei of the thalamus
Where do they receive input from
the medial nuclei (MD) and the pulvinar (Pul) -
receive most input from the cerebral cortex itself, forming cortico-thalamo-cortical relays
Where do the MD and Pul of the thalamus project to
areas of association cortex, which do not have a simply defined unimodal input, but instead have inputs from many other areas
Where is the prefrontal cortex
in the association cortex
anterior to the motor areas
of cerebral cortex, much of which receives input from the medial nuclei
What does the temporal parietal occipital association cortex receive inputs from
Pul
Why is the function of the medial nuclei and pulvinar poorly understood
humans have comparatively large areas of association cortex, the medial nuclei and pulvinar are very large
in humans, but they cannot be studied in animals,
How many areas did Brodmann describe
What are they based on
52
cytological structure
Where do the following areas correspond to in Brodmann’s areas:
a)primary motor cortex
b) the premotor and supplementary motor areas
c)primary somatosensory
cortex
d) the primary visual cortex resides
e)auditory cortex
primary motor cortex corresponds to area
4
the premotor and supplementary motor areas to area 6;
primary somatosensory
cortex corresponds to areas 3, 1 and 2;
the primary visual cortex resides in area 17
auditory cortex in area 41
What are the primary cortices?
what area of the hemisphere do they take up
What is the remaining area? Is this special?
motor, somatic sensory, visual, auditory and olfactory
65-70 cm2 of an estimated average total of 1200 cm2
remaining 1130 cm2 comprise the so-called “association areas”: in no other species do the
association areas make up so large a proportion of the whole cortex
What is the uncus
The most anterior part of the para-hippocampal gyrus in the medial temporal lobe is called the uncus because it resembles a hook; the grey matter of the uncus is believed to be olfactory cortex
Where is the auditory cortex in the brain
On the lateral surface of the hemisphere, auditory cortex is on the superior gyrus of the temporal lobe, partly concealed in the lateral fissure.
Describe the layers of the cerebral neocortex
e found in 6 layers, stacked one upon the other running
from the surface to the depth of the cortex.
What does layer IV of the cerebral cortex receive input from
What does layer V do
layer IV receives input from the thalamus,
whilst layer V is the major output layer to subcortical structures (e.g. the pyramidal cell layer in motor cortex that forms the corticospinal tract)
What does layer VI of the cerebral cortex do
what about II and III
sends feedback to the thalamus
whilst layers II and III project to other cortical areas.
Is the layered arrangement of the cerebral cortex uniform?
The cells making up the thickness of the
cortex are not uniform; depending on their function, different regions of neocortex show
variations in the arrangements of cells and fibres, complicating the basic six-layered pattern.
What are the layers of the cerebral cortex (out to in)
molecular outer granular outer pyramidal inner granular layer inner pyramidal multiform
Describe the cells of layers I and II in the cerebral cortex
layer I: contains fibres running parallel to the cortical surface but very few neurons
(therefore is not visible with the Golgi or Nissl stain).
(layer II): characterised by the presence of small rounded neurons.
Describe the cells of layers III and IV in the cerebral cortex
(layer III), and contains
triangular-shaped “pyramidal” neurons (output neurons).
layer IV; neurons receiving input
What do layers V and VI contain of the cortex
(layer V; output neurons).
Layer VI :thin innermost layer with some scattered cells in it - the multiform layer
What are the variations on the layers in the primary sensory cortex
Since this area receives major thalamic inputs, the major input layer (layer IV) is
correspondingly well developed, and the “output” layers reduced
Which layer is particularly well developed in the human primary visual cortex
granular layer IV
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.
What are the variations on the layers 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 the layers of the association cortex briefly
it lacks anatomic
specialisation in any particular layer.
sometimes described as ‘homotypic’.
Do all parts of the cortex have 6 layers?
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).
What are the older 3 layers of the cortex called
Older 3 layered cortex is known as palaeocortex or allocortex, and intermediate 4-5
layered cortex is known as juxtallocortex.
What is functional in auditory processing disorders
the apparatus of the ear is functional but CNS deficits make auditory processing difficult
How can olfactory deficits occur
during normal aging and in certain clinical conditions (e.g. Alzheimer’s
disease).
Give 3 olfactory 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).
What is Retrosigmoid craniotomy
a classical surgical approach that involves removing and replacing the bone (craniotomy).
Where is a retrosigmoid craniotomy sited
What does it allow access to
posterior to the sigmoid sinus and inferior to the transverse
sinus
allows access to the lateral cerebellum and cerebellopontine angle, where cranial
nerves VII and VIII emerge
When is a retrosigmoid craniotomy used
when removing an ependymoma, a type of tumour that arises from the ependymal cells that line the ventricles
Give a fact about ependymoma
t is one of the most
common tumours in childhood, where it usually arises in the vicinity of the 4th ventricle
What is the prognosis for a child after they have had an ependymoma removed
If they are removed completely at surgery, often the tumour does not recur and no further therapy is required.
What are the 2 different ascending somatosensory systems from the skin
One carries tactile (touch) and proprioceptive sensation,
the other nociception (perceived as pain) and thermal sensation
Generally what part of the spinal cord carries the nociceptive and thermal sensations?
carried by afferents through the dorsal roots to terminate in the spinal cord dorsal horn, close to their entry.
After the nociceptive afferents have terminated in the spinal cord dorsal horn, what happens next
at least 1 synapse in superficial dorsal horn
project across spinal cord in ventral commissure to contralateral anterolateral white matter where they ascend
What part of the spinal cord do the nociceptive afferents ascend in
the contralateral anterolateral white matter
What is the nociceptive and thermal afferent somatosensory afferent system called?
anterolateral ascending system
AKA spinothalamic tract
How do afferents of the tactile system ascend in the spinal cord
enter and ascend in dorsal columns on ipsilateral side without a synaptic relay
The axons of the tactile system enter the spinal cord and ascend in the dorsal columns on the
ipsilateral side without a synaptic relay. Does this mean they don’t give any branches?
no - they do give branches to the spinal cord
Where do the fibres of the tactile system terminate
at the rostral end of the spinal cord in the gracile and cuneate nuclei (dorsal column nuclei)
Where do the axons from the dorsal column nuclei project to after the fibres of the tactile system have terminated here
axons from the nuclei cross the midline to ascend through the medial brainstem as the medial lemniscus
What is another name for the tactile system
dorsal column-medial lemniscus system
Where do the fast conducting fibres of the medial lemniscus project to
where next
thalamus
d from there third order neurons carry tactile and conscious proprioceptive
information to the somatosensory cortex in the postcentral gyrus of the parietal lobe
Give the series involved in the spinothalamic tract
nociceptor/ thermal receptor-> dorsal root-> spinal cord dorsal horn -> >1 synapse in superficial dorsal horn -> ventral commissure-> contralateral anterolateral white matter-> ASCENT ->brainstem/thalamus
Give an overview of the steps in the tactile system afferents
axons enter and ascend in dorsal columns (no synapse) ->
gracile and cuneate nuclei ->
axons cross midline and ascend in medial lemniscus->
thalamus ->
somatosensory cortex in postcentral gyrus
What does the spinal cord consist of
a central region of nerve cells and processes (grey matter)
surrounded by bundles of mainly myelinated axons (white matter) travelling to and from the
brain, and between different spinal levels.
Which parts of the spinal cord have extensive grey matter
regions of the cord that innervate the brachial and lumbar/ sacral plexuses to the limbs, where the dorsal and ventral horns are enlarged
(associated with limb innervation).
If a segment of spinal cord has enlarged dorsal and ventral horns, what does this suggest
innervates lumbosacral or brachial plexuses
ie associated with limb innervation
What are the special features of the thoracic cord
small dorsal and ventral horns, but
has two extra cell groups not found at other levels.
intermediolateral nucleus
Clarke’s nucleus/ column
Describe the intermediolateral nucleus
Where is this
composed of sympathetic pre-ganglionic neurons, the axons of which run to the chain of sympathetic ganglia
thoracic spinal cord
Describe Clarke’s nucleus
Where is this found
AKA Clarke’s column
has relay neurons for proprioception from lower limbs
thoracic cord
Describe the different appearances of the spinal cord at the following levels: cervical thoracic/ upper lumbar lumbosacral lower sacral
Cervical level:
Large and pronounced oval shape, with thick white matter
Thoracic and upper Lumbar level:
Circular in shape, with a thin “H” profile to
the grey matter
Lumbosacral:
Circular shape, expanded grey matter, white
matter thinning out
Lower Sacral:
Circular outline, little white matter.
How is the white matter in the spinal cord arranged generally
into 3 bundles/ columns/ fasciculi: dorsal, ventral and lateral
How can the dorsal column of the spinal cord be further subdivided in at C and T levels
into a lateral cuneate and a medial gracile division carrying fibres from upper and lower limb respectively.
At what levels is surrounding white matter in the spinal cord thickest
why
cervical
all of the ascending axons have entered the cord, and few descending fibres from the brain have terminated
How can spinal grey matter be divided
into a series of layers (Rexed’s laminae)
these represent functional specialisations
what is the most important division of the Rexed’s laminae
What is its function
Why is it important
substantia gelatinosa (layer II),
a critical site for processing noxious information, and therefore a therapeutic target.
What over lies Rexed’s laminae
what does this contain
Lissauer’s tract
incoming axons carrying pain and temperature information that travel up or down the cord to an adjacent segment
before entering the dorsal horn.
What do they deep layers of the dorsal horn contain
laminae IV and V
relay neurons many with axons that cross the midline in the ventral commissure to ascend in the anterolateral column
What are the largest cells in the spinal cord
Where are they found in a cross section
motorneurons that project to muscles
ventral horn
Which part of the spinal cord is associated with reflex actions
The major region in the centre of the cord (lamina VII) contains spinal interneurons concerned with local processing (e.g. reflexes)
Which parts of the brainstem are important for pain and temperature sensation from the Head and neck
where are these structures prominent
Spinal nucleus and tract of the trigeminal nerve (V)
in the low medulla, where they are continuous with (and homologous to) the substantia gelatinosa and Lissauer’s tract of the spinal cord.
What is the thalamus functionally
the major input route to the cerebral cortex, relaying information from the
medulla, cerebellum and brain stem, and from other areas of the hemisphere
What are the ventral nuclei of the thalamus concerned with
somatosensory relay and motor coordination
What is the internal capsule
massive tract of white matter linking cortex and thalamus.
also contains descending fibres
and fibres running between the nuclei of the thalamus and between different cerebral cortical
regions.
Are proprioceptive sensory axons long?
yes
There is no synapse at the spinal level,
What is the sensory decussation
Where tactile second order neurons arising in the gracile and cuneate nuclei send their
heavily myelinated axons as a ribbon-like bundle (the medial lemniscus) across the mid-line
Where do second order proprioceptive neurons travel after the sensory decussation
to synapse on third order neurons that project to the primary somatosensory cortex via the internal capsule
What is the substantia gelatinosa
nociceptors’ principal site of termination is in this superficial part of the grey matter
it consists of
unmyelinated fibres, fine cell processes and very small cell bodies
Where do endogenous opioid peptides act on the nociceptor pathway
This first synapse for pain and temperature in the dorsal horn
Which side of the body do second order pain axons arise from
same side as stimulus
What happens to the primary sensory axons for pain and temperature after they enter dorsal root but before they terminate in the dorsal horn
primary afferents bifurcate into short ascending and descending branches that run for about a spinal segment in Lissauer’s tract and give rise to branches that enter the spinal cord dorsal horns
How can second order pain neurons be considered diverse
one group is located in lamina V of the spinal grey matter, and these also have input from the tactile system (wide dynamic range neurons).
Another group are in lamina I and these are
nociceptive specific
Do both groups of second order pain axons cross the midline?
yes
cross the midline in the ventral (anterior) commissure immediately below the central canal, and ascend contralaterally in
the anterolateral white matter – note that this is not a distinct tract
Describe the third order pain axons from the thalamus
ascend via the internal capsule to sensory processing areas of the cerebral cortex
Where do anterolateral system fibres terminate in the brainstem
especially in the reticular formation, where they influence
the level of arousal through actions on the sympathetic system (medulla) and other
ascending systems
Give an example of modulation of pain afferents by descending pathways from higher centres
the raphe nuclei embedded in the medullary reticular formation, and the periaqueductal grey of the midbrain
Are the tactile and nociceptor systems separated in the head and neck?
yes - trigeminal pain afferents turn caudally and head to the brainstem while tactile afferents terminate in chief sensory nucleus of V
Where does the trigeminal nerve enter the brainstem
at the pons
What do primary pain afferents from the face do after entering the pons
turn caudally and descend through the brainstem forming a fibre bundle, the spinal tract of V, which is prominent in the low medulla (and extends into the upper cervical spinal cord). then synapse in adjacent spinal nucleus of V in the caudal medulla
What colour is the spinal nucleus and what is it continuous with
very pale
substantia gelatinosa
Where do pain second order afferents from the spinal nucleus of V travel to next
cross the midline and ascend to the thalamus (trigeminothalamic fibres) with the anterolateral system fibres from the spinal cord.
Where does the pain ascending pathway from the face cross the midline
after leaving the spinal nucleus of V before ascending to the thalamus
Where do incoming tactile fibres of the face terminate
chief sensory nucleus of V
Why is the chief sensory nucleus of V hard to find on specimens
it is buried among pontine fibres
Where is the chief sensory nucleus of V
pons at the same level as the incoming trigeminal fibres
After the tactile fibres of the face reach the chief nucleus of V, where do they go
How does this differ for proprioceptive fibres from the jaw muscles?
From here fibres cross to join the medial
lemniscus and ascend to the thalamus.
they ascend to a small nucleus in the midbrain
What are the pathways historically known as “unconscious” pathways
project to the cerebellum , and there is a particularly heavy projection of proprioceptors
(sensory fibres from muscle and joints).
Historically these were considered not to be concerned with perception (hence they were called “unconscious” pathways) but are concerned with motor function
What provides the pathway from lower limb proprioceptors to the cerebellum
Clarke’s column
the characteristic nucleus in the dorsal horn of spinal cord in the thoracic segments,
Briefly how do proprioceptors from the upper limb reach the brain
via part of the cuneate nucleus to the cerebellum (unconscious) and thalamus/ cortex (conscious)
What are the signs of Brown-Sequard Syndrome
after spinal cord hemisection, tactile sensation from below the lesion site is lost on the same side (the dorsal columns are uncrossed), whereas
nociception and thermal sensation will be normal on the side ipsilateral to the lesion.
On the contra-lateral side, nociception and thermal sensation will be lost below the lesion, but tactile sensation will be normal
Lesions at which level of the ascending somatosensation pathways show separation of the 2 pathways in a similar way to Brown Sequard Syndrome?
Give an example
lesions at the medulla
infarction of the inferior cerebellar arteries may damage the laterally located anterolateral system, leaving the tactile system intact.
Thus a patient may sense a pin prick on the contralateral body as a gentle touch.
What is tabes dorsalis: what disease what does it mean what does it affect what is damaged
‘dorsal wasting’
seen in late stage cases of syphilis
affects nervous system
causes degeneration of central projections from dorsal root ganglia
Which dorsal root ganglia are especially affected by tabes dorsalis
fasciculus gracilis
fasciculus cuneatus
What do ventral commissure axons do
What are they vulnerable to
carry pain and temperature information
vulnerable in expansion of the central canal in the disease syringomyelia.
What are spinal dural arteriovenous fistulae
rare vascular malformations which are a consequence of an abnormal connection between a meningeal branch of a segmental artery (which normally constitutes the vascular supply of the spinal dura) and an intradural
radiculomedullary vein
What is usually responsible for segmental venous drainage of the spine
intradural radiculomedullary vein
What does a spinal dural arteriovenous fistula do
causes high pressure blood to flow retrograde into the coronal venous plexus of
the spinal cord causing venous congestion. This causes oedema and injury to the spinal cord.
How do spinal dural arteriovenous fistulae typically present?
sensory disturbances due to their
dorsal location but if untreated they progress to cause motor weakness
How do you treat a spinal dural arteriovenous fistula
dividing the abnormal connection inside the dura
Where can the spinal dural fistula be found in treatment
dural sleeve covering the nerve root where an abnormal vein with arterialised blood can be found. The dural sleeve with the nerve root inside constitutes the spinal nerve which can be found exiting the neural foramen just inferior to the place where the vertebral lamina connects to the vertebral body, i.e. the pedicle.
Name 3 prominent motor structures on the ventral surface of the brainstem
the cerebral peduncles,
medullary pyramids,
inferior olivary nuclei
How does the cerebellum connect with other motor structures
cerebellar peduncles
What is the principal route through which the brain addresses the spinal cord
corticospinal tract
Where do the motor areas of the cerebrum
frontal lobes (anterior to the central sulcus)
Which neurons form the corticospinal tract
describe the path of these fibres
pyramidal neurons in layer V
run in the internal capsule of the forebrain, which becomes the cerebral peduncles in the midbrain, which pass through the pons, then emerge caudally as the medullary pyramids in
the ventral medulla.
How do corticobulbar fibres travel
travel with the pyramidal neurons of layer V then leave the pathway to innervate motor cranial nerves ( V, VII, IX, X, XI, XII (not those controlling eye
movements))
Do the corticospinal fibres cross the midline
most do and continue as the lateral corticospinal tract
uncrossed fibres remain as the ventral corticospinal tract
How big is the human corticospinal tract
> 1 million fibres enter on either side
Where is the major representation of motor function in the brain
Where is it
Primary motor cortex
(Brodmann’s area 4, also called M1),
immediately anterior to the central sulcus
What are the 2 other key motor areas in the brain, other than M1
Where are they in relation to M1
What are other motor structures in the brain that have been found
‘Premotor cortex’ and the ‘Supplementary motor areas’ (both parts of Brodmann’s area 6)
anterior to M1
‘cingluate’ motor areas
What does damage to the following result in
a) M1
b) premotor cortex
c) supplementary motor areas
a) paralysis
b and c) complex deficits, in which movements are poorly prepared or planned
What two features distinguish
the histological structure of the primary motor cortex from other areas?
(i) layer V contains a population of “giant” pyramidal
neurons. These cells are only found in primary motor cortex and are among the largest cells (giving rise to the fastest conducting axons) in the brain.
(ii) The motor cortex is the thickest area of cortex, yet contains few small rounded cells (granule cells). The motor cortex is therefore sometimes called ‘agranular cortex’.
On which prosections can cerebral peduncles be seen
brainstem prosections and in cross-sections through the upper and lower midbrain
do all the cortical fibres in the pons just pass through
some pass through (the corticospinal and corticobulbar fibres), others terminate in the pons (corticopontine)
Where do the corticospinal fibres emerge from in the medulla?
What happens to them here
emerge from the pons as the prominent medullary pyramids,
decussate as the fibres descend into the spinal cord
What demarkates the boundary between the medulla and spinal cord
motor decussation
What does ‘bulb’ refer to in the ‘corticobulbar’
motor nuclei in the medulla/ ‘bulb’
Which head muscles are not innervated directly by the corticobulbar fibres?
Why?
the oculomotor nuclei (III, IV & VI) are not directly innervated by the corticospinal
tract: the eyes need to move consensually (together) and are controlled by brainstem
structures
