Neuroanatomy Flashcards
1
Q
Describe the ascending auditory pathway to the dorsal cochlear and ventral cochlear nuclie
A
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
2
Q
Where are the ventral and dorsal cochlear nuclei
A
on the dorsolateral surface of the medulla
3
Q
What is the ascending auditory pathway from the cochlear nuclei
A
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
4
Q
Where is the SON
A
close to the medial meniscus in the pons
5
Q
How are the SON and ION related
A
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
6
Q
What forms the main ascending auditory pathway
What is this known as
A
fibres from the SON combining with fibres from the cochlear nuclei which bypassed the SON
the lateral lemniscus
7
Q
What is the route of the main ascending auditory pathway to the MGN
What happens after the MGN
A
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
8
Q
What is the result of a unilateral lesion to the auditory pathway above the cochlear nuclei
A
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.
9
Q
Briefly list the steps in the ascending auditory pathway
A
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
10
Q
what are the vestibular nuclei
A
four vestibular nuclei (superior, inferior, lateral and medial)
11
Q
What do you need to know about the vestibular nuclei (2)
A
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.
12
Q
What are the second order fibres in the olfactory pathway
A
axons of the mitral cells
13
Q
Describe the olfactory pathway to the projections from the olfactory tract
A
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
14
Q
What is the entry for striate arteries supplying internal capsule and striatum
What olfactory structure underlies it
what is this region susceptible to
A
anterior perforated substance
olfactory tubercle
stroke
15
Q
Where does the pyriform cortex project to
what is next in the pathway and what do these structures do
A
amygdala and entorhinal cortex
these project to the hypothalamus and brainstem reticular
formation, which generate endocrine and autonomic responses to olfactory experience
16
Q
Where does the olfactory tubercle project to? what is the subsequent pathway
A
thalamus with further projections to the insula and the
orbitofrontal cortex which underlie olfactory perception
17
Q
What are the optic nerve fibres
A
axons of retinal ganglion cells
18
Q
Describe the visual pathway up to the LGN
A
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
19
Q
What are the destinations of the projections from the optic tract other than the LGN
What is the role of each
A
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.)
20
Q
Where do visual fibres from the LGN head?
A
N pass around the
lateral ventricle in the optic radiation and terminate in the primary visual cortex of the
occipital lobe
21
Q
How can you distinguish the primary visual cortex
A
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
22
Q
Where are the motor neurons innervating the eye muscle located
A
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
23
Q
Which brain regions influence the oculogyric nuclei
A
vestibular nuclei and the superior colliculus
24
Q
What is the medial longitudinal fasiculus
A
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.
25
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
26
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
27
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
28
How does subcortical information usually reach the cerebral cortex
via the thalamus
29
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)
30
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)
31
What are posterior to the Vp, Vl, and Va parts of the thalamus
LGN
| MGN
32
Where does the anterior thalamic nuclear group project
to the cingulate gyrus and is probably important for perception of internal emotional state
33
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.
34
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
35
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
36
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
37
What does the temporal parietal occipital association cortex receive inputs from
Pul
38
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,
39
How many areas did Brodmann describe
What are they based on
52
cytological structure
40
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
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
42
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
43
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.
44
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.
45
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)
46
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.
47
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.
48
What are the layers of the cerebral cortex (out to in)
```
molecular
outer granular
outer pyramidal
inner granular layer
inner pyramidal
multiform
```
49
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.
50
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
51
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
52
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
53
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.
54
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.
55
Describe the layers of the association cortex briefly
it lacks anatomic
specialisation in any particular layer.
sometimes described as ‘homotypic’.
56
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).
57
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.
58
What is functional in auditory processing disorders
the apparatus of the ear is functional but CNS deficits make auditory processing difficult
59
How can olfactory deficits occur
during normal aging and in certain clinical conditions (e.g. Alzheimer’s
disease).
60
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).
61
What is Retrosigmoid craniotomy
a classical surgical approach that involves removing and replacing the bone (craniotomy).
62
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
63
When is a retrosigmoid craniotomy used
when removing an ependymoma, a type of tumour that arises from the ependymal cells that line the ventricles
64
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
65
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.
66
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
67
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.
68
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
69
What part of the spinal cord do the nociceptive afferents ascend in
the contralateral anterolateral white matter
70
What is the nociceptive and thermal afferent somatosensory afferent system called?
anterolateral ascending system
AKA spinothalamic tract
71
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
72
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
73
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)
74
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
75
What is another name for the tactile system
dorsal column-medial lemniscus system
76
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
77
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
```
78
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
79
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.
80
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).
81
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
82
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
83
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
84
Describe Clarke's nucleus
Where is this found
AKA Clarke's column
has relay neurons for proprioception from lower limbs
thoracic cord
85
```
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.
86
How is the white matter in the spinal cord arranged generally
into 3 bundles/ columns/ fasciculi: dorsal, ventral and lateral
87
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.
88
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
89
How can spinal grey matter be divided
into a series of layers (Rexed's laminae)
these represent functional specialisations
90
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.
91
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.
92
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
93
What are the largest cells in the spinal cord
Where are they found in a cross section
motorneurons that project to muscles
ventral horn
94
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)
95
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.
96
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
97
What are the ventral nuclei of the thalamus concerned with
somatosensory relay and motor coordination
98
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.
99
Are proprioceptive sensory axons long?
yes
| There is no synapse at the spinal level,
100
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
101
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
102
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
103
Where do endogenous opioid peptides act on the nociceptor pathway
This first synapse for pain and temperature in the dorsal horn
104
Which side of the body do second order pain axons arise from
same side as stimulus
105
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
106
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
107
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
108
Describe the third order pain axons from the thalamus
ascend via the internal capsule to sensory processing areas of the cerebral cortex
109
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
110
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
111
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
112
Where does the trigeminal nerve enter the brainstem
at the pons
113
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
114
What colour is the spinal nucleus and what is it continuous with
very pale
substantia gelatinosa
115
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.
116
Where does the pain ascending pathway from the face cross the midline
after leaving the spinal nucleus of V before ascending to the thalamus
117
Where do incoming tactile fibres of the face terminate
chief sensory nucleus of V
118
Why is the chief sensory nucleus of V hard to find on specimens
it is buried among pontine fibres
119
Where is the chief sensory nucleus of V
pons at the same level as the incoming trigeminal fibres
120
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
121
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
122
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,
123
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)
124
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
125
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.
126
```
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
127
Which dorsal root ganglia are especially affected by tabes dorsalis
fasciculus gracilis
| fasciculus cuneatus
128
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.
129
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
130
What is usually responsible for segmental venous drainage of the spine
intradural radiculomedullary vein
131
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.
132
How do spinal dural arteriovenous fistulae typically present?
sensory disturbances due to their
| dorsal location but if untreated they progress to cause motor weakness
133
How do you treat a spinal dural arteriovenous fistula
dividing the abnormal connection inside the dura
134
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.
135
Name 3 prominent motor structures on the ventral surface of the brainstem
the cerebral peduncles,
medullary pyramids,
inferior olivary nuclei
136
How does the cerebellum connect with other motor structures
cerebellar peduncles
137
What is the principal route through which the brain addresses the spinal cord
corticospinal tract
138
Where do the motor areas of the cerebrum
frontal lobes (anterior to the central sulcus)
139
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.
140
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))
141
Do the corticospinal fibres cross the midline
most do and continue as the lateral corticospinal tract
uncrossed fibres remain as the ventral corticospinal tract
142
How big is the human corticospinal tract
>1 million fibres enter on either side
143
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
144
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
145
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
146
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’.
147
On which prosections can cerebral peduncles be seen
brainstem prosections and in cross-sections through the upper and lower midbrain
148
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)
149
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
150
What demarkates the boundary between the medulla and spinal cord
motor decussation
151
What does 'bulb' refer to in the 'corticobulbar'
motor nuclei in the medulla/ 'bulb'
152
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
153
What is a distinctive feature of the ventral medulla
what are they associated with
inferior olives
associated with climbing fibre input to the cerebellum
154
Most mammals lack the corticomotorneuronal connections present in humans. what do they have instead?
The great majority of corticospinal fibres travelling in the lateral and ventral corticospinal tracts terminate on spinal interneurons in the spinal grey matter, where they can influence both motor and sensory information processing. In most mammals (e.g. cats, dogs, rodents) this pathway through spinal interneurons is the major pathway through which movement is controlled.
in some primates this pathway exists in parallel to the cortico-motorneuronal pathway
155
What is the cortico-motorneuronal pathway especially important for
distal muscle control (eg control of intrinsic hand and foot muscles)
underlies manual dexterity
156
What happens to the myelin of degenerate fibres
What does this mean for their microscopic appearance
degenerated fibres demyelinate so they appear pale in comparison to the heavily myelinated dark staining fibres
157
What are the descending motor systems (5)
corticospinal and corticobulbar pathways
vestibulospinal tracts
reticulospinal fibres
rubrospinal tract
158
Why are the vestibulospinal tracts, reticulospinal fibres, rubrospinal tract hard to find
fibres are smaller and less obvious anatomically, having fibres that mingle with ascending and other descending or propriospinal fibres in the spinal cord white matter.
159
Where in the spinal cord is the vestibulospinal tract found
Where do the fibres of this tract arise
ventral columns of the spinal cord
in the vestibular nuclei in the dorsal medulla
160
What is the vestibulospinal tract mainly concerned with (3)
extensor (antigravity) limb muscles and proximal muscles (neck and trunk) and is involved in maintaining posture and equilibrium.
161
where do the reticulospinal fibres originate
from many cell groups in the reticular formation of the pons and medulla.
162
What is the reticular formation
a poorly understood but extensive region
of grey matter extending through the core of the brainstem from spinal cord to
medulla
163
Describe the descending motor fibres from the reticular formation
fast conducting and project throughout the length of the spinal cord.
These pathways are important for posture and for coordinated body movement (e.g.
locomotion, reaching)
164
Describe the red nucleus in humans
| input and output
large but has few (if any) fibres that descend to the spinal cord.
inputs from the cerebellar nuclei and the motor areas of the cerebral cortex
output is
mainly to the inferior olivary nucleus
165
What is the function of the red nucleus thought to be in humans
motor skills learning
166
What is the cerebellum involved in in the motor system
eedforward motor control, in predicting commands for future movements.
167
Which brain structure allows us to automatically shift our eyes to allow us to read effectively
cerebellum
168
Describe the structure of the cerebellar cortex
forms large numbers of folia (folds). Cerebellar cortex is much thinner than the cerebral cortex, so the folds are smaller and more tightly packed.
• midline -the vermis
• Large lateral masses (the cerebellar hemispheres)
• On the ventral aspect of the brain, the hemisphere is connected to the pons by the large middle cerebellar peduncle, containing fibres originating from the pons projecting into the cerebellum.
• On the ventral aspect of the cerebellum, in the cerebello-pontine angle, is a very
small, semi-detached part of cerebellar cortex called the flocculus
• On each side, small parts of the cerebellar cortex ‘overhang’ the dorso-lateral aspect
of the medulla. This part is called the tonsil.
169
What is the flocculus (3)
a very small, semi-detached part of cerebellar cortex in the cerebello-pontine angle
concerned with vestibular function
The facial and vestibulocochlear nerves enter the brain at this
location
170
What is the clinical importance of the cerebellar tonsil
due to its proximity to the medulla and foramen magnum, coning can occur
171
What is coning
in patients with raised intracranial pressure there is risk of the tonsils collapsing into the foramen magnum if CSF is withdrawn by lumbar puncture, resulting in pressure on the brainstem and sudden death due to pressure on the “vital centres” for respiratory and autonomic control in the medulla
172
How is coning avoided
Lumbar puncture is usually contra-indicated in a
patient with symptoms and signs suggestive of raised intra-cranial pressure (e.g.
papilloedema, swelling of the optic nerve head).
173
Which other brain structures does the cerebellar cortex connect to directly
none
| All of the cortical output is directed to a group of nuclei buried below the cortical folds, the deep cerebellar nuclei
174
True or false
| cerebellar cortical output is inhibitory
true
175
What are the true deep nuclei of the cerebellum (3 on each side)
the dentate nucleus, the nucleus interpositus (globose and emboliform), and the fastigial nucleus
176
Which areas of the cerebellar cortex don't send output via the the dentate nucleus, the nucleus interpositus, or the fastigial nucleus
Why does this still make sense
(the flocculus, and the buried flocculonodular lobe) send outputs to the vestibular nuclei in the medulla
(the evolutionary origin of the deep cerebellar nuclei is from the vestibular
nuclei).
177
Where is the output of the deep cerebellar nuclei to
```
projections to brainstem descending motor pathways, and mostly to the motor areas of
cerebral cortex (via the thalamus).
```
178
What is the largest deep cerebellar nucleus
dentate
also most important
it is most likely the only one you can see
179
How does the dentate nucleus appear in a cross section
as a convoluted line of grey matter within the white matter.
180
What connects the cerebellum to the brainstem on each side
What is the output of each
```
the small inferior
cerebellar peduncle (from the medulla);
```
the large middle cerebellar peduncle (from the
pons)
the superior cerebellar peduncle (deep nuclear output).
181
Which of the cerebellar peduncles is largest
what does this reflect
middle
the enormous traffic between cerebral cortex and cerebellum via the pons
182
What is the superior cerebellar peduncle important for
How can it be seen on a section
major output pathway from
the deep nuclei (mainly the dentate nucleus in humans)
is obvious dorsally in the pons, and where it crosses the midline decussates in the low mid brain
183
Where do the fibres from the superior cerebellar peduncle travel
through and to the red nucleus
and then to the motor parts of the thalamus (ventrolateral nucleus, projecting to primary motor
cortex; ventroanterior nucleus, to the premotor and supplementary motor areas)
184
What separates the superior cerebellar peduncles
what does this form
A thin plate of tissue bridges the gap between the superior peduncles on either side, so forming the roof of the rostral part of the fourth ventricle.
185
Where are the inputs to the cerebellum from
via pons and inferior olive
186
How do neurons from the cerebral cortex reach the cerebellum
pass through the internal capsule and cerebral peduncles to terminate ipsilaterally on neurons in the pons; these neurons send their axons across the midline through the middle cerebellar peduncle, to the contralateral cerebellum, as mossy fibres
187
Which cell type is the major input for the cerebellum
mosst
188
What does the difference between the size of the cerebral peduncles of the midbrain and pyramids of the medulla indicate
the number of fibres that terminate in the pons
189
Where do fibres that end in the pons originate from?
many cerebral cortical areas, especially sensory and sensory association areas (including many
visual, tactile and auditory related fibres)
190
How does information reach the cerebellum via the ascending spinocerebellar mossy fibres (uncrossed)
Give an example of fibres that do this
through the smaller inferior cerebellar
peduncle; many of these carry somatosensory information, for example from proprioceptors
(Clarke’s nucleus)
191
What forms the climbing fibre input to the cerebellum
Fibres from the inferior olive in the medulla
| via the inferior cerebellar peduncle.
192
What are climbing fibres important for
learning, they are thought to mediate plasticity in the mossy fibre - granule cell – Purkinje cell pathway that refines the cerebellar processing to generate and coordinate movement.
193
Where do outputs from the deep cerebellar nuclei travel
leave in the superior cerebellar peduncle, enter the lower midbrain where they cross the midline, pass through and around the red nucleus in the upper midbrain and ascend to terminate in the parts of the thalamus concerned with motor function.
194
Does the cerebellum represent contra or ipsilateral movement
(think about jellicent)
As the cerebral cortex represents contralateral body sensation and movement, the cerebellum represents ipsilateral movement and sensation (thus contralateral connections with the cerebral cortex)
195
How many layers does the cerebellum have
3
196
What are the 3 layers of the cerebellum
| from out to in
molecular layer
Purkinje cell layer
granular
197
Describe the molecular layer of the cerebellar cortex
a low cell density
consists mainly of the thin axons of granule cells (parallel fibres) which run parallel to the folia and cell dendrites.
198
Describe the Purkinje layer of the cerebellum (2)
a single cell thick and
| the Purkinje cells are large enough to be visible under a low power microscope
199
Describe the granular layer of the cerebellum
innermost layer
| containing vast numbers of small granule cells.
200
What lies beneath the layers of the cerebellar cortex
the cerebellar white matter containing fibres running to and from the cerebellar cortex
201
What is the function of cerebellar Purkinje cells
cerebellar output
202
Describe the structure and arrangement of Purkinje cells (3)
extensive dendrites that form a planar sheet.
They lie in a plane at right angles to the long axis of the folia.
The fibres of the molecular layer run parallel to the long axis of the folia, and thus intersect the Purkinje cell dendrites at right angles, which they make synapses on dendritic spines as they pass.
203
What does the arrangement of the Purkinje and parallel fibres in the cerebellar cortex allow (2)
allows each parallel fibre to contact many Purkinje cells along a single folium
allows each Purkinje cell to receive synaptic contacts from an enormous number of parallel fibres (~ 250,000).
204
Which are the only cerebellar cortical cells that send their axons out of the cortex
What do they do
Purkinje
| inhibit cells in the deep cerebellar nuclei (GABA)
205
Describe histological staining of Purkinje cells
stained by the Golgi method (based on silver impregnation)
which selects only some neurons (and glia) but stains them in their entirety,
shows their
dendritic arborization particularly well.
206
What can a stroke above the motor decussation cause
contralateral weakness (hemiparesis).
More severe strokes will give contralateral paralysis (hemiplegia)
207
What are upper and lower motor neurons
What do upper motor lesions usually involve
upper motor neurons (corticospinal or corticobulbar fibres),
lower motor neurons (spinal motoneurons)
motor cortex or its output
208
Where do upper motor lesions usually occur
What are their signs
give 3 causes
above the pyramidal decussation
produce contralateral signs.
Strokes, cerebral palsy and multiple sclerosis
209
What can cause lower motor lesions
eg polio
210
What do upper motor lesions result in (4)
s involve an immediate flaccid paralysis, which gradually becomes
spastic with hyperreflexia,
clonus
a positive Babinski sign: voluntary movement is impaired, but reflex muscle contraction remains.
211
What do lower motor lesion usually result in
muscular weakness, flaccid paralysis, muscle wasting and areflexia.
212
True or false
there is a substantial number of corticospinal fibres in humans that descend ipsilaterally, so some ipsilateral limb control is possible
false
Although a substantial number do descend ipsilaterally in the ventral spinal cord, there is little evidence that these can contribute to ipsilateral limb function, particularly of the hands: they either cross the midline before terminating, or they control axial (limb girdle and trunk) muscles
213
Can the ispilateral descending motor fibres in the spinal cord rearrange after a stroke
no
cannot reorganise to allow recovery of function in adults or in children over a few months old (although they can do so following damage prenatally or in early neonatal life –
an example of developmental windows for plasticity).
214
What are arteriovenous malformations
Why are they dangerous
what is the treatment
congenital vascular anomalies consisting of direct arterial to venous connections (‘fistulas’) without an intervening capillary bed and can occur
in the brain and spinal cord
have a propensity to bleeding.
Treatment to prevent future haemorrhage can involve surgical resection, focused radiotherapy, or
endovascular embolization.
215
Give 3 other names for a cavernoma
Cavernous Malformation,
Cavernous Angioma,
Cavernous Haemangiomas
216
What are cavernomas
Where do they occur and is there a genetic factor
are they more dangerous than an AVM?
composed of thin dilated vascular channels that do not have a feeding artery and therefore do not appear on angiograms
They can occur in the brain or spinal cord and are familial in a proportion of cases.
The risk of bleeding is usually lower than AVMs but if multiple haemorrhages occur then surgical resection is considered
217
Describe the effects of a unilateral stroke on the face (not facial nerve)
why is this
complete jaw and tongue paralysis does not follow a unilateral stroke, although movements will be weaker on the affected side (opposite to the side of the brain affected by stroke)
Corticobulbar fibres to some motor nuclei provide bilateral innervation, (e.g. nerves V and XII)
218
What often causes a lopsided tongue
Damage to the corticospinal innervation of the hypoglossal nucleus
219
How does the innervation of the upper and lower face differ
What does this mean for a stroke
the motor nuclei of the branches of the facial nerve (VII) to the upper facial muscles are also bilaterally innervated by the cortex. On the other hand, the motor nuclei of the
branches of the facial nerve to the lower facial muscles are unilaterally innervated, and these may be completely paralysed after a stroke
stroke frequently produces a contralateral lower facial paralysis (loss of ability to smile or make expressions with the mouth), while the upper face retains some function through intact ipsilateral projections from motor cortex.
220
What is ataxia
(“bad movement”): movement becomes clumsy and uncoordinated, speech may become slurred
221
What types of movement make ataxia very obvious
This usually occurs after damage to the cerebellum. What do these symptoms indicate about cerebellar function?
n large movements such as reaching and pointing
where poor scaling of movement is a problem (over- or under-reaching, inaccuracy, jerkiness).
the cerebellum contributes to pre-programmed movement, where the current state of the body and information from sensory systems must be taken into account to allow plans for future movement.
222
What does the cerebellum represent for the motor system as a whole
behaves as a ‘model’ system,
allowing the future outcome of a given situation (sensory signals indicating a future event, or a motor command for movement) to be predicted, and therefore for appropriate preparation be made
223
What does 'basal ganglia' usually refer to
a functional system of forebrain and midbrain structures including the large nucleus called the neostriatum (composed of caudate nucleus and putamen) and the globus pallidus
224
What is the neostriatum often referred to as
Where does the name come from
striatum
originates from the appearance of the grey matter of the nuclei that is “striated” by the fibre bundles of the internal capsule which pass through
225
What is the relation of the internal capsule to the caudate and putamen
completely separates these posteriorly
226
As a guide, where can the caudate nucleus always be found
follows the course of the lateral ventricles, and so it can
always be located in the wall of the anterior horn, body and inferior horn of the lateral
ventricle
227
Where is the putamen nucleus found
teral to the internal capsule, medial to the insula ('buried cortex')
228
Name 3 structures functionally linked to the striatum and globus pallidus
nuclei of the diencephalon, the thalamus and the subthalamic nucleus, and a nucleus in the midbrain, the
substantia nigra
229
What are the 2 major divisions of the substantia nigra
a dopaminergic component (‘pars compacta’), which innervates the neostriatum, and a nondopaminergic component (‘pars reticulata’)
230
How do the relations of the caudate and putamen change as they pass from posteriorly
where do the globus pallidus and thalamus appear
caudate and putamen are continuous ventrally and anteriorly in the forebrain, but then the internal capsule penetrates and separates them more posteriorly
Caudate has a large 'head' anteriorly
globus pallidus appears more posteriorly, medial to the putamen. The thalamus also appears in more posterior sections, on either side of the third ventricle.
231
Where does input to the caudate and putamen come from
all areas of the cerebral cortex, with particularly prominent projections from the prefrontal cortex to the caudate and from the sensorimotor cortex to the putamen
232
Where do the putamen and caudate join
antero-ventrally where the anterior limb of the internal capsule peters out and no longer separates the nuclei.
They are in fact a single structure that has been split during development by the growth of the internal capsule.
233
What is the shape of the caudate nucleus
tadpole-shaped mass of grey matter with a large head in the lateral wall of the anterior horn of the lateral ventricle, a narrow body in the lateral wall of the middle part of the lateral ventricle, and a narrow flat tail curling with the lateral ventricle into the roof of the inferior horn
234
What forms the ventral striatum
What does it contain
The ventral-anterior part of the caudate-putamen that is still joined
nucleus accumbens
235
Where is output from the neostriatum directed principally
to the globus pallidus and to the substantia nigra of the midbrain.
236
What are the 2 divisions of the globus pallidus
what is the in/output of each
Fibres from the neostriatum terminate in both divisions;
the internal segment forms the major output pathway of the basal ganglia, to the motor areas of the thalamus (ventro-anterior and ventro-lateral) and the medial nucleus of the thalamus.
The external segment of the globus pallidus sends its projection to the subthalamic nucleus, which sends a return projection to the internal segment of the globus pallidus
237
What does the pars compacta look like
in fresh and fixed tissue it appears as the dark pigmented area in the midbrain, next to the cerebral peduncles. In a cross section through the midbrain, where myelin has been stained, it appears as a lighter area
238
Where is the subthalamic nucleus
lies at a similar cross-sectional location to the substantia nigra, but at the junction of the midbrain and diencephalon
very hard to find
239
What is the in/output of the subthalamic nucleus
Why is it well placed for its role
receives input from the external
segment of the globus pallidus and projects to internal globus pallidus.
It is therefore well
placed to regulate the output of the entire striatum.
240
True or false
| the caudate and putament both project to and receive input from the substantia nigra
true
Both caudate and putamen project to the substantia nigra pars compacta (which contains the dopaminergic neurons) and pars reticulata (output for basal ganglia in the control of eye movements). In turn they receive dopaminergic innervation from the substantia nigra pars compacta
241
What are the effects of DA loss on the different parts of the globus pallidus
excess inhibition in the external globus pallidus and reduced inhibition in the internal globus pallidus
final outcome of these alterations is the same: excess inhibition in the thalamus, leading to reduced motor cortex activity and, as a consequence, reduced movement.
242
Which of the basal ganglia's outputs are involved in complex executive functions
medial dorsal nucleus of the thalamus, which in turn projects to the prefrontal cortex
243
What are the 3 mains types of fibre on the internal capsule
Efferent corticobulbar and cortico-spinal fibres
Efferent corticopontine fibres
Afferent thalamocortical fibres
244
Where do efferent corticobulbar and cortico-spinal fibres in the internal capsule begin and end
Where do they lie within the capsule
originate primarily from the motor areas of the cerebral cortex. Within the internal capsule, the corticobulbar fibres (to the medulla, controlling head and neck muscles) and the corticospinal fibres lie close to the genu (“bend”).
245
Which part of the internal capsule is affect by middle cerebral artery stroke or haemorrhage
the genu
246
Where do efferent corticopontine fibres in the internal capsule begin and end
from all lobes of the cerebral cortex, destined for the pons. In turn the neurons in the pontine nuclei project on to the cerebellum
247
Which structure reflects the importance of intercommunication between the cerebral cortex and cerebellum in humans
the large size of the pons and corticopontine pathway
248
Where do afferent thalamocortical fibres ascend from
Give an example of how specific groups of thalamocortical fibres can be seen
various thalamic nuclei to the cerebral cortex
the lateral geniculate body of the thalamus gives rise to a bundle of large, fastconducting fibres which run around the lateral ventricle and then posteriorly to the visual cortex as the 'optic radiation'
A parallel 'auditory radiation' arises from the
medial geniculate nucleus
These may be visible on some of the horizontal
sections.
249
What is the striatum and internal capsule supplied by
small arteries originating from the middle and anterior cerebral arteries (effectively end arteries).
Some of the most important vessels arise from the middle cerebral artery and are termed ‘striate arteries
250
What are pyramidal disorders
The consequences of damage to the striatum are often referred to in textbooks and in clinical practice as extrapyramidal disorders, whereas those of internal capsule or motor cortex damage are pyramidal.
it is a misleading term
251
What are the symptoms of Parkinson's
slowness in the execution of movement, rigidity and tremor (although the latter appears less related to dopaminergic pathology).
252
What causes Huntington's chorea
what does it result in
in part due to death of cells in the neostriatum,
spontaneous
unnecessary and unwanted complex limb movements are produced (almost the converse of
Parkinsonism).
253
What do lesions of the subthalamic nucleus lead to
hemiballismus, a violent disorder in which flailing limb movements are produced
254
What is deep brain stimulation
a surgical procedure that involves placing electrodes in
selected deep nuclei of the brain, usually (although not exclusively) to target movement
disorders such as Parkinson’s disease.
255
What are the nuclei usually targetted in DBS
what is the aim
subthalamic nucleus, globus pallidus interna, ventral anterior thalamus, and pedunculopontine nucleus
to disrupt pathological patterns of neural activity that develop (e.g. in Parkinsonism)
256
What is ETV
Endoscopic third ventriculostomy
a surgical procedure that involves an endoscope first through the frontal lobe into the lateral ventricle, then through the foramen of Munro into the third ventricle. At this point it makes a hole (‘ventriculostomy’) in the floor of the third ventricle to allow CSF to pass from the ventricle into the subarachnoid space and then onwards to be absorbed
257
What does ETV alllow
diversion of CSF from any blockage downstream of the third ventricle, such as from a tumour obstructing the aqueduct of Sylvius, and therefore preventing CSF build up (‘hydrocephalus’) with potentially raised intracranial pressure.
258
What can haemorrhage from the striate branches of the middle cerebral artery, or blockage of them by thrombosis or embolism lead to
causes a virtually complete vascular deprivation (and therefore
death) of a corresponding part of the striatum and internal capsule: a paralytic 'stroke'.
Damage to the internal capsule will lead to weakness or paralysis of the opposite side of the body (contralateral hemiparesis or hemiplegia). The region of the internal capsule that is most commonly affected is the genu, where corticospinal fibres to the head, neck & part of the upper limb are located.
259
What are prefrontal and limbic association areas of cortex essential for (4)
cognitive processes such as self-awareness, foresight, abstract reasoning, planning capacity, and complex emotional behaviour
260
Which pair of structures form a rim of 'old cortex'
what are these structures involved in
The cingulate and parahippocampal gyri form a rim of ‘old’ cortex on the medial wall of the hemisphere
mixture of functions including olfaction, recognition memory and emotion.
261
Where can the cingulate and parahippocampal gyri be found
what happens if there is dysfunction of the cingulate cortex
they form a rim of ‘old’ cortex on the medial wall of the hemisphere
contributes to certain psychiatric illnesses (e.g. schizophrenia and depression)
262
What is the hippocampal formation important for
what does this structure comprise
declarative memory
Cornus Ammonis regions 1, 2 and 3,
the dentate gyrus
the subiculum.
263
Describe Cornus Ammonis regions 1, 2, and 3 together with the dentate gyrus
they are primitive 3 layered cortex (thinner than the 6 layered neocortex) folded into the medial temporal lobe in the inferior horn of the lateral ventricle
264
Which disease is considered to begin in the hippocampus
Alzheimer's
265
Where/what is the amygdala
what is it well connected to (3)
a subcortical nucleus in the medial temporal lobe that is well connected with the orbitofrontal cortex, the hypothalamus and the nucleus accumbens
266
What are the 4 important chemical pathways in the brain
what are they important for
acetylcholine, dopamine, noradrenaline and serotonin
have widespread effects on mood and arousal
267
Briefly compare the defined morphology of the primary motor cortex to that of the primary visual cortex
primary motor cortex is agranular but has large layer V pyramidal neurons, which form the corticospinal tract axons,
whereas primary visual cortex has a complex layer IV, which receives thalamic input.
268
How do primary cortical areas differ from association areas
primary areas of cerebral cortex are cortical areas with a dedicated function relating to one specific modality
association areas of cortex are not focussed on one specific function but allow different types of information to be processed, or associated together
269
What do 'secondary' cortical areas (eg V2) allow
allow for different components of a single modality to be processed together
270
What do higher association areas of cortex allow
enable more complex processing; for example, different types of sensory modality (auditory, visual and somatosensory) can be combined in the parietal-temporal-occipital area
271
Where is Wernicke's area
what is this important for
in the Parietal-temporal-occipital association cortex
speech comprehension (in the left hemisphere for most humans) and lesions here result in the language deficit, ‘Wernicke’s aphasia’
272
Where is Broca's area
what is this area important for
in the premotor association cortex, adjacent to the premotor cortex (usually left hemisphere)
speech production (lesions lead to Broca's aphasia)
273
Where is the cingulate gyrus in relation to corpus callosum
The cingulate gyrus lies above the corpus callosum
Posteriorly, it continues round the callosum and downwards to become continuous with a strip of cortex lying on the most medial part of the temporal lobe, the parahippocampal gyrus.
274
Which parts of the cingulate and parahippocampal gyri are involved in the following:
olfaction
recognition memory
emotion
olfaction: anterior part of parahippocampal gyrus
recognition memory: posterior part of parahippocampal gyrus – entorhinal cortex
emotion: anterior cingulate gyrus
275
Where is the subgenual cortex
what is deep brain stimulation of this cortex used for
below the genu of the corpus callosum (it is part of the cingulate gyrus)
used to treat intractable (treatment resistant) depression
276
Where do output fibres from the cingulate gyrus run
mostly to the parahippocampal gyrus.
277
What is the principal tract connecting the cingulate and parahippocampal gyri
the cingulum
| A large association tract (white matter bundle) running below the surface of the cingulate cortex
278
What are the 2 regions of the parahippocampal gyrus
name some things included in each region
anterior region: pyriform cortex (a.k.a. uncus) and primary olfactory cortex
posterior region: entorhinal cortex
279
What is the entorhinal cortex involved in
what are some key inputs
involved in recognition memory
receives large projections from the cerebral cortex, particularly from those areas dealing with highly processed sensory information (parietal-temporal-occipital cortex)
280
Give an example to damage to a sub-region in the prefrontal cortex which demonstrates its specialised role
damage to the ventrolateral prefrontal cortex is associated with ‘attentional control’
281
What part of the brain is the orbitofrontal cortex part of
prefrontal cortex
can be found on the ventral surface of the frontal lobes (lying above the orbit)
282
Why is the orbitofrontal cortex famous
it was the area most severely damaged in the brain of Phineas Gage, after his railroad accident.
Damage to this structure is associated with profound alterations in emotional and social behaviour.
283
Where does input to the orbitofrontal cortex come from (4)
outputs?
what does it have particularly close connections to (4)
from all neocortical association areas as well as the hippocampus, amygdala and hypothalamus.
sends projections to all areas that it receives from
close connections with the cingulate cortex, amygdala and hypothalamus. One of its main output pathways is the nucleus accumbens
284
How can the orbitofrontal cortex influence action
via one of its main output pathway in the nucleus accumbens
285
What is the fimbria in the brain (2)
a strip of white matter lying on the surface of the hippocampus
one of the output tracts of the hippocampal formation
286
What are the 2 key output tracts of the hippocampal formation
fimbria
subiculum
287
Where is the subiculum an output tract from to
from hippocampal formation to the overlying cortex
288
describe the course of the fimbria
The fimbria forms the fornix on each side; these leave the temporal lobes and merge to form one fornix that follows the inferior aspect of the corpus callosum, towards the hypothalamus
289
What is the subiculum
the cortex between the parahippocampal gyrus and the hippocampus
290
true or false
the parahippocampal gyrus, subiculum and hippocampus,
dentate gyrus are continuous with each other
true
| they represent a single sheet of cortex folded into the inferior horn
291
What type of memory is the hippocampal formation thought to be involved in
episodic memory
292
Which brain region has recently been implicated in social memory in animals.
CA2
293
What is the hippocampus vulnerable to particularly (3)
highly vulnerable to damage e.g. due to hypoxia.
Alzheimer’s disease may start here.
It is also very sensitive to corticoids (e.g. cortisol) and thus to stress.
294
The major input into the hippocampal formation is from the parahippocampal gyrus (entorhinal cortex). What information is it thought to carry?
carries information originating in neocortex, especially from sensory association areas, thought to reflect recognition
295
What is the destination of information passing from the hippocampal formation via the fimbria-fornix
the mammillary bodies of the hypothalamus and parts of the thalamus (diencephalic memory system)
296
Where does the fornix run importantly and what does this allow
how does it then pass
runs into the median plane at its highest point and fibres are exchanged between the two sides in the fornical commissure (which you won't see) linking the two hippocampi
Running forwards and then down, the fornix curves away from the callosum to split on the anterior commissure.
The post-commissural part runs to the mammillary body
297
What type of circuitry exists in the hippocampus
a classic trisynaptic loop circuitry
298
describe the classic trisynaptic loop circuitry within the hippocampus
many inputs reach the hippocampus through the perforant pathway from the entorhinal cortex (1)
which makes synapses with the dendrites of the dentate gyrus granule cells and also with the apical dendrites of the CA3 pyramidal cells. The dentate granule cells project via mossy fibres (2)
to the CA3 pyramidal cells. The CA3 pyramidal cells project via the Schaffer collaterals (3)
to the CA1 pyramidal cells, which in turn have connections (4) with the subiculum.
299
What is the output from the trisynaptic loop of the hippocampus
from CA3 pyramidal cells which project through the
fimbria/fornix to the hypothalamus.
The subiculum also projects through the fimbria/fornix to the hypothalamus, as well as back to the entorhinal cortex.
300
What does amygdala mean
almond
301
What/ where is the amygdala
a subcortical mass of grey matter which lies deep to the primary olfactory cortex of the uncus at the temporal pole
302
Which sections should you take to see the amygdala
coronal brain slices or in MRIs taken at the levels of the hypothalamus and anterior temporal lobe
303
What borders the hypothalamus anteriorly and posteriorly
how can it usually be seen
ant: optic chiasm
post: mammary bodies
Usually the infundibulum (pituitary stalk) is visible between these two ventral surface landmarks
304
Where is the hypothalamus located within the diencephalon
located inferior to and a little anterior to the thalamus
305
When viewing the hypothalamus in coronal section, what is also visible
third ventricle will be visible on the midline
306
What brin structure is the nucleus accumbens conventionally part of
however what else is it related to
striatum
has close anatomical and functional links with the amygdala
(also has anatomical relation to the caudate and putamen, and to the anterior limb of the internal capsule)
307
Name 3 places which give extensive input to the nucleus accumbens
from the orbitofrontal cortex, cingulate cortex and
| from the amygdala.
308
What behaviours is the nucleus accumbens functionally concerned with
emotional and motivated behaviours
309
Name 2 psychiatric problems assocaited with the nucleus accumbens
schizophrenia
addiction
310
Describe the cholinergic system in the brain
| geography, function, clinical
forebrain system
arises close to the septal nuclei and basal forebrain and projects throughout the cortex.
has been associated with learning and memory,
cholinergic deficits have been implicated in Alzheimer’s disease
311
Describe the dopaminergic system in the brain
| geography, function, clinical
midbrain system
(i) Substantia nigra, which projects into the ‘motor’ loops of the basal ganglia,
essential for the initiation of movement
(degeneration in this system is known to contribute to the core symptoms of Parkinson’s disease)
(ii) Ventral tegmental area, which projects to the nucleus accumbens where it is thought to be involved in motivation, and may be an important substrate for the actions of drugs of abuse.
312
Describe the NA system in the brain
| geography, function
midbrain/pontine noradrenergic system
arises in locus coeruleus
thought to be involved in overall attentional functions
313
Describe the serotoninergic system in the brain
| geography, function, clinical
medullary serotoninergic system
arising in the raphe nuclei
may modulate emotional behaviour and is implicated in impulsive behaviours and obsessive-compulsive disorders.
It is the main target of antidepressant SSRI drugs and of the recreational drug, ecstasy
314
What can damage in association areas of cortex can result in
complex deficits such as
apraxias (high-order action deficit due to damage in posterior parietal or premotor cortical areas),
agnosias (high-order visual deficit)
aphasias (high-order language deficit due to damage in
Wernicke’s or Broca’s areas or associated regions and connections)
315
What does amnesia refer to
pathological memory loss
316
What is anterograde amnesia
what can cause it (4)
specifically refers to memory loss of events after the damage
typically caused by anoxia, ischaemia, encephalitis, thiamine deficiency
317
What does retrograde amnesia refer to
memory loss of events prior to the trauma
318
What can cause amnesia generally (give 2 specific causes)
can be due to damage in the medial temporal lobe (e.g. patient ‘H.M.’)
or
damage in the diencephalon (e.g. Korsakoff’s syndrome, caused by dietary deficiency of thiamine, vitamin B-1, typically due to alcoholism, associated with anterograde and some retrograde memory loss).
319
Which disease is helpful in understanding the role of the amygdala
Urbach-Weithe disease (a rare genetic disorder, calcification of the amygdala) and is associated with deficits in emotional behaviour
320
Give 4 psychiatric/ neurological drugs that act on the ascending chemical systems
Selective Serotonin/ Noradrenaline Reuptake Inhibitors (depression),
l-DOPA (Parkinson’s disease),
neuroleptics (schizophrenia)
pro-cholinergic drugs (Alzheimer’s
disease).
321
What is hippocampal sclerosis also known as
why is it important clinically
Medial temporal sclerosis
it's the most common cause for intractable temporal lobe epilepsy
322
What is a common history of stablished refractory temporal lobe epilepsy
Up to a third of patients with established refractory temporal lobe epilepsy have a history of seizures in childhood.
323
True or false
| the hippocampus is uniformly affected by hippocampal sclerosis
false
| the dentate gyrus, and the CA1, CA4 and to a lesser degree CA3 sections of the hippocampus are primarily involved
324
What is seen histologically in medial temporal sclerosis
neuronal cell loss, gliosis and sclerosis.
325
How do you manage hippocampal sclerosis
initially managed medically, but in patients who are refractory to medical management, temporal lobectomy or selective amygdalo-hippocampectomy may be performed.
326
How successful is lobectomy in treating mesial temporal sclerosis
Anterior temporal lobectomy is successful in 75-90% of patients.
327
Describe the cranial end of the neural tube
what forms at the caudal end
there are three primary expansions (brain vesicles):
forebrain (or prosencephalon), midbrain (or mesencephalon) and hindbrain (or rhombencephalon)
The cavities within the primary brain vesicles are the precursors of the adult ventricular system
spinal cord
328
What does the mesencephalon of the neural tube further develop into (3)
into a caudal medulla oblongata (or just medulla) and a more rostral pons, and the cerebellum develops on its dorsal surface.
329
What does the forebrain of the neural tube further develop into (3)
into a caudal diencephalon (mainly the thalamus and hypothalamus) and a rostral telencephalon (or telencephalic vesicle, one on either side) and these give rise to the cerebral hemispheres
330
What does the forebrain in a human adult consist of
Telencephalon: Cerebral cortex (outer layer) and Basal ganglia (deeper structures)
Diencephalon: Thalamus & Hypothalamus
331
What 3 structures form the brainstem
Midbrain, Pons, Medulla Oblongata
332
What forms the hindbrain
Pons, Medulla Oblongata & Cerebellum
333
Which sulci are constant among humans
lateral sulcus (Sylvian fissure)
central sulcus
Parieto-occipital sulcus
334
Describe the lateral sulcus
a deep fissure in the lateral side, (sometimes called the Sylvian fissure) separates the temporal lobe from the frontal and parietal lobes
335
Describe the central sulcus
division between frontal and parietal lobes
336
Describe the Parieto-occipital sulcus
on the medial surface,
| separating the occipital and parietal lobes
337
What is the bulb
old name for the medulla
e.g.
nerve fibres from cerebral cortex to the medulla are cortico-bulbar fibres.
338
What does grey matter refer to
the cell bodies and dendrites located in the outer layers of the cerebral cortex and cerebellar cortex, in the deep nuclei (collections of neurons) of the brain, and in the spinal cord dorsal and ventral horns.
339
What does white matter refer to
the axons that connect different CNS regions, many of which are myelinated, and which may form named nerve tracts
340
What does grey matter look like (2)
In the living brain the grey matter is pink, having many capillaries; in the fixed brain it is brown
341
Where is the white matter located in the spinal cord and brainstem? How does this compare with the cerebral and cerebellar cortices?
located on the outer surface.
The cerebral and cerebellar cortex have the opposite organisation to the spinal cord:
the neurons form a folded outer sheet, with axons running below
342
What are deep nuclei
(‘sub cortical’)
e.g. vestibular nuclei, deep cerebellar nuclei, the amygdala and the basal ganglia, are equivalent to peripheral nerve ganglia
343
What type of cell is abundant in the CNS other than neurons
What do they do
glial cells
several types with different functions (myelination, phagocytosis of debris, homeostatic control of the local neural environment, maintaining BBB).
344
How can white and grey matter be seen microscopically
using Nissl stains (toluidine blue, cresyl violet etc) to stain nuclei and cell bodies (both neuronal and glial).
White matter can be seen using myelin stains (Weigert-Pal method, osmic acid).
345
Primary motor and primary sensory areas can be determined in relation to gyri and sulci. What are these? (give location and area number if applicable)
* Primary motor cortex (Brodmann’s area 4) is anterior to the central sulcus.
* Primary somatosensory cortex (Brodmann’s areas 3, 2 and 1) is posterior to the central sulcus.
* Primary visual cortex (area 17) is located at the occipital pole, particularly in the calcarine sulcus on the medial face of the hemisphere.
* Primary auditory cortex is in the lateral temporal lobe.
* Pain is represented in the insula (buried cortex) and in the anterior cingulate cortex, just above the corpus callosum.
• Primary olfactory cortex is in the medial temporal lobe. Olfaction and taste are also represented in parts of the insula.
346
Describe the brain's ventricular system
2 lateral ventricles (below cerebral cortex) communicate via the inter-ventricular foramen (of Munro) with the cavity of the 3rd (III) ventricle, on the midline in the diencephalon
aqueduct connects the 3rd ventricle with the 4th (IV) ventricle in the hindbrain (its roof being formed by the cerebellum).
4th ventricle is continuous with the central canal of the spinal cord and with the subarachnoid space, via the foramina of Magendie and Luschka
347
What are the foramina of the ventricular system
inter-ventricular foramen (of Munro): connects lateral and 3rd ventricle
foramina of Magendie and Luschka: connects 4th ventricle with central canal of spinal cord and subarachnoid space
348
What do the ventricles do
produce and contain cerebrospinal fluid
349
What makes CSF specifically
a plexus of blood vessels wrapped in choroid epithelium (formed from pia mater and ependyma), called the choroid plexus, forms CSF from blood in the lateral, 3rd and 4th ventricles
350
How does CSF escape the ventricular system
via the foramen of Magendie and the foramina of Luschka into the subarachnoid space surrounding the brain and spinal cord.
351
what happens to the meninges in brain prosections
dura mater is usually left in the cranium when the brain was removed, but the arachnoid mater can be seen covering the cerebral cortex on some specimens
352
Describe cranial pia mater
forms an intimate covering for all superficial parts of the brain and spinal cord, but is not visible to the naked eye
353
What are cisterns
In some places the pia and arachnoid are widely separated to form cisterns containing accumulations of CSF.
Cisterns are not separate entities but communicate with each other by way of the general subarachnoid space.
354
What are the 2 important cisterns
cisterna magna, in the angle between the medulla oblongata and the cerebellum
the lumbar cistern (from which CSF can be sampled).
355
describe the venous sinuses
formed from the periosteal and meningeal layers of the dura mater, return venous blood from the cerebral circulation via the internal jugular vein and are also sites for return of CSF into the systemic circulation via arachnoid villi into the superior sagittal sinus.
356
How much of cardiac output does the brain require
15-20% of resting cardiac output,
blood flow through the brain approaches a litre per minute.
357
Hoes does the ICA enter the skull
what does it split into
through the carotid canal, passes through the cavernous sinus in a characteristic S-shape (carotid siphon), and penetrates the dura into the subarachnoid space
bifurcates into the anterior and middle cerebral arteries
358
Describe the course of the anterior cerebral artery
supplies the frontal lobes
then passes into the longitudinal fissure where it runs above the corpus callosum to supply more medial aspects of the parietal and occipital lobes.
These include medial aspects of somatosensory and motor cortical areas, which relate to the lower limbs.
359
Which is the largest cerebral artery
how does it pass
middle
passes into the more lateral and inferior parts of the hemispheres through the lateral sulcus.
Its branches supply somatosensory and motor cortex relating to upper limb and face, the basal ganglia and cerebral white matter.
360
Describe the appearance of the vertebral arteries
One or both of the vertebral arteries can be found on the ventral aspect of the medulla (they are frequently unequal in size).
They converge at the caudal pons to form the midline basilar artery, which grooves the ventral surface of the pons
361
What do AICA and PICA supply
provide the major blood supply to the brain stem (midbrain, pons, medulla). PICA and AICA together with the superior cerebellar arteries supply the cerebellum
362
How does the basilar artery terminate
by bifurcating into two posterior cerebral arteries which supply the medial occipital lobes, notably visual cortex, and parts of the temporal lobes.
363
Around which brain structures does the circle of Willis form
around the optic chiasm and stalk of the pituitary
364
How do veins in the brain drain
Superficial veins drain into the superior and inferior sagittal sinuses,
deep veins drain into the great cerebral vein and then the straight or transverse sinuses.
The sinuses meet at the confluence and drain into the internal jugular veins, which remove exhausted blood and CSF from the brain
365
Which brain part is used to indicate death
why
irreversible loss of function of the brain stem has been accepted as an indicator of death.
if the brain stem is irreversibly damaged then the forebrain, even if undamaged, cannot again function normally
366
what does brainstem death indicate other than death
indicates a permanent inability to maintain basic homeostatic functions (breathing, cardiovascular control). Although these can be replaced by life-support machinery, recovery cannot occur after brain stem death
367
How can brainstem function be assessed
clinical examination of cranial nerve function.
368
What causes stroke generally
vessel occlusion or vessel rupture / leakage
369
How can cerebral vessel rupture occur
due to the bursting of an aneurysm, an excessive localised swelling of the wall of an artery
370
What are the symptoms of middle cerebral artery blockage
most of the motor cortex and somatic sensory cortex are deprived of blood supply, resulting in paralysis and a loss of cutaneous and proprioceptive sensibility in the contralateral upper limb and head and neck.
NB lower limb is likely to be spared because the anterior cerebral artery supplies the parts of the motor and sensory cortices in which they are ‘represented’
371
Why are Potential spaces in the cranium of clinical importance
any bleed (extradural, subdural or subarachnoid haemorrhage) will increase the volume of fluid within the cranium and exert pressure on brain tissue.
372
What can cause hydrocephalus
narrow passageways in the ventricles are vulnerable to blocking by “space-occupying lesions” (such as tumours) or by intracranial bleeds.
Blockade of CSF flow causes accumulation of CSF proximal to the block, and a rise in pressure, which results in hydrocephalus
This can occur at various sites in the circulatory pathway of CSF
373
What are 2 ways to surgically access the brain
craniotomy: surgical removal of a portion of the skull
keyhole surgery:
minimally invasive surgery carried out through a very small incision, with special nstruments and techniques including fibre optics.
374
What is spinal anaesthesia
Anaesthetic can be introduced into the CSF in the lumbar cistern, where the
anaesthetic substance acts directly on the spinal cord itself
375
Where is the cauda equina
Within the lumbar cistern a sheaf of spinal roots, occupying the subarachnoid space.
376
Why can a lumbar puncture be performed at the lumbar cistern
cauda equina's e mobile spinal roots will roll away from a needle introduced through the dura into the subarachnoid space, allowing a sample of CSF to be taken from the lumbar cistern
377
How can you diagnose e.g. meningitis, subarachnoid haemorrhage
CSF can be obtained from the lumbar cistern as a routine procedure, or more exceptionally from the cisterna magna.
378
What does x ray Cerebral angiography require
what is this imaging used for
injection of radio-opaque fluid into the internal carotid or vertebral vessels
to examine the vascular tree for constrictions or dilatations. Angiograms can also be generated using MRI, and used in combination with CT
379
What is CT
a form of radiography that uses multiple x-ray images through the brain from different angles to generate a series of continuous slices and produce sectional images of the brain
380
What is MRI used to image
provides images of the brain by measuring regional variations in proton density when placed in a magnetic field and stimulated by a particular radio frequency.
MRI images can be produced relatively rapidly and with high resolution and high contrast in any desired plane.
The MRI settings may be altered to highlight bone or soft tissues
381
What is PET
injections of short-lived radioisotopes are given; these attach to a molecule used by the body (e.g. glucose), circulate and are metabolised within the tissues.
The high-energy gamma rays emitted by the radioisotopes are detected by the scanner depending on the rates of metabolism or level of blood flow.
Radiolabelled ligands can also be used to localise specific receptor types in the
living brain with the same method.
382
What are the symptoms of tabes dorsalis
What are the symptoms of syringomyelia
results in a bilateral absence of touch below the level of the lesion. There is also a loss of proprioceptive feedback below the site of the lesion leading to a characteristic stamping gait
characteristic "cape-like" distribution of loss of pain and temperature sensation in the upper limbs and trunk but preservation of touch and pressure sensation (as central cavitation usually disrupts the decussating fibres of the anterolateral system but not the ascending fibres of the DC-ML system)
