Lecture 5: Brainstem and Cranial Nerves (I) Flashcards
1
Q
Brainstem consists of the
A
Consists of the
midbrain, pons and medulla
2
Q
Brainstem is positioned between
A
Positioned between
the forebrain and spinal cord, and connected to the cerebellum dorsally
3
Q
Brainstem provides a pathway for
A
Provides a pathway for axonal tracts running between the forebrain, cerebellum and spinal cord
4
Q
Brainstem is associated with
A
Associated with 10 pairs of cranial nerves
5
Q
Ventral =
A
anterior
6
Q
Dorsal =
A
posterior
7
Q
Cranial nerves - PNS or CNS?
A
Considered a part of the PNS rather than the CNS as they are considered peripheral nerves
8
Q
Cerebral peduncles translation
A
little feet of the cerebrum
9
Q
Cerebral peduncles other name
A
crus cerebri
10
Q
What are the cerebral peduncles?
A
Collection of axonal tracts that connects one major brain region to another
white matter that connects brainstem to the cerebrum
11
Q
What do the cerebral peduncles include?
A
includes axons that descend from the cerebral cortex to the brainstem and spinal cord
(passing longitudinally on the ventral surface of the midbrain)
12
Q
What does the cerebral peduncle help to do?
A
help to anchor the cerebrum to the brainstem
13
Q
III cranial nerve and cerebral peduncles
A
anterior
14
Q
IV cranial nerve and cerebral peduncles
A
posterior
15
Q
Colliculus define
A
any of a number of small swellings in the roof of the midbrain, involved in vision and hearing.
16
Q
Superior cerebellar peduncle associated with
A
midbrain
17
Q
Middle cerebellar peduncle associated with
A
pons
18
Q
Inferior cerebellar peduncle associated with
A
medulla
19
Q
How many mounds make up the mid brain
A
4 colliculi
20
Q
What should you find in order to visualise the superior colliculus and the inferior colliculus?
A
Find the cerebral aqueduct
21
Q
Superior colliculi =
A
visual relay & reflex centres
22
Q
Functions of the superior colliculi
A
• receive inputs from the retina (anteriorly)/visual cortex (posteriorly going forward) &
project to vision-related areas in cortex
• concerned with the detection of movement of
objects in the visual field - track objects with eyes and to do so need to move eyes therefore muscles of the eye are innervated
• relay vision information to neurons innervating
the muscles that control eye movement
part of the visual pathway therefore relay information and also involved in reflexes
23
Q
Inferior colliculi =
A
auditory relay and reflex nuclei
24
Q
Functions of the inferior colliculi
A
- relaying auditory information from hearing receptors of the ear to the sensory cortex - in particular on the primary auditory cortex which is the transverse temporal gyrus
- act in reflexive responses to sound (e.g., startle reflex)
25
Substantia nigra location
located deep to the cerebral peduncle
internal structure in the midbrain
consists of two parts
26
Substantia nigra contains
contains melanin pigment which is the precursor of dopamine and gives the dark colouring
27
Function and damage to the substantia nigra
functionally linked to the basal nuclei/ganglia****
dopamine neuron degeneration-Parkinson’s disease - part of the substantial nigra contains dopamine neurons and these die in Parkinson's disease
28
Two parts of substantia nigra
pars compacta (SNpc) and pars reticulata (SNpr)
SNpr is ventral/anterior to SNpc
SNpc dopamine neurons are located here
SNpr is between the cerebral peduncle and compacted
29
SNpr
pars reticulata
30
SNpc
pars compacta
31
SNpr has connections similar to ....
SNpr has connections similar to the internal division of the globus pallidus (GPi) = inhibitory input to the thalamus
32
Red nucleus in relation to substantia nigra
deep to substantia nigra
33
Why is the red nucleus red?
rich blood supply and contains iron pigment therefore red due to lots of erythrocytes and the presence of iron pigment
34
Red nucleus function
relay nucleus in some descending motor pathways therefore part of the movement pathway
35
Cerebral peduncle and red nucleus and substantia nigra named most anterior to most posterior
cerebral peduncle is most anterior then substantia nigra and then the red nucleus
36
Parts of the midbrain
```
• Cerebral peduncles
• Colliculi (superior colliculi and inferior colliculi)
• Substantia nigra
• Red nucleus
• Cranial nerves
- oculomotor (III) - trochlear (IV)
```
* Cerebral aqueduct
* Superior cerebellar peduncle • Mammillary bodies
37
Pons - cranial nerves associated
```
5-8
5 = trigeminal
6 = abducens
7= facial
8=vestibulocochlear
```
38
Other structures that the pons is associated with
4th ventricle and middle cerebellar peduncle
39
Mamillary body is associated with
the hippocampus
40
What are mammillary bodies in the brain?
The mammillary bodies are a pair of small round bodies, located on the undersurface of the brain that, as part of the diencephalon, form part of the limbic system. They are located at the ends of the anterior arches of the fornix.
41
Pons composed of
Composed of conduction tracts - both ascending sensory & descending motor tracts
Composed of pontine nuclei e.g. pneumotaxic centre - not only composed of tracts also have specific clusters of neuronal cell bodies called nuclei (pontine nuclei)
42
Pons (bridge)
fibres forming a bridge from the pons into the cerebellum but also it is a bridge between the cerebrum and going down to the medulla and spinal cord
43
Pneumotaxic centre (respiratory centre)
Part of the pons, example of pontine nuclei
helps to maintain normal rhythm of breathing
(together with medullary centre ) - groups of neurons controlling breathing in the pons AND the medulla
44
4th ventricle and pons relationship
4th ventricle is posterior to the pons, 4th ventricle is associated with the pons
45
Components of the medulla
• Pyramids
• Olives
(these two sit in the medulla)
• Cranial nerves
- glossopharyngeal (IX)
- vagus (X)
- accessory (XI)
- hypoglossal (XII)
• 4th ventricle
• Inferior cerebellar peduncle
(these two are associated with the medulla)
46
Cranial nerves associated with the medulla
```
9-12
9= glossopharyngeal
10 = vagus
11 = accessory
12 = hypoglossal
```
47
Pyramid location and origin
Located in the midline of the medulla, one on each side and inferior to each pyramid is the pyramidal decussation
neurons of origin of these axons are the pyramidal neurons in the cerebral cortex (which look like pyramids)
48
Pyramid decussation
axons of pyramidal tracts cross over to the opposite side at the level just above the medulla- spinal junction (at the level of the foramen magnum) - cross over happens at the level of the first spinal nerve therefore at the junction of the medulla and the spinal cord
cross over of axons in the pyramid in the medulla
49
Pyramid and olive location relative to each other
pyramid more at midline, olive protrudes out and is more lateral to the pyramid
50
pyramids formed by
formed by the large
| pyramidal (corticospinal) tracts descending from the (primary) motor cortex
51
Olives
containing inferior olivary nuclei, which relay sensory information to the cerebellum
52
medulla and 4th ventricle
4th ventricle is associated with the medulla (floor)
53
Dorsal column composure
two tracts actually form large part of spinal cord called the dorsal column. This is fasiculus cunneatus and fasiculus gracilis
54
Fasciculus gracilis
medial, part of dorsal column
Sensory information from the LOWER limb
55
Fasiculus cunneatus
lateral, part of dorsal column
sensory information from the upper limb
56
Medulla plays a role in
maintaining body homeostasis
| cardiovascular centre, respiratory centres, other reflex centres
57
Medulla - Cardiovascular centre
Cardiac centre adjusts rate and force of heart beat to meet the body’s needs
Vasomotor centre adjusts blood vessel diameter to regulate blood pressure
Cluster of neurons specifically associated with cardiovascular function
58
Medulla - respiratory centres
control rate and depth of breathing (together with centre in pons)
along with pontine centre for respiration
controls lungs etc
59
Medulla - other reflex centres
controls activities such as coughing, sneezing, gagging, swallowing, vomiting, sweating
60
Pons AND medulla stroke
death due to inability to control breathing
61
Medulla has a functional association with the
hypothalamus - the medulla does not work by itself
62
Medulla and hypothalamus
The hypothalamus is an important autonomic (rather than conscious, parasympathetic and sympathetic) control centre. It sends its instructions to the medullary reticular centres (network of neurons), which carry them out by synapsing with the target structure(s) - to carry out the effect such as fibres to the heart, GI tract etc
63
Cross sectional anatomy of medulla
structure internally is different to the spinal cord
* Segmental arrangement of spinal cord ceases - each level of the spinal cord has a spinal nerve associated with it which is called a segmental arrangement, this is present in the spinal cord but ceases at the medulla
* Reorganisation of white and grey matter - medulla has little clusters of grey matter and white matter everywhere else
* Columns of white matter become distinct tracts- spinal cord has anterior columns which consist of a number of tracts, for medulla there is one major tract which is the corticospinal/pyramidal tract
* Grey matter arranged into distinct nuclei
64
How many pair of cranial nerves are there?
12 pairs
65
How many cranial nerve pairs are associated with brainstem?
10 pairs
66
How many cranial nerve pairs are attached to the forebrain?
2 pairs
67
Cranial nerves - function
sensory and/or motor nerves - some are mixed and some are pure
68
Sensory functions of cranial nerves
- touch, pain for face e.g. pain in teeth
- hearing, vision, smell (special senses)
- visceral organs e.g. GI tract
69
Motor functions of cranial nerves
- eye movement
- jaw & tongue muscles, facial expression
- visceral organ activity
70
Cranial nerve I
Olfactory
71
Cranial nerve II
Optic
72
Cranial nerve III
Oculomotor
73
Cranial nerve IV
Trochlear
74
Cranial nerve V
Trigeminal
75
Cranial nerve VI
Abducens
76
Cranial nerve VII
Facial
77
Cranial nerve VIII
Vestibulocochlear
78
Cranial nerve IX
glossopharyngeal
79
Cranial nerve X
Vagus
80
Cranial nerve XI
Accessory
81
Cranial nerve XII
Hypoglossal
82
Most anterior cranial nerve
Number 1 - olfactory nerve
83
Most posterior cranial nerve
Number 12 - hypoglossal nerve
84
Caudal
posterior
85
rostral
anterior
86
Sensory and/or Motor? - Olfactory nerve
Sensory
87
Sensory and/or Motor? - optic nerve
Sensory
88
Sensory and/or Motor? - oculomotor nerve
Motor
89
Sensory and/or Motor? - trochlear nerve
Motor
90
Sensory and/or Motor? - trigeminal nerve
Both
91
Sensory and/or Motor? - abducens nerve
Motor
92
Sensory and/or Motor? - facial nerve
both
93
Sensory and/or Motor? - vestibulocochlear nerve
sensory
94
Sensory and/or Motor? - glossopharyngeal nerve
both
95
Sensory and/or Motor? - vagus nerve
both
96
Sensory and/or Motor? - accessory nerve
motor
97
Sensory and/or Motor? - hypoglossal nerve
motor
98
Cranial nerves associated with forebrain
```
olfactory nerve (I)
optic nerve (II)
```
2 in total associated
99
Cranial nerves associated with midbrain
```
oculomotor nerve (III)
Trochlear nerve (IV)
```
2 in total associated
100
Cranial nerves associated with pons
```
trigeminal nerve (V)
abducens nerve (VI)
Facial nerve (VII)
Vestibulocochlear nerve (VIII)
```
4 in total associated
101
Cranial nerves associated with medulla
```
Glossopharyngeal (IX)
Vagus nerve (X)
Accessory nerve (XII)
Hypoglossal nerve (XII)
```
4 in total associated
102
Olfactory nerves
cranial nerve I
tiny sensory nerves (filaments or fascicles )
run from the nasal mucosa, pass through cribriform plate
of ethmoid bone to synapse with the olfactory bulb
the olfactory receptor cells sit in the nasal mucosa, they are the olfactory nerves
Provide sense of smell (therefore sensory) - have these fine filaments of nerves sitting and detecting smell whilst they are sitting in your nasal mucosa and then sending the information up to the olfactory bulb which then sends its axons back as the olfactory tract
103
Conduction pathway of smell with olfactory nerves
Olfactory receptor cells first which go up to the olfactory bulb with their filaments through the holes, then have the olfactory tract where the information is passed posteriorly and goes to various parts of the cerebrum so firstly it goes to the olfactory cortex in the temporal lobe which is where we become consciously aware of what we are smelling (is it burning, is it nice), then also have a pathway to the hippocampus where we have a memory of smells, also to the amygdala where we can have emotional responses to smells and lastly there is a pathway to the hypothalamus which is going from the hypothalamus back to the medulla particularly to the reticular formation/network which goes on to innervate the gastrointestinal tract where you can have responses by the viscera to the smell such as making enzymes in the digestive tract etc
104
Damage to olfactory nerves
damage causes impaired sense of smell known as anosmia
This can happen when you fracture the ethmoid bone through a fracture of the skull as it can damage the fine filaments of the olfactory nerves
105
Cribriform plate
holes in the ethmoid bone which fascicles/filaments go up through
106
Optic nerves
Cranial nerve II
Axons arising from the retina of the eye to form optic nerve
Each optic nerve passes through its optic foramen of the orbit. Nerves converge to form optic chiasm (axons partially cross over) & continue on as optic tracts
Enables vision (aim of the optic system)
107
Retina processing
Local currents are produced in response to light
rods and cones first (most posterior and closest to pigmented layer) then information transferred to bipolar neurons and then the information is passed on to retinal ganglion cells and it is the axons of these cells that form the optic nerve which project to subcortical and cortical visual areas
108
Visual projection pathway
retina - optic nerve - optic chiasm - optic tract - superior colliculus and lateral geniculate nucleus - optic radiation - occipital lobe (visual cortex)
Superior colliculus - send information back to visual cortex through optic radiation back to the visual cortex
lateral geniculate nucleus of the thalamus is a thalamic nuclei
109
Nasal retina sees
a temporal visual field
110
Temporal retina sees
nasal visual field
111
left side of each retina sees
the right visual field
112
right side of each retina sees
the left visual field
113
which retinas cross
nasal retinas
