brainstem and cranial nerves Flashcards
1
Q
what does the brainstem connect
A
The brainstem connects the spinal cord to the forebrain
2
Q
what are the three functions of the brainstem
A
- cranial nerve functions
- conduit function
- integrative functions
3
Q
describe the three functions of the brainstem
A
- Cranial nerve functions
- The brainstem contains functional centers associated with 11 of the 12 pairs of cranial nerves - Conduit function
- it contains ascending and descending pathways that transmit sensorimotor information to and from the cortex. - Integrative functions
- e.g. respiratory and cardiovascular activities, consciousness, sleep, and wakefulness that occur via the reticular formation that runs throughout length of brainstem.
4
Q
what does damage to the brainstem result in
A
- results in sensorimotor dysfunction accompanied by abnormalities in cranial nerve function
5
Q
what are the main parts of the brainstem
A
- midbrain
- pons
- medulla
6
Q
what is the most rostral part of the brainstem
A
- midbrain
7
Q
what is the most caudal part of the brainstem
A
- medulla
8
Q
then does the brainstem become the foramen magnum
A
beyond the foramen magnum
9
Q
what is the midbrain associated with
A
- auditory
- visual
- pupillary reflexes
- eye movements
- Crainal nerves II to IV
10
Q
what is the pons associated with
A
- cranial nerve V-VII.
- mastication (V)
- eye movement (VI)
- facial expression, blinking and salivation (VII)
- equilibrium and audition (VIII).
11
Q
what is the medulla associated with
A
- cranial nerves VIII-XII
- equilibrium
- audition
- deglutition
- coughing
- vomiting
- salivation,
- tongue movement
- respiration & circulation.
12
Q
how is the brainstem organised
A
- into 3 sections in the dorsal ventral axis
- they receive input from all the parts of the nervous system and exert widespread influences on CNS functions
13
Q
describe what is in the dorsal part
A
in the dorsal part are located the cranial nerve nuclei;
14
Q
describe what is in the ventral part
A
in the ventral part are located fibres of descending pathways
15
Q
describe what is the middle part
A
in the middle part (which is often called the tegmentum) are located the ascending pathways and various nuclei associated with the reticular formation
- it runs the length of the brainstem and receives input from all parts of the nervous system
16
Q
name the divisions of the 12 cranial nerves
A
- purely sensory (I, II VIII)
- purely motor,(III,IV, VI, XI XII)
- mixed (V,VII, IX, X) nerves
17
Q
where do sensory nerve nuclei tend to be located compared to motor nuclei
A
sensory nerve nuclei tend to be located in the lateral brainstem, while motor nuclei tend to be located medially.
18
Q
describe the origins of mixed nerves from the brainstem
A
= nerves that have both sensory and motor fibres have more than one nucleus of origin - they have ne sensory and one motor therefore they tend of be located in between
19
Q
more than one nerve will…
A
will originate from a single nucleus
- for example, the sense of taste is spread across at least two nerves but merges into a single nucleus
20
Q
where are the sensory receptor bodies
A
- located just outside the CNS in an ganglion
21
Q
what is the brainstem organised
A
- Neurons with similar functions are brought into close proximity to reduce the amount of neural wiring needed.
- Different functions are affected by local damage depending on whether the lesion is lateral or near the mid-line.
22
Q
what can brainstem disorders by analysed by
A
- Is it LATERAL or MEDIAL
2. What is the LEVEL of the LESION - specific cranial nerves delineate the actual level
23
Q
what is cranial nerve I
A
olfactory nerve
24
Q
why is the olfactory nerve unique
A
- it is the only sensations that projects directly into the cortex
- does not go through the brainstem or thalamus
25
describe the structure of the olfactory nerve
- The olfactory receptors are located within the upper nasal mucosa and detect chemical stimuli.
- very short
- central axons pasS through the cribiform plate to connect with mitral cells in the olfactory bulb
- The axons of the mitral cells form the olfactory tract and connect either with cells of the anterior olfactory nucleus or pass directly to the ipsilateral primary olfactory cortex (piriform cortex), which includes the amygdala and uncus regions of the temporal lobe
26
how is smell and taste linked
connections are made with the olfactory nerve and with the reticular formation nuclei that influence visceral functions such as salivation, gastric secretion and peristalsis. = In this way smell and taste are linked.
27
what does the anterior olfactory nucleus do
they transmit the smell to the contralateral cortex
28
what does damage to the olfactory nerve cause
anosmia - loss of smell
29
how do you test the olfactory nerve
Ask the patient to close both eyes and 1 nostril and identify different smells such as coffee, soap, herbal aromas presented to the open nostril.
- Do not use volatile substances such as alcohol or ammonia as these stimulate the chemical receptors of the trigeminal nerve that innervate the nasal mucosa.
30
what nerve is CNII
optic nerve
31
where does optic nerve originate from
The optic nerve is in fact a CNS tract originating in the diencephalon
32
what happens if the optic nerve is damaged
it does not regerneate
33
describe the structure of the optic nerve
- The rods and cones are the receptors for vision while retinal ganglion cell axons (RGC) make up the optic nerve.
- RGCs from the nasal side of each eye cross each other at the optic chiasm to run in the contralateral optic tract whereas those from the temporal retina do not.
34
where does the optic nerve terminate
- A small proportion of fibres leave the tract to terminate in midbrain nuclei to participate in visual reflexes.
- The majority of optic tract axons terminate in the lateral geniculate nucleus of the thalamus in an orderly manner termed retinotopy.
35
what does lesions of the visual pathway cause
lesions of the visual pathway cause predfictable deficits in the visual field and the nature of the deficit identifies the site of lesion in the pathway.
36
how do you do an examination of the optic nerve
1. Pupillary reflexes- checks pupil reactions
2. Visual acuity – test ability to distinguish objects, usually letters.
3. Visual fields – assesses peripheral and central retina, and the visual pathway.
4. Colour vision – assess function of retinal cones and optic nerve.
5. Fundoscopy – checks retinal vessels.
37
what do cranial nerves II, IV AND VI do
- they innervate the muscles that control voluntary eye movements and pupillary size
38
what are the two types of voluntary eye movements
- conjugate
| - vergence
39
What is conjugate eye movements
when the eyes move in the same direction together e.g. up, down, left or right
40
what is vergence eye movements
when eye focus shifts between near and far objects
41
what do specialised gaze centres do
- specialised gaze centres in the rainstem and cortex help control eye muscle movements keeping them focussed on an object.
42
what are the specialised gaze centres
the horizontal gaze centre
the vertical gaze centre
the mergence centre
43
where are the specialised gaze centres located
- Horizontal gaze center (called the paramedian pontine reticular formation) is located in the pons,
- the vertical gaze center - in the periaqueductal gray matter (PAG) of the midbrain
- vergence center - the rostral midbrain
44
what are the 2 most well non cortical gaze centres
- frontal eye fields
| - occipital eye field
45
what does the frontal eye field do
that initiate voluntary eye movement e.g. look left
46
what does the occipital eye field do
that initiate pursuit movement e.g. follow that object
47
how are the CNIII, CNIV AND VI interconnected
- actions are all integrated within the brainstem and the nucleic are connected by the medial longitudinal fascicles (MLF) that is linked to the vestibular nerve
48
what is CNIII
oculomotor nerve
49
How many eye muscles does the oculomotor nerve innervate
- innervates 5 eye muscles
50
what does the oculomotor nerve do
- constricts the pupil, and is involved in the processes of lens accommodation and convergence
51
where is the oculomotor nuclei located
- The oculomotor nucleus is located in the rostral midbrain and
52
what are the two parts of the oculomotor nerve
- consists of 2 parts
| - a motor nucleus supplying the muscles and a parasympathetic nucleus (Edinger-Westphal nucleus)
53
what do the two parts of the oculomotor nerve do
- innervates the ciliary muscle, which is responsible for focussing the lens
- It provides the efferent arc for the pupillary and consensual light reflexes.
54
what is cranial nerve CN IV
the trochlear nerve
55
where does the trochlear nerve innervate
The trochlear nerve is the only cranial nerve to exit from the dorsal surface of the brainstem
56
what does the trochlear nerve innervate
it crosses and innervates the contralateral superior oblique muscle
57
what does the contralateral superior oblique muscle does
- contractions of this muscle causes inward rotation, downward and lateral movement of the eye
58
what is CN VI
Abducent nerve
59
describe the root of the abduncent nerve CN VI and what is it susceptible to
- CN VI has the longest intracranial course of all the cranial nerves, travelling along the base of the brainstem in the cavernous sinus to enter the orbit. Thus, it is particularly susceptible to lesions associated with raised intracranial pressure.
60
what does the abducent nerve innervate
- This nerve innervates the lateral rectus muscle that abducts the eye.
61
describe the clinical test for examination of eye movements
What is the position of the eyes in primary gaze (looking straight ahead)?
Check gaze in the six cardinal directions using a cross or "H" pattern.
Is there double vision in any direction of gaze?
Is there conjugate eye movement in each direction of gaze
Can the eyes converge to a near object?
Examine pupil size – are they equal and reactive to light?
62
what does damage to CN III, CN IV and CN VI result in
- results in paralysis of those affected muscles and often results in double vision in the direction of the movement of the affected muscle, with the image that is further out arising from the affected eye.
63
what is most commonly damaged out of CN III, CN IV and CN VI
Isolated lesions of CN IV are rare whereas isolated lesions of III and VI are more common.
64
what does damage alone to CN III cause
- ptosis
- strabismus
- diplopia,
- the eye deviates down and out
- mydriasis
- loss of the pupillary
- accommodation (cycloplegia) reflexes.
65
what does damage along to CNIV cause
It causes outward rotation (extortion) of the eye
| - weakness of downward gaze leading to vertical diplopia that is worse when looking down.
66
what does damage alone to CN VI cause
- strabismus
- horizontal diplopia,
- the eye deviates medially.
67
what is pupil size controlled by
the autonomic nervous system
68
what causes dilation and relaxation of the pupil
he parasympathetic nerve fibres mediate constriction and dilation is caused by sympathetic fibres.
69
what does damage to the sympathetic system result in
horners syndrome
- this is characterised by pupil constriction (miosis)
- decreased facial sweating
- slight ptosis
70
what is cranial nerve CN V
trigeminal nerve
71
what does the trigeminal nerve do
- provides sensory innervation to the face and motor innervation to the muscles of mastication
72
what are the 3 branches of the trigeminal nerve
1) Ophthalmic (CN V1) – purely sensory
2) Maxillary (CN V2) – purely sensory
3) Mandibular (CN V3) – mixed (sensory & motor)
73
what does the ophthalmic nerve division innervate
- innervates parts of the eyeball, lacrimal apparatus and nose.
- Its cutaneous terminal branches exit through the supraorbital foramen to supply the skin of the scalp, forehead and upper eyelid
74
what does the maxillary nerve division innervate
- sensory innervation to the upper jaw teeth, palate, nasal mucosa and maxillary air sinuses.
- Its cutaneous terminal branches exit through the infraorbital foramen to supply the skin of the maxilla and upper lip.
75
what does the mandibular nerve division innervate
- sensory innervation to the lower jaw teeth, temporomandibular joint, mouth mucosa and anterior two-thirds of the tongue.
- Its cutaneous terminal branches exit through the mental foramen to supply the skin of the lower jaw and lower lip.
- The mandibular nerve also innervates skin on the side of the head.
76
what are the muscles of mastication supplied by
The mandibular division of the trigeminal nerve supplies all the muscles of mastication (involved in chewing) and some involved in swallowing and hearing (tympanic membrane innervation
77
what are specific sensations transmitted to (trigeminal nerve)
- they are transmitted to the main, spinal and mesencephalic sensory nuclei - of the trigeminal nuclear complex
78
where does the spinal trigeminla nucleus extend from and do
- The spinal trigeminal nucleus (SpVc) extends from the medulla to pons
- is the principal nucleus for nociceptive processing.
79
where is the main sensory principal nucleus located (trigmeinal nerve) and what does it do
- The main sensory (principal) nucleus, PrV, is located in the pons
- is concerned with discriminative tactile information processing from the face/head
- It is the cranial equivalent of the gracile nucleus.
80
where does the mesencephalic nucleus extend from and what does it do
- The mesencephalic nucleus extends from the rostral pons into the midbrain and contains the cell bodies of the trigeminal muscle & periodontal (proprioceptive) afferents.
- Their central branches terminate within trigeminal motor nucleus & supratrigeminal nucleus (part of V motor nucleus that is the pattern generator involved in the control of mastication). These are located in the pon
81
how do you test sensory innervation of the trigeminal nerve
1. Test the forehead, cheeks, and jaw (3 divisions) for pain and light touch sensations using pinprick and cotton wool respectively. Two-point discrimination can be tested on the lips. Test each division separately and compare the 2 sides of the face.
2. Corneal reflex (CN V and VII). Assesses the afferent (CN V) and efferent (CN VII) pathways. Gently touching the cornea with a wisp of cotton (the sclera is not sensitive) normally induces the patient to blink both eyes (direct and consensual response). Test each eye. A diminished or absent corneal reflex is usually thought to represent a lesion in the reflex arc. Decreased blink on one side regardless of the side of stimulation indicates a seventh nerve lesion. Note that the use of contact lens may decrease this response.
82
how do you test motor innervation of the tirgminal nerve
1. Check muscles for wasting (most easily seen in temporalis muscle above the zygomatic arch).
2. Ask patient to clench their teeth. (checks masseter muscle)
3. Ask the patient to open the mouth against resistance.
4. Observe that the mandible travels vertically (normal) rather than deviating to one side (indicating pterygoid weakness on the side to which the jaw deviates).
5. Jaw Jerk. Tests stretch reflex of the jaw-closing muscles (masseter and temporalis muscles). Normal subjects have either no jaw jerk or a very slight jaw jerk. Brisk jaw jerks can be normal, but often indicate bilateral lesions of upper motoneuron (corticobulbar) pathways.
83
what is cranial nerve CN VII
facial nevre
84
describe the motor and sensory root of the facial nerve
- it has a larger motor root and a smaller sensory root
85
what does the facial nerve CN VII do
- controls the muscles of facial expression, lacrimation and taste sensations
86
what is the sensory root of the facial nerve
The nervus intermedius (NI) is the sensory root
87
what does the sensory root of the facial nerve do
carries taste fibres from the anterior two thirds of the tongue to the gustatory center in the solitary nucleus (NTS) in the medulla.
88
what do other fibres of the facial nerve do
- innervate the posterior skin of the external ear and terminate in the spinal trigeminal nucleus.
89
what dot he parasympathetic secretomotor neurones originate
Parasympathetic secretomotor neurones originate in the superior salivatory and lacrimal nuclei (pons) and pass through the NI to innervate the salivary, lacrimal and nasal cavity glands.
90
where does the facial nerve arise from and go
The Facial nerve arises from the facial motor nucleus (pons) and winds around the abducens nucleus to form the facial colliculus that innervates the muscles of facial expression.
91
what does the facial colliculus do
innervates the muscles of facial expression
92
what do the motor fibres of the facial nerve do
- innervates the muscles of facial expression.
| - innervate the stapedius muscle of middle ear.
93
what does the facial motor nucleus receive
- The facial motor nucleus receives descending corticobulbar input from the contralateral motor cortex.
- However, there is a bilateral innervation to upper face muscles e.g. those involved in blinking, and forehead wrinkling.
94
what does the facial motor nucleus provide
- provides the efferent arch to several reflexes
| - most important is the corneal reflex - bilateral blink response to the unilateral touch of the cornea
95
what does damage to the efferent arch impair
Damage to the efferent arc impairs the ipsilateral reflex but not the contralateral response. It may also lead to corneal ulceration.
96
how do you test the facial nerve
Raise eyebrows – tests frontalis muscle
Close both eyes to resistance - tests orbicularis oculi muscle
Smile - tests buccinator muscle
Show teeth – tests zygomaticus major muscle
Puff out cheeks- test buccinator muscle
Protrude lips or whistle - tests orbicularis oris muscle
Test the Corneal Reflex
97
where is the facial nerve most damaged
- The facial nerve is most frequently damaged as it passes through the facial canal due to neuritis (viral inflammation)
- This can lead to Bells Palsy.
- Upper motoneuron lesion leads to facial weakness that is worse for the lower face muscles than the upper ones. Sensory functions are normal.
