SDL 4 - Brainstem, Cerebellum & Cranial Nerves Flashcards
What are the 5 major subdivisions of the brain?
Which of the 5 subdivisions make up the brainstem?
- Telencephalon
- Diencephalon
- Mesencephalon
- Metencephalon
- Myelencephalon
The brainstem is made up from the mesencephalon, metencephalon and myelencephalon
Label the cranial nerves
Which structures are labelled?
what are their functions?
Cerebral peduncle:
- contain the large ascending (sensory) and descending (motor) nerve tracts that run to and from the cerebrum from the pons
Interpeduncular fossa:
- separates the cerebral peduncles
Decussation of pyramids:
- motor fibres from the 2 pyramids cross over and pass down opposite sides of the spinal cord
Anterolateral sulcus:
- rootlets of hypoglossal nerve emerge here
What is the name of the ridge that is visible on either side of the ventral midline of the medulla?
What is its function?
The pyramids lie either side of the ventral midline
they are formed by an accumulation of descending nerve fibres carrying motor information
What happens to the fibres of the pyramidal tract at the caudal end of the medulla?
The descending fibres decussate (cross over) the midline of the CNS at the caudal end of the medulla
As they decussate, they partially obliterate the midline longitudinal fissure
Label the dorsal view of the brainstem
In which regions of the brainstem is the central canal expanded to form the fourth ventricle?
It is located dorsal to the pons and upper medulla oblongata
What are the distinguishing features of the ventral surface of the medulla oblongata?
- 2 pyramids separated by the anterior median fissure
- Anterolateral sulcus that separates the pyramids from the olive
- Posterolateral sulcus that emerges dorsal to the olives
What are the distinguishing features of the ventral surface of the pons?
- Cerebellopontine angle - where the medulla and pons join the cerebellum laterally
- Basilar groove for basilar artery
What are the distinguishing features of the ventral surface of the midbrain?
- Cerebral peduncles
- separated by the interpeduncular fossa
What are the outlines of the transverse sections through different brainstem levels
What are the main functions of the cerebellum?
Coordination of movement
maintenance of balance and posture
Where is the cerebellum located?
It is below the occipital lobes of the telencephalon
(separated from it by the tentorium cerebelli)
It is located posterior to the brainstem and to it via three paired cerebellar peduncles
Label the cerebellum from above
Label the cerebellum viewed from the position of the pons
Are peduncles white or grey matter structures?
White matter
They contain a nerve tract that permits communication between the cerebellum and the other parts of the central nervous system
To which region of the brainstem does each cerebellar peduncle connect?
Superior:
- connects midbrain to cerebellum
Middle:
- connects pons to cerebellum
Inferior:
- connects medulla to cerebellum
Which vessels provide the arterial supply to the cerebellum?
From ventricular arteries:
- posterior inferior cerebellar artery (PICA)
From basilar artery:
- anterior inferior cerebellar artery (AICA)
- superior cerebellar artery (SCA)
What are the major functions of the cerebellum?
coordinates voluntary movements such as posture, balance, coordination, and speech, resulting in smooth and balanced muscular activity
What 3 abnormal signs are associated with cerebellar damage?
Past-pointing:
- if the eyes are closed, a pointing finger overshoots its intended mark towards the side of the cerebellar damage
Intention tremor:
- Broad, low frequency tremor
- The amplitude of an intention tremor increases as an extremity approaches the endpoint of deliberate and visually guided movement
Dysdiadochokinesis:
- impaired ability to perform rapid alternating movements
How is dysdiadochokinesis tested for?
Ask the patient to tap the palm of one hand with the fingers of the other
then rapidly turn over the fingers and tap the palm with the back of them, repeatedly
How is intention tremor tested for?
Finger-to-nose test
the physician has the individual touch their nose with their finger while monitoring for irregularity in timing and control of the movement
if someone has intention tremor, they will have coarse side-to-side movements that increase in severity as the finger approaches the nose
Which cranial nerves attach to the midbrain?
- Oculomotor nerve (III)
- Trochlear nerve (IV)
Which cranial nerves attach to the pons?
- Trigeminal nerve (V)
Pontomedullary junction:
- abducens nerve (VI)
- facial nerve (VII)
- Vestibulocochlear nerve (VIII)
Which cranial nerves attach to the medulla oblongata?
- Glossopharyngeal nerve (IX)
- vagus nerve (X)
- Accessory nerve (XI)
- hypoglossal nerve (XII)
Which cranial nerves emerge from the cerebellopontine angle?
- Vestibulocochlear nerve (VI)
- facial nerve (VII)
Which cranial nerve emerges from the interpeduncular fossa?
- Oculomotor nerve (II)
Which cranial nerve emerges immediately lateral to the medullary pyramid?
- Hypoglossal nerve (XII)
- this emerges in the anterolateral sulcus
Which cranial nerves emerge lateral to the olive?
- Vagus nerve (X)
- Glossopharyngeal nerve (IX)
- Accessory nerve (XI)
These emerge in the posterolateral sulcus
Which cranial nerves emerge from the dorsal surface of the brainstem?
- Trochlear nerve (IV)
Where are the true peripheral olfactory nerves?
The paired structures on the inferior surface of the brain (olfactory bulbs and tracts) are CNS structures
they receive information from the true peripheral olfactory nerves
the olfactory nerve comes from the nasal epithelium
It enters the cranial cavity via the cribiform plate of the ethmoid bone
What does damage to the olfactory nerve usually cause?
Anosmia:
- the inability to smell anything at all
Hyposmia:
- reduced ability to smell
Dysosmia:
- smells are mixed up
- e.g. The pleasant smell of a rose might smell like garbage
What aspects of vision are subserved by the optic nerve?
The optic nerve transmits visual information from the retina to the brain
it is involved with the light reflex and the accommodation reflex
How is the light reflex tested in clinic?
Light shone in one eye should cause both pupils to constrict (miosis)
a lower intensity of light should cause the pupils to dilate
How is the accommodation reflex tested in clinic?
Accommodation means change in the lens shape when looking at a distant object and a close object
this is tested by asking the patient to focus on an object as it is moved further away, closer and side to side
What is supplied by the oculomotor (III), trochlear (IV) and abducens (V) nerves?
They supply the muscles that move the eye
Where do cranial nerves III, IV and VI attach to the brainstem?
Where to they pass out of the skull?
What are the 3 divisions of the trigeminal nerve?
What type of nerve is it?
V1 - opthalmic
V2 - maxillary
V3 - mandibular
the trigeminal nerve is a mixed nerve as it contains motor and sensory fibres
What is supplied by the motor and sensory branches of the trigeminal nerve?
Sensory:
- skin, teeth and mucous membranes of the face
- anterior scalp
- dura
Motor:
- four main muscles of mastication
- tensor tympani muscle
Where are the cell bodies of (most of) the trigeminal sensory fibres located?
There are 3 sensory nuclei - mesencephalic, principal sensory and spinal nuclei
they extend from the midbrain to the medulla
Through which foramina do the three divisions of the trigeminal nerve exit the cranial cavity?
How do the divisions of the trigeminal nerve form?
Each division has several branches that carry either sensory, motor or autonomic fibres
What nerves hang from the pterygopalatine ganglion?
what do they supply?
Greater and lesser palatine nerves
They supply the roof of the mouth, soft palate, tonsil, and lining membrane of the nasal cavity
How do you test the functioning of the sensory component of the trigeminal nerve?
Pin or cotton swab test
One or both sides of the face are touched with a pin or cotton swab
the patient is asked whether they felt anything and where they felt it
What are the 2 reflexes associated with the trigeminal nerve?
Jaw jerk reflex:
- in someone with an upper motor neurone lesion, the jaw jerk reflex can become quite pronounced
Blink reflex:
- stimulated by touching of the cornea by a foreign object
- Also involves the facial nerve
What is trigeminal neuralgia?
A chronic pain condition affecting the trigeminal nerve
mild stimulation of the face may trigger a jolt of excruciating pain
what do the motor fibres in the trigeminal nerve innervate?
Muscles of mastication
they are innervated by the mandibular branch (V3)
masseter, temporal and medial and lateral pterygoids
In a trigeminal nerve injury, which side will the jaw deviate to when opened against resistance?
The jaw deviates towards the lesion
This is due to weakness of the lateral pterygoid on the affected side
What type of nerve is the facial nerve?
How do the fibres leave the brainstem?
It is a mixed nerve
The motor fibres to the muscles of facial expression and to the stapedius muscle leave the brainstem in a large motor root of the facial nerve
All other fibres leave the brainstem in a much smaller bundle - the nervus intermedius
What are the sensory functions of the facial nerve?
- Supplies a small area around the concha of the auricle
- provides special taste sensation to the anterior 2/3 of the tongue
Where are the parasympathetic functions of the facial nerve?
Supplies many of the glands in the head and neck including:
- Submandibular and sublingual salivary glands
- Nasal, palatine and pharyngeal mucosal glands
- Lacrimal glands
What is the pathway of the facial nerve through the skull like?
It follows a complex course through the skull, from the internal acoustic meatus to the stylomastoid foramen
It give various branches as it does so
Label the branches of the facial nerve?
Where does this branching occur and what do these branches supply?
The facial nerve branches within the substance of the parotid gland
Temporal branches:
- innervate frontalis, orbicularis oculi and corrugator supercilli
Zygomatic branches:
- innervates orbicularis oculi
Buccal branches:
- innervate orbicularis oris, buccinator and zygomaticus
Mandibular branches:
- innervates the mentalis
Cervical branch:
- innervates the platysma
Label the following diagram
What is the function of the nerve fibres making up the chorda tympani?
It originates from the taste buds, runs through the middle ear and carries taste messages to the brain
it joins the lingual nerve (branch of mandibular nerve), which supplies special taste sensation to the anterior 2/3 of the tongue
What is the function of the greater petrosal nerve?
It innervates the lacrimal gland
How are the motor functions of the facial nerve tested?
Which muscles are tested in each case?
Ask the patient to raise their eyebrows, screw up their eyes, purse their lips and show their teeth
- frontalis raises the eyebrows
- Orbicularis oculi screws up the eyes
- Orbicularis oris purses the lips
- zygomaticus allows for showing the teeth (smiling)
What is Bell’s palsy?
It is caused by damage to the facial nerve
it results in facial paralysis and an inability to control the facial muscles on the affected side
symptoms include muscle twitching, weakness or total loss of the ability to move one (or both) sides of the face
What other common condition can cause facial weakness?
Stroke
How can you tell the difference between ipsilateral facial weakness due to Bell’s palsy and a stroke?
- A stroke damages the motor cortex, leading to contralateral facial weakness of the lower face only
- there is preservation of the muscles of the upper face on both sides, due to the dual innervation of the upper face
- lesions that damage the facial nerve result in ipsilateral facial weakness involving both the upper and lower face
Damage to the facial nerve may result in hyperacusis?
What is this and why does it occur?
A hearing disorder characterized by an increased sensitivity to certain frequencies and volume ranges of sound
(sounds sound much louder than they should)
Damage to the facial nerve affects the stapedial reflex, which dampens down the intensity of sounds
What is the vestibulocochlear nerve (VIII)?
How is it tested?
The sensory nerve from the inner ear
It is tested through the Rinne’s and Weber’s tests
What type of tumour may develop on the vestibulocochlear nerve adjacent to its attachment to the brainstem?
What is the consequence of this?
Acoustic neuroma
as the tumour enlarges, other cranial nerves may show signs of damage as they become compressed
If it compresses the trigeminal nerve, it causes constant or intermittent facial numbness and tingling
The facial nerve can rarely be affected in the same way
