Brain stem overview and cranial nerve nuclei Flashcards
What is the brainstem?
Central portion of the brain orientated rostro-caudally linking rostrally, the diencephalon and so the cerebra, to the cerebellum dorsally and the spinal cord caudally.
It has 3 types of functions;
1). A conduit - longitudinal tracts to and from the brain and cerebellum and spinal cord
2). Cranial nerve functions via brainstem nuclei
3). And integrative & modulatory functions through the reticulum
Exerts neuronal influence over a wide array of vital and non-vital processes
What does the brainstem do ?
Exerts neuronal influence over;
- heart rate
- respiration (Pre-Bötzinger complex)
- Antigravity and postural muscles
- Eye movement
- Head tracking
- Lower motor neuron excitation
- Autonomic activation
- Pain perception modulation
- Arousal
- Sleep
- Vomiting
Where is the brain stem located?
Posterior cranial fossa
Anterior:
- Clivus
- Nerves & vessels
Posterior;
- Cerebellum & attachments
Inferiorly;
- Foramen magnum & spinal cord
Superiorly;
- Tentorium cerebelli & diencephalon `
Where might tumours in the brainstem manifest
Tumors, such as chordomas and chondrosarcomas, may form on the clivus.
What are some of the external features of the brainstem ?
External features of the brainstem;
- Midbrain
- Pons
- Medulla
- Superior colliculus
- Inferior colliculus
- Cerebella peduncles
- Cuneate tubercle
- Gracile tubercle
- Pineal body
- Mamillary bodies
- Cerebral peduncle
- Inferior Olive
- Pyramids
What are some of the internal features of the brainstem ?
Internal features of the brainstem;
- Tegmentum
- Aqueduct
- Superior colliculus
- Tectum
- Periaqueductal gray matter
- Cerebral peduncle
- Substantia nigra
- Crus cerebri
- Tectum; superior colliculus + inferior colliculus
- Crus cerebri (basis pedunculi)
- Cerebral aqueduct
- Pyramid
- Superior medullary velum
- Fourth ventricle
- Inferior medullary velum
- Tegmentum
General areas shown here contain tracts, cranial nerve nuclei and the roots of cranial nerves
What are some internal features of the brainstem in respect to corticospinal descending tracts?
Corticospinal descending pathways carries motor information from the lower cortex to lower motor neurons in the spinal cord.
90% decussate in the medullary pyramids
10% remain ipsilateral until bilaterally innervating LMNs in the spinal cord.
A brainstem lesion of the lateral corticospinal tract will produce contralateral UMN signs
What are some internal features of the brainstem in respect to corticobulbar descending tracts?
Corticobulbar descending pathways.
Carry motor information from the
motor cortex to motor nuclei of the
brainstem.
Innervation from this pathway is
bilateral with the fibre decussation
occurring at the level of the nucleus
A brainstem lesion of these tracts will
produce effects dependant on where
the lesion is
What are the 4 descending tracts originating in the brainstem?
image ->
What are the features of the Medial lemniscal pathway?
Medical lemniscal pathway carries JPS and mechanical information (discriminating
touch vibration & pressure etc) from the dorsal columns
Pathway decussates after the
gracile/cuneate nuclei and ascends medially
to the thalamus
Pathway terminates in the sensory cortex
Brainstem lesion of this tract produces
contralateral loss of JPS and discriminating
touch
What are the features of the spinal lemniscal pathway?
Spinal lemniscal pathway is the extension of the spinothalamic tract through the brainstem, it carries pain and temperature sensation.
Pathway decussates quickly in spinal cord and ascends laterally to the thalamus
Pathway terminates in the sensory cortex
Brainstem lesion of this tract produces contralateral loss of pain and temperature sensation
What are the features of the spinocerebellar pathway?
Spinocerebellar tract, carries proprioceptive information. Tract ascends ipsilaterally in the lateral portion of the brainstem to the pons, where it enters the brainstem.
Brainstem lesion of this tract produces and ipsilateral defect
What is the generally summary of tracts, if they are medial or lateral of brainstem and their function?
S - go to side = lateral
M - go to medial
What is the reticulum ?
Reticulum
Found throughout the brainstem, located in central tegmentum
Diffuse network of neurons without detectable nuclei but which work predominantly in groups of neurotransmitter related networks
Responsible for wide variety of functions, e.g regulation of pain sensation, arousal of the cortex and modulation of descending motor output
What is the brainstem nuclei?
Brainstem nuclei
In the spinal cord the motor and sensory nuclei are arranged across the horns in a ventral-dorsal order
As medulla is ascended, the tectum increases, ‘pushing’ the nuclei into a more medial-lateral arrangement
Note that this rotation does not affect the positions of the general motor or sensory areas with respect to each other
Final generalist layout in the brainstem is seen in this image
How is the cranial nerve nuclei organised?
three lateral sensory columns of nuclei on each side and three medial motor columns of nuclei on each side
In reality there is som overlap between columns however in general this diagram is true
How many cranial nerves are there, where do they exit from and what is their function?
Cranial nerves follow the rule of 4
- 4 in or above midbrain
- 4 in Pons
- 4 in medulla
There are pure motor, pure sensory and mixed nerves
A single nerve can therefore map to more than one nucleus
Knowing which nerves map onto what nuclei, and where they are located in the brainstem is vital for brainstem diagnosis.
Once Open, Olives Tend To Attract French Vegan Gays, Virgins And Hoes
What nuclei control the somatic motor output to the eye and tongue?
Occularmotor nucleus (III) - control of extra ocular eye muscles except superior oblique and lateral rectus
Trochlear nucleus (IV) - control of superior oblique muscle of eye
Abducens nucleus (VI) - control of lateral rectus muscles of the eye
Hypoglossal nucleus (XII) - control of tongue muscles
What nuclei control the special visceral (pharyngeal derived) motor output?
Note - this more ‘lateral’ motor nuclei are ‘special’ so doesn’t follow the medial rule !
Trigeminal motor nucleus (V) - controls muscles of mastication
Facial nucleus (VII) - control of muscles of facial expression (NB ventral to the vestibulocochlear nucelus)
Nucleus ambiguus (IX + X) - motor to pharynx and larynx
Assessory nucleus (XI) - motor to sternocleidomastoid and trapezius muscles
Remember - controls;
Chewing (5)
Grimace (7)
Swallow (9-10)
Speak (9-10)
Shrug (11)
What nuclei have autonomic (general visceral / autonomic) control?
Edinger-Westphal nucleus (III) - control of pupillary constriction and lens accommodation
Superior Salivatory nucleus (VII) - control f lacrimal sublingual and submandibular glands, salivary glands (VII + IX)
Inferior Salivatory nucleus (IX) - control of parotid gland
Dorsal motor nucleus of Vagus (X) - secretomotor to lungs and gut; control of heart rate
What nuclei receive sensory information ?
Trigeminal mesencephalic (V) - somatic sensory - proprioception from the mouth
Trigeminal pontine (principal) (V) - somatic sensory nucleus - discriminating touch from face
Vestibulocochlear nucleus (VII) - special sensory - balance and hearing
Solitary nucleus (VII + IX + X) - Visceral sensory - carotid baroceptors (IX) and visceral afferent from pharynx, larynx, lungs, gut (X)
Trigeminal spinal nucleus (V) - somatic sensory - pain and temperature sensation from face, back of tongue, pharynx and ear
Give a summary of cranial nerve linkages to brainstem nuclei Dorsal view
Image
Give a summary of cranial nerve linkages to brainstem nuclei lateral view
Image
What are some non-cranial nerve nuclei of the brainstem
Image
What are some basically clinical clues to localising a brainstem lesion?
Mid brain - defect in eye movement
Pons - defect in mastication
Medulla - defect in swallowing
Side of lesion;
- A brainstem lesion will usually produce ipsilateral cranial nerve defects
How should we try and find a diagnosis when examining a patient?
Initial clue that it is brainstem lesion - signs on both sides of body (above and below neck) but asymmetrical distribution
You can localise the lesion by asking;
- Which cranial nuclei are involved ? this gives level in brainstem
- Which tracts are involved ? This indicates if lesion is medial, lateral or bilateral
Which side is affected
- Ipsilateral - sympathetic; LMN cranial nerve, limb ataxia
- Contralateral - limb/body UMN & loss of pain / temperature sensation and fine touch / proprioception
Recall summary table;
- 4 structures which to midline of brainstem begin with letter “M”
- 4 structures which to the side of brainstem begin with letter “S”
