Brainstem Flashcards
What is the brainstem?
That part of the CNS, exclusive of the cerebellum that lies between the cerebrum and the spinal cord
Midbrain, pons, medulla oblongata
Label a posterior view of the brainstem
The area with the four lumps at the top is the roof of the MIDBRAIN
The pons is the floor of the 4th ventricle
Nearly everything in the brainstem is bilateral but there are a couple of structures that are midline
PINEAL GLAND - midline - releases melatonin and is important in regulating the circadian rhythm
Instead we train it with vision
Colliculus = low lying hills
Superior Colliculus - important in the coordination of eye and head movements at the same time (think about watching tennis)
Inferior Colliculus - auditory reflexes - if there is a loud bang you tend to look in the direction of the bang immediately
There is only ONE cranial nerve that emerges from the BACK of the brainstem:
TROCHLEAR NERVE (CN IV)
This supplies one of the extrinsic muscles of the eye
The DORSAL COLUMNS defines the medulla in the dorsal aspect
Dorsal columns are involved in two main sensory pathways:
Touch
Proprioception
Label the anterior view of the midbrain
At the top you get the optic chiasm (one of the midline structures) where the optic nerves converge and 50% of the fibres cross to the contralateral side of the brain
Immediately behind the optic chiasm is the pituitary stalk (infundibulum)
Behind the infundibulum you can see the inferior part of the hypothalamus - mammillary bodies
The mammillary bodies are part of the limbic system
Emerging midline just above the transverse fibres of the pons is the oculomotor nerve (CN III)
Oculomotor nerve - main nerve involved in eye movements
The midbrain consists of the cerebral peduncle - the main motor fibres coming from the motor cortex down to the spinal cord
NOTE: peduncle - a fibre tract that has a structural AND functional role (it holds the cerebrum onto the brainstem)
Label the pons
There is only one cranial nerve that emerges from the lateral part of the pons - TRIGEMINAL (CN V)
Trigeminal Nerve - touch and sensation throughout the head and neck
There is a very small root next to the large one because the trigeminal also has motor function
All the muscles involved in mastication are innervated by the trigeminal
Tranverse fibres
Which nerves emerge at the ponto-medullary junction?
most medially is the abducens (CN VI) supplies the lateral rectus muscles and causes adbuction from the midline
moving laterally the facial nerve (CN VII)
moving laterally vestibulocochlear (CN VIII) involved in balance and hearing
Describe the structures of the medulla oblongata
THREE different cranial nerves emerge from the lateral medulla
Glossopharyngeal (CN IX) - sensory and motor innervation of the tongue and pharynx
Vagus (CN X) - main parasympathetic nerve that projects down into the viscera
Accessory (CN XI) - supplies the sternocleidomastoid (allows turning of the head) and the trapezius
The Hypoglossal Nerve (CN XII) emerges separately to the other three from the medulla
The hypoglossal nerve supplies the musculature of the tongue
There are pyramids on the anterior surface of the medulla
Fibres come down from the cortex through the peduncles and disappear from view behind the pons because of the transverse fibres
These fibres re-emerge below the pons as pyramids
NOTE: extra-pyramidal symptoms are motor symptoms that aren’t linked to this direct pathway
90-95% of fibres cross over at the base of the medulla at a point called the PYRAMIDAL DECUSSATION
What are the functional subtypes of the cranial nerves?
General somatic afferent - Sensation from skin and mucous membranes
General Visceral Afferent (GVA) - Sensation from GI tract, heart, vessels and lungs
General Somatic Efferent (GSE) - Muscles for eye and tongue movements
General Visceral Efferent (GVE)- Preganglionic parasympathetic
Functional Classification II
Special Somatic Afferent - Vision, hearing and equilibrium (only the cranial nerves)
Special Visceral Afferent - Smell (CN I) and Taste (comes from THREE cranial nerves that all go back to the nucleus solitarius)
Special Visceral Efferent - Muscles involved in chewing, facial expression, swallowing, vocal sounds and turning the head
How does the embryonic spinal cord differ from the mature one
Information goes into the spinal cord via the dorsal root and leaves the spinal cord via the ventral root
This is different to the embryonic brainstem
How does the development of the 4th ventricle effect the development of the nuclei?
In the brainstem the alar plate opens up and you have a ventricle here
Because of this separating of the alar plate, the afferent nuclei tend to be more lateral and the efferent nuclei are more medial
MOTOR = MEDIAL
SENSORY = LATERAL
Which cranial nerves are motor and which are sensory?
Motor: 3,4,6, 11, 12
Sensory: 2 8
Both: 5, 7, 9, 10
Explain the arrangement of the cranial nerve nuclei
General Somatic Efferent = general somatic motor nuclei
Oculomotor = most rostral
Trochlear = immediately behind it (these are involved in eye movement)
Abducens = cranial nerve emerges at the ponto-medullary junction but the nucleus is within the pons
Hypoglossal = in the medulla
Special Visceral Efferent
Trigeminal = first one - it is in the pons
Facial = also in the pons
Ambiguus = involved in swallowing and phonation - in the medulla (contain both glossopharyngeal and vagus)
Accessory = innervates the sternocleidomastoid and trapezius - located in the cervical spinal cord
General Visceral Efferent
Edinger Westphal - provides parasympathetic input to the eye - in midbrain
Salivatory - there are THREE sets of salivatory nuclei at the ponto-medullary border
Vagus - in the pons
Distinguish the different parts of the brain stem
Midbrain - typical mickey mouse appearance, another feature is the substantia nigra (dopaminergic neurones which produce neuromelanin which is black
Pons - is the region with the fourth ventricle and transverse fibres. There are cerebellar peduncles holding the cerebellum onto the back of the brainstem. The main peduncle is the middle cerebellar peduncle
Medulla - main feature is the pyramids, also a bulge in the side called inferior olivary nucleus
Lower medulla - At the junction with the spinal cord the cross-section is very round
The dorsal columns can be seen here (touch and proprioception)
The smaller of the columns is the gracilis - sensory information from the lower limb
More laterally you have the cuneatus - sensory information from the upper limb
The Central Canal can be seen in the cross-section of the lower medulla
You also see the crossing over of the fibres at the pyramidal decussation in the lower medulla
What is lateral medullary syndrome?
Caused by thrombosis of the vertebral artery or the posterior inferior cerebellar artery.
A blockage of either of these arteries results in:
Vertigo
Ipsilateral Cerebellar Ataxia - problem with gait on the same side of the body as the lesion (broad-based gate - they tend to shuffle)
Ipsilateral loss of pain/thermal sense (face)
Horner’s Syndrome - loss of sympathetic innervation to the head and neck
Ptosis
Lack of sweating around the eye
Hoarseness
Difficulty swallowing
Contralateral loss of pain/thermal sense in the trunk and limbs
