Brainstem and Cranial Nerves

Brainstem

A stalk like structure containing neurons that are essential to life and pathways that facilitate communication between the cerebrum, the cerebellum and the spinal cord
It is continuous with the spinal cord below and the diencephalon above
Divided into three parts; the midbrain, pons and medulla

What is in the brainstem?

Ascending white matter tracts, descending white matter tracts, nucleus gracilis and cutaneous (dorsal columns), vestibular nuclei (vestibulospinal pathway), reticular nuclei (reticulospinal pathway), red nucleus (rubrospinal pathway), cranial nerve nuclei, respiratory and cardiovascular centres and reticular activating system

Midbrain

Substantia nigra - part of basal ganglia that produces dopamine to aid in movement regulation
Red nucleus - rubrospinal tract
Superior and inferior colliculi - visual and auditory processing
Cerebral peduncles - largest part of the midbrain - corticospinal tract
Cranial nerves III and IV
Cerebral aqueduct - connects third and fourth ventricle

Pons

4th ventricle
Superior, middle and inferior cerebellar peduncles - white matter tracts
Reticular formation - a network of nuclei that control functions such as sleep and pain
Vestibular nuclei - vestibulospinal tract
Reticular nuclei - reticulospinal tract origin
Cranial nerves V, VI, VII and VIII
Respiratory and cardiovascular centres

Medulla

Dorsal column nuclei - proprioception and touch - where dorsal column synapses
Gracile tubercle - lower limb proprioception and touch
Cuneate tubercle - upper limb proprioception and touch
Reticular formation
Vestibular nuclei - origin of vestibulospinal pathway
Pyramids - corticospinal tract decussation
Respiratory and cardiovascular centres
Cranial nerves IX, X, XI, XII

Why lesions in the brainstem can produce motor and sensory loss in limbs

Ascending and descending tracts passing through the midbrain, pons and medulla so damage here will disrupt pathways
Pathways include: dorsal column, spinothalamic tract and spinocerebellar tract (sensory) and the reticulospinal, vestibulospinal and corticospinal (motor)

Coma

A prolonged period of loss of consciousness
Can be medially induced or result from a head injury and affects brainstem functions, preventing awareness and response to stimuli
Brainstem controls vital functions like sleep and aids consciousness so damage to this area will prevent this

How consciousness is assessed clinically

Using the Glasgow Coma Scale
Questions that give a score of between 3 and 15
15 is a full state of consciousness and 3 would be brain dead or dead

Reticular formation

Reticulated matrix extending throughout the length of the brainstem
Projections that regulate complex functions of the CNS
Ascending projections from the RF modulate arousal and consciousness (RAS and raphe nuclei)
Descending projections modulate sensory and motor pathways - motor control (reticular nuclei) and pain modulation (raphe nucleus)

Cranial nerves

Set of 12 pairs of nerves that directly connect the brain to the head, neck and shoulders

I

Olfactory nerve
Sensory
Smell

II

Optic nerve
Sensory
Vision

III

Oculomotor
Motor
Eye movement, pupil control and eyelid elevation

IV

Trochlear
Motor
Eye movement and control of binocular movement

V

Trigeminal
Sensory and motor
Sensation of face (pain)
Chewing muscles (massification)

VI

Abducens
Motor
Lateral eye movement

VII

Facial
Sensory and motor
Taste (anterior 2/3 of tongue)
Facial expression muscle

VIII

Vestibulocochlear
Sensory
Hearing, balance and equilibrium

IX

Glossophalangeal
Sensory and motor
Taste perception, pharynx sensation
Swallowing and muscles of pharynx

X

Vagus
Sensory and motor
Visceral sensation, pressure reception in aorta
Coughing, lungs, pharynx, larynx, trachea etc. and heart

XI

Accessory
Motor
Head, neck and shoulder movement

XII

Hypoglossal
Motor
Tongue movement and speech articulation

Lesions leading to ataxia

Uncoordinated movement
Movement tracts pass through brainstem so damage would disrupt passage of information about movement meaning it is uncoordinated

How to remember cranial nerves

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