what are the three functions of the brainstem
- A Conduit – longitudinal tracts to and from the brain and cerebellum and spinal cord
- Cranial nerve functions via brainstem nuclei
- And integrative & modulatory functions through the reticulum
what are the boundaries of the brainstem
Anterior: • Clivus • Nerves & vessels Posterior: • Cerebellum & attachments nferiorly: • Foramen magnum & spinal cord Superiorly: • Tentorium cerebelli & diencephalon
Corticospinal descending pathway
A brainstem lesion of the lateral corticospinal tract will produce contralateral UMN signs
Carries motor information from the 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
Corticobulbar descending pathways.
A brainstem lesion of these tracts will produce effects dependant on where the lesion is
Corticobulbar 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
Medical lemniscal
pathway
Brainstem lesion of this tract produces contralateral loss of JPS and discriminating touch.
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
Spinal lemniscal pathway is
Brainstem lesion of this tract produces a
contralateral loss of pain and temperature sensation.
the extension of the spinothalamic tract through the Brainstem, it carries pain and temperature sensation
• Pathway decussates quickly in the spinal cord and ascends laterally to the thalamus
• Pathway terminates in the sensory cortex
Spinocerebellar tract
Brainstem lesion of this tract produces an ipsilateral defect.
carries proprioceptive information. Tract ascends ipsilaterally in the lateral portion of the brainstem to the pons, where it enters the brainstem.
where is the reticulum found
Found throughout the brainstem, located in the central tegmentum.
what is the reticulum
Diffuse network of neurons without detectable nuclei but which work predominantly in groups of neurotransmitter related networks.
what is the reticulum responsible for
wide variety of functions, eg regulation of pain sensation, arousal of the cortex and modulation of descending motor output
ranial nerves follow the rule of 4,
- There are 4 cranial nerves in or above the midbrain
- There are 4 cranial nerves in the Pons
- There are 4 cranial nerves in the medulla
Oculomotor nucleus (Oculomotor N. 3)
Function: control of extraocular eye muscles except superior oblique and lateral rectus
Trochlear nucleus (Trochlear N. 4)
Function: control of superior oblique muscle of the eye
Abducens nucleus (Abducens N. 6)
Function: control of lateral rectus muscle of the eye
Hypoglossal nucleus (Hypoglossal N. 12)
Function: control of tongue muscles
Trigeminal motor nucleus (Trigeminal N. 5)
unction: Controls muscles of mastication
Facial nucleus (Facial N. 7)
Function: control of muscles of facial expression (NB ventral to the Vestibulocochlear nucleus)
Nucleus ambiguus
function: Motor to pharynx and larynx
Accessory nucleus
function: Motor to sternocleidomastoid and trapezius muscles
chewing
5
grimace
7
swallow
9-10
speak
9-10
shrug
11
Edinger-Westphal nucleus (Occulomotor N. 3)
Function: control of pupillary constriction and lens accommodation
Superior Salivatory nucleus (Facial N. 7)
Function: control of lacrimal sublingual and submandibular glands, salivary glands (Facial N. 7 & Glossopharyngeal N. 9) NB Nucleus Ambiguus also supplies N. 9
Inferior Salivatory nucleus (Glossopharyngeal N. 9)
Function: control of parotid gland
Dorsal motor nucleus of the Vagus (Vagus N. 10)
Function: secretomotor to lungs and gut; control of heart rate
Trigeminal mesencephalic – somatic sensory
Function: Proprioception from the mouth
Trigeminal pontine (principal) – somatic sensory nucleus (Trigeminal N. 5)
Function: Discriminating touch from face
Vestibulocochlear nucleus (Occulomotor N. 8) - Special sensory
Function: Balance and hearing
Solitary nucleus - Visceral sensory
Function: Taste (Facial N. 7, Glossopharyngeal N. 9, Vagus N. 10), carotid baroceptors (Glossopharyngeal N. 9) & visceral afferent from pharynx, larynx lungs, gut (Vagus N. 10)
Trigeminal spinal nucleus (Trigeminal N. 5) – somatic sensory
Function: pain and temperature sensation from face, back of tongue, pharynx larynx and ear
