Brainstem
Midbrain
Pons
Medulla
superiormost component of the brainstem.
middle structural component
of the brainstem.
acts as a bridge between the
midbrain and medulla.
inferiormost component
of the brainstem.
immediately rostral to the spinal cord.
Structure
positioned longitudinally between
the forebrain and spinal cord;
connected to the cerebellum dorsally.
associated w/ 10 pairs of cranial nerves
cranial nerves III-XII
III. Oculomotor
IV. Trochlear
V. Trigeminal
VI. Abducens
VIII. Vestibulocochlear
IX. Glossopharyngeal
X. Vagus
XI. Accessory
XII. Hypoglossal
Midbrain level
structures
cerebral peduncles / crus cerebri in the anterior aspect of the brainstem.
the corpora quadrigemia in the
posterior aspect of the brainstem.
includes axons that contribute to the corticospinal tract
cerebral cortex → brainstem → spinal cord
cranial nerves
III and IV.
the oculomotor nerve is
localised ventromedially.
the trochlear nerve is
localised dorsally.
has the structural function of anchoring the cerebrum to the rest of the brainstem through the corticospinal tract.
consists of the superior and inferior colliculi
involved in the relay of specific sensory information to higher order processing centres.
also involved in the generation of
reflexive motor patterns.
localised in close proximity to the cerebral aqueduct (esp. the corpus quadrigemia)
the superior colliculi receive inputs from
the retina or the visual cortex, and project
to vision-related areas in the cerebral cortex.
the inferior colliculi receive inputs from
auditory receptors in the ear to relay information to somatosensory cortices of the brain.
superior colliculi functional properties:
● detection of object movement in visual field.
● coordination of eye movement responses.
● relay visual information to visuomotor neurons.
● responses coordinated via the oculomotor nerve
inferior colliculi functional properties:
● each acts primarily as auditory relay nuclei.
● also acts in reflexive responses to sound.
● i.e. the "startle reflex"
contains the substantia nigra,
which is functionally linked to the
basal nuclei w/in the forebrain.
contains melanin which attributes its dark colour
and serves as a precursor for the chemical dopamine,
a neurotransmitter that exists in high amounts in this nucleus.
the degeneration of dopamine neurons in the substantia nigra leads to Parkinson's Disease.
consists of two parts
pars compacta
pars reticulata
the part of the substantia nigra that
contains most of the dopamine neurons.
localised ventrally to the pars compacta.
has connections similar to the internal division of the basal
ganglia globus pallidus ─ relaying inhibitory input to the
thalamus, which relays it to the cerebral cortex
damage leads to impaired inhibition of
unwanted motion sequences, which leads to
uncoordinated movement in the form of
tremor (Parkinson's disease).
in close association w/ the red nucleus, which
is a highly vascular structure that lies deep to the
substantia nigra ─ acts as a relay nucleus in some
descending motor pathways.
the superior cerebellar peduncle
in the dorsal aspect.
mammillary bodies in the
ventral aspect (near pituitary)
pons-level structures
middle cerebellar peduncle in
the dorsal aspect, connecting the
brainstem and cerebellum.
in close association to the fourth ventricle (forms its lateral walls).
cranials nerves V-VIII
trigeminal nerve
abducen nerve
facial nerve
vestibulocochlear nerve
composed of bidirectional conduction tracts of white matter that project from the cell bodies of pontine nuclei.
the pneumotaxic centre of the pons
helps to maintain normal respiratory rate
with regulatory centres in the medulla.
composed of white and grey matter organised into distinct structural compartments:
white matter → pyramids
(localised ventromedially)
grey matter → olives
(localised ventrolaterally)
medulla level structures
inferior cerebellar peduncle
in close association w/ the fourth ventricle (forms part of its floor).
cranial nerves IX-XII
glossopharyngeal nerve
vagus nerve
accessory nerve
hypoglossal nerve
contains the inferior olivary nuclei which
relays sensory / proprioceptive information to
the cerebellum from the cerebral cortex.
formed by large descending corticospinal
tracts from the primary motor cortex.
contains the pyramidal decussation, where
the corticospinal tract decussates contralaterally.
the pyramidal decussation ─ just
above the spinomedullary junction at
the level of the foramen magnum.
localised in a way that it provides a
pathway for axonal tracts running
between the forebrain, cerebellum,
and spinal cord.
contains two tracts at its base that
are continuous to the spinal cord,
both of which are afferent.
fasciculus gracilis (axially)
→ forms spinal gracile tract
fasciculus cuneatus (laterally)
→ forms spinal cuneate tract
carries sensory information from
the upper limbs of the body.
carries sensory information from
the lower limbs of the body.
plays an important role in
maintaining homeostasis.
respiratory centre controls rate and depth of ventilation
other reflexive centres for activities such as coughing, sneezing, gagging, swallowing, vomiting and sweating.
cardiovascular centre
cardiac centre regulates heart rate and contractile force.
vasomotor centre adjust vessel size to control blood pressure.
The medulla has a functional association with the hypothalamus.
sends autonomic control instuctions to the
reticular centres of the medulla, which then
carries these instructions out via interactions
w/ target structures, mainly the viscera.