Brain stem

Brain stem:
Small narrow area that comprises the medulla, pons and midbrain – extension of spinal cord inside cranium, occupying posterior cranial fossa of skull. Function is to regulate automatic behaviours necessary for survival.

Midbrain (mesencephalon):
between diencephalon and pons; surrounds cerebral aqueduct (connects 3rd and 4th ventricles); can be divided into 3 anatomic subdivisions – tectum, tegmentum and cerebral crus
pathways between higher and lower brain centres
corpora quadrigemina – the visual and auditory reflex centres
red nucleus – subcortical motor centres; relay centre for many efferent cerebellar tracts
substantia nigra – nuclear mass in midbrain; motor nucleus; contains precursor of the neurotransmitter, dopamine
also contains nuclei of 3rd and 4th cranial nerves

Pons:
between midbrain and medulla oblongata – appears as an anterior bulge in brainstem; forms a bridge between the medulla and midbrain
main up mostly of conduction tracts (‘pons’ = ‘bridge’)
large umber of transverse fibres on anterior surface to connect the two cerebellar hemispheres
involved in regulation of respiration
contains 5th, 6th and 7th cranial nerves

Medulla oblongata:
conical shape (appears like a ‘swollen tip’ of spinal cord); below pons and merges into spinal cord, about 3cm long
anterior surface has fibres of the corticospinal or pyramidal tract
fibres cross over before entering spinal cord
conduction pathway between higher brain centre and spinal cord
nuclei regulate respiration, heart rate and blood pressure (cardiac, respiratory and vasomotor centres)
contains cranial nerves 8 to 12
has centres for vomiting, coughing sneezing and swallowing

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