14.3 The Hindbrain

medulla oblongata

adult brain region that develops from embryonic myelencephalon; begins at foramen magnum of skull; slightly wider than spinal cord

pyramids of medulla oblongata

ridges on anterior surface, resemble side by side baseball bats; separated by anterior median fissure

cranial nerves that begin or end in medulla oblongata

cranial nerves VIII (in part), IX, X, and XII

olives of medulla oblongata

prominent bulges lateral to each pyramid

gracile and cuneate fasciculi of spinal cord

continue as two pairs of ridges on posterior medulla; contain sensory fibers that synapse in nuclei of these

tracts in medulla

all ascending and descending fibers connecting brain and spinal cord pass through the medulla

medial lemniscus

where the axons of gracile and cuneate nuclei decussate and form ascending tract to thalamus

corticospinal tracts

descending motor tracts in pyramids; carry signals down to skeletal muscles

inferior olivary nuclei of medulla

relay center for signals to the cerebellum

reticular formation

loose network of nuclei extending through entire brainstem; contains cardiac center, vasomotor center, and respiratory centers

pons

adult brain region that develops from embryonic metencephalon; measures 2.5 cm long; rostral to the medulla oblongata; contains of thick stalks (cerebellar peduncles)

cerebellar peduncles of the pons

thick stalks on posterior pons that connect it (and the midbrain) to the cerebellum

cranial nerves of the pons

cranial nerves V, VI, VII, and VIII

sensory roles of pons

hearing, equilibrium, taste, facial sensations

motor roles of pons

eye movement, facial expressions, chewing, swallowing, urination, and secretion of saliva and tears

reticular formation in pons

contains additional nuclei concerned with sleep, respiration, and posture