18.3 Brain Stem and Reticular Formation

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Reticular Formation

Netlike region of interspersed gray and white matter extending throughout the brainstem.

Medulla Oblongata

Begins at the foramen magnum and extends to the inferior border of the pons.

Pyramids

Bulges of white matter on the anterior aspect of the medulla. Formed by the largest motor tracts that pass from the cerebrum to the spinal cord.

Decussation of Pyramids

Crossing of axons just superior to the junction of the medulla and the spinal cord.

Nuclei

Masses of gray matter where neurons form synapses with one another.

Cardiovascular Center

In the medulla, regulates rate and force of heartbeat and diameter of blood vessels.

Medullary Rhythmicity Area

In the medulla, adjusts basic rhythm of breathing.

Medulla

nuclei from this part of the brain control reflexes for vomiting, coughing, and sneezing.

Olive

In the medulla, where neurons relay impulses from proprioreceptors to the cerebellum.

Gracile Nucleus

In the medulla, controls proprioception and sensation of fine touch in lower body.

Cuneate Nucleus

In the medulla, controls proprioception and sensation of fine touch in the upper body.

Medial Lemniscus

Band of white matter composed of ascending sensory axons; extends through the medulla, pons and midbrain.

Vestibulocochlear

Nerves that convey impulses related to hearing.

Glossopharyngeal

Nerves that control muscles during swallowing and tastebuds of posterior 1/3 of tongue.

Vagus

Nerves that recieve signals from viscera, control cardiac and smooth muscle of visceral organs, controls secretion of digestive fluids.

Accessory

Nerves whose cranial portion arise in the medulla; controls skeletal muscles of soft palate.

Hypoglossal

Nerves that control muscles of tongue while speaking or swallowing.

Pons

Part of brain located directly superior to the medulla and anterior to the cerebellum. Bridge that connects parts of the brain with one another.

Pontine Nuclei

Large synaptic relay station consisting of scattered gray centers; forms the ventral region of the pons.

Pneumotaxic and Apneustic

Areas of the pons that control inhaling, exhaling, and rhythm of breathing.

Trigeminal

Control muscels involved in chewing.

Facial

Motor part of these nerves goes to facial muscles, salivary glands, tear ducts, and nasal mucus sinuses. Sensory part controls anterior 2/3 of taste buds.

Abducens

Control lateral eye muscles.

Midbrain

Extends from the pons to the diencephalon.

Cerebral Peduncles

Pair of tracts in the anterior part if the midbrain. Contain corticospinal, corticobulbar, and corticopontine motor neurons which conduct nerve impulses from the cerebrum to the spinal cord. Also contain axons of sensory neurons that extend from the medulla to the thalamus.

Tectum

Posterior part of the midbrain.

Superior Colliculi

Two superior elevations of the tectum; coordinates eye movements with visual stimuli.

Inferior Colliculi

Two inferior elevations of the tectum; coordinates head movement response to auditory stimuli.

Substantia Nigra

Left and right nuclei in the midbrain that secrete dopamine.

Red Nuclei

Left and right nuclei in the midbrain that function with the cerebellum to coordinate muscle movement.

Mesencephalic Nucleus

Only nucleus in the CNS that is not a synaptic relay station between neurons. Contains cell bodies of snesory neurons carrying proprioceptive signals from skeletal muscles of the head.

Oculomotor

Motor part of these nerves controls movement of eyeballs and constriction of pupils and shape of lens. Goes to intrinsic and extrinsic eye muscles.

Trochlear

Control movement of eyeball via trochlear nerves.Goes to superior oblique eye muscle.

Reticular Activating System

Consist of sensory axons that project into cerebral cortex. Functions in arousal and consciousness. Prevents sensory overload.

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