Hindbrain & Midbrain Anatomy and Physiology

Comprehensive vocabulary flashcards covering the gross anatomy, internal structures, histology, nuclei, and physiological functions of the hindbrain and midbrain.

Forebrain

A major division of the brain that processes sensory information, helps with reasoning and problem-solving, and regulates autonomic, endocrine, and motor functions.

Midbrain

A division of the brain that helps regulate movement and process auditory and visual information, serving as the connection between the hindbrain and forebrain.

Hindbrain

A major division of the brain that helps regulate autonomic functions, relay sensory information, coordinate movement, and maintain balance and equilibrium.

Myelencephalon

The division of the embryonic hindbrain swelling that differentiates into the medulla oblongata.

Metencephalon

The division of the embryonic hindbrain swelling that differentiates into the pons and cerebellum.

Medulla oblongata

The brainstem structure that begins after the pons and ends at the spinal cord, wider and structurally distinct from the cord, through which all connecting nerve fibers pass.

Pyramids (medulla oblongata)

A pair of ridges running along the anterior surface of the medulla oblongata containing the corticospinal tracts.

Olive (medulla oblongata)

A prominent bulge located lateral to each pyramid on the anterior surface of the medulla oblongata.

Ascending fibers

Nerve fibers running through the medulla oblongata that carry sensory signals upward from the body to the brain.

Descending fibers

Nerve fibers running through the medulla oblongata that convey motor signals downward from the brain to the body.

Corticospinal tracts

The largest group of descending motor fibers located within the medullary pyramids that transmit signals from the cerebrum to the spinal cord to control muscles.

Decussation

The anatomical crossing of nerve fibers from one side of the central nervous system to the contralateral side.

Pyramidal decussation

The crossing point in the medulla where $90\%$ of corticospinal tract fibers switch sides, resulting in contralateral motor control below the neck.

Nervous nuclei (medulla)

Clusters of gray matter in the medulla oblongata involved in sensory functions (hearing, touch, taste, pain) and motor functions (chewing, salivation, swallowing, speech).

Inferior olivary nucleus

A nucleus in the medulla oblongata that relays signals received from other regions of the brain and spinal cord to the cerebellum.

Reticular formation

A loosely organized core of gray matter nuclei running through the brainstem (medulla and pons), midbrain, and upper spinal cord that connects with the cerebrum.

Somatic motor control (reticular formation)

A function of the reticular formation responsible for maintaining muscle tone, balance, posture, tracking objects with the eyes, and controlling breathing and swallowing muscles.

Habituation

A reticular formation process wherein the brain learns to ignore repetitive, unimportant stimuli while remaining responsive to significant stimuli.

Cardiac center

A specialized reticular formation area in the medulla oblongata that regulates the rate and force of the heartbeat.

Vasomotor center

A medullary reticular formation center that regulates blood pressure by altering blood vessel diameter through vasodilation and vasoconstriction.

Respiratory centers (medulla)

Two areas within the reticular formation of the medulla oblongata that regulate the rhythm and depth of breathing.

Swallowing center (medulla)

A reticular formation area located in the medulla oblongata that coordinates the involuntary swallowing response.

Pons

The middle structure of the brainstem between the medulla and midbrain that forms an anterior bulge and physically connects the brainstem to the cerebellum.

Transverse fascicles

Horizontal white matter tracts in the anterior half of the pons that cross (decussate) toward the cerebellar peduncles.

Longitudinal fascicles

Vertical white matter tracts passing through the anterior pons that connect the cerebrum to the spinal cord.

Cranial nerves of the pons

Four pairs of cranial nerves that begin or end in the pons, mediating sensory inputs (hearing, equilibrium, taste, facial touch/pain) and motor outputs (eye movement, facial expression, chewing, swallowing, salivation).

Cerebellum

The largest region of the hindbrain and the second largest region of the brain overall, containing over $50\%$ of all brain neurons.

Vermis

The narrow, central midline bridge of tissue that connects the left and right cerebellar hemispheres.

Folia

The parallel, narrow, leaf-like folds of gray matter across the surface of the cerebellum, separated by shallow sulci.

Arbor vitae

The distinctive branching, tree-like formation of white matter visible in a sagittal section of the cerebellum.

Cerebellar cortex

The outer surface layer of gray matter of the cerebellum where all incoming afferent signals to the cerebellum terminate.

Deep nuclei (cerebellum)

Four internal masses of gray matter per cerebellar hemisphere from which all output signals leaving the cerebellum originate.

Granule cells

Tiny, densely spaced neurons in the cerebellum that constitute the most abundant neuron type in the human brain.

Purkinje cells

Large, globular neurons of the cerebellar cortex with extensive dendritic fans whose axons project to synapse on deep cerebellar nuclei.

Cerebellar peduncles

Three paired bundles of nerve fiber stalks that anchor the cerebellum to the brainstem and transmit afferent and efferent signals.

Inferior cerebellar peduncles

The pair of peduncles connecting the cerebellum to the medulla oblongata, conveying most incoming spinal sensory input into the cerebellum.

Middle cerebellar peduncles

The pair of peduncles connecting the cerebellum to the pons, carrying the majority of input from the rest of the brain to the cerebellum.

Superior cerebellar peduncles

The pair of peduncles connecting the cerebellum to the midbrain, carrying the vast majority of cerebellar efferent output to other brain centers.

Cerebellar lesions

Pathological damage or injury to the cerebellum resulting in noticeable deficits in muscle coordination and motor control.

Timekeeper function (cerebellum)

A non-motor cognitive ability of the cerebellum enabling judgment of elapsed time between consecutive sensory events.

Tectum

The roof-like dorsal portion of the midbrain located posterior to the cerebral aqueduct, composed of four collicular bulges.

Superior colliculi

The rostral pair of midbrain tectal bulges that control the extrinsic muscles of the eye to visually track moving objects and direct gaze toward peripheral targets.

Pretectal nuclei

Nuclei in the midbrain responsible for controlling pupillary diameter and accommodating lens focus.

Inferior colliculi

The caudal pair of midbrain tectal bulges that relay auditory inputs from the inner ear and detect interaural time delays for sound localization.

Substantia nigra

A dark, melanin-pigmented motor center in the midbrain that releases inhibitory signals to suppress unwanted muscle movements, whose degeneration causes Parkinson's disease tremors.