Brainstem and Cranial Nerves - Dr. Hoffman NS102

Practice flashcards covering the external and internal anatomy of the brainstem, specific nuclei like the Red Nucleus and Substantia Nigra, the Reticular Activating System, and the 12 cranial nerves.} Red Nucleus.

Brainstem

The structural division of the brain consisting of the midbrain, pons, and medulla oblongata responsible for regulating vital functions like cardiac activity and respiration.

other functions:

• Relay/conduit: ascending and descending nerve connections to and from the motor and sensory systems of the brain pass through the brainstem

• Integration and regulation of sensory information (reticular formation)

• Cranial nerve origin and termination

Rostral Limit of the Brainstem

The midbrain-diencephalon junction where the brainstem meets the thalamus and hypothalamus, located just below the optic tracts.

Caudal Limit of the Brainstem

The level of the foramen magnum and the pyramidal decussation; everything below this point is the spinal cord.

Cerebellar Peduncles

White matter tracts that attach the cerebellum to the dorsal surface of the midbrain, pons, and upper medulla.

Superior Cerebellar Peduncle

The connection between the midbrain and the cerebellum which carries the anterior spinocerebellar tracts.

Middle Cerebellar Peduncle

The largest peduncle that connects the pons to the contralateral hemisphere of the cerebellum via the corticopontocerebellar pathway.

Inferior Cerebellar Peduncle

The connection between the medulla and the cerebellum which carries the posterior and cuneocerebellar spinocerebellar tracts.

Tectum

Also known as the corpora quadrigemina, this is the 'roof' of the midbrain formed by two pairs of bumps called the superior and inferior colliculi.

Superior Colliculi

A pair of bumps on the midbrain's dorsal surface that receive direct input from the retina and respond to visual stimuli.

Inferior Colliculi

A pair of bumps on the midbrain's dorsal surface that receive input from the auditory pathway and auditory cortex.

Cerebral Peduncles

Large ascending and descending fiber tracts on the ventral surface of the midbrain that link the brainstem to the thalamus and cortex.

Crus Cerebri

The anterior/ventral portion of the cerebral peduncles that carries motor tracts.

Tegmentum

A general area throughout the entire brainstem containing critical nuclei and tracts for movement, sensation, and autonomic regulation; it forms the 'floor' of the midbrain.

Red Nucleus

A nucleus located in the midbrain tegmentum involved in motor coordination and the origin of the rubrospinal tract, which controls fine hand movements.

Substantia Nigra

A basal ganglia structure in the midbrain containing dopaminergic neurons rich in neuromelanin; its degeneration is associated with Parkinson's disease.

Periaqueductal Gray (PAG)

Gray matter surrounding the cerebral aqueduct in the midbrain involved in pain modulation, opioid reception, and autonomic defensive reactions like fear or heart rate changes.

Transverse Pontine Fibers

Horizontally-oriented fibers that form the bulbous ventral 'bridge' of the pons, relaying info from the primary motor cortex to the contralateral cerebellum.

Pyramids

Paired white matter structures on the ventral surface of the medulla containing descending motor fibers of the corticospinal and corticobulbar tracts.

Pyramidal Decussation

The point in the caudal medulla where the motor tracts of the pyramids cross to the opposite side.

Inferior Olives

Prominent bulges lateral to the pyramids in the rostral medulla involved in cerebellar motor-learning and movement control.

Gracile and Cuneate Nuclei

Locations in the caudal medulla where second-order neurons of the DCML pathway synapse before decussating to form the medial lemniscus.

PreBötzinger Complex (preBötC)

A group of glutamatergic pacemaker neurons in the ventral medulla that serves as the primary respiratory rhythm generator for automatic breathing.

Reticular Formation

A diffuse network of nuclei forming the central core of the brainstem that modulates pain, muscle tone, autonomic functions, and consciousness.

Ascending Reticular Activating System (RAS)

A functional system that filters sensory stimuli and sends continuous input to the cortex to maintain arousal and alertness.

• can convey sensory information to the cortex of a sleeping individual, which can awaken that person.

**With injury or pathological insult to areas of the RAS unconsciousness, coma, or a vegetative state may result.

Trigeminal Nerve (CN V)

The largest cranial nerve, having both sensory and motor functions, providing sensation to the head and face and innervating muscles for chewing.

• Rich innervation: provides sensation to head, face, mouth, sinuses

• Motor branch innervates muscles involved in chewing

• Implicated in dental pain, headache, migraine pathophysiology

Vagus Nerve (CN X)

this long mixed nerve drives the parasympathetic 'rest and digest' activities for visceral targets like the heart and gut.

sensory, motor, & parasympathetic branch of ANS

• Drives autonomic parasympathetic activity to visceral targets for “rest and digest”

• Slows heart rate and reduces blood pressure

• Promotes digestion

Olfactory Nerve (CN I)

A sensory nerve dedicated to the sense of smell; it is one of the nerves that does not enter the brainstem.

Optic Nerve (CN II)

A sensory nerve dedicated to vision; it travels to the superior colliculus and lateral geniculate nucleus.

Hypoglossal Nerve (CN XII)

A motor nerve responsible for tongue movement, swallowing, and speech.

corticopontocerebellar pathway

motor cortex sends a copy of the motor plan to the cerebellum via the corticopontine tract. Helps smooth movements and coordination.

analgesia

pain reduction

• PAG is rich with opioid receptors

pontine nuclei

nuclei of the pons are located in the ventral (“basal”) pons and contain neurons involved in motor activity;receive information from the ipsilateral primary motor cortex and then relay that information to the contralateral cerebellum via the middle cerebellar peduncle.

• contralateral decussation of these axon fiber tracts from the pontine nuclei form the transverse fibers and pontine

“bulge” by crossing from one side of the pons to the contralateral cerebellum.

• connections allow unconscious modification of motor actions and error correction–the process of learning motor skills.

descending reticular activating system (RAS)

neurons act on many levels of the spinal cord to coordinate movements and autonomic system functions, including the muscles that control cardiac and respiratory function.