Anatomy - Brainstem and Cranial Nerves

Posterior cranial fossa

The brainstem together with the cerebellum occupy the?

Brainstem

Located anterior to the cerebellum. Continuous with the diencephalon superiorly and the spinal cord inferiorly

Midbrain, Pons, Medulla oblongata

What are the 3 segments of the brainstem?

Brainstem

Sensory: Receive sensory information from the cranial structures.Motor: Control the muscles of the head through the cranial nerves

Scattered nuclei

This aids in higher brain functions and governing an individual’s state of arousal (keeping an individual awake)

Long fiber tracts

Often referred to as ascending and descending pathways go in and out of the brain via the brainstem

Ascending pathways

Carry sensory information from the trunk and extremities. This will be processed in the cerebrum, where we appreciate sensations like pain, light touch, and pressure

Descending pathway

Carry motor fibers which will control the skeletal muscles of the trunk and extremities. This allows an individual to move

Cerebral Aqueduct of Sylvius

Cavity traversing the midbrain.This becomes continuous with the triangular cavity of the 4th ventricle which can be appreciated at the level of the pons and upper medulla

Cerebellar Peduncles

Connects the brainstem to the cerebellum, posterior to it. Serves as a pathway between the cerebellum and other parts of the CNS, such as the brain & spinal cord

Superior (brachium conjunctivum), Middle (brachium pontis), Inferior (restiform body)

What are the 3 separate cerebellar peduncles?

Brainstem

A compact structure involving nuclei and nerve fiber tracts: small lesion —> devastating effects

Crus Cerebri

2 pillar-like structures emerges from the pons

Interpeduncular Fossa

In between crus cerebri; hollow groove or depression. Where CRANIAL NERVE III (oculomotor) can be best appreciated

Cranial Nerve IV (Trochlear Nerve)

Found on either side of crus cerebri. Comes from posterior side of midbrain. Inferior to the inferior colliculi. Will course going to the lateral side of the crus cerebri anteriorly

Corpora quadrigemina (Tectum)

2 pairs of swelling on the posterior side of the brainstem

Substantia Nigra

Pigmented region that separates the crus cerebri from the tegmentum and tectum. For movement and reward function

Cerebral aqueduct of Sylvius

Located in the midline of the brain and is a cavity that is surrounded by an area called the periaqueductal grey mater.

Edinger-Westphal nucleus

In the area of the periaqueductal grey mater, lies the motor nucleus of cranial nerve III and its accessory nucleus, called the ___________, which carries the parasympathetic function of cranial nerve III

Tectum

Posterior to the periaqueductal grey mater is a midbrain area which contain the colliculi. This area contains the nucleus of the superior colliculus, which is important in the control of visual reflexes

Interpeduncular fossa

Fibers of the motor nucleus of the oculomotor and Edinger-Westphal nucleus will give rise to CN III that exits at the?

Pretectal Nucleus

Controls the Edinger-Westphal on both sides. Plays a role in the pupillary light reflex reaction

Medial Longitudinal Fasciculus

Bundle of white mater in the middle region of the tegmentum. Links the three cranial nerves which control the eyeball: CN III- Oculomotor, CN IV- Trochlear, CN VI- Abducens

Mesencephalic Nucleus of CN V

Present in the midbrain. One of the sensory nuclei of the trigeminal nerve

Ascending Tracts

Long tracts will pass through the brainstem in order to connect the spinal cord to the cerebrum and vice versa. Meaning these fibers originating from the spinal cord, will form a bundle of white mater on the lateral side of the tegmentum. These tracts are the Spinothalamic Tract and the Medial Lemniscus.

Descending Tracts

Organized in the crus cerebri, particularly the corticospinal tract and the corticobulbar tract.

Red Nucleus

Are pale pink structures present in the area which is usually involved in motor coordination. The fibers of CN III traverses this structure

Trochlear Nerve (CN IV)

Origin: motor nucleus. Innervates: superior oblique muscles (one of the extraocular muscles of the eye). Arises from: behind the midbrain. Exits: posteriorly and prior to its exit the fibers crosses the midline

Trochlear Nefve (CN IV)

The longest cranial nerve intracranially. The ONLY cranial nerve that exits at the posterior side of the brainstem. The ONLY crossed cranial nerve

Pontine Protuberance

Large bulging structures at the anterior brainstem. Identifying feature of the pons

Basilar Groove

At the middle of the pontine protuberance. Central depression/groove. Occupied by the basilar artery: one of the main arteries of the brainstem

Trigeminal Nerve (CN V)

Found at the lateral sides of the pontine protuberance

Ponto-Medullary Junction

Junction between the pons and medulla. A sulcus where several cranial nerves emerge from the brainstem: Abducens nerve (CN VI), Facial Nerve (CN VII), Vestibulocochlear Nerve (CN VIII)

Posterior Surface of the Pons

Forms the upper half of the floor of the 4th ventricle. Triangular in shape. The 4th ventricle cavity can be clearly seen if the cerebellum is removed.

Facial colliculus

Prominent swelling. Produced by the root of the Facial nerve (CN VII) winding around the nucleus of the Abducens nerve (CN VI)

Basis Ponti

Continuation of the crus cerebri

Pontine Nuclei

Scattered at the middle of the basis ponti

Pontocerebellar (Pontine fibers)

Horizontally arranged. Arise from the pontine nuclei. Externally, horizontally arranged fibers can be appreciated as it courses laterally and forming the middle cerebellar peduncle

Middle Cerebellar Peduncle

Input pathway that connects the pons’ pontocerebellar/pontine fibers to the cerebellum

Corticospinal and Corticobulbar Tract

Interspersed within the basis ponti are bundles of descending motor tracts coming from the crus cerebri of the midbrain. Organized in crus cerebri, and continue to descend in the pons, inserting in bundles of fascicles among fibers of pontine nucleus until it reaches the medulla oblongata

Tegmentum

Continuation of the tegmentum of the midbrain. Contains ascending pathways that originated from the spinal cord. This contains the fibers of: Medial lemniscus, Spinothalamic tract

Medial Lemniscus and Spinothalamic Tract

Located in the most anterior part of the tegmentum

Medial Longitudinal Fasciculus

Organized on the medial region of the tegmentum

Spinal Nucleus of Trigeminal Nerve (CN V)

Located at the lower regions of the pons and will extend until the medulla oblongata

Motor Nucleus of Abducens Nerve (CN VI)

Main highlight of the level of facial colliculus. Will give rise to the Abducens Nerve (CN VI)

Motor Nucleus of Facial Nerve (CN VII)

Will give rise to the Facial Nerve (CN VII). Fibers of Facial nerve winds around motor nucleus of abducens, which creates a bump or swelling at posterior wall of pons (Facial colliculus)

Superior Salivatory Nucleus

Parasympathetic nucleus of Facial Nerve (CN VII). Responsible for controlling the secretion of certain salivary glands

Nucleus Tractus Solitarius

Sensory nucleus of the Facial Nerve (CN VII). Relay station for the taste sensation, originating from the taste receptors of the tongue and the pharyngeal mucosa

Medulla Oblongata

Last segment and most inferior region of the brainstem

Open Medulla

Upper half of the medulla that coincides with the lower region of the 4th ventricle.

Closed Medulla

Lower half of medulla; central canal can be seen in its cross section.

Fasciculus gracilis

Matches with the gracile tubercle in the medulla. Found medially.

Fasciculus cuneatus

Ends in the cuneate tubercle as it reaches the posterior medulla. Found laterally.

Inferior Cerebellar Peduncle

Attaches the medulla to the cerebellum.

Inferior Olivary Nucleus

Most prominent with a crumpled U-shape nucleus. Forms a projected swelling in the lateral surface of the medulla. Coordinates movements and is associated with learning.

Motor Nucleus of CN XII (Hypoglossal nerve)

Located as the posterior wall of the medulla. Give rise to Hypoglossal nerve CN (XII).

Vestibular Nucleus and Cochlear Nucleus

Near the area of cerebellar peduncle; the vestibular nucleus is made up of 4 individual nuclei. Give rise to vestibulocochlear nerve CN (VIII); will exit at the anterolateral pontomedullary junction.

Dorsal Motor Nucleus

Adjacent to the hypoglossal nucleus. The parasympathetic component of the vagus nerve.

Nucleus Tractus Solitarius

Process taste sensation coming from the tongue and oropharynx.

Nucleus Ambiguus

Shared by several cranial nerves. The motor nucleus that supplies the muscles of deglutition.

Vagus Nerve

Contributes nerve fibers for the formation of CN X: Dorsal Motor Nucleus, Nucleus Tractus Solitarius, Nucleus Ambiguus

Medial Longitudinal Fasciculus

Integrates the function of CN III, CN IV, and CN VI.

Pyramidal tract

What is the other name of the corticospinal tract?

Level of Sensory Decussation

What level of the medulla oblongata is being described: No 4th ventricle will be seen. Hence, it is now within the closed medulla. Posterior bumps: Gracile Tubercle and Cuneate Tubercle, Anterior bumps: Pyramids

Medial Lemniscus

At the level of sensory decussation, the crossed fibers of the dorsal column will now change its name to?

Central Canal

Will be continuous with the cavity of the spinal cord

Gracile and cuneate nuclei

The presence of these structures is the main reason for the bumps on the posterior surface of the closed medulla.

Medial Lemniscus

The nuclei which synapses to the fasciculus will now create their own fibers where most of which will cross the opposite side. As these dorsal column fibers cross the central canal, they are now called?

Inferior Salivatory Nucleus

A parasympathetic nucleus of CN IX, the only role of which is to supply the parotid gland. Additionally, the nucleus tractus solitarius, as well as the nucleus ambiguus are also present within the area.

Level of Motor Decussation

Identify the level of the medulla oblongata being described: No longer have the prominent bumps at the posterior side of the medulla. More prominent: Tracts of Fasciculus Gracilis and Fasciculus Cuneatus. Anteriorly: Pyramid, Middle: Central Canal

Corticospinal tract

The main structure that forms the anterior pyramid are the fibers of this structure. At the level of the lower medulla, 85% of the fibers will cross the opposite side such that the left side will cross towards the right side and the right side will cross towards the left side.

Lateral Spinothalamic Tract

An ascending tract whose fibers carry pain and temperature sensation from the trunk and extremities.

Spinal Accessory Nucleus

Also known as the motor nucleus of CN XI. Will give rise to the 11th cranial nerve or the spinal accessory nerve

Cranial Nerves

Responsible for the sensation of pain when there’s a “bad tooth,” smiling, simultaneous movement of the eyes, smelling fragrances, etc.

Sensory fibers

Carry information from the periphery going to CNS (particularly the cerebrum) where all information is being interpreted and appreciated.

Cerebral Cortex

Most of the time, the ascending tracts end up in the?

BA 3, 1, 2

In the cerebrum lecture, the primary somatosensory region of the brain is

CN I (Olfactory), II (Optic), VIII (Vestibulocochlear)

What cranial nerves will carry purely sensory fibers?

CN III, IV, VI

Why is it that our eyes could look at the side without moving or rotating our head? Due to the muscles surrounding the eye that allows it to move and focus on the area where the visual stimulus is. These surrounding muscles are being controlled by?

Extraocular Muscles of the Eye

Known to be innervated by cranial nerves III, IV, and VI

Superior, Lateral, Medial, Inferior

What are the rectus/recti muscles?

Superior, Inferior

What are the oblique muscles?

Cardinal Movements of the Eye

Brought about by contraction of extraocular muscles

Lateral rectus RE, Medial rectus LE

By looking at the right side, what extraocular muscles will be activated?

Superior rectus, Inferior oblique BE

By gazing upward, what extraocular muscles will be activated?

Inferior rectus, Superior oblique BE

By looking downward, what extraocular muscles will be activated?

CN III (Oculomotor Nerve)

Has two component nuclei – motor nucleus of the oculomotor and the Edinger-Westphal nucleus

Motor Nucleus of CN III

Basically supply most of the extraocular muscles of the eye except for the superior oblique and the lateral rectus.

Levator palpebrae superioris

Aside from the extraocular muscles, the CN III will also innervate this muscle, which is responsible for the eye-opening.

Edinger-Westphal Nucleus

The parasympathetic component of the Cranial Nerve III (CN3). Its main role is to constrict the pupil so that excessive light entering the eye is regulated, thus allowing us to see the visual image clearly.

Constrictor pupillae

The ring-like muscle surrounding the pupil that is supplied by Cranial Nerve III

Pupillary Light Reflex

It is done by intentionally applying a light stimulus in front of the eye.

Direct Pupillary Light Reflex

In a normal eye, when a light is shone on one side, it will result in the pupillary constriction of the same side. The side where the reaction occurs is called the?

Consensual Pupillary Light Reflex

Notice that what is happening on the side where the light stimulus is applied is also happening on the contralateral side, even without the presence of the same stimulus. This reaction is called the?

Optic and Oculomotor Nerve

The Pupillary Light Reflex is participated by what cranial nerves?

Optic nerve

What is the sensory arm in the pupillary light reflex pathway?

Oculomotor nerve

What is the efferent/motor arm in the pupillary light reflex pathway?

Trochlear nerve

The 4th cranial nerve. Contains only 1 nucleus. The motor nucleus of gives rise to this nerve which is known to exit at the back of the midbrain as the cross fibers of CN 4. Has a pure motor nucleus that supplies only 1 muscle which is the superior oblique muscle.

Abducens Nerve

The 6th cranial nerve. Has only 1 component nucleus which is the motor nucleus. The motor nucleus of this nerve will give rise to the nerve which will exit the brainstem via the pontomedullary junction. Has a motor nucleus which will give rise to the nerve that will supply the lateral rectus muscle of the eye.

Trigeminal Nerve

The largest cranial nerve, will also have a large nucleus that expands the entire length of the brain stem