L6 Brain Stem Motor I

The first-order neurons, carrying sensory information from the periphery, synapse in these nuclei.

These nuclei contain the cell bodies of lower motor neurons (LMNs) that control skeletal muscle movements.

These nuclei are involved in controlling movements of muscles within the head, including the tongue and eye muscles.

Located only in the hindbrain, these nuclei contain LMNs that control skeletal muscles in the pharyngeal arches.

These nuclei contain the cell bodies of parasympathetic preganglionic neurons, responsible for controlling involuntary functions like heart rate and digestion.

These nuclei are specialized for processing auditory information.

These nuclei are responsible for processing information about balance and spatial orientation.

These nuclei process tactile (touch), temperature, and pain information from the body.

The earliest part of the brain to achieve its adult form, responsible for various functions such as visual reflexes, auditory reflexes, and motor control.

A midbrain structure that contains the cell bodies of most dopaminergic neurons, which play a crucial role in movement and reward.

A specific sign of a midbrain atrophy seen on MRI, often associated with a neurodegenerative disease called Progressive Supranuclear Palsy (PSP).

A symptom of Wilson's Disease, a congenital copper toxicity syndrome. This is a specific pattern of inflammation observed on T2-weighted MRI.

A collection of nuclei in the midbrain, involved in eye movement control and coordination. This includes the superior cerebellar peduncle and cranial nerve III (CN3).

The oculomotor nerve (CN III) originates from the midbrain, specifically at the level of the superior colliculus. It is responsible for controlling the majority of extraocular muscles, which are the muscles that move the eye. These muscles include the superior rectus, medial rectus, inferior rectus, and inferior oblique muscles. Additionally, CN III also controls the levator palpebrae superioris muscle, which is responsible for raising the eyelid. The nerve also houses the Edinger-Westphal nucleus, which plays a crucial role in pupillary constriction and accommodation.

Oculomotor nerve injury can result in three noticeable signs: ptosis, exotropia, and mydriasis. Ptosis, or drooping of the eyelid, occurs due to the loss of function of the levator palpebrae superioris muscle. Exotropia, also known as lateral strabismus, happens due to the loss of function of the extraocular muscles, leading to the eye turning outward. Lastly, mydriasis, or dilation of the pupil, is caused by the loss of parasympathetic function controlled by the Edinger-Westphal nucleus.

A blown pupil refers to a dilated pupil that is unresponsive to light. This condition typically results from a lesion affecting the superficial autonomic fibers of the oculomotor nerve before affecting the deeper motor fibers. This type of pupil-specific dilation is often observed in cases like uncal herniation, where pressure is applied to the cranial nerve.

Pupil-sparing ophthalmoplegia refers to a condition where the motor fibers of the oculomotor nerve are affected, leading to paralysis of eye muscles, but the pupillary fibers are spared. This suggests that the damage to the oculomotor nerve is deeper and affects the motor fibers more than the parasympathetic fibers. Internal diseases of the nerve or vascular disorders are common causes.

The trochlear nerve (CN IV) originates from the midbrain at the level of the inferior colliculus. Its fibers exit the brainstem dorsally and then decussate to control the contralateral superior oblique muscle. This means that the left trochlear nerve controls the right superior oblique muscle, and vice versa.

The superior oblique muscle, innervated by the trochlear nerve (CN IV), is responsible for intorsion (rotating the eye inward) and depression of the eye, especially when it is adducted (turned inward).

Damage to the trochlear nerve (CN IV) results in a condition where the affected eye cannot properly depress and intort when turned inward (adducted). This causes the eye to drift upward and outward (hypertropia and excyclotropia).

A common sign of trochlear nerve palsy is a head tilt away from the side of the affected eye. This tilt helps to compensate for the eye's upward and outward deviation.

The primary gaze is the position of the eyes when looking straight ahead.

The ability of the eye to rotate inward (intorsion) and outward (extorsion) around the axis of sight is termed torsional movement.

Each extraocular muscle plays a specific role in moving the eye.

The 8 non-resting positions of the eyeball refer to the various directions the eye can move: up, down, left, right, up and left, up and right, down and left, down and right.

Eye movements are controlled by a complex network of muscles, nerves, and brain centers which work together to coordinate smooth and precise eye movements.

A rare neurological disorder that affects the ability to control vertical eye movement, particularly looking upward. This can cause difficulty with reading, walking, and other daily activities.

A hallmark symptom of Dorsal Midbrain Syndrome that manifests as an inability to move the eyes upward.

A common finding in Dorsal Midbrain Syndrome, where the eyelids are pulled back, widening the eyes.

The ability to move the eyes horizontally is controlled by a cluster of nuclei located in the pons, a region in the brainstem. It coordinates the movement of eyes left and right.

The horizontal gaze center is situated in the pons, specifically in an area called the paramedian pontine reticular formation.

A crucial nerve that emerges from the brainstem and innervates the lateral rectus muscle, responsible for moving the eye outwards. Damage to this nerve can result in difficulty turning the eye outward.

The inability to move the eye outward, often caused by damage to the abducens nerve.

A bundle of nerve fibers that connects nuclei involved in eye movement, allowing for coordinated eye movements. It runs through the brainstem and is crucial for smooth eye movement.

Damaged MLF. Characterized by problems moving one eye to the side opposite the lesion, with a jerky movement (nystagmus) in the other eye. Often seen in multiple sclerosis due to the MLF's myelinated nature.

A group of neurons in the midbrain crucial for controlling eye movements. It receives input from the frontal eye fields and the PPRF (paramedian pontine reticular formation).

A midbrain nucleus responsible for controlling the superior oblique muscle, involved in downward and outward eye movement.

The inability to move the eye laterally away from the side of the lesion. This is often caused by damage to the abducens nerve, which controls the lateral rectus muscle.

A phenomenon where the injured eye drifts outward (exotropia), while the unaffected eye exhibits involuntary jerky movements (nystagmus) when attempting to look toward the injured side. This is often observed in internuclear ophthalmoplegia.

A region in the brainstem located ventral to the cerebral aqueduct in the midbrain and ventral to the 4th ventricle in the pons and medulla. Contains cranial nerve nuclei and most of the reticular formation.

A region in the brainstem located in the dorsal midbrain, comprised of the superior colliculi and the inferior colliculi.

The most ventral region of the brainstem, containing corticospinal and corticobulbar tracts.

A column of motor neurons in the brainstem that innervates skeletal muscles within the head. Think of it as innervating things that "wiggle inside the head" e.g.tongue and eyes.

A column of motor neurons in the brainstem that provides motor innervation to all pharynx muscles except Stylopharyngeus.

The earliest part of the brain to reach its adult form, it contains important structures for visual reflexes, auditory reflexes, and motor control. It also houses the cell bodies for most of the brain's dopaminergic neurons.

The trochlear nerve (CN IV) originates in the midbrain and controls the superior oblique muscle, responsible for intorsion (rotating the eye inward) and depression (downward movement) of the eye, especially when it's turned inward (adducted).

The medial and lateral rectus muscles, when activated, always perform the same action regardless of the eye's position.

The other four extraocular muscles (superior, inferior, superior oblique, inferior oblique) have actions that change depending on the current angle of the eye, creating more intricate movements.

The "H" Test is a clinical assessment used to evaluate individual extraocular muscles, by observing the eye's movement and position as it traces the shape of an 'H'.

The test involves assessing the eye's vertical movements, while other muscles are maximally contracted, allowing for isolation of individual muscle function.

The extraocular muscles' actions sometimes seem counterintuitive because they depend on the angle of the eye and the relative position of their insertions.

The frontal eye fields are responsible for voluntary contralateral saccades, while other areas of the cortex, particularly the temporal lobe, control pursuit movements (smooth tracking of moving objects).

The 'Rectus' muscles have the ability to adduct the eye (move it inwards toward the nose), while the 'Oblique' muscles can abduct the eye (move it outwards away from the nose).

Superior muscles can intort the eye, rotating it inwards, while Inferior muscles can extort the eye, rotating it outwards.

The medial longitudinal fasciculus (MLF) is a bundle of nerve fibers that connects nuclei involved in eye movement. This allows for coordinated eye movements by transmitting signals between different brain regions responsible for controlling eye muscles.

Internuclear ophthalmoplegia is a neurological condition caused by damage to the medial longitudinal fasciculus (MLF). It is characterized by difficulty moving one eye to the side contralateral (opposite) to the lesion, with a jerky movement (nystagmus) in the other eye.

Damage to the MLF results in a contralateral effort nystagmus, where the eye opposite the lesion shows involuntary jerky movements when attempting to look towards the lesion. This is because the signal from the brain about where to look is not properly transmitted to the eye muscles.

Internuclear ophthalmoplegia is often seen in individuals with multiple sclerosis, as the MLF is highly myelinated. The myelin sheath, which surrounds the nerve fibers, is often damaged in multiple sclerosis, leading to disruption of signal transmission.

The oculomotor nucleus is a group of neurons located in the midbrain that plays a crucial role in controlling eye movements. It receives input from the frontal eye fields and the paramedian pontine reticular formation (PPRF), which are involved in planning and initiating eye movements.

The trochlear nucleus is a midbrain nucleus responsible for controlling the superior oblique muscle, which is a muscle that rotates the eye inward (intorsion) and helps to depress the eye, particularly when it is turned inward (adducted).

The abducens nerve (CN VI) originates in the pons and innervates the lateral rectus muscle, which is responsible for moving the eye outwards. Damage to the abducens nerve can result in difficulty turning the eye outwards towards the side of the lesion, a condition called abducens nerve palsy.

The oculomotor nucleus receives input from the frontal eye fields, which are located in the frontal lobe of the brain. These fields play a crucial role in planning and initiating voluntary eye movements.

The Medial and Lateral Rectus muscles are the only extraocular muscles whose actions remain constant regardless of the eye's position. They always adduct (move inwards) or abduct (move outwards) the eye, respectively.

The other four extraocular muscles (Superior Rectus, Inferior Rectus, Superior Oblique, and Inferior Oblique) have actions that are dependent upon the eye's current position. They may cause intorsion, extorsion, adduction, or abduction depending on where the eye is pointed.

The actions of the extraocular muscles can be counterintuitive because they depend on the angle of the eye and the relative position of their insertions. For example, the superior oblique muscle may cause intorsion when the eye is adducted but cause depression when the eye is abducted.

The frontal eye fields are the primary cortical center responsible for generating voluntary saccades (quick, jerky eye movements) on the opposite side of the body. The posterior temporal lobe is primarily involved with controlling pursuit movements (smooth, tracking movements of the eye).

Adduction is when a muscle moves the eye inwards, towards the nose. Abduction is when a muscle moves the eye outwards, away from the nose.

Intorsion is when a muscle rotates the eye inward, towards the nose. Extorsion is when a muscle rotates the eye outward, away from the nose.

The oculomotor nerve (CN III) originates from the midbrain, specifically at the level of the superior colliculus. It controls most extraocular muscles (eye movement) and the levator palpebrae superioris muscle (eyelid raising). The Edinger-Westphal nucleus within CN III is responsible for pupillary constriction and accommodation.

Oculomotor nerve injury can lead to three main signs: ptosis (drooping eyelid), exotropia (eye turning outwards), and mydriasis (pupil dilation). Ptosis happens due to levator palpebrae superioris muscle dysfunction. Exotropia occurs because of extraocular muscle loss. Mydriasis is caused by parasympathetic function loss from the Edinger-Westphal nucleus.

A blown pupil refers to an enlarged, unresponsive pupil to light. It usually happens when a lesion affects the superficial autonomic fibers of CN III before damaging deeper motor fibers. This is often seen in uncal herniation, where pressure is applied to the nerve.

Pupil-sparing ophthalmoplegia is when the motor fibers of the oculomotor nerve are more affected than pupillary fibers, leading to eye muscle paralysis but a normal pupil. This suggests the damage is deeper, affecting motor fibers more. Internal nerve diseases or vascular disorders are often the cause.

The trochlear nerve (CN IV) originates from the midbrain at the level of the inferior colliculus. It controls the contralateral superior oblique muscle, meaning the left trochlear nerve controls the right superior oblique muscle, and vice versa.

The superior oblique muscle, innervated by the trochlear nerve (CN IV), is responsible for intorsion (rotating the eye inward) and depression (downward movement) of the eye, especially when it's turned inward (adducted).

Damage to the trochlear nerve (CN IV) results in the affected eye being unable to properly depress and intort when turned inward (adducted). This leads to the eye drifting upwards and outwards. A common sign is a head tilt away from the affected eye, to compensate for this deviation.