organ systems - brain stem & endocrine

Brainstem 2: Which cranial nerves are primarily involved in controlling eye movements?

CN III (oculomotor), CN IV (trochlear), and CN VI (abducens).

Brainstem 2: What are the six extraocular muscles?

Medial rectus, lateral rectus, superior rectus, inferior rectus, superior oblique, and inferior oblique.

Brainstem 2: What is the primary action of the medial rectus?

Adduction of the eye.

Brainstem 2: What is the primary action of the lateral rectus?

Abduction of the eye.

Brainstem 2: What are the primary actions of the superior rectus?

Elevation of the eye; the lecture describes the recti as agonist/antagonist pairs for vertical movement.

Brainstem 2: What is the primary action of the inferior rectus?

Depression of the eye.

Brainstem 2: What are the primary actions of the superior oblique?

Depression and intorsion of the eye when looking straight ahead.

Brainstem 2: What happens when the superior oblique contracts while the eye is initially turned nasally?

It pulls the eye downward.

Brainstem 2: What happens when the superior oblique contracts while the eye is initially turned temporally?

It intorts the eye without depression.

Brainstem 2: What are the primary actions of the inferior oblique?

Elevation and extorsion of the eye; its action depends on the initial position of the globe.

Brainstem 2: What is the trochlea?

A fibrocartilaginous ring through which the superior oblique passes before turning laterally to insert on the globe.

Brainstem 2: Where is the oculomotor nucleus located relative to the sulcus limitans?

Medial, consistent with the organization of motor regions medial and sensory regions lateral to the sulcus limitans.

Brainstem 2: Which muscles are innervated by the oculomotor nucleus?

Medial rectus, inferior rectus, superior rectus, inferior oblique, and levator palpebrae superioris.

Brainstem 2: What muscle elevates the upper eyelid?

Levator palpebrae superioris.

Brainstem 2: What is the Edinger-Westphal nucleus?

A group of parasympathetic preganglionic neurons near the oculomotor motoneurons that mediates pupillary and accommodation reflexes.

Brainstem 2: What two reflexes does the Edinger-Westphal nucleus mediate?

The pupillary light reflex and the accommodation reflex.

Brainstem 2: What is the pupillary light reflex?

Constriction of the pupil in response to light reaching the retina.

Brainstem 2: What is the pathway from the retina to the pretectal nuclei in the pupillary light reflex?

Visual input from the retina passes via the brachium of the superior colliculus to the pretectal nuclei.

Brainstem 2: Why does illumination of one eye produce both direct and consensual pupillary constriction?

Pretectal nuclei project bilaterally to the Edinger-Westphal nuclei, producing constriction in both the illuminated and opposite eye.

Brainstem 2: What is the direct pupillary response?

Constriction of the pupil on the same side as the illuminated eye.

Brainstem 2: What is the consensual pupillary response?

Constriction of the pupil opposite the illuminated eye.

Brainstem 2: What is the accommodation reflex?

A near-vision reflex involving increased lens curvature, pupillary constriction, and coordinated convergence.

Brainstem 2: What is the medial longitudinal fasciculus (MLF)?

A pathway carrying fibers between nuclei involved in generating eye movements.

Brainstem 2: What is ptosis?

Drooping of the upper eyelid.

Brainstem 2: Why can oculomotor nerve damage cause ptosis?

CN III innervates the levator palpebrae superioris, the main upper eyelid retractor.

Brainstem 2: What sympathetic muscle contributes to upper eyelid retraction?

The superior tarsal muscle (Müller's muscle).

Brainstem 2: What happens with damage to sympathetic innervation of the superior tarsal muscle?

Partial drooping of the eyelid.

Brainstem 2: Where is the trochlear nucleus located?

In the caudal midbrain at the level of the inferior colliculus, just dorsal to the MLF.

Brainstem 2: Which muscle does the trochlear nerve innervate?

The superior oblique muscle on the contralateral side.

Brainstem 2: What is unique about CN IV motor innervation?

It is the only cranial nerve that innervates musculature on the contralateral side.

Brainstem 2: What happens with a trochlear nerve lesion?

Weakness of downward eye movement with vertical diplopia; the affected eye drifts upward.

Brainstem 2: How may patients compensate for vertical diplopia from trochlear palsy?

They may tilt the head forward (tuck the chin) to help fuse the visual fields.

Brainstem 2: How may patients compensate for torsional diplopia from trochlear palsy?

They may tilt the head to the opposite side to help fuse the images.

Brainstem 2: What is the characteristic head posture in trochlear nerve palsy?

Head tilt toward the unaffected side and forward.

Brainstem 2: What is unique about the mesencephalic nucleus of CN V?

It contains unipolar sensory cell bodies with peripheral sensory fibers, making it comparable to a sensory ganglion.

Brainstem 2: What sensory information enters the mesencephalic nucleus of CN V?

Primarily input from muscle and tendon receptors associated with muscles of mastication.

Brainstem 2: Where do central axons of mesencephalic trigeminal neurons project?

Bilaterally to the motor nucleus of CN V.

Brainstem 2: What does the motor nucleus of CN V innervate?

The muscles of mastication.

Brainstem 2: What receptors contribute to the trigeminal chewing reflex?

Receptors in periodontal ligaments and adjacent gingiva that are sensitive to pressure on the teeth.

Brainstem 2: Where does facial touch input prominently project?

The chief sensory nucleus of CN V and also the spinal tract of V to the spinal nucleus.

Brainstem 2: Where does small-fiber pain and temperature information from the face project?

Through the spinal tract of V to the caudal portion of the spinal nucleus, the subnucleus caudalis.

Brainstem 2: What muscle is innervated by CN VI?

The lateral rectus.

Brainstem 2: Where is the abducens nucleus located?

Just beneath the floor of the fourth ventricle.

Brainstem 2: Where does the abducens nerve exit the brainstem?

At the pontomedullary junction, medial to the facial nerve.

Brainstem 2: What does an abducens nerve lesion cause?

Paralysis of the ipsilateral lateral rectus and inability to abduct that eye.

Brainstem 2: What does most of the facial nerve's motor output innervate?

Muscles derived from the second pharyngeal arch, including muscles of facial expression and the stapedius.

Brainstem 2: Where do facial motor fibers originate?

The facial motor nucleus.

Brainstem 2: What parasympathetic fibers does CN VII carry?

Axons of parasympathetic preganglionic neurons whose cell bodies are in the superior salivatory nucleus.

Brainstem 2: What taste information does CN VII carry?

Taste afferents from the anterior two-thirds of the tongue.

Brainstem 2: Where do facial taste afferents terminate?

The rostral portion of the nucleus of the solitary tract.

Brainstem 2: What somatic sensory information does CN VII carry?

Somatic afferents from a restricted portion of the external ear.

Brainstem 2: What is the lacrimation reflex?

A reflex causing tear secretion in response to irritation of the eye.

Brainstem 2: What nerve carries the afferent limb of the lacrimation reflex?

The ophthalmic branch of CN V.

Brainstem 2: Where do parasympathetic fibers for the lacrimation reflex synapse?

In the pterygopalatine ganglion.

Brainstem 2: What is the corneal reflex?

Touching the eye activates CN V afferents, which ultimately activate bilateral facial motoneurons to produce a blink.

Brainstem 2: Which muscle closes the eye during the corneal reflex?

Orbicularis oculi.

Brainstem 2: Why is the blink bilateral when one eye is touched?

Spinal trigeminal nucleus neurons bilaterally activate motoneurons in the facial motor nuclei.

Brainstem 2: What type of nerve is CN VIII generally considered?

Sensory, although it also carries efferent fibers that innervate hair cells.

Brainstem 2: Where do vestibular afferents terminate?

In the superior, lateral, medial, and inferior vestibular nuclei.

Brainstem 2: Where do auditory afferents terminate?

In the dorsal and ventral cochlear nuclei of the rostral medulla.

Brainstem 2: Why are vestibular and cochlear nuclei located laterally in the brainstem?

They process somatic afferent inputs.

Brainstem 2: What visceral sensory information does CN IX carry?

Afferents from the carotid body, carotid sinus, middle ear mucosa, pharyngeal walls, and posterior third of the tongue.

Brainstem 2: Where do most CN IX visceral sensory afferents terminate?

They enter the solitary tract and synapse in the nucleus solitarius.

Brainstem 2: What taste information does CN IX carry?

Taste from the posterior third of the tongue.

Brainstem 2: What parasympathetic function does CN IX carry?

Parasympathetic fibers for the parotid gland.

Brainstem 2: Where do CN IX parasympathetic fibers arise?

From scattered cells in the rostral medullary reticular formation collectively called the inferior salivatory nucleus.

Brainstem 2: What muscle does CN IX motor output innervate?

Stylopharyngeus.

Brainstem 2: What is the function of stylopharyngeus?

It helps elevate the pharynx during swallowing and speaking.

Brainstem 2: What nucleus gives rise to CN IX stylopharyngeus motor fibers?

The nucleus ambiguus.

Brainstem 2: Why is the vagus nerve called 'vagus'?

Vagus is Latin for 'wandering,' reflecting its extensive distribution in the body.

Brainstem 2: What major parasympathetic fibers travel in CN X?

Preganglionic parasympathetic fibers to thoracic and abdominal viscera.

Brainstem 2: Where do most vagal parasympathetic preganglionic neurons originate?

The dorsal motor nucleus of the vagus.

Brainstem 2: Where do vagal parasympathetic fibers to the heart originate?

From preganglionic neurons near the nucleus ambiguus.

Brainstem 2: Where do most vagal visceral sensory fibers terminate?

In caudal portions of the nucleus of the solitary tract after entering the solitary tract.

Brainstem 2: What muscles are innervated by vagal motor fibers from the nucleus ambiguus?

Most striated muscles of the larynx and pharynx.

Brainstem 2: What somatic sensory fibers does CN X carry?

A small collection from the skin of the outer ear.

Brainstem 2: What is the gag reflex?

Pharyngeal stimulation activates CN IX afferents, which engage brainstem nuclei and activate nucleus ambiguus motoneurons controlling pharyngeal muscles.

Brainstem 2: What muscles does CN XI innervate?

Sternocleidomastoid and trapezius.

Brainstem 2: Where are the motoneurons of CN XI located?

In the upper segments of the spinal cord, forming the spinal accessory nucleus.

Brainstem 2: What does CN XII innervate?

The intrinsic muscles and most extrinsic muscles of the tongue.

Brainstem 2: Where is the hypoglossal nucleus located?

From the caudal medulla through most of the rostral medulla.

Brainstem 2: What is the reticular formation?

A diffusely organized area forming the central core of the brainstem.

Brainstem 2: What are the three longitudinal zones of the reticular formation?

The medial zone, lateral zone, and the raphe nuclei near the midline.

Brainstem 2: What neurotransmitter is produced by many raphe nucleus neurons?

Serotonin.

Brainstem 2: What is the main projection role of the medial reticular formation?

It is the source of most long ascending and descending projections and gives rise to reticulospinal pathways involved in motor control.

Brainstem 2: What are major functions of the lateral reticular formation?

Cranial nerve reflexes and visceral functions, including coordination of autonomic responses.

Brainstem 2: What is the ascending reticular activating system (RAS)?

The portion of the reticular formation that provides sustaining input needed for normal conscious cerebral function.

Brainstem 2: What can bilateral damage to the midbrain reticular formation cause?

Prolonged coma.

Brainstem 2: What is Bell's palsy?

An idiopathic facial nerve (CN VII) palsy, likely often associated with viral infection, causing facial paralysis and potentially sensory and parasympathetic deficits.

Brainstem 2: What are common signs of Bell's palsy?

Facial paralysis, inability to close the eyes, and in some cases decreased lacrimation/salivation and loss of taste from the anterior two-thirds of the tongue.

Brainstem 2: How is the facial motor nucleus cortically innervated?

Its dorsal portion receives input from both cerebral cortices, while its ventral portion mainly receives contralateral cortical input.

Brainstem 2: What is central facial palsy (central seven)?

An upper motor neuron lesion affecting facial motor pathways that causes contralateral lower facial paralysis while upper facial motor control remains intact.

Brainstem 2: What can a posterior communicating artery aneurysm cause?

Oculomotor nerve palsy because CN III courses adjacent to the artery.

Brainstem 2: What is the typical eye position in oculomotor nerve palsy?

Down and out.

Brainstem 2: Why does oculomotor palsy produce a 'down and out' eye?

CN III paralysis leaves the superior oblique (CN IV) and lateral rectus (CN VI) as the intact major extraocular muscles.

Brainstem 2: What eyelid finding occurs with oculomotor palsy?

Ptosis due to loss of levator palpebrae superioris innervation.

Brainstem 2: What pupil finding occurs with oculomotor palsy?

Mydriasis (pupillary dilation) due to loss of parasympathetic input to the sphincter pupillae.

Brainstem 2: Why can a 'blown pupil' be an early sign of oculomotor palsy?

The parasympathetic fibers course in the outer portion of the oculomotor nerve and can be affected by compression.

Endocrine Control & Hypothalamus: What are hormones?

Chemical messengers secreted into the blood by endocrine cells or specialized neurons.

Endocrine Control & Hypothalamus: What are three basic ways hormones act on target cells?

They control the rate of enzymatic reactions, control transport of molecules across cell membranes, or control gene expression and synthesis.