Brainstem (Quiz 3)

All cranial nerve nuclei pass through brainstem except ___ & ___

1 & 2 (olfaction & vision)

brainstem connects rest of CNS & PNS to ____

cerebellum

Brainstem is responsible for basic functions such as

control of cardiac function, respiratory function, sleep, hunger, thirst, etc

Midbrain

smallest part of brainstem (~1.5 cm)

visual, gustatory, co-ordination of movement

important structures of midbrain

• paired crus cerebri

• tectum containing quadrigeminal bodies

• nuclei for cranial nerve III

Paired Crus Cerebri (midbrain)

connect cerebrum with the rest of the CNS and PNS by means of the cerebral peduncles

quadrigeminal bodies (midbrain)

• superior colliculi: visual response

• inferior colliculi: auditory responses

Medial geniculate body (nucleus of thalamus but apparent at this level)

(Midbrain nucleus)

auditory relay

Substantia nigra

(Midbrain nucleus)

supplies dopamine to basal ganglia

Superior colliculus

(Midbrain nucleus)

visual relay (localization of visual stimuli)

Inferior colliculus

(Midbrain nucleus)

auditory relay (localization of sound in space)

Red nucleus

(Midbrain nucleus)

motor coordination; component of extrapyramidal pathway

Oculomotor nucleus (III)

(Midbrain nucleus)

motor innervation medial rectus, superior rectus, inferior rectus, inferior oblique, and levator palpebrae superioris muscles of eye

Edinger-Westphal nucleus (III)

(Midbrain nucleus)

Sphincter muscle of iris

Corticospinal tract

(Midbrain tract)

Motor efferent from cerebral cortex to spinal nerve nuclei

Corticobulbar tract

(Midbrain tract)

Motor efferent from cerebral cortex to brainstem cranial nerve nuclei

Temporopontine fibers

(Midbrain tract)

fibers arising from temporal lobe and terminating in pontine nuclei

Frontopontine fibers

(Midbrain tract)

Fibers arising from frontal lobe, passing through cerebral peduncle and terminating in pons

Medial longitudinal fasciculus

(Midbrain tract)

arises from vestibular nuclei; important for generation of vestibulo-ocular reflex; tract within brainstem connecting III, IV, VI cranial nerves for ocular movement; interacts with VIII vestibular nerve for head-eye movement and coordination; descends to olivary complex as tectospinal and medial vestibulospinal tracts

Medial, spinal lemniscus

(Midbrain tract)

Information from nuclei gracilis and cuneatus of medulla to thalamus

Spinothalamic tract (anterolateral and ventrolateral)

(Midbrain tract)

touch. pain, thermal to ventral posteromedial nucleus of thalamus

Trigeminal lemniscus

(Midbrain tract)

pain, tactile, thermal sense of face to ventroposteromedial nucleus of thalamus

Pons

• bridge

• contains 4 cranial nerve (IV, V, VI, VII) nuclei as well as superior & middle cerebellar peduncle

• cerebellopontine angle

Cerebellopontine angle

juncture off cerebellum and pons

tumors developing here can impact both vestibular (balance) & auditory function

Principle motor nucleus of trigeminal nerve (V)

(Pons nucleus)

motor innervation of muscles of mastication, tensor tympani, and tensor veli palatini

Principle (pontine) sensory nucleus of trigeminal nerve (V)

(Pons nucleus)

Sensory innervation for face and scalp

Mesencephalic nucleus of trigeminal nerve (V)

(Pons nucleus)

Proprioception of muscles of mastication

Abducens nucleus (VI)

(Pons nucleus)

Motor innervation of lateral rectus muscle; rotates eye outward

Facial nucleus (VII)

(Pons nucleus)

Motor innervation of muscles of facial expression; sensory taste information from anterior 2/3 of tongue

Nucleus of trochlear nerve (IV)

(Pons nucleus)

Motor innervation to superior oblique eye muscle to depress eye

Cochlear nuclei (anteroventral, dorsal, posteroventral)

(Pons nucleus)

first relay in brainstem auditory pathways

Vestibular nuclei

(Pons nucleus)

balance and orientation in space

Superior olivary complex (medial superior olive, lateral superior olive), medial nucleus of trapezoid body

(Pons nucleus)

auditory localization of sounds in space

Periolivary nuclei (dorsomedial, dorsal, lateral, medial periolivary nuclei, and nucleus of trapezoid body)

(Pons nucleus)

Auditory sources for olivocochlear bundle (efferent auditory system)

Superior cerebellar peduncle

(Pons tract)

Output of cerebellum; efferent fibers of cerebellothalamic tract; project to thalamus and red nucleus

Anterior (ventral) spinocerebellar tract

(Pons nucleus)

Proprioceptive information to cerebellum via superior cerebellar peduncle

Posterior (dorsal) spinocerebellar tract

Proprioception (muscle spindle and Golgi tendon organ [GTO]) from lower limbs and trunk to cerebellum via inferior cerebellar peduncle

Medial longitudinal fasciculus

(Pons nucleus)

Arises from vestibular nuclei; important for generation of vestibulo-ocular reflex; tract within brain connection III, IV, VI cranial nerves for ocular movement; interacts with VIII vestibular nerve for head-eye movement coordition; descends to olivary complex as tectospinal and medial vestibulospinal tract

Lateral lemniscus

(Pons nucleus)

Auditory tract between cochlear nucleus and inferior colliculus

Middle cerebellar peduncle

(Pons nucleus)

Carries somatic sensory information to cerebellum

Pontocerebellar fibers

(Pons nucleus)

Fibers from pons to cerebellum via middle cerebellar peduncle; input to pons in cerebral cortex

Corticopontine fibers

(Pons nucleus)

fibers from cortex; carry motor plan to cerebellum via pontocerebellar tract

Corticospinal tract

(Pons nucleus)

Motor efferent from cerebral cortex to spinal nerve nuclei

Corticobulbar tract

(Pons nucleus)

Motor efferent from cerebral cortex to brainstem cranial nerve nuclei

Anterior median fissure

(medulla)

continues from spinal cord between the pyramids

Pyramids

(medulla)

pyramidal decussation (lower medulla) is internal where most descending motor fibers from corticospinal tract cross over to opposite sides

Ventrolateral sulcus & dorsolateral sulcus

(medulla)

where CN IX, X, XI, XII exit the medulla

Olive

(medulla)

(inferior olivary nuclear complex - localizing sound in space) is between the ventrolateral and dorsolateral sulci - relay center for motor & proprioceptive information to cerebellum

Reticular formation

(medulla)

extends up to other parts of brainstem

Fasciculus gracilis & fasciculus cuneatus

(medulla)

mediate kinesthetic sense, muscle stretch, & proprioceptive sense

Inferior cerebellar peduncle

(medulla)

communication with crebellum

Cuneate nucleus

Fine touch and proprioception from the upper body

Gracile nucleus

Kinesthetic and light touch information from the lower body

Inferior olivary nucleus

Mediates information from the cerebrum to the cerebellum via the inferior cerebellar peduncle

Hypoglossal nucleus (CN XII)

Motor innervation of tongue muscles

Nucleus ambiguus (CN IX, X, XI)

Motor nucleus for velum, pharynx, and larynx muscles; important for swallowing

Spinal nucleus of trigeminal (CN V)

Mediates touch, pain, and temperature sensation from the face; projects to the ventral posteromedial nucleus of the thalamus

Dorsal motor nucleus of vagus (CN X)

Parasympathetic function for the gastrointestinal tract, lungs, and abdomen

Vestibular nuclei (CN VIII: medial, lateral, inferior, superior)

Project to the cerebellum, oculomotor nerve, and tectum; provide input for position and movement of the body in space

Nucleus solitarius (CN VII, IX, X)

Receives taste information from CN VII and IX; mediates gag and cough reflexes, carotid sinus and aortic baroreceptor reflexes, and chemoreceptor reflexes related to blood oxygen; outputs to the hypothalamus and other centers

Superior and inferior salivatory nuclei (CN VII)

Parasympathetic innervation of the sublingual, parotid, and submandibular glands; lacrimal glands; and mucous membranes of the oral and nasal cavities

Lateral reticular nucleus

Nucleus of the reticular activating system

Inferior cerebellar peduncle

Afferent input to the cerebellum carrying posterior spinocerebellar, cuneocerebellar, trigeminocerebellar, olivocerebellar, and vestibulocerebellar information

Posterior spinocerebellar tract

Conveys proprioception from the trunk and lower limbs to the cerebellum via the inferior cerebellar peduncle

Anterior spinocerebellar tract

Conveys proprioceptive information to the cerebellum via the superior cerebellar peduncle

Spinal lemniscus (spinothalamic tract)

Conveys touch, pain, and temperature information to the ventral posteromedial nucleus of the thalamus

Medial longitudinal fasciculus

Coordinates vestibulo-ocular reflexes and head-eye movements; connects vestibular nuclei with cranial nerves III, IV, and VI; descends to vestibulospinal pathways

Trigeminothalamic tract (spinal tract of CN V)

Carries sensory information from the trigeminal sensory nucleus to the ventral posteromedial nucleus of the thalamus

Medial lemniscus

Contains axons from the gracile and cuneate nuclei

Fasciculus gracilis

Conveys touch, vibration, and pain sensation from the limbs to the gracile nucleus

Fasciculus cuneatus

Conveys touch, pressure, vibration, pain, and proprioception from cervical to upper thoracic regions to the cuneate nucleus

Pyramidal decussation

Site where approximately 75% of corticospinal fibers cross the midline to form the lateral corticospinal tract; approximately 25% remain ipsilateral to form the anterior corticospinal tract

Lateral corticospinal tract

Carries motor commands from the cerebral cortex to spinal nerve nuclei Anterior corticospinal tract

Anterior corticospinal tract

Carries motor commands from the cerebral cortex to spinal nerve nuclei

Decussation of lemnisci

Site where fibers from the cuneate and gracile nuclei cross before reaching their targets

Lateral spinothalamic tract

Conveys pain, touch, and temperature information to the thalamus

Spinotectal tract

Carries sensory information from the spinal cord to the inferior and superior colliculi

Rubrospinal tract

Carries information from the red nucleus toward the spinal cord; facilitates upper-body flexion

Tectospinal tract

Part of the extrapyramidal system; conveys visual orienting information from the superior colliculus to ocular and neck muscles

Tractus solitarius

Conveys descending fibers of cranial nerves VII (facial), IX (glossopharyngeal), and X (vagus) through the medulla