Brainstem: Internal Features

Question 1

Main Components of Brainstem

Answer 1

• cranial nerve nuclei and related
• long tracts
• cerebellar circuitry
• reticular formation and related structures

Question 2

Brainstem Lesions

Answer 2

• cranial nerve abnormalities-tract deficits: sensory or motor determines deficit
• long tract abnormalities
• ataxia: unable to control body in space –> clumsy –> poor proprioception
• reticular formation dysfunction: impaired level of consciousness, autonomic dysregulation: could be cardiac pulmonary-altered consciousness coma

Question 3

Brainstem Sections

Answer 3

• tectum: midbrain only-roof made up of superior and inferior colliculi dorsal to cerebral aqueduct
• tegmentum: “covering” ventral to cerebral aqueduct in midbrain, ventral to 4th ventricle in pons and medulla, main bulk of brainstem nuclei and reticular formation
• basis: ventral portion where large collections of corticospinal and corticobulbar tracts lie

Question 4

Orientation in Midbrain Axial Slices

Answer 4

• midbrain…
• cerebral aqueduct
• periaqueductal gray surrounds cerebral aqueduct and does pain modulation
• midbrain reticular formation
• cerebral peduncles: substantia nigra and basis pedunculi
• superior colliculus: rostral-oculomotor nuclei and red nuclei
• inferior colliculi-caudal: trochlear nuclei and brachium conjunctivum (decussation of superior cerebellar peduncles)

Question 5

Midbrain-Tectum

Answer 5

• corpora quadrigemina…
• superior colliculi (control of eye movement): afferents=occipital lobe (corticotectal fibers) and eye field of frontal lobe
• inferior colliculi: afferents=ascending auditory fibers (lateral lemniscus) to thalamus, then to auditory cortex of temporal lobe
• superior: eye movements
• inferior: auditory

Question 6

Midbrain-Tegmentum

Answer 6

• substantia nigra: pars compacta produces dopamine
• red nucleus: involved in motor control; afferents=cerebellum (superior cerebellar peduncles) and motor cortex
• efferents=decussate and travel down rubrospinal tract-inferior olivary nucleus of the medulla at level of superior colliculi

Question 7

Orientation in Pons Axial Slices

Answer 7

• pons “bridge”
• 4th ventricle: separates tegmentum from cerebellum
• lateral: middle cerebellar peduncle
• ventral: basis pontis-corticospinal tracts, corticobulbar tracts, pontine nuclei-cerebellar function

Question 8

Pons

Answer 8

• ventral portion…
• pontocerebellar fibers (responsible for bulbous portion of pons) from the pontine nuclei (ventral pons), decussate and are carried through massive middle cerebellar peduncle to respective cerebellar hemisphere: pontine nuclei help with coordination of movement, receive corticopontine fibers (motor cortex) -coordination of movement
• dorsal portion (tegmentum)…
• superior cerebellar peduncle: consists mainly of ascending cerebellar efferents destined for red nucleus of midbrain and thalamus (coordination of movement)
• middle-messages from pons to cerebellum

Question 9

Orientation in Medulla Axial Slices

Answer 9

• inferior cerebellar peduncles
• pyramidal tracts
• pyramidal decussation
• anterolateral system and medial lemniscus
• rostral medulla: inferior olivary nucleus; 4th ventricle
• caudal medulla: posterior columns, posterior column nuclei

Question 10

Medulla-Caudal

Answer 10

• caudal medulla: junction of medulla and spinal cord
• decussation of pyramids
• trigeminal sensory nuclei

Question 11

Medulla-Rostral

Answer 11

• ventral surface of pyramids are still prominent
• inferior olivary nucleus
• vestibular nuclei
• inferior cerebellar peduncle
• cochlear medulla

Question 12

Inferior Olivary Nucleus

Answer 12

• aids the control of movement
• receives impulses from the sensory and motor cortices and red nucleus of the midbrain (rubrospinal-flexor muscle tone)
• connected to cerebellum through inferior cerebellar peduncle
• coordination and muscle tone

Question 13

Vestibular Nuclei

Answer 13

• receives afferents from vestibular nerve
• links to nuclei that supply extraocular muscles (abducens, trochlear and oculomotor nuclei) through the medial longitudinal fasciculus-coordination of head and eye movements

Question 14

Inferior Cerebellar Peduncle

Answer 14

• olivocerebellar fibers
• connections between vestibular nuclei and cerebellum
• fibers of ventral and dorsal spinocerebellar tracts

Question 15

Reticular Formation

Answer 15

• net like
• central core of nuclei that run entire length of brainstem
• rostral reticular formation: maintain an alert conscious state-work functionally with diencephalon
• caudal reticular formation: working with cranial nerves and spinal cord; motor, reflex, and autonomic functions; also helps to control tone, balance, and posture during movement-regulates CV systems, breathing, sleep-wake and being able to filter incoming stimuli to discriminate irrelevant background stimuli
• treat patients with deficits here in closed environment-quiet rooms without much distraction or stimulation
• complex matrix of neurons
• widespread afferent and efferent connections with other parts of CNS

Question 16

Reticular Formation and Tracts

Answer 16

• receives collaterals from most ascending and descending tracts
• descending reticulospinal tracts originate from the medullary and pontine nuclei of reticular formation: influence muscle tone and posture often times during movement
• ascending fibers from the reticular formation receives information from multiple sensory sources and via the thalamus they help to activate the cerebral cortex and heighten arousal (reticular activating system)

Question 17

Reticular Formation and Afferents

Answer 17

• receives a great variety of afferent information
• integrates this information
• disperses the efferents widely, influencing almost all parts of CNS: reticulospinal, reticulobulbar, reticulothalamic

Question 18

What Bypasses Retifcular Formation

Answer 18

• auditory systems, visual systems, dorsal columns
• can be inferred by startle to loud sound or sudden bright light
• diffuse neuronal network in medullary and pontine reticular formation
• respiratory center: control of respiration
• cardiovascular center: control of cardiovascular function

Question 19

Safety Mechanism of Reticular Formation

Answer 19

• bilateral destruction is generally required to abolish function-cross innervation
• mediates consciousness, attention span, alerting responses, and sleep-wake cycle
• in concert with forebrain…
• control of breathing, pulse, BP, electrolyte imbalance, pupillary size and ocular movements, oxygen and carbon dioxide
• GI and genitourinary system motility
• coughing, sneezing, swallowing, vomiting, hiccupping, gagging, chewing, sucking, feeding
• postural reflexes, extensor and flexor tone, vestibular reflexes, extensor tone and cortically induced movements
• reduces transmission of pain impulses by inhibition of neurons in substantia gelatinosa
• arnold Chiari malformation can compress brainstem resulting in some deficits

Question 20

Reticular Formation-Raphe Nuclei

Answer 20

• NT: serotonin
• ascending fibers to forebrain are involved with sleep
• descending fibers to spinal cord are involved with modulation of pain
• in animal experiments, stimulation of raphe nuclei and periaqueductal grey matter abolishes response to pain

Question 21

Destruction in Reticular Formation

Answer 21

• destruction to rostral pontine reticular formation results in transitory loss of consciousness (short time)
• destruction to rostral midbrain reticular formation results in permanent loss of consciousness
• stimulation will arouse a sleeping animal
• lesions in caudal half result in: respiratory apnea, hypotension, horner’s syndrome (damage to sympathetic pathways)
• respiration: volitional breathing = pyramidal tract; automatic breathing = reticular formation

Question 22

Horner’s Syndrome

Answer 22

• 3 cardinal symptoms
• anhidrosis: inability to sweat normally
• ptosis: drooping of eyelids
• miosis: excessive constriction of pupils

Question 23

Odine’s Curse

Answer 23

• pyramidal tract intact
• reticular formation destroyed
• respiratory arrest during sleep
• must remain awake forever in order to breathe
• aka central hypoventilation syndrome
• congenital or acquired

Question 24

SIDS

Answer 24

• defect may be in respiratory centers of medulla

- exact cause not known

Question 25

Bilateral Brainstem Lesion

Answer 25

- destruction of vital centers | - respiration/cardiovascular

Question 26

Unilateral Brainstem Lesion

Answer 26

- ipsilateral cranial nerve dysfunction (LMN) - contralateral UE/LE UMN signs - contralateral hemisensory loss - ipsilateral coordination deficit

Question 27

Lateral Medullary Syndrome (Wallenberg Syndrome)

Answer 27

- ipsilateral: face pain, dysesthesia, anesthesia, dysphagia, dysarthria, ataxia, dysmetria, intention tremor, Horner's syndrome - contralateral: loss of pain and temperature - general: nausea, vomiting, vertigo, hiccupping

Question 28

Bulbar Palsy

Answer 28

- medullary | - paralysis of glossopharyngeal, vagus, and hypoglossal resulting in dysphagia and dysarthria

Question 29

Pseudobulbar Palsy

Answer 29

- damage to corticobulbar tracts (medullary) - dysphagia, dysarthria, emotional lability, characterized by exaggerated laughing or crying - partial interruption of corticobulbar tracts

Question 30

Locked-In Syndrome

Answer 30

- pontine - complete quadriplegia and bulbar/facial palsy due to complete interruption of both pyramidal tracts: infarct, neoplasm, trauma, or demyelination - ventral pons-bilateral corticospinal and corticobulbar tracts - patient is conscious and mentally intact but can only make vertical eye movements: vertical eye movements are controlled by region in tegmentum in rostral midbrain

Question 31

Decorticate Rigidity

Answer 31

- damage to mesencephalon above red nucleus - disconnection of cortex - disinhibition of red nucleus: increased rubrospinal facilitation to UE - disruption of lateral corticospinal tract = no antagonism for extensor tone from vestibulospinal and pontine reticulospinal in LE resulting in extension - generally comatose - flexing in UE pointing to cortex - arm adduction and forearm pronation, flexion of wrist and elbow, extension of hips and legs

Question 32

Decerebrate Rigidity

Answer 32

- further rostrocaudal deterioration of upper brainstem - red nucleus damaged - more severe than decorticate - vestibular system driven - what happens if decorticate rigidity continues (deterioration continues and damage gets worse usually resulting in death) - comatose - UE extended (adduction, wrist flexion and pronation) - hyperextension of trunks - LE extended/internally rotated - prominent plantar flexion - opisthotonos is severe hyperextension of trunk