Brainstem: Internal Features Flashcards
1
Q
Main Components of Brainstem
A
- cranial nerve nuclei and related
- long tracts
- cerebellar circuitry
- reticular formation and related structures
2
Q
Brainstem Lesions
A
- 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
3
Q
Brainstem Sections
A
- 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
4
Q
Orientation in Midbrain Axial Slices
A
- 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)
5
Q
Midbrain-Tectum
A
- 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
6
Q
Midbrain-Tegmentum
A
- 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
7
Q
Orientation in Pons Axial Slices
A
- pons “bridge”
- 4th ventricle: separates tegmentum from cerebellum
- lateral: middle cerebellar peduncle
- ventral: basis pontis-corticospinal tracts, corticobulbar tracts, pontine nuclei-cerebellar function
8
Q
Pons
A
- 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
9
Q
Orientation in Medulla Axial Slices
A
- 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
10
Q
Medulla-Caudal
A
- caudal medulla: junction of medulla and spinal cord
- decussation of pyramids
- trigeminal sensory nuclei
11
Q
Medulla-Rostral
A
- ventral surface of pyramids are still prominent
- inferior olivary nucleus
- vestibular nuclei
- inferior cerebellar peduncle
- cochlear medulla
12
Q
Inferior Olivary Nucleus
A
- 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
13
Q
Vestibular Nuclei
A
- 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
14
Q
Inferior Cerebellar Peduncle
A
- olivocerebellar fibers
- connections between vestibular nuclei and cerebellum
- fibers of ventral and dorsal spinocerebellar tracts
15
Q
Reticular Formation
A
- 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
16
Q
Reticular Formation and Tracts
A
- 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)
17
Q
Reticular Formation and Afferents
A
- receives a great variety of afferent information
- integrates this information
- disperses the efferents widely, influencing almost all parts of CNS: reticulospinal, reticulobulbar, reticulothalamic
18
Q
What Bypasses Retifcular Formation
A
- 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
19
Q
Safety Mechanism of Reticular Formation
A
- 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
20
Q
Reticular Formation-Raphe Nuclei
A
- 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
21
Q
Destruction in Reticular Formation
A
- 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
22
Q
Horner’s Syndrome
A
- 3 cardinal symptoms
- anhidrosis: inability to sweat normally
- ptosis: drooping of eyelids
- miosis: excessive constriction of pupils
23
Q
Odine’s Curse
A
- 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
24
Q
SIDS
A
- defect may be in respiratory centers of medulla
- exact cause not known
25
Q
Bilateral Brainstem Lesion
A
- destruction of vital centers
- respiration/cardiovascular
26
Q
Unilateral Brainstem Lesion
A
- ipsilateral cranial nerve dysfunction (LMN)
- contralateral UE/LE UMN signs
- contralateral hemisensory loss
- ipsilateral coordination deficit
27
Q
Lateral Medullary Syndrome (Wallenberg Syndrome)
A
- 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
28
Q
Bulbar Palsy
A
- medullary
- paralysis of glossopharyngeal, vagus, and hypoglossal resulting in dysphagia and dysarthria
29
Q
Pseudobulbar Palsy
A
- damage to corticobulbar tracts (medullary)
- dysphagia, dysarthria, emotional lability, characterized by exaggerated laughing or crying
- partial interruption of corticobulbar tracts
30
Q
Locked-In Syndrome
A
- 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
31
Q
Decorticate Rigidity
A
- 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
32
Q
Decerebrate Rigidity
A
- 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
