Download Brainstem parts External features

Brainstem (L13-L14)
Localization
-posterior cranial fossa (transverse section)
-neighbors  rostral – diencephalon; caudal – spinal cord; dorsal – cerebellum;
ventral – clivus; lateral – temporal lobe, cerebellum
midsaggital section
Brainstem parts
External
features
-apparent origin of cranial nerves  called apparent b/c the nerves actually originate
in a nucleus
-summary  exit/entrance from/to the brainstem
*oculomotor n (III) – ventral, from interpeduncular fossa (mesencephalon)
*trochlear n (IV) – dorsal, from the quadrigeminal plate (mesencephalon)
*trigeminal n (V) – ventro-lateral pons
*abducent n (VI) – ventral, in the ponto-medullary junction, above pyramids
*facial n (VII) – ventro-lateral, ponto-medullary junction
*vestibulocochlear n (VIII) - ventro-lateral, ponto-medullary junction
*glossopharyngeal n (IX) - ventro-lateral, ponto-medullary junction
*vagus n (X) – medulla, dorso-lateral sulcus, behind the olive
*accessory n (XI) – medulla, multiple radices in the dorso-lateral sulcus of the spinal
cord
*hypoglossal n (XII) – medulla, ventro-lateral sulcus, in front of the olive
Internal
features
-mesencephalic nuclei  both nuclei are part of the extrapyramidal system
-ascending (sensory) tracts
Lateral view
ventral view
-descending (motor) tracts
Lateral view
-cerebellar tracts
ventral view
Reticular
formation
Rostral reticular -the consciousness system  ascending reticular activation system
formation
-coma  caused by dysfunction of the upper brainstem RF & related structures, or
dysfunction of extensive bilateral regions of the cerebral cortex
-major inputs:
-Arousal circuits:
CHOLINERGIC PROJECTION SYSTEM
-neurotransmitter  acetylcholine
-role  alertness, memory, learning
-problems  delirium, Alzheimer’s memory loss
DOPAMINERGI PROJECTION SYSTEM
-neurotransmitter  dopamine
-role  movements, initiative, working memory
-problems  Parkinson’s disease, addiction & hallucination
NORADRENERGIC PROJECTION SYSTEM
-neurotransmitter  norepinephrine
-role  modulation of attention, sleep-wake states, mood elevation
-problems  attention-deficit disorder, narcolepsy, depression, anxiety
SEROTONINGERGIC PROJECTION SYSTEM
-neurotransmitter  serotonin
-role  alertness, mood elevation, breathing control, temperature regulation
-problems  obsessive-compulsive disorder, depression, anxiety, aggression, eating
disorders, SIDS
SLEEP-WAKE CYCLE
Caudal reticular RESPIRATORY CONTROL
-nucleus solitaries – cardiorespiratory nucleus  also controls HR & BP
formation
Pathways
-beginning (motor) and the end (sensory) of the pathways  cortical areas
-somatotopy of the cerebral cortex – homunculi
Ascending
sensory
-receptors
-overview of pathways
LESIONS IN THE CENTRAL SENSORY PATHWAYS
-(1), (2) cortical & subcortical lesions  paresthesia (tingling) and numbness in
corresponding regions on the opposite side
-(3) Subthalamic lesion: all sensations abolished in the contralateral half of the body
-(4) Partial lesion sparing pain and temperature pathways: hypesthesia (decreased
tactile sensation) on contralateral side
-(5) Trigeminal lemniscus and lateral spinothalamic tract: loss of pain and
temperature sensation in the contralateral half
-(6) Medial lemniscus and anterior spinothalamic tract: all sensory qualities on the
opposite side of the body are abolished
-(7) Trigeminal nucleus, spinal trigeminal tract and lateral spinothalamic tract: pain
and temperature sensation loss on the ipsilateral side of face and contralateral side
of the body
-(8) Posterior funiculi: ipsilateral loss of position sense, vibration sense, two-point
discrimination, ipsilateral sensory ataxia
-(9) Posterior horn: ipsilateral loss of pain and temperature sensation, dissociation
sensory deficit
-(10) Dorsal root lesion: ipsilateral sensory disturbances from pain to complete loss
of sensation
Descending
motor
-origin of the movements
LESIONS IN THE CENTRAL MOTOR PATHWAYS
-(1) Cortex: flaccid and partial paralysis (paresis) of the muscles represented in the
affected area
-(2) Internal capsule: chronic, contralateral, spastic hemiplegia (complete paralysis)
-(3) Cerebral peduncles: contralateral spastic hemiparesis
-(4) Pons: contralateral hemiparesis or bilateral paresis (size dependent)
-(5) Pyramid: flaccid contralateral paresis
-(6) Cervical spinal cord: ipsilateral spastic hemiplegia
-(7) Thoracic spinal cord: ipsilateral spastic paralysis of the leg
-(8) Peripheral nerve: flaccid paralysis
-spastic paralysis  extrapyramidal lesion!