Brainstem pathways, reflexes

• Ascending tracts• 1. going through brainstem

– spinothalamic tract– ant., post., rostral spinocerebellar

• 2. ending in brainstem– Fasciculus gracilis, cuneatus– spinoreticular tract

• 3. beginning in brainstem– medial lemniscus– trigeminal and dorsal trigeminal lemniscus – lateral lemniscus– to cerebellum: olivocerebellar, cuneocerebellar,

pontocerebellar– nigrostriatal tract– Monoaminergic tracts

sensory systemsoverview

somatosensory viscerosensory

protopathic

(organs)

epicritic

proprioceptive

spinothalamic tract+ trigeminal lemniscus

ant. post spinocerebellar

dorsal column/medial lemniscus+ dorsal trigeminal lemniscus

(dorsal column/medial lemniscus)

• 1. Pain

lat. spinothalamictract

receptors:bare nerve endingsnociceptors - polymodal

thin myelinated fibers:

A-delta, in the beginningsharp, sudden pain(neo-spinothalamic)

unmyelinated C fibers:for a longer time,more dull pain(paleo-spinothalamic)

tickling itching

spinothalamic modalities

• 2. Temperature

lat. spinothalamic tract

warm receptors:

free nerve endings

C fibers

(active: 35-45 oC)cold receptors: bare (free) nerve endingsA delta fibers, aktiv: <35 oC, >45 oC (!)(Paradox: goosebumps in hot water!)

• 3. Crude touch, non-discriminative touch

crude touchwithout exactlocalization

sexual stimuli

anterior spinothalamic tract

now you can see why simply “touch” is not enoughis carried by both pathways, just different kind of touch!!!

it is a more “primitive” sensory system, develops earliera crude impression from surroundings

• 4. viscerosensory fibers run in spinothalamicsystem – poor localization!!!

epicritic sensibility/dorsal column medial lemniscus modalities

fine touch-discriminative touch(2-point discrimination) pressure,vibration

EXACT localization

Two main somatosensory systems

1. Posterior column-medial lemniscussystem (DCML) – conveys vibration, fine touch,proprioception, pressure

2. Spinothalamic – anterolateral system– conveys pain, temperature, crude touch

the two sensory systems converge, and reach thalamus together - end in VPL

spinal cord

Medulla

Medulla

pons

Mesenc

proprioception

muscle spindle, Golgi tendon organ, (Pacini corpuscles)remember: proprioceptive information:• proprioceptive reflex • spinocerebellar system ant. and post • dorsal column- medial lemniscus system – for LOCALIZATION

and CONSCIOUS BODY POSITION

cerebellar tracts• 3 main inputs to cerebellumall starting or going through brainstem

1. vestibular: vestibulocerebellar tract2. spinal cord: spinocerebellar tracts3. cortex – pons- pontocerebellar tracts

(others:olivocerebellar, reticulocerebellar etc)

brainstem- cerebellum – 3 Pedunculi

face/head area somatosensoryinformation– n. V.

nucl. spinaltract of

n V

princ. nucl..of n V

mesnucl

of n V.

temp, pain, crude touch

vibration, fine touch

proprioceptive

trigeminallemniscus

dorsalistrigeminallemniscus

face – nervus V.

trigeminal lemniscus joinsspinothalamic tract

proprioceptive sens.mesencephalic nucleusn. V. trigeminal lemniscus and

dorsal trigeminal lemniscuscan be called together astrigeminothalamic tract

dorsal trigeminal lemniscusjoins medial lemniscus

Examination

pain (pinprick test)–spinothal.

2-point discriminationfine touch - DCML

VibrationDCML

graphesthesiaDCML

temperaturespinothal.

http://www.prohealthsys.com/physical/sensory.php

cottontip-light touchnot specific for eitherpathway!!!

position senseDCML

Spinocerebellar contra dorsal column ataxia

spinocerebellar:

always ataxia

dorsal column:

increased ataxiain darknessor closing the eyes

visual inputcan compensate

Romberg test positive

blind and deaf– what remains?Helen Keller- a true storyonly somatosensory info

today: pregnancyviral infections –eg. CMV, rubella

At the age of 18 months, encephalitis??, is left blind and deafthe family found a teacher when she was 6, she taught her with drawingon her hand!! , Helen did her doctoral thesis (!!) in comparative literature

descending tracts

somatomotorvisceromotor

from motor centers from autonomic centers

Hypothalamus

hypothalamospinal tract

spinal cord lateral horn

-pyramidal tract

-other motor tracts-1. rubrospinal-2. tectospinal-3. vestibulospinal-4. reticulospinal-5. olivospinal

brainstem

• descending tracts• 1. going through brainstem

– corticospinalis (pyramidal tract) – hypothalamospinal

• 2. ending in brainstem– corticonuclear tract (pyramidal tract)– corticopontine– corticorubral

• 3. ending in brainstem– tectospinal– vestibulospinal– rubrospinal– reticulospinal– monoaminergic tracts (eg. raphespinal)

medial longitudinal fascicle / begins and ends in brainstem, both ascending and descending

PyramisDecussatio pyramidorum

Medulla Oblongata:

Capsulainterna

spinal cord: Neuron 2. interneuron (10% direct motoneuron)Neuron 3. Motoneuron – ant. horn

motor cortex(Br 4,6, 3,1,2):

Neuron 1

Mesencephalon:Pedunculuscerebri

Neuron 2. brainstemmtor brainstem nucleiV → masticationVII → facial expressionIX, X → pharynx, larynxXII → tongue

corticonuclear(corticobulbar,

corticomesencephal.

Tr. corticospinalis- cruciatus (oldalköteg)- directus (elülső köteg)

1. pyramidal tract

MesencephalonCrus cerebriMitte

Pons:Basis

Medulla:Pyramis

Medulla:Decussatio

Tr. cortico-spinalislat/cruciatus

Tr. corticospinalis ant/directus

spinal cord

corticospinal tract – gors through brainstem

• central lesion:– spastic paralysis– Babinski Reflex– contra- or ipsilateral

depends on the lesion site

Decussatio

facial n. trigeminal n.corticonuclear (corticomesencephalic, corticobulbar)

partially bilateral innervation!!

n. X n. XII

clinical

• central lesion:= supranuclear• peripheral= in nucleus or after

facial nerve palsy

central

peripheral

facial nerve palsy

central – contralateral, BUT

forehead, m. orbicularis oculi functionsperipheraltotal ipsilateral palsy

eg. internal capsule lesion eg. inflammation in facial canal, acustic neurinoma.

examples

other cranial nerve palsy: IX, X, XII

„Extrapyramidal” tract

proximál muscles

mimic

tone

automatic movements (driving)

1. rubrospinal – nucleus ruberstimulates flexorsinhibits extensorswith the pyramidal tract responsible for FiNEmovements

bigger role in an alreadylearnt movement

2. tectospinal tract Retina

Colliculus superior

spinal cord

Tractustectospinalis

Tr. opticus

HAMM...

head movesto visual stimuli

•lateral vestibulospinal tract:from nucleus vestibularis lateralis –all through spinal cordstimulates extensorpostural stabilization

3. vestibulospinas

•medial vestibulospinal tract:

nucleus vestibularis medialis, only cervical and upper thoracal spinal cordcoordinates head movements

4. reticulospinal –Formatio reticularis (Pons, Medulla)

medialis : pons

tone, reflexes

bilateral

lateralis: medulla

brainstem reflexes

1. monosynaptic, proprioceptive reflex:

nucleusmesencephalicusn. trigemini (V)

PonsNucleusmotorius

n. trigemini (V)

Receptor:masseterspindle

afferent(N. V/3)

efferentsN. V/3

masseter reflex

2. polysynapticreflexes

-autonomic reflexes:see reticular formationrespir, cardiac, vomiting etc

Facial reflexesCornea Reflexafferent: N. V/1

strong light:Afferent: optic nerve-Colliculus superior-n. facialis nucleus

both casesefferents: facial nerve– reflectoryclosing of eyes(M. orbicularis oculi – Pars palpebralis, Pars orbitalis)

strong light

Medialis Medulla syndrome

Nucl. XII: ipsilateralis tongue deviation (m. genioglossus)pyramidal tract: paralysis (before crossing - contralateral)medial lemniscus – after decussation – contralateral epikritic sensibility loss

Wallenberg syndrome: lateral part of medulla, posterior inferior cerebellar artery

Locked in syndromepons basis lesion: motor functions lost, except n III, IV sensory intact

Pons

ALS: amiotrophic lateralsclerosis- degeneration of motoneurons in spinal cord AND brainstem

Tractography – shows tracts

END