Neuro: Lesions Of Motor & Sensory Pathways

Front 1

Grey and White Matter parts, CNS vs PNS

and exception

Back 1

Grey matter - cell body - cortex, nucleus (CNS group of cell bodies), or Ganglion (PNS group of cell bodies)

White matter - myelinated axon. Nerves (PNS) or Tracts (CNS). Grouped into fasciculus/funiculus

EXCEPTION: Basal ganglia are major subcortical nuclei in the brain (CNS) but called ganglion still

Front 2

Lemniscus and Peduncle

Back 2

Lemniscus is a flat or ribbon-like fiber tract

Peduncle is a massive group of fibers that can be multiple tracts together - gross feature not a pathway

Front 3

Tract naming

Back 3

Origin to destination

i.e. corticospinal (cortex to spineal cord), mamillothalamic (mamillary bodies to thalamus), spinocerebellar (spinal cord to cerebellum), corticobulbar (cortex to brain stem)

Front 4

"Big Four" Pathways and general function

Back 4

Corticospinal tract - voluntary motor

Dorsal column/medial lemniscus - fine touch (discriminative/non painful), vibration, conscious proprioception (knowing where limbs are in dark)

Spinocerebellar tract (dorsal) - unconscious proprioception

Spinothalamic tract - pain and temperature

Front 5

What four things can C6 refer to

Back 5

Spinal cord level
vertebral segment
dermatome ("sensory level")
Myotome ("motor level")

Front 6

Corticospinal tract pathway start to finish

Back 6

First order neuron (upper motor neuron) originates in precentral gyrus (motor)

Passes through internal capsule and 90% decussates (passes to other side gradually) in CAUDAL MEDULLA to lateral corticospinal tract

10% or so undecussated and go to anterior corticospinal tract

Synapse on second order neuron (lower motor neuron) in ventral gray of cord

Second motor neuron innervates muscle

*Internal capsule is just a landmark NOT part of path.

Front 7

Motor Homonculus

Back 7

Motor innervation to body around precentral gyrus. Based on complexity not size.

Goes toes to trunk then shoulder and elbo then wrist to hand to pinky finger to thumb

Then to neck then brow then eyelid, eyeball, face, lips, jaw

then Jaw, tongue, swallowing

Dispraportionately high amount for HANDS, FACE and SWALLOWING

Buried more medial than toes area is an area muscles for genital sphincters or voluntary anal sphincters

ALL VOLUNTARY MOTOR

Front 8

Upper and Lower Motor Neuron with Sensory Neuron connections

Back 8

Upper Motor Neuron - motor cortex to ventral gray horn. Modulatory influence on stretch reflex ar

Lower Motor Neuron - ventral grey horn to NMJ, EFFERENT of stretch reflex arc, MAINTAINS TONE

Sensory Neuron - Stretch receptor in muscle and tendon. MAINTAINS TONE, AFFERENT of arc. Synapses with lower motor neuron and Brain and muscle.

Front 9

Neurons that maintain tone of a muscle

Back 9

Lower Motor Neuron and Sensory Neuron

Upper can modulate the influence

Front 10

Maintenance of Tone in Upper Motor, Lower Motor, and Sensory Neuron

Back 10

Input from stretch receptors causes lower motor neuron to supply tonic stimulation to the muscle

The upper motor neuron modulates this and tends to "override" the tonic signal from sensory neuron

Front 11

Reflex Arc Upper Motor, Lower Motor, and Sensory Neuron

Back 11

Afferent Sensory Neuron detects sudden stretch

Signal is strong and results in strong response from lower motor neuron

Strong signal usually overcomes mild cortical input from UMN

Front 12

Upper Motor Neuron Lesion Signs and Why

Back 12

Spastic paresis - paralysis or weakness due to the hypertonia, contracture is the extreme

Hypertonia

Hyperreflexia - exaggerated reflex

No muscle atrophy - constant workout

Positive Babinski test



Because loss of voluntary UMN signal and modulation of tone and reflexes by UMN, circuit of Sensory and LMN is unchecked so exaggerated LMN response

Front 13

Lower Motor Neuron Lesion Signs and Why

Back 13

Flaccid paresis/parlysis

Muscle fasciculations - due to random firing, mini twitches (vs constant contract)

Hypotonia - gooey

Hyporeflexia

Muscle atrophy - less tone = less exercise

Negative Babinski



Because loss of LMN for voluntary movement, and loss of efferent component of reflex arc and tone pathway.


Only works when actively tell it (UMN override) to work so no tone and loss of strength and function

Front 14

Babinski's Sign

Back 14

Stimulation to sole of foot leading to toes curling downward.

ABNORMAL FINDING

If toes curl upward (dorsiflex) suggests UMN inhibition is removed (UMN lesion) and POSITIVE BABINSKI

Front 15

Spasticity and Clonus

Back 15

Spasticity - increased muscle tone and increased reflex contraction (UMN)

Clonus - rhythmic contractions (shaking) and relaxations seen when a spastic muscle is stretched

Front 16

Corticospinal Tract Injury signs in a) Cortical stroke
b) Brainstem stroke
c) Cervical cord injury
d) Lumbar cord injury
e) Large lumbar cord injury


Spinal Shock caveat

Back 16

UMNs synapse at different levels, will see normal signs if lesion is below synapse level (ie. already LMN started and axon left). LMN signs AT site of lesion (b/c damages LMN there) and UMN lesions below lesion (b/c LMN is fine and UMN is not modulating)

a) All UMN signs
b) All UMN signs
c) No signs to arms (depending on level; low cervical this case), LMN (hypotonia, flaccid paralysis) to hands, and UMN (hypertonia, hyperreflexia) to torso, legs and feet
d) No signs to arm, hand, torso, LMN signs to legs and UMN signs to feet
e) Covers more area, can have normal till legs and feet both having LMN signs b/c the LMN is damaged


Spinal shock - the initial period after an injury, areas BELOW where UMN signs are expected may INITIALLY present as HYPOTONIC, HYPOREFLEXIVE (ie. LMN signs) BUT reflexes and tone gradually RETURNS in exaggerated form of UMN lesion. Can take days to weeks. May incorrectly estimate level

Front 17

Dorsal Columns/Medial Lemniscus Path

Back 17

Discriminating Touch, Conscious Proprioception

Starts at receptor, first order neuron axon enters cord at tract of Lissaur, Legs run in fasciculus gracilis (medial dorsal funiculi), arms run in fasciculus cuneatus (lateral dorsal funiculi)

Synapse on nucleus gracilis and nucleus cuneatus (caudal medulla)

2nd order neuron leaves nucleus, decussates immediately and continues to thalamus (as medial lemniscus- ribbon like).

3rd order neuron runs from thalamus to post central gyrus (sensory cortex) - end of functional system.

Can walk up dermatome to test

Front 18

Sensory Homonculus difference

Back 18

Same order around as motor homonculus. area for genitals and sphincters is larger though (buried inside)

Front 19

Dorsal (Posterior) Spinocerebellar Tract

Back 19

Unconscious Proprioception

Involves Clarke's Column - T1-L3 level. Below runs with fasciculus gracilis (dorsal funiculi) then synapses in Clark's Column. 2nd order neuron joins dorsal spinocerebellar tract

At level of Clark's column synapses in it and joins dorsal spinocerebellar tract

ABOVE Clark's column when enters runs with fasciculus cuneatus and synapes in lateral cuneate nucleus (caudal medulla) and projects to ipsilateral cerebellum


Lateral cuneate nucleus is kind of like a branch of clark's column but runs separately. Goes to cerebellum though


NO REAL DECUSSATION - goes to ipsilateral cerebellum

Front 20

Spinothalamic Tract Path

Back 20

Tract gives more info than others and can resolve localization of lesion ambiguities

Pain and Temperature

First order neurons originate in pain receptors, enter cord at tract of Lissaur, synapse in substantia gelatinosa or nucleus proprius almost immediately

Second order neuron crosses anterior white commisure rising about 1-2 levels and then form contralateral spinothalamic tract to thalamus

3rd order neuron from thalamus projects to cortex (technically tract ends at thalamus but projects to cortex)

Front 21

Best of Big 4 tract to resolve localization of lesion ambiguities

Back 21

Spinothalamic Tract

Front 22

Decussation level of Spinothalamic Tract, Corticospinal Tract, Dorsal Column/Medial lemniscus

Back 22

Spinothalamic - almost immediately as enter cord, occuring at every level

Corticospinal Tract - ALL together at caudal MEDULLA

Dorsal Columns - ALL together at same level

Front 23

Spinothalamic Findings for

a) Cord Transection between L2-L3

b) Cord Hemisection between L2-L3

Back 23

a) complete loss of pain and temperature below L2 BIL

b) Injury loss of pain and temperature only on OPPOSITE side of injury (b/c crosses over AND retained L3 (b/c crosses anterior commisure while rising so L3 preserved ideally if lesion is only in spinothalamic tract (L3 axon would still be in commisure)

Ipsilateral pain and temp preserved