Descending tracts

Question 1

Where are motor neurone cell bodies

Answer 1

Upper: primary motor cortex
Lower: ventral horns of spinal cord or forebrain/brainstem (cranial nerves)

Question 2

Are motor neurones in CNS or the PNS

Answer 2

Upper completely in CNS

Lower cross into PNS to synapse onto muscles

Question 3

Net effect of UMN on LMN

Answer 3

Inhibitory

Question 4

Describe patellar tap reflex

Answer 4

Spindle fibre detects stretch of quadriceps when patellar ligament is tapped.
Afferent neurone synapses onto LMN in ventral horn at L3 spinal level causing quadriceps contraction.
Collateral branch of afferent neurone descends to L5 spinal level and synapses on inhibitory interneurone causing hamstring relaxation via LMN.

Question 5

Describe Babinski’s reflex

Answer 5

Noxious stimulus to plantar aspect of foot (heel to base of toes medially) causes dorsiflexion, hip flexion and knee flexion
Normal in babies but should be inhibited as descending tracts develop. Positive reflex in children or adults suggests UMN damage

Question 6

UMN signs

Answer 6

Hyperreflexia 
Hypertonia - spasticity and clasp knife reflex
Weakness
Babinski sign 
Initial flaccid paralysis

Question 7

What determines direction of spasticity

Answer 7

Direction of stronger muscle in antagonistic pair

Question 8

What is responsible for clasp knife reflex

Answer 8

Golgi neurones stimulate inhibitory interneurones at high force so muscle suddenly gives way

Question 9

Where can LMN get damaged

Answer 9

Cell bodies
Axons
NMJ
Muscle

Question 10

LMN signs

Answer 10

Flaccid paralysis
Hyporeflexia or areflexia
Hypotonia
Muscle wasting 
Fasciculation - uncoordinated muscle contraction
Fibrillation - ectopic APs in muscle

Question 11

Can LMN regenerate

Answer 11

Not if cell body damaged

If cell body intact, Wallerian degeneration occurs and regrowth.

Question 12

What are the extrapyramidal tract functions

Answer 12

Tectospinal tract - tectum assesses danger and directs head movement in response to dangerous stimuli
Rubrospinal tract - only projects to C1-2
Reticulospinal tract - regulates muscle tone and paralyses the body during REM
Vestibulospinal tract - balance and posture

Question 13

What are the pyramidal tracts

Answer 13

Lateral corticopsinal tract 90%

Anterior corticospinal tract 10%

Question 14

Pathway of lateral corticospinal tract neurones

Answer 14

UMN pass through medullary pyramids.
At the decessation of the pyramids the fibres cross to the contralateral side.
Fibres terminate in ventral horns and synapse onto LMN.

Question 15

Pathway of anterior corticospinal tract neurones

Answer 15

UMN pass through the medullary pyramids.
The fibres stay ipsilateral at the decessation of the pyramids.
Fibres cross over at their certain spinal level to synapse on LMN in contralateral ventral horn.

Question 16

Functions of corticospinal tracts

Answer 16

Anterior - posture and peripheral movement

Lateral - precise movement

Question 17

UMN between primary motor cortex and medulla

Answer 17

Neurones form corona radiata which condenses to form the internal capsule
Internal capsule has lentiform nucleus laterally and thalamus medially
Fibres connect to midbrain via cerebral peduncles

Question 18

Describe structure of internal capsule

Answer 18

V shaped in transverse section:
Anterior limb
Genu - corticobulbar tract
Posterior limb - corticospinal tract in topographical organisation

Question 19

CNVII lesion vs stroke

Answer 19

Stroke - contralateral lower half face paralysis due to bilateral innervation to superior facial nerve nuclei
CNVII - ipsilateral upper and lower facial paralysis

Question 20

Blood supply of internal capsule

Answer 20

Middle cerebral artery