Session 4 - Pyramidal Tracts

Question 1

What are the two main classes of descending tracts?

Answer 1

Pyramidal tracts

Extrapyramidal tracts

Question 2

What do pyramidal tracts do?

Answer 2

Maintain somatic control of muscle by making direct (monosynaptic) contact with LMN supplying distal muscle of extremities

Question 3

What are the two mains part of the pyramidal tract?

Answer 3

Corticospinal

Corticotubular

Question 4

What are the two different part of the corticospinal tract?

Answer 4

Lateral and anterior

Question 5

Outline the path of the corticospinal tract

Answer 5

 Skeletal Muscle α-LMN
 Lateral decussates in Medullary Pyramids
 Anterior remains ipsilateral

Question 6

Where does the corticotubular pyramid extend to?

Answer 6

 Cranial Nerve Nuclei

Question 7

What are extrapyramidal tracts?

Answer 7

Indirect contact (polysynaptic) with motor neurones, via regulation of ventral horn interneurons.

Question 8

What is the difference in relationships with LMN’s between pyramidal and extra-pyramidal systems

Answer 8

Pyramidal system has direct (monosynaptic) contact with lower motor neurones supplying the distal muscles of extremities (e.g. the hand)

The extra-pyramidal system has an indirect contact with the rest of the motor neurone pool.

Question 9

Give three causes of upper motor neurone lesions

Answer 9

 Stroke
 Spinal cord injury
 Motor neurone disease

Question 10

Give three causes of LMN lesions

Answer 10

 Trauma
 Peripheral neuropathy
 Motor neurone disease

Question 11

Give key signs of UMN lesions

Answer 11

	Hypertonia
	Hyerreflexia
	Clonus
	+’ve Babinski sign
	No fasiculations
	Clasp-knife reflex 
	No muscle wasting
	Muscle weakness

Question 12

Give key signs of LMN lesions

Answer 12

	Hypotonia
	Hyporeflexia
	Fasciculations
	Muscle wasting
	Muscle weakness

Question 13

Where does hypertonia, hyperreflexia and spastic paralysis come from in a UMN lesion?

Answer 13

Loss of descending inhibition of spinal reflexes

Question 14

What is clasp knife reflex?

Answer 14

 Increased tone gives resistance to movement, but when sufficient force is applied resistance suddenly decreases

Question 15

What is clonus caused by?

Answer 15

 Loss of descending inhibition leads to self re-excitation of hyperactive reflexes

Question 16

What is a positive Babinski sign?

Answer 16

 Scrape along lateral edge of foot and in towards great toe
 Dorsiflexion of hallux, extension/flaring of toes (Loss of descending inhibition means the reflex is unable to be suppressed)

Question 17

What is hypotonia caused by in LMN lesions?

Answer 17

 Lack of LMN means muscle cannot contract to produce tone

Question 18

Name the extra-pyramidal tracts

Answer 18

Tectospinal tract
Vestibulospinal tract
Reticulospinal tract
Rubrospinal and rubrobulbar tract

Question 19

Where does the tectospinal tract arise and what does it do?

Answer 19

– Main inputs are from the superior and inferior colliculi in the midbrain; decussate in the midbrain
– Innervate Motor neurone pools of neck – coordinate eye-head movements, responses to visual & auditory stimuli

Question 20

Where does vestibulospinal tract arise and what does it do?

Answer 20

– Originates from vestibular nuclei in the Pons; remain ipsilateral;
– Innervates motor-neurone pools of anti-gravity muscles - balance reflexes.

Question 21

Where does reticulospinal tract arise and what does it do

Answer 21

– Widespread inputs, including from motor cortex, medulla oblongata, pons and midbrain
- remain ipsilateral
– Medullary (lateral tract) - Flexor reflex facilitation
- Extensor reflex inhibition
– Pontine (medial tract) - Extensor reflex facilitation
– Role in regulation of posture and rhythmic movements

Question 22

Where does rubrospinal tract arise and what does it do?

Answer 22

– Originates from red nucleus (tegmentum of the mid-brain at superior colliculus), inputs include motor cortex
- Decussates at level of nucleus
– Control flexor tone in distal muscles, also tone of facial muscles

Question 23

Where do corticospinal tracts arise from?

Answer 23

1/3 motor cortex
1/3 secondary motor cortex
1/3 parietal lobe

(2/3 precentral gyrus, 1/3 post-central gyrus)