B3- Ascending and descending pathways

Question 1

Name the 3 ascending (sensory) tracts

Answer 1

Spinothalamic
Dorsal columns (medial lemniscus pathway)
Spinocerebellar

Question 2

Which sensations do the spinothalamic tracts transmit?

Answer 2

Lateral= pain and temperature
Anterior= crude touch and pressure

Question 3

Where do the neurones synapse within the spinothalamic tract?

Answer 3

1: First-order neurone = dorsal root ganglion - substantia gelatinosa
2: Decussates within the spinal cord, passing the ventral white commissure
3: Second-order neurone = ventral posterior nucleus of the thalamus
4: Travels through internal capsule
5: Third-order neurone = primary sensory cortex

Question 4

Which sensations do spinocerebellar tracts transmit?

Answer 4

Unconscious proprioceptive information - helps coordinate movement.
Transmits information from muscle spindles, mechanoreceptors (e.g. golgi tendon organs) and tactile receptors –> cerebellum

Question 5

What are the 4 types of spinocerebellar tracts and where do they transmit information from?

Answer 5

• Dorsal spinocerebellar = lower limbs, ascends ipsilaterally to cerebellum via inferior peduncle
• Ventral spinocerebellar = lower limbs, decussates twice to cerebellum via superior peduncle
• Rostral spinocerebellar = upper limbs, ascends ipsilaterally to cerebellum, mostly via inferior peduncle
• Cuneospinocerebellar = upper limbs, ascends ipsilaterally to cerebellum, via inferior peduncle

Question 6

Which sensations do the dorsal columns transmit?

Answer 6

Information of fine touch, proprioception or vibration.
Fasicuclus cuneatus = sensation from upper limb (T6 and above)
Fasciculus gracilis = sensation from lower limb (lower than T6)

Question 7

Where do neurones synapse within the dorsal column?

Answer 7

1: First order neurone = fasciculus cuneatus in lateral dorsal column, fasciculus gracilis in medial dorsal column
2: Second order neurone= nucleus gracilis or cuneatus in the medulla
3: Decussate as internal arcuate fibres, then travel in contralateral medial lemniscus
4: Third order neurone= ventral posterior nucleus of thalamus
5: Ascend through internal capsule to terminate at sensory cortex

Question 8

Name the 6 descending (motor) tracts

Answer 8

Extrapyramidal:
- Vestibulospinal
- Reticulospinal
- Rubrospinal
- Tectospinal
Pyramidal:
- Corticospinal
- Corticobulbar

Question 9

What are the 2 main types of descending tracts? How are they distinguished?

Answer 9

Extrapyramidal tracts: go from brainstem to the spinal cord
Pyramidal tracts: from cortex to brainstem and spinal cord

Question 10

What information do extrapyramidal tracts transmit?

Answer 10

Involuntary and automatic control of musculature, i.e. muscle tone, balance, posture and locomotion

Question 11

What information do pyramidal tracts transmit?

Answer 11

Voluntary control of musculature of the body and face

Question 12

What is the role of the vestibulospinal tract?

Answer 12

Transmits information about balance and posture by innervating anti-gravity muscles, including arm flexors, leg extensors

Question 13

What is the pathway of the vestibulospinal tract? Does it provide ipsilateral or contralateral innervation?

Answer 13

1: Arises from vestibular nuclei in pons and medulla, receiving inputs from balance organs
2: Tracts convey information to the ipsilateral spinal cord
= Ipsilateral

Question 14

What are the 2 reticulospinal tracts and what is their role?

Answer 14

Medial reticulospinal tract= from pons
- Facilitates voluntary movement and increases muscle tone

Lateral reticulospinal tract= from medulla
- Inhibits involuntary movements and decreases muscle tone

Question 15

Do reticulospinal tracts provide ipsilateral or contralateral innervation?

Answer 15

Ipsilateral

Question 16

Which reticulospinal tract has bilateral axons?

Answer 16

Lateral reticulospinal

Question 17

What is the role of the rubrospinal tract?

Answer 17

Role in fine control of hand movements and tone of limb flexors

Question 18

What is the pathway of the rubrospinal tract? Does it provide ipsilateral or contralateral innervation?

Answer 18

1: red nucleus of midbrain
2: fibres decussate in ventral tegmental decussation
3: descend to spinal cord
= Contralateral innervation

Question 19

What is the role of the tectospinal tract?

Answer 19

Coordinates movement of the head in relation to visual stimuli

Question 20

What is the pathway of the tectospinal tract? Does it provide ipsilateral or contralateral innervation?

Answer 20

1: superior colliculus of midbrain
2: neurons decussate in dorsal tegmental decussation
3: descend to the cervical spinal cord
= Contralateral innervation

Question 21

What is the pathway of the corticobulbar tract?

Answer 21

1: UMN arise from precentral gyrus (primary motor cortex)
2: descend through internal capsule to the brainstem, terminating on motor nuclei of cranial nerves
3: synapse with LMN, which projects to the muscles

Question 22

What type of innervation does the corticobulbar tract provide to cranial nerve nuclei?

Answer 22

Mostly bilateral innervation, i.e. for CN III, IV, V, VI, IX, X, XI
Exceptions = CN XII (hypoglossal = contralateral) and CN VII (facial= upper half is bilateral, lower is contralateral)

Question 23

Explain how a left sided lesion of the facial nerve nuclei would affect the muscles of the face

Answer 23

Upper part of the face (above eyes) wont be affected due to bilateral innervation
Lower part of the face (below eyes) would be affected, i.e. weakness or paralysed

Question 24

What is the role of the corticospinal tracts?

Answer 24

Fine, voluntary and skilled movement

Question 25

What is the pathway of the corticospinal tracts?

Answer 25

1: motor cortex, passes corona radiata and internal capsule 2: pass crus cerebri of midbrain, pons and into the medulla 3: Forms 2 columns in the medulla = 'pyramids' - 75-90% decussate = lateral corticospinal tract, which then descend and terminate in the ventral horn -> LMN - 10-25% remain ipsilateral = anterior corticospinal tract, decussate near termination (ventral horn of upper thoracic and cervical spinal cord)

Question 26

Do the corticospinal tracts provide ipsilateral or contralateral innervation?

Answer 26

Fibres innervate contralateral side of spinal cord and movement of contralateral side of body

Question 27

What would a lesion in the corticospinal tracts lead to?

Answer 27

Hemiparesis

Question 28

Which descending tract controls facial and jaw musculature, swallowing and tongue movements?

Answer 28

Corticobulbar (innervates cranial nerve nuclei)