B3- Ascending and descending pathways Flashcards
Name the 3 ascending (sensory) tracts
Spinothalamic
Dorsal columns (medial lemniscus pathway)
Spinocerebellar
Which sensations do the spinothalamic tracts transmit?
Lateral= pain and temperature
Anterior= crude touch and pressure
Where do the neurones synapse within the spinothalamic tract?
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
Which sensations do spinocerebellar tracts transmit?
Unconscious proprioceptive information - helps coordinate movement.
Transmits information from muscle spindles, mechanoreceptors (e.g. golgi tendon organs) and tactile receptors –> cerebellum
What are the 4 types of spinocerebellar tracts and where do they transmit information from?
- 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
Which sensations do the dorsal columns transmit?
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)
Where do neurones synapse within the dorsal column?
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
Name the 6 descending (motor) tracts
Extrapyramidal:
- Vestibulospinal
- Reticulospinal
- Rubrospinal
- Tectospinal
Pyramidal:
- Corticospinal
- Corticobulbar
What are the 2 main types of descending tracts? How are they distinguished?
Extrapyramidal tracts: go from brainstem to the spinal cord
Pyramidal tracts: from cortex to brainstem and spinal cord
What information do extrapyramidal tracts transmit?
Involuntary and automatic control of musculature, i.e. muscle tone, balance, posture and locomotion
What information do pyramidal tracts transmit?
Voluntary control of musculature of the body and face
What is the role of the vestibulospinal tract?
Transmits information about balance and posture by innervating anti-gravity muscles, including arm flexors, leg extensors
What is the pathway of the vestibulospinal tract? Does it provide ipsilateral or contralateral innervation?
1: Arises from vestibular nuclei in pons and medulla, receiving inputs from balance organs
2: Tracts convey information to the ipsilateral spinal cord
= Ipsilateral
What are the 2 reticulospinal tracts and what is their role?
Medial reticulospinal tract= from pons
- Facilitates voluntary movement and increases muscle tone
Lateral reticulospinal tract= from medulla
- Inhibits involuntary movements and decreases muscle tone
Do reticulospinal tracts provide ipsilateral or contralateral innervation?
Ipsilateral
Which reticulospinal tract has bilateral axons?
Lateral reticulospinal
What is the role of the rubrospinal tract?
Role in fine control of hand movements and tone of limb flexors
What is the pathway of the rubrospinal tract? Does it provide ipsilateral or contralateral innervation?
1: red nucleus of midbrain
2: fibres decussate in ventral tegmental decussation
3: descend to spinal cord
= Contralateral innervation
What is the role of the tectospinal tract?
Coordinates movement of the head in relation to visual stimuli
What is the pathway of the tectospinal tract? Does it provide ipsilateral or contralateral innervation?
1: superior colliculus of midbrain
2: neurons decussate in dorsal tegmental decussation
3: descend to the cervical spinal cord
= Contralateral innervation
What is the pathway of the corticobulbar tract?
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
What type of innervation does the corticobulbar tract provide to cranial nerve nuclei?
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)
Explain how a left sided lesion of the facial nerve nuclei would affect the muscles of the face
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
What is the role of the corticospinal tracts?
Fine, voluntary and skilled movement
What is the pathway of the corticospinal tracts?
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)
Do the corticospinal tracts provide ipsilateral or contralateral innervation?
Fibres innervate contralateral side of spinal cord and movement of contralateral side of body
What would a lesion in the corticospinal tracts lead to?
Hemiparesis
Which descending tract controls facial and jaw musculature, swallowing and tongue movements?
Corticobulbar (innervates cranial nerve nuclei)
