AA And DD Tracts

Question 1

What do ascending and descending spinal tracts carry

Answer 1

• AA sensory like pain
• DD motor

Question 2

What do axons gather in

Answer 2

Funiculi which are found in dorsal, lateral and ventral parts of spinal cord

Question 3

Types of AA tracts from spinal to cerebral cortex

Answer 3

• dorsal column medial lemiscus system
• spinothalmic (anterolateral)
• spinocerebella system (most lateral)

Question 4

how to AA travel through each order neurons

Answer 4

• 1st in dorsal root ganglion and gather sensory input
• 2nd in spinal cord or brain stem
• 3rd in thalamus
• 4th in cerebral cortex

Question 5

What are crossings in AA tracts eg from right body to left brain

Answer 5

Decussations which happen at different levels for each tract

Question 6

What does dorsal column medial lemiscus system detect

Answer 6

• vibration, proprioception, 2 point discrimination and touch
• go to 1st order axons from mechanoreceptors, proprioceptors to dorsal root ganglion where 1st order cell bodies reside
• to dorsal column of spinal cord

Question 7

Dorsal column parts for upper and lower

Answer 7

• sensation from lower body form gracilis fascicle (medial part)
• sensation from upper body form cuneate fascicle (lateral part)
  This is topographic organisation
  These go to medulla where gracilis and cuneate nuclei reside

Question 8

AA from nuclei

Answer 8

• synapse on bodies of 2nd order neurons
• these decussate form medial lemniscus to thalamus (ventral posterolateral nucleas)
• synapse on 3rd order neurones
• AA to primary somatosensory cortex which contain 4th order neurones

Question 9

What does spinothalamic/ anterolateral system do

Answer 9

• crude touch from free nerve endings
• pain from nociceptors
• pressure from mechanoreceptors
• temp from thermoreceptors

Question 10

How do AA spinothalamic travel

Answer 10

• 1st order axons to dorsal root ganglion then AA 1 or 2 segments before
• direct or indirectly (via interneurons) synapsing with 2nd order bodies on dorsal/ post horn
• then decussate to form anterior spinothalamic tract (crude touch and pressure) and lateral spinothalamic tract (pain and temp)

Question 11

AA spinothalmic from cord to brain

Answer 11

• via conterlateral spinal cord to conterlateral thalamus (ventral posterior lateral nucleus)
• end by synapsing on 3rd order neurones in nucleas
• 3rd order axons go to cerebrum, primary somatosensory cortex where they synapse on 4th order neurones in nucleas

Question 12

AA spinocerebellar tract

Answer 12

• coordinate mm in trunk and limbs
• unconscious proprioectors like stance and how flexed joints are
• 1st order dorsal root to synapse on grey matter
• make 2 tracts either by desiccating straight away to ventral spinocerebellar tract (most lat ant) or stay on ipsilateral side and make dorsal spinocerebellar tract

Question 13

AA spinocerebellar tract from spinal cord to brain

Answer 13

• ventral to superior cerebellar peduncle then desiccating again to ipsilateral cerebellar cortex where it synapses on neurones in cerebellar cortex
• dorsal never desiccates and AA to inferior cerebellar peduncle ending up same as ventral
  3 not 4

Question 14

Where and upper and lower motor neurones located

Answer 14

• upper in cerebral cortex and deep nuclei of brain stem
• lower in anterior horns of spinal cord

Question 15

What r direct motor pathways (pyramidal tracts)

Answer 15

• fine conscious mm movements
• somatosensory cortex has the primary motor context anterior to it
• this contains pyramidal cells which r upper motor neurones

Question 16

What are anterior corticospinal tract of DD

Answer 16

• controls mm of the trunk
• descends from internal capsule and cerebral peduncle to spinal cord
• runs medial to anterior spinothalamic tract before desiccating to ventral horn for lower motor neurones
• these lead via ventral root and peripheral nerves reach trunk mm

Question 17

Lateral corticospinal tract

Answer 17

• from internal capsule and cerebral peduncle to spinal cord
• always decussates at the medulla (decussation of pyramids)
• continues to to conterlateral spinal cord medial to posterior spinocerebellar tract until synapsing w lower motor neurones in ventral tract
• leave ventral root and peripheral nn and reach mm of extremities

Question 18

Corticobulbar pathway

Answer 18

• starts in motor cortex
• upper motor neurones form corticobulbar tract which travels lateral to corticospinal tract to reach brain stem
• axons depart the tract and synapse directed w conterlateral lower motor neurones for CNV, VII, XI, XII in pons and medulla

Question 19

Corticobulbar pathway from the posterior brain stem- branch into 2 fibres

Answer 19

• some synapse w both ipsilateral and contralateral motor nuclei
• CNV (mastication mm), CNXI (neck mm), part of CNVII (mm in upper face)
• receive from both hemispheres of the brain

Question 20

Rest of Corticobulbar tract

Answer 20

• upper motor neurones that control CNVII lower half of face and CNXII tongue movement cross over in brain stem without branched and only synapse with contralateral nuclei
• so only receive from contralateral cerebral cortex

Question 21

What are indirect motor pathways or extra pyramidal tracts

Answer 21

• DD tracts
• upper motor neurones that originate from deep nuclei of the brain stem not the motor cortex
• they innervate larger mm that play a roll in balance, posture, coarse movements

Question 22

Lateral vestibule spinal tract

Answer 22

• extensor mm of trunk, extremities
• balance info gathered by 4 vestibular nuclear in medulla (sup, med, lat, inf)
• lateral nuclei have upper motor neurones which make up vestibulospinal tract
• descends to ipsilateral spinal cord and synapses w short interneurons which activate lower motor neurons in the ventral horn
• axons leave via ventral root and peripheral to reach extensor mm that they innervate larger

Question 23

Reticulospinal tract

Answer 23

• motor input from extensor mm to help balance
• medulla to mid brain on brain stem sits reticular formation which controls sleep, alertness, cardiovascular control and motor control
• they control motor neurones who axons make 2 reticulospinal tracts

Question 24

Pontine (medial) reticulospinal tract

Answer 24

• DD to ipsilateral spinal cord where it continues without decissating
• indirectly activates lower motor neurones in ventral horn who’s axons travel to extensor mm

Question 25

Medullary (lateral) reticulospinal tract

Answer 25

- gives of ipsilateral and contralateral branch - both travel through ventralmedial spinal cord where they directly rot indirectly inhibit lower motor neurones in the ventral horn that innervate extensor mm

Question 26

Tectospinal tract

Answer 26

- motor neck mm - dorsal side of midbrain has superior colliculi which receives sensory input from the eyes and hold upper motor neurones who’s axons make the tectospinal tract - on the way to spinal cord the tract desiccates behind the cerebral aqueduct and continues to contralateral spinal cord - it DD to cervical region where it ends by synapsing on the lower motor neurons in ventral horn where go through ventral horn and peripheral nerves to mm of the neck

Question 27

Rubrospinal tract

Answer 27

- motor impulses for flexor mm of extremities producing smoother, more coordinated conscious movement - post mid brain has red nucleas that receives input from cerebral and cerebellar cortex, it holds upper motor neurones who’s axons make the rubrospinal tract which desiccates immediately after leaving the red nucleas and descends to the contralateral spinal cord in the neck - where it synapses w interneurons to activate lower motor neurons in ventral horn which send theyre motor axons out to innervate flexor mm