spinal pathways

Question 1

where is the primary somatosensory cortex located

Answer 1

POST-central gyrus on PARIETAL lobe

sensory fibres have crossed midline -> left side is represented on right + vice versa

Question 2

is the descending or ascending pathway responsible for sensory transmission

Answer 2

ascending - sensory from peripheral nerves to cerebral cortex

descending -> motor

Question 3

ascending pathways

Answer 3

conscious - dorsal column-medial lemniscal + anterolateral/spinothalamic

unconscious -> spinocerebellar

Question 4

what does DCML detect

Answer 4

fine touch + proprioception (perceive loacation, movement on body parts)

fibres cross in medulla

Question 5

1st order neurons of DCML pathway, upper vs lower limb transport

Answer 5

1st - peripheral nerves -> medulla
- upper limb (T6+above) –> fasciculus cuneatus (lateral)
- lower limb (T7 onwards) –> fasciclus gracilus (medial)

Question 6

2nd + 3rd order neurons of DCML pathway

Answer 6

2nd - nucleus cuneate/gracilis –> thalamus
- cross in medulla so travel in contralateral medial lemniscus to reach thalamus

3rd - thalamus –> ipsilateral primary sensory cortex

Question 7

spinothalamic pathway

Answer 7

anterior spinothalamic -> sensory of crude touch + pressure (crude = unable to localise touch)

lateral -> sensory of pain + temp

fibres cross segementally

Question 8

spinothalamic first order neurons

Answer 8

periphery -> enter spinal cord -> ascend 1-2 levels -> synapse at tip of dorsal column (substantia gelatinosa)

Question 9

spinothlamic 2nd + 3rd order neurons

Answer 9

substantia gelatinosa -> thalamus
- after synapsing with 1st order, they decussate within spinal cord + then form 2 distinct tracts :

• crude touch + pressure enter anterior
• pain + temp enter lateral

–> both run alongside each other

3rd = thalamus -> ipsilateral primary sensory cortex

Question 10

how would a spinal cord lesion affect the ascending pathways

Answer 10

DCML -> ipsilateral loss of proprioceptive + fine touch

spinothalamic -> contralateral loss of pain + temp

brown-sequard = hemisection of spinal cord
- above symptoms ^
- + descending (ipsilateral hemiparesis)

Question 11

where is the primary motor cortex located

Answer 11

PRE-central gyrus on FRONTAL lobe
-> right controls muscles on left side + vice versa

Question 12

all neurones in the descending pathway are …

Answer 12

upper motor neurons

-> at termination of descending tracts, neurons synpase with a lower motor neurone

Question 13

pyramidal vs extrapyramidal tracts

Answer 13

descending pathways
pyramidal
- voluntary + automatic control of muscles of body + face
- form visible ridges (pyramids) on anterior surface of medualla

extra-pyramidal
- involuntary + automatic control of all muscles
–> muscle tone, balance, posture

Question 14

corticospinal tract (pyramidal)

Answer 14

fine, precise movement, particulary of distal limbs (fingers)
- descends through internal capsule to brainstem
- 85% of fibres cross in caudal medulla at the decussation of the pyramids
– then synapse onto horn when appropriate level reached (lateral CST)

crossed - lateral CST
uncrossed - ventral CST

Question 15

what different pathways do the fibres that cross in the corticospinal tract vs the ones that dont

Answer 15

crossed fibres (85% in caudal medulla)
-> form lateral CST

uncrossed fibres –> ventral CST + cross segmentally

note
- upper limb medial to lower limb in tract
- ventral cst -> more axial muscles, lateral -> more limb

Question 16

clinical relevance of corticospinal tract

Answer 16

a CVA of internal capsule can result in a lack of descending control of the corticospinal tract

-> results in a spastic paralysis with hyperflexion of the upper limbs = decorate posturing

Question 17

extrapyramidal tracts

Answer 17

DO NOT decussate - ipsilateral innervation
- vestibulospinal
- reticulospinal

DO decussate - contralateral innervation
- tectospinal
- rubrospinal

Question 18

tectospinal

Answer 18

coordinate movements of heaf in relation to visual stimuli

superior colliculus receives input from optic nerve
- neurons then quickly decussate + enter spinal cord
- terminate at cervical levels

Question 19

rubrospinal tract

Answer 19

decussate as the emerge from RED nucleus -> descend into spinal cord

Question 20

reticulospinal tract

Answer 20

reticular formation forms central core of brainstem, inputs from everywhere, does everything

medial arises from PONS -> facilitates voluntary movement + increase muscle tone

lateral arises from medulla -> inhibits voluntary movement + decrease muscle tone

Question 21

general role of fibres originating from pons

Answer 21

facilitate EXTENSOR movements + inhibit flexor

those from medulla do opposite

Question 22

vestibulospinal

Answer 22

controls balance + posture
- by innervating “anti-gravity” muscles via LMN - flexors of arms, extensors of legs

originate in vestibular nuclei of pons + medulla
- in turn receive input from vestibular apparatus + cerebellum + conveys to spinal cord (ipsilaterlaly)

Question 23

clinical relevance of vestibulospinal pathway

Answer 23

patients presenting with decerebate rigidity + paraplegia in extension
-> lesions below red nucleus result in lack of descending cortical cortrol

both lateral CST + rubrospinal damaged so reticulospinal takes over –> arms + legs extended, head back

Question 24

decerebate posturing

Answer 24

arm + legs both flexxed - arms by site wrists flexed

both lateral CST + rubrospinal damaged so reticulospinal takes over
-> worse than decorticate