8 - ascending pathways for the body

Question 1

each modality is detected by ..

Answer 1

specific receptos/specialised nerve endings

Question 2

can you have a dermatome for cranial nerves?

Answer 2

no - by definition dermatomes are regions of skin supplied by SPINAL neves - can do same for CN but not called dermatome

Question 3

what dermatome is the nipple?

Answer 3

T4

Question 4

what infection recurs and is characterised by vesicles confined to one dermatome?

Answer 4

Herpes Zoster - reactivation = shingles

Question 5

why is synaptic transmission between the 3 neurones in this chain not just a simple relay mechanism?

Answer 5

transmission modified by convergence (many to one) and divergence (one to many), descending pathways can also modify

Question 6

modalities for spinothalamic pathway?

Answer 6

pain, temperature, crude touch, some pressure

Question 7

what sort of fibres from receptors in spinothalamic?

Answer 7

thin, slow, little/no myelination (think: don’t want to feel pain all the time - sharp pain = lots of fibres to brain)

Question 8

where does the spinothalamic pathway cross the midline?

Answer 8

level of spinal cord

Question 9

the tracts change names once reach brainstem, what are they called now?

Answer 9

spinothlamic tract > spinal lemniscus

dorsal tract > medial lemniscus

Question 10

where do pain and temp fibres (spinothalamic) synapse?

Answer 10

substantia gelatinosa (Rexed lamina II)

Question 11

where do the cell bodies of the first, second and third order neurons lie for all general sensory pathways?

Answer 11

first order - peripheral ganglia (e.g. DRG) = pseudounipolar

second order - reside in ipsilateral grey matter. Axons ascend to VPL in thalamud

third order - reside in thalamus and ascend to somato-sesory cortex

Question 12

which modalities are ipsi and contralateral?
fine touch, vibration, pressure, proprioception

crude touch, pain, temperature

Answer 12

ipsi - fine touch, vibration, pressure, proprioception

contra -crude touch, pain, temperature

Question 13

describe the general sensory pathway for crude touch, pain and temperature.

Answer 13

spinothalamic

1. thin. slow fibre from receptor, cell body in DRG, enter SC via Lissauer’s tract
2. fibres may synapse 2nd cell body immediately, or ascenf 1-2 segments in DRH. Once synapsed, crosses midline immediately via VENTRAL WHITE COMMISSURE. Then ascend in spinothalamic tract until thalamus - here somatotopic organisation
3. synapse 3rd cell body in VPL of thalamus –> post central gyrus

Question 14

how is the spinothalamic tract somatotopically organised?

Answer 14

more superior body (arm) is more anterior in the tract

Question 15

how do you differentiate between crude touch, pain and crude touch due to pain?

Answer 15

pain and temp - synapse in sub gel and cross midline immediately

crude touch - reach DRG, ascend LT, synapse and only then cross

if someone pinched you, both these pathways would fire

Question 16

where does the spinothalamic pathway cross? And what is it called past the medulla?

Answer 16

cross at level of spinal cord

called spinal lemniscus

Question 17

describe the pathway for discriminative touch, vibration, pressure, proprioception

Answer 17

DORSAL COLUMN PATHWAY

thick, fast fibres of these modalities have their primary cell bodies in DRG, then enter DGH. The primary neurones travel up one of the dorsal columns (gracile if LL, cuneate if above T6)

synapse with secondary at the respective tubercle. Here they cross the midline and somatopically organise in the medial lemniscus –>

travels to thalamus, synapse in VPL, then to SSC

Question 18

where do the secondary neurones cross the midline for either general sensory pathway?

Answer 18

ST - immediately, after synapsing in DGH

DC - immediately, after synapsing in the tubercles

Question 19

how is the medial lemniscus somatotopically organised?

Answer 19

more superior (arm) = more posterior

Question 20

what do the secondary neurones cross the midline via, in either pathway?

Answer 20

ST - ventral white commissure
DC - internal arcuate fibres (in
closed medulla)

Question 21

the cuneate fascile only appears above what level?

Answer 21

T6

Question 22

where do fibres for leg, arm and face get somatotopically organised to on the somatosensory cortex?

Answer 22

Leg - close to the longitudinal fissure
arm - middle
face - lateral side

Question 23

what type of fibres in dorsal column pathway?

Answer 23

large diameter, heavily myelinated, fast