Unit 7 - Somatosensory Pathway

Question 1

somatosensory pathway

Answer 1

min of 3 neurons in transmission from periphery to cerebral cortex

1°, 2°, 3°

at each synapse, modification of signal can occur

most sensory stimuli do not reach our consciousness - 99%

conscious perception occurs at the level of the cerebral cortex

Question 2

ascending tracts - dorsal column - medial lemniscal system

type of sensation

difference between 1st, 2nd and 3rd order

Answer 2

dorsal column - medial lemniscal system

tactile sensation and propriocepton

1st order - mainly Aβ (main mechanoreceptors) that terminte in dorsal column nuclei, also Ia and type II

2nd order - crossover and project to thalamus

3rd order - somatosensory cortex

Question 3

path of ascending tracts

Answer 3

Ascends from dorsal horn on IPSILATERAL side to medulla and synapse at that point with the second order neuron

Crosses to contralateral side and ascends to the midbrain to contralateral thalamus

Filtering out of unnecessary info - if it is necessary it goes to 3rd order neuron

Question 4

anterolateral/spinothalamic ascending tract

senses

Answer 4

temperature and pain

1st order terminate in spinal cord (Aδ and C)

2nd order cross, terminate in thalamus (ventral posterior complex - VP)

3rd order to somatosensory cortex

Wherever they enter, they synapse - contralateral side

Question 5

ascending tracts that don’t connect with somatosensory system

Answer 5

spinoreticular

spinocerebellar

spino-olivary

Question 6

where does most sensory info project to

Answer 6

thalamus

EXCEPTIONS

olfactory

equilibrium

Question 7

structure of VP complex

Answer 7

Question 8

gyrus of somatosensory cortex (SI)

Answer 8

post central gyrus of parietal lobe

Question 9

function of SI

arrangement of SI

what do neurons in SI form

Answer 9

conscious awareness of somatic sensory signals - intensity and location

somatotopic map - homunculus

greater representation to functions that are critical e.g. facial expression - More sensation you have in your body, the more cortical space is dedicated to the area

neurons in SI form functionally distinct columns

fast and slow adapting in different areas

Question 10

pathway to SI

Answer 10

Sensory receptors become activated - transmit info via Aδ and C fibres

Info travels via spinothalamic tract

To cortex - primary somatosensory cortex

Question 11

somatotopic order in the human primary somatic sensory cortex

Answer 11

Question 12

3b and 1

Answer 12

cutaneous stimuli (pain and temp)

Question 13

area 3a

Answer 13

proprioception

Question 14

area 2

Answer 14

tactile (mechanoreceptors) and proprioception

Question 15

SI sends projections to

Answer 15

SII - lateral sulcus

Question 16

SII projects to

Answer 16

limbic structures (e.g. amygdala and hippocampus)

learning and memory of stimulus

Emotional response etc to sensory stimulus

Painful stimulus - you cry

Hippocampus - don’t touch hot surface again

Question 17

SI projections that integrate sensory and motor info

Answer 17

parietal area to motor and premotor area

integration of sensory and motor info - proprioception

Question 18

SI projections - that fine tune ascending projections

Answer 18

SI to thalamus, brainstem and spinal cord

Question 19

overview of projections

Answer 19

Question 20

3b and 1

Answer 20

cutaneous stimuli

Question 21

3a

Answer 21

proprioception

Question 22

2

Answer 22

tactile and proprioception