Lecture 4 part 2

Question 1

study slide 4

Answer 1

ye

Question 2

study slide 5

Answer 2

ye

Question 3

what are the three main functions of the somatosensory system?

Answer 3

• conscious perception
• modulation of movement (cerebellar) – regulates quality of movement
• arousal & alertness (via brainstem & thalamus)

Question 4

what are the two sensory/ascending somatosensory pathways?

Answer 4

posterior/dorsal column or medial lemniscal –> also called the fasciculus grascilis and fasciculus cuneatus as it ASCENDS

anterolateal pathway–spinothalamic tract aka trigeminal thalamic

both are LONG pathways, so they DECUSSATE

Question 5

what does the posterior ascending pathway sense?

Answer 5

vibration, joint position, and fine touch

Question 6

what does anterolateral pathway sense?

Answer 6

pain, temp, and crude touch

Question 7

describe the neurons in a somatosensory pathway

Answer 7

usually a 3-neuron system

1st neuron: runs from the periphery to spinal cord or medulla

2nd neuron: either a) gets input fromthe spinal cord/medulla to thalamus & cerebellum or b) input to motor neuron on effector organ (= reflex)

3rd neuron: input from the thalamus to cerebral cortex

Question 8

study slide 12

Answer 8

ye

Question 9

after the ascending tract has entered the spinal cord, either in the dorsal or anterolateral column, it will decussate:

the dorsal column decussates in the MEDULLA, and has two-point discrimination–fine touch (remember, it has vib, proprioception, and fine touch) whereas the ANTEROLATERAL decussates in the SPINAL CORD (remember it has nociception and temperature)

slide 14

Answer 9

ye

Question 10

study slide 15

Answer 10

ye

Question 11

if someone cannot feel light touch, proprioception, or lacks 2 pt discrimination –> they have a problem with dorsal column/medial lemniscal

if someone can’t feel pain or temperature, but can feel that a sharp object is touching them, they have anterolateral pathway problems (slide 16)

Answer 11

ye

Question 12

study slide 18 and 19

Answer 12

ye

Question 13

the spinothalamic tract mediates the DISCRIMINATORY aspects of pain –> e.g. dull, aching

Answer 13

ye

Question 14

where does the anterolateral tract enter?

Answer 14

dorsal horn…??

Question 15

anterolateral tract decussates right away–in spinal cord, to the anterolateral horn??

Answer 15

ye

Question 16

study slide 24

Answer 16

ye

Question 17

primary somatosensory functions in concious perception–it allows for two point discrimination, identification of objects by palpation (stereognosis); if someone cannot identify object by palpation (astereognis) = ISSUE WITH SOMATOSENSORY PATHWAY; also helps with identifying writing on skin

-requires both the use of the unimodal and multimodal association cortices

Answer 17

ye

Question 18

describe the difference in roles of A-delta to C-type fibres

Answer 18

A-delta– functions in ACUTE (A = acute = A-delta); less discriminative sensation (sharp)

C fibre = CHRONIC = least discriminative sensations (dull pain, unmyelinated fibres)

Question 19

describe gate control theory

Answer 19

–transmission of impulses from AFFERENTS (to spinal cord neurons) controlled by a GATE

–gate is influenced by relative amounts of activity –> dependent on large and small fibres

the SMALL fibre activity is nociceptive, and opens the gates = feel pain

the LARGE fibres are NON-nociceptive, and their activation CLOSES the gates–>blocks transmission of pain via inhibitory neurons in the substantia gelatinosa of the spinal cord

Question 20

study slide 30

Answer 20

ye

Question 21

pain vs nociception

Answer 21

pain = unpleasant sensory and emotional experience; does not need to be tied to a stimulus (may feel even if there is no tissue damage)

while nociception:

• sensory component of pathway, the activation of nociceptors; IS tied to a stimulus
• involved anterolateral pthway

Question 22

define noxious

Answer 22

a type of stimuli that could cause tissue damage if exposure is prolonged

Question 23

study slide 32

Answer 23

ye