Brain 2: Primer for Somatosensory pathways

Question 1

Somatic sensation is what? What are the 4 things you can have perceptionof?

Answer 1

Question 2

What are the two types of proprioception? What are they?

Answer 2

Conscious: limb or joint position

Non-conscious: maintenance of normal muscle tone, posture, cordination (cerebellum)

Question 3

Describe local reflexes

Answer 3

These somatic neurons can enter the spinal cord, synapse in gray matter and result in a local reflex at the same level OR it may ascend (move up) in the CNS, which means travel through white matter tract from the spinal cord to the brainstem to the thalamus and then cortex

Question 4

Whats going on here?

Answer 4

Somatic sensory neuron is acending throug CNS

Question 5

Answer 5

Question 6

In somatosensory neurons, how many neurons link the target to the cortex?

Answer 6

3, first order (primary) sensory neuron, second order (secondary) seonsory neuron, and third order (tertiary) sensory neuron

Question 7

Where is the cell body of a first order sensory neuron?

Answer 7

Cell body in dorsal root ganglion. Has both a peripheral process and central process

Question 8

Where does a secondary sensory neuron project it project?

Answer 8

projects to thalamus

Question 9

Where does a third order sensory neuron project?

Answer 9

Projects to somatosensory cortex in the postcentral gyrus

Question 10

What are the 2 main pathways in the spinal cord for conscious somatic sensation?

Answer 10

Question 11

What information does the dorsal column medial lemniscal pathway carry?

Answer 11

Conscious proprioception, vibration, fine discriminative touch

Question 12

What information does the spinothalamic tract (anterolateral system) carry?

Answer 12

Pain, temperature

Question 13

Answer 13

Question 14

Describe the fine touch test: 2 point discrimination.

What is a positive finding on this test?

Answer 14

Question 15

Explain what happens to the first order sensory neuron of fine touch, conscious proprioception, and vibratory sense

Answer 15

Central process of first order neuron ascends in dorsal (posterior) columns of spinal cord to medulla. Then synapses on 2nd order neuron cell body in nucleus gracilis (lower limb) or nucleus cuneatus (upper limb)

Question 16

Answer 16

Question 17

What happens to the secondary sensory neurons? For fine touch, vibratory touch and conscious proprioception

Answer 17

Question 18

Answer 18

Question 19

What does decussate mean?

Answer 19

Crosses midline

Question 20

All of the thousands of second order somatosensory axons from DCML pathway that are ascending together through spinal cord and brain stem are called?

Answer 20

Medial lemniscus

Question 21

The nuclei in the thalamus that receive somatosensory information are called what?

Answer 21

ventral posterior lateral (VPL) nuclei of thalamus. One on each side of thalamus

Question 22

Explain what happens to the first order primary sensory neuron for pain and temperature (anterolateral or spinothalamic)

Answer 22

Cell body starts in dorsal root ganglion, and central process will extend into the dorsal horn of the spinal cord, and it will synapse there (different from the somatosensory neuron, which ascended). Can synapse in substantia gelatinosa or nucleus proprius

Question 23

Explain what happens to the seconday spinothalamic sensory neuron

Answer 23

Crosses midline (decussates) at anterior commissure, then ascends in white matter via spinothalamic tract. Projects to thalamus, specifically the ventral posterior lateral (VPL) nuclei of thalamus.

Question 24

Where do DCML neurons decussate?

Answer 24

In the medulla

Question 25

Where do spinothamalic neurons decussate?

Answer 25

In the spinal cord

Question 26

Where do both 3rd order neurons (spinothalamic and DCML) project?

Answer 26

Somatosensory cortex in postcentral gyryus

Question 27

How are sensory pathways organized in the cortex? Where are regions representing the hand next to? Whats the somatotopic map on cortex called?

Answer 27

Question 28

Unconcsious proprioception transmits information needed for maintaining what?

Answer 28

Muscle tone, posture and coordination

Question 29

Info for unconscious proprioception arises from what? What are the two tracts they travel through? Where do they terminate?

Answer 29

Question 30

Do unsconsious proprioception neurons have 1st order, 2nd order, 3rd order neurons ect?

Answer 30

No, there usually is like 2 neurons, and they are not really named. They start in stretch receptors.

Question 31

Describe what happens to the first neuron in unconcious proprioception pathway, from lower part of body. Where does it synapse?

Answer 31

First neuron travels with DCML path for a short distance. Goes through fasiculus gracilis (because it's coming through lower part of the body). BUt will synapse in different nucleus ,dorsal nucleus of Clarke (C8-L3 SC levels).

Question 32

What are the spinal cord levels for the dorsal nucleus of Clarke?

Answer 32

C8-L3

Question 33

Answer 33

Question 34

What is the tract called that unconcsious proprioception, second order neurons travel through? What does it travel through on its way to the cerebellum?

Answer 34

Dorsal (posterior) spinocerebellar tract, travels thorugh the inferior cerebellar peduncle

Question 35

What do we call it when the neuron stays on the same side as it travels? Which type of neuron does this?

Answer 35

ipsilateral. Unconcsious proprioception

Question 36

If the unconscious proprioception neuron was arising from muscle stretch receptors in the upper extremities, where would we find the first order axons? Where will it synapse? After that, what is the tract that it will ascend in called? Finally, what wil it travel through to reach cerebellum?

Answer 36

fasiculus cuneatus synapse in external cuneate nucleus in medulla (lateral to cuneate nucleus) Ascend in cuneocerebellar tract travel through inferior cerebellar peduncle to reach cerebellum

Question 37

What is the difference in the location of the 1st order neuron cell bodies between the DCML Gracilis and Cuneatus pathways?

Answer 37

Cuneatus: dorsal Root Ganglion above T6 and Gracilis is dorsal root ganglion below T6