Sensory Biology

Question 1

What are the four basic divisions in somatosensation?

Answer 1

1. Touch
2. Proprioception (not detected by the skin)
3. Pain (nociception)
4. Temperature

Question 2

Where are the sensory neurons located?

Answer 2

In the Dorsal root ganglia (or the trigeminal ganglion for the face)

Question 3

What is special about sensory neurons?

Answer 3

They are pseudounipolar (2 axons and no dendrite)

Question 4

Each ganglion innervates a _______ called a ______

Answer 4

• single region of the body

- dermatome

Question 5

For touch, what are the four basic receptors?

Answer 5

1. Merkel Receptors
2. Messiner receptors
3. Ruffini
4. Pacinian

Question 6

What are Merkel Receptors?

Answer 6

small receptive field, slow adapting, medium threshold for mechanical stretch, edges and points and fine texture, braille

Question 7

What are Messiner receptors?

Answer 7

medium receptive field, rapid adapting, small threshold for mechanical stretch, motion and grip

Question 8

What are Ruffini receptors?

Answer 8

large receptive field size, slowly adapting, very large threshold for mechanical stretch, skin stretch and finger position

Question 9

What are Pacinian receptors?

Answer 9

large (entire finger) receptive field size, rapidly adapting, and very small threshold for mechanical stretch, vibration and grasping

Question 10

What are the 3 somatosensory response characterizations?

Answer 10

1. Speed of conduction
2. Adapting or non adapting
3. Receptive field size

Question 11

Where in the body is the best two-point discrimination? (smallest receptive field size)

Answer 11

In the fingers

Question 12

What is the process of mechanosensory transduction?

Answer 12

1. ion channel permeable to Na+
2. membrane stretched/something pulls on it
3. ion channel opens, leads to excitatory response

Question 13

Where is Piezo expressed?

Answer 13

• merkel cells

- slowly adapting nerve fibers (that innervate merkel cells)

Question 14

What is the general pathway for touch sensation?

Answer 14

ascend ipsilaterally and don’t synapse until the brainstem

Question 15

What is the pathway for touch sensation?

Answer 15

1. Mechanosensory input ascends ipsilaterally through the dorsal columns
2. synapse and cross at the midline near the brain
3. (gracile and cuneate nucleus extends through the medial lemniscus to the thalamus and then the cortex)

Question 16

What do proprioceptors detect?

Answer 16

• change in muscle length

- tension in on the muscle to detect body positioning

Question 17

Proprioceptors are part of _______

Answer 17

local circuit in the spinal cord that underlies the knee jerk reflex

Question 18

Why should you practice the piano?

Answer 18

• Expansion of a cortical representation by a repetitive behavioral task
• somatosensory cortex is plastic

Question 19

Where are the dorsal root ganglion located?

Answer 19

along the spinal cord

Question 20

What are the different deratomes? (5)

Answer 20

1. Trigeminal - face
2. Cervical - shoulders/arms
3. Thoracic - trunk
4. Lumbar - legs
5. Sacral - genitals, leg

Question 21

Rapidly adapting responses will _______

Answer 21

go away quickly

Question 22

What are rapidly adapting responses ideal for?

Answer 22

• detecting change in stimulus intensity

- ignoring constant stimuli

Question 23

What experiment was used to test conduction velocity?

Answer 23

• probe held against skin injects small current which stimulates nerve
• another electrode affixed at various nerve locations measure speed of impulse + other properties

Question 24

Which receptors have the largest receptive fields?

Answer 24

• Pacinian

- Ruffini

Question 25

What do muscle spindles detect?

Answer 25

changes in muscle length

Question 26

What do golgi tendon organs detect?

Answer 26

tension on muscle

Question 27

What is the general pathway for proprioception?

Answer 27

1. Proprioceptive axons travel in spinal cord with axons containing cutaneous info
2. Axon collaterals synapse in dorsal horn

Question 28

Where are the central projections for proprioception?

Answer 28

central projections include cerebellum

Question 29

What are Somatotopic areas?

Answer 29

areas that are near each other on body map near each other on brain

Question 30

The size of cortical representation is proportional to

Answer 30

proportional to degree of sensory innervation