Sensory Biology Flashcards
What are the four basic divisions in somatosensation?
- Touch
- Proprioception (not detected by the skin)
- Pain (nociception)
- Temperature
Where are the sensory neurons located?
In the Dorsal root ganglia (or the trigeminal ganglion for the face)
What is special about sensory neurons?
They are pseudounipolar (2 axons and no dendrite)
Each ganglion innervates a _______ called a ______
- single region of the body
- dermatome
For touch, what are the four basic receptors?
- Merkel Receptors
- Messiner receptors
- Ruffini
- Pacinian
What are Merkel Receptors?
small receptive field, slow adapting, medium threshold for mechanical stretch, edges and points and fine texture, braille
What are Messiner receptors?
medium receptive field, rapid adapting, small threshold for mechanical stretch, motion and grip
What are Ruffini receptors?
large receptive field size, slowly adapting, very large threshold for mechanical stretch, skin stretch and finger position
What are Pacinian receptors?
large (entire finger) receptive field size, rapidly adapting, and very small threshold for mechanical stretch, vibration and grasping
What are the 3 somatosensory response characterizations?
- Speed of conduction
- Adapting or non adapting
- Receptive field size
Where in the body is the best two-point discrimination? (smallest receptive field size)
In the fingers
What is the process of mechanosensory transduction?
- ion channel permeable to Na+
- membrane stretched/something pulls on it
- ion channel opens, leads to excitatory response
Where is Piezo expressed?
- merkel cells
- slowly adapting nerve fibers (that innervate merkel cells)
What is the general pathway for touch sensation?
ascend ipsilaterally and don’t synapse until the brainstem
What is the pathway for touch sensation?
- Mechanosensory input ascends ipsilaterally through the dorsal columns
- synapse and cross at the midline near the brain
- (gracile and cuneate nucleus extends through the medial lemniscus to the thalamus and then the cortex)
What do proprioceptors detect?
- change in muscle length
- tension in on the muscle to detect body positioning
Proprioceptors are part of _______
local circuit in the spinal cord that underlies the knee jerk reflex
Why should you practice the piano?
- Expansion of a cortical representation by a repetitive behavioral task
- somatosensory cortex is plastic
Where are the dorsal root ganglion located?
along the spinal cord
What are the different deratomes? (5)
- Trigeminal - face
- Cervical - shoulders/arms
- Thoracic - trunk
- Lumbar - legs
- Sacral - genitals, leg
Rapidly adapting responses will _______
go away quickly
What are rapidly adapting responses ideal for?
- detecting change in stimulus intensity
- ignoring constant stimuli
What experiment was used to test conduction velocity?
- probe held against skin injects small current which stimulates nerve
- another electrode affixed at various nerve locations measure speed of impulse + other properties
Which receptors have the largest receptive fields?
- Pacinian
- Ruffini
What do muscle spindles detect?
changes in muscle length
What do golgi tendon organs detect?
tension on muscle
What is the general pathway for proprioception?
- Proprioceptive axons travel in spinal cord with axons containing cutaneous info
- Axon collaterals synapse in dorsal horn
Where are the central projections for proprioception?
central projections include cerebellum
What are Somatotopic areas?
areas that are near each other on body map near each other on brain
The size of cortical representation is proportional to
proportional to degree of sensory innervation
