Chapter 12: Sense of touch

Question 1

Two types of touch

Answer 1

Passive

Active

Question 2

Receptors are found in:

Answer 2

hairy skin and glabrous skin

-Specificity theory- Each receptor is specialized

-Pattern- Perception arises from patterns of receptor activity

Question 3

Types of fibers

Answer 3

• A-alpha fibers - myelinated, muscles and tendons (Control motor movement and orientation of limbs)
• A-beta fibers - myelinated, mechanical stimulation
• A-delta fibers- myelinated, pain and temperature

-C fibers- unmyelinated, pain and temperature

Question 4

Bell-Magendie Law

Answer 4

-Division between afferent (to) and efferent (from) pathways

-Ventral root goes to the muscles from the brain (efferent)

-Dorsal root send info to the brain (afferent)
–Spinothalamic pathway - temp + pain
–Lemniscal Pathway - Sense of touch

Question 5

Somatosensory Area (S1)

Answer 5

-Primary somatosensory cortex

-Somatotopic layout- Adjacent areas of the body are processed on adjacent areas of the cortex

-Cortical Magnification - small areas of the body processed on large areas of the cortex

Question 6

Types of Mechanoreceptors

Answer 6

Merkel (Slow Adaptation 1)
-Coarse Textures
-Edges, points and curves
- Very small receptive field

Ruffini (Slow Adaptation 2)
-Motion Direction, hand shape
-Skin stretch
-Fairly Large receptive field

Meissner (Rapid Adaptation 1)
-Low frequency vibration + grasp stability
-Skin Motion
-Fairly small receptive field

Pacinian (Rapid Adaptation 2)
-High Frequency vibration, fine textures
-Vibrations
-Relatively large receptive field

-Different firing rates based on stimulus, this helps recognition of object features

Question 7

Thermoreceptors

Answer 7

-Free nerve endings that are scattered throughout the skin
- A-delta and C- Fibers

Question 8

Warmth and Cold Fibers

Answer 8

-Detect local and global temperature changes from physiological zero
-Help maintain homeostasis

Question 9

Nociceptors (Pain)

Answer 9

-Free Nerve Endings
-A -delta and c-fibers

Two Stages:
-Quick and sharp (A-delta)
- Throbbing (C)

Question 10

Gate Control Theory of Pain

Answer 10

Pain Perception is an interaction of bottom-up and top-down signals
-Spinothalamic pathway

Theory:
- Small fibers (A-delta and C) open the gate to pain
—-Excitatory connection to gate control neurons

-Large Fibers (Mechanoreceptors) close the gate
—-Inhibitory connection to gate control neurons

Question 11

Pain Threshold

Answer 11

Covaries w/ sensitivity across body

Question 12

Phantom Limb phenomenon

Answer 12

Sensation of a physically amputated limb
-Results from neural plasticity

Question 13

Tactile Sensitivity

Answer 13

Varies across body and is based on cortical magnification