Somatosensation Flashcards
1
Q
Body senses
A
- Exteroceptive: external stimuli applied to skin (touch)
- Propioceptive: body position
- muscles, joints, balance, organs
- alcoholics have problems with this
- Interoceptive: general body conditions
- body temp, glucose levels, homeostasis
2
Q
Types of skin
A
- hairy + glabrous
- 2 layers: dermis (inner) and epidermis (outer)
- protection from evaporation and direct contact with world
- largest sensory organ
3
Q
Receptors
A
- at the heart of all receptors are unmyelinated axon branches
1. PACINIAN: lies deep to dermis, 2mm long- largest receptor (fluid filled)
- about 2500 in each hand, most dense in fingers
- hairy and glabrous skin
- rapidly adapting
- RUFFINIS: hair and glabrous skin
- slow adapting
- MEISNERS: glabrous skin (edges)
- specialized
- rapid adapting
- MERKELS: nerve terminal + flattened non-neural epithelial cells
- slow adapting
- KRAUSE: border region of dry skin + mucous membrane
- lips and genitals
- nerve terminals look like knotted balls
4
Q
Receptive fields
A
- meisners: small receptive field
- high sensitivity and discrimination
- pacinian: large receptive field
- lower sensitivity
- pacinian more sensitive to pressure than meisners
- meisners optimal frequency = 50hz
- pacinian 300hz
5
Q
Mechanosensitive ion channels
A
- all mech receptors have unmyelinated axon terminal which have mech ion channels
- Merkel cell has channel called PIEZO2 that open in response to pressure
- force can come from within cell or outside cell
6
Q
2 point discrimination
A
HIGHEST 1. Fingers and thumb 2. Lips 3. Big toes 4. Soles of feet 5. Forearm 6. Back 7. Calf LOWEST
7
Q
Braille
A
- fingers have highest density of mechanoreceptors
- fingertips have many Merkel cells with small receptive fields
- more brain tissue devoted to sensory of fingers
8
Q
Primary afferent axons
A
- enter spinal cord through dorsal root
- Aa= largest, fastest, most myelination
- propioception of skeletal muscles
- Ab=second largest, fastest, myelinated
- mechanoreceptors of skin
- Ad= smallest myelinated
- pain and temperature
- C= slowest, unmyelinated
- pain, temperature, itch —> NOCICEPTION
9
Q
Spinal cord
A
- cervical= C1-C8
- thoracic=T1-T12
- lumbar= L1-L5
- sacral=S1-S5
10
Q
Dermatome
A
- area of skin innervated by the right and left dorsal roots of a single spinal segment
- if a dorsal root is cut, other nerves can compensate
- SHINGLES: all neurons of a single dorsal root ganglion infected with a virus
11
Q
Dorsal column-medial lemniscus pathway
A
- pathway for touch
- Ab branch enters IPSILATERAL DORSAL COLUMN
- primary sensory axons terminate in DORSAL CLOUMN NUCLEI
- decussation to MEDIAL LEMNISCUS at level of medulla
- medial lemniscus rises through medulla, pons, midbrain to VENTRAL POSTERIOR NUCLEUS (VP) in thalamus
- neurons then project to S1
12
Q
Trigeminal nerve pathway
A
- somatic sensation from face supplied by trigeminal nerve
- enters brain at pons
- twin nerves on either side branch into 3 peripheral nerves
- axons synapse in the IPSILATERAL TRIGEMINAL NUCLEUS
- decussate to VP nucleus
- project to S1
13
Q
Somatosensory cortex
A
- S1= Area 3b= primary cortex on post-central gyrus
- areas 3a, 1, and 2 on post-central gyrus
- areas 5 and 7 on posterior parietal cortex
- area 1= texture
- area 2=size and shape
- areas 5 and 7 = processing/association/dealing with space
-thalamic inputs terminate in layer IV of the cortex then project to other layers
14
Q
Area 3b
A
- primary Cortex because:
1. Receives dense inputs from VP nucleus
2. It’s neurons are extremely responsive to somatosensation
3. Lesions here impact somatosensation
4. When electrically stimulated evokes somatic sensory experiences
15
Q
Somatotropin
A
- mapping of bodies surface sensations onto structure of brain
- legs and feet at top of gyrus
- head at bottom of gyrus
- HOMUNCULUS
