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
16
Q
Rodents
A
-sensory input from each whisker/vibrisae goes to special cluster of neurons called barrels
17
Q
Plasticity
A
-brain will change map if sensory area removed from body or if an area increases its function
18
Q
Posterior parietal
A
- involved in somatic sensation, visual stimuli, movement , planning, attentiveness
- damage can cause neurological disorders
- agnosia, astereognosia, neglect syndrome
19
Q
Agnosia
A
-inability to recognize objects through simple sensory skills
20
Q
Astereognosia
A
- cant recognize objects by feeling them
- deficits limited to contralateral side
21
Q
Neglect syndrome
A
- entire visual field is ignored/suppressed
- commonly from damage to right hemisphere
22
Q
Pain
A
- feeling of irritating, sore, stinging, aching, throbbing sensations
- perceptual —> taking sensory info and making judgements about it
23
Q
Nociception
A
- processes that provide pain signals
- usually involve tissue damage
- sensory
- opioid addicts have no tolerance for pain because of tolerance for opioids
24
Q
Nociceptors
A
- free nerve endings: Ad + C fibres
- many types: polymodal, mechanical, thermal, chemical
- found in almost all tissues except hair
25
Transduction
- stretching, bending of nociceptive membrane —> depolarize
- damaged cells at site of injury can release substances that cause ion channels to open
- proteases, ATP, K+
26
Hyperalgesia
- reduced threshold for pain, increased sensitivity to painful stimuli, and spontaneous pain
- primary and secondary
27
Substances that mediate inflammation and modulate nociceptor excitability
-makes nociceptors more sensitive
1. Bradykinin: make heat activated channels more sensitive
2. Prostaglandins: increase sensitivity of nociceptors to other stimuli
- aspirin inhibits enzymes required for prostaglandin synthesis
3. Substance P: causes vasodilation + releases histamine
- cause of secondary hyperalgesia
28
1st and 2nd pain
- 1st pain: Ad fibres (slightly myelinated)
- sharp pain
2nd pain: C fibres (unmyelinated)
-dull, lasting pain
29
Primary nocicpetive afferents
- have cell bodies in dorsal root ganglion and enter DORSAL HORN
- fibres branch immediately, travel short distance up and down spinal cord in a region called ZONE OF LISSAURE
- synapse on outer part of dorsal horn in SUBSTANTIA GELATINOSA
- cross over in SPINAL CORD
- substance P in storage granules in axon terminals in substantia gelatinosa
- can be released by high frequency trains of APs
- synaptic transmission mediated by Subs P required to experience intense pain
30
Referred pain
-visceral nociceptor activation is perceived as cutaneous sensation due to mixing of axons entering spinal cord
31
Spinothalamic pathway
- pain pathway
- second order neurons immediately decussate in spinal cord
- ascend through SPINOTHALAMIC TRACT through medulla, pons, midbrain and synapse in INTRALAMINAR + VP NUCLEI
32
Thalamus and cortex
- spinothalamic tract + trigeminal lemniscus axons synapse over wider region of thalamus
- pain and touch stay separate
33
Afferent regulation
- pain evoked by nociceptors can be reduced by spontaneous activity in low threshold mechanoreceptors (Ab fibres)
- gate theory of pain: nociception +sensory diminishes pain due to interneurons and projection neurons
34
Descending regulation
- PAG neurons send axons to raphe nuclei in medulla
| - raphe nuclei uses serotonin and projects axons to DORSAL HORN where they can depress activity of nociceptive neurons
