Somatosensory Physiology Flashcards
What happens if you damage peripheral or central components of the somatosensory system ?
Neuropathy
Neuralgia
Phantom pain
What is the fundamental function of the somatosensory system ?
Provide communication between us and the outside world
What are primary afferents ?
Axons carrying info to he spinal cord from somatic receptors
- enter via the spinal nerve and dorsal roots
What are motor efferents ?
Axons carrying info from the spinal cord to the periphery
- leave the spinal cord via the ventral roots and spinal nerve
What are dermatomes ?
Subdivisions of the body surface
Each one represents area of the skin innervated by left and right dorsal roots of single spinal segment
Dermatome boundaries are overlapping. What are the advantages/disadvantages of this ?
Advantage - means if you lose some sensory input then it is not completely lost from that area
Disadvantage - difficult to determine exactly where pain is felt
What are the 4 classes of somatosensory receptors ?
Tactile
Nociceptice
Proprioception
Thermal
What a Meissners corpuscles ?
Cutaneous receptor Looping axonal terminal intertwined with supporting cells Low threshold mechanoreceptor Just below epidermis Detect low freq 30-50Hz Detect rough texture and movement
What are merkels disks ?
Cutaneous receptors
Low threshold mechoreceptors
Dome structure on top of an axon terminal
Located in epidermal/dermal border
Detects form, shape, rough edges and texture
What are pacinian corpuscles ?
Cutaneous receptors
Low threshold Mechanoreceptor
Sensory axon surrounded by fluid filled capsule
Located in deep dermis
Detects high freq vibrations of 250-350Hz
Detects fine texture and movement
What are ruffinis endings !?
Cutaneous receptors
Low threshold mechanoreceptor a
Nerve terminals intertwined with collagen fibres
In deep dermis
Detect stretching indentation and lateral movements of skin
What are the rapidly activity cutaneous mechanoreceptors ?
Pacinians and Meissners
Important for motor feedback during motor tasks
What are the slowly activity cutaneous mechanoreceptors ?
Ruffinis and merkels disks
Which mechanoreceptors are characteristic of discrete receptive fields of the hand and which have more broad receptive zones ?
Discrete zones= Meissners and merkels
Broad zones= pacinian and ruffinis
What is human 2 point discrimination thresholds ?
Different parts of ten body pick up different mechanical thresholds
High sensitivity= fingertips and face
Low sensitivity= torso and limbs
What are the theories of mechanotransduction ?
Pressure sensitive sodium channels Transduction by - stretch activation - tethering - indirect gated
What are the example channels involved in mechanotransduction ?
DEG/ENaC
TRPN and TRPA
TRPV
What happens when capsaicin binds to VR1 ?
Causes influx of calcium
What receptor family is involved in thermoregulation ?
Trp
Which receptors are activated by menthol and capsaicin ?
Menthol = trpm8 Capsaicin= trpv1
What fibres are associated with nociceptors ??
Unmyelinated c fibres
Thinly myelinated a-delta fibres
What does muscle spindle and Golgi tendon organ detect ?
Muscle spindle - changes in muscle length
Golgi tendon organ - changes in muscle tension
What are the properties of group 1(a-alpha) afferents ?
13-20 micrometer diameter
80-120m/sec conduction
Proprioceptors of skeletal muscle
What are the properties of group 2(a-beta) afferents ?
6-12 micrometer diameter
35-75m/sec conduction
Mechanoreceptors of skin
What are the properties of a-delta afferents ?
1-5 micrometer diameter
5-30m/sec conduction
Pain and temperature
What are the properties of c afferents ?
0.2-1.5micrometer diameter
0.5-2 m/sec conduction
Pain, temperature and itch
Which laminae do each of the afferent fibres terminate in ?
A-alpha- 6-9 - can directly innervate motor neurons in laminae 9
A-beta- 3-6
A-delta- 1 and 2
C- 1 and 2
What info is carried in the dorsal colun medial lemniscus pathways ?
Gracilis- lower body and legs- everything caudal to t6
Cuneatus - upper body and arms- everything rostral to t6
Carry innocuous inputs from skin receptors
How many areas did Brodmann subdivide the cortex into ?
47
Where is s1 and what does it do ?
Post central gyrus - areas 1, 2, 3a, 3b
Receives string somatosensory inputs from thalamus
Where is s2 and what does it do ?
Adjacent to s1 along lateral sulcus
Important in sensory and motor integration
Receives inputs from corpus callosum to form joined up body image
Where are the association area and what do they do ?
Areas 5 and 7 of postural parietal cortex
Integrate multimodal senses
What is asteroagnosia ?
Inability to identify objects on the basis of touch alone
What is neglect syndrome ?
Body part or visual field is disregarded
