TOUCH AND PROPRIOCEPTION Flashcards
somatic sensory system (3 functionally different distinct system)
- Cutaneous mechanoreceptors 2. Proprioception 3.Free nerve ending
Cutaneous mechanoreceptors
- fine touch 2. vibration 3. pressure
proprioception
position of self, static associated with muscles, tendons, and joints KINESTHESIA-Sensation or perception of motion
Free Nerve Ending
1.Pain 2. Temperature 3.coarse touch 4. pleasantness of touch
somatosensory afferents
convey information from skin surface to central circuits -Dorsal root ganglia -Cranial nerve ganglia
Dermatomes
somatic information originates from activity of afferent nerve fibers -
Dorsal/posterior root ganglion
Pseudounipolar neuron
-Neuron that splits into two branches, one runs to the periphery and the other to spinal cord.
Dermatomes
Lamine (I-X) mid-thoracic level
- I & II are machanoreceptors
- I-V are Adelta and C nociceptor
Craniel nerves: Trigeminal nerves (v)
- ophthalmic division (v1)
- maxillary dividion (v2)
- mandibular division (v3)
Transduction in a machanosensory afferent
- Sensory transduction: Converting stimulus into electrical energy.
- Somatic sensory afferents: alters nonselective cation channels (positive charges) in afferent nerve ending. Also generates a receptor potential (depolarize an action potential in afferent fibers)
Afferent fibers are incapsulated by receptors cells
- Mechanoreceptor: Help tune to particular feature and lower threshold for action potential
- Free nerve ending: lack incapsulation by specialized receptor, sensation of pain, and higher threshold for action potential
somatic afferent response properties
- axon diameter
- receptive field
- density of afferent fiber
- temporal dynamics
Axon Diameter
- 1a,1b, and II afferents: large and fast, supply sensory receptors for muscles proprioception
- A Beta afferent: smaller, convey touch
- Aδ and C afferents: small and slow, pain and temp
Myelination in peripheral nervous system
myelinating schwann cells wrap around axons
Receptive field (RF) & density
Two-point discrimination: min. interstimulus distance to perceive two stimulateneously applied stimuli
Temporal dynamics
- slowly adapting afferent: Generate sustained discharge during ongoing stimulus and Provide spatial info; size and shape of stimulus
- Rapidly adapting afferents: fire rapidly when a stimulus is first presented, falls silent with continued stimulus and convey change in movement.
- Determined by receptor type
The skin harbors a variety of morphologically distinct receptors
Tactile information
- haptics or active touching
- Stereognosis capacity to identify an object by tactile information
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Mechanoreceptors
Four distincts classes
- MERKEL
- 2.MEISSNER
- 3.PACINIAN
- 4.RUFFINI
Merkel
- Tip of epidermal sweat ridges (location)
- form and texture (function)
- small receptor field
- edges, points, curvature, corners
Meissner
- Dermal papillae;close to skin surface (location)
- Motio detection, grip control (function)
- skin motion
- small receptor field
