4: Somatosensory System Flashcards
What are the 4 Somatosensory Sub-Modalities?
- Touch (Mechanoreceptive)
- Temperature (Thermoreceptive)
- Pain (Nociceptive)
&&& Body Position (Proprioceptive) - motor lecture
What is a Dermatome?
-Slice/ section of the skin which has axons that enter the spinal cord at a specific spinal route
What are Free Nerve Endings Responsible For?
-Temperature & pain reception
What are Meissner Corpuscles Responsible For?
- Detects low freq vic: 2-50Hz
- Small receptive fields, rapid adaptation
- Communicants w axon in unknown way
- Specialized cell outside of the axon
What are Merkel Cells Responsible For?
- Merkel cell = neurite complex
- Detect static pressure ie. fine spatial discrimination (like brail).. feel gap b/w things
- Spatial tactile perception/ aqcuity: sensitivity to force of touch
- Small receptive field, slow adaptation
What are Ruffini Endings Responsible For?
- Skin stretch sensation
- Large receptive fields, slow adaptation
What are Pacinian Corpusles Responsible For?
- Detect high-freq vibrations: 100-200Hz
- Large receptive field
- Rapid adaptation
Why do we feel Second Pain?
-B/c of the difference in conduction times; when you touch something hot, you’ll first notice that you feel you’re touching something (A-beta), then you’ll feel first pain (A-delta) which will make you withdraw your hand & experience relief.. soon after, second pain will occur & this is when C-fibre axons reach your brain
Explain an Axons Route through the DCML.
- Comes in
- Ascends ipsolaterally
- Reaches caudal medulla & synapses
- 2nd order neuron in mechanosensory pathway receives gluta from neuron
- -Its axon decussates & ascends to thalamus
- VPL gets info from somatosensory system
- -Sends info to cortex
What Happens to a Subject Experiencing Brown-Sequard Syndrome?
- Ipsilateral loss of light touch (touch is always ipsilateral = DCML = A-beta)
- Contralateral loss of pain & temp (STT)
Explain Mechano-transduction.
Mechano-transduction = force that’s turned into an elec signal
Na Channels
- Produced in cell bod & ganglion & located there
- Cell memb contains stretch gated ion channels
- -Open in response to pressure on the cell; the cell is pressed & the membrane stretches, ion channels open b/c of the stretched memb
- Channels are open & Na goes down its conc grad & cell starts to depol
- force applied to cell = graded potential = membrane is stretched & more chans will go into the open state
- -Channels do not get wider, more just open
Weak Stimulus
-May not reach threshold, cell would stretch, ion chans would open, Na would rush in, cell = depol, charge = more but cell may not reach threshold therefore no AP w/o being over threshold
What is a Property of Receptive Fields?
-Stimuli touch closer to center will cause +AP to fire than those on periphery
- If you have two touches that occur simultaneously w/in receptive field, it can be difficult for the brain to understand this
- -Could mistake two touches for one
- –^Problem is solved through receptive field overlap
What is the Purpose of a Caliper?
- Piece of metal you can spread (like tweezers) & use to ensure that both pieces will touch your skin @ the same time
- Helps recognize the two-point discrimination threshold by body region
What are the Benefits of Adaptation?
- Ignore constant, innocuous stimuli to reduce distraction
- Avoid saturation of neuronal firing rates, allowing detection of change in stimuli intensity over a larger range of intensities
What is the Cost of Adaptation?
- Poor judgment of absolute stimulus intensity
- -Eliminates one-to-one mapping from stimulus intensity to firing rate
However, evolution has selected for adaptation as highly advantageous
- Benefit is worth the cost
- If force changes, this will affect your survival
- -More important to detect change than the exact value of a stim
