Chapter 12: Somatosensory Flashcards
What are the sensory sunmidalities in the skin?
Mechanoreceptors: touch, vibration, pressure
Thermoreceptors: temperature
Nociceptors: pain
What are Mechanoreceptors in the skin sensitive to?
Bending, stretching, vibration, pressure
What are the specialized nerve endings in the skin?
Merkel’s Disk, Meissner’s corpuscule, Pacinian Corpuscule, Ruffini ending
What are the Free nerve endings?
Thermal receptors and Nociceptors
What are the two Mechanoreceptors specialized doe proprioception? What does each one sense?
Muscle spindles: muscle length
Golgi tendon organs: muscle tension
What are the four qualities of a stimulus?
Modality
Location
Intensity and duration
What are the 5 sensory modalities?
Vision, hearing, touch, taste and smell
How is intensity signaled?
Firing rate
How is duration signaled?
Time course of response
Between Meissner’s corpuscule, Merkel’s disk, Pacinian corpuscule and Ruffini’s ending, which are slowly adapting and which are rapidly adapting?
Meissner’s and Pacinian are rapid
Merkel’s and Ruffini’s are slowly
What are the different types of mechanosensitive ion channels?
- channels sensitive to stretch of lipid bilateral
- channels sensitive to force applied to extra cellular proteins linked to channel
- channels sensitive to force applied to intracellular proteins linked to channels
How is spatial resolution enhanced?
Most 2nd order neurons have surround (lateral) inhibition in their receptive fields
Explain 2 point discrimination and its link with surround inhibition if 2nd order neurons
Certain 2nd order neurons have surround inhibition which allows for an enhanced spatial resolution in a certain area: on spot will have a much stronger stimulus than what’s around it
Where is two pont discrimination best?
In areas with highest innervation density: eg fingertips
What are the primary afferent axons?
Axons bringing information from the somatic sensory receptors to the spinal cord or brain stem.
Associate the sensory receptor with the axon size type
Proprioceptors of skeletal muscle—Aalpha
Mechanoreceptors of skin—Abeta
Pain temperature—Asigma
Pain, itch, temperature—C
What are the 4 divisions of spinal cord?
Cervical
Thoracic
Lumbar
Sacral
What is the dermatome?
The area of the skin and deeper tissues innervantes by a si file dorsal root
What are the two general sensory pathways?
Dorsal Column- Medial lemniscal pathway system (touch, vibration, pressure, proprioception)
Spinothalamic tract: pain and temperature
Describe the dorsal column-medial lemniscal pathway
1) dorsal columns (spinal cord)
2) dorsal column nuclei (medulla)
3) decussation into medial lemniscus (brainstem)
4) ventral posterior lateral nucleus (VPL) in Thalamus
5) primary somatosensory cortex (S1)
Which axons project vibration and touch?
Myelinated Abeta axons
Describe the trigeminal touch pathway
1) large Mechanoreceptor axons from face project through the trigeminal nerve to the principal sensory trigeminal nucleus.
2) From the principal sensory trigeminal nucleus, the pathway decussates and projects to the VPM in the thalamus.
3) from the thalamus it projects to the primary somatosensory cortex
What do lightly myelinated Adelta fibers register?
Register fast, sharp first pain
What do unmyelinated C fibers register?
Register duller, longer lasting second pain
Describe the spinothalamic tract
1) A-alpha and C afferent synapse in the substantia gelatonisa of dorsal horn
2) the pathway decussates and travels up the cord I. The spinothalamic tract to the thalamus (VPL) and then to S1
Explain what the ventral posterior complex projects to and from there where that part projects to and so on (1)
Ventral posterior complex to Brodmann’s areas 1,2,3a,3b
From there they all project to secondary somatosensory cortex which projects to amygdala and hippocampus
Area 2 also projects to parietal areas 5 and 7 which projects to motor and pre motor cortical areas
What stimuli do areas 3b and 1 receive?
Cutaneous stimuli
What stimuli do areas 3a and 2 receive?
Proprioceptive stimuli from muscles and joints
Explain the functional columns in neocortex
- can be found within somatotopic map
- Neurons with same modality from pia to white matter
- rows of slowly adapting neurons and others of rapidly adapting neurons
Why can you say about cortical map plasticity?
There can be a reorganization of cortical maps: maps are dynamic and adjust depending on the amount of sensory experience
What is the posterior parietal cortex involved in?
1) involved in somatic sensation
2) involved in analysis of “where” things are from visual inputs
3) involved in sensation of where things are on your body or your interpersonal space
Tectospinal Tract
Controls orienting reflex (looking towards light)
Projects out of superior colliculus, where RBG project, decussating right away and going into cervical musculature, including neck and shoulders.
Area 4
Primary motor cortex, stimulate leads to movement of muscles on contralateral side.
Area 6 - Broadman’s Area, “Higher Motor Areas”
Simulation leads to more complex movements
Lateral: Primary motor area
Medial: Supplementary motor area
Movement planning
BA6 fires same amount of action potentials when acting out something as much as being given instructions to do so.
