Touch Flashcards
What is the somatosensory system?
- provides information about touch, pressure, temperature, and pain, both on the surface of the skin and inside the body
What are the 3 interacting somatosensory systems?
- the exteroceptive system
- the interoceptive system
- the proprioceptive (kinesthesia) system
What is the exteroceptive system?
- cutaneous/skin senses
- responds to external stimuli applied to the skin
What is the interoceptive system?
- organic senses
- provides information about conditions within the body and is responsible for efficient regulation of its internal milieu
What is the proprioceptive system?
- monitors information about the position of the body in space, posture, and movement
What are the cutaneous senses?
- skin
- encode different types of external stimuli
What are the different types of external stimuli the cutaneous senses encode?
- pressure
- vibrations
- temperature
- pain
What is pressure caused by?
- touch
- mechanical deformation of the skin
When do vibrations occur?
- we move our fingers across a rough surface
What is temperature produced by?
- objects that heat or cool the skin
What is pain caused by?
- many different types of stimuli, but primarily tissue damage
What is the anatomy of the skin?
- epidermis
- dermis
- hypodermis
- Merkel’s disk
- Ruffini corpuscles
- Pacinian corpuscles
- Glbrous skin
- free nerve endings
- Meissner’s corpuscles
How many layers of the skin are there?
- 3 (outermost, middle, deepest)
What is the dermis?
- the outermost layer of skin
- cells here get oxygen from the air (not the blood)
- collection of dead skin cells, no blood vessels
What is the dermis?
- middle layer of the skin
What is the hypodermis?
- subcutaneous
- below the skin
- deepest layer of the skin
What are Merkel’s disks?
- respond to local skin indentations (simple touch)
What are Ruffini corpuscles?
- sensitive to stretch and the kinesthetic sense of finger position and movement
What are Pacinian corpuscles?
- respond to skin vibrations
What are Meissner’s corpuscles?
- only found in glabrous skin
- detect very light touch and localized edge contours (brail-like stimuli)
What are free nerve endings?
- primarily respond to temperature and pain
What is Glabrous skin?
- hairless skin
What are the 2 categories of thermal receptors?
- those that respond to warmth
- those that respond to coolness
- pain information is also conveyed by some of these cells
What are thermal receptors?
- carry temperature information
- pain information is also conveyed by some of these cells
- information is poorly localized
- the axons that carry it to the CNS are unmyelinated or thinly myelinated (slow action potential)
- some of the receptor proteins that are sensitive to temperature can also be activated by certain ligands
What are the ligands that can activate receptor proteins sensitive to temperature?
- capsaicin molecules activate heat receptors
- menthol molecules activate cold receptors
What is the thermal grill illusion?
- 4 pins; 2 warm, 2 cold
- when pins move together, can’t tell that it’s two temperatures
- sensory system gets confused when sharp change in temp, think it’s painful
What are sensation of pain and temperature transduced by?
- free nerve endings in the skin
What are nociceptors?
- detectors of noxious stimuli
- pain receptor cells
What are the high-threshold mechanoreceptors?
- one type of pain receptor cell
- pressure receptor cell
- free nerve endings that respond to intense pressure, like striking, stretching, or pinching
How does touch information travel from the body to the brain?
- axons from skin, muscles, and internal organs enter the CNS via spinal nerves
- 2 main pathways
What are the 2 main pathways of touch?
- spinothalamic tract
- dorsal columns
What is the spinothalamic tract pathway?
- poorly localized information (crude touch, temp, pain) crosses over the midline in the spinal cord (ascends contralaterally), just after the first synaptic connection
- this information ascends to the thalamus through the spinothalamic tract
What is the dorsal columns pathway?
- highly localized information (fine touch) ascends ipsilaterally through the dorsal column of the spinal cord
- first synapse in this pathway is in the medulla
- the information crosses over to the contralateral side as it ascends to the thalamus
Where do the 2 pathways meet?
- get bundled together in the midbrain
- synapse in the thalamus
- information goes to primary somatosensory cortex in the parietal lobe
Where is the somatosensory homunculus?
- in parietal lobe, in somatosensory cortex
- right next to primary motor cortex
What is the somatosensory homunculus?
- somatotopic map
- when different sites of primary somatosensory cortex are electrically stimulated, patients report somatosensory sensations in specific parts of their bodies
- the relationship between cortical stimulations and body sensations is reflected in a somatotopic map of the body surface
What is tactile agnosia?
- damage to somatosensory association cortex
- have trouble identifying objects by touch alone
- can often draw objects that they are touching, without looking, and they can sometimes identify objects from their drawings
What is phantom limb?
- a form of pain sensation that occurs after a limb has been amputated
- amputees report that the missing limb still exists and that it often hurts
- due to confusion in the somatosensory cortices (primary and association)
- brain gets nonsense signals and has difficulty interpreting them
What is the treatment for phantom limb?
- pharmacological, electrical, or behavioural have not proven to be very effective
- mirror box is cheap and easy but effectiveness is unclear
