Flashcards in Somatosensory System Deck (57)
What three broad categories is the somatosensory system divided into?
Exteroceptive - cutaneous senses
Proprioceptive - posture and movement
Enteroceptive - internal state of the body
Where are first order neurones cell bodies located?
Dorsal root ganglia
Cranial ganglia - innovates anterior head
Where are second order neurones cell bodies located?
Dorsal horn or brainstem nuclei
Where are third order neurones cell bodies located?
What does threshold mean?
The intensity of stimuli required to excite the sensory unit.
Low threshold receptors
Respond to low intensity generally non damaging stimuli
Mediate fine discriminatory touch
Thermoreception - cold to warm
Low threshold receptors - increasing stimuli strength
Increased rate of firing which denotes an increased intensity. However qualitative nature doesn't change so long as only other receptors aren't activated
e.g pressure doesn't become pain
High threshold receptors
Respond only to high intensity potentially damaging stimuli
Chemical - Substances
Polymodal - at least two of the above
Allows alterations to the firing rate in response to altered intensity or fire at a constant rate regardless of changing intensity.
Slow adapting neurones
e.g. stretch receptors
Fires continuously whilst deformed
Provides continual information
Amplitude of AP is still dependant on frequency
Fast adapting neurones
Number of impulses is proportional to the rate of change
Detects change in stimuli strength
Very fast adapting
Respond to only very fast movement
e.g. Pacinian corpuscles and vibration
Conduction Velocity -Group 1
Thick myelination and large diameter
Proprioceptors of skeletal muscles
Conduction Velocity -Group 2
Moderate myelination and moderate diameter
Mechanoreceptors of the skin
Conduction Velocity -Group 3
Thin myelination and small diameter
Pain and Temperature
Conduction Velocity -Group 4
No myelination and thin diameter
Temp pain and itch
What is a receptive field?
Territory in which a sensory unit can be excited
What correlates inversely with receptive field?
The larger the receptive field the smaller sensory acuity, so less sensitive to touch.
What is sensory acuity?
The ability to differentiate between two separate points, in this case two points of pressure pain etc
Why is sensory acuity inversely proportional to the receptive field?
As increasing the receptive field decreases the innervation density.
A patch of skin may contain overlapping receptive fields with different modalities? T/F
Where are meissners corpuscles present?
Abundant in areas of very high activity, not present in hairy skin
Sensitive to light touch
Where are merkels discs present?
Same distribution but also found in hairy skin.
Free nerve ending distribution.
List the hair end organs
Krause end bulbs
Krause End bulb distribution
Borders of dry skin and mucous membrane
Ruffins endings distribution
Within dermis and joint capsules
Paccinian corpuscles distribution
Dermis and fascia