Somatosensory System Flashcards
What are the three main divisions of the somatosensory system?
Exteroceptive (cutaneous senses)
Proprioceptive (posture and movement)
Enteroceptive (internal body)
Once sensory neurones reach membrane potential what occurs?
Action potentials are triggered
What is the modality of a sensory unit?
The stimulus that the primary afferent neurones are tuned to
What is the threshold of a sensory unit?
The intensity of a stimulus required to excite a sensory unit
Give examples of low threshold units
Low threshold mechanoreceptors (fine discriminatory touch)
Low threshold thermoreceptors (cool/cold/warm/hot)
Give examples of high threshold units
High threshold mechanoreceptors
Thermal noiceptors (extreme degrees of heat)
Chemical nociceptors
Polymodal nociceptors
What is adaption in terms of a sensory unit?
When the sensory unit determines whether it should change its firing rate
What occurs in fast adaption?
When a constant stimulus causes the unit to stop firing quickly
Give an example of a sensory receptor that conducts rapidly
Proprioceptors of skeletal muscle
Give an example of a sensory receptor that conducts slowly
Itch
What is the receptive field of a sensory receptor?
The site at which a sensory unit can be excited
What are Merkel cell-neurite complexes formed from?
Many expanded nerve terminals with a closely associated Merkel cell
What are Meissner corpuscles formed from?
A capsule where several axons zigzag between Schwann cells
What are Ruffini endings sensitive to?
Shearing forces
What do Pacinian corpuscles detect?
Pressure
Give some of the sensory receptors of hairless skin
Merkel-cell neurite complex
Ruffini endings
Pacinian corpuscles
Meissner corpuscles
What does the dorsal column pathway detect?
Fine touch
Pressure
What does the spinothalamic tract detect?
Pain
Temperature
Within the dorsal column, sensory input to T6 and below runs in what?
Fasciculus gracilius
Within the dorsal column, sensory input ot above T6 travels in what?
Fasciculus cuneatus
What are the capabilities of the dorsal column pathway?
Stereogenosis
Vibration detection
Fine touch
Where do central terminals of the trigeminal nerve synapse?
Second order neurones in chief nucleus/spinal nucleus
What are the areas of the central sulcus (SI) called?
Broadmann area (1/2/3a/3b)
The receptive fields of SI neurones form what?
A somatotopic map of the body surface
Thalamic inputs to the SI terminate on which layer of the cortex?
Layer IV
What happens to the area of SI representing a finger if the finger is lost?
After several months it responds to stimulation from adjacent digits
What does the posterior parietal cortex (SII) do?
Receives and intergrates information from the SI as well as visual and auditory areas
