Neuroanatomy of Somasthesis Flashcards
Name the four tactile mechanoreceptors and their properties:
Merkel: Slow Adapting, small receptive field, superficial, (responds to light pressure)
Ruffini: Slowly adapting, deep tissue, large receptive field, responds to pressure or stretch.
Meissner: fast adapting, superficial, small receptive field, 10-50 hz vibration response
Pacinian: fast adapting, deep, large receptive field, 100-300 hz vibration response
What type of nerve endings are found in joints?
Free nerve endings and encapsulated pacinian and ruffinian-like receptors
25% of the axons in the posterior columns originate from what structure?
Nucleus proprius.
Where do the inputs to the nucleus proprius come from? What function does this structure serve?
Convergent DRG synapses including nociceptive fibers. Integrate inputs for two point discrimination letter detection and direction detection. Secondary source of pain input.
What structures modulate the spinal response to nociceptive input?
Periaqueductal Gray, paragigantocellularis, portions of reticular formation.
What is the axon reflex?
Skin trauma causes release of bradykinins and prostaglandins which cause further stimulation of nociceptive fibers. Nociceptive activity is sent recurrently to distal nerve fiber endings which release substance P and cyclic GRP onto mast cells and blood vessels. This promotes histamine release and vasodilation which results in greater increase of bradykinins creating a positive feedback loop.
What is the gate control theory as pertaining to the anterolateral pathway?
States that neurons in the anterolateral pathway are controlled by inhibitory neurons in the substantia gelatinosa that release enkephalin and that these inhibitory neurons can be activated by cutaneous fibers (A-alpha, A-beta) thus reducing the perception of pain.
Describe how descending projections from the brainstem may modulate pain transmission:
Serotonergic and noradrenergic neurons from the brain may activate enkaphaline releasing interneurons in the substantia gelatinosa.
What neurotransmitters mediate pain transmission?
Substance P, glutamate
Name three cortical areas that are activated by nociceptive stimuli?
Primary somatosensory cortex, Anterior cingulate cortex, secondary somatosensory cortex.
Describe the neural pathway that is activated by (non-painful) cutaneous stimulation to the face:
Activated mechanoreceptors send axons to the principle trigeminal nucleus and rostral spinal trigeminal nucleus which cross the midline and ascend the ventral trigeminothalamic tract to the ventral posteromedial nucleus.
Describe the neural pathway that is activated by painful stimulation to the face:
Activated mechanoreceptor sends axons to the caudal spinal trigeminal nucleus which crosses the midline and ascends to the ventral posteromedial nucleus through the ventral trigeminothalamic tract.
What is homoplaseous evolution?
Features derived independently among species as opposed to inheritance from a common ancestor.
Describe the general hierarchy of somatosensory information processing starting at the thalamus:
Ventral posteromedial and ventral posterolateral nuclei of thalamus project to brodmann’s area 3a which projects to 3b. 3b projects to 1 and 2. Areas 1 and 2 project to secondary somatosensory cortex (brodmann’s areas 5 and 7)
As information ascends the hierarchy of sensory processing do receptive fields get larger or smaller?
Larger
