Somatosensory system
You can explain the concepts proprioception, dermatome and somatotropic maps.
You know the different mechanoreceptors and their properties.
You can explain the different track of the mechanosensory system and the anterolateral system.
You can explain the relation between receptive field size and precision and sensitivity of perception.
You know why chilli pepers taste "hot", why your chest aches when you have heartburn and how
phantom pain is perceived.
Somatosensory system; information from you body to the brain. Two different projections; mechanosensory
(cross over in medulla) and pain/temperature (cross over right away).
Dermatome, of which part of your body the ganglion is detecting information.
The primary somatosensory cortex is located dorsal of the
central sulcus. This contains a representation of the body in
separated regions; somatotropic maps = different areas in the
cortex that correspond to sensory information of different body
parts. Reconstructing the body based on the somatotropic maps
in the somatosensory and motor cortex give rise to the little
man, homunculus.
Somatosensory cortex receives input from two types of dorsal
root afferents, the track of these fibers is different, but both
direct to thalamus and then to S1 cortex.;
Touch and pressure; mechanosensory fiber, detect
stimulation using mechanoreceptors. Crosses in the
caudate medulla
Nociceptive afferent; pain and temperature afferent;
anterolateral system; it crosses over directly.
How do you sense ‘touch’? Start with touch and proprioception
(piezo). The mechanosensory fiber. Touch is detected as a change in pressure
on the skin. Pressure sensors (ion channels) change phospholipid pressure in
the membrane leaflet which operates opening/closing of ion channels. When
open they conduct positive ions which can thrive action potentials. Flows of
ions over the membrane; current and change in membrane potential; action
potential.
Receptive fields; how fine your sense detection is. Receptive fields are a
central concept of the senses. It is the space that one of this fibers can
actually gather information.
Large receptive fields have low sensory precision, as stimulations
within the field are difficult to discriminate.
Large receptive field have generally a high sensitivity for stimulation,
as any stimulus in a large are will result in a response.
Small receptive field are very precise but need a lot of stimulation.
, A lot of space in S1 then small receptive field e.g. your hands are very large represented in homunculus.
Touch, pressure and movement is detected by different
mechanoreceptors in the skin.
Pacinian corpuscle; mainly pressure, vibration.
Ruffini corpuscle; mainly motion detection, how your skin is
being stretched. Skin stretch.
Meissner corpuscle; most common one, in most places of your
body, little bit less precise than Merkel cell. Skin motion.
Merkel cell is more precise, really small receptive field. Edges,
points, corners, curvatures.
Some fibers detect change (rapid adapting) or persistent stimulation
(slow adapting).
When you rube/move your finger (you also activate ruffini and Meissner
corpuscles) and you have a finer touch.
Proprioception; receptors for this are found in muscles and tendons.
Muscle spindles; changes in muscle length
Golgi tendon; changes in muscle tension
Together these continuously map the positioning of the limbs. Where you
are in space. Projections of proprioception follow the same route as
mechanosensory fibers. Project to the ventral horn and through Clarkes
nucleus to the cerebellum (timing of voluntary movement) as well as the
thalamus.
Dermatome; the innervated area of sensory axons of a single dorsal root
ganglion.
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