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4 types of receptors
(types of receptor) Free nerve endings
feels temperature and pain
(types of receptor) Pacinian (3)
-respond to displacement of the skin (pressure)
- best suited for sensing sudden change
(types of receptor) Ruffini (2)
-best suited to signal gradual changes in skin stretch
(types of receptor) Merkel
-best suited to signal gradual changes in skin indentation
-orderly entry of dermatomes into the spinal cord
-info from legs is maintain at a lower level
-topography is maintained all way to the cortex
(important features of pathway) steps from skin to brain
- 1. info enters via dorsal root ganglion
- 2. info projects to and synapses on to cells of dorsal column nuclei
- 3. Contralateral projection to ventral posterior nucleus of thalamus
- 4. primary somatosensory cortex
lateral geniculate nucleus
medial geniculate nucleus
ventral posterior medial nucleus
ventral posterior nucleus
"little man" on sensory map
simplest interaction between sensory and motor systems
the status of a muscle is monitored by two receptor systems which are?
-tendon organs and muscle spindles
Muscle spindles respond more when...
muslce is stretched because they are in embedded in the muslce itself
when muscles or tendons get stretched there is often an immediate effort by the body to work against that stretch
Withdrawal reflex (3)
-touch something painful and withdraw immediately
-motor neurons fire to contractmuscles based on sensory infor from your skin
*similar to stretch reflexes
-happens through activation of excitatory and inhibitory interneurons
(withdrawal reflex) Antagonistic muscles
-muscles that extend the limb and muscles to retract it
*biceps and triceps
(withdrawal reflex) Reciprocal innervation
-exciting one muscle while inhibiting the other to make the process fast
*antagonistic muscles have this
Cortical neurons can also control...
inhibitory interneurons and prevent reflexes from occuring
-we have "top down control" over everything
Loss of cortical control...
can lead to reflexes taking over
Physical stimulus of Chemosensation
*food, air, fluids
For perception of taste the molecules that interact with...
taste receptors are in food and drink
For the perception of smell...
the molecules are airborn
whats does the gustatory system process?
information about taste
Taste perception begins with the interaction between...
- molecules and taste receptors that lie within our oral cavity
- *on the tongue
5 primary tastes of the gustatory system
- - sweet
- -savory (umami)
(gustatory receptors) tastes are first detetced by specialized receptors called...
where are the taste buds located?
- they are usually in clusters around papillae
- *about 5o taste buds per papillae
4 different types of papillae
*they differ in their distribution on the tongue
taste buds are made up of...
- multiple cells that are the taste receptors
taste recpetors react to different tastes
Salty, sour receptorss are activated directly via...
(salt and sour receprtors) Na+ of NaCl passes through ion channel to...
directly depolarize and activate "salty" taste receptor
(salt and sour receptors) H+ of acids passes through ion channels, blocks K+ channels to...
depolarize and actiivate sour taste receptor
shape of sweet, bitter, or savory chemicals interacts with..
- receptors on the taste receptor cell
- *activates G-protein
Each taste buds contains...
- receptors of all types
- *proportions vary though
taste fibers seem to encode...
one taste best
3 Take home message for taste buds preference.
- activation of the specific receptor is the key
- activation of that receptors nerve fiber is key
- -evidence for implication:
- if we could actiivate a bitter receptor with sugar, we'd experience the sensation of bitter
Stimulation of taste receptors...
activates taste nerves
(taste nerves) Chorda tympani nerve
- -innervates anterior 2/3 of tongue
- *carries information
(taste nerves) Glossopharyngeal nerve
- innervates posterior third of tongue
- *carries information
(taste nerves) Trigeminal nerve
-codes somatosensory experience of taste
Vision, audition, taste, and touch all use...
different regions of the thalamus as a relay synapse on way to the cortex
steps to central projections
- from the tongue, taste efferents project to the rostral part of the nucleaus of solitary tract (NTS)
-NTS neurons project to taste nucleus in the thalamus (ventral posterior medial, parvocellular)
3 Individual differences
-genetic differences in the expression of taste receptors
- - great variety in the number of fungiform papillae between people
- *within the fungiform papillae, there is a varibility in the number of "bitter" and pain receptors
- -better able to detect bitter, find bitter tastes more intense
- *ability to supertaste is inherited
- **taste receptor gene
2 Other difference that supertasters experience
- - have more fungiform papillae
- -have more pain receptors
Influences that supertasters have on feeding behaviors
- -children tend to prefer cereals, sweeter drinks
- -dont like alcohol, coffee, bitter vegetables
- -heat/pain from spicy food is more intense
Flavor is comprised of...
- -odor (olfactory)