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4 types of receptors
-"free-nerve endings
- pacinian
-ruffini
-merkel
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(types of receptor) Free nerve endings
feels temperature and pain
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(types of receptor) Pacinian (3)
-respond to displacement of the skin (pressure)
-rapidly adapting
- best suited for sensing sudden change
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(types of receptor) Ruffini (2)
-adapt slowly
-best suited to signal gradual changes in skin stretch
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(types of receptor) Merkel
-adapt slowly
-best suited to signal gradual changes in skin indentation
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Topography (3)
-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
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(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
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(thalamus) Vision
lateral geniculate nucleus
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(thalamus) Audition
medial geniculate nucleus
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(thalamus) Gustation
ventral posterior medial nucleus
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(thalamus) Somatosensation
ventral posterior nucleus
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Homunculus
"little man" on sensory map
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reflex
simplest interaction between sensory and motor systems
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the status of a muscle is monitored by two receptor systems which are?
-tendon organs and muscle spindles
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Muscle spindles respond more when...
muslce is stretched because they are in embedded in the muslce itself
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stretch reflexes
when muscles or tendons get stretched there is often an immediate effort by the body to work against that stretch
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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
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(withdrawal reflex) Antagonistic muscles
-muscles that extend the limb and muscles to retract it
*biceps and triceps
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(withdrawal reflex) Reciprocal innervation
-exciting one muscle while inhibiting the other to make the process fast
*antagonistic muscles have this
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Cortical neurons can also control...
inhibitory interneurons and prevent reflexes from occuring
*babinki reflex
-we have "top down control" over everything
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Loss of cortical control...
can lead to reflexes taking over
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Physical stimulus of Chemosensation
molecules
*food, air, fluids
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For perception of taste the molecules that interact with...
taste receptors are in food and drink
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For the perception of smell...
the molecules are airborn
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whats does the gustatory system process?
information about taste
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Taste perception begins with the interaction between...
- molecules and taste receptors that lie within our oral cavity
- *on the tongue
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5 primary tastes of the gustatory system
- - sweet
- -salty
- -sour
- -bitter
- -savory (umami)
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(gustatory receptors) tastes are first detetced by specialized receptors called...
taste buds
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where are the taste buds located?
- they are usually in clusters around papillae
- *about 5o taste buds per papillae
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4 different types of papillae
- -fungiform
- -foliate
- -circumvallate
- -filliform
*they differ in their distribution on the tongue
-
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taste buds are made up of...
- multiple cells that are the taste receptors
-
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taste recpetors react to different tastes
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Salty, sour receptorss are activated directly via...
ion channels
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(salt and sour receprtors) Na+ of NaCl passes through ion channel to...
directly depolarize and activate "salty" taste receptor
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(salt and sour receptors) H+ of acids passes through ion channels, blocks K+ channels to...
depolarize and actiivate sour taste receptor
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shape of sweet, bitter, or savory chemicals interacts with..
- receptors on the taste receptor cell
- *activates G-protein
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Each taste buds contains...
- receptors of all types
- *proportions vary though
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taste fibers seem to encode...
one taste best
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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
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Stimulation of taste receptors...
activates taste nerves
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(taste nerves) Chorda tympani nerve
- -innervates anterior 2/3 of tongue
- *carries information
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(taste nerves) Glossopharyngeal nerve
- innervates posterior third of tongue
- *carries information
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(taste nerves) Trigeminal nerve
-codes somatosensory experience of taste
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Vision, audition, taste, and touch all use...
different regions of the thalamus as a relay synapse on way to the cortex
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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)
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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
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Supertaster
- -better able to detect bitter, find bitter tastes more intense
- *ability to supertaste is inherited
- **taste receptor gene
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2 Other difference that supertasters experience
- - have more fungiform papillae
- -have more pain receptors
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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
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Flavor is comprised of...
- -taste
- -odor (olfactory)
- -texture
- -temperature
- -spiciness
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