Lecture 7

Lecture 7:  Reflexes 

 
 

-polysynaptic reflexes = withdrawal reflex

-ESPS  flexor

-IPSP  extensor

      If touch hot pot you pull your hand away

      These feed to lower motorneuron in spinal cord

-polysynaptic means going through an interneuron

-if get strong withdrawal reflex you get a crossover response

      EPSPs go to the extensor on opposite side

      IPSPs go to the flexor on opposite side

      If touch a hot enough pot when you pull the hand away that you touch the pot with you push down with your opposite hand (crossover response)

-reflexes can be overcome by concentration

-Touch Receptors:

      -Pacinian corpuscle = has an axon into it, myelin sheath, Schwann cells encapsulate it creating lammaeli

            When push down on this get an indentation of these layers, layers filled with a gelatinous fluid, pushing down causes distortion and distortion channels, Na channels, will open

            Summation occurs at the first Node of Ranvier NOT at the initial segment and then it will fire 

-adaptation = happens rather quickly, fluid flows back in and is redistributed

      Occurs because of the cocktail onion shape of the lammaeli and this is why even if constant pressure is being applied you don't feel it (adaptation)

-other touch/pressure receptors will adapt by inactivating Na/Ca channels or by activating K channels

-receptors that adapt are called phasic

-receptors that don't adapt and can't send a message = tonic

-hot/cold sensations:  can only detect calories of heat

      You detect the flow of calories

      If calories flow out of the body sense COLD

      If calories of heat flow into the body sense WARM

-individual naked nerve endings that function as temperature receptors respond to absolute temperature

      Two groups of naked nerve endings responding, have a warm and cold receptor

            Warm receptor functions between 30 and 45 degrees Celsius

            Cold receptor function between 10 and 38 degrees Celsius

      We will adapt to temperatures between 20 and 40 degrees Celsius (about 68-104 degrees Fahrenheit) – like when jump in a pool that is 75 degrees you perceive the pool as cold

-hypothermia is what kills people and not drowning – takes approximately 10 minutes

-below 20 degrees Celsius it is COLD

-above 40 degrees Celsius it is WARM 

-PAIN

      -two pathways to the brain

            1.  quick, sharp pain followed by dull, achy sensation

      -autonomic nervous system is a strictly efferent system

-TASTE

      -five basic tastes:

            1.  sweet = sugar, sucrose (fructose, glucose)

                  Bind to metabotropic receptor, increase cyclic AMP

Activates protein kinase A in cytoplasm and phosphorylates a K channel causing it to close and this allows you to say "sweet"

1. sour = actually detecting acids, at the apex of the cell have K leak channels, hydrogen ions from the acids come in through the leak channel and block the exiting of the K and you taste sour
   
2. bitter = alkyloids
   

   bind to metabotropic receptor which utilizes the IP3-DAG system, IP3 is released into cytoplasm, opens Ca channels in the ER and you taste bitter
   

3. salty = have an ungated passive Na channel in the outer membrane of the taste bud and when Na passes into it you taste salty
   

   no Na in do not taste salty
   

   if eat a high salt diet and then eat a salty potato chip you say that is too salty
   

   if eat a low Na diet and stay on it for a few days and are give the same chip to eat you don't think it is as salty 
   

   if stay on low Na diet for weeks you won't have this craving a salt
   

4. umami = amino acids
   

   detects L-aspartate and L-glutamate
   

   (like the MSG test)
   

   -taste is delicious or savory
   

-tongue most sensitive to bitter, sour, sweet, salty

-taste buds are not different histologically, they can respond to all tastes, but each taste bud has a specific taste it responds the best to

-within the taste bud individual gustatory cells only respond to one taste

-there is a sweet pathway (attraction) and a bitter pathway (aversion) to brain

-can only taste things soluble in water 

-OLFACTION

      -80% of what you consider flavor is actually smell

      -ciliated cells in the nasal mucoso constantly sitirring and waving in a nonsynchronous manner to mix the molecules so that the receptors can detect the molecules

      -moleucules bind to metabotropic receptors in the nose

            Some are cyclic AMP others are IP3-DAG, in most cases they serve to open Ca channels

      -each bipolar cell contains only one type of receptor

      -each receptor can bind several odorants

      -the different types of receptors that are firing are doing so in a spatial form

      -using spatial patterning to send a message to the brain to tell it what you're smelling and this allows humans to identify 10,000 dif odors 

-EYE

      Detects electromagnetic waves from wavelength of 400-750nm (visible light)

      Detects EM waves using rods and cones

            Rods  function in dim light, they're very sensitive, can respond to a single photon of light, doesn't see colors (black and white are colors), all you see is shades of grey with a rod

            Cones  function in bright light, record color images

                  White = all colors at once

                  Black = none of the colors

-a rod has free floating discs in outer segment

      -each of these discs has a photopigment in the outer surface of its membrane, this pigmented membrane is going to pinch off the end of the rod and consume discs and and three new discs are made every hour, discs are made at the bottom and migrate upward

-photopigment called rhodopsin (is 11 cis-retinale + scotopsin)

      This opsin is called scotopsin in rods (the opsin of rhodopsin)

      -when only looking with rods (not enough light stimulating cones) using scotopic vision

-if we turn up the light to bright light, the rod gets flooded with too much light and can't function and you are only using cones, this is called photopic vision

-when use both rods/cones  mesopic

-which one, rods/cones, is based upon how much light is available

-rod has peak absorption of 505 nm

-in dark the rod fires, ion channels open and Na and Ca flood in

-the ion channels are held open by cyclic GMP and Na/Ca come in

-think of Na as the main thing that causes the release of the NT

-Ca plays a special role in NT release

      Cyclic GMP formed by glymulate cyclase, but is inactivated by Ca entering the cell, this causes cyclic GMP to be reduced and the amount of Ca coming in is reduced, when Ca is reduced more cyclic GMP is made

            THIS IS A CYCLE, it does not open or close it just finds a happy medium

-when get rid of the light, hitting the rod, this process changes

 
 

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