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Human Physio Topic 7


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Visceral afferent
-come from visceral receptors (receptors that detect stimuli that arise w/in the body). Visceral receptors transmit info to CNS by class of afferent neurons: visceral afferents -carries info from the organs (& other viscera) to the CNS -not consciously aware of this: -subconscious information sent from the internal viscera to the CNS -e.g., concentration of CO2 in the blood (chemoreceptors) -e.g., blood pressure (baroreceptors) e.g., degree of stretch or distention in gastroint. tract (mechanoreceptors)
Afferent division
-sends info from body to CNS -filters/modifies sensory information -Stimulus intensity can be measured by the number of afferent neurons that are transmitting action potentials. -Most sensory information is transmitted through a series of three neurons to a final destination in the sensory cortex. -Stimulus intensity can be measured by the frequency of action potentials transmitted by an afferent neuron.
What are the special senses?
-vision -touch -hearing -taste -smell
Somatosensory system
-body surface sensations -e.g., skin, muscles, joints, inner ear, limb position
Sensory information
-afferent input that does reach level of conscious awareness -pathway: sensory afferent
What can we perceive?
-Color -Sound -Smells -shape -texture -taste -temperature
What can we NOT perceive?
-magnetic fields (birds can) -light polarization (birds can) -radio waves - x rays
Humans are limited in even perceptions that we do have, including:
-we can't hear high frequencies that dogs can -some features of stimuli are accented or ignored during precortical processing -cerebral cortex further manipulates data to "complete the picture" -our perceptions do NOT replicate reality
-the function of sensory receptors: its the conversion of one form of energy into another. -a receptor functions by converting stimulus energy to an action potential -converts energy of a sensory stimulus into changes in the membrane potential called receptor potential or generator potential.
How is a receptor specialized for specific stimuli?
-eyes see but do not hear 0but if you are hit in the eyes (hitting is a mechanical stimulus) you see "stars"
What are the 6 kinds of receptors?
1. photoreceptors = light 2. thermoreceptors = temp 3. mechanoreceptors = vibration, stretch 4. osmoreceptors = osmolarity 5. chemoreceptors = chemicals 6. nociceptors = pain
What is an example of a compound sensation that can occur?
Wet = thermo + mechano
What are the 2 types of receptor structures? Briefly explain each.
1. Seperate cells - produce a receptor potential, which is a graded potential. -most special senses are like this 2. Modified ending of afferent neuron - produces a generator potential, which is a graded potential -olfactory is the only special sense like this
Receptor potential
change in membrane potential of a receptor cell caused by a stimulus
the energy form of a stimulus
Sensory afferent
carries sensory info from the muscles and skin. Often at conscious level
pressure, vibration, temperature, limb location, balance
Special Senses
vision, hearing, smell, taste, touch
Do our senses replicate reality?
-we can detect some stimuli but with limitations -The afferent division and CNS filter/modify sensory info -some signals ignored while others enhanced -Cerebral cortex manipulates data to fill the gaps and "complete the picture"
Give an example of how a receptor is specialized for specific stimuli
-eyes see but do not hear -BUT if you are hit in the eye (hitting is a mechanical stimulus) your photoreceptors are activated, causing a perception of light- you "see stars"
When a receptor is stimulated (either type), it results in...
1. the non-selective opening of all small ion channels 2. Net influx of Na+ ions 3. Depolarization occurs 4. Graded potential, not AP, so the bigger the stimulus, the bigger the change in potential
Conversion of receptor and generator potentials into Action Potentials: Modified endings of afferent neuron
1. local current flow occurs from end of afferent neuron to axon of same afferent neuron 2. Causes opening of Na+ channels 3. If threshold reached in axon, then AP occurs
Conversion of receptor and generator potentials into Action Potentials: Separate Cell
1. Separate receptor cell stimulated - opens Ca++ channels 2. Ca++ influx causes release of chemical messenger 3. messenger binds to protein receptor on membrane of afferent axon 4. Na+ channels open on afferent axon 5. Threshold is reached if enough Na+ channels are opened --> AP occurs
Conversion of receptor and generator potentials in APs - important to note: (Fig 10.8)
*The stronger the stimulus, the higher the frequency of AP that occur in afferent neuron *As more receptors are activated, more APs are produced
Adaptation of receptors to stimuli (fig 10.3)
1. Slow adapting (tonic) responses -do NOT adapt to stimuli -continue to produce APs as stimuli continue -e.g., muscle stretch receptors 2. Fast adapting (phasic) receptors -rapidly adapt -stop producing APs
Phantom Pain
-Somatosensory pathway -Activation of the pathway at any point results in the same sensation as a true stimulation -Range: mild & temporary to intense & chronic -Tx: difficult & low success
Somatosensory pathways
-relay info to brain -body surface sensations -discrete chains of neurons -activation of a sensory pathway at any given point in the pathway results in same sensation as true stimulation -Phantom pain
Coding of Sensory INTENSITY: Frequency Coding
A stronger stimulus results in a larger receptor potential - stronger stimuli produce a higher frequency of AP's -Stronger stimulus --> higher frequency of APs
Coding of Sensory INTENSITY: Population Coding
-A stronger stimulus activates (recruits) a greater # of receptors -3 receptors -Strong stimulus --> greater # of activated receptors (i.e., weak may activate just 1 receptor while strong stim activates all 3)
Coding of Sensory LOCATION:
-Receptive fields ~depends on size & # of receptive fields, amount of overlap b/w receptive fields and lateral inhibition
Modifications of Lateral Inhibition
-A stimulus that strongely excites receptors in a given location inhibits activity in the afferent pathways of other nearby receptors -X(left),Y(middle),Z(right) receptors: Y is the strongest and location of stimulus -Y has higher frequency of APs -1st order AP occurs and 2nd order decreased activity occurs but Y is much greater still than X and Z
Modification by the CNS: Endogenous analgesia systems
-Brain has ability to block pain ~pain-blocking -Activated in response to other stimuli (e.g., stress) -Enkephalin blocks transmission b/w 1st (nociceptive afferent neuron) and 2nd order neurons -
What kind of receptors are for taste and smell?
Describe 3 important aspects of Taste & Smell
1. Receptors are chemoreceptors -receptor binds specific chemical and generates neural signal 2. Stimulation can cause "pleasurable" or "objectional" -Important for avoiding toxins, finding mates and finding good food
What is the human evidence for Human Pheromones?
-Infants identify mother by smell -mothers identify baby by smell -identify sex by smell (axillary extracts) -identify kin by smell (axillary extracts) -Women prefer men who have axillary extracts unrelated to them
What is the definition of a pheromone?
chemical signal released by an organism to communicate with other members of its species
What are the 4 primary tastes?
1. Sour 2. Salty 3. Bitter 4. Sweet
Taste buds are ...
modified epithelial cells
How many taste buds are there and where are they primarily located?
-10,000 -on tongue
How many receptor cells do taste buds have?
~ 50 (range of 50-150)
Describe 4 different characteristics of receptor cells:
1. Each receptor has its own biding site that selectively binds chemicals 2. Binding a chemical causes depolarization of receptor membrane 3. APs can be initiated in afferent nerons with which they synapse 4. Lifespan: 10 days
What causes the taste sensation Sour?
acids (H+)
What is the taste sensation salt primarily?
What is the taste sensation Sweet become activated by?
Glucose or related sugars that bind to the receptor
Olfactory Receptors
-Smell -Only special sense receptor that is modified ending of afferent neurons -axons collectively form olfactory nerve -only neurons/ receptor cells constantly replaced -5 million receptors of 1000 diff kinds -Responds to odors -opens Na/Ca++ channels - depolarizes cell -
Umami taste receptors detect the presence of what type of chemicals?
Amino acids
Taste is also heavily influenced by what?
Vomeronasal organ
-specialize organ in nose for detecting Pheromones
Taste Sensation: Sour
-caused by acids (H+) 1. H+ blocks K+, reducing K+ 2. Depolarization occurs 3. Ca++ enters cell 4. Releases neurotransmitters
Taste Sensation: Salt
-caused by Na+ ions (NaCl) 1. Na+ moves thru specialized Na+ channels 2. Depolarization 3. Ca++ channels open, Ca++ enters cell (which causes..) 4. release of neurotransmitter
Taste sensation: Sweet
-caused by organic molecules (glucose and related sugars) 1. Activates "G protein" 2. Blocks K+ channels, reducing them 3. Depolarization 4. Ca++ open & enter 5. Neurotransmitter released
Taste sensation: Bitter
-many chemicals bind to bitter receptors (caffeine, nicotine..) 1. Bitter blocks K+, reducing K+ 2. Depolarization 3. Ca++ open & enter 4. release of neurotransmitter OR*** Some use G protein ultimately causing release of neurotransmitter
-caused by amino acid (glutamate) 1. Net influx of Na+ 2. depolarization 3. ultimately causes release of neurotransmitter
Umami is percieved as what?
"savory" or "meaty" or "delicious"
activates G protein, blocks K+, decreases K+, depolarize --> release of neurotransmitter
H+ blocks K+, decreases K+, depolarizes --> release neurotrans
Bitter block K+, decrease K+, depolarize --> release neurotrans
Na+ channel increased, depolarize --> realse of neurotrans
Capsaicin -binds to receptor protein nocireceptors in mouth and throat -receptor proteins sensitive to alcohol, acid & high temp -Brain interprets as hot temp -doesn't damage cells -major irritant -release of endorphins --> people may feel euphoria
When an afferent receptor that is a separate cell receives a stimulus, _____ enters the cell

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