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
- Transduction
- -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
- Modality
- the energy form of a stimulus
- Sensory afferent
- carries sensory info from the muscles and skin. Often at conscious level
- Somatosensory
- 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?
- chemoreceptors
- 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?
- NaCl
- 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?
- smell
- 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
- Umami
- -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"
- Sweet
- activates G protein, blocks K+, decreases K+, depolarize --> release of neurotransmitter
- Sour
- H+ blocks K+, decreases K+, depolarizes --> release neurotrans
- Bitter
- Bitter block K+, decrease K+, depolarize --> release neurotrans
- Salty
- Na+ channel increased, depolarize --> realse of neurotrans
- A
- A
- Spicy
- 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
- Ca++