physio e3l1: ch10a (afferent/sensory) and 10b (somatosensory system: skin, muscle,joint)

2 types of sensors

1. exteroreceptors

2. interoreceptors

   1. chemoreceptors

   2. barareceptors

   3. mechanoreceptors

1. extero = external environment

2. intero = internal environment

3. blood gas and pH, GI tract contents

4. blood pressure via blood vessel stretch

5. GI tract and bladder stretch

   1. pacinian corpuscle = vibration/pressure

2 sensory systems and types

1. somatosensory system = skin, MS, joint

   1. somesthetic sensations = skin

   2. proprioception = perception of limbs and body

2. special senses = confined to specific organ

   1. vision hearing taste etc…

1. modality

2. law of specific nerve nergies

3. adequate stimulus

4. inadequate stimulus?

1. transduction

   1. how?

1. modality = type(s) of energy/stimulus the receptor can detect

2. law of spec… = specific type of sensory receptor for each modality

3. adequate stimulus = modality a receptor responds to the best

4. inadequate stimulus will produce the perception of the adequate stimulus

signal transduction:

1. what is it

2. how + 2 effects

3. 2 types of receptors

1. transduction = converting stimulus E → electrical E

   1. receptor generates graded potential when triggered by sensory stimuli

      1. subthreshold graded potential OR

      2. suprathreshold graded potential (reaches threshold+) → AP

1. specialized receptor = neuron and receptor are 1 part

2. specialized receptor cell = neuron and receptor are 2 different parts

receptor adaptation:

1. what is it

2. why and what effect?

3. 2 types

4. after image? example

1. receptor adaptation = decrease in likelihood of receptor to respond to stimulus

   1. constant stimulus decreases amplitude of receptor potential → decrease perception of stimulus

1. 2 types

   1. tonic receptors = adaptation happens slowly,

      1. on a mV dgraph - mVecreases doesn’t reach 0 while stimulus is present

      2. muscle spindle

   2. phasic receptors = fast adaptation followed by after image,

      1. on a mV graph - mV reaches 0 while stimulus present, negative mV if after image

      2. touch

1. A result of receptor adaptation where after removing the stimulus there’s an initial (short-lived) AP as if the stimulus was there

   1. taking off a hat and still feeling as if its there

1. labeled lines =

2. specific sensory cortex*

3. sensory homunculus*

   1. how proportional/not proportional?

1. sensory unit*

2. receptive field

1. specific neural pathway → specific modality → specific location in the brain

2. destination of sensory/afferent input in the brain

3. shows how sensitive different types of sensory input are in the brain

   1. proportional to acuity (sensitivity) of body region

   2. not proportional to size of body region

1. single afferent neuron and all receptors associated w/ it

2. area in which a sensory unit is activated

sensory (afferent) pathway:

1. where does it go?

2. 3 parts

   1. location (PNS or CNS)

   2. site of synapse/with what

1. receptor → brain (cortex final destination)

2. 3 parts

   1. 1st order neuron (afferent neuron) = synapse w/ 2nd order neuron in the spinal cord OR medulla

      1. PNS and CNS

   2. 2nd order neuron = synapse w/ third order neuron in the thalamus

      1. CNS

   3. 3rd order neuron = axons terminate in cortex

      1. CNS

coding for a stimulus type:

1. what is it

2. 3 things it depends on?

3. integrating multiple types of sensory info?

   1. receptors for wet?

1. coding for stimulus = how brain gets info about stimulus

1. depends on:

   1. what type of receptor is activated, the modality

   2. specific pathway, the labeled line

   3. integration of sensory information

3. integrating a combination of sensory info may produce unique sensation

   1. no receptors for wet = combo of temp + pressure

2 ways for coding for stimulus intensity:

1. __________

   1. refractory period (RP)

   2. absolute RP

   3. relative RP

      1. what happens if you raise RP

2. ________

   1. recruitment

1. frequency coding = frequency of APs

   1. RP = period of no AP, perhaps in between Ads

   2. absolute RP = cannot get AP even if you get stimulus

   3. relative RP = receptors are taking a break, but can get AP if stimulus strong enough

      1. longer time in between APs

2. population coding = # of receptors activated

   1. recruitment = stronger stimulus activates more receptors

      1. receptors can be from the same neuron or from other afferent neurons

coding of stimulus location:

1. acuity

   1. based on what

2. 2 factors to determine location/acuity?

   1. more overlap = ?

3. location/role of inhibitory neurons

1. precision of stimulus perception based on receptive fields

2. factors

   1. size of receptive field

   2. degree ov overlap b/t adjacent receptive fields

      1. more overlap = harder to determine

3. inhibitory neurons increase acuity via modulation (axoaxonic) of APs from adjacent overlapping neurons

   1. b/t afferent (1st order) neuron and 2nd order neuron

coding of stimulus location:

1. two-point discrimination

   1. measures what

   2. depends on what

2. sight and hearing

   1. depends on what

   2. how diff from two-point

1. tactile acuity = ability to perceive 2 points on skin

   1. smaller receptive field size is greater acuity

2. sight and sound unrelated to coding by receptive fields

   1. sight = N/A

   2. hearing = depends on time and intensity differences b/t ears

4 somatosensory receptors:

1. proprioceptors =

2. mechanoreceptors =

   1. 2 types, nerve endings?

3. thermoreceptors =

   1. what type of receptor / nerve endings

   2. overlap/paradoxically cold?

4. nociceptors =

   1. type of receptors

   2. nerve endings

   3. 3 types

which are TRP receptors?

1. proprioceptors = muscle/joint position

1. mechanoreceptors = pressure/stretch

   1. rapidly adapting

   2. slowly adapting

      1. free nerve endings = temp/pain

      2. merkels disk + Ruffini’s ending = touch

1. thermoreceptors = war

   1. TRP receptors = respond to temp and some chemicals, and exhibit rapid adaptation (IcyHot chemicals also fire)

      1. warm and cold receptors = free nerve endings

      2. cold receptors → cold/warm overlap → warm receptors→ warm/cold overlap→ cold for painfully hot

1. nociceptors = pain

   1. TRP receptors

   2. 2 free nerve endings = A-delta and C fibers

   3. 3 types

      1. mechanical

      2. thrmal

      3. polymodal = mechanical thermal, chemicals released from damaged tissue

3 somatosensory pathways:

1. what are they

2. where decussate

3. what sensations

1. dorsal column, posterior column, medial lemniscal pathway

   1. decussate in medulla

   2. touch and pressure, proprioception

2. lateral spinothalamic tract

   1. decussate in spinal cord

   2. pain and temp

3. anterior spinothalamic tract

   1. decussate in spinal cord

   2. crude touch and pressure

pain response:

1. sensation produced by what, perception depends on what

2. 2 types of pain

3. pain pathway

4. visceral pain and referred pain

1. produced bytissue damaging stimulus, depends on past expieriences

2. 2 types

   1. A-delta fibers = fast/sharp pain, myelinated and easily localized

   2. C fibers = slow/achy pain, unmyelinated and poorly localized

3. 1st order neurons A-delta or C fibers → 1st order neurotransmitter = substance P → spinothalamic (lateral) tract

4. visceral pain = internal organs

5. referred pain = when visceral pain has shared pathway w/ somatic sensation

Pain response modulation:

1. what type

2. modulated v. unmodulated

   1. parts

   2. what happens if you stimulate the interneuron?

1. unmodulated pain = axoaxonic modulation w/ interneurons

   1. 1st order neuron = nocireceptor w/ 2 branches

      1. one straight to synapse w/ 2nd order

      2. one that inhibits inhibitory interneuron = pain

1. modulated pain = axoaxonic modulation w/ interneurons

   1. same 1st order neuron setup + mechanoreceptor collateral that stimulates the inhibitory interneuron

      1. stimulating the inhibitory interneuron = pain decreases

pain modulation:

1. endogenous alalgesia

   1. how

   2. at 1st and 2nd ordre neuron

1. hyperalgesia

2. stump pain

3. phantom limb pain

1. endogenous analgesia via endogenous opioids

   1. enkephalin

      1. at 1st order neuron = blocks release of substance P

      2. at 2nd order neuron = competitive inhibitor of opioid receptors

2. hyper algesia = cytokines enhance pain

3. stump pain = residual amputee pain from cut nerve endigns

4. phantom limb pain = 2nd and 3rd order neuron activation from other places

taste:

1. how do taste receptor cells respond to tastes

2. 4 tastes, from what 5 receptors?

3. 
   

1. many taste receptor cells respond to many tastes, the but have an adequate stimulus / taste they respond to more than others

2. 4 tastes/5 receptors

   1. sour = H+

   2. salty = Na+

   3. Sweet = simple carbs

   4. bitter = nitrogen

   5. umami (flavor enhancer not a taste) = glutamate/amino acids

1. 2 parts coding of taste

2. neural pathway for taste

1. coding

   1. pattern theory = not strict receptor specificity, multiple receptors and neurons

   2. requires sense of smell

2. taste receptor cells → 3 afferent neurons

   1. CN 7 = facial nerve = anterior 2/3 tongue

   2. CN 9 = glossopharyngeal = posterior 1/3

   3. CN 10 = vagus = pharynx

olfaction:

1. how does it work/adaptation

2. 3 cell types in olfactory epithelium

3. why no smell when cold?

4. difference from taste?

5. olfactory binding proteins?

1. chemicals in air dissolve into mucus and bind chemoreceptors in olfactory epithelium → CN 1, olfactory nerve… rapid adaptation

2. 3 olfactory epithelium

   1. receptor cells = respond to odorants dissolved in mucus

   2. basal cells = receptor-precursor cells continuously replaced

   3. sustentacular cells = support/maintain extracellular environment

3. thicker mucus layer when cold

4. 
   

5. in mucus, transport hydrophobic odorants to chemoreceptors

olfaction:

1. olfactory signal transduction

1. olfactory coding:

   1. how detect/distinguish?

   2. how increase signal

2. how different from taste?

3. 3 olfactory neural pathway steps

1. metabotropic w/ G protein (Golf) → Aden. cyclase → cAMP → open cation channels → depolarization +

2. coding

   1. specific receptor cells for each type of odorant

   2. increase air flow = more chemicals

3. has specific olfactory receptor cells for each type of odorant

4. 3 steps

   1. CN 1 → olfactory bulb: synapses w/ 2nd order neuron

   2. bulb → olfactory tract

   3. tract → then cortex and limbic system (memory)