A&P unit 4 - sensory physiology

What are the 3 ways sensory receptors can be categorized?

1) distribution - where found in body

2) stimulus origin

3) stimulus modality - stimulating agent

general sense receptors

-sensory category = distribution

-simple receptors all thru body

-includes somatic (skin, mucous membrane, propioreceptors) and visceral (in internal organs monitor pH, temp, pain)

special sense receptors

-sensory category = distribution

-complex receptors only found in head

-5 special senses - olfaction, gustation, vision, audition, equilibrium

exteroreceptors vs interoreceptors

-sensory category = stimulus origin

-extero - detect from external environ. → skin & special senses

-intero - visceral, detect from interal organs

propioreceptors

-sensory cateogory = stimulus origin

-detect limb mvmt of body → somatosensory neurons of muscles and joints

mechanoreceptor

-receptor category = stimulus modality

detect mechanical energy

thermoreceptor

-receptor category = stimulus modality

detect heat and cold

osmoreceptor

-receptor category = stimulus modality

detect changes in solute concentration of body fluid

chemoreceptor

-receptor category = stimulus modality

detect specific chemicals → smell, taste, O2 lvls in blood

nociceptors

-receptor category = stimulus modality

detect pain. sensitive to tissue damage

sensory process when sensor is connected to neuron

-normal AP process

→ chem Na opens, lead to VG opening, to AP

sensory process in a separate cell close to neuron

-stimulus activates Na influx (chem gated), depolarizes

-this opens VGC Ca channels

-Ca channels allow NT exocytosis

-NT goes to neuron, opens chem gated then VG gated Na, AP

What are the 4 things sensory neurons are responsible for sending to CNS

1) modality = type of stimulus

2) stimulus location

3) stim. intensity

4) stim. duration

sensory neuron modality

-what is stimulus? type of stimulus

-ex. temp vs touch stimulus

-based on labeled line = specific type of receptor sends to specific region in CNS

sensory neuron generic pathway

1) sense receptor activated on 1° sense neuron → GP → AP

2) 1° neuron synapses to 2° neuron in spinal cord or brain stem

3) 2° neuron synapses to 3° neuron in thalamus

4 3° neuron synapses to 4° neuron in specific area of cerebrum

receptive field

specific region (of skin) where a stimulus can activate a sensory neuron

-higher density = smaller RF size (many RFs packed into one spot, so they’re small but packed together)

How does receptive field density influence acuity?

-acuity = ability to sense/differentiate a signal

-more small dense RFs = higher acuity, lower discriminatory distance

-aka dense can detect more

(in the image, 1&2 detect 2 diff stim, but 3 is so big that 2 diff stim get detected as being in the same area)

How does detecting stimulus intensity work?

-intensity = # of receptive fields detected, determined by frequency sent to CNS

↑ stim strength = ↑ receptor/graded potential

↑ receptor potential = ↑ AP frequency (NOT strength)

↑ frequency = ↑ NT release = greater effect

localized vs widespread pressure

local = only few receptive fields activated

widespread = more receptive fields activated

→ more RFs = more intensity

adaptation (duration)

all receptors get less sensitive to a constant stimulus over time

tonic receptor

-limited adaptation, signal stays mostly the same

-pain receptors, head position receptors in inner ear

phasic receptor

-adapt rapidly to stimulus

-pressure receptors

tactile receptors

touch receptors

-most common, found in skin

-can be encapsulated or unencapsulated

free nerve endings

-unencapsulated tactile receptor

-closest to skin surface. simplest

-phasic or tonic

-sense temp or pain

hair receptor

-unencapsulated tactile receptor

-wrap around hair fibers

-phasic

-sense hair mvmt

Merkel’s disc

-unencapsulated tactile receptor

-tonic

-light, sustained touch/texture

Pacinian corpuscles

-encapsulated tactile receptor

-phasic

-deep pressure and vibration

-they are wrapped in connective tissue layers

Ruffini endings

-encapsulated tactile receptor

-tonic

-deep sustained pressure or stretch of skin

Meissner’s corpuscle

-encapsulated tactile receptor

-phasic

-light fluttering touch

sensation vs perception

sensation = stimuli act on body, receptors move it to CNS

perception = CNS interprets signals consciously

perception is not the same as sensation

How is stimuli detection imperfect?

-limited detection range

-cerebrum further manipulates sensory data → fills in info

-precortical processing (features of stimuli can be accentuated or repressed → lateral inhibition)

lateral inhibition

-happens via inhibitory neurons → blocks out stimuli around the main receptor, so only signal from the main receptor goes thru

-allows for better identification of where the stimulus comes from

3 types of nociceptors

-mechanical = cutting, crushing, pinching

-thermal = temp extreme change

-polymodal =respond to any dmg, including chemicals released from dmged tissues (histamine, bradykinin)

compare fast and slow pain

decussation

-nociceptor pain signal switches sides (signal felt on left hand gets sent to right part of brain)

-happens at spinal cord (2° neuron)

substance P pain pathway

neurotoxins - 3FTx

“3 finger neurotoxin”

ACH antagonist, binds to ACH receptors. Without ACH, cannot control muscle contraction

→ lead to paralysis and death if untreated