Traffic Week 6 - afferent Flashcards
information carried toward CNS is from..
- from viscera
2. from surface areas
perception
our conscious interpretation of the world created by the brain from a pattern of nerve impulses from sensory receptors
Receptor Physiology (perry and alf)
peripheral ends of afferent neurons have receptors that detect stimuli (changes in internal or external environment)
receptor physiology does what…(AP, adequate, specialized)
AP, respond to stimulus, special cell
- convert stimulus to an AP (transduction)
- each kind of receptor is specialized to respond to one kind of stimulus (the adequate stimulus)
a. receptor may respond to other stimuli as well, but it will lead to the sensation usually detected by that receptor - receptor may be a special cell associated with the peripheral ending of a neuron
types of receptors (based on what they respond to) (POTMNC)
POTMNC
- types of receptors (based on what they respond to)
1. photoreceptors–light
2. mechanoreceptors - mechanical stimuli
3. thermoreceptors – temperature
4. osmoreceptors - concentration of body fluids
5. chemoreceptors – chemicals
6. nociceptors(pain receptors)-tissue damage or distortion (intense stimulation of any receptor perceived as pain)
graded receptor potentials
stimulus alters membrane permeability of receptor
a. opens ion channels -main effect is Na+flowing in (depolarization), if summation of depolarizations reaches threshold, AP generated (called a generator potential)
b. if receptor is a separate cell, it releases a chemical messenger that opens chemically-gated Na+ channels in the nearby neuron, which generates an AP when threshold reached (called a receptor potential)
graded potential (stronger the stimuli)
stronger stimuli➝ greater frequency of APs (frequency code)
d. stronger stimuli often result in stimulation of a larger area ➝ more receptors activated (population code)
adaptation
- continued stimulation does not result in APs
- tonic and phase receptors
- mechanisms not well known, maybe inactivation of Na+ channels
somatosensory pathways (route it takes)
1st afferent, 2nd spinal, 3rd thalamus
- first-order sensory neuron is an afferent neuron with receptor, synapses with…
- second-order sensory neuron in spinal cord or medulla, synapses with…
- third-order sensory neuron - in thalamus, and so on
acuity (discriminative ability) (field)
- each sensory neuron has a receptive field (area it responds to)
- greater density of receptors results in greater acuity
- lateral inhibition (reduce activity of neighbors) also results in greater acuity
a. areas nearest stimulus stimulated to a greater
extent, areas farther away stimulated less b. most strongly stimulated pathway inhibits
other pathways via inhibitory neurons in CNS
pain (mechanic) (categories)
protective (tissue damage is occurring or about to occur)
- 3 categories of nociceptors
1. mechanical
2. thermal
3. polymodal - sensitized by prostaglandins (fatty acid derivatives from lipid bilayer, act locally)
fast pain pathway
- from mechanical and thermal nociceptors on large, myelinated fibers
- localized, sharp sensation
slow pain pathway
- from polymodal nociceptors on small, unmyelinated C fibers
- dull, aching, poorly localized sensation 3. activated by chemicals released from damaged tissue(e.g., bradykinin)
CNS connections (1st order)
first-order afferent fibers, second-order fibers, abnormal
built-in analgesic system
- neural mechanisms can suppress transmission in pain pathways at the spinal cord (presynaptic inhibition of release of substance P)
a. inhibiting fibers come from periaqueductal gray
matter and reticular formation in brain stem - uses opiate receptors on afferent pain fiber terminal a. morphine
b. endogenous opiates (e.g.,endorphins, enkephalins, dynorphin) - activation of analgesic system unclear a. pain modulators include exercise, acupuncture, hypnosis and some types of stress
