2/23/99

Physiology II

 

Unit of function is the synapse

·         Pre-synaptic inhibition—can’t intake calcium which does not allow neurotransmitter to be released

·         Does not block the intake of the signal into the neuron

·         Cancer and opiums—does not block the damage, but the ability to transmit it is blocked

·         Motor neuron

·         Long axon making contact w/ skeletal muscle

·         Cell body is at the end

·         Has short dendrites around the cell body to intake signals

·         Sensory neurons

·         Input form Pacinian corpuscle, Merckle’s disc

·         Cell body is in the middle

·         Axon that goes to the next level of organization

·         Thermoreceptors—changes in temperatures

·         Detecting change

·         Proprioceptors—changes in pressure

·         Nociceptors—detect tissue damage; almost a chemical receptors (bradykinin, potassium)

·         Electromagnetic—light on the retina (rods and cones)

·         Chemoreceptors—taste and smell

·         Baroreceptors—oxygen pressure

·         Labeled line—specificity for modalities

·         Tactile stimulation of the hand goes to a specific area of the brain

·         Big myelinated fibers—proprioception, determine position in relation to gravity

·         Small, unmyelinated fibers—slow for pain

·         Receptors—adaptation/accommodation

·         Some are extremely adaptive—when change stops, they stop firing

·         Others do not adapt

·         Pacinian Corpuscle—very sensitive—pain

·         Body hair receptors—very sensitive

·         These stop firing after a few milliseconds

·         Joint Capsule receptors—adapt slightly; want to fire slightly or we would not know where are limbs are

·         Muscle spindle—

·         Pain—nonadaptive

·         Tonic receptors—few, fire constantly, muscle spindle always fires just at different rates

·         Phasic—respond to change, position of the body

·         Receptor potential—generator potential

·         Pacinian Corpuscle

·         create a stimulus, pressure changes the permeability of the membrane

·         looks like an onion

·         inside is negative, positive comes in with membrane change

·         get above threshold, fire action potential

·         circulate action potential through node of Ranvier to allow propagation of the action potential

·         important information goes fast—proprioceptive sensations, dealing w/gravity

·         less important information goes slower—thermal sensations, itch, tickle, arousal

·         classifications

·         myelinated/unmyelinated

·         diameter

·         myelinated 20-12, unmyelinated 12-0.5

·         conduction

·         big, fast is class A—alpha, beta, gamma, delta

·         small, slow is class C—can’t localize

·         IA, IB, II,III,IV

·         Functions (decreasing order of rate of conduction)

·         Myelinated

·         Fasts—muscle spindles (primary ending)

·         Muscle golgi tendon (contraction)

·         Secondary muscle spindles

·         Hair receptors

·         Pacinian corpuscles--vibration

·         Meissner’s, expanded tips—high discriminated touch

·         Deep pressure and touch

·         Prickling pain

·         Unmyelinated

·         Crude touch and pressure—can’t localize

·         Tickle—slowest, least specific

·         Aching pain

·         Cold—more cold receptors on surface on human body than warm (some myelinated fibers)

·         Warmth (some myelinated fibers)

·         Most pain is C type fibers

·         Motor functions

·         Skeletal A alpha

·         Muscle spindle A gamma

·         Sympathetic C

·         Receptor field

·         Allows for perception of a signal

·         Weak stimulus only fires a few

·         Moderate stimulus if push further into the tissue, duller object, dirty fires more signals

·         Strong stimulus—

·         2 point discrimination—about 3mm on fingertips, on back is about 70mm

·         greater the amount of input, the more receptors brought in, the more spatially separated the stronger the response

·         receptor potential/stimulus strength

·         until 40% of max have a linear response—low range detection

·         over 40% starts to level off and can stop functioning—adaptation can be reach if that type

·         more impulses at one time depends if a signal is started

·         neuronal pools—

·         on periphery, there are more inhibitory receptors compared to excitatory receptors

·         lateral inhibition—focusing of signal able to fire

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