Transcript substance P
audition vision olfaction taste smell some addtl senses ◦ vestibular ◦ organ ◦ muscular tension sensory transduction ◦ - conversion of physical energy from the environment into changes in electrical potential sensory coding◦ Making sense of that input vision - light waves - taste – chemicals in fluid – hearing – sound wavestouch- pressure, temperature changes, smell- chemical in air vision taste hearing - touch smell - rods and cones in retina - taste buds on tongue - hair cells in inner ear (cochlea) - specialized receptors under skin - hair cells in olfactory epithelium Receptors show adaptation ◦ most sensitive to changes rather than constant stimulation ◦ why is this important? General pathway for most sensory information: General pathway for most sensory information: ◦ sensory neurons – sensory nerves spinal tracts – thalamus – primary cortex – higher association cortex Certain sensory neurons have a spontaneous firing rate. For these cells any change in their firing rate will convey important info (i.e. color vision) Different rhythms of firing also can convey different information * most highly developed sense in humans optic nerve for one eye - 1,000,000 axons auditory nerve contains about 30,000 axons adaptability and plasticity of visual system - make sense out of nonsense iris ◦ largely a muscle that expands and contracts pupil in response to light ◦ phenotypically unique – iris scan sclera ◦ tough opaque tissue pupil ◦ often used to determine neurological function light waves along the visual spectrum 1. 2. inverted image on retina region important for transduction is at very back of the eye retina - structure of eye important for transduction - retina contains neurons, glial cells and two types of photoreceptors responsible for transduction numerous differences between rods and cones rods shaped like a rod insensitive to color work well under low illumination cones shaped like a cone sensitive to color work best in bright light rods shaped like a rod insensitive to color work well under low illumination 20,000,000/eye location: found around the periphery of the retina cones shaped like a cone sensitive to color work best in bright light 5,000,000/eye location – found around the fovea of the retina ◦ responsible for sharp images and vision a low ratio of synaptic connections between neurons ensures higher definition and sharpness compared to a higher ratio sharp, acute vision less sharp focused visual input sharp, acute vision less sharp focused visual input rods shaped like a rod insensitive to color work well under low illumination 20,000,000/eye location: found around the periphery of the retina requires extended time until optimal function cones shaped like a cone sensitive to color work best in bright light 5,000,000/eye location – found around the fovea of the retina responsible for sharp images and vision works optimally very quickly there are at least two levels of communication within the neural cells of the eye ◦ rods and cones – bipolar cells – ganglion cells (axons make up the optic nerve) to CNS there are at least two levels of communication within the neural cells of the eye ◦ rods and cones – bipolar cells – ganglion cells (axons make up the optic nerve) to CNS ◦ across a single layer (rods and cones communicate with each other; bipolar cells communicate with each other; etc) optic nerve (ganglion cell axons) – make a blind spot on each eye! component (trichromatic ) or YoungHelmholz ◦ occurs at level of cones 3 different cones more sensitive to different wavelengths (ie colors) trichromatic or Young-Helmholz ◦ occurs at level of cones explains major type of color blindness ◦ deficits in certain types of cones can explain major type of color blindness At level of cones- GREAT! ◦ there are different cones that produce greater changes in electrical potentials depending on the color (wave) ◦ abnormalities in cones can explain red/green color blindness Very rare to see complete color blindness - only usually seen with brain injury ~ 7% of US males (10,000,000) compared to 0.4% women - red/green X-linked phenomenon X Y X XX XY Xb XXb XbY What happens in hereditary color deficiency? Red or green cone peak sensitivity is shifted. Red or green cones absent. 40 437 nm B 533 nm 564 nm G R 41 5% of Males 437 nm B 564 nm G R (green shifted toward red) 42 1% of Males (there is no green curve) 437 nm B 564 nm R (no green cones; only red and blue) 43 1% of Males (there is no red curve) 533 nm 437 nm B G (no red cones; only green and blue) 44 At level of cones- GREAT! negative afterimage – ◦ phenomenon that occurs as a result of overactivity or inhibition of neurons (due to color stimulation) opponent process theory ◦ occurs at level of bipolar cells and higher black/white, red/green; yellow/blue; one color excites bipolar cell; other color inhibits it says nothing about complexity as information reaches occipital lobe – says nothing about color constancy ◦ color constancy and the retinex theory- occurs at the level of the cortex…… prestriate – primary occipital cortex; multiple layers of higher association cortex Copyright © 2006 by Allyn and Bacon Touch (mechanical stimuli) Temperature (thermal stimuli) Pain (nociceptive stimuli) Specialized receptors respond to the various stimuli Copyright © 2006 by Allyn and Bacon Ruffini ending Merkel’s disks Free nerve endings Figure 7.15 Copyright © 2006 by Allyn and Bacon Pacinian corpuscles a necessary sense too little or too much – yikes! No obvious cortical representation (although there are regions that appear to be involved in the emotional component) Substance P◦ Most pain is a result of substances released by damaged tissues including substance P What else causes substance P release? Substance P is a large peptide and synthesis can take time SO Release of large amounts of substance P results in a brief time (when more is being synthesized) that is “pain-free” Substance P Endogenous opioids ◦ endorphins – endogenous morphine-like substances may explain acupuncture, placebo effects Descending pain control – pain can be suppressed by cognitive and emotional factors PAG – periaqueductal gray Copyright © 2006 by Allyn and Bacon 3 discoveries made this possible ◦ Electrical stimulation of the PAG has analgesic (pain-blocking) effects ◦ PAG and other brain areas have large amounts of opiate receptors ◦ Existence of endogenous opiates (natural analgesics) - endorphins Copyright © 2006 by Allyn and Bacon MIDBRAIN Congenital insensitivity to pain Extremely rare – less than 100 cases currently in the U.S. Inability to thermoregulate (through skin) or feel pain types: cancers, debilitating arthritis, back pain, undiagnosed, migraine Approximately 80 million people in the United States suffer Chronic pain consumes approximately $70 billion per year Chronic low back pain affects nearly 31 million Americans and represents the most common cause of disability in persons less than 45 years of age drugs – morphine derivatives ◦ oxycontin ESB periaqueductal gray drugs – morphine derivatives ◦ oxycontin ESB periaqueductal gray acupuncture pain management types: cancers, debilitating arthritis, back pain, undiagnosed phantom limb drugs – antidepressants; antiseizure meds cutting dorsal roots anesthetizing stump