Ch 50 Bio

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Ch 50 Bio
2013-04-04 13:31:58
50 Bio

Ch 50 Bio
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  1. Functions of Sensory pathways
    sensory reception, transduction, transmission, and perception
  2. Types of sensory receptors
    mechanoreceptors, chemoreceptors, electromagnetic receptors, thermoreceptors, pain receptors
  3. Mechanoreceptors
    • Sense physical deformation.
    • Consist of ion channels linked to cilia outside of cell and internal structures (cytoskeleton). Bending or stretching generates tension which alters the permeability of ion channels.
  4. Chemoreceptors
    General or specific chemoreceptors:

    General: transmit info about total solute concentration of a solution. ex osmoreceptors in mammalian brain

    Specific: respond to individual kinds of molecules ex glucose, oxygen, carbon dioxide
  5. electromagnetic receptors
    detect electromagnetic energy such as visible light
  6. Thermoreceptors
    Detect heat and cold. Each specific to a particular temperature range. Located in skin and anterior hypothalamus. Send information to posterior hypothalamus (thermostat). 

    Capsaicin in peppers triggers influx of Ca2+ in sensory neurons. Receptors that bind to capsaicin respond to high temperatures.
  7. Pain receptor also known as
  8. Pain receptors
    Class of naked dendrites in epidermis. Respond to excess heat, pressure, or chemicals released from damaged or inflamed tissues. Nociceptor density is highest in skin but can be found in other organs. Prostaglandins, which are released by damaged tissue, worsen pain by increasing nociceptor sensitivity to pain stimuli.
  9. Sensing gravity/balance in invertebrates
    Most invertebrates rely on mechanoreceptors in organs called statocysts which contain ciliated receptors cells that enclose a membrane in which there is one or more statoliths, which are dense granules. When the statoliths are pulled down by gravity, they move the cilia of the receptor cells that they come into contact with which stimulates  the cells. These cells then send this information to the brain.
  10. Sensing sound in invertabrates
    Many insects have hairs that resonate to different sounds. These insects have hairs of different lengths and thicknesses, each of which resonate to a different sound wave. Certain insects may have hairs "tuned" to the frequency of a sound that is produced by a predator or a prey. Insects can also detect sound by means of a membrane (tympanic membrane) that covers a chamber filled with air.
  11. Amplification
    Is the strengthening of a stimulus by cells in sensory pathways. This often requires a signal transduction pathway involving a second messenger. Could also involve accessory structures (ex auditory canal)
  12. Sensory adaptation
    Decrease in responsiveness to continued stimulation
  13. Stretch receptors in muscle
    Sensory neuron dendrites surround the middle of small skeletal muscle fibers. Groups of these muscle fibers form into a spindle shape and are surrounded by conn. tissue and are distributed through muscle. When muscle is stretched, spindle fibers stretch, depolarizing sensory neurons, which generates an action potential.
  14. How does the sense of touch work?
    Sense of touch relies on mechanoreceptors that are dendrites of sensory neurons,which are embedded in conn. tissue in the skin.
  15. Middle ear consists of what
    Three small bones called the malleus, incus and stapes. The stapes hits the oval window of the cochlea to transmit the signal to it. Also contains Eustachian tube which equalizes the pressure in the inner ear.
  16. Components of the cochlea
    Two large canals: vestibular (upper) and tympanic (lower) which are both filled with perilymph. These canals are separated by the cochlear duct which contains endolymph. The floor of the cochlear duct contains the organ of corti, which contains ear mechanoreceptors (hair cells with hairs protruding into the cochlear duct). The hairs of the hair cells are attached to a structure called the tectorial membrane.
  17. How does cochlea work?
    Sound waves cause the basilar membrane to vibrate, which causes the hairs to bend which results in the depolarization of the hair cells. 
  18. Hair cells in the ear
    The hair cells produce rod-shaped hairs which are made of actin.
  19. What is hearing
    Hearing is the perception of sound waves produced by the brain
  20. How does hearing work?
    • Vibrating objects cause sound waves which cause the tympanic membrane to vibrate. The three middle ear bones transmit the vibrations of moving air to oval window on cochlea which creates pressure waves in fluid in cochlea. The waves in the fluid travel through the vestibular canal, which causes it to push down on the cochlear duct and the basilar membrane causing the tectorial membrane to vibrate up and down.  Hairs bent and mechanoreceptors in hair cells respond by opening or closing ion channels in the membrane. Bending in one direction depolarizes cell, which increases neurotransmitter release to neuron. Bending in other direction causes hyperpolarization which results in reduced neurotransmitters released to the neuron that has attached itself to the hair cell. Look @ following pics:
  21. What happens to the wave that passes through the vestibular canal?
    Once waves pass through the vestibular canal, they move around the apex of the cochlea and continue through the tympanic canal. Waves dissipate when they strike the round window at the end of the tympanic canal.
  22. What is the apex?
    Where tympanic canal and vestibular canal meet
  23. The eye
  24. Bipolar cells
    Receives information from several rods and cones
  25. Ganglion cells
    Receive information fromseveral bipolar cells
  26. Horizontal and amacrine cells
    Integrate information across the retina
  27. What is the basic configuratio of photoreceptor visual pigments
    Consists of a light absorbing molecule (retinal) bonded to a protein (opsin). Retinal is a vitamin A derivative
  28. Rod pigments
    Rod pigment is called rhodopsin (retinal combined with a specific opsin).
  29. How does rhodopsin work
    Absorption of light shifts bond in retinal from cis to trans arrangement. Changes molecuele from an angled shape to a straight shape. Change in shape destabalizes and activates rhodopsin.Changes color of molecule from purple to yellow (bleaching)
  30. What happens to the rod/cone cells when they are stimulated
    Following light absorption, signal transduction in photoreceptor closes Na+ channels. In the dark, the binding of cGMP to the channels keeps the channels open. Activated rhodopsin activates a G protein which activates a cGMP hydrolyzing enzyme, which causes Na+ ion channels to close, which causes p[hotoreceptor cell to hyperpolarize, not depolarize.
  31. How is the signal transduction pathway in the photoreceptor cells turned off after there is no more light?
    Enzymes convert rhodopsin back to cis form, which turns the signal transduction pathway (the one involving the G protein) off. If light is suddenly turned off, rods do not regain responsiveness for several minutes (temporarily blinded going from bright sunlight to darkened room)
  32. Processing of visual info in the retina by bipolar cells
    Rpds and cones form synapses with bipolar cells. In the dark, rods and cones depolarized -- continually releasing neurotransmitter glutamate. Some bipolar cells depolarize in respons and others hyperpolarize, depending on the glutamate receptor. When light is turned on, rods and cones hyperpolarize, shutting off the release of glutamate. The response of the bipolar cells is that they either depolarize or hyperpolarize. They do the opposite of whatever they did before when there was no light.
  33. Processing of visual info in the retina by ganglion cells
    Ganglion cells transmit signals from bipolar cells to the brain along their axons (which make up the optic nerve).
  34. How do amacrine and horizontal cells integrate info?
    Horizontal and amacrine cells help integrate visual information before it is sent to the brain.

    Some horizontal cells carry information from one photoreceptor to other photoreceptors and several bipolar cells. When illuminated photoreceptor stimulates horizontal cell, it inhibits more distant photoreceptors and bipolar cells that are not illuminated. This is called lateral inhibition and it results in sharpened edges and enhanced contrast

    Amacrine cells distribute some information from one bipolar  cell to several ganglion cells, which results in lateral inhibition.
  35. Receptive field
    A single ganglion cell receives information from an array of photoreceptors responding to light coming from different locations. Receptive field is the part of the visual field which ganglion responds to. Fewer photoreceptors supplying single ganglion cell resuult in smaller receptive field. Results in a sharper image. Ganglion cells in the fovea have small receptive fields which means that visual acuity is high there.
  36. Optic chiasm
    Optic nerves from the left and right eyes cross here. Near the cerebral cortex.
  37. Where do the ganglion cell axons lead to?
    Axons from the left visual field (from both the left and right eye) converge and travel to the right side of the brain. Axons from the right visual field travel to the left side of the brain. Most of the axons lead to lateral geniculate nuclei, which relays info. to the primary visual cortex in the cerebral cortex. Other neurons relay information to higher-order visual processing centers.
  38. What role does cerebral cortex play in visual perception?
    Turns 2D image to 3D image. Color, motion, depth, shape, detail.
  39. Types of cones
    There are three different types of cones in humans which contain three different visual pigments: red green and blue. The pigments are called photopsins (which are formed by the binding of retinal to three different types of opsin proteins.
  40. How does brain detect hues of colors?
    Brain detection of hues depends on differential stimulation of two or more cone classes.
  41. Abnormal color vision
    Genes for red and green pigments are x-linked. A single defective copy of either gene in males disrupts vision. Will affect perception of green or red.
  42. Short-sightedness
    Eye is elongated which causes image to be focused in front of retina
  43. Far-sightedness
    Eyeball is shortened. Image is focused behind the retina
  44. Five taste perceptions
    sweet sour salty bitter umami
  45. Two categories of taste receptors
    1. Sweet, umami, and bitter receptors are GPCR. Tastant binding to receptor triggers signal transduction pathway involving G protein, phospholipase C, and second messengers Ca2+, which causes opening of channel resulting in Na+ influx.

    2. Sour receptor. Part of the transient receptor potential family. Formed from pair of TRP proteins. Similar to capsaicin receptor. In taste buds, TRP sour receptors assemble into a channel in plasma membrane of taste cell, binding of an acid to receptor triggers change in ion channel resulting in depolarization.
  46. How does mammalian brain perceive certain tastes like sweet or salty?
    Mammalian brain perceives sweet or biter taste solely on basis of which sensory neurons are activated. It doesn't matter which chemical is used. A bitter receptor can be on a sweet taste cell and will be perceived as sweet.
  47. Smell in humans
    Olfactory receptor cells are neurons. They line the upper portion of the nasal cavity and send impulses directly to the olfactory bulb of the brain. Receptive ends of cells contain cilia extending into layer of mucus coating nasal cavity. Odorant binds to specific GPCR (odorant receptor) on plasma membrane of olfactory cilia. Triggers signal transduction leading to production of cAMP, which opens Na+ and Ca2+ ion channels, which leads to depolarization
  48. Role of calcium and regulatory proteins in muscle contraction
    At rest, actin fibers have their myosin binding sites blocked by tropomyosin which have troponin complexes bound to them. The troponin complexes have binding sites for calcium ions and when the calcium ions bind, the tropomyosin no longer blocks the actin, which results in muscle contraction.
  49. How does a neuron actually stimulate a muscle fiber?
    A motor neuron releases acetylcholine to the muscle fiber which causes it to depolarize and leads to an action potential. This action potential spreads to the inner part of the muscle fiber through T tubules. The action potential along the T tubules causes the release of calcium from the sarcoplasmic reticulum. The calcium then binds to the troponin complexes, allowing the muscle to contract.
  50. What type of muscle fiber would a cross-country runner have?
    Slow-twitch oxidative
  51. What type of muscle fiber would a sprinter have?