Physio Midterm

• Vision


  The special sense of sight that is based on the transduction of light stimuli received through the eyes

  
• Eyes


  • Located within either orbit in the skull
  • Bony orbits surround the eyeballs, protecting them and anchoring the soft tissues of the eye
  • Eyelids, with lashes at their leading edges, help to protect the eye from abrasions by blocking particles that may land on the surface of the eye
  • Inner surface of each lid is a thin membrane known as the palpebral conjunctiva
  • Conjunctiva extends over the white areas of the eye (the sclera), connecting the eyelids to the eyeball
  • Tears are produced by the lacrimal gland, located beneath the lateral edges of the nose
  • Tears flow through the lacrimal duct to the medial corner of the eye, washing away foreign particles

  
• Extraocular muscles


  • Six muscles that originate from the bones of the orbit and insert into the surface of the eyeball
  • Four arranged at the cardinal points around the eye (superior rectus, medial rectus, inferior rectus, lateral rectus)
  • Contraction of each muscle moves the eye towards that muscle
  • Superior oblique muscle rotates the eye medially
  • Inferior oblique muscle rotates the eye laterally
  • Levator palpebrae superioris muscle elevates and retracts the upper eyelid

  
• Innervation of extraocular muscles

  • Lateral rectus innervated by abducens nerve
  • Superior oblique innervated by trochlear nerve
  • All other muscles innervated by oculomotor nerve
• Eye structure


  • Hollow sphere composed of three layers of tissue: fibrous tunic (sclera and cornea), vascular tunic (choroid, ciliary body, iris), and neural tunic (retina)
  • Anterior cavity between cornea and lens, filled with aqueous humor
  • Posterior cavity behind lens, filled with vitreous humor
  • Retina contains photoreceptors (rods and cones) that transduce light into neural signals

  
• Fovea


  • Small area at the exact center of the retina that lacks supporting cells and blood vessels, containing only photoreceptors
  • Provides the sharpest visual acuity because it has the least amount of light absorption by other retinal structures

  
• Moving away from the fovea

  Visual acuity drops significantly
• Photoreceptors


  • Rods and cones
  • Rods contain rhodopsin pigment, cones contain opsins sensitive to different wavelengths of light (red, green, blue)

  
• Photoreceptors have an inner segment containing the nucleus and organelles, and an outer segment specialized for photoreception

  
• Photoreceptors


  • Inner segment containing nucleus and other organelles
  • Outer segment with membrane arrays containing photosensitive opsin molecules

  
• Rod photoreceptors

  • Outer segments are long columnar shapes with stacks of membrane-bound discs that contain rhodopsin pigment
• Cone photoreceptors


  • Outer segments are short, tapered shapes with folds of membrane instead of discs
• There are three cone photopigments called opsins, each sensitive to a particular wavelength of light

  
• The pigments in human eyes are specialized in perceiving three different primary colors: red, green, and blue

  
• Photon


  A single unit of light, a packet of energy with properties of both a particle and a wave
• Visible light is electromagnetic radiation with a wavelength between 380 and 720 nm
• Opsin pigments


  Transmembrane proteins that contain the cofactor retinal
• Photoisomerization


  Photons cause some of the double-bonded carbons within the retinal molecule to switch from a cis to a trans conformation
• Until the retinal molecule is changed back to the 11-cis-retinal shape, the opsin cannot respond to light energy, which is called bleaching
• Rhodopsin, the photopigment in rods, is most sensitive to light at a wavelength of 498 nm

  
• The three color opsins have peak sensitivities of 564 nm, 534 nm, and 420 nm corresponding roughly to the primary colors of red, green, and blue
• Rods are sensitive to vision in low light conditions, and cones are sensitive to brighter conditions

  
• A single photon can result in an action potential from a rod's corresponding RGC
• By comparing the activity of the three different cones, the brain can extract color information from visual stimuli
• In a dark room, everything appears as a shade of gray because cones cannot react to low-intensity light, and rods do not sense the color of light
• Sensory nerves

  • Axons leaving sensory receptors have a topographical arrangement, with location of receptor relating to location of axon in nerve
• Spinal nerves

  • Contain afferent axons from sensory receptors in periphery mixed with efferent axons to muscles/effector organs
  • Dorsal root contains only axons of sensory neurons, ventral root contains only axons of motor neurons
  • Some branches synapse with local neurons, others travel up/down spine to interact with neurons at other levels
• Cranial nerves


  • Convey specific sensory information from head and neck directly to brain
  • Mostly ipsilateral, with right side of head connected to right side of brain
• Psychopharmacology


  The study of drug-induced changes in mood, thinking, and behavior
• Psychopharmacology studies drugs that may originate from natural sources such as plants and animals, or from artificial sources such as chemical syntheses in the laboratory
• Early Psychopharmacology


  • Hunter-gatherer or surviving tribal cultures used drugs depends on what the particular ecosystem a given tribe lives in can support, and are typically found growing wild
  • These societies generally attach spiritual significance to such drug use, and often incorporate it into their religious practices
  • With the dawn of the Neolithic and the proliferation of agriculture, new drugs came into use as a natural by-product of farming. Among them were opium, cannabis, and alcohol derived from the fermentation of cereals and fruits
• Drug

  A chemical substance used in the treatment, cure, prevention, or diagnosis of disease or used to otherwise enhance physical or mental well-being
• Types of Drugs

  • Pharmaceutical Drugs
  • Recreational Drugs
  • Over-the-Counter Drug
• Over-the-Counter Drug

  Medicines sold directly to a consumer without a prescription from a healthcare professional, as compared to prescription drugs, which may be sold only to consumers possessing a valid prescription
• OTC drugs are selected by a regulatory agency to ensure that they are ingredients that are safe and effective when used without a physician's care
• Drug Effects

  • Depressants (Downers)
  • CANNABIS
  • HALLUCINOGENS
  • Stimulants (Upper)
  • Cocaine
  • ECSTASY
  • Opiates & Opioids
  • HEROIN
  • METHAMPHETAMINE
  • Methadone
• Depressants (Downers)

  Chemicals that slow down the central nervous system and suppress brain activity causing relief from anxiety
• CANNABIS

  Makes users feel relaxed and heighten their sensory awareness. Users may experience a more vivid sense of sight, smell, taste and hearing
• HALLUCINOGENS

  Drugs that alter users' state of consciousness and produce different kinds of hallucinations. Leads to strong changes in thought, mood and senses in addition to feelings of empathy and sociability
• Stimulants (Upper)

  Act on the central nervous system and are associated with feelings of extreme well-being, increased mental and motor activity