Chapters 6-7 (Part 2): Sensory Systems
Chapters 6-7 (Part 2): Sensory Systems PSB2000
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This 5 page Class Notes was uploaded by Sierra Gnecco on Thursday October 6, 2016. The Class Notes belongs to PSB2000 at Florida State University taught by Maria Greenwood in Fall 2016. Since its upload, it has received 5 views. For similar materials see Introduction to Brain and Behavior in Natural Sciences at Florida State University.
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Date Created: 10/06/16
PSB2000 Chapters 6 & 7 Part II Sensory Systems By Sierra Gnecco Chapter 7 7.4: Chemical Senses: Smell & Taste (cont.) Gustatory System ● Taste receptor cells are found on the tongue and in parts of the oral cavity. They typically occur in clusters known as taste buds. ○ Often located around small protuberances called papillae. There are four types of papillae: ■ Fungiform- “fungus or mushroom,” small, 1mm or less in diameter. (6 taste buds per papillae) ■ Foliate- “folded”, also used for tasting. ■ Circumvallat “around,” very large, also used for tasting. (most have 10 on back of tongue) ■ Filiform- latin for thread, supports cells. (no taste receptors) ● There are five different kinds of taste receptor cells, one for each primary taste. ○ Sweet, sour, bitter, salty, and umami (savory) ○ Umami was discovered by a Japanese chemist, Kikunae Ikeda, in the late 1800s. ● New genetic technology led to the discovery of the g-protein-linked receptors that were in the membranes of the taste receptor cells umami, sweet, and bitter. ● Salty and sour have ion channels. ● Tas○ Taste pore → taste cell → gustatory afferent nerve ○ Afferent nerves leave the mouth as part of the Chorda tympani (branch of facial nerve, VII), glossopharyngeal (IX), and vagus (X) cranial nerves, which carry info from the front of the tongue, the back of the tongue, and the back of the oral cavity, respectively. These fibers end in the solitary 2 nucleus of the medulla, where they synapse on neurons that project to the ventral posterior nucleus of the thalamus. The gustatory axons of the ventral posterior nucleus project to the primary gustatory cortex in the insula. ○ Summary: Cranial nerves → solitary nucleus (nucleus of the solitary tract) → ventral posterior nucleus of the thalamus → primary gustatory Brain Damage & the Chemical Senses ● Anosmia- the inability to smell. ○ Most common cause: blow to the head that causes a displacement of the brain within the skull and shears the olfactory nerves (cracking cribriform plate). ○ Hyposmia – reduced ability to detect odors. ○ Parosmia (troposmia) – brain perceives odor as an unnaturally unpleasant odor (i.e. flowers smelling like feces or cake frosting smelling like burnt wood). ○ Euosmia – brain perceives odor that is normally aversive as pleasant (reverse the above). ○ Phantosmia – olfactory hallucination; detecting odors that aren’t there. Can be pleasant or aversive. ● Ageusia- the inability to taste. ○ Rare b/c sensory signals from the mouth are carried via three separate pathways. ● Less complete deficits in olfaction: Alzheimer’s disease, Down syndrome, epilepsy, multiple sclerosis, Korsakoff’s syndrome, and Parkinson’s disease. Chapter 6 6.1: Light Enters the Eye and Reaches the Retina ● Light is defined as waves of electromagnetic energy between 380-760 nanometers. ● Light → cornea → pupil → lens → retina ● The amount of light reaching the retinas is regulated by the irises. ● Cornea- protective outer layer of the eye which refracts (bends) light. 3 ● Pupil- hole in center of the iris where light enters the eye. ○ Adjusts its size in response to changes in illumination. This represents a compromise b/w sensitivity (ability to detect presence of dimly lit objects) and acuity (ability to see the details of objects). ● Lens- focuses incoming light on the retina. Refracts light; changes to adjust focal distance (accommodation). 6.2: The Retina and Translation of Light into Neural Signals ● Retina- neural tissue; where photoreceptors lie. ○ It converts light to neural signals, conducts them toward the CNS, and participates in the processing of signals. ○ Comprised of five layers of diff. types of neurons: receptors, horizontal cells, amacrine cells, and retinal ganglion cells. ● The amacrine and horizontal cells are specialized for lateral communication (communication across the major channels, vertically connected). ● Retinal neurons communicate both chemically via synapses and electrically via gap junctions. ● Light reaches the receptor layer after passing through the layers. ● Photoreceptors (rods and cones) → Bipolar cells → Retinal ganglion cells → Axons of retinal ganglion cells form optic nerve, which leaves back of eyeball, and goes to brain. ● Blind spot- the gap in the receptor layer left after the bundle of retinal ganglion cell axons leave the eye. ○ No photoreceptors in the blind spot. Cone & Rod Vision ● Cones- cone-shaped receptors responsible for color vision ● Rods- rod-shaped receptors responsible for black/white/grey vision. ● Duplexity theory- cones and rods mediate different kinds of vision. ○ Cones: Photopic vision- good lighting and provides high-acuity colored perceptions of the world, poor sensitivity. ○ Rods: Scotopic vision- dim illumination, high sensitivity and poor acuity. 4 6.3: From Retina to Primary Visual Cortex ● Optic nerve (begins at optic disc) → optic chiasm (½ of neurons cross to the contralateral side) → optic tract projects to the superior colliculus and the lateral geniculate nucleus (LGN) of the thalamus → primary visual cortex. Other material ● Blindsight- A response to visual stimuli outside conscious awareness of “seeing” ○ How? ■ Place cells- fire when an animal passes a certain landmark ■ Head-direction cells track which way the face is pointing ■ Border cells- fire when an animal is close to a wall or boundary of some kind. ● Change blindness- no memory of something which an individual was not paying attention to. ○ If were are not paying close attention to something and it disappears, we do not notice the disappearance of the object. ○ Typically, a change is detected by motion (superior colliculus). ■ We can recognize when something is moving more than we can recognize when something is disappearing or changing color. ○ Ex: You’re watching a movie and paying attention to the main character talking. Something disappears in the background while the character is talking, but you do not notice it b/c your attention is not upon that object. ● Red-green color blindness ○ S-cones: Short ~400 nm) ○ M-cones: M edium ~525nm) ○ L-cones: Long (~700nm) ■ 2 kinds of cones: ● S & L b/c M-cone filled with L opsin. The M-cone becomes red. ● S & M b/c L-cone filled with M opsin. The L cone becomes green. 5