Sensory Perception Lecture Notes PDF

Perception General senses Special senses Lab 4 Outline Quick intro, including how sensory receptors work (in general) Brief discussion of touch More detail on the special senses: Smell Taste Vision Hearing and equilibrium Brief discussion of pain *We will also test many...

Perception General senses Special senses Lab 4 Outline Quick intro, including how sensory receptors work (in general) Brief discussion of touch More detail on the special senses: Smell Taste Vision Hearing and equilibrium Brief discussion of pain *We will also test many of these senses in Lab 4! Sensory Reception: Intro (Mainly anatomy review…) Do we have 5 senses? Sight, smell, taste, and hearing & equilibrium are all SPECIAL senses Receptors are specialized cells… are limited to the head, and are innervated by cranial nerves “Touch” = general senses Sensory receptors: Cells that respond to specific stimuli, and send information about that stimulus toward the CNS Can be classified based on: location, types of stimuli, or type of receptor Receptors: Classified by type of stimulus Chemoreceptors: Respond to chemicals in solution Thermoreceptors: Sensitive to temperature changes Nociceptors: Respond to painful stimuli (potential or actual harm) due to tissue damage from trauma, ischemia, or heat/chemicals… Mechanoreceptors: Sensitive to mechanical force (involve mechanically gated ion channels, as described in neural physiology unit) Photoreceptors: Respond to light energy How do sensory receptors get stimulated? Energy from the stimulus (mechanical, heat, light, etc.) produces a change in a receptor protein This receptor protein is usually a membrane protein on the sensory receptor cell Changing the receptor protein changes some property of the membrane (“receptor potential”) It might open or close an ion channel… altering the membrane potential…making an action potential more or less likely  Sensory Transduction The conversion of stimulus energy into a receptor potential (which could become an action potential…) Transducers convert energy from one form to another Sensory receptors convert energy from sensory stimuli (mechanical energy, light energy, etc.) into nerve impulses (electrical signals) In your sensory receptors: a signal from outside of the cell is transduced so that it can be transmitted throughout the body (as electrical signals) Conversion of receptor potential into action potentials (Sherwood, 2013) Receptor cells: Two main mechanisms of action Direct effect on membrane potential: The stimulus directly causes the opening or closure of ion channels which changes the membrane potential (making an action potential more or less likely to occur, or affecting the release of neurotransmitter…) Indirect effect on membrane potential: The stimulus binds to a receptor protein, then activates a second messenger (inside of the receptor cell). This triggers a cascade of events that change membrane potential (making an action potential more or less likely to occur, or affecting the release of neurotransmitter…) Figure 17-2: Different types of receptors (examples) Figure 17-2: Different types of receptors (examples) Figure 17-2: Different types of receptors (examples) Adaptation – see Figure 15-3 Decreased sensitivity to a continued stimulus Adaptation can be central (within the CNS) or peripheral (at the sensory receptor itself) Receptors can be tonic or phasic: Tonic receptors Phasic receptors “Touch”: Fig. 15-4 Many different receptors each giving different types of information! (see also Fig. 15- 2)  Special senses (Chapter 17) More specialized in terms of their: Structure (including support structures etc.) Nerve endings Are located only in specific parts of the body Five special senses: Smell (olfaction), taste (gustation), vision, hearing, and balance (equilibrium)  Olfaction: Anatomy review (Fig. 17-1) Olfactory epithelium: ▪Pseudostratified ciliated columnar epithelium with olfactory receptor cells Olfactory receptor cells: ▪Olfactory dendrites (SA!) exposed to external environment ▪Stimulated by odorant molecules brought in Olfaction Receptors are chemoreceptors Mucus acts as a solvent to dissolve airborne odorants (see diagram on following slide) Odorant binds to specific receptor, triggering a series of events inside the receptor cell that leads to the opening of Na+ channels Indirect effect Receptor cell is a neuron Many different types of receptors!! Unique feature of olfactory receptor cells: neurons that are exposed to the external environment and have a short Olfaction – One example of how a stimulus generates an AP (Seeley et al, 2006): see also Fig. 17-2 in your text  Gustation: Anatomy review Sensory receptor organ: Taste Buds Found on papillae Receptor cells are in epithelia of papillae Each papilla contains 50-250 taste buds! Each taste bud contains: Gustatory (taste) cells Basal cells Supporting cells Primary “tastes”? sweet, salty, sour, umami, bitter Saladin 2007 (see also Gustation (taste) Tastants dissolve in saliva in the mouth, enter the taste pore, and stimulate the taste cells Chemoreceptors Different mechanisms for different “tastes”… Salty, Sweet, Sour, Bitter, and Umami Some types of taste stimuli have direct effects, others have indirect effects (No need to memorize the specific mechanism for each type of taste!) See Fig. 17-2 in your text Gustation – examples (direct and indirect effects) sweet salt bitte r sour umami (Seeley et al, 2006 – see also Figure 17-2) Vision: Anatomy review A complex organ, with some photoreceptive cells Wall has 3 layers: Fibrous layer Vascular layer Inner layer Where photoreceptors are Internal cavity filled with fluids (humors) Lens divides the cavity into: Anterior cavity (filled Fig. 17-5 Vision: Intro Your eye functions like a camera to capture visual info Receptors to respond to light (are photoreceptors) Can only perceive light in the visible spectrum Light is bent (refraction) by the cornea and the lens to focus the image on the retina (hopefully!) If the cornea and/or lens bend the light too much or not enough, the image falling on the retina will not be in focus and you’ll Vision: Photoreceptors Two types of photoreceptors in your retina: Rods: for vision in low light (more in peripheral vision) Cones: colour vision (in bright light), visual acuity (found in macula, esp. the fovea – no rods here) Both contain outer segments that are packed with discs Discs contain visual Saladin 2007 (see also Vision: Photoreceptors Sherwood (2013) Rod and Cone cells Outer Segment (Photoreceptor sensitive light pigments) Inner Segment Synaptic Ending Vision: Rod cells and membrane potentials cones: bright light, colour rods: dim light, black and white (why you can’t see colours well at night Vision: (see also Fig. 17-15) Cone sensitivity to different colours (Seeley et al, 2006) The process of afterimage formation Prolonged viewing of, say, the red stimulus (upper right corner) causes adaptation in the red-sensitive cones (due to “fatigue” of the visual pigments for that wavelength of light) When the retina is subsequently exposed to a white light the red cones on that part of the retina are unable to respond The green cones are not fatigued, so the ganglion cells receiving stimulus form green sensitive cones send messages through the red-green channel, and the brain receives only a “green” signal Averted vision: Andromeda galaxy! https://www.youtube.com/watch?v=lDx5tPs8lEo Role of the lens: near vs. distance vision (Fig. 17- 11) So… why do most people need reading glasses as they age? - as we age the proteins stop losing elasticity, muscles dont contract and relax as easy Role of the lens: refractive problems (Fig. 17-13- part) Hearing  Hearing: anatomy review Structures of the external ear gather sound waves and funnel them in towards the tympanic membrane Vibrations of the tympanic membrane trigger vibrations of the ossicles of the middle ear (malleus, incus, stapes) The stapes then transmits the vibrations to the perilymph-filled vestibular duct of the inner ear (see next slide…) (Figure 17-  Hearing: more anatomy review (cont’d from previous slide) This causes the vestibular membrane to vibrate This causes the endolymph in the cochlear duct to vibrate This causes the basilar membrane to vibrate, and this movement is detected by the hair cells of the organ of Corti. (Ta da!) The vibrations are then transmitted out via the scala tympani and Hearing: Anatomy review  Hearing Receptors are hair cells in the organ of Corti (which is in the cochlea, in the inner ear) Stereocilia on each hair cell are attached to each other by tip links Move these stereocilia, and the K+ channels (mechanical) are opened, (Saladin, 2007) The role of stereocilia in sound transduction (Sherwood, 2013)  Hearing: pitch and volume How do we perceive different pitches? (high/low) Pitch is related to the frequency of the sound waves Waves of different frequencies cause vibrations of different parts of the basilar membrane Different cells are stimulated, which we interpret as different pitch (see Fig. 17-31, for example) How do we perceive different volumes? (loud/quiet) Volume is related to the amplitude of the sound waves Larger waves (greater amplitude) = louder sound (Sherwood, 2013) Larger waves (with more energy) cause more  Equilibrium: quick anatomy review Semicircular canals and vestibule of inner ear (“vestibular apparatus”) Semicircular canals: info on movement of the head in different directions (angular acceleration) Utricle and saccule: give info on linear acceleration (forward/back, up/down), plus position of head relative to gravity (see Fig. 17-25) Equilibrium: Receptor cells (Fig. 17-24) Equilibrium : Receptor cells (Fig. 17-24d)  Pain! Some topics… (a brief introduction!) What is pain? An indication of potential or actual tissue damage! Nociceptors are stimulated by things like chemicals released by damaged cells (among other things) This sensory input sometimes gets “confused” and results in referred pain (mapped in the figure shown here) Referred Pain (Saladin, 2007) See also Fig. 15-9  Projection pathways for pain (Saladin, 2007) Nociceptors are the sensory receptors that detect painful stimuli Like other sensory input coming in to the spinal cord, it enters via the dorsal root and synapses with a new neuron there This second neuron carries the info up towards the brain Some info is relayed through the thalamus, then out to the cerebral cortex (where we become consciously aware of the sensation) Some info is sent to other brain structures like the reticular formation (to make Spinal gating of pain signals (Saladin, 2007) This image shows essentially the same info on the previous slide (just in a “schematic” form), but adds in info about some pain-reduction pathways There are a few different pathways that our bodies can use to block the transmission of pain info up to the brain (even though nociceptors are tonic receptors that keep sending info!) We can tap into these pathways with other types of stimulation, such as rubbing or putting pressure on the injured spot. Treatments like acupuncture and acupressure likely work by recruiting these same pain- relieving pathways!  Take home message(s)? All sensory receptors perform sensory transduction (in some way) Different receptors do this in different ways, but they all convert the stimulus into something that can (ultimately) lead to an action potential in a sensory neuron Many senses combine inputs from different types of sensory receptors that contribute to our overall perception of that info We’ll play with this a little bit during class and in Lab 4 too! Examples will include taste and smell (and other things), vision and balance, and hearing and vision (In class we’ll also play with a few different tricks/illusions)