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Physiology 1021
Anita Woods

Vision- Eye and Retina November-22-12 12:38 PM Objectives: 1. Understand the fundamental componentsof the visual system a. Eye b. Retina- converts light energy to electrical energy c. Optic Nerves, Optic Chiasm, Optic Tract d. Lateral Geniculate Nucleus (LGN) e. Primary VisualCortex f. Extrastriate Visual Cortex 2. Know the principleretinal targets a. Lateral Geniculate Nucleus (LGN) b. Superior Colliculus (SC)- Tectum- Midbrain c. Pretectum- Edinger-Westphalnucleus - controls pupillary constriction d. Hypothalamus- suprachiasmatic nucleus(SCN) - Synchronization of di 3. Understand visual activity - The electromagnetic spectrum is a continuum of electromagnetic energy: energy produced by electric charges that are radiated as waves - The energy can be described by its wavelength:distancebetween peaks of the wave - Humansperceive light with wavelengths between 400nm-700nm - Short-wavelengths: gamma rays - Long wavelengths:radio waves Visual Acuity - Acuity: the capacityof the visual system to resolve fine spatial detail Three Factors a) The stimulus b) The eye c) The central visual pathways Snellen Acuity - Chart viewed at 20 ft. • At 20ft: viewer can detect 1 degree critical features(20/20) • At 20ft: you can see like normal peopleat 40ft. (20/40)- lower acuity • At 20ft: you can see like normal peopleat 15ft. (20/15)- higher acuity  Blind: 20/200 4. Know the basic structure and function of the eye a. Pupil: "hole" in the center b. Iris: the color of the eye - regulates size of pupil c. Cornea: clear sheet in front of the iris d. Sclera: the "white of the eye, the majority of the eye e. Conjunctiva: inside of the eyelid f. Extraocular Eye Muscles g. Optic Nerve Cross-Section a. Lens b. Ciliary Muscles c. Aqueous Humor- between cornea and lens d. VitreousHumor- between lens and retina e. Retina b. Ciliary Muscles c. Aqueous Humor- between cornea and lens d. VitreousHumor- between lens and retina e. Retina f. Fovea- region of highest acuity vision 5. Know the structureand function of the retina The retina contains five basic cell types: a. Photoreceptors - light sensitive - Convert light to energy b. Bipolar cells c. Ganglion cells - Output cells - Make up optic nerve d. Horizontal cells - Communicate laterally - Sideways information e. Amacrinecells - Communicate laterally - Sideways information The Retina has two alternating layers: a. Nuclear layers: where cell bodies are b. Plexiform layers: where the synapsesand axons are The Retina has 6 layers: a. Ganglion cell layer b. Inner Plexiform layer c. Inner Nuclear layer d. Outer Plexiform layer e. Outer Nuclear layer f. Photoreceptor Outer Segments Three Facts about the Retina - The retina is a sheet of several layers of cells that lies against the posterior (back) wall of the eye - The retina is set up backwardsto the way that you would expect it to be • Hits photoreceptors last as opposed to first - A pigment epithelium lines the back of the retina, againstthe photoreceptors 6. Know the differences between rods and cones and how they are distributedin the retina Photoreceptors: Two major parts 1) Outer Segment- the photosensitive part 2) Inner Segment- contains cell body Two Types (distinguished by shape): 1) Rods - Light sensitive (black and white system) - Used during dim lighting condition-scotopic vision - 120 million rods in each retina 2) Cones - Colour sensitive - Used during daylight conditions- photopic vision - Fovea contains only cones - 5 million cones in each retina Distribution of Rods and Cones in the Retina 1. Nasal retina is physically larger than temporal retina and containsthe blind spot (no photoreceptors) 1. Nasal retina is physically larger than temporal retina and containsthe blind spot (no photoreceptors) - Blind spot: the brain fills with information from the other eye 2. Rods and cones are not evenly distributed across the retina 3. In the periphery, rods outnumber cones (20:1) 4. Cones are concentrated in central vision (fovea)-the fovea containsno rods - Fovea: a pit, with the ganglion and bipolar cells pushed to the side, so light has an easier time striking the photoreceptors 5. Rods are concentrated in peripheral vision 6. No photoreceptors can be found in the optic disk 7. Know where phototransduction occurs Phototransduction:light into electricity - Occurs in the photoreceptor outer segment 8. Understand color impairments and why they occur - 2% of all men lack red or green pigment. They are referred to as red-green colour blind and are dichromats - About 6% of all men have red or green pigmentsthat do not absorb the same wavelengthsas the rest of the population - Therefor 8% of all males have some form of colour blindness - Males do not have an extra X chromosome to mask the deleterious trait whereaswomen do Vision- Pathways and Brain November-22-12 12:45 PM Objectives: 1. Understand the visual field, two hemifields, and binocular vision The Visual Field: - Your visual field is what you can see - You can see over 180 degrees - Each eye can view about 150 - There is a large region of overlap Binocular filed Outside of Binocular Field - Monocular crescent 2. Know why the optic chiasm is important for vision - In the optic chiasm, ganglion cell axons orientating from nasal retina cross to the contralateral side - The right side vision crosses and goes to the left brain - Axons from temporal retina do not cross, they stay ipsilateral - Why do the nasal retina fibers cross? - Your left hemisphere "sees" the right side of your world and vice versa. - The left side of each retina goes to the left hemisphere and vice versa - Temporal retina stays ipsilateral and nasal retina crosses to the contralateral side 3. Know the functional consequences of damage to an eye, an optic tract, the optic chiasm, or the lateral geniculate nucleus a. Damage to the eye: transection of an optic nerve Ex. Closing an eye - Lose peripheral of one eye - Lose monocular crescent of one eye b. Damage to an Optic Tract - Carrying information from opposite eye - Left optic tract --> right vision - LGN impairment would result the same way - Primary visual cortex would have the same impairment c. Damage to the Optic Chiasm - destroying crossing fibres from visual retina - Lose monocular vision on either side - Maintain binocular field - Tunnel vision d. Damage to the Lateral Geniculate Nucleus - The same as damage to the optic nerve - Left LGN --> right vision 4. Understand the principle findings of the experiments of Hubel and Wiesel Primary Visual Cortex, V1, or Striate Cortex - All neocortex, including V1, contain six layers. (I is on the surface and VI is the deepest) - It is 2-3mm thick - The first place in the brain where cells receive signals from both eyes Information Processing in V1(Primary visual cortex, or striate cortex) 1. Specialized neurons respond best to specific aspects of stimuli - Orientation, movement, size - Orientation, movement, size 2. These specializations can be demonstrated physiologically, by recording from neurons Experiments (V1 Physiology) - Spots of light stimulate ganglion cells - Spots of light do little to stimulate neurons in V1 - Sliding a slit of light across the visual field caused neurons to discharge - They found that V1 neuron respond best to bar-like stimuli with specific orientations 5. Understand orientation selectivity and directional selectivity Orientation Selectivity - Prefer specific orientation - Orientation changes create greater responses - Defines the receptive field of certain neurons Directional Selectivity - Respond to a direction of movement (right to left rather than left to right) V1 Neurons - Cortical neurons fire in response to specific features of the stimulus, such as orientation or direction of movement - Feature detectors - As we move further from the retina, neurons will be found to only respond to more complex stimuli 6. Understand parallel processing streams in visual cortex Parallel Processing Streams in Visual Cortex a. Dorsal Stream (Parietal Cortex) - "where" and "how" pathway - Spatial analysis - Motion - Visual control of movement Ex. A car in the parking lot b. Ventral Stream (Temporal Cortex) - "what" pathway - Object and pattern identification Ex. My car or another car Audition November-22-12 12:49 PM Objectives: 1. Describe sound and the variablesthat comprise sound - Variations in air pressure (patches of compressedair) Variables: a. Frequency(pitch)- the number of compressedair patches Hertz (Hz)- # of cycles/second b. Intensity (loudness)- the difference in pressure between compressed air pathces (Amplitude) 2. Understand the human frequency range - 20 (low) --> 20,000 (high) Hz Outer Ear Air Filled Middle Ear Air Filled 3. Know the structureof the auditory system Inner Ear Fluid Filled Three Major Divisions a. Outer Ear - Auricle (Pinna)-movable in some animals - Auditory Canal (External AuditoryMeatus) • 3cm long • Protects the ear drum • Enhancesintensities of sound by meansof resonance b. Middle Ear - Tympanicmembrane (ear drum) - Ossicles (three small bones) 1. Malleus (Tympanic 2. Incus Membrane) 3. Stapes Eustachian Tube c. Inner Ear (AuditoryTube) - Oval window - Cochlea Resonance- a mechanism that enhancesthe intensity of certain frequencies becauseof the reflection of sound waves in a closed tube The frequencythat is most intensified is the resonancefrequency - It is determined by the length of the tube. These frequencies are 2000-5000 Hz in humans 4. Understand how sound passes through the auditory system and is converted to electrical signal Outer Ear Middle ear Outer Ear Pinna Tympanicmembrane(ear drum) Oval window Auditory Canal Ossicles Cochlea Malleus Organ of Corti Incus Hair Cells Stapes The middle ear also contains the AuditoryTube (Eustachian Tube) - An airway between the middle ear and the pharynx(it is importantin changing air pressure) The Hair cells synapse with spiral ganglion cells and... Spiral Ganglion --> Ventral CochlearNucleus --> Superior Olive --> Inferior Colliculus --> MGN --> AuditoryCortex AuditoryNerve Lateral Lemniscus - Informationgoes to both sides of the brain immediately 5. Know why the ossicles are necessary 1. Becausesound vibrationsare ineffective for moving a fluid 2. The ossicles amplify the force exerted against the oval window 3. The ossicles convert air pressure changes into mechanical pressure 6. Understand the organization of the cochlea and how frequency is represented on the basilar membrane Cochlea:spiral-shaped- a coiled tube that looks like a snail (2 and 3/4 turns) - If you unroll the tube it is about 3.5cm long and 2mm in diameter - At the beginning of the tube, there are two windows with membranes (sheets of nylon of the holes): 1. The oval window- what the stapes contacts 2. The round window The Cochlea has three chambers: 1. Scala Vestibuli- filled with perilymph - Reissner's membraneseparate 2. Scala media- filled with endolymph - Basilar membrane separates 3. Scala Tympani- filled with perilymph The Basilar Membrane - Contains the Organ of Corti (photoreceptorsof the auditorysystem- create action potentials) - where hair cells are, have about100 stereocilia on their heads - Tips of hair cells contactthe tectorialmembrane - Movementof the hairs againstthe tectorialmembranechangesthe activity of the hair cells - Hair cells depolarizewhen the stereocilia bend - The tectorial membranehangs over the organ of corti Helicotrema- a hole between the scala vestibuli and scala tympani - Connectsthe top and bottomchambers - Base: thin and stiff (high frequencies are encoded) - Apex: thick and less rigid (low frequenciesare encoded) Sound Pathwayin the Cochlea Stapes --> Oval Window --> Scala Vestibuli --> Helicotrema --> Scala Tympani --> Round Window 7. Describe the two types of hair cells 1. Inner Hair Cells (pitch) - Auditory receptorcells in the inner ear that are primarilyresponsiblefor auditorytransduction and the perceptionof pitch 2. Outer Hair Cells - Auditory receptorcells in the inner ear that amplify the response of the inner hair cells - Motile response: a response to sound of the outer hair cells in which the cells move. The cells tilt and get slightly longer, which amplifiesbasilar membranevibration and therefor amplifiesthe response of the inner hair cells How signals get out of the cochlea - Hair cells synapsewith ganglion cells - The cell bodies of these neurons are located in the spiral ganglion - The axons of these neurons form the auditoryportion of the VestibulocochlearNerve (Cranial Nerve VIII) - Therefor, spiral ganglion cells are similar to retinal ganglion cells (the output neurons) 8. Understand the basic organizationof the auditorypathway 9. Describe how frequency is represented in primary auditorycortex Primary AuditoryCortex - A tonotopic map can be identified in the auditory cortex - Low frequencies are represented anteriorlyin the auditory cortex and high frequenciesare represented posteriorly 10. Understand the consequencesof cortical damageand how most peopleloss hearing - Input from both ears goes to both hemispheres of the brain, therefor when the auditorycortex of one hemisphereis damaged it does not result in the loss of hearing on one side (like vision) - Loss of ability to localize sound in the oppositehemifield - Most loss of hearingis due to the death (age) or destruction (loud noise) of hair cells - Hair cells do not regenerate Movement and Motor Control November-27-12 10:07 PM Objectives: 1. The motorunit - One motorneuron and al the muscle fibers it comesin contact with  The basic unit needed to perform an movement  Functional unit within a muscle 2. How the brain determineswhich muscles to use for a movementand how it gains information about them The central nervous system needs informationon: a. Which muscle group it will move(learned skill) b. The present length of the muscle it will move(contract/extend) c. The present tension in the muscle it will move The brain uses specialized proprioceptorsto gain information about muscle length and tension a. Muscle length- muscle spindles - In muscle b. Muscle tension- Golgi tendon organ - In tendons 3. Muscle receptors 1. Alpha motorneuron (brain to muscle) - Has its cell body within CNS, found within ventral horn - Releases Acetylcholine - Always excitatory(turn one on, evokea contraction) 2. Muscle Spindle - Senses the length of muscle and changing length - Found in muscles - Found in parallel to muscle fibers - Muscle stretch --> spindle stretch 3. Intrafusal Muscle Fiber 4. Extrafusal Muscle Fiber 5. 1a Afferent Neuron - Sensory neuron (muscle length) - Special pathway: dorsal column pathway - Faster, more direct 6. 1b Afferent Neuron - Sensory neuron (muscle tension) 7. Gamma motorneuron 4. Reflex mechanisms Reflex: involuntary response to a stimulus which requires the integrity of the nervous system resulting in a contraction or secretion 1. Reflex Arc Involves: a. A receptor (muscle spindle) specialized sensory nerve endings b. An afferent neuron: propagates sensory impulses to the CNS c. Synapse (spinal cord or brain stem) or an interneuron joining two synapses d. Motorneuron: innervates the effector organ e. Effector (muscle or gland) Reflex latency: time lapse between the stimulus and the response Depends on: - Latency of the receptor to respond - Length of the nerve pathway - Conduction time along the pathway - Number of synapses Interneurons can be either excitatoryof inhibitory a. Excitatory-excites alpha motorneuron b. Inhibitory- stops alpha motor neuron, transmitters,action potential --> no contraction Reflex Arcs can activate 2 types of pathways: 1. Monosynapticreflex: - One synapse between afferent and efferent neurons - Muscle spindle turned on activates 1a afferent neuron, synapses monosynapticallyinto motor neuron that goes to the muscle 2. Polysynapticreflex: - More than one synapse - Golgi tendon organ turns on 1b afferent neuron, goes into an inhibitory interneuron, inhibits alpha motorneuron going back to the muscle that had an increase in tension 3. Reciprocal Innervation: - The co-ordination of bodily movementsin which sensory impulses to the spinal cord excite extensor motorneurons and inhibit flexor motor neurons Ex. Knee flexion- quads are excited while hamstrings are inhibited 2. Stretch Reflex a. Stimulus: tap to tendon stretches muscle b. Receptor:muscle spindle stretches and fires c. Afferent path: action potential travels through sensory neuron d. Integrated center: sensory neuron synapses in spinal cord onto... e. Efferent path 1: somaticmotorneuron i. Effector 1: quadriceps muscle ii. Response: quadriceps contract, swinging lower leg forward f. Efferent path 2: interneuron inhibiting somaticmotor neuron i. Effector 2: hamstring muscle ii. Response: hamstring stays relaxed allowing extension of leg (reciprocal inhibition) 3. Alpha-gamma co-activation - A process by which alpha motorneurons and gamma neurons are activated simultaneously a. Alpha motorneuron (extrafusal fibers) fires and gamma motorneuron (intrafusal fibers) fires b. Muscle contracts - Ends of intrafusal muscle fibers contract and shorten c. Centers of intrafusal fibers stretch; firing rate of afferent neuron remains
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