PSL 250 Week 5 Lecture notes
PSL 250 Week 5 Lecture notes PSL 250
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This 10 page Class Notes was uploaded by Ren K. on Friday September 30, 2016. The Class Notes belongs to PSL 250 at Michigan State University taught by Dr. Patrick Dillion in Fall 2015. Since its upload, it has received 8 views. For similar materials see Introductory Physiology in Physiology at Michigan State University.
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Date Created: 09/30/16
PSL 250 - Lecture 12 - Cerebellum - Sleep - Spinal Cord Cerebellum ● Structure on the back of your brainstem. ● Controls coordinated movements and learned movements. ○ Balance ■ Maintains balance and controls eye movements. ○ Coordination ■ Connected to the motor cortex, receives “motor plan”. ■ Afferent inputs gives current muscles position. ■ Coordinates function with “aim” , i.e. movement matches motor plan. ■ As practice occurs, motor cortex, parietal lobe and cerebellum takes over. ■ Planning is reduced, initiation of activity is faster and smoother input to cortex. ○ Input to cortex. ■ Allow cortex to know current position and movement. ■ Cortex uses this information to plan future movements. Brain Stem ● Medulla, pons, and midbrain. ● Interface between the spinal cord and higher brain centers. ● Cranial nerves supply sensory and motor function to head and neck. ● Different centers in brainstem controls the heart rate, breathing, wakefulness. Reticular Activating System - RAB ● Neural net, awareness of surroundings. ● Cortical, pain, auditory, visual input. ● Output to cortex and thalamus - all cortex controls consciousness/ sleep. Sleep ● Low frequency activity in hypothalamus + thalamus = sleep. ● Reason needed unknown. EEG Patterns ● Slow wave patterns in EEG give slow wave sleep its name. ● EEG patterns during REM sleep similar to being awake. Slow Wave sleep ● 4 stages, each progressively deeper over about 75 minute cycle. ● Circadian rhythm causes the increase in adenosine, leading to sleep. ● Caffeine blocks adenosine response. ● Sleep Factor - muramyl dipeptide = strong sleep inducer. REM - Rapid Eye Movement (Paradoxical Sleep) ● 15 minutes long, at the end of a slow wave sleep cycle. ● Paradoxical sleep - hard to awaken, most likely to wake self. ● High visual cortex, low frontal, high memory areas = dreams become illogical. ● New synaptic contacts made causes the increase in long term memory. ● Will make up missed REM sleep. Spinal cord ● Neural tissue, encased in vertebral column (v pronounced like f) ● Carries APs between the brain and the body. ● Gray matter in the middle , cell bodies and interneurons. ● White matter on the outside, myelinated neuronal tracts. Tracts ● Tracts are bundles of neural axons that carry APs. ● Ascending tracts carry APs towards the brain ● Descending tracts carry APs from the brain to efferent neurons. Dorsal Roots ● Entry points for afferent neurons to the spinal cord, bilateral. ● Afferent cell bodies are in the dorsal root ganglia. Ventral Roots ● Carry efferent APs out of the spinal cord. ● Cell bodies of efferent neurons in the gray matter. Reflexes ● Natural response without a conscious input. Reflex arc ● Receptor - Afferent neuron - CNS - efferent neuron - effector. ● CNS portion may have 1 or more synapses. ● Effectors are muscles and glands. ● Monosynaptic reflex - 1 synapse. ● Polysynaptic reflex - Multiple Synapses ● Interneurons between afferent and efferent neurons. Withdrawal Reflex ● Polysynaptic reflex ● Multiple neurons between afferent and motor neurons. ● Prolonged response and feedback. ● Very strong reflex, but with potential CNS input. Stretch Reflex ● Muscle length information ● Monosynaptic reflex - knee jerk. ● Activation of afferent neuron produces the reflex response through synapse to efferent neuron. ● No control by upper CNS. PSL 250 - Lecture 13 - Afferent Nervous System - Pain - Taste - Smell Sensory Receptors - Sensation ● Connect an environmental signal to the body. ● Transduction is the conversion of a stimulus to a physiological signal. ● The brain converts the physiological signal into a perceived sensation. Stimulus ● Environmental signal. ● Binds and changes a receptor - signal now in body. ● Each receptor binds one stimulus best. Sensation ● Conscious senses - 5 senses, also time. ● Unconscious - position, temperature, BP changes. Types of Receptors ● Must bind stimulus - no dendrites on receptor cells (example : smell) ● Modified nerve endings to interact with stimulus. Physical ● Physical changes open ion channels. ● Changes membrane potential. ● Touch receptors, hair cells in ears, photoreceptors, baroreceptors. Chemical ● Taste, Smell. ● Chemoreceptors - chemical binds receptors - opens channel, changes m.p. Receptor Potentials ● Also called generator potentials, local potentials. ● Depolarization of receptor cells. ● Size of potential proportional to size of stimulus. ● Receptor fields vary in size, depend on number of afferent neurons. Magnitude ● More stimulus - greater RP. ● In receptor cells without AP, release of NT is proportional to RP. Frequency Dependence ● Continuous stimulus - larger GPs - more APs to CNS. ● AP number is translated by the CNS as the size of the stimulus. Adaptation ● Decreases AP number despite prolonged stimulus. Phasic Receptors ● Adapt over time - rate is variable. ● Touch receptors adapt quickly. ● Pain, BP receptors adapt slowly. Tonic Receptors ● Virtually do not adapt - few true tonic receptors; smell receptors. ● Postural receptors in trunk are near tonic. Sensory specificity ● Normal stimulus produces a response that the brain interprets. ● Different stimulus needs more strength for a response. ● Brain still interprets as “normal” response - see “stars” Pain ● Sharp, localized, passes quickly. ● Fast, myelinated afferents - glutamate NT. Slow Pain ● Diffuse, dull, long lasting. ● Slow, unmyelinated afferents - substance P NT. Substance P ● Presence suspected before discovery. ● NT unique to afferent, slow pain neurons. Opioid Receptors ● Natural analgesics block pain by binding to opioid receptors. ● Activation alters ion channels and membrane potential. Enkephalins/Endorphins ● Peptides, multiple types, different sizes. ● Short half life, 25 seconds. ● Morphine - effective for hours. Chemical Senses ● Molecular binding to a receptor. ● Flavor - combination of smell and taste Taste ● Molecules dissolve in saliva and reach taste bud receptors to be tasted. Taste Buds ● Receptors at taste pore ● Tight junctions keep saliva away from the rest of the taste bud. ● Surrounding epithelial cells are basal cells, which are surrounded by basal cells. ● Turnover rate of taste buds - 10 days. Neural Tracts ● Sensory neurons send taste information ● Neurons to thalamus - parietal lobe, “what” taste ● Neurons to limbic system - “like” it? Taste Receptors ● Salty = Na+ ● Sweet = organic sugars ● Acid, sour = H+ ● Bitter, bases (quinine ations, poisons, most sensitive receptor. ○ Most poisons are positively charged and bitter - rule of thumb if lost in woods - if sweet eat it, otherwise spit it out. ● Umami - MSG (glutamate) ○ AKA the best flavor. Glutamate is an amino acid. ○ Monosodium Glutamate. ○ Glutamate is a common neuron receptor in the brain. ● Flavor - combination of taste and smell ● Taste - just what you perceive on the tongue. Smell ● Olfactory mucus membrane on roof of nasal cavity > 1000 odor receptors. ● Largest gene family, >1% of human genome ● Molecules must diffuse through mucus (H2O soluble) and bind to a receptor to activate. ● Must be volatile enough to float to the top of the cavity. Olfactory Receptors ● Part of dendrites of the olfactory neurons - covered by mucus. ● Neurons turn over every few weeks. ● Unusual - dendrites as receptors, new neurons. Olfactory adaptation ● Unusual: receptors are primarily tonic. ● Unusual: most adaptations in CNS - brain can overcome adaptation. ● Adaptation to one smell does not affect others. PSL 250 - Lecture 15 - Hearing and Equilibrium Outer Ear ● Little amplification ● Direction detection. Tympanic membrane ● The tympanic membrane is the eardrum. ● Overlapping membranes. ● Separates outer and middle ears. ● Vibrates to external air waves. Middle Ear ● Air filled ● Amplifies sound 20x Ear Bones ● Malleus - incus - stapes ● Hammer - anvil - stirrup ○ Need to know order + english version. ● Carry waves from the tympanic membrane to the oval window. PSL 250 - Lecture 14 - Vision Eye ● Designed to receive light and produce electrical signals. Cornea ● Clear, non cellular front of the eye. ● Light passes through, not refracted (bent) Lens - Ciliary body ● Lens refracts light to focus on retina. ● Ciliary body has light parallel to the lense. ● Muscle contraction allows lens to round up - focus near. ● Muscles relax for distance vision. Iris ● The iris opens and closes the pupil. ● Smooth muscle - contractions adjust to light level. Aqueous Humor ● Between the cornea and the lense - constant production and drainage. ● Glaucoma: a decrease in drainage or express production of aqueous humor causing an increase in pressure and retinal damage. ● Keeps your eye from drying out. ● Beta blockers decrease production of aqueous humor, cholinergic agonists increase drainage. Vitreous Humor ● Gel-like: bulk of eye volume. ● Between the retina and the lense - maintenance of the eyeball shape. ● No refraction. ○ In rare cases, the gel can pull away from the back of the eye. Retina ● Visual receptors at the back of the eye. ● Multiple cell layers. Choroids ● Highly pigmented layer behind the retina. ● Absorbs light - no reflection - no signal. ● Responsible for just one image as the lightwave comes into your eye. ● If the light bounced around, you would see multiple images. ● Choroid prevents multiple signals from being generated. Refraction ● Bending of light waves. ● Glycoproteins in lens refract light, focus it on the retina. ● In high concentrations, glycoproteins easily reflect light waves. ● At the back of the eye, you have photoreceptors. ● When light enters, it has to go through other cell types. Retina ● Light passes through bipolar and ganglion cells to reach photoreceptor cells. ● Bipolar and ganglion cells pulled back at fovea. ● Fovea has the best color vision - dense cone concentration. Photoreceptors ● Rods - shades of gray - most photoreceptors. ● Cones - color receptors - fewer overall receptors. ● Rods and cones produce receptor potentials - no APs. ● Both converge on bipolar cells. Bipolar cells ● Generator potentials - activated by rods/cones. ● No APs - synapse with ganglion cells. ● Edge effect - center/surround on/off effect. Ganglion cells ● Reach threshold and fire APs that leave eye for CNS. ● Carry visual information to lateral geniculate, part of thalamus that belongs to the cortex. Optic Nerve ● Bundle of ganglion cell axons. ● Creates blind spot as axons pass through retina. ● Cortex fills in blind spot with expected image. Lateral Geniculate ● Receives information from ganglion cells. ● Part of the thalamus - edits information to the cortex. Visual Cortex ● Multiple areas in the occipital lobe ● Integrates input of visual perception. ● Relative positions - 3D images. Accommodation ● Change in lense thickness alters focal point for near and far vision. ● Ciliary muscles control focus. Presbyopia ● Lense gradually hardens over decades. ● Hardening reduces rounding of lens for near vision. ● At 40-45 years old, difficulty focusing on near objects. ● Reading glasses or bifocals can aid this. Myopia-Hyperopia ● Inability to focus on the retina. ● Myopia - nearsighted, eyeball too long, focus in front of the retina. ● Hyperopia - farsighted, eyeball too short, focus behind the retina. ● Corrective lenses or laser surgery on the cornea can aid this. Rhodopsin ● Visual pigment in rod cells. ● Combination of opsin and retinene (Vitamin A derivative) ● Light hits retinene and partially splits it from opsin (bleaching) ● Opsin now active - G protein system - recycles 14 per second. ● Retinene rebinds to opsins, awaiting new light. Color Vision ● 3 different opsins with retinene. ● Shading of retinene limits frequency range - peaks at red (also sees yellow), green and blue wavelengths. Color blindness ● Missing one opsin ● Can’t distinguish certain wavelengths with equal activation of remaining opsins.
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