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44 Cards in this Set
- Front
- Back
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PNS: Afferent System
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– Sends information from internal and external
environment to CNS • Visceral afferent- pathway from internal viscera • Sensory afferent – Somatic (body sense) sensation » Sensation arising from body surface and proprioception (limb/joint position) – Special senses » Vision, hearing, taste, smell |
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Mechanisms
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• Transduction
• Transmission • Modulation • Perception |
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Receptors
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• At peripheral endings of afferent neurons
– Detect stimuli – Transduction - convert forms of energy into electrical signals (graded or action potentials) • Types – Photoreceptors - visible wavelengths of light – Mechanoreceptors - mechanical energy/distortion – Thermoreceptors - heat and cold – Osmoreceptors – concentration of solutes in fluid – Chemoreceptors - sensitive to specific chemicals • smell and taste • O2 and CO2 concentrations in blood • chemical content of digestive tract – Nociceptors - pain receptors |
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Receptor Potentials
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• Afferent signaling (separate organ or afferent ending)
• Stimulus alters permeability = graded receptor potential (positive ion flow – Na+) • Magnitude of receptor potential = stimulus intensity • AP propagated along afferent neuron to CNS |
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Receptor adaptation
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• May adapt slowly or rapidly to sustained stimulation
• Types of receptors according to their speed of adaptation – Tonic receptors – slow adaptation– muscle/joint receptors – Phasic receptors – rapid adaptation – tactile cutaneous |
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Somatosensory Pathways
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• Chains of neurons interconnected for sensory processing
– First-order - Afferent with peripheral receptor (detects stimulus) – Second-order- SC or medulla – Third-order – located in thalamus |
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Two pathways
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– Anterior spinothalamic tracts (pain, temp)
– Dorsal columns (light touch, proprioception) |
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1st order neurons
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determine pathways
very in PNS with fiber size and extent of myelination |
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A alpha (I)
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– very fast (muscle stretch/spindle, tension/Golgi tendon organ
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A Beta (II)
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– most non-noxious cutaneous, joint, muscle length/spindle
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A delta (III)
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– mildly noxious cutaneous, joint, muscle
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C
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– prolonged noxious input (all areas)`
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A gamma
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gamma efferent
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B
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sympathetic preganglionic motor axons
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Dorsal Column Pathway
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1. touch receptor/joint stretch receptor
2. Fasciculus gracilus/cuneatus 3. Nucleus gracilus/cuneatus-clusters of cell bodies that give rise to 2nd order neursons 4. medial lemniscus tract- axons of 2nd order neurons 5. Thalamus- cell bodies of 2nd order neurons 6. Primary somatosensory cortex |
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Spinothalamic pathway
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1. pain/temp receptors
2. crosses right over with axons of 1st order neurons 3. Medulla 4. Lateral Spinothalamic tract- axons of second order neurons 5. Thalamus- 3rd order neurons 6. primary somatosensory cortex |
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Stimulus Property
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1. Type of Stimulus (stim modality)
- type receptor activated and pathway over which info is transmitted 2. Location of stim - location of the activated receptive field and pathway that is subsequently activated 3. intensity of stim - frequency of action potentials in the activated afferent neuron and the number of receptors activated |
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Acuity/localization
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• Refers to discriminative ability
• Influenced by receptive field size and lateral inhibition |
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Perception
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• Conscious interpretation of external world derived from
sensory input • Perception relies on current cognition, mood, previous experience (mutliple cortical area manipulate information) |
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Pain
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• Protective mechanism - bring conscious awareness that
tissue damage is occurring/will occur • Storage of painful experiences • Accompanied/motivated by behavioral responses and emotional reactions • Perception influenced by past/present experiences • Nociceptors do not adapt to sustained or repetitive stimulation • Three categories – Mechanical nociceptors – Thermal nociceptors – Polymodal nociceptors |
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first pain
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occurs on stimulation of mechanical and thermal nocioceptors
carried by small mylinated A delta fibers produces, sharp prickling sensation easily localized occurs first |
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second pain
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stimulation of polymodal nocioceptors
carried by small unmylinated C fibers dull, aching, burning sensation poorly localized occurs, |
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Visual Pathways- Anatomy
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• Protection – bony socket, eyelids, lashes, tears
• Structure – spherical, fluid-filled, three tissue layers – Sclera/cornea • Sclera – tough outer CT layer; forms visible white portion • Cornea – anterior, transparent permits light transmission – Choroid/ciliary body/iris • Choroid - underneath sclera, vasculature • Choroid layer, anterior to forms ciliary body and iris – Retina • Outer pigmented layer • Inner neural (rods/cones) |
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Fluid-filled cavities
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– Posterior (lens/retina) - vitreous humor
– Anterior cavity (cornea/lens) – nutrients, capillary network with ciliary body – Drains in Canal of Schlemm |
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Iris
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– Controls amount of light entering
– 2 smooth muscle networks • Circular (or constrictor) muscle • Radial (or dilator) muscle – Pigmented = eye color – Unique ID |
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Pupil
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– round opening/light
transmission |
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Convex structures produce
convergence |
– Cornea – large contribution to
refractive ability (constant-LASIK?) – Lens – refractive ability adjusted by altering curvature |
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Accommodation
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– Change in strength and shape of
lens – Accomplished by action of ciliary muscle and suspensory ligaments – Age-related reduction in accommodation ability - presbyopia |
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Retina
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extension of the CNS: 3 excitable layers
– Outermost layer - rods and cones – Middle layer - bipolar cells – Inner layer - ganglion cells, axons = optic nerve • optic nerve leaves is the optic disc • blind spot - no image can be detected (no rods/cones) |
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Fovea
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• Pinhead-sized depression
center of retina, • most distinct vision (only cones) |
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Mucula lutea
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• immediately surrounding
fovea, high actuity • Degeneration – 1 cause of blindness in West, “doughnut vision” |
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Visual Transduction
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• Photopigment - photochemical alterations
– Opsin - integral disc membrane protein – Retinene -Light-absorbing (vitamin A derivative) • Types – Rods (Rhodopsin) absorbs all visible wavelengths (gray) – Cone pigments –specific wavelengths |
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Processing (rods/cones)
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– Dark
= high GMP, Na channel open - depolarization, release inhibitory transmitters to bipolar cell (inhibit cells) – Light = low GMP, Na channels close – hyperpolarization, stop inhibitory transmitter release (removal of inhibition) |
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Bipolar cell
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– excitability transmits to
ganglion cells – propagation to visual cortex |
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Dark exposure
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• sympathetic radial dilator activity (also distance vision)
• dark adaptation – reconstitution of rod photopigments broken down by previous light exposure |
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Light exposure
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parasympathetic constrictor activity (also near vision
• light adaptation - rapid breakdown of cone photopigments |
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Hearing outline
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• Anatomy
– Outer, middle, inner • hearing • Transmission of sound waves • Hair cells and transduction • Cochlea and canals/ducts • Pitch and loudness • auditory cortical processing |
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External ear
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– Consists of pinna, external
auditory meatus, and tympanum – Transmits airborne sound waves to fluid-filled inner ear – Amplifies sound energy |
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Middle ear
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– Transmits airborne sound waves to
fluid-filled inner ear – Amplifies sound energy |
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Inner ear
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– Cochlea - receptors for sound
wave detection – Vestibular apparatus - equilibrium |
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Formation of Sound Waves
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• Traveling vibrations of air
• Alternate regions air compression and rarefaction • Pitch (tone) - frequency • Intensity (loudness) - amplitude • Timbre (quality) - overtones |
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Sound Wave Transmission (1)
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• Tympanic membrane – vibration with sound
waves • Middle ear - transfers vibrations through ossicles (malleus, incus, stapes) to oval window (entrance into fluid-filled cochlea) • Waves in cochlear fluid - basilar membrane motion |
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Sound Transmission-Transmission (2)
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• Receptive hair cells bent as basilar
membrane is deflected up and down – Stereocilia contact overlying tectorial membrane (stationary) – Bending opens mechanically-gated channels – receptor potentials generated |
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Chemical Senses
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Chemoreceptors
• influence appetite/sensations, GI secretions, • housed in taste buds – oral cavity/throat (50 cells/bud – 10 day lifespan) – Fungiform papillae and circumvallate papillae – Taste pore – allow fluids/molecules entry – Taste receptor cells (gustatory cells) • Modified epithelial cells with microvilli • receptor sites that bind selectively with chemical molecules |
