Law of specific nerve energies PDF

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Law of specific nerve energies...

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Law of specific nerve energies ○ •info from a given sensory nerve can only be experience as one stimulus type sensory modality •sensation produced by “adequate” or normal stimulus is one that the brain will perceive ■ oEx: A punch to the eye is perceived as a flash of light 3. Sensory receptor categories ○ o Mechanoreceptors: touch, pressure, pain, sound o Chemoreceptors: dissolved chemical o thermo receptors: temp o photoreceptors: light o Pain Receptors: tissue damage 4. Generator potentials ○ • sensory receptors behave like neurons • stimulus causes a change in ion permeability which then causes depolarization: receptor or generator potentials • enough intensity or stimulus can cause the membrane’s potential to reach its threshold causing an AP, similar to EPSP a. Tonic vs phasic, examples ○ • Tonic: constant rate as stimulus is applied o Generator potential, proportional to intensity of stimulus Increased intensity=increase in AP frequency MAGNITIUDE OF AP DOES NOT CHANGE ONLY FREQUENCY o Ex: pain • Phasic: quick bursts, but reduce to constant stimulation=Adaption o Ex: smell, touch Types of cutaneous receptors ○ Touch, pressure, pain, hot, cold 6. Taste and smell ○ • Taste (Gustation): o Receptors: taste buds Located on bumps of tongue called papillae o Special endothelial cells: Cells depolarize and cause AP Cells release NT onto sensory neurons Microvilli come into contact with chemicals Each taste bud is sensitive to each category of taste: • Salty, sour, bitter, sweet, umami • Smell (Olfaction): o Olfactory Receptors (bipolar neurons): in olfactory epithelium of nasal cavity with ciliary dendrite Proteins in cilia bind odors Open in Na+ and Ca2+ channels 7. Vestibular apparatus, inner ear

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a. Structure ■ • Consists of bony labyrinth surrounding a membranous labyrinth i. Maculae, semicircular canals ■ o Otilith Organs o Semicircular canals o Macula: composed of modified epithelial cells w/ 20/50 hair like extensions called: ii. Endolymph (high K) ■ o Fluid within the scala media inside cochlea b. Role in equilibrium i. Linear acceleration A. Utricle and saccule ■ Otilith Organs: • Utricle: horizontal • Saccule: vertical Angular acceleration Semicircular canals iii. Mechanism ■ o Macula: composed of modified epithelial cells w/ 20/50 hair like extensions called: Stereo cilia: true cilia Kino cilium: not true cilia (only one) • Stimulate: o Stereo cilia move towards the Kino cilium causing ion channels to open up and cause depolarization o Releases NT that depolarize dendrites in vestibulocochlear nerve • Inhibit: o Bending away from Kino cilium hyperpolarizes sensory dendrites Codes for detection of direction Otolithic membrane, depolarization and K+ entry iv. Nystagmus and vertigo ■ Nystagmus: when a person is spinning, eye movements are towards the opposite direction towards a fixation point o when body is at a stop, cupula is bent by fluid inertia and eye movements are still effected o jerky eyemovement • Vertigo: Nystagmus can cause a loss of equilibrium called vertigo o Can be accompanied by dizziness, pallor, sweating, nausea, and vomiting o Ex: Sea sickness Dramamine blocks nicotinic receptors, which inhibits the depolarization of the vestibular nerves, meaning that info from the inner war doesn’t make it to the CNS

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Ears and hearing ○ -Hearing: neural perception of sound waves (pressure waves) ○ -Frequency: measures in Hz (cycles/sec), pitch directly related to frequency ○ -Intensity: how loud related to amp of waves measured in dB a. Outer ear structure ■ Tympanic membrane, function Middle ear structure, function ○ i. Malleus, incus, stapes, oval window ■ Malleus (hammer): 1st little bone carries vibration to incus ■ Incus (anvil): 2nd little bone carries vibration to stapes ■ Stapes (stirrup):3rd little bone carries vibrations to oval window ■ Oval window: entry into inner ear where vibration enters Inner ear ○ Structure and function ■ ii. Cochlea ● A. Scala vestibuli, cochlear duct, scala tympani ●

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B. Organ of Corti (location of signal transduction) ○ a. Mechanism of signal transduction ■ • Located in cochlear duct ■ • Sound transduction occurs here and turn into neural impulses (AP’s) ■ • Low frequency can travel all the way through vestibule to tympani ■ • As freq. increases, they travel less so they pass directly through vestibular and basilar membrane to tympani ■ • High freq. produce mac stimulation of spinal organ close to base of cochlea ■ o Lower freq. stimulates closed to APEX

Transduce light into nerve impulses ■ A limited part of the electromagnetic spectrum can excite photoreceptors ■ Light hits cornea and enters the anterior chamber ■ Then its hits the pupil and regulates how much light enters the eye ■ Then the lens changes shape to focus on an image ■ Hits retina (photoreceptors) The retina ○ Structure ■ back of eye rods and cones then bipolar cells then ganglia cells ■ neurons in axons in the retina are gathered at a point called optic discs (blind spot) ■ blood vessels enter here ■ extension of brain

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multilayered epithelium neurons, pigmented epithelium, photoreceptors, rods and cones, bipolar cells, ganglion cells Mechanism of signal transduction ■ light passes through the three layers to stimulate rods and cones ■ stimulation is then passes through the bipolar cells and then ganglionic cells ■ ganglion cells combine to form the optic nerve, which leaves eye at blind spot to the occipital lobe Dark current, light current (inverse of sensory systems) ■ Dark Current: ● Na+ and Ca2+ channels open ● Gated by cGMP (required to keep open) ● Open channels mean depolarization and release of NT ● This NT is glutamate is used to INHIBIY the bipolar cells so message can’t be sent to the brain ○ Light Current: ■ Na+/Ca2+ channels are closed ■ Due to cascade that ultimately causes the conversion of cGMP to GMP which causes Na/Ca channels to close ■ This causes the removal of inhibition on the bipolar cell and starts the nerve impulse from the bipolar to the ganglionic cell...