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94 Cards in this Set
- Front
- Back
What 3 types of molecules allow for communication between cells?
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(1) neurotransmitters (nervous system)
- rapid, direct, specific (2) local mediators (paracrine system) (3) hormones (endocrine system) - slower, spread throughout body, affect different cells & tissues in different ways |
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paracrine system
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releases local mediators into interstitial fluid & acts on neighboring cells; includes proteins, amino acid derivations, or fatty acid derivatives (e.g. prostaglandins)
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prostaglandins
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- fatty acide derivative local mediators
- affect smooth muscle contraction, platelet aggregation, inflammation & other reactions - synthesis inhibited by aspirin |
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nervous system
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- allows for rapid & direct communication b/t specific body parts
- changes in muscular contractions or glandular secretions - brain, spinal cord, nerves, neural support cells, sense organs (eye, ear) |
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neuron
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- specialized cell that can transmit electrical signal from one cell to another via electrical or chemical means
- cannot divide - depends almost entirely on glucose for chemical energy - not dependent on insulin to transport glucose into cytosol - consists of dendrites, cell body, axon + branches |
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dendrites
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receive signal to be transmitted in a neuron
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axon hillock
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electrical signal transferred here from cytosol (which is highly conductive); generates action potential in all directions, including down axon
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axon
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carries action potential to synapse
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unipolar neuron
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sensory only
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bipolar neuron
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retina, inner ear, olfactory area of brain
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multipolar neuron
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most neurons of the brain
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action potential
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disturbance in electric field across membrane of neuron
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resting potential
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- equilibrium b/t passive diffusion of ions across membran & Na+/K+ pump
- pump moves 3 Na+ out and 2 K+ in, increasing positive charge along membrane outside cell - electrochemical gradient of Na+ increases, so force pushing it back into cell increases until rate in = rate out (same for K+) - at equilibrium, inside of membrane has negative potential difference (voltage) compared to outside |
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voltage-gated sodium channels
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- integral membrane proteins in neurons that change configuration when membrane voltage is disturbed to allow Na+ to flow through membrane into cell
- positive feedback mechanism as more and more Na+ flows into cell, changing voltage & causing more channels to open |
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depolarization
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Na+ concentration moves toward equilibrium & K+ concentration remains higher in cell, so membrane reverses polarity to be positive on the inside & negative on the outside
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voltage-gated potassium channels
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less sensitive to voltage changes than sodium channels, so don't start to open until sodium channels are closing; allow K+ to flow out of the cell
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repolarization
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when K+ flows out of cell through voltage-gated potassium channels, causing the inside of the cell to become more negative again
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hyperpolarization
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voltage-gated potassium channels are slow to close, so for a fraction of a second during repolarization, the inside membrane becomes even more negative than the resting potential
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steps of an action potential
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1. Membrane is at rest ~ -70mV. Na+ and K+ channels are closed.
2. Na+ channels open and cell depolarizes. 3. K+ channels open as Na+ channels start to inactivate. 4. Na+ channels inactivated & open K+ channels repolarize membrane. 5. K+ channels close & membrane equilibriates to resting potential. |
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accommodation
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threshold stimulus is reached, but very slowly & an action potential does not occurr
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absolute refractory period
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short period of time in which no stimulus will create another action potential
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relative refractory period
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time during which only an abnormally large stimulus will create an action potential
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What is the slowest part of nervous system cellular communication?
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transmission of signal from one cell to another through a synapse
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electrical synapses
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composed of gap junctions b/t cells in cardiac muscle, visceral smooth muscle & a few neurons in CNS; transmit signals much faster than chemical synapses & in both directions; uncommon
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chemical synapse
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- more common than electrical synapses
- unidirectional - vesicles w/ NT lie inside presynaptic membrane - Ca(2+) voltage-gated channels in membrane are activated by AP arriving at synapse & open, letting Ca(2+) flow into cell, causing NT vesicles to be released into synaptic cleft through exocytosis - NT diffuse across cleft via Brownian motion - NT receptor proteins on postsynaptic membrane causes it to become more permeable to ions, which move across it through ionophores (proteins) & complete transfer of neural impulse - method prevents attenuation of electrical resistance from one cell to the next - slowest step in the transfer of a nervous signal |
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neural fatigue
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can occur if a cell is fired too often and cannot replenish its NT vesicle supply
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How does a cell deal with a neurotransmitter released back into the synaptic cleft?
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- destroy NT with enzyme in matrix of synaptic cleft & recycle parts in presynaptic cell
- presynaptic cell directly absorbs NT through active transport - NT may diffuse out of synaptic cleft |
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Can a single synapse be both inhibitory & excitatory?
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No.
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Can a single neurotransmitter be both inhibitory & excitatory?
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Yes. (e.g. acetylcholine - inhibitory on heart, excitatory on visceral smooth muscle of intestine)
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In what 2 ways might receptors act?
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(1) ion channel itself (opened when respective NT attaches)
(2) act via second messenger system (preferred for prolonged changes, such as those involved in memory) |
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second messenger system
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- activates another molecule in the cell to make changes
- often initiated by G-proteins attached to receptor protein along inside of postsynaptic membrane - when activated by NT, alpha-subunit breaks free & can: (1) activate separate specific ion channels (2) activate a second messenger (e.g. cyclic AMP/GMP) (3) activate intracellular enzymes (4) activate gene transcription |
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postsynaptic potentials
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- firing of one or more synapses creates a change in neuron cell potential
- can be excitatory (EPSP) or inhibitory (IPSP) - usually requires 40-80 synapses firing on same neuron for an EPSP to create an action potential |
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glial cells (neuroglia)
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- outnumber neurons 10:1
- can divide (fill space during TBI) - 6 types: microglia, ependymal cells, satellite cells, astrocytes, oligodendrocytes & neurolemmocytes (Schwann cells) |
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microglia
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type of neuroglia; arise from monocytes & phagocytize microbes & cellular debris in CNS
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ependymal cells
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type of neuroglia; epithelial cells that line space containing CS fluid
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ependymal cells
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type of neuroglia; use cilia to circulate CS fluid
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satellite cells
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type of neuroglia; support ganglia (groups of cell bodies in PNS)
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astrocytes
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type of neuroglia; star-shaped neuroglia in CNS that physically support neurons & help maintain mineral/nutrient balance in interstitial space
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oligodendrocytes
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type of neuroglia; wrap around axons in CNS to create electrically insulating sheathes of myelin
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Schwann cells
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type of neuroglia; produce myelin in PNS
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myelinated neurons
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- faster rate of conduction d/t myelin
- appear white (neuronal cell bodies appear gray) - tiny gaps b/t myelin called "nodes of Ranvier" - AP "jumps" from node to node in "saltatory conduction" |
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sensory (afferent) neurons
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receive signals from receptor cell that interacts w/ environment & transfers signal to other neurons (99% of sensory info is discarded by the brain); located dorsally from spinal cord
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interneurons
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transfer signals from neuron to neuron (account for 90% of human neurons)
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motor (efferent) neurons
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carry signals to muscles or gland called "effector"; located ventrally from spinal cord
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dorsal
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toward the back
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ventral
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toward the front/abdomen
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nerves
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bundles of neuron processes (axons & dendrites) [called "tracts" in CNS)
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simple reflex arc
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receptor --> dorsal root ganglion --> sensory neuron --> interneuron --> motor neuron --> effector
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central nervous system (CNS)
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- interneurons & support tissue w/in brain & spinal cord
- integrates nervous signals b/t sensory & motor neurons |
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peripheral nervous system (PNS)
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- connects CNS to peripheral parts of the body
- cranial & spinal nerves project to brain & SC - sensory & motor functions - divided into somatic & autonomic nervous systems |
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somatic nervous system
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- responds to external environment
- sensory & motor functions - motor neurons only innervate skeletal muscle, cell bodies located in ventral horns of spinal cord, synapse directly on effectors & use acetylcholine as NT [conscious, voluntary control] - sensory neuron cell bodies located in dorsal root ganglion |
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autonomic nervous system (ANS)
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- sensory portion receives signals from viscera (organs in central body cavity)
- motor portion conduct visceral signals to smooth muscle, cardiac muscle & glands - generally involuntary function - divided into sympathetic & parasympathetic systems (most internal organs have both acting antagonistically) - pathways mainly controlled by hypothalamus |
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sympathetic ANS
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"fight or flight"
- increase heart rate & stroke volume - constricts blood vessels around digestive & excretory systems to increase blood flow around skeletal muscles - signals originate in neurons w/ cell bodies in SC |
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parasympathetic ANS
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"rest & digest"
- slows heart rate - increases digestive & excretory activity - signals originate in neurons w/ cell bodies in both brain & SC |
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nucleus
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a group of cell bodies located in the CNS
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ganglion
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a group of cell bodies located outside the CNS
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preganglionic neurons
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neurons with cell bodies in CNS
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postganglionic neurons
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- neurons with cell bodies outside the CNS
- cell bodies of sympathetic are far from effectors in paravertebral ganglion (parallel to SC) or in prevertebral ganglia (in abdomen) - cell bodies of parasympathetic lie in ganglia inside/near effectors |
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Where is acetylcholine used?
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- all preganglionic neurons in the ANS
- postganglionic neurons in the parasympathetic ANS [somatic & parasympathetic nervous systems] |
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Where are epinephrin & norepinephrine used?
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postganglionic neurons of the sympathetic NS
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cholinergic receptors
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- receptors for acetylcholine
- nicotinic (postsynaptic cells of synapse b/t ANS preganglionic & postganglionic neurons; on skeletal muscle membranes at neuromuscular junctions) - muscarinic (effectors of parasympathetic NS) |
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adrenergic receptors
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receptors for epinephrine & norepinephrine
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integrating functions of the spinal cord
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- walking reflexes
- leg stiffening - limb withdrawal from pain |
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lower brain parts
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- medulla
- pons - mesencephalon - hypothalamus - thalamus - cerebellum - basal ganglia |
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functions of lower brain
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- integrates subconscious activities
- respiratory pressure - arterial pressure - salivation - emotions - reaction to pain & pleasure |
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higher brain parts
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- cerebrum (cerebral cortex)
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function of cerebral cortex
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store memories & process thoughts (cannot function w/out lower brain)
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What are the 5 types of sensory receptors?
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(1) mechanoreceptors - touch
(2) thermoreceptors - temperature (3) nociceptors - pain (4) electromagnetic receptors - light (5) chemoreceptors - taste, smell, blood chemistry |
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path of light through the eye
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cornea
aqueous humor pupil lens vitreous humor retina optic nerve |
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cornea
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- first point on eye to be struck by light
- nonvascular & largely made of collagen - most bending of light occurs here |
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anterior cavity
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- light enters here after cornea
- filled with aqueous humor (fluid formed by ciliary processes that leaks out of canal of Schlemm) |
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glaucoma
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can be caused by blockage of canal of Schlemm and resulting increased ocular pressure
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lens
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- light enters here from anterior cavity
- spherical, but tugged by suspensory ligaments which flattent it & are connected to ciliary muscle |
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What happens when the ciliary muscle contracts?
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opening of circle around lens decreases, allowing lens to become more sphere-like, bringing its focal point closer to the lens
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What happens when the ciliary muscle relaxes?
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opening of circle around lens increases, causing lens to flatten, increasing its focal distance
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vitreous humor
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gel-like substance that light focuses through onto the retina
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retina
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- light focused through vitreous humor onto this
- image on retina is real & inverted - covers back (distal portion) of eye & contains rods & cones (photoreceptors; light-sensitive) |
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rods
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- sense all photons with wavelengths in visible spectrums
- CANNOT distinguish colors - contain pigment rhodopsin (protein bound to retinal prosthetic group derived from vitamin A) - photon isomerizes retinal causing rod cell membrane to hyperpolarize, which creates action potential |
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cones
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CAN distinguish colors; 3 types, each with different pigment stimulated by different spectrum of wavelength
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general characteristics of rods & cones
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- tips contain pigments (light sensitive photochemicals)
- Vitamin A is precursor to all pigments in these cells |
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fovea
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small point on retina containing mostly cones; vision is most acute on this point of retina
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iris
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- colored portion of eye that creates pupil (opening)
- made of circular and radial muscles - IN DARK: sympathetic NS contracts iris, dilates pupil & allows more light into eye - IN BRIGHT: parasympathetic NS contracts iris, constricts pupil & screens out light |
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What are the 3 main parts of the ear?
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(1) outer ear
(2) middle ear (3) inner ear |
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auricle (pinna)
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skin & cartilage flap that directs sound wave into external auditory canal
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tympannic membrane
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eardrum; sound carried hear from external auditory canal; begins the middle ear
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3 small bones of the middle ear
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(1) malleus
(2) incus (3) stapes act as lever system translating wave to oval window (which is smaller than eardrum, creating an increase in pressure) |
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perilymph
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fluid in inner ear
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cochlea
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sound wave moves through this part of the inner ear; alternating increase & decrease in pressure moves vestibular membrane in and out
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organ of Corti
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contains hair cells (sterocilia, a specialized type of microvilli) that detect movement of vestibular membrane in & out and transduces that into neural signals sent to brain
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semicircular canals
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in inner ear; canal of fluid & hair cells responsible for balance - when body moves, momentum of fluid changes & impacts hair cells, causing body to sense motion; canals oriented at right angles to each other to detect movement in all directions
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path of sound through the ear
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pinna
auditory canal tympanic membrane ossicles oval window cochlea hair cells auditory nerve brain |
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sense of smell
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olfactory (uses chemoreceptors)
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sense of taste
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gustatory (uses chemoreceptors)
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What are the 4 primary taste sensations?
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(1) bitter
(2) sour (3) salty (4) sweet [umami?!?!?!] |