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EXSC 224: Exam 1
3 functions of nervous system
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sensory input, integration, motor output
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Central Nervous System (CNS)
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includes brain, spinal cord
--integrative and control centers >> motor output
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Peripheral Nervous System (PNS)
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includes cranial nerves and spinal nerves
--communication lines between CNS and the rest of the body
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sensory (affarent) division
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-towards CNS
-transmits all sensory info
-somatic and visceral sensory nerve fibers
-conducts impulses from receptors to CNS
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motor (efferent) division
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-motor nerve fibers
-conducts impulses from CNS to effectors (muscles and glands)
--affects all muscle types
--divides into somatic and autonomic nervous systems
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somatic nervous system
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-voluntary movement (somatic motor)
-skeletal muscles
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autonomic nervous system (ANS)
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-involuntary movement
-heartbeat, gastric motility, BP, gland secretion
--divides into sympathetic and parasympathetic divisions
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sympathetic division
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-fight or flight
-increases heart rate and breathing
-decreases smooth muscle contractions
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parasympathetic division
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-dominant when at rest
-decreased heart rate and breathing
-activates the GI tract
-rest and digest
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two cell types of nervous system
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neuroglia (glial cells) -- supporting cells
neurons
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types of neuroglia cells
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-astrocytes
-microglia
-ependymal cells
-oligodendrocytes
-satellite cells
-schwann cells
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astrocytes
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-most abundant, versatile, highly branched
-hold neurons together; cling to synaptic endings and capillaries
-support and brace neurons
-higher numbers than neurons
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microglia
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-small, resident macrophage w/ thorny processes
-migrate to injured neurons-- first defense
-phagocytize microorganisms and neuronal debris
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ependymal cells
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-line brain ventricles, aqueducts, central canal of spinal cord
-held together via tight junctions (water-tight)
-separate CNS interstitial fluid and cerebrospinal fluid in cavities
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oligodendrocyte
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-produce myelin sheath >> lipid insulator
-branched cells; "white matter" around neurons
-processes wrap CNS nerve fibers; able to wrap multiple
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satellite cells
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-surround neuron cell bodies in PNS
-assoc. w/ sympathetic, parasympathetic, and sensory
-regulate access to nutrients
-ONLY IN PNS
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schwann cells
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-produce myelin
-assoc. w/ only 1 neuron
-vital to regeneration of damaged peripheral nerve fibers
-speeds up conduction of signal via myelin
-no ion channels or proteins
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neurons
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-primary to nervous system
-CNS ONLY
-high metabolic rate--continuous oxygen and glucose dependent
-cell to cell interaction and electrical signaling
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axon hillock
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cone-shaped area from which axon arises; has to be stimulated for action potential to occur in axon
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dendrite
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-receptive region of a neuron
-short, tapering and diffusely branched
-conveys input towards cell body>> graded potential
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axons
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-one axon per cell, branches from axon hillock
-larger axon = faster conductor
-small axon = slow conductor
-knoblike axon terminals = boutons
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node of ranvier
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gap between schwann cells; exposed axon
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white matter
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dense collections of myelinated fibers
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gray matter
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mostly neuron cell bodies and unmyelinated fibers
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functional classification of neuorns
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1) sensory (affarent)
2) interneurons ((assoc. neurons)
3) motor (efferent)
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sensory (affarent)
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transmit impluse: sensory receptors to CNS
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interneurons (assoc. neurons)
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shuttle signals thru CNS
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motor (efferent)
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carry impulses from the CNS
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voltage (V)
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measure of potential E generated by separated charge; determined by action potential
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potential difference
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voltage measured between two points
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resistance (R)
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hindrance to charge flow (by plasma membrane)
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insulator
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substance w/ high electrical resistance
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conductor
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substance w/ low electrical resistance
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depolarization
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change in membrane potential towards zero (become less negative)
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hyperpolarization
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membrane potential increases; moves away from zero (become more negative)
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absolute refractory period
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in depolarized state
--cannot depolarize again; stimuli won't affect
--ends when membrane potential falls below threshold>> reset Na voltage gated channels >> enter relative refractory period
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relative refractory period
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not yet at normal state
--is able to depolarize again
--required greater stimulus than at normal resting state
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conduction velocity
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-varies within neurons
-determined by axon diameter and myelination
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effects of axon diameter
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-larger diameter fibers have lower resistance to local current flow and faster impulse conduction
--faster impulse due to more Na+ channels
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effects of myelination
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-continuous conduction in unmyelinated axons is slower that saltatory conduction in myelinated axons
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how are nerve fibers classified?
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diameter
degree of myelination (present or not)
speed of conduction
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Group A fibers
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largest diameter
all myelinated
fastest conduction
ex. somatic sensory and motor (volutary)
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Group B fibers
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intermediate diameter
lightly myelinated
moderate speed
ex. ANS fibers and involuntary motor
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Group C fibers
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smallest diameter
unmyelinated
slowest speed
ex. ANS fibers and pain fibers (dull ache)
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what is the synapse?
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the junction that mediates information transfer from one neuron to another neuron OR from one neuron to an effector cell
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what are the three types of synapses?
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axo-dendritic synapse: axon to dendrite
axo-somatic synapse: axon to soma
axo-axon synapse: axon to axon (very rare)
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what is the difference between a presynaptic and postysnaptic neuron?
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pre: conducts impulse towards the synapse
post: transmits impulse away from the synapse
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what is the difference between electrical and chemical synapses?
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E:
rare in CNS after development
common in rest of body
very rapid
unidirectional or bidirectional
important in embryonic nervous and heart tissues, some brain
C:
specialized for release and reception of neurotransmitter
unidirectional
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what is the synaptic cleft?
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fixed structure; fluid-filled space of a synapse
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how does information transfer occur?
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presynaptic neuron experiences rise in AP > triggers release of neurotransmitter in bouton > graded potential occurs in postsynaptic neuron
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what are the different type of postsynaptic potentials?
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EPSP- excitatory
IPSP- inhibatory
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what are the different types of integration summation?
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-temporal summation (additive)
-spacial summation
-spacial summation of EPSPs and IPSPs
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what are the characteristics of norepinephrine?
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-neurotransmitter version of adrenaline
-excitatory to brain
-inhibatory to GI tract
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what are the characteristics of dopamine?
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-"happy" neurotransmitter
-excitatory/inhibatory depending on receptor
-found in cocaine>> activates pleasure sensors
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what are the characteristics of seratonin?
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-found mainly in CNS
-middle #s= stable mood
-too high or too low #s= depression/suicide
-inhibatory
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what characteristics does ATP have as a neurotransmitter?
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-stimulates pain associated with nerve endings
-in severe conditions, breaks down from ADP to AMP to adensosine
-adenosine promotes neuron fatigue>> slows neuron activity
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