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92 Cards in this Set
- Front
- Back
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What is the nervous system
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Control and communicating system of the body
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What are the functions of the nervous system
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Sensory input-monitoring stimuli
Integration-Interpretation of sensory input Motor output-Response of stimuli |
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What is the structure and function of the peripheral nervous system?
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Structure includes cranial nerves and spinal nerves
Function includes: communication lines between the CNS and the rest of the body |
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What are the two subdivisions of the peripheral nervous system?
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Sensory (afferent) division
Structure: Somatic and visceral sensory nerve fibers Function: conducts impulses from receptors to the CNS Motor (efferent) division Structure: Motor nerve fibers Function: Conducts impulses form the CNS to effectors (muscles and glands) |
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What are the two subdivisions of the motor (efferent) division
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Somatic Nervous system
structure:Somatic motor (voluntary) Function: conducts impulses from the CNS to skeletal muscles Autonomic Nervous system Structure: Visceral motor (involuntary) Function: conducts impulses from the CNS to cardiac muscles smooth muscles and glands |
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What are the subdivisions of the Autonomic nervous system
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Sympathetic division
Function: mobilizes body systems during activity FIGHT OR FLIGHT Parasympathetic division Function: Conserves energy Promotes house keeping functions during rest REST AND DIGEST |
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What are the two principle cell types of the nervous system?
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Neurons and supporting cells ( direct neurons, insulate neurons, and bundle neurons)
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What are the functions of supporting cells of the nervous system?
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Provide a supportive scaffolding for neurons, guide young neurons to the proper connections, and promote health and growth of neurons
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Describe Astrocytes
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Abundant, versatile and highly branched glial cells
Wrap neuron processes especially at synaptic endings, and cover capillaries that form part of the blood-brain barrier allows certain substances to pass to brain |
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What are the most common glial cells?
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Astrocytes
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Describe Microglia cells
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Small, ovoid cells with spiny processes
-phagocytic Brain immune cells |
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Describe ependymal cells
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squamous to columnar cells
Line central cavities of CNS Cilia help circulate |
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Describe oligodendrocytes
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Branched cells that wrap CNS axons- provide myelin sheath
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Describe Schwann cells
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Surround axons of PNS-provide myelin sheath
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Describe satellite cells
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Surround soma within ganglia- little moons of satellite of cell bodies
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What are the structural units of the nervous system
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Composed of a body, axon, and dendrites
Long-lived, amitotic (never go mitosis) with high metabolic rate |
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What does the plasma membrane function in?
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Electrical signaling
Cell to cell signalling during development |
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What does the nerve cell body contain?
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Nucleus and a nucleolus
Major biosynthetic center No centrioles-hence amitotic nature Well developed nissl bodies Axon hillock-coneshaped area where axons arise two types of processes: axons and dendrites |
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What is the function of Axons?
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Generate and transmit action potentials
Secrete neurotransmitters from axon terminals movement along axons |
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What are the two types of movement along axons?
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Anerograde-Toward axon terminal
Retrograde-Away from axon terminal |
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Describe the dendrites of motor neurons
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Short, tapering and diffusely branched processes
Primarily receptive or input Electrical signals are graded potentials (not action potential) |
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Describe Myelin Sheath of motor neurons
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Protein-lipid segmented sheath around most axons
protection and electric insulation increase speed of nerve impulse transmission |
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Describe Schwann cells in regards to the PNS
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Has concentric layers of membrane that make up the myelin sheath called neurilemma
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Describe the nodes of ranvier
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Gaps in myelin sheath between adjacent schwann cell
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Describe unmyelinated axons
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A schwann cell surrounds nerve fibers with one wrap
Schwann cells partially enclose 15 or more axons 15 |
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How many axons do schwann cells partially enclose?
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15 or more
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Describe the axons of the CNS
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Both myelinated and unmyelinated fibers
myelin sheaths-oligodendrocytes nodes of ranvier are widely spaced no neurilemma |
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What is white and gray matter?
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White matter- myelinated fibers
Gray matter- soma and unmyelinated fibers |
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What are the categories in which neurons are classified in regards to their function?
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Sensory (afferent)- transmit impulses toward CNS
Motor (efferent)- carry impulses away CNS Interneurons (association neurons)- shuttle signals through CNS pathway |
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What is voltage?
What is potential difference What is current What is resistance What is insulator What is conductor |
Potential energy generated by separated charge
Voltage between two points Flow of charge between two points Hindrance to charge flow substance with high resistance to current substance with low resistance to current |
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What is Ohn's law
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Current=Voltage / Resistance
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What are the types of plasma membrane ion channels?
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Leakage (passive channels)-always open
Chemically (ligand) gated channels- open with binding of a specific neurotransmitter Voltage-gated channels- open and close in response to membrane potential Mechanically gated channels- open and close in response to physical deformation of receptors |
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What happens when gated channels are open
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Ions move quickly across the membrane
Movement is due to electrochemical gradients Creates an electrical current Voltage changes across the membrane |
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What are ion pumps?
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Use ATP to pump the ions against their gradients
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What are the basic principles of electricity
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opposite charges attract each other
Energy is required to separate opposite charges across membrane energy is liberated when the charges move toward one another if opposite charges are separated the system has potential energy |
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What is electrochemical gradient?
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ions flow from an are of high concentrations to an area of low concentration
Sodium-outside to inside Potassium-inside to outside Chloride-outside to inside proteins-trapped in cell |
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What can change a membrane potential signal?
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Anything that changes membrane permeability (opens or closes ion channels)
Alters ion concentrations |
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What are the types of signals
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Graded potentials- Once they start don't stop
Action potentials- little voltage change- wear out |
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What are the three events that cause changes in membrane potentials
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Depolarization- the inside of the membrane becomes less negative
Repolarization-the membrane returns to its resting membrane potential Hyperpolarization-Inside of membrane becomes more negative than the resting potential |
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What are graded potentials?
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Short-lived, local changes in membrane potential
Decrease with intensity and distance strong or additive graded potentials can initiate action potentials Travel short distances |
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Why is the current quickly dissipated in graded potentials?
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Due to leaky plasma membrane
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What are action potentials?
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Brief reversal of membrane potential
Generated by muscle cells and neurons Principle means of neural communication via axons Action potential=nerve impulse |
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Describe the action potential resting state
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Voltage Na+ and K+ channels are closed
Leakage accounts for small movements of Na+ and K+ Each Na+ channel has two voltage regulated gates |
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Describe Na+ channel voltage regulated gates
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Activation gates: closed in the resting state
Inactivation gates: open in the resting state |
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Action Potential: depolarization phase
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Na+ permeability increases; membrane potential reverses due to graded potential
Na+ gates are opened;K+ gates are closed At threshold depolarization becomes self-generating |
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Action Potential: Repolarization phase
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Sodium inactivation gates close
Membrane permeability to Na+ declines to resting levels Sodium gates close, voltage-gated K+ gates open K+ exits cell, internal negativity of resting neuron is restored |
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Action Potential: Hyperpolarization
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Potassium gates remain open causing excessive efflux of K+
Efflux causes hyperpolarization of the membrane Neuron is insensitive to stimulus and depolarization |
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What happens if extracellular K+ goes up?
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Won't diffuse no ion concentration difference- death not just skeletal but cardiac
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Action Potential: Repolarization
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Restores resting electrical conditions
Does not restore resting ionic conditions |
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What is the role of the sodium-potassium pump
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Ionic redistribution back to resting conditions
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What are the phases of the action potential?
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1-resting state: -70mv
2-depolarization: opening sodium channels 3-repolarization: by opening potassium channels 4-hyperpolarization: |
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Where do liganated channels, graded potentials occur?
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Dendrites and soma
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Propagation of action potential= 0ms
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Na+ influx causes a region to depolarize
Positive ions move toward the polarized(negative) portion of the membrane Sodium gates are closed until threshold is reached |
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Propagation of action potential= 2ms
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Current created depolarizes adjacent membrane in a forward direction
Voltage gated channels change the membrane permeability impulse propagates away from its point of origin due to hyperpolarization |
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Propagation of action potential =4ms
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Action potential moves away from stimulus
Sodium gates close, potassium gates open creating a current flow at first repolarizing & then hyperpolarizing the membrane |
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What is the all or non phenomenon
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Action potentials either happen completely or not at all.
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Describe stimulus intensity of action potentials
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Strong stimuli can generate an action potential more often than weaker stimuli but all action potentials are alike
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What determines stimulus intensity?
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CNS determines stimulus intensity by frequency of action potentials
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What is the absolute refractory period
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Time from opening of Na+ gates until closing of Na+ gates
Prevents neuron from generating an action potential Ensures each action potential is separate Enforces one-way transmission of nerve impulses |
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What is the relative refractory period
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Interval following the absolute refractory period
Sodium gates are closed Potassium gates are open Repolarization/hyperpolarization is occurring Threshold level is elevated allowing strong stimuli to increase frequency of action potential events |
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What is the rate of impulse propagation determined by?
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Axon diameter- the larger the diameter the faster the impulse
Presence of myelin sheath-myelination dramatically increases impulse speed |
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What are nerve fibers classified as?
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Diameter
Degree of myelination Speed of conduction Nerves have different functions based on their combination of these factors |
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Explain Saltatory conduction
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Current passes only at nodes of Ranvier
Action potentials are triggered only at nodes and jump from node to node |
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What is Multiple Sclerosis
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Autoimmune disease
Myelin sheaths in the CNS are lost (demyleinated) or become nonfunctional as scarring occurs after the oligodendrocytes die. Slow transmission of action potentials Damage cannot be repaired |
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What is the treatment for multiple sclerosis
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Immune suppressants: corticosteroids
All are focused at stopping immune cells from crossing the BBB |
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What is a synapse?
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Junction that transfers information between neurons or effector cells
1000-10,000 per cell any area of a neuron: axon, dendrite, soma |
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What are the types of synapses?
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Presynaptic neuron: conducts impulses toward synapse
Postsynaptic neuron: transmits impulses away from synapse |
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Describe electrical synapses
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Less common than chemical synapses
Can be bi-directional Connexins: similar to gap junctions |
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Why are electrical synapses important in the CNS?
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arousal from sleep
Mental attention Emotions and memory Ion and water homeostasis |
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Describe chemical synapses
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Specialized for release and reception of neurotransmitters
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What are chemical synapses composed of?
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Axonal terminal of the presynaptic neuron, contains synaptic vesicles
Receptor region on dendrites or soma of postysnaptic neuron Synaptic cleft |
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What is the synaptic cleft
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Fluid filled space separating presynaptic and postsynaptic neurons
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What does the synaptic cleft do
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Prevents nerve impulses from directly passing from one neuron to the next
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Describe transmission across the synaptic cleft
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Chemical event
Unidirectional communication between neurons The rate limiting step in neural conduction |
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Describe synaptic delay
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Neurotransmitter released, diffuse across the synapse and bind to receptors
Synaptic delay-time needed (0.3-0.5 ms) Synaptic delay is rate-limiting step of neural transmission |
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According to what do neurotransmitter receptors mediate changes in membrane potential?
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Amount of neurotransmitter released
Amount of time neurotransmitter is bound to receptors |
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What are the two types of postsynaptic potentials
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EPSPs- excitatory postsynaptic potentails
IPSP-inhibitory postysnaptic potentials |
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What are Excitatory postsynaptic potentials
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Graded potentials that can initiate an action potential
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Characteristics of exitatory postysnaptic potentials
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Ligand gated channels
Na+ and K+ flow in opposite directions at same time Postsynaptic membranes do not generate action potentials |
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What are inhibitory synapses and IPSPs
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Neurotransmitter binding to a receptor at inhibitory synapses:
Membrane becomes more permeable to K+ and/or Cl- Leaves charge on inner surface more negative=hyperpolarized reduces postysnaptic neuron's ability to produce an action potential |
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How must EPSP's summate to induce an action potential
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temporally and or spatially
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What is temporal summation
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presynaptic neurons transmit impulses in rapid fire order
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What is spatial summations
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Postsynaptic neuron is stimulated by a large number of terminals at the same time
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What happens if IPSPs and EPSPs summate?
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cancel each other out
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What are neurotransmitters?
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Chemicals used for neuronal communication
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What are the functions of neurotransmitters?
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Many drugs work by either mimicking or blocking a neurotransmitter or its receptor
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What determines response
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The receptor for the neurotransmitter determines response- excitatory vs inhibitory
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What are the two types of neurotransmitters?
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Excitatory neurotransmitter/receptors cause depolarizations
Inhibitory neurotransmitter/receptors cause hyperpolarizations |
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What are the neurotransmitter receptor mechanisms?
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Direct: neurotransmitters open ion channels
promote rapid responses Indirect: act through second messangers promote long lasting effects |
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What are G protein linked receptors?
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Indirect responses that are slow, complex, prolonged and diffuse
Also called metabotropic receptors-wiedspread |
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What is the mechanism for G protein linked receptors
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neurotransmitter binds to G protein linked receptor
G protein is activated and GTP is hydrolyzed to GDP Activated G protein complex activates adenlate cyclase which catalyzes the formation of cAMP from ATP which is a second messenger that brings about various cellular responses |
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What are the types of circuits in neuronal pools
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Divergent- one incoming fiber stimulates ever increasing number of fibers, often amplifying circuits
Convergent-resulting in either strong stimulation or in either strong stimulation or inhibition Reverberating-Chain of neurons containing collateral synapses with previous neurons in chain Parallel after discharge- incoming neurons stimulate several neurons in parallel arrays complex mental processing |
