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126 Cards in this Set
- Front
- Back
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How many neurons and synapses?
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100B neurons, 100T synapses
100K miles of nerves 85K neurons lost every day |
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Major anatomical subdivisions of nervous system
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Central nervous system (CNS) - brain & spinal cord
Peripheral nervous system (PNS) other nerves & ganglia |
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Parts of PNS
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Sensory Division: Visceral & Somatic Sensory divisions
Motor Division: Visceral & Somatic Motor Divisions Visceral Motor: Sympathetic & Parasympathetic divisions (Autonomic Nervous System) |
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Functional Divisions of PNS: Sensory (afferent) divisions
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Incoming Information:
Visceral & Somatic Receptors signal to CNS |
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Functional Divisions of PNS: Motor (efferent) division - Visceral motor subdivision (aka autonomic nervous system)
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Info Output: cardiac muscle, smooth muscle, glands
Sympathetic system: fight or flight Parasympathetic system: rest and relax |
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Functional Divisions of PNS: Motor (efferent) division - Somatic Motor subdivision
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Info Output: Effectors, Skeletal muscle, Skin
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Cells of the Nervous System
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Neurons: carry impulses
Neuroglia: (aka - supporting cells, glia, or glial cells) |
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Neuroglia of CNS
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Astrocytes
Oligodendrocytes Microglia Ependymal cells |
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Neuroglia of the PNS
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Schwann cells
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Fundamental Properties of Neurons
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Excitability (responsiveness) - can respond to stimuli (changes in body and external environment
Conductivity - can produce traveling electrical signals Secretion-release chem. neurotransmitter at synapse |
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Parts of a Neuron: List
and Information Flow |
- Dendrites, Cell Body (soma), Axon Hillock, Axon, Synaptic knob
- Transition from local to action to chemical (repeat) |
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Parts of a Neuron: Dendrites
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Receive signal
transfer signal toward soma |
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Parts of a Neuron: Axon hillock
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- first part of the axon plus the part of the cell body where the axon exits
- lowest threshold for the action potential |
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Parts of a Neuron: Axon
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- aka nerve fiber
- signals away from soma - site of rapid conduction of action potential |
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Parts of a Neuron: Synaptic Knob
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- Swelling at end of axon
- Contains synaptic vesicles -- neurotransmitter |
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Chemical Synapse
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- Functional junction between synaptic knob of one neuron and dendrites or soma of next neuron
- Cells do not touch |
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Information Flow in Neurons: Dendrites 1
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Local Potential
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Information Flow in Neurons: Cell Body (Soma)
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Local Potential
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Information Flow in Neurons: Axon Hillock
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Local Action Potential
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Information Flow in Neurons: Axon
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Local Potential
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Information Flow in Neurons: Synaptic Knob
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Transition Action to Chemical Signal
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Information Flow in Neurons: Synapse
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Chemical signal crosses synaptic cleft
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Information Flow in Neurons: Dendrites 2
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Open ion channels initiate next local potential
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Information Flow in Neurons
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Transition from local
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Multipolar Neuron
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Most common
Many dendrites One axon |
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Unipolar Neuron
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Sensory from skin and organs to spinal cord
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Types of Neurons by Function
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Sensory neurons
Interneurons Motor neurons |
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Functional Types of Neurons - Sensory Neurons
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Sensory (Afferent) Neurons conduct signals from receptors to the CNS
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Functional Types of Neurons - Interneurons
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Interneurons (Association Neurons) are confined to the CNS
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Functional Types of Neurons - Motor Neurons
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- All are multipolar neurons in the PNS
- Send signals out to effectors - organs that carry out responses called effectors; muscles and gland cells - aka Afferent Neurons |
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Neuronal Signalling Sequence
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1. Sensation - Sensory Neurons
2. Integration - Interneurons 3. Response - Motor Neurons |
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Axonal Transport - Where are Proteins Made?
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Proteins are made in the Soma and must be transported to axon and axon terminal
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Axonal Transport - What happens to waste products in Axon Terminal?
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Waste products in the axon terminal must be transported (recycled) to the soma
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Anterograde Axonal Transport
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Movement from soma toward axon terminal
- Repair axolemma, gated ion channel proteins, enzymes, neurotransmiters |
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Retrograde Axonal Transport
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Movement from axon terminal toward soma
- recycled materials, waste products |
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What is Kinesin?
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A protein that "walks" along microtubules (as in the axon)
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Neuroglia
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aka glial cells
- 90% of CNS cells - 50% of volume - 5 main types |
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Five Main Types of Neuroglia
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- Astrocytes -Oligodendrocytes
- Schwann cells (PNS only) - Microglia - Ependymal cells |
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Astrocytes (Most abundant glial cell) - Functions
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- Maintain neural spatial relationships
- Induce formation of blood brain barrier - Control interstitial environment |
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Microglia
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- Type of white blood cell
- Migrating immune defense |
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Oligodendrocytes
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- Form myelin in CNS
- Each wraps processes around many nerve fibers |
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Schwann Cells
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- Form myelin in PNS
- Each wraps processes around single spot on one nerve fiber |
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Ependymal Cells
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- Line cavities within CNS ventricles and spinal canal
-- Move fluid via cilia - Make cerebrospinal fluid (choroid plexus) |
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Myelin Sheath 1
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- Insulating layer around a nerve fiber -- Prevents ions from passing through plasma membrane
- Formed from wrappings of plasma membrane -- 20% protein & 80% lipid (looks white) |
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Where is Myelin Sheath Made?
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- Made by oligodendrocytes in CNS
- Made by Schwann cells in PNS - Axolemma is axon outermost layer - Neurilemma is myelin outermost layer |
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How is Myelin Sheath Made?
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- In PNS, hundreds of layers wrap axon
- Outer coil mostly schwann cell cytoplasm (neurilemma) - External to neurilemma is a thin sleeve of fibrous connective tissue (endoneurium) (then basal lamina) |
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Nodes of Ranvier
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- Gaps between myelin segments (between Schwann cells)
-- Found in both CNS & PNS |
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PNS Myelin Sheath Formation
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- Myelination begins during fetal development
-- Proceeds most rapidly during infancy |
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Unmyelinated Axons
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- Neurilemma (maybe endoneurium/basal lamina) without myelin sheath
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Factors in Speed of Conduction of Action Potentials
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> Diameter = < Resistance = > Speed
> Myelin = > Speed of conduction A Fibers are larger, myelinated fibers, faster conduction C Fibers are thinner, unmyelinated, slower conduction |
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Speed of Conduction - A Fibers
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- Large diameter, Myelinated
- Fastest fibers, up to 140 meters per second (300mph) |
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Speed of Conduction - C Fibers
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- Small diameter, unmyelinated
- Slowest fibers, 0.5 mps (1mph) - Located in visceral efferent nerves |
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Electrical States of Neurons - Polarization
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- Any state, other than 0mV
-- positive or negative - Most cells are polarized: -70mV |
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Electrical States of Neurons - Depolarization
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- Membrane potential becomes less negative than the resting potential
-- membrane potential moves toward 0mV |
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Electrical States of Neurons - Repolarization
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- Membrane returns to resting potential after depolarization
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Electrical States of Neurons - Hyperpolarization
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- Membrane becomes more negative inside
-- more negative than resting potential |
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Electrolyte Balance
Na+ K+ Ca++ |
Na+ More outside the cell (ECF)
Ca++ More outside the cell (ECF) K+ More Inside the cell (ICF) |
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Na+ K+ ATPase Pump
- Primary Active Transport (made of proteins) Na+ Movement |
3 Na+ ions out of cell
- 3 Na+ ions from ICF bind to carrier - Carrier phosphorylated - ATP -- ADP - Carrier changes conformation - release Na+ to ECF |
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Na+ K+ ATPase Pump
- Primary Active Transport (made of proteins) K+ Movement |
2 K+ ions into cell
- Carrier binds 2 K+ ions from ECF - Carrier loses phosphate - reverts to original shape - Releases K+ ions to ICF |
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Why is Na+ K+ ATPase Pump Important?
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- Important for establishing membrane potential & Na/K gradients
- For maintaining cell volume |
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Channel Proteins - Integral proteins that form pores (channels) for diffusion of water or solutes
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1. Leak Channels - Constantly open - Specific
2. Gated-channels - open and close in response to stimuli - important in nerve signal and muscle contraction |
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Channel Proteins - Gated Channels - 3 Kinds
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1. Ligand-regulated gates at synapses bind to chemical messengers
2. Voltage-regulated gates action potential changes across plasma membrane 3. Mechaniclaly regulated gates (receptors) - physical stress such as stretch and pressure |
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Membrane Transport - Diffusion
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- Net molecular diffusion down concentration gradient
- Tends toward a steady state (0 net diffusion = equilib.) - Through lipid bilayer or protein channels -- Passive, no ATP |
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Passive Ion Movement - Electrical Gradient
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- Ions move along electrical gradient
- Charge diff. between adjacent areas produces gradient |
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Passive Ion Movement - Electrochemical gradient
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- Net effect of electrical + concentration gradients
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Passive Ion Movement - Equilibrium Potential
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- Voltage at which the electrical gradient balances the concentration gradient
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Membrane Potential - Separation of charges across plasma membrane
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- Creates ability to do work
- Present in all cells (not just neurons) |
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Membrane Potential - Where are the Charges Found?
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- Negative charges along inside plasma membrane, positive charges just outside
- Most of ICF and ECF is electrically neutral |
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Membrane Potential - How does it Develop?
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- Develops due to differences in the concentration and permeability of key ions -- K+ and Na+
- Distribution of Cl- ions is passively driven by the established membrane potential (high in ECF) |
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Membrane Potential - in Excitable Tissues
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- Produce rapid, transient changes in membrane potential
- Change their resting potentials into electrical signals -- muscle & nerve cells |
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Normal Resting Potential vs Hyper- & Depolarization
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Polarized: -70mV
Hyperpolarized: < -70mV Depolarized: > -70mV |
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If Only K+ Decided Membrane Potential:
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- K+ would leak out of cell along chemical gradient until diffusion counterbalanced by electrical gradient
- Eq. (membrane) potential of potassium = -90mV -- 90mV of potential work, negative inside cell |
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If Only Na+ Decided Membrane Potential:
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- Na+ would leak into cell along chemical gradient until diffusion counterbalanced by its electrical gradient
- Equilibrium (membrane) Potential of sodium = +60mV -- 60mV of potential work, positive inside cell |
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Resting Membrane Potential - How is Potential maintained when cell is not sending signals?
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- Na+-K+ pumps have a small direct effect on membrane potential (20%)
- Transports 3 Ns+ ions to ECF & 2 K+ ions to ICF - Pumping of Na/K = leaking of Na/K |
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What is the Effect of K+ on the Membrane Potential?
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- K+ brings the resting membrane potential down to -70mV from about -10mV
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Resting Membrane Potential - Why is MP mostly a result of concentration gradient and diffusion of K+?
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- At rest, membrane is more permiable to K+ than to Na+
- Many K leak channels - Few Na leak channels - So, more K+ diffuses into the ECF than Na+ into the ICF - Resting Potential = -70mV |
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Electrical Signals
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- Changes in membrane potential in response to a triggering event
-- Local change in electrical field: transmission of AP - Chemical messenger: e.g. neurotransmitter |
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What are 2 Types of Membrane Changes?
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1. Graded/Local potential
2. Action Potential - Caused by a change in ion flow across plasma membrane through gated channels |
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Electrical Signals: Graded/Local Potentials (1)
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- Local disturbances in membrane potential (1mm max)
-- can depolarize or hyperpolarize membrane - Occur when cell is stimulated - Caused by local changes in ion flow - gates opening |
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Depolarization due to Opening of Gated Na+ channels
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- Na+ rushes in down concentration and electrical gradients
- Na+ diffuses for short distance inside membrane producing a change in voltage called a local potential |
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Electrical Signals: Graded/Local Potential (2)
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- Graded: Stronger triggering event=greater elec. change
- Local: spread only 1mm - Decremental: get weaker as the spread (with distance) - Excitatory (depolarization) or Inhibitory (hyperpolar.) |
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Electrical Signals: Graded/Local Potential - Duration
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- Duration of electrical change is proportional to duration of triggering event
-- Longer triggering event = Longer electrical change |
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Spread of Local Potentials: Localized Current Flow
- Current |
- Current: movement of electrical charges (ions)
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Spread of Local Potentials: Localized Current Flow
- Ion Movement |
- Ions move from depolarized (active) region to adjacent resting membrane regions
- bi-/multidirectional - passive current flow via Elec Grad - Contiguous: touches every part of membrane |
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Spread of Local Potentials: Decremental Conduction
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- Magnitude decreases further form the initial active area
- depolarization spreads only about one millimeter |
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Electrical Signals: Action Potential
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- Large brief changes in membrane potential ~100mV
- Identical propagation long distance along membrane - Plasma Membrane must reach threshold =~-50mV -- All or None |
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Electrical Signals: Action Potential - 3 Phases
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- Depolarization to ~ +30mV
- Repolarization to resting potential (~-70mV) - Hyperpolarization to ~ -90mV |
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4 Characteristics of an Action Potential
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- All or None
- Irreversible - Nondecremental - Unidirectional |
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Stimulation, Threshold, and AP Relationship
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- Subthreshold stimulation = No AP
- Stronger stimulation = more APs, not more depolarized - Speed of propagation depends on properties of nerve carrying signal, not on stimulation strength. |
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Ions and Ion Channels in an AP
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- Na+ & K+ voltage gated channels
- Depolarizaiton by influx of Na+ ions - Re- / hyperpolarization by end of Na+ influx & K+ efflux - Pump maintains huge gradient even after many APs |
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Voltage-Gated K+ Channel
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- One Gate: Activation Gate
-- slow response to threshold ~ -55mV - Two states: Open & Closed ready to open - ~300x > permeability to K+ Slow Close = Hyperpolarized |
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Voltage-Gated Na+ Channel
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- Two Gates: Activation and Inactivation (thresh ~ -55mV)
-- Activation gate: fast, gate-like -- Inactivation gate: slow ball & chain - Close ready to open, - Open, - Closed unable to open |
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Action Potentials: Voltage Gate Sequence
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1. Na+ gate opens and Na+ rushes in (Depolarization)
2. Na+ gate closes, K+ gate opens K+ out (Repolarization) 3. K+ gate closes slowly as K+ moves out (Hyperpolarizes) 4. K+ closed and Na+ diffuses to restore RMP |
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Types of AP propagation - Contiguous Conduction
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- AP spreads along every bit of membrane by local current flow. Moves adjacent membrane to threshold.
- Activates next point of axonal membrane - Self perpetuating cycle of ion and electrical changes |
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Types of AP propagation - Saltatory Conduction
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- Describes spread of APs in myelinated fibers
- AP jumps from node to node - up to 300x faster than contiguous conduction |
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Saltatory Conduction
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Voltage-gated Na+ channels needed for APs
- Few in myelin-covered regions - Many in nodes of Ranvier - Fast diffusion occurs between nodes |
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Refractory Periods: Time when another AP either cannot be generated or is harder to generate - Two Types
- Absolute Refractory Period |
- Impossible to fire new AP
- Maintain one-way flow - Prevent oscillations of APs |
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Refractory Periods: Time when another AP either cannot be generated or is harder to generate - Two Types
- Relative Refractory Period |
- Harder to fire new AP
- Limits frequency of APs -- Longer refractory period = lower AP frequency -- Different refractory periods for different neurons |
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Absolute Refractory Period
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- No stimulus can initiate another AP
- Na+ voltage-gated channels are closed and unable to open - Must fall below threshold before they can open again |
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Relative Refractory Period
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- Time when another AP can be produced only by a stronger than normal triggering event
- Many K+ channels still open: Cell is hyperpolarized - Some Na+ channels still active: fewer able to react |
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Neural Coding: Qualitative Information
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1. Codes what type of info - pain, touch, sound, etc.
-- Depends on which neurons fired |
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Neural Coding: Quantitative Information
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2. Codes how intense stimulus is - Stronger = more rapid fire rate -- Able to overcome hyperpolarization faster -- CNS judges stimulus strength from frequency
- Strong stimuli excite more neurons (recruitment) |
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Neurotransmitters
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- Chemical messengers
- Small rapid acting molecules (100+ known) - Released by one neuron and bind to receptors of next |
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Current View of the Chemical synapse
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- First neuron releases neurotransmitter from synaptic knob
- Chemical crosses gap between neurons - Second neuron changes chem signal to electric signal |
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Chemical Synapse
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- Junction between two neurons
- Presynaptic neuron - Postsyaptic neuron |
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Anatomy of a Chemical Synapse
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- Synaptic Knob contains syaptic vessicles
- Synaptic Cleft between cells - Subsynaptic membrane contains Ligand (chemically)-gated channels |
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Synapse Locations: Synapse may be -
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- Axodendritic
- Axosomatic - Axoaxonic - Some neurons receive over 100,000 synaptic inputs |
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Excitatory Synapse
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- Neurotransmitter binding Na+ & Ca+ channel
- Many Na+ flow into cell - Depolarization brings cell closer to threshold - Excitatory Postsynaptic Potential (EPSP) |
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Inhibitory Synapse
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- Binding opens K+ or Cl- channels
- Outflow of K+ or influx of Cl- hyperpolarizes cell - Larger stimulus required to reach threshold - Inhibitory Postsynaptic Potential (IPSP) |
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Cleaning up Chemical Synapses
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- NT Re-uptake by pre-synaptic cell and reused
- Degredation - NT broken down by enzymes - Diffusion NT diffuses away into the ECF - Absorbed by glial cells |
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Changing Chemical Signal into Electrical Signal
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- Ion channel changes alter MP of post-synaptic neuron
-- Local potential in dendrites and cell body - Excitatory causes depolarization - Inhibitory causes hyperpolarization |
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Neural Pathways
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- Convergence: one cell is influenced by many others
- Divergence: one cell influences many others - 100B neurons - 100T synapses |
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Neurotransmitter Actions
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- Always excitatory
- Always inhibitory - Depends on at which synapse |
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Neurotransmitter Speed
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- Fast at chemically-gated synapse
- Slower and longer lasting at 2nd messenger pathways |
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Neuromodulators
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- Long-term depression or enhancement of synapse
-- Don't usually produce IPSPs or EPSPs - Act via 2nd messenger - often cosecreted with NTs - e.g. neuropeptides, nitrous oxide |
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Types of Neurotransmitters
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- 100 types in 5 categories:
- Acetylcholine - Amino Acid NTs - Monoamines - Neuropeptides - Dissolved Gasses - Others |
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Synaptic Transmission
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1. Excitatory cholinergic synapse (ACh)
2. Inhibitory GABA-ergic synapse (GABA) 3. Excitatory Adrenergic synapse (NE) |
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Excitatory Cholinergic Synapse
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- Nerve Signal Opens V-gated Ca+ channels
- Triggers release of ACh which crosses synapse - ACh Triggers opening of Na+ channels to produce LP - Depolarization may reach threshold and trigger AP |
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Inhibitory GABA-ergic Synapse
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- Nerve signal triggers GABA release which crosses gap
- GABA receptors trigger opening of Cl- channels - Cl- flow leads to post-synaptic hyperpolarization |
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Cessation of Synaptic Signal - Mechanisms to turn off stimulation
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- Diffusion of NT away from synapse (astrocytes)
- Synaptic knob reabsorbs amino acids and monoamines by endocytosis - breaks down with MAO - Acetylcholinesterase degrades ACh in SCleft for recycle |
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Ecitatory Adrenergic Synapse
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- NT is Norepinephrine (NE)
- Acts through 2nd messenger system - G protein activates adenylate cyclase to convert ATP to cAMP |
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cAMP has multiple effects. What are they?
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- synthesis of new enzymes
- activating enzymes - opening ligand gates - produce a postsynaptic potential |
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Neuronal Interactions
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- Summation (temporal and spatial)
- Presynaptic modulation (inhibition and facilitation) - Neuronal pools: reverbrating & after-discharge circuits |
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PreSynaptic Inhibition
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One presynaptic neuron suppresses another
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Summation
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Combination of temporal or spatial inputs that may reach threshold
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Presynaptic modulation
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Axon is innervated by another axon terminal to inhibit or enhance NT release
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