PPT Notes Chapter 11 Flashcards

Question

Electricity Definitions

Answer 1

Voltage (V) – measure of potential energy generated by separated charge Potential difference – voltage measured between two points Current (I) – the flow of electrical charge between two points Resistance (R) – hindrance to charge flow Insulator – substance with high electrical resistance Conductor – substance with low electrical resistance

Answer 2

* Reflects the flow of ions rather than electrons * There is a potential on either side of membranes when: * The number of ions is different across the membrane * The membrane provides a resistance to ion flow

Answer 3

4 Types of plasma membrane ion channels: 1. Passive, or leakage, channels – always open 2. Chemically gated channels – open with binding of a specific neurotransmitter 3. Voltage-gated channels – open and close in response to membrane potential 4. Mechanically gated channels – open and close in response to physical deformation of receptors

Answer 4

* Example: Na+-K+ gated channel * Closed when a neurotransmitter is not bound to the extracellular receptor * Na+ cannot enter the cell and K+ cannot exit the cell * Open when a neurotransmitter is attached to the receptor * Na+ enters the cell and K+ exits the cell

Answer 5

Example: Na+ channel * Closed when the intracellular environment is negative * Na+ cannot enter the cell * Open when the intracellular environment is positive * Na+ can enter the cell

Answer 6

When gated channels are open: * Ions move quickly across the membrane * Movement is along their electrochemical gradients * An electrical current is created * Voltage changes across the membrane

Answer 7

* Ions flow along their chemical gradient when they move from an area of high concentration to an area of low concentration * Ions flow along their electrical gradient when they move toward an area of opposite charge * Electrochemical gradient – the electrical and chemical gradients taken together

Answer 8

* The potential difference (–70 mV) across the membrane of a resting neuron * It is generated by different concentrations of Na+, K+, Cl-, and protein anions (A-) * Ionic differences are the consequence of: * Differential permeability of the neurilemma to Na+ and K+ * Operation of the sodium-potassium pump

Answer 9

* Used to integrate, send, and receive information * Membrane potential changes are produced by: * Changes in membrane permeability to ions * Alterations of ion concentrations across the membrane * Types of signals – graded potentials and action potentials

Answer 10

Changes are caused by three events * Depolarization – the inside of the membrane becomes less negative * Repolarization – the membrane returns to its resting membrane potential * Hyperpolarization – the inside of the membrane becomes more negative than the resting potential

Answer 11

* Short-lived, local changes in membrane potential * Decrease in intensity with distance * Magnitude varies directly with the strength of the stimulus * Sufficiently strong graded potentials can initiate action potentials * Voltage changes are decremental * Current is quickly dissipated due to the leaky plasma membrane * Only travel over short distances * Dendritic reception is a graded potential

Answer 12

* A brief reversal of membrane potential with a total amplitude of 100 mV * Action potentials are only generated by muscle cells and neurons * They do not decrease in strength over distance * They are the principal means of neural communication * An action potential in the axon of a neuron is a nerve impulse

Answer 13

* Na+ and K+ channels are closed * Leakage accounts for small movements of Na+ and K+ * Each Na+ channel has two voltage-regulated gates * Activation gates – closed in the resting state * Inactivation gates – open in the resting state

Answer 14

* Na+ permeability increases; membrane potential reverses * Na+ gates are opened; K+ gates are closed * Threshold – a critical level of depolarization (–55 to –50 mV) * At threshold, depolarization becomes self-generating

Answer 15

* Sodium inactivation gates close * Membrane permeability to Na+ declines to resting levels * As sodium gates close, voltage-sensitive K+ gates open * K+ exits the cell and internal negativity of the resting neuron is restored

Answer 16

* Potassium gates remain open, causing an excessive efflux of K+ * This efflux causes hyperpolarization of the membrane (undershoot) * The neuron is insensitive to stimulus and depolarization during this time

Answer 17

Repolarization * Restores the resting electrical conditions of the neuron * Does not restore the resting ionic conditions * Ionic redistribution back to resting conditions is restored by the sodium-potassium pump

Answer 18

1 – resting state 2 – depolarization phase 3 – repolarization phase 4 – hyperpolarization

Answer 19

* Na+ influx causes a patch of the axonal membrane to depolarize * Positive ions in the axoplasm move toward the polarized (negative) portion of the membrane * Sodium gates are shown as closing, open, or closed

Answer 20

* Ions of the extracellular fluid move toward the area of greatest negative charge * A current is created that depolarizes the adjacent membrane in a forward direction * The impulse propagates away from its point of origin

Answer 21

The action potential moves away from the stimulus Where sodium gates are closing, potassium gates are open and create a current flow

Answer 22

* Threshold – membrane is depolarized by 15 to 20 mV * Established by the total amount of current flowing through the membrane * Weak (subthreshold) stimuli are not relayed into action potentials * Strong (threshold) stimuli are relayed into action potentials * All-or-none phenomenon – action potentials either happen completely, or not at all

Answer 23

* All action potentials are alike and are independent of stimulus intensity * Strong stimuli can generate an action potential more often than weaker stimuli * The CNS determines stimulus intensity by the frequency of impulse transmission

Answer 24

* Conduction velocities of neurons vary widely * Effect of axon diameter * Larger diameter fibers have less resistance to local current flow and have faster impulse conduction * Effect of myelination * Continuous conduction in unmyelinated axons is slower than saltatory conduction in myelinated axons * Effects of myelination * Myelin sheaths insulate and prevent leakage of charge * Saltatory conduction in myelinated axons is about 30 times faster * Voltage-gated Na+ channels are located at the nodes * APs appear to jump rapidly from node to node

Answer 25

* An autoimmune disease that mainly affects young adults * Symptoms: visual disturbances, weakness, loss of muscular control, speech disturbances, and urinary incontinence * Myelin sheaths in the CNS become nonfunctional scleroses * Shunting and short-circuiting of nerve impulses occurs * Impulse conduction slows and eventually ceases

Answer 26

Some immune system–modifying drugs, including interferons and \*Copazone: * Hold symptoms at bay * Reduce complications * Reduce disability

Answer 27

Nerve fibers are classified according to: * Diameter * Degree of myelination * Speed of conduction * Group A fibers * Large diameter, myelinated somatic sensory and motor fibers * Group B fibers * Intermediate diameter, lightly myelinated ANS fibers * Group C fibers * Smallest diameter, unmyelinated ANS fibers

Answer 28

A junction that mediates information transfer from one neuron: * To another neuron, or * To an effector cell Presynaptic neuron—conducts impulses toward the synapse Postsynaptic neuron—transmits impulses away from the synapse

Answer 29

Axodendritic—between the axon of one neuron and the dendrite of another Axosomatic—between the axon of one neuron and the soma of another Less common types: * Axoaxonic (axon to axon) * Dendrodendritic (dendrite to dendrite) * Dendrosomatic (dendrite to soma)

Answer 30

* Less common than chemical synapses * Neurons are electrically coupled (joined by gap junctions) * Communication is very rapid, and may be unidirectional or bidirectional Are important in: Embryonic nervous tissue Some brain regions

Answer 31

Specialized for the release and reception of neurotransmitters Typically composed of two parts Axon terminal of the presynaptic neuron, which contains synaptic vesicles Receptor region on the postsynaptic neuron

Answer 32

* Fluid-filled space separating the presynaptic and postsynaptic neurons * Prevents nerve impulses from directly passing from one neuron to the next * Transmission across the synaptic cleft: * Is a chemical event (as opposed to an electrical one) * Involves release, diffusion, and binding of neurotransmitters * Ensures unidirectional communication between neurons

Answer 33

* AP arrives at axon terminal of the presynaptic neuron and opens voltage-gated Ca2+ channels * Synaptotagmin protein binds Ca2+ and promotes fusion of synaptic vesicles with axon membrane * Exocytosis of neurotransmitter occurs * Neurotransmitter diffuses and binds to receptors (often chemically gated ion channels) on the postsynaptic neuron * Ion channels are opened, causing an excitatory or inhibitory event (graded potential)

Answer 34

Within a few milliseconds, the neurotransmitter effect is terminated * Degradation by enzymes * Reuptake by astrocytes or axon terminal * Diffusion away from the synaptic cleft

Answer 35

* Neurotransmitter must be released, diffuse across the synapse, and bind to receptors * Synaptic delay—time needed to do this (0.3–5.0 ms) * Synaptic delay is the rate-limiting step of neural transmission

Answer 36

* Graded potentials * Strength determined by: * Amount of neurotransmitter released * Time the neurotransmitter is in the area Types of postsynaptic potentials EPSP —excitatory postsynaptic potentials IPSP —inhibitory postsynaptic potentials

Answer 37

* Neurotransmitter binds to and opens chemically gated channels that allow simultaneous flow of Na+ and K+ in opposite directions * Na+ influx is greater that K+ efflux, causing a net depolarization * EPSP helps trigger AP at axon hillock if EPSP is of threshold strength and opens the voltage-gated channels

Answer 38

* Neurotransmitter binds to and opens channels for K+ or Cl– * Causes a hyperpolarization (the inner surface of membrane becomes more negative) * Reduces the postsynaptic neuron’s ability to produce an action potential

Answer 39

* A single EPSP cannot induce an action potential * EPSPs can summate to reach threshold * IPSPs can also summate with EPSPs, canceling each other out * Temporal summation * One or more presynaptic neurons transmit impulses in rapid-fire order * Spatial summation * Postsynaptic neuron is stimulated by a large number of terminals at the same time

Answer 40

* Repeated use increases the efficiency of neurotransmission * Ca2+ concentration increases in presynaptic terminal and postsynaptic neuron * Brief high-frequency stimulation partially depolarizes the postsynaptic neuron * Chemically gated channels (NMDA receptors) allow Ca2+ entry * Ca2+ activates kinase enzymes that promote more effective responses to subsequent stimuli

Answer 41

* Release of excitatory neurotransmitter by one neuron may be inhibited by the activity of another neuron via an axoaxonic synapse * Less neurotransmitter is released and smaller EPSPs are formed

Answer 42

* Most neurons make two or more neurotransmitters, which are released at different stimulation frequencies * 50 or more neurotransmitters have been identified * Classified by chemical structure and by function [We will look at 7 classes]

Answer 43

* Acetylcholine (Ach) * Released at neuromuscular junctions and some ANS neurons * Synthesized by enzyme choline acetyltransferase * Degraded by the enzyme acetylcholinesterase (AChE) * Biogenic amines include: * Catecholamines * Dopamine, norepinephrine (NE), and epinephrine * Indolamines * Serotonin and histamine * Broadly distributed in the brain * Play roles in emotional behaviors and the biological clock * Amino acids include: * GABA—Gamma (y)-aminobutyric acid * Glycine * Aspartate * Glutamate * Peptides (neuropeptides) include: * Substance P * Mediator of pain signals * Endorphins * Act as natural opiates; reduce pain perception * Gut-brain peptides * Somatostatin and cholecystokinin * Purines such as ATP: * Act in both the CNS and PNS * Produce fast or slow responses * Induce Ca2+ influx in astrocytes * Provoke pain sensation * Gases and lipids * Nitric oxide (NO) * Synthesized on demand * Activates the intracellular receptor guanylyl cyclase to cyclic GMP * Involved in learning and memory * Carbon monoxide (CO) is a regulator of cGMP in the brain * Gases and lipids * Endocannabinoids * Lipid soluble; synthesized on demand from membrane lipids * Bind with G protein–coupled receptors in the brain * Involved in learning and memory

Answer 44

* Neurotransmitter effects may be excitatory (depolarizing) and/or inhibitory (hyperpolarizing) * Determined by the receptor type of the postsynaptic neuron * GABA and glycine are usually inhibitory * Glutamate is usually excitatory * Acetylcholine * Excitatory at neuromuscular junctions in skeletal muscle * Inhibitory in cardiac muscle

Answer 45

* Direct action * Neurotransmitter binds to channel-linked receptor and opens ion channels * Promotes rapid responses * Examples: ACh and amino acids * Indirect action * Neurotransmitter binds to a G protein-linked receptor and acts through an intracellular second messenger * Promotes long-lasting effects * Examples: biogenic amines, neuropeptides, and dissolved gases

Answer 46

Types * Channel-linked receptors * G protein-linked receptors

Answer 47

* Ligand-gated ion channels * Action is immediate and brief * Excitatory receptors are channels for small cations * Na+ influx contributes most to depolarization * Inhibitory receptors allow Cl– influx or K+ efflux that causes hyperpolarization

Answer 48

* Transmembrane protein complexes * Responses are indirect, slow, complex, and often prolonged and widespread * Examples: muscarinic ACh receptors and those that bind biogenic amines and neuropeptides

Answer 49

* Neurotransmitter binds to G protein–linked receptor * G protein is activated * Activated G protein controls production of second messengers, e.g., cyclic AMP, cyclic GMP, diacylglycerol or Ca2+ * Second messengers * Open or close ion channels * Activate kinase enzymes * Phosphorylate channel proteins * Activate genes and induce protein synthesis

Answer 50

Functional groups of neurons that: * Integrate incoming information * Forward the processed information to other destinations * Simple neuronal pool * Single presynaptic fiber branches and synapses with several neurons in the pool * Discharge zone—neurons most closely associated with the incoming fiber * Facilitated zone—neurons farther away from incoming fiber

Answer 51

* Diverging circuit * One incoming fiber stimulates an ever-increasing number of fibers, often amplifying circuits * May affect a single pathway or several * Common in both sensory and motor systems * Converging circuit * Opposite of diverging circuits, resulting in either strong stimulation or inhibition * Also common in sensory and motor systems * Reverberating (oscillating) circuit * Chain of neurons containing collateral synapses with previous neurons in the chain * Parallel after-discharge circuit * Incoming fiber stimulates several neurons in parallel arrays to stimulate a common output cell

Answer 52

* Serial processing * Input travels along one pathway to a specific destination * Works in an all-or-none manner to produce a specific response * Example: reflexes—rapid, automatic responses to stimuli that always cause the same response * Reflex arcs (pathways) have five essential components: receptor, sensory neuron, CNS integration center, motor neuron, and effector * Parallel processing * Input travels along several pathways * One stimulus promotes numerous responses * Important for higher-level mental functioning * Example: a smell may remind one of the odor and associated experiences

PPT Notes Chapter 11 Flashcards

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