Neurons: Cellular and Network Properties

POWERPOINT® LECTURE SLIDE PRESENTATIONby LYNN CIALDELLA, MA, MBA, The University of Texas at AustinAdditional text by J Padilla exclusively for physiology at ECC

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

HUMAN PHYSIOLOGYAN INTEGRATED APPROACH FOURTH EDITION

DEE UNGLAUB SILVERTHORN

UNIT 2UNIT 2

PART A

8 Neurons: Cellular and Network Properties


About this Chapter

Organization of the nervous system

Electrical signals in neurons

Cell-to-cell communication in the nervous system

Integration of neural information transfer


Nervous System SubdivisionsNervous System Subdivisions


Organization of the Nervous System

Figure 8-1

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8-2

Model Neuron

Dendrites receive incoming signals; axons carry outgoing information


Cells of Nervous System (NS):Axons Transport Slow axonal transport

Moves material by axoplasmic flow at 0.2–2.5 mm/day

Fast axonal transport

Moves organelles at rates of up to 400 mm/day

Forward transport: from cell body to axon terminal

Backward transport: from axon terminal to cell body


Cells of NS: Glial Cells and Their Function

Figure 8-5 (1 of 2)

Glial cells maintain an environment suitable for proper neuron functionGlial cells maintain an environment suitable for proper neuron function


Graded Potential The cell body receives

stimulus

The strength is determined by how much charge enters the cell

The strength of the graded potential diminishes over distance due to current leak and cytoplasmic resistance

The amplitude increases as more sodium enters, the higher the amplitude, the further the spread of the signal

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8-8a

Electrical Signals: Graded Potentials

Subthreshold and suprathreshold graded potentials in a neuron

If a graded potential does not go beyond the treshold at the trigger zone an action potential will not be generated


Electrical Signals: Graded Potentials

Figure 8-8b

Depolarizing grading potential are excitatory

Hyperpolarizing graded potentials are inhibitory

Graded potential= short distance, lose strength as they travel, can initate an action potential

Depolarizing grading potential are excitatory

Hyperpolarizing graded potentials are inhibitory

Graded potential= short distance, lose strength as they travel, can initate an action potential


Electrical Signals: Trigger Zone

Graded potential enters trigger zone- summation brings it to a level above threshold

Voltage-gated Na+ channels open and Na+ enters axon – a segment of the membrane depolarizes

Positive charge spreads along adjacent sections of axon by local current flow – as the signal moves away the currently stimulated area returns to its resting potential

Local current flow causes new section of the membrane to depolarize – this new section is creating a new set of action potentials that will trigger the next area to be depolarized

The refractory period prevents backward conduction; loss of K+ repolarizes the membrane – Once the Na+ close they will not open in response to backward conduction until they have reset to their resting position- ensures only one action potential is initiated at time.


Electrical Signals: Voltage-Gated Na+ Channels

Figure 8-10c

Na+ channels have two gates: activation and inactivation gates

Na+ channels have two gates: activation and inactivation gates


Changes in Membrane Potential

Terminology associated with changes in membrane potential (chpt 5 figure)

Animation: Nervous I: The Membrane PotentialPLAY


Electrical Signals: Action Potentials

Figure 8-9 (1 of 9)

Cell is more positive outside than inside

Cell is more positive outside than inside

Rising phaseRising phase



Figure 8-9 (2 of 9)

As ions move across the membrane the potential increases

As ions move across the membrane the potential increases




Figure 8-9 (3 of 9)

Graded potentials have brought the membrane potential up to threshold

Graded potentials have brought the membrane potential up to threshold




Figure 8-9 (4 of 9)

Beyond threshold potential the sodium gated channels allow the ion to move in, making the inside of the cell more positive

Beyond threshold potential the sodium gated channels allow the ion to move in, making the inside of the cell more positiveRising phaseRising phase



Figure 8-9 (5 of 9)

Na+ continues to move into the cell until it reaches electrical equilibrium. At that point Na+ movement stops

Na+ continues to move into the cell until it reaches electrical equilibrium. At that point Na+ movement stops

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8-9 (6 of 9)


Falling phaseFalling phase

K+ moves out of the cell along its gradient and the inside of the cell becomes more and more negative

K+ moves out of the cell along its gradient and the inside of the cell becomes more and more negative



Figure 8-9 (7 of 9)

Hyperpolarization (undershoot) occurs when the potential drops below resting; caused by the continuing movement of K+ out of the cell

Hyperpolarization (undershoot) occurs when the potential drops below resting; caused by the continuing movement of K+ out of the cell



Figure 8-9 (8 of 9)

Leaked Na+ & K+ in cell increases potential toward resting voltageLeaked Na+ & K+ in cell increases potential toward resting voltage

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8-9 (9 of 9)


Returns to its original state where the outside is more positive than the inside and the membrane potential is -70mv

Returns to its original state where the outside is more positive than the inside and the membrane potential is -70mv


Electrical Signals: Ion Movement During an Action Potential


Electrical Signals: Refractory PeriodAction potentials will not fire during an absolute refractory period


Action Potential Travel Down Axon

Each region of the axon experiences a different phase of the action potential

Each region of the axon experiences a different phase of the action potential


Electrical Signals: Myelinated Axons

Saltatory conduction- signal seems to “jump” from node to node moving swiftly- compensates for smaller diameter.

Demyelination slows down signal conduction because the current leaks. Sometimes conduction does not reach the next node and dies out.

Saltatory conduction- signal seems to “jump” from node to node moving swiftly- compensates for smaller diameter.

Demyelination slows down signal conduction because the current leaks. Sometimes conduction does not reach the next node and dies out.


Electrical Signals: Speed of action potential Speed of action potential in

neurons is influenced by: Diameter of axon

Larger axons are faster- less resistance to ion flow due to the larger diameter. Large diameter axons are only found in animals with small less complex nervous systems.

Resistance of axon membrane to ion leakage out of the cell Myelinated axons are faster – the

myelin sheath insulates the membrane allowing the action potential to pass along myelinated are sustaining conduction without slowing down by ion channels opening.

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 8-13b

Electrical Signals: Coding for Stimulus Intensity

Since all action potentials are identical, the strength of a stimulus is indicated by the defrequency of action potentials. Neurotransmitter amounts released are directly propertional to frequency as long as a sufficient supply is available

Since all action potentials are identical, the strength of a stimulus is indicated by the defrequency of action potentials. Neurotransmitter amounts released are directly propertional to frequency as long as a sufficient supply is available

POWERPOINT® LECTURE SLIDE PRESENTATIONby LYNN CIALDELLA, MA, MBA, The University of Texas at AustinAdditional text by J Padilla exclusively for physiology at ECC


HUMAN PHYSIOLOGYAN INTEGRATED APPROACH FOURTH EDITION

DEE UNGLAUB SILVERTHORN

UNIT 2UNIT 2

PART A

5Membrane Dynamics


Electricity Review

Law of conservation of electrical charges- the net amount of electrical charge produced in any process is zero.

Opposite charges attract; like charges repel each other- happens with protons & electrons

Separating positive charges from negative charges requires energy – membrane pumps use active transport so separate ions

Conductor versus insulator – a conductor allows the charges to move towards each other and an insulator keeps them separate- does not carry current.

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 5-32b

Separation of Electrical Charges

Resting membrane potential is the electrical gradient between ECF and ICF

Inside of the cell is more negative than the outside

Electrical gradient create the ability to do work just like concentration gradients

Inside of the cell is more negative than the outside

Electrical gradient create the ability to do work just like concentration gradients

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 5-32c

Separation of Electrical Charges

Resting membrane potential is the electrical gradient between ECF and ICF. Resting membrane potential is due mostly to potassium- it is the equilibrium potential of K+

A relative scale shifts the charge to a -2

A relative scale shifts the charge to a -2


Potassium Equilibrium Potential


Sodium Equilibrium Potential

Can be calculated using the Nernst Equation

Concentration gradient is opposed by membrane potential

Concentration gradient is opposed by membrane potential


Electrical Signals: Nernst Equation

Predicts membrane potential for single ion- membrane potentials result from an uneven distribution of ions across a membrane.

Membrane potential is influenced by : Concentration gradient of ions – Na+, Cl-, & Ca2+

have higher [extracellular] and K+ has a higher [intracellular]

Membrane permeability to those ions - only K+ is allowed to move in so this ion contributes to the resting potential


Electrical Signals: GHK Equation

Predicts membrane potential using multiple ions- resting membrane potential= the contribution of all ions that cross the membrane X membrane permeability values. Ion contribution is proportional to membrane permeability for that ion. Potentials will be affected if ion concentrations change.

P=permeability value


Electrical Signals: Ion Movement

Resting membrane potential determined by K+ concentration gradient

Cell’s resting permeability to K+, Na+, and Cl–

Gated channels control ion permeability Mechanically gated – respond to physical forces

(pressure)

Chemical gated - respond to ligands (neurotransmitter)

Voltage gated - respond to membrane potential changes

Threshold voltage varies from one channel type to another – the minimum stimulus required and the response speed varies for each type


Cell-to-Cell: Postsynaptic Response

Fast and slow responses in postsynaptic cells involve ion channels and G-protein receptor

Figure 8-23

Postsynaptic cell

Presynaptic axon terminal

GR

Ion channels open

More Na+ in

More K+

out or Cl– in

EPSP = excitatory

depolarization

IPSP = inhibitory

hyperpolarization

Ion channels close

LessNa+ in

Less K+

out

EPSP = excitatory

depolarization

Alters openstate of

ion channels

Activated secondmessenger pathway

Inactivepathway

Modifies existingproteins or regulates

synthesis of newproteins

Coordinatedintracellular

response

Rapid, short-actingfast synaptic potential

NeurotransmitterSlow synaptic potentialsand long-term effects

Chemically gated ion channel

G protein–coupledreceptor


Cell-to-Cell: Chemical Synapse

Chemical synapses use neurotransmitters; electrical synapses pass electrical signals.

Chemical synapses are most common. Electrical synapses are found in the CNS and other cells that use electrical signals (heart)

Chemical synapses are most common. Electrical synapses are found in the CNS and other cells that use electrical signals (heart)


Cell-to-Cell: Calcium

Events at the synapse

Exocytosis: Classic versus kiss-and-run

Voltage-gated Ca2+ channel

Postsynapticcell

Ca2+

Ca2+

Dockingprotein

Synapticvesicle

Actionpotential

Axonterminal

Receptor

An action potential depolarizes the axon terminal.

The depolarization opens voltage-gated Ca2+ channels and Ca2+

enters the cell.

Calcium entry triggers exocytosis of synaptic vesicle contents.

Neurotransmitter diffuses acrossthe synaptic cleft and binds with receptors on the postsynaptic cell.

Cellresponse

Neurotransmitter binding initiatesa response in the postsynapticcell.

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5

1

2

3

4

5

1

2

3


Cell-to-Cell: Acetylcholine

Synthesis and recycling of acetylcholine at a synapse


Integration: Long-Term Potentiation

Figure 8-30

Long-term potentiation- mechanism used in learning and memory using Glutaminergic Receptors.Long-term potentiation- mechanism used in learning and memory using Glutaminergic Receptors.


Cell-to-Cell: Inactivation of Neurotransmitters


Cell-to-Cell: Neurocrines

Seven classes by structure -

Acetylcholine –(Ach) neurotransmitter composed of choline and coenzyme A (acetyl CoA), binds to cholinergic receptors

Amines – neurotransmitter, derived from a single amino acid: Dopamine, Norepinephrine, Epinephrine, Serotonin, Histamine

Amino acids – an amino acid that functions as a neurotransmitter: Glutamate, Aspartate, Gamma-aminobutyric, Glycine

Purines –made from adenine

Gases – act as neurotransmitter, half-life of 2-30 sec.

Peptides -neurohoromones, neurotransmitters, and neuromodulator,

Lipids – eicosanoids


Cell-to-Cell: Amine

Derived from single amino acid

Tyrosine Dopamine -neurotransmitter/neurhormone

Norepinephrine -tyrosine , neurotransmitter/neurhormone, secreted by noradrenogenic neurons,

Epinephrine - neurotransmitter/neurhormone, also called adrenaline, secreted by adrenogenic neurons

Others Serotonin – neurotransmitter, is made from tryptophan

Histamine – neurotransmitter, is made from histadine


Cell-to-Cell: Amino Acids

Glutamate: primary excitatory CNS

Aspartate: primary excitatory brain (select regions)

Gamma-aminobutyric(GABA): Inhibitory brain

Glycine Inhibitory spinal cord

May also be excitatory


Cell-to-Cell: Neurocrines

Peptides -involved in pain and pain relieve pathways Substance P and opioid peptides

Purines- bind purinergic receptors AMP and ATP

Gases- produced inside the body, function and mechanisms not totally understood NO and CO

Lipids -bind cannabinoid receptors in brain and immune system cells Eicosanoids


Cell-to-Cell: Receptors

Cholinergic receptors Nicotinic on skeletal muscle, in PNS and CNS

Monovalent cation channels Na+ and K+

Muscarinic in CNS and PNS

Linked to G proteins

Adrenergic Receptors and - two classes

Linked to G proteins- initiate second messenger


Integration: Injury to Neurons

Figure 8-32

If the cell body is not damaged the neuron will most likely survive. Axon healing is similar to growth cone of a developing axon.

If the cell body is not damaged the neuron will most likely survive. Axon healing is similar to growth cone of a developing axon.

Neurons: Cellular and Network Properties

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