Chapter 8Chapter 8

(1)

Dee Unglaub Silverthorn, Ph.D.

H ^UMAN P ^HYSIOLOGY H ^UMAN P ^HYSIOLOGY

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AN INTEGRATED APPROACH

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Chapter 8 Chapter 8

Neurons:

Cellular and Network Properties

(2)

About this Chapter About this Chapter

• How the nervous system is organized

• Nerve cell types and roles

• Excitability and electrical signals

• Graded and action potentials initiation and conduction

• Neurotransmitters and signal conduction cell to cell

• Modulation and integration of the signals

• Damage and diseases of the nerves

(3)

• Rapid communication for homeostatic balance

• Emergent properties of intelligence &

emotion

• Central Nervous system (CNS)

• Peripheral Nervous system (PNS) Organization of the Nervous System

Organization of the Nervous System

(4)

Organization of the Nervous System Organization of the Nervous System

Figure 8-1: Organization of the nervous system

(5)

(6)

• Dendrites

• Cell Body

• Axon

• Terminal

A Typical Neuron Overview A Typical Neuron Overview

Figure 8-2: Model neuron

(7)

• Pseudounipolar

• Bipolar

• Anaxionic

• Multipolar–CNS

• Multipolar–efferent

Diverse Neuron Forms and Functions

(8)

Diverse Neuron Forms and Functions Diverse Neuron Forms and Functions

Figure 8-3: Anatomic and functional categories of neurons

(9)

• Cell body site of energy generation and synthesis

• Axonal transport

• Vesicles –

• Fast axonal transport to terminal

• Retrograde to cell body

• Electrical depolarizations

Metabolism and Synthesis in a Neuron

(10)

Metabolism and Synthesis in a Neuron Metabolism and Synthesis in a Neuron

Figure 8-4: Axonal transport of membranous organelles

(11)

• Support neuron bodies, form myelin sheaths

• Barriers between compartments

• Scavenger/defense & metabolic assistance Glial Cell Functions

Glial Cell Functions

(12)

Glial Cell Functions Glial Cell Functions

Figure 8-5: Glial cells and their functions

(13)

Electrical Signals:

Ionic Concentrations and Potentials Electrical Signals:

Ionic Concentrations and Potentials

• Nernst & GHK Equations predict

• Membrane potential

• Cell concentration gradients

• [Na ⁺ , Cl ^- & Ca ²⁺ ] higher in ECF

• [K ⁺ ] higher ICF

• Depolarization causes electrical signal

• Gated channels control permeability

(14)

(15)

Electrical Signals:

Ionic Concentrations and Potentials Electrical Signals:

Ionic Concentrations and Potentials

Table 8-2: Ion Concentrations and Equilibrium Potentials

(16)

(17)

Graded Potentials Graded Potentials

• Incoming signals

• Vary in strength

• Lose strength over distance

• Are slower than action potentials (AP)

• Travels to trigger zone

• Subthreshold –

• Too weak

• No generation of AP

• Suprathreshold – generate AP

(18)

Graded Potentials Graded Potentials

Figure 8-7: Graded potentials

decrease in strength as they spread

out from the point of origin

(19)

Trigger Zone: Cell Integration and Initiation of AP Trigger Zone: Cell Integration and Initiation of AP

• Excitatory signal: depolarizes, reduces threshold

• Inhibitory signal: hyperpolarizes, increases

threshold

(20)

(21)

Trigger Zone: Cell Integration and Initiation of AP

(22)

Trigger Zone: Cell Integration and Initiation of AP Trigger Zone: Cell Integration and Initiation of AP

Figure 8-8b: Subthreshold and suprathreshold graded potentials in a neuron

(23)

• "All or none"

• Signal does not diminish over distance Action Potential Stages: Overview

Action Potential Stages: Overview

(24)

Action Potential Stages: Overview Action Potential Stages: Overview

Figure 8-9: The action potential

(25)

(26)

• Initiation

• Depolarization

• Signal peak

• Repolarization

Membrane & Channel Changes during an Action Potential

Membrane & Channel Changes during an

Action Potential

(27)

Membrane & Channel Changes during an Action Potential

Membrane & Channel Changes during an

Action Potential

(28)

• Positive feedback loop

• Absolute refractory period

• Relative refractory period Regulating the AP

Regulating the AP

(29)

Regulating the AP

(30)

Regulating the AP Regulating the AP

Figure 8-12: Refractory periods

(31)

• Firing rate

• "Wave" of APs

• Proportional neurotransmitter (NT) release

• Stronger GP initiates more APs & more NT

Frequency of Action Potentials

(32)

Frequency of Action Potentials Frequency of Action Potentials

Figure 8-13: Coding for stimulus intensity

(33)

• Kinetic energy

• Depolarizes ahead

• Drives AP to terminal

Conduction of Action Potentials

(34)

Conduction of Action Potentials Conduction of Action Potentials

Figure 8-14a: Conduction of action potentials

(35)

Conduction of Action Potentials

(36)

Conduction of Action Potentials Conduction of Action Potentials

Figure 8-14c: Conduction of action potentials

(37)

• Larger diameter faster conduction

• Myelinated axon faster conduction

• Saltatory conduction

• Disease damage to myelin

• Chemicals that block channels

• Alteration of ECF ion concentrations Speed of Conduction

Speed of Conduction

(38)

Speed of Conduction Speed of Conduction

Figure 8-16b: Axon diameter and speed of conduction

(39)

Speed of Conduction

(40)

Cell to Cell Conduction: the Synapse Cell to Cell Conduction: the Synapse

• Electrical synapses: gap junctions

• Very fast conduction

• Example: cardiac muscle

• Chemical synapses

• Pre synaptic terminal

• Synthesis of Neurotransmitters

• Ca ²⁺ releases Neurotransmitters

• Synaptic cleft

• Postsynaptic cell: Neurotransmitter

receptors

(41)

Cell to Cell Conduction: the Synapse

(42)

Synapse Mechanism Synapse Mechanism

Figure 8-20: Events at the synapse

(43)

Acetylcholine synthesis

(44)

• Neurotransmitters

• Neuromodulators

• Neurohormones Neurocrines

Neurocrines

(45)

Neurocrines

(46)

Neurocrines Neurocrines

Table 8-4-2: Major Neurocrines

(47)

Multiple Receptors modify signal Multiple Receptors modify signal

• Amplification – depolarization

• Inhibition – hyperpolarization

• Duration

• Fast – channel opening

• Slow – protein synthesis

(48)

Multiple Receptors modify signal Multiple Receptors modify signal

Figure 8-22: Fast and slow responses in postsynaptic cells

(49)

• Recycled

• Enzyme degradation

• Diffuse away

Inactivation of Neurotransmitters

(50)

Inactivation of Neurotransmitters Inactivation of Neurotransmitters

Figure 8-23: Inactivation of neurotransmitters

(51)

• Information transfer at each exchange

• Signal can be lost

• Signal can be enhanced

• Divergence – one cell to many

• Convergence – many cells to one Integration of Signals

Integration of Signals

(52)

Integration of Signals Integration of Signals

Figure 8-24a: Convergence and divergence

(53)

Integration of Signals

(54)

Integration of Signals Integration of Signals

Figure 8-25: Locations of synapses on a postsynaptic neuron

(55)

Convergent Integration: Additive Summation Convergent Integration: Additive Summation

• Multiple excitatory GPs

• Temporal summation

• Additive strength at trigger zone

(56)

Convergent Integration: Additive Summation Convergent Integration: Additive Summation

Figure 8-26a: Spatial summation

(57)

Chapter 8Chapter 8

Dee Unglaub Silverthorn, Ph.D.

H UMAN P HYSIOLOGY H UMAN P HYSIOLOGY

PowerPoint

Lecture Slide Presentation by

AN INTEGRATED APPROACH

T H I R D E D I T I O N

Chapter 8 Chapter 8

Neurons:

Cellular and Network Properties

About this Chapter About this Chapter

• How the nervous system is organized

• Nerve cell types and roles

• Excitability and electrical signals

• Graded and action potentials initiation and conduction

• Neurotransmitters and signal conduction cell to cell

• Modulation and integration of the signals

• Damage and diseases of the nerves

• Rapid communication for homeostatic balance

• Emergent properties of intelligence &

emotion

• Central Nervous system (CNS)

• Peripheral Nervous system (PNS) Organization of the Nervous System

Organization of the Nervous System

Organization of the Nervous System Organization of the Nervous System

• Dendrites

• Cell Body

• Axon

• Terminal

A Typical Neuron Overview A Typical Neuron Overview

Figure 8-2: Model neuron

• Pseudounipolar

• Bipolar

• Anaxionic

• Multipolar–CNS

• Multipolar–efferent

Diverse Neuron Forms and Functions

Diverse Neuron Forms and Functions

Diverse Neuron Forms and Functions Diverse Neuron Forms and Functions

Figure 8-3: Anatomic and functional categories of neurons

• Cell body site of energy generation and synthesis

• Axonal transport

• Vesicles –

• Fast axonal transport to terminal

• Retrograde to cell body

• Electrical depolarizations

Metabolism and Synthesis in a Neuron

Metabolism and Synthesis in a Neuron

Metabolism and Synthesis in a Neuron Metabolism and Synthesis in a Neuron

Figure 8-4: Axonal transport of membranous organelles

• Support neuron bodies, form myelin sheaths

• Barriers between compartments

• Scavenger/defense & metabolic assistance Glial Cell Functions

Glial Cell Functions

Glial Cell Functions Glial Cell Functions

Figure 8-5: Glial cells and their functions

Electrical Signals:

Ionic Concentrations and Potentials Electrical Signals:

Ionic Concentrations and Potentials

• Nernst & GHK Equations predict

• Membrane potential

• Cell concentration gradients

• [Na + , Cl - & Ca 2+ ] higher in ECF

• [K + ] higher ICF

• Depolarization causes electrical signal

• Gated channels control permeability

Electrical Signals:

Ionic Concentrations and Potentials Electrical Signals:

Ionic Concentrations and Potentials

Table 8-2: Ion Concentrations and Equilibrium Potentials

Graded Potentials Graded Potentials

• Incoming signals

• Vary in strength

• Lose strength over distance

• Are slower than action potentials (AP)

• Travels to trigger zone

• Subthreshold –

• Too weak

• No generation of AP

• Suprathreshold – generate AP

H ^UMAN P ^HYSIOLOGY H ^UMAN P ^HYSIOLOGY

• [Na ⁺ , Cl ^- & Ca ²⁺ ] higher in ECF

• [K ⁺ ] higher ICF