Neuronal Function in the Nervous System. Learning Objectives 1. Explain parts of a typical nerve...

Neuronal Functionin the Nervous System

Learning Objectives 1. Explain parts of a typical nerve cell and describe their

functions. 2. Discuss common types of nerve and glia cells. 3. Describe functions of nerve and glia cells. 4. Explain electrical and chemical properties of nerve

cells. 5. Describe mechanism of impulse generation and its

conduction. 6. Explain nerve cell responses to injuries in the nervous

system. 7. Explain differential regenerative processes between

central and peripheral nervous system. 8. Discuss common neurotransmitters and their

functions.

Nerve Cells Basic anatomic and functional unit of

the nervous system Primary Function:

Two Primary Types

Neuron Three Basic Elements

General Process

Neuron, Myelinated Axon, and Synapse Bhatnagar & Andy, 1995, Figure 5.1.A

Nerve Cell Structure of Neurons: Cell Body Two major components

1. Cytoplasm

The Cell Body Bhatnagar & Andy, 1995, Figure 5.1.B

Nerve Cell Structure of Neurons: Cell Body 2. Nucleus

The Cell Body Bhatnagar & Andy, 1995, Figure 5.1.B

Nerve Cell Structure of Neurons: Dendritic and Axonal Processes Cytoplasmic extensions

Dendrites

Nerve fibers

Nerve Cell Structure of Neurons: Myelin Sheath Speed of nerve conduction is

determined by:

Myelin

Nerve Cell Structure of Neurons: Myelin Sheath Myelin

Nerve Cell Structure of Neurons: Synapse Connection point between neurons Three Parts:

1. Knob (Synaptic vesicles)

2. Synaptic Cleft

3. Receptive Sites of Connecting Nerve Cells

Nerve Cell Structure of Neurons: Synapse Process of Nerve Impulses

Nerve Cell Types Classification:

Three Cell Types: 1. Multipolar

2. Bipolar

3. Unipolar

Nerve Cell Types Bhatnagar & Andy, 1995, Figure 5.2

Neuroglia Cells Function:

Location:

Neuroglia Cells in the Central Nervous System Four Types of Glia Cells in the CNS

1. Astrocytes Location:

Function:

Neuroglia Cells in the Central Nervous System

2. Ogliodendroglia

3. Ependymal

4. Microglia

Neuroglial Cells in the Peripheral Nervous System Schwann cells

Function:

Impairments: Demyelinating Neuropathologies

Benign Tumors of Schwann Cells

Central and Peripheral Nervous Systems Cytological Differences

1. Different myelin forming cells PNS

CNS

Central and Peripheral Nervous Systems Cytological Differences

2. Presence of endoneurium

PNS

CNS

Nerve Impulse Communication

Principles of Process Chemical component

Excitability of nerve cells

Action potential

Nerve Impulse Process

Excitability of nerve cells

An action potential

Activation releasing neurotransmitter

Opening of channels in postsynaptic receptors

Nerve Impulse Process Resting State

Cell is in resting state

In this resting state

Action Potential: Resting Potential with Polarized Membrane

Bhatnagar & Andy, 1995, Figure 5.5A

Nerve Impulse Process Resting Membrane Potential

Voltage inside the cell membrane

Outside the cell membrane

Inside the cell membrane

Ionic channels

Action Potential Bhatnagar & Andy, 1995, Figure 5.5D

Membrane Channels Membrane channels are gated

Flow of ions through the membrane Depends on:

1. The density of the channels 2. The size of the opening 3. The ion concentration gradient across the

membrane

Membrane Channels Distribution of sodium and

potassium across the cellular membrane Is constantly adjusted by the sodium-

potassium pump

Because of the membrane pore size

Membrane Channels With the attraction of opposite ions

and the repulsion of identical ions

With this tug of war An electrochemical gradient forms

along the membrane

Action Potential: Resting Potential with Polarized Membrane


Nerve Excitability

Excitability Refers to:

Nerve Excitability

Stimuli can include:

Nerve Excitability

During the resting state The neuron undergoes several short changes in the

intracellular potentials

Triggering an action potential

Action Potential: Generation of Action Potential with Depolarized Membrane

Bhatnagar & Andy, 1995, Figure 5.5B

Nerve Excitability

In membrane depolarization

Nerve Excitability

Membrane potential from this peak returns to the absolute refractive period

Nerve Excitability

Not all stimuli Are strong enough to change the membrane

potentials to 10 mV Many weak stimuli with subthreshold strength

If temporally and spatially summated Can initiate a nerve impulse

Each weak stimulus arrives in a sequence and their cumulative effect is strong enough to initiate an impulse

Impulse Conduction

Nerve impulse is passively conducted a short distance in the axon

Action Potential: Generation of Action Potential with Depolarized Membrane


Impulse Conduction

This gradually changes the membrane potential in the neighboring area

Action Potential: Conduction of Action Potential Along Membrane

Bhatnagar & Andy, 1995, Figure 5.5C

Impulse Conduction

Saltatory Conduction in Myelinated Axons

Impulse Conduction

Action potential or nerve impulse

Excitatory Postsynaptic Potential (EPSP)

Inhibitory Postsynaptic Potential (IPSP)

Neuronal Responses to Brain Injuries

Nerve Cells in the Human Brain Are incapable of further cell division and

regeneration

Synapses serve as good points of reference for discovering the impact of cellular injuries

Neuronal Responses to Brain Injuries Understanding the Processes of Spontaneous

Recovery

Two Types of Degenerative Changes Occur After Axonal Sectioning

1. Axonal or Retrograde Reaction

2. Wallerian (Anterograde) Degeneration

Types of Neuronal Response to Injury


Neuronal Response to Injury: Axonal Retrograde Reaction


Neuronal Response to Injury: Wallerian Degeneration


Axonal Regeneration in Peripheral Nervous System

Regeneration of Fibers in the PNS

Neuronal Response to Injury: Peripheral Nerve Regeneration

Bhatnagar & Andy, 1995, Figure 5.6D

Axonal Regeneration in Central Nervous System

Axons severed in the CNS

Neurotransmitters Neurotransmitters

Along with projections from the reticular formation

Regulate brain mechanisms that control: Cognition Language Speech Hearing Brain Tuning Moods Attention Memory Personality Motivation

Neurotransmitters

Two types of transmitters in the nervous system: 1. Small molecules

Include: Acetylcholine Dopamine Norepinephrine Serotonin Glutamate y-aminobutyric acid (GABA)

2. Larger molecules Peptides

Neurotransmitters: Acetylcholine Synthesis and Dissolution

Acetylcoenzyme A and choline

Acetylcholinesterase

Neurotransmitters: Acetylcholine in the PNS Location of Cells in PNS:

Function:

Impairments:

Neurotransmitters: Acetylcholine in the CNS Location of Cells In CNS:

Function:

Impairments:

Sites of Cell Bodies and Their Projections in the Brain: Acetylcholine


Neurotransmitters: Dopamine Location of Cells:

Two Important Dopaminergic Projections 1. Mesostriatal System (Midbrain and Striatum)

Pathways:

Impairments:

Neurotransmitters: Dopamine

Two Important Dopaminergic Projections 2. Mesocortical System (Midbrain and Cortical)

Pathways:

Function:

Impairments:

Sites of Cell Bodies and Their Projections in the Brain: Dopamine


Neurotransmitters: Norepinephrine Location of Cells:

Pathways: Ascending Fibers:

Descending Fibers

Function:

Impairments:

Sites of Cell Bodies and Their Projections in the Brain: Norepinephrine


Neurotransmitters: Serotonin Location of Cells:

Pathways:

Function:

Impairment:

Sites of Cell Bodies and Their Projections in the Brain: Serotonin

Bhatnagar & Andy, 1995, Figure 5.7D

Neurotransmitter: y-Aminobutyric Acid (GABA) Location of Cells:

Location of Projections:

Function:

Impairment:

Sites of Cell Bodies and Their Projections in the Brain: GABA

Bhatnagar & Andy, 1995, Figure 5.7E

Neurotransmitters: Peptides

Characteristics:

Function:

Bhatnagar & Andy Figure 5.7 Abbreviations AmygAmygdala DB Diagonal Band of Broca HAB Habenula Hypo Hypothalamus IPN Interpeduncular Nucleus NN Nerves NUC Nucleus Nuc. aac. Nucleus Accumbens Sub Substantia Thal Thalamus VTA Ventral Tegmental Area

Define the Following Technical Terms: Action potential Astrocytes Autoimmune Axon Axonal reaction Chromatolysis Cytological Cytoplasm Dendrites Depolarization Endoneurium Excitatory postsynaptic

potential Glia cells Hyperplasia Hypertrophy

Inhibitory postsynaptic potentials

Macrophage Microglia Myelin Nerve cell Neurilemma Nissl bodies Node of Ranvier Oligodendroglia Permeability Phagocyte Polarization Schwann cells Synapse Wallerian degeneration

Review Questions 1. With a diagram of a typical nerve cell, identify the

major structures and describe their functions. 2. List the major glia cells and describe their functions. 3. Explain how the following terms are related to impulse

generation: Action potential Depolarization Membrane excitability Polarized membrane Repolarized membrane Resting potential Subthreshold stimulus Summation

Review Questions 4. Describe chemical and electrical events

that are related to impulse transmission beginning with resting potentials and ending in generation of action potentials.

5. Describe the effects of inhibitory and excitatory postsynaptic potentials on a postsynaptic neuron.

6. Discuss how nerve and glia cells respond to injuries. Specifically discuss chromatolysis, wallerian degeneration, axonal reaction, and regeneration of axonal fibers.

Review Questions 7. Describe how axonal growth in the CNS is

different from that in the PNS. 8. Name primary neurotransmitters in the

central nervous system and briefly discuss their functions.

9. Describe the pathophysiology of multiple sclerosis and myasthenia gravis.

Neuronal Functionin the Nervous System

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