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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
Neuron, Myelinated Axon, and Synapse Bhatnagar & Andy, 1995, Figure 5.1.A
Nerve Cell Structure of Neurons: Myelin Sheath Speed of nerve conduction is
determined by:
Myelin
Neuron, Myelinated Axon, and Synapse Bhatnagar & Andy, 1995, Figure 5.1.A
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
Neuron, Myelinated Axon, and Synapse Bhatnagar & Andy, 1995, Figure 5.1.A
Nerve Cell Structure of Neurons: Synapse Process of Nerve Impulses
Neuron, Myelinated Axon, and Synapse Bhatnagar & Andy, 1995, Figure 5.1.A
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
Bhatnagar & Andy, 1995, Figure 5.5A
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 Bhatnagar & Andy, 1995, Figure 5.5D
Action Potential: Generation of Action Potential with Depolarized Membrane
Bhatnagar & Andy, 1995, Figure 5.5B
Nerve Excitability
In membrane depolarization
Action Potential Bhatnagar & Andy, 1995, Figure 5.5D
Nerve Excitability
Membrane potential from this peak returns to the absolute refractive period
Action Potential Bhatnagar & Andy, 1995, Figure 5.5D
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
Bhatnagar & Andy, 1995, Figure 5.5B
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
Bhatnagar & Andy, 1995, Figure 5.6A
Neuronal Response to Injury: Axonal Retrograde Reaction
Bhatnagar & Andy, 1995, Figure 5.6B
Neuronal Response to Injury: Wallerian Degeneration
Bhatnagar & Andy, 1995, Figure 5.6C
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
Bhatnagar & Andy, 1995, Figure 5.7A
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
Bhatnagar & Andy, 1995, Figure 5.7B
Neurotransmitters: Norepinephrine Location of Cells:
Pathways: Ascending Fibers:
Descending Fibers
Function:
Impairments:
Sites of Cell Bodies and Their Projections in the Brain: Norepinephrine
Bhatnagar & Andy, 1995, Figure 5.7C
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
Graphics
THINGS TO DO BEFORE LECTURE Reticular Formation Cytological