Download Protection and Nourishment of the Brain

Neuronal Function
in the Nervous System
Learning Objectives
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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
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Basic anatomic and functional unit of the
nervous system
Primary Function:
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Two Primary Types
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Neuron
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Three Basic Elements
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General Process
Neuron, Myelinated Axon, and
Synapse
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Bhatnagar & Andy, 1995, Figure 5.1.A
Nerve Cell Structure of
Neurons: Cell Body
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Two major components
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1. Cytoplasm
The Cell Body
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Bhatnagar & Andy, 1995, Figure 5.1.B
Nerve Cell Structure of
Neurons: Cell Body
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2. Nucleus
The Cell Body
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Bhatnagar & Andy, 1995, Figure 5.1.B
Nerve Cell Structure of Neurons:
Dendritic and Axonal Processes
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Cytoplasmic extensions
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Dendrites
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Nerve fibers
Neuron, Myelinated Axon, and
Synapse
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Bhatnagar & Andy, 1995, Figure 5.1.A
Nerve Cell Structure of
Neurons: Myelin Sheath
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Speed of nerve conduction is
determined by:
Myelin
Neuron, Myelinated Axon, and
Synapse
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Bhatnagar & Andy, 1995, Figure 5.1.A
Nerve Cell Structure of
Neurons: Myelin Sheath
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Myelin
Nerve Cell Structure of
Neurons: Synapse
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Connection point between neurons
Three Parts:
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1. Knob (Synaptic vesicles)
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2. Synaptic Cleft
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3. Receptive Sites of Connecting Nerve Cells
Neuron, Myelinated Axon, and
Synapse
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Bhatnagar & Andy, 1995, Figure 5.1.A
Nerve Cell Structure of
Neurons: Synapse
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Process of Nerve Impulses
Neuron, Myelinated Axon, and
Synapse
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Bhatnagar & Andy, 1995, Figure 5.1.A
Nerve Cell Types
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Classification:
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Three Cell Types:
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1. Multipolar
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2. Bipolar
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3. Unipolar
Nerve Cell Types
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Bhatnagar & Andy, 1995, Figure 5.2
Neuroglia Cells
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Function:
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Location:
Neuroglia Cells in the Central
Nervous System
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Four Types of Glia Cells in the CNS
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1. Astrocytes
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Location:
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Function:
Neuroglia Cells in the Central
Nervous System
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2. Ogliodendroglia
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3. Ependymal
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4. Microglia
Neuroglial Cells in the
Peripheral Nervous System
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Schwann cells
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Function:
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Impairments:
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Demyelinating Neuropathologies
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Benign Tumors of Schwann Cells
Central and Peripheral
Nervous Systems
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Cytological Differences
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1. Different myelin forming cells
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PNS
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CNS
Central and Peripheral
Nervous Systems
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Cytological Differences
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2. Presence of endoneurium
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PNS
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CNS
Nerve Impulse
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Communication
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Principles of Process
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Chemical component
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Excitability of nerve cells
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Action potential
Nerve Impulse
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Process
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Excitability of nerve cells
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An action potential
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Activation releasing neurotransmitter
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Opening of channels in postsynaptic receptors
Nerve Impulse Process
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Resting State
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Cell is in resting state
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In this resting state
Action Potential: Resting Potential
with Polarized Membrane
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Bhatnagar & Andy, 1995, Figure 5.5A
Nerve Impulse Process
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Resting Membrane Potential
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Voltage inside the cell membrane
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Outside the cell membrane
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Inside the cell membrane
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Ionic channels
Action Potential
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Bhatnagar & Andy, 1995, Figure 5.5D
Membrane Channels
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Membrane channels are gated
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Flow of ions through the membrane
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Depends on:
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1. The density of the channels
2. The size of the opening
3. The ion concentration gradient across the
membrane
Membrane Channels
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Distribution of sodium and potassium
across the cellular membrane
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Is constantly adjusted by the sodiumpotassium pump
Because of the membrane pore size
Membrane Channels
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With the attraction of opposite ions and
the repulsion of identical ions
With this tug of war
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An electrochemical gradient forms along
the membrane
Action Potential: Resting Potential
with Polarized Membrane
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Bhatnagar & Andy, 1995, Figure 5.5A
Nerve Excitability
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Excitability
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Refers to:
Nerve Excitability
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Stimuli can include:
Nerve Excitability
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During the resting state
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The neuron undergoes several short changes in the
intracellular potentials
Triggering an action potential
Action Potential
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Bhatnagar & Andy, 1995, Figure 5.5D
Action Potential: Generation of
Action Potential with Depolarized
Membrane
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Bhatnagar & Andy, 1995, Figure 5.5B
Nerve Excitability
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In membrane depolarization
Action Potential
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Bhatnagar & Andy, 1995, Figure 5.5D
Nerve Excitability
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Membrane potential from this peak returns to the
absolute refractive period
Action Potential
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Bhatnagar & Andy, 1995, Figure 5.5D
Nerve Excitability
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Not all stimuli
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Are strong enough to change the membrane potentials to 10
mV
Many weak stimuli with subthreshold strength
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If temporally and spatially summated
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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
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Nerve impulse is passively conducted a short distance
in the axon
Action Potential: Generation of
Action Potential with Depolarized
Membrane
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Bhatnagar & Andy, 1995, Figure 5.5B
Impulse Conduction
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This gradually changes the membrane potential in
the neighboring area
Action Potential: Conduction of
Action Potential Along Membrane
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Bhatnagar & Andy, 1995, Figure 5.5C
Impulse Conduction
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Saltatory Conduction in Myelinated Axons
Impulse Conduction
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Action potential or nerve impulse
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Excitatory Postsynaptic Potential (EPSP)
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Inhibitory Postsynaptic Potential (IPSP)
Neuronal Responses to Brain Injuries
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Nerve Cells in the Human Brain
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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
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Understanding the Processes of Spontaneous
Recovery
Two Types of Degenerative Changes Occur After
Axonal Sectioning
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1. Axonal or Retrograde Reaction
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2. Wallerian (Anterograde) Degeneration
Types of Neuronal Response to Injury
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Bhatnagar & Andy, 1995, Figure 5.6A
Neuronal Response to Injury: Axonal
Retrograde Reaction
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Bhatnagar & Andy, 1995, Figure 5.6B
Neuronal Response to Injury:
Wallerian Degeneration
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Bhatnagar & Andy, 1995, Figure 5.6C
Axonal Regeneration in Peripheral
Nervous System
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Regeneration of Fibers in the PNS
Neuronal Response to Injury:
Peripheral Nerve Regeneration
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Bhatnagar & Andy, 1995, Figure 5.6D
Axonal Regeneration in Central
Nervous System
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Axons severed in the CNS
Neurotransmitters
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Neurotransmitters
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Along with projections from the reticular formation
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Regulate brain mechanisms that control:
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Cognition
Language
Speech
Hearing
Brain Tuning
Moods
Attention
Memory
Personality
Motivation
Neurotransmitters
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Two types of transmitters in the nervous
system:
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1. Small molecules
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Include:
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Acetylcholine
Dopamine
Norepinephrine
Serotonin
Glutamate
y-aminobutyric acid (GABA)
2. Larger molecules
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Peptides
Neurotransmitters:
Acetylcholine
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Synthesis and Dissolution
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Acetylcoenzyme A and choline
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Acetylcholinesterase
Neurotransmitters:
Acetylcholine in the PNS
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Location of Cells in PNS:
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Function:
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Impairments:
Neurotransmitters:
Acetylcholine in the CNS
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Location of Cells In CNS:
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Function:
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Impairments:
Sites of Cell Bodies and Their
Projections in the Brain:
Acetylcholine
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Bhatnagar & Andy, 1995, Figure 5.7A
Neurotransmitters: Dopamine
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Location of Cells:
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Two Important Dopaminergic Projections
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1. Mesostriatal System (Midbrain and Striatum)
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Pathways:
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Impairments:
Neurotransmitters: Dopamine
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Two Important Dopaminergic Projections
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2. Mesocortical System (Midbrain and Cortical)
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Pathways:
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Function:
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Impairments:
Sites of Cell Bodies and Their
Projections in the Brain: Dopamine
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Bhatnagar & Andy, 1995, Figure 5.7B
Neurotransmitters: Norepinephrine
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Location of Cells:
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Pathways:
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Ascending Fibers:
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Descending Fibers
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Function:
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Impairments:
Sites of Cell Bodies and Their
Projections in the Brain:
Norepinephrine
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Bhatnagar & Andy, 1995, Figure 5.7C
Neurotransmitters: Serotonin
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Location of Cells:
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Pathways:
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Function:
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Impairment:
Sites of Cell Bodies and Their
Projections in the Brain: Serotonin
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Bhatnagar & Andy, 1995, Figure 5.7D
Neurotransmitter: y-Aminobutyric
Acid (GABA)
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Location of Cells:
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Location of Projections:
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Function:
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Impairment:
Sites of Cell Bodies and Their
Projections in the Brain: GABA
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Bhatnagar & Andy, 1995, Figure 5.7E
Neurotransmitters: Peptides
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Characteristics:
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Function:
Bhatnagar & Andy Figure 5.7
Abbreviations
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Amyg
DB
HAB
Hypo
IPN
NN
NUC
Nuc. aac.
Sub
Thal
VTA
Amygdala
Diagonal Band of Broca
Habenula
Hypothalamus
Interpeduncular Nucleus
Nerves
Nucleus
Nucleus Accumbens
Substantia
Thalamus
Ventral Tegmental Area
Define the Following Technical
Terms:
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Action potential
Astrocytes
Autoimmune
Axon
Axonal reaction
Chromatolysis
Cytological
Cytoplasm
Dendrites
Depolarization
Endoneurium
Excitatory postsynaptic potential
Glia cells
Hyperplasia
Hypertrophy
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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
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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
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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
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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 Function
in the Nervous System
Graphics
THINGS TO DO BEFORE
LECTURE
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Reticular Formation
Cytological