Download INTEGUMENTARY SYSTEM

NERVOUS SYSTEM
NERVOUS TISSUE
Nervous System - General
Control System
Regulator of Homeostasis
Electrical Impulses
Rapid & Transient Effects
Nervous System - Functions
Sensory - Monitors Internal & External
Environments
Integrative
- Analyzes Sensory Information
- Stores
- Makes Decisions Regarding Appropriate
Responses
Motor – Controls muscles & glands;
responds to sensory information
Nervous System Divisions
Central Nervous System (CNS)
- Brain, Spinal Cord
- Dorsal Body Cavity
- Integration & Command Center
Peripheral Nervous System (PNS)
-
All Neural Tissue outside CNS
Nerves (Cranial & Spinal)
Carries Info. Between CNS & Rest of Body
Sensory & motor
Peripheral Nervous System
Sensory
- Afferent
- Conveys sensory information to CNS
Motor
- Efferent
- Conveys motor commands to muscles
& glands
PNS Motor Divisions
Somatic Nervous System (SNS)
- Voluntary Control of Skeletal Muscles
Autonomic Nervous System (ANS)
- Involuntary Control of Smooth Muscle,
Cardiac Muscle & Glands
- Sympathetic Division
- Parasympathetic Division
Cells of Nervous System
Neurons
- Basic Unit of Nervous System
- Most Specialized Cell in Body
- Conduct Impulses
Neuroglia (“Nerve Glue”)
- Support, Framework (fill spaces) &
Phagocytes
- Most Numerous
- Can Divide & Multiply
Neurons - Structure
Cell Body (Soma)
- Nucleus & Various Organelles
* Nissl Bodies (Rough ER)
* Neurofibrils (Cytoskeletal)
Dendrites
- Numerous, Short, Branched Processes
- Receive Impulse from other Neurons or
Receptors
- Carry Impulse Towards Cell Body (Afferent)
Fig. 8.3
Neurons – Structure continued
 Axon
- Long, Usually Singular Process
- Many Mitochondria, Neurofibrils
- Carries Impulse Away from Cell Body
(Efferent)
- Carries Impulse Towards:
* ANOTHER NEURON
* MUSCLE FIBER
* GLAND CELL
Neurons – Axon continued
- Axon Hillock (Joins Cell Body & Axon)
- Collaterals (Axon Branches)
- Axon/Synaptic Terminals
*Numerous, Fine Processes at end of
Axon & Axon Collaterals
*Some with Synaptic Knobs
Neurons – Axon continued
- Myelination
*Most Axons
*Enclosed in Schwann Cells
(Neurolemmocyte)
Myelin Sheath – Multilayered,
Inner, Fatty
Neurolemma – Outer Schwann
Cell Membrane & Cytoplasm
Fig. 8.6
Neurons – Axon Myelination
continued
*Insulates & Increases Speed of
Conduction
*Nodes of Ranvier
Occur Along Axon Between
Schwann Cells
No Myelin
Neurons – Functional
Classification
 Sensory
- Afferent
- Connect Receptors & CNS
 Motor
- Efferent
- Carry Commands from CNS to Effectors
 Interneurons (Association)
- CNS
- Integrate Sensory & Motor
- Most Numerous
Neurons – Structural
Classification
 Unipolar
- One Process (Dendrites & Axon Fused)
- Sensory
 Bipolar
- Two Processes: One Dendrite, One Axon
- Rare (Special Senses)
 Multipolar
- Several Dendrites, One Axon
- Common
- Motor & Interneurons
Neurons - Terminology
Gray Matter – Unmyelinated Fibers &
Cell Bodies
White Matter – Myelinated Axons
Nerve – Bundle of Fibers (Axons) in PNS
Tract – Bundle of Fibers in CNS
Ganglia – Clusters of Neuron Cell Bodies
in PNS
Nuclei – Clusters of Neuron Cell Bodies in
CNS
Neuroglia
 CNS
- Astrocytes
* Large, Star-shaped
* Link Neurons & Blood Vessels; Help form
Blood-brain Barrier
- Oligodendrocytes
* Form Myelin Sheath
- Microglia
* Derived from WBCs, Phagocytes
Fig. 8.5abc
Neuroglia continued
- Ependymal Cells
* Epithelium
* Line Ventricles & Central Canal
* Produce & Help Circulate CSF
 PNS
- Schwann Cells (Neurolemmocytes)
* Form Myelin Sheath
- Satellite Cells
* Support, Cushion Ganglia
Nerve Impulse Transmission
Two mechanisms involved
- Transmission along a neuron
*An electrical process
- Transmission between neurons
*A chemical process
*Occurs at synapse
Neuron Physiology
Transmission Requirements:
- Resting Membrane Potential (Cell
Membrane is Polarized)
- Ion Channels in Cell Membrane (Allow
Ions to Cross When Open)
- Delivery of Threshold Stimulus
Conduction Along Neuron
Resting Membrane Potential (+/Na+
outside, -/K+ inside
Appropriate Threshold Stimulus Opens
Na+ Channels
Na+ Diffuses into Neuron, Results in
Depolarization
Depolarization wave spreads from dendrite
to axon
Fig. 8.11
Conduction Along Neuron
continued
Na+ Channels Close, K+ Channels Open &
K+ Diffuses Out of Neuron
Results In Repolarization
Action Potential = Depolarization +
Repolarization (dendrite to axon)
Repolarization Required before another
Action Potential
Sodium-Potassium Pump moves Na+ out &
K+ in (Requires Energy)
Conduction continued
All-or-None Principle
- Neurons respond to stimuli by generating an
impulse (action potential), or don’t respond at
all
Refractory Period
- Neurons must repolarize their cell membranes
before they respond to subsequent stimuli
Types of Conduction
 Continuous
- Typical of Unmyelinated Neurons (Slower)
- Steps as Previously Described
 Saltatory
- Occurs along Myelinated Neurons
- No Current where Myelin occurs
- Action Potential Leaps from Node of Ranvier
to Node
- Faster!
Fig. 8.12
Synaptic Transmission
 Arriving Action Potential Depolarizes Synaptic
Knob
 Ca++ Enters Cytoplasm of Presynaptic Neuron
 Exocytosis of Synaptic Vesicles, Releasing
Neurotransmitter
 Neurotransmitter Diffuses across Synaptic Cleft
& Binds to Receptors on Postsynaptic Membrane
 Na+ Channels Open, Postsynaptic Membrane
Depolarizes
Fig. 8.13
Neurotransmitters
Excitatory – Cause Depolarization/Na+
ions channels open (Dopamine)
Inhibitory – Raise the Threshold/ K+ or Clion channels open (Serotonin & GABA)
Removed by Specific Enzymes