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 Cl - ion channels open (Serotonin & GABA) Removed by Specific Enzymes