1. Fundamentals of the Nervous System and Nervous Tissue
Chapter 11

2. Nervous System
The master controlling and communicating system of the body
Functions
Sensory input – monitoring stimuli occurring inside and outside the body
Integration – interpretation of sensory input
Motor output – response to stimuli by activating effector organs

3. Levels of Organization
Central Nervous System (CNS)
Brain and Spinal Cord
Integration and Control Centers
Associative neurons (interneurons)
Peripheral Nervous System (PNS)-
Cranial and Spinal Nerves
Sensory - afferent -input to CNS
Somatic fibers – impulses from skin, skeletal muscles, & joints
Visceral fibers – transmit impulses from visceral organs
Motor -efferent-output from CNS
Somatic -voluntary control
(skeletal muscles)
Autonomic –involuntary (glands, cardiac and visceral muscles)
Sympathetic –stress
Parasympathetic - normal conditions
Levels of Organization

4. Histology of Nerve Tissue
The two principal cell types of the nervous system are:
Neurons – excitable cells that transmit electrical signals
Supporting cells – cells that surround and wrap neurons
The supporting cells (neuroglia or glial cells):
Provide a supportive scaffolding for neurons
Segregate and insulate neurons
Guide neurons to the proper connections
Promote health and growth
Astrocytes
Most abundant, versatile, and highly branched glial cells
They cling to neurons and their synaptic endings, and cover capillaries
Functionally, they:
Support and brace neurons
Anchor neurons to their nutrient supplies
Guide migration of young neurons
Control the chemical environment

5. Neuroglia (cont.) Central Nervous System Glial Cells
Microglia – small, ovoid cells with spiny processes
Phagocytes that monitor the health of neurons
Ependymal cells – range in shape from squamous to columnar
They line the central cavities of the brain and spinal column
Oligodendrocytes – branched cells that wrap CNS nerve fibers
Peripheral Nervous System Glial Cells
Schwann cells (neurolemmocytes) – surround fibers of the PNS
Satellite cells surround neuron cell bodies with ganglia

6. Neuron Excitable cells that generate and conduct impulses
Amitotic - extreme longevity
High metabolic rate – require glucose and O2
Structure
Cell body - site of protein synthesis
nucleus with prominent nucleolus,no centrioles
Nissl bodies (chromatophilic substance)
Dendrites - carry impulses toward cell body
many per neuron, short and branched
respond to neurotransmitters
postsynaptic terminal
Axon next page

7. Myelinated Axons Axons - carry impulses away from cell body
long thin process, one per neuron
branched at end (axon terminals -presynaptic knobs)
secrete neurotransmitters from the axonal terminals
Schwann cells form Myelin Sheath:
Envelopes an axon in a trough
Encloses the axon with its plasma membrane
Has concentric layers of membrane that make up the myelin sheath
Nodes of Ranvier – gaps between Schwann cells.
Neurilemma – remaining nucleus and cytoplasm of a Schwann cell

8. Nerve Fibers (Axons) and Myelin Sheath
Axon conduction speed depends on::
Diameter of axon
Degree of myelination
Myelin Sheath
Whitish, fatty (protein-lipoid cell membrane)
Protect the axon
Electrically insulate fibers from one another
Increase the speed of nerve impulse transmission
Unmyelinated axons
Schwann cell surrounds nerve fibers but coiling does not take place
Schwann cells partially enclose 15 or more axons
Axons of the CNS
Both myelinated and unmyelinated fibers are present
Myelin sheaths are formed by oligodendrocytes
White matter – dense collections of myelinated fibers
Gray matter – mostly soma and unmyelinated fibers

9. Classification of Neurons
Multipolar - motor, associative
many extensions
most numerous
Bipolar - special sensory
two extensions
olfactory, rods and cones
not common
Unipolar - most sensory
one process from cell body
peripheral extension responds to a stimuli
cell bodies form ganglia
Reflex Arc
Neural Circuits

10. Electrical Current and the Body - Neurophysiology
Reflects the flow of ions rather than electrons
There is a polarized potential on either side of membranes when:
The number of ions is different across the membrane (ion gradient)
The membrane provides a resistance to ion flow until a stimulus occurs.
Resting Membrane Potential - polarized
Na+ high outside cell
K+ high inside cell
Negative ions do not move across the cell membrane
Na+K+ pump maintains the ion concentration
K+ leak out faster than Na+ leak in  negative inner membrane
For a nerve impulse to be propagated in a nerve cell, this resting potential (polarization) must be disturbed or depolarized.
Action potentials, or nerve impulses, are:
Electrical impulses carried along the length of axons
Always the same regardless of stimulus

11. Types of plasma membrane ion channels:
Found all over the neuron – maintain resting membrane potential
Passive, or leakage, channels – always open
Normally found at Synapse to regulate neurotransmission
Chemically gated channels (ligand gated)– open with binding of a specific neurotransmitter
Normally found in Axon for conduction of an Action Potential
Voltage-gated channels – open and close in response to membrane potential
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12. Voltage Ion Channels and Action Potential
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