Organization of the

Nervous System and

the Neuron

Organization of the Nervous System

The Nervous System “maintains body homeostasis with

electrical signals; providesfor sensation, higher

mental functioning, and emotional response; and

activates muscles and glands.”

3 Overlapping Functions of Nervous System

SENSORY INPUT-

INTEGRATION-

MOTOR INPUT-

Works with the Endocrine System to maintain homeostasis.

1.Nervous System-

2.Endocrine System-

Organization of the nervous system can be

based on:

1.Structural Classification-

2.Functional Classification-

STRUCTURAL CLASSIFICATION

FUNCTIONAL CLASSIFICATION

Nervous Tissue

Nervous tissue is made up of two types of cells-Supporting and Neurons

Supporting cells of the CNS are called Neuroglia or “nerve glue”.

Neuroglia includes many types of cells that generally support, insulate, and protect neurons.

Types of Neuroglial cells-

•Astrocytes-

•Microglia-

•Ependymal cells-

•Oligodendrocytes-

What about “gliomas”???

Supporting Cells of the Peripheral Nervous System

•Satellite cells-

•Schwann cells-

THE NEURON

•Nerve fibers may be microscopic up to a length of 3-4 feet•Neurons never touch each other•Axonal terminals release neurotransmitters into the synapse•Most long nerve fibers are myelinated or covered with a white fatty sheath called myelin which protects and insulates fibers and increases transmission rate of nerve impulses

Neurilemma is found covering the neuronsof the Peripheral Nervous System and helps regenerate damaged nerve fibers

Which brings us to bundles of nerve fibers-

•Tracts-•Nerves-

And gray matter vs. white matter-

Neurons classified according to structure

and function1.Functional-

Sensory or Afferent-Motor or Efferent-Associative or Interneurons-

2. Structural- based on # of processes extending from cell body

Physiology of Neurons

Neurons have two major functions

1.Irritability-

2. Conductivity-

Irritabililty- the short version

•Resting or inactive neuron is polarized•A stimulus excites the neuron to become active and generate an impulse•The stimulus changes the permeability of the neuron’s membrane• Sodium gates open and Na diffuses into the cell•Neuron is now depolarized• Depolarization activates the neuron to transmit an action potential or nerve impulse

Depolarization is followed almost immediatelyby repolarization

Until the neuron repolarizes it cannot conductanother impulse= absolute refractory period

There also exists a relative refractory periodwhen a stronger than usual stimulus is required

Alcohol, sedatives, anesthetics-

Cold and continuous pressure-

Warm or remove pressure-

• YouTube - Neurotransmitter Synapse 3D Animation

No contact between neurons except at electrical synapses (escape reflexes, retina, heart)

Axonal terminals release neurotransmitters which cause depolarization of next neuron

Neurotransmitter is removed from synapse by re-uptake at axonal terminal or enzymatic breakdown

Conductivity

Peripheral Nervous System

• Those nerves found outside the central nervous system

• Each nerve is made of bundles of neuron fibers

• Neuron fibers are surrounded by a delicate tissue sheath

• Groups of fibers are bound by coarser connective tissue wrapping to form bundles called fascicles

CRANIAL NERVES

• • • •

SPINAL NERVES

• • • •

Spinal Nerves

DISORDERS AFFECTING NEURONS

POLIOMYELITIS

MULTIPLE SCLEROSIS-

BELL’S PALSY-

SHINGLES-

And then there’s…

CARPAL TUNNEL SYNDROME-