Nervous System Structural Organization

- Central Nervous System (CNS)

- Peripheral Nervous System (PNS)

What does the CNS consist of?

the brain and spinal cord

What does the PNS consist of?

- cranial nerves

- spinal nerves

- ganglia

cranial nerves

nerves that extend from the brain

spinal nerves

nerves that extend from the spinal cord

ganglia

clusters of neuron cell bodies located outside the CNS

What are the functional divisions of the nervous system?

- somatic (afferent) division

- motor (efferent) division

Somatic (afferent) division

receives sensory information (input) from receptors and transmits this information to the CNS

Motor (efferent) division

transmits motor impulses (output) from the CNS to muscles or glands

The sensory division is divided into two components:

- somatic sensory component

- visceral sensory component

somatic sensory component

the general somatic senses - touch, pain, pressure, vibration, temeperatrue and proprioception

visceral somatic component

transmit nerve impulses from blood vessels and viscera to the CNS; includes temperature and stretch of the organ wall

The motor is subdivided into two components:

- somatic motor component

- autonomic motor component

somatic motor component

(somatic nervous system) = SNS

conducts nerve impulses from the CNS to skeletal muscles; aka the voluntary nervous system

autonomic motor component

(autonomic nervous system) = ANS

innervates internal organs, regulates smooth muscle, cardiac muscle, and glands; aka the vsiceral motor system or involuntary nervous system

What are the 2 distinct cell types that form nervous tissue?

neurons and glial cells

Neurons

excitable cells that initiate and transmit nerve impulses

Glial cells

nonexcitable cells that support and protect the neurons

What are the characteristics of neurons?

high metabolic rate, extreme longevity and non-mitotic

What is the structure of the neuron?

has a cell body, dendrites and axons

What is the cell body of the a neuron?

serves as the neuron's control center and is responsible for receiving, integrating and sending nerve impulses

Dendrites

conducts nerve impulses toward the cell body; receives inputs and then transfer it to the cell body for processing

The more dendrites a neuron has...

the more nerve impulses that neuron can receive from other cells

Axon

- transmits a nerve impulse away from the cell body toward another cell; sometimes called the nerve fiber

Neurons can be classified by their..

structure or function

neurons classified by structure

- pseudounipolar (usually sensory neurons)

- bipolar (mainly in retina)

- multipolar

neurons classfied by function

- motor neurons (carry signals from CNS; efferent)

- sensory neurons (carry signal to CNS; afferent)

- association neruons (neurons in CNS)

Glial Cells

occurs both in CNS and PNS; sometimes reffered to as neurogila; physically protect and help nourish neurons and provide an organized framework for all the nervous tissue; outnumbers neurons

4 types of glial cells in CNS

1) oligodendrocytes

2) Microglia

3) Astrocytes

4) Ependmymal cells

Oligodendrocytes

produce myelin sheaths that insualtes the CNS

Microglia

phagocytize waste

Astrocytes

nourish neurons; aid in signal transmission (memory), synapse formation; neuron growth

Ependymal Cell

lines cavities of CNS; produce cerebrospinal fluid

2 types of glial cells in PNS

1) neurolemmocytes

2) satellite cells

neurolemmocytes

covers unmyelinated axons

satellite cells

protects and regulates nutrients of the cell bodies in ganglia

Myelination

neuroglial cells fill with fat/protein substance forming a myelin sheath that wraps around the axon

- in CNS = oligodendrocytes

- in PNS = neurolemmocytes

neurofibiril nodes

spaces between cells

Neuronal synapses

an axon transmits a nerve impulse to another neuron at a synapse

synaptic knobs

swellings formed by synaptic ends at the ends of axon branches

presynaptic neruons

transmit nerve impulses along their axonal membranes toward a synapse

post synaptic neurons

conduct nerve impluses through their dendritic and cell body membranes away from the synapse

synaptic cleft

space between the presynaptic and postynatic cells

electrical synapses

 has the flow of ions passing from the presynaptic and postsynaptic cell through gap junctions

chemical synapse

releases a chemical neurotransmitter from the presynaptic cell, which binds to the postsynaptic cell and induces a response

The larger the diameter of the axon...

 the fast is the rate of conduction