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Chapter 12

Nervous Tissue

Lecture slides prepared by Curtis DeFriez, Weber State University


Nervous System Overviewv The nervous system detects environmental changes that impact the

body, then works in tandem with the endocrine system to respond

to such events.

§ It is responsible for all our behaviors, memories, and movement.

• It is able to accomplish all these functions because of the

excitable characteristic of nervous tissue, which allows for

the generation of nerve impulses (called action potentials).


v Everything done in the nervous system involves 3 fundamental steps:

1. A sensory function detects internal and external stimuli.

2. An interpretation is made (analysis).

3. A motor response occurs (reaction).

Nervous System Overview


v Over 100 billion neurons and 10–50 times that number of

support cells (called neuroglia) are organized into

two main subdivisions:

§ 1. The central nervous

system (CNS)

§ 2. The peripheral nervous

system (PNS)



Nervous System Overviewv As the “thinking” cells of the brain, each neuron does, in

miniature, what the entire nervous system does as an organ: Receive, process and transmit information by manipulating the flow of charge across their membranes.

v Neuroglia (glial cells) play a major role in support and

nutrition of the brain, but they do not manipulate

information.

§ They maintain the internal environment so that neurons can do their jobs.


Divisions of the Nervous Systemv Most signals that stimulate muscles to contract and glands to secrete

originate in the CNS.

v The PNS is further divided into:

§ 1. A somatic nervous system (SNS)

§ 2. An autonomic nervous system (ANS)• the sympathetic division • the parasympathetic division

§ 3. An enteric nervous system (ENS)


Divisions of the Nervous System*


Divisions of the Nervous Systemv Ganglia are small masses of neuronal cell bodies located

outside the brain and spinal cord, usually closely

associated with cranial and spinal nerves.

§ There are ganglia which

are somatic, autonomic,

and enteric (that is, they

contain those types

of neurons.)


Neurons and Neurogliav Neurons and neuroglia combine in a variety of ways in different

regions of the nervous system.

§ Neurons are the real “functional unit” of the nervous system,

forming complex processing networks within the brain and

spinal cord that bring all regions of the body under CNS control.

§ Neuroglia, though smaller than neurons, greatly outnumber them.

• They are the “glue” that supports and maintains the

neuronal networks.


v Though there are several different types of neurons, most have:

§ A cell body

§ An axon

§ Dendrites

§ Axon terminals

Neurons


§ Neurons gather information at dendrites and

process it in the

dendritic tree and

cell body.

§ Then they transmit

the information

down their axon to

the axon terminals.

Neurons


Neurogliav Neuroglia do not generate or conduct nerve impulses.

§ They support neurons by:

• Forming the Blood Brain Barrier (BBB)

• Forming the myelin sheath (nerve insulation) around

neuronal axons

• Making the CSF (Cerebral Spinal Fluid) that circulates

around the brain and spinal cord

• Participating in phagocytosis


Neurogliav In the CNS:


Neurogliav In the PNS:


Neurogliav There are 4 types cells of neuroglia in the CNS:

§ Astrocytes

§ Oligodendrocytes: produce myelin in CNS

§ Microglia

§ Ependymal cells

v There are 2 types of neuroglia in the PNS:

§ Satellite cells - support neurons in PNS

§ Schwann cells - produce myelin in PNS


Neuroglia*


Neuroglia and Myelin§ Schwann cells: cells in the peripheral nervous system (PNS)

that produce the myelin sheath around neuronal axons.

also called neurilemma cell.


Neuroglia and Myelin§ Myelin: is an insulating layer, or sheath that forms around

nerves, including those in the brain and spinal cord. It is

made up of protein and fatty substances.


Neuroglia and Myelin§ Nodes of ranvier: These are the gaps formed between the

myelin sheath where the axons are left uncovered.

§ Because the myelin sheath is largely composed of an

insulating fatty substance, the nodes of Ranvier allow the

generation of a fast electrical impulse along the axon.


Neuronal Regeneration*v The cell bodies of neurons lose their mitotic features at birth

and can only be repaired through regeneration after an

injury (they are never replaced by daughter cells as occurs

with epithelial tissues.)


Gray and White Matterv White matter of the brain and spinal cord is formed from

aggregations of myelinated axons from many neurons.

§ The lipid part of myelin imparts the white appearance.

v Gray matter (gray because it lacks myelin) of the brain and

spinal cord is formed from neuronal cell bodies

and dendrites.


Synaptic Transmission*Signal transmission at the synapse is a one-way transfer from presynaptic neuron to a postsynaptic neuron.


Neurotransmitters*v Both excitatory and inhibitory neurotransmitters are

present in the CNS and PNS.

v The same neurotransmitter may be excitatory in some

locations and inhibitory in others.

§ For example, acetylcholine (ACh) is a common

neurotransmitter released by many PNS neurons (and

some in the CNS).

Ach is: Excitatory at the NMJ(Neuro Muscular Junction)

Inhibitory at other synapses.


The End

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