SPH405

GOAL: Students will develop an understanding of the general structure of the human nervous system.
OBJECTIVES: After lecture and reading students will answer the following questions at 90% in class and 100% on the first examination:

1. What are the main divisions of the Human Nervous system?



2. What is the relationship between the Central Nervous System and the Peripheral Nervous System?



3. What structures comprise the Peripheral Nervous System?



4. What structures comprise the Central Nervous System?



5. What is the relationship between afferent and efferent functions?

Let's begin our study of the human nervous system with a look at it's general anatomy and physiology. This will be an opportunity for students to familiarize themselves with some of the terms we will use in future lectures. If some of these terms and names are a little intimidating now, relax! Soon, they will become part of your everyday vocabulary. Well, maybe part of your work-day vocabulary.

GROSS ANATOMY OF THE NERVOUS SYSTEM: The human nervous system is divided, for purposes of description, into two parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The reason I said, "...for purposes of description," is that we must remember that the nervous system really is one whole entity. We divide it to make study easier: to give ourselves some structure.
CNS
PNS
Organization of the Nervous System

Like any other body system, the nervous system is composed of cell collections called TISSUES.
The tissues the form the nervous system are composed of Neurons and Glial Cells.

You will recall from your anatomy classes that Neurons are special cells that conduct electrochemical changes to and from each other. these electrochemical changes are changes in the electric potential that exist on either side of the cell membranes of Neurons. They are called, appropriately enough, "Action Potentials." Imagine a thin sheet of skin, with little "Plusses" on the outside and little "Minuses" on the inside. These swap places in a wave as the neurons do their business. Gallery of Neurons

1. The nervous system is composed of bundled Neuron Projections called "Nerve Fibers" distributed all over the body. These bundles are commonly called, "Nerves."



2. The constituent fibers of the Nervous System may be sensory (afferent) or motor (efferent) in function.



1. Sensory (Afferent) fibers transmit impulses initiated by a peripheral stimulus to Central Nervous System structures.



2. Peripheral Nervous System afferent cells terminate at their distal ends on a sensory surface, within the substance of various tissue.



3. They may be connected to special types of cells, which are excited only by special forms of physical energy (special senses).



4. Efferent neurons have their terminate at motor end-plates on muscle fibers. they initiate the shortening of muscle fibers and cause movement.

Neurons convey impulses in only one direction.

Glial cells are structural cells that support the neurons. Glial cells hold Neurons in place, insulate them from one another, and nourish them. Glial Cells

The Central Nervous System mediates input and output from and to the Peripheral Nervous System.

INPUT to the central nervous system is conveyed from the peripheral nervous system with AFFERENT impulses. These include special senses of the following: touch, vision, hearing, somosenthesis, proprioception, and touch.
The purpose of afferent fibers is to inform the organism about changes in the internal or external environment so that appropriate responses may be evoked.

1. Stimulation may come from the external or internal environment.



1. External stimuli may consist of pain, touch or temperature; sound light, etc.



2. Internal stimuli may include chemical or endocrine stimulation.

Not all the input stimuli transmitted by peripheral nerves reach the conscious mind (ie., m. stretch reflex).

More about Afferent Axons

OUTPUT from the central nervous system to the peripheral nervous system is conveyed with EFFERENT impulses.

1. Motor (efferent or effector) stimuli originate in central structures and propagate to the periphery.



2. Efferent neurons enable the animal to respond to stimuli from the external or internal environment through muscular or glandular action.



3. Not all of the actions of the effectors are under volitional control.



1. Some responses are unconscious or REFLEXIVE (pupils, spinal erectors)



2. Some reflexes result from primitive, phylogenetically less evolved patterns.



1. These patterns are over ridden as the individual develops.



2. They can reappear if there is an injury.

The CENTRAL NERVOUS SYSTEM (CNS) is composed of the brain and the spinal cord.

1. It is made up of a mass of nerve fibers (neurons) embedded in a matrix of connective tissue (neuroglia)



1. The neurons of the CNS are interconnected.



1. They can communicate so that the response(s) to external stimuli can be totally integrated and adjusted perfectly (as possible) to the current situation.



2. These interconnections are organized in physical (spatial) and functional (temporal) ways.



3. Interconnections (pools) can be established by learning.



2. Support cells hold the neurons together and nourish them.



3. The CNS is coated in three layers of nutritive and protective tissue called meninges.



2. The CNS is contained in the bones of the cranium and spinal column.



3. The central nervous system is functionally a mediator between the receptor and effectors of the PNS. It controls, regulates and initiates all cognitive and sensorimotor functions.

Question: what behaviors does the CNS initiate ?

The PERIPHERAL NERVOUS SYSTEM has two components: The cranial and spinal nerves and the autonomic nervous system.

SPINAL AND CRANIAL NERVES are connected to the spinal cord and brainstem (the extension of the spinal cord into the skull).

They communicate with the CNS by connections (synapses) to the spinal cord or to the brainstem.

There are 31 pairs of spinal nerves.

1. They attach to the spinal cord.



2. They convey impulses between the central nervous system and the trunk or the extremities.

Question: why are these nn important for speech and hearing?

There are 12 pairs of cranial nerves

1. They attach to the brainstem.



2. Most of them convey impulses between the CNS and the head and neck structures.



3. One reaches all the way to the colon.

The AUTONOMIC NERVOUS SYSTEM regulates the internal systems of the body to maintain optimum survival conditions.

1. It innervates smooth muscles, cardiac muscles, and glands.



2. The ANS has two main divisions: the sympathetic division and the parasympathetic division.



1. The sympathetic division is felt to prepare the body for emergency actions.



1. It is widely distributed throughout the body.



1. Especially to the smooth muscles of the arteries.



2. Its outflow is thoraco-lumbar.



2. The parasympathetic division is geared to maintain regular bodily functions.



1. It is more focally distributed.



2. Its outflow is cranio-sacral.



3. The most prominent landmark of the ANS is the sympathetic trunk.



1. It is a bilateral chain of ganglia.



1. Ganglia are collections of neuron cell bodies.



2. It runs along either side of the spinal column.



3. It connects to the central nervous system

There are some structural and functional differences between the central and peripheral divisions of the nervous system.

1. Structurally: the central nervous system is more redundant than the peripheral nervous system.



2. Functionally: the neurons of the peripheral division heal more readily than those of the central division.

Go on to Group Assignment 1
or
Go back to General Organization

E-mail Bill Culbertson at bill.culbertson@nau.edu
Call Bill Culbertson at (520) 523-7440

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