Chapter 13.1 Pages 408-414 The Nervous System. Introduction The Organization of the Nervous System

Chapter 13.1

Pages 408-414

The Nervous System

IntroductionThe Organization of the Nervous System

A) IntroductionThe Organization of the Nervous System

Brain Spinal Cord

Somatic Nerves Autonomic Nerves

MotorSensory

Nervous System

Peripheral Nervous System

MotorSensory

Central Nervous System

Sympathetic

Voluntary Involuntary

Sensory Motor Parasympathetic


the Central Nervous System (CNS)consists of:

the nerves of the brainthe spinal cord

acts as a coordinating centre for incoming and outgoing information


the Peripheral Nervous System (PNS)consists of nerves that carry information

between the organs of the body and CNS is subdivided into:

the somatic nervesthe autonomic nerves.


the somatic nervous system controls skeletal muscle, bones, and skin

sensory somatic nerves relay information about the environment to the CNS

motor somatic nerves initiate a response


the autonomic nervous system controls involuntary actions of the

smooth muscles and heart and glandsa system of two types of nerves that

oppose each in action (parasympathetic versus sympathetic)

Video

Anatomy of a Nerve Cell


The nervous system has two different types of cells: glial (neurological) cells and neurons.

glial cells are non-conducting cells

important for the structural support and metabolism of the nerve cells.

glial comes from the Greek word for “glue”

neurons arethe functional units of the nervous systema cell that conduct nerve impulses

all neurons contain:cell bodiesdendritesaxons.



cell body main part of the neuron that contains the nucleus processes input from the dendrites and relays it to

the axon.

dendrites receive information, either from the environment or

other neurons. is an extension of cytoplasm that conduct nerve

impulses toward the cell body


axon is an extension of cytoplasm that

carries the nerve impulses away from the cell body.

a neuron has one axon that can form many branches.

an axon carries impulses towards other neurons or to effectors.

most nerves are made up of many axons held together by connective tissue.



myelin sheatha white coating of fatty protein

that covers the axon. produced by Schwann Cells in

the PNS produced by oligodendrocytes

in the CNSacts as an insulator preventing the

loss of charged ions from the nerve cells – signal travels faster!

an axon is said to be myelinated if it has a myelin coating


Medical Break ~Multiple Sclerosis (MS)~ Multiple sclerosis is a disease in which the myelin degenerates. It is currently thought that T cells, plays a key role in the

development of MS. The axons themselves can also be damaged by the attacks. Symptoms of MS usually appear in episodic acute periods of

worsening (relapses) or in a gradually-progressive deterioration of neurologic function, or in a combination of both




nodes of Ranvierthe areas between the sections of myelin sheathnerve impulses jump from one node to another

which speeds up the movement of nerve impulses.nerve impulses move much faster along

myelinated nerve fibres than nonmyelinated ones. speed is also affected by axon diameter, the

larger the diameter the faster the axon.


neurilemmaa thin outer membrane

around the axon, found in all nerves of the peripheral nervous system

formed by the Schwann cells and promotes the regeneration of the damaged axons.

this is how feeling returns to areas that have been cut (only PNS!).


white matter (white from myelination) in the brain and grey matter (no myelin sheath) in the brain and spinal cord lack neurilemmas.

this is why CNS injuries are usually permanent.



Dendrites

Stimulus

Nucleus

Cellbody

Axonhillock

Presynaptic Cell

Axon

Synaptic terminalsSynapse

Postsynaptic CellNeurotransmitter

Introduction to Information Processing


there are three stages in information processing:sensory input integrationmotor output


sensory inputsensory (also called afferent) neurons

transmit information from sensory receptors that detect external stimuli (light, sound, touch, heat, smell and taste) and internal stimuli

the cell bodies of sensory neurons are located in clusters called ganglia which are located outside the spinal cord.


Integration interneurons (also called association neurons)

link neurons to other neurons. interneurons are only found in the brain and

spinal cord. the majority of neurons in the brain are

interneurons. interneurons integrate and interpret the sensory

information and connect sensory neurons to outgoing motor neurons.


motor outputmotor neurons (efferent neurons) relay

information to the effectors.effectors are the cells or organs that

respond to the external stimulus. Example: muscles, organs and glands.


SensorSensory input

Integration

EffectorMotor output

Peripheral nervoussystem (PNS)

Central nervoussystem (CNS)


Reflex Arcreflexes are involuntary and often

unconscious the simplest nerve pathway is the reflex arc.

a neural circuit through the spinal cord that provides a framework for a reflex action.

usually does not involve the brain.


contains five essential components: a sensory receptor sensory neurons interneurons (found in the spinal

cord usually) motor neurons the effector



example of a reflex arc: Patellar Reflexstimulus: tapping the tendon below the

kneecapsensory receptors: detect the slight

stretching of the tendon.


the impulse travels down the sensory neuron to the spinal cord. (from the PNS CNS)

the CNS relays a message back to PNS along two motor neurons.

the impulse causes the quadriceps to contract and hamstring to relax.

this causes your lower leg to rise.


C) Introduction to Information Processing

Try it!

Questions 1-5 page 414

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Chapter 13.1 Pages 408-414 The Nervous System. Introduction The Organization of the Nervous System