functions of the nervous system slide 7.1a copyright © 2003 pearson education, inc. publishing as...

Functions of the Nervous SystemFunctions of the Nervous System

Slide 7.1aCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

1. Sensory input – gathering information To monitor changes (stimuli) occurring inside

and outside the body

2. Integration To process and interpret sensory input and

decide if action is needed

3. Motor Output

A response to the integrated stimuli

The response activates muscles or glands

Functions of the Central Nervous Functions of the Central Nervous System (CNS)System (CNS)

Slide 7.3bCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Figure 7.1

Example: As you’re driving you see a red light and automatically move your foot to the brake.

Structural Classification of the Structural Classification of the Nervous SystemNervous System

Slide 7.2Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Central nervous system (CNS)

Brain

Spinal cord

Peripheral nervous system (PNS)

Nerves outside the brain (cranial) and spinal cord (spinal)

Functional Classification of the Functional Classification of the Peripheral Nervous SystemPeripheral Nervous System


1. Sensory (afferent) division

Nerve fibers that carry information to the central nervous system

2. Motor (efferent) division

Nerve fibers that carry impulses away from the central nervous system

Figure 7.1

Functional Classification of the Functional Classification of the Peripheral Nervous SystemPeripheral Nervous System

Slide 7.3cCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Motor (efferent) division – has two subdivisions

1. Somatic nervous system Voluntary Allows us to control our skeletal muscles

2. Autonomic nervous system Involuntary Automatically controls our cardiac and

smooth muscles

Figure 7.1

Organization of the Nervous SystemOrganization of the Nervous System


Figure 7.2

Types of Nervous TissueTypes of Nervous Tissue


There are only 2 types of nervous tissue:

1. Neuroglia – support cells; name means nerve glue

2. Neurons – the actual nerve cells

Figure 7.3a

Neuroglia or Support CellsNeuroglia or Support Cells


They can not transmit a nerve impulse

They never lose their ability to divide (most neurons do)

This means most brain tumors are formed by these cells (gliomas)

4 kinds of neuroglia support the CNS: astrocytes, microglia, ependymal cells, and oligodendrocytes

2 kinds of neuroglia support the PNS; Schwann cells and satellite cellsFigure 7.3a

CNS Support Cells (Neuroglia)CNS Support Cells (Neuroglia)


1. Astrocytes Abundant, star-shaped cells

Brace or support neurons

Form barrier between capillaries and neurons

Control the chemical environment of the brain

Figure 7.3a



2. Microglia Spider-like phagocytes

Dispose of debris

3. Ependymal cells Line cavities of the

brain and spinal cord

Cilia help to circulate the cerebrospinal fluid

Figure 7.3b, c



4. Oligodendrocytes

Produce myelin sheath (a fatty layer of insulation) around nerve fibers in the central nervous system

Figure 7.3d

PNS Support Cells (Neuroglia)PNS Support Cells (Neuroglia)

Slide 7.7bCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

1. Satellite cells Protect neuron cell bodies

2. Schwann cells Form myelin sheath in the peripheral

nervous system

Figure 7.3e

Nervous Tissue: NeuronsNervous Tissue: Neurons


Neurons = nerve cells

Cells specialized to transmit messages

All neurons have a:

Cell body – nucleus and metabolic center of the cell

Processes – fibers that extend from the cell body

Neuron AnatomyNeuron Anatomy


Cell body & extensions outside the cell body Dendrites –

conduct impulses toward the cell body

Axons – conduct impulses away from the cell body

Figure 7.4a

Axons and Nerve ImpulsesAxons and Nerve Impulses


One axon ends in many axonal terminals (hundreds to thousands)

Axonal terminals contain hundreds of tiny vesicles with neurotransmitters

Axonal terminals are separated from the next neuron by a gap

This gap is called the synaptic cleft or synapse

Neuron AnatomyNeuron Anatomy


Most long neurons are covered with myelin (white, fatty substance)

This forms the myelin sheath

In the PNS, Schwann cells form it while in the CNS, oligodendrocytes form it

In the CNS, myelinated neurons are called the white matter and unmyelinated neurons are called the gray matter

Figure 7.4a

Multiple SclerosisMultiple Sclerosis


In this disease, the myelin sheath is slowly destroyed and hardened (called scleroses)

This short circuits the nerve transmissions and the person loses the ability to control muscles

It’s an autoimmune disease which means the body attacks the protein in the sheath for some unknown reason

There’s no cure but it’s treated with interferon and bovine myelin

Figure 7.4a

Classification of NeuronsClassification of Neurons


Can classify neurons by their function:

1. Sensory (afferent) neurons – toward CNS

2. Motor (efferent) neurons – away from CNS

3. Interneurons (association) neurons – connect sensory & motor neurons

Neuron ClassificationNeuron Classification


Figure 7.6

Classification of NeuronsClassification of Neurons


Can classify neurons by their structure or number of processes they have:

1. Multipolar neurons– many extensions; by far the most common

2. Bipolar neurons – 2 extensions

3. Unipolar neurons – 1 extension

Structural Classification of NeuronsStructural Classification of Neurons


2 Functional Properties of Neurons2 Functional Properties of Neurons


1. Irritability – ability to respond to stimuli and convert it to an impulse

2. Conductivity – ability to transmit an impulse to other neurons, muscles or glands

Starting a Nerve ImpulseStarting a Nerve Impulse


1. Polarized membrane – at rest a neuron has fewer + ions inside than outside = no activity

2. Depolarization – a stimulus depolarizes the neuron’s membrane which allows sodium (Na+) to flow inside the membrane

Figure 7.9a–c

Starting a Nerve ImpulseStarting a Nerve Impulse


3. The build up of + sodium ions inside initiates an action potential in the neuron = nerve impulse

4. The nerve impulse is all or none – it travels down the entire axon

5. Repolarization – almost immediately the extra + ions are moved back out of the neuron and it becomes polarized again Figure 7.9a–c

Nerve Impulse PropagationNerve Impulse Propagation


Impulses travel faster when fibers have a myelin sheath

Impulses cross the synapse to the next neuron by release of a neurotransmitter

Figure 7.9c–e

How Neurons Communicate at How Neurons Communicate at SynapsesSynapses


Figure 7.10

Things that affect the conduction of Things that affect the conduction of impulsesimpulses


Alcohol, sedatives and anesthetics all block nerve impulses by not allowing sodium into the neuron.

No sodium means no action potential or nerve impulse

Cold and continuous pressure also impair nerve impulses because they disrupt blood flow

Examples: can’t write your name if hands are cold or your foot “falling asleep”

Figure 7.10

The ReflexesThe Reflexes

Slide 7.23

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Reflex – rapid, predictable, and involuntary responses to stimuli

Reflex – like a one way street; always go the same direction

Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector

Figure 7.11a

Simple Reflex ArcSimple Reflex Arc

Slide 7.24


Figure 7.11b, c

Types of ReflexesTypes of Reflexes

Slide 7.25


1. Autonomic reflexes

Regulates smooth & cardiac muscle plus glands

Regulates body functions: digestion, elimination, blood pressure & sweating

Also includes salivating & pupil dilation

2. Somatic reflexes

Involves the skeletal muscles – pulling away from a hot object

functions of the nervous system slide 7.1a copyright © 2003 pearson education, inc. publishing as...

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