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Nervous Regulation

Chapter 14

Key Concepts

Describe how organisms respond to changes in their environment

Describe a nerve impulse

Design and experiment to determine the instinctive behavior of a planarian

Key Words









The Regulatory Process

Section Objectives:

Explain the functions of a nervous system.

Define stimulus.

Describe the structure and the function of a neuron.

Name the different types of nerves and describe their functions.

Functions of Regulation

Environment always changing

Organism changes, adjustments

Inside and outside the body

Irritability – ability of a cell to respond to its environment

Nervous and endocrine systems

Controls regulation and coordination


Mechanisms of Nervous Regulation

Network of cells – nerve cells

Carry messages – impulses

Receptors – sense organs

Sensitive to changes

Physical force, chemicals

Inside or outside of body


Structure respond to commands of nervous system


Anything that causes a receptor to start impulses in a nerve pathway.

Cause electrical and chemical changes in receptors.

3 events in nervous regulation:

1. Stimulus activates a receptor

2. Impulses are started in associated pathways.

3. Effectors responds to the impulse.


Specialized group of nerve cells that controls and coordinates the activities of the nervous system.

More complex the organism, the more complex are the function and structure of the brain.

Structure of Neurons

Interconnected circuits

A way to remember the relationship between: dendrites, cell body, and axon.


Another look at a Neuron


Myelin Sheath


Does it work ?

The Synapse

Terminal branches

Many branches at ends

Almost touch each other

Place between the terminal branch of a neuron and the membrane of another cell

Microscopic gap

One of more synapses

As many as 1000 other neurons

Synaptic junction between neurons

A bridge


Stored in synaptic vesicles

Presynaptic membrane

Synaptic cleft

Trigger an action potential

Types of Nerves and Neurons

Sensory receptor

Motor neuron

Mixed neurons

Interneurons or associated neurons

Section Review Quiz
( put all answers on loose-leaf paper )

1. What are the three types of structures found in a true nervous system?

2. What happens when a receptor is stimulated?

3. List the three parts of a nerve cell.

4. What is a synapse?

5. What would happen if the motor neurons in one of your legs stopped functioning?

The Nerve Impulse

Section Objectives:

Describe the electrical state of a resting neuron and the function of the sodium-potassium pump.

List the changes that occur as an impulse travels along an axon.

Explain how the nervous system distinguishes between stimuli of different types and strengths.

Identify the structures of a synapse and describe the transmission of an impulse across a synapse and at a neuromuscular junction.

The Resting Neuron

No impulse transmission occurs

Outside has a net positive charge

Inside has a net negative charge

Cell membrane electrically polarized

Difference in charge on inside and outside

Caused by concentration of ions

Na + ion and K + ion

Sodium – potassium pump

Active transport

Sodium ions out

Potassium ions in

The Nerve Impulse

Membrane changes in the area of the impulse.

Permeability of the membrane to sodium ions increase.

Higher amount of sodium ions causes them to diffuse rapidly inside of membrane.

Thus reverses polarization

becomes positive charge.

Outside becomes negative charge

Continues throughout nerve cell

Like a relay race

Returns to normal in milliseconds

Refractory period

Brief period during which nerve cell membrane cannot be stimulated to carry impulses.

Rate of Impulse Conduction

Two factors:

1. Size of nerve fiber

2. Whether or not it has a myelin covering.

Small fibers without myelin

2 m / s

Large myelinated fibers

More than 100 m /s

Saltatory conduction

Impulse jumps from one node of Ranvier

Axon is bare

Faster and uses less energy

Nerve Cell Thresholds

Stimulus must have a certain minimum strength

Threshold - Cell’s minimum level of sensitivity

Below threshold – stimulus cannot start impulses

Above – will start impulse

All or none basis

Distinguishing Strength and Type of Stimulus

Measurement by two effects:

1. Stronger impulses causes more impulses to be transmitted each second.

2. Different neurons have different thresholds.

Recognition of type

Light sensitive

Sound waves

Transmission at the Synapse

Synaptic knob

Synaptic gap

Chemical process

Synaptic vesicles




Chemical compound

Enzymnes – acetylcholinesterase

Excitatory neurotransmitters

Inhibitory neurotransmitters

Serotonin, epinephrine, an amino acid called glycine

Neuromuscular Junctions

Impulses pass from motor neurons to muscles at these special points.

Motor end plates


Muscle contraction

Drugs and the Synapse

Poisons and drugs

Nerve gas


Botulin toxin ( bacteria poison )

Some insecticides

Interfere with function of acetylcholine at neuromuscular junctions

Cause muscle paralysis



Mind Drugs

Effect mind and emotions

Alter activity of body systems


Stimulants – speed up body activity

Amphetamines - bind to certain receptors

Uppers – short lived feelings of well being and excitement followed by depression

Caffeine – found in tea, coffee, cola – increases synaptic transmission

Sleeplessness and nervousness

Depressants – slow down body activities


Downers – produce a depressant effect, blocks formation of norepinephrine

Hallucinatory drugs – interfere with the effect of serotonin, an inhibitory transmitter.



Section Review Quiz
( put all answers on loose-leaf paper )

1. What name is given to a neuron that is not sending a nerve impulse?

2. What is the sodium-potassium pump?

3. What crosses the synapse when a nerve impulse is traveling over a pathway of nerve cells?

4. What are neuromuscular junctions?

Adaptations for Nervous Regulation

Section Objectives:

Describe the response of protists to stimuli.

Compare and contrast the nervous systems of the hydra, earthworm, and grasshopper.

Regulation in Protists

Do not have true nervous system

Able to respond to stimuli


No specialized receptors

Can tell difference between food and nonfood

Light sensitive

Harmful chemicals

Filaments are like


Paramecium cilia and beating control

Respond to stimuli food, strong acids away from solid matter

Some have organelles

Regulation in Hydra

Form of a nerve net

Irregular network between the two layers of the body wall

Connect receptor cells to muscles and gland cells

Impulses spread slowly through nerve net

Response show coordination

Regulation in the Earthworm

More complex nervous system

Central nervous system


Really a pair of ganglia joined together

Ventral nerve cords

Enlarge into ganglia in each segment

Ganglion – group of cell bodies and interneurons that switch, relay, coordinate nerve impulses

Peripheral nervous system

Nerves branching from CNS to all parts of body

Contain sensory and motor neurons

Receptors sensitive to light, vibrations, chemicals and heat

Travel in one direction

Regulation in the Grasshopper

Similar to earthworm’s

Brain in head region

Pair of solid ventral nerve cords

Run length of body


Nerve branches to all parts of body

Sense organs more highly developed than earthworm.

Has eyes

Antennae or " feelers "

Taste organs that respond to a variety of stimuli

Sensitive to sound

Section Review Quiz
( put all answers on loose-leaf paper )

1. Name the types of stimuli to which some protists respond?

2. What type of nervous system does the hydra have?

3. Name the two parts of the nervous system of the earthworm.

4. What specialized sense organs does the grasshopper possess?

5. Based on their capacity for nervous regulation, place each of the following organisms in order from most complex to least complex: ameba, earthworm, grasshopper, human, hydra, and paramecium

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