19: The Nervous System

Section Objectives:Analyze how nerve impulses travel within the

nervous system.

Interpret the functions of the major parts of the nervous system.

Compare voluntary responses and involuntary responses.

The Nervous System• Controls and coordinates the

body’s responses to changes in the environment

• HOW:• Stimulus: a change in the

external or internal environment which initiates an impulse

• Impulse~ an electro-chemical charge generated along a neuron

• Receptors~ structures specialized to detect certain stimuli

• Response~ a reaction to a stimulus

• Effectors~ what responds to a stimulus such as muscles or glands

Neurons: Basic Units of the Nervous System

• Neurons conduct impulses throughout the nervous system.

• A neuron is a long cell that consists of three regions: a cell body, dendrites, and an axon.

Neurons: Basic Units of the Nervous System

• Dendrites~ receive impulses and carry them toward the cell body

• Axon~ carries impulses away from the cell body and toward other neurons, muscles, or glands.

• Cell body~ contains the nucleus

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signaldirection

myelin coating

Myelin coating Axon coated with insulation

made of myelin cells speeds signal

signal hops from node to node 330 mph vs. 11 mph

Multiple Sclerosis immune system (T cells) attacks myelin coating loss of signal

Multiple Sclerosis immune system (T cells) attacks myelin coating loss of signal

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Fun facts about neurons• Most specialized cell in

animals

• Longest cell– blue whale neuron

• 10-30 meters

– giraffe axon• 5 meters

– human neuron• 1-2 meters

Nervous system allows for 1 millisecond response timeNervous system allows for 1 millisecond response time

Neurons: Basic Units of the Nervous System

3 Types of neurons.

• 1. Sensory neurons: carry impulses from the body to the spinal cord and brain (sense receptors)

• 2. Motor neurons carry the response impulses away from the brain and spinal cord to a muscle or gland. (effectors)

• 3.Interneurons: connect sensory &motor neurons within the brain and spinal cord

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Types of neuronssensory neuron(from senses)

interneuron(brain & spinal chord)

motor neuron(to muscle)

How an impulse is transmitted

• 1. Resting: no impulse, cell is polarized ( + on outside & - on inside)– Sodium/Potassium pump in axon using ATP maintains this

polarity

How an impulse is transmitted

• 2.Impulse: stimulus excites neuron– Na+ gates open– Na+ goes inside,

therefore inside becomes more +

– Depolarization occurs ~ a nerve impulse

– Impulse moves in one direction

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Synapse ~ connection between neurons & effector cells

synapse

Junction between nerve cells– 1st cell releases chemical

(neurotransmitter) to trigger next cell– where drugs affect nervous system

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Nervous System

• Central nervous system (CNS)– brain & spinal cord

• Peripheral nervous system (PNS)– nerves from senses– nerves to muscles

2 systems work together

cerebrum

cerebellum

spinal cord cervicalnerves

thoracicnerves

lumbarnerves

femoral nerve

sciatic nerve

tibialnerve

Anatomy of the brain• Cerebrum:

– Conscious activities– Intelligence– Memory– Language– Voluntary activity

• Cerebellum:-Coordinates motor activity-balance

Medulla Oblongata:involuntary activities such as breathing,&heart rate

Central Nervous System (CNS)

Peripheral Nervous System (PNS)

Somatic Nervous

System (voluntary)

Relays information to and from skin and skeletal

muscles.

Nervous System

Autonomic Nervous

System (involuntary)

Relays information to internal organs.

Sympathetic Nervous

System Controls organs in times of stress.

Parasympathetic Nervous System

Controls organs when body is at rest