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

The Nervous System

• 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• Neuron ≡ Basic Unit 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.

• 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

Neurons

2003-2004

signaldirection

myelin coating

Myelin sheath 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 and/or slowing of signal impulse

Multiple Sclerosis immune system (T cells) attacks myelin coating loss and/or slowing of signal impulse

2003-2004

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

Types of Neurons

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

2003-2004

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 (active transport);slower

How an impulse is transmitted• 2.Impulse: stimulus excites

neuron– Na+ channels open– Na+ goes inside, therefore

inside becomes more +– Depolarization occurs = a

nerve impulse– Impulse moves in one

direction– Depolarization works with

concentration gradient

2003-2004

Synapse: a connection

synapse

• Junction between nerve cells• Connection between neurons &

effector cells

2003-2004

Synapse: a connection

synapse

– 1st cell releases chemical (neurotransmitter) to trigger next cell

– where drugs affect nervous system

2003-2004

The Nervous Systems

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

• Peripheral nervous system (PNS)– nerves from senses– nerves to muscles/glands– Both 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:A̶ Coordinates motor activity & balance

Anatomy of the brain• Midbrain:

A̶ reptilian brain (instincts, emotions)

• Hindbrain/Brain stem:A̶ 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

The Nervous System