The Nervous System
Central Nervous System
Peripheral Nervous System

Organs of the Nervous System
• The nervous system consists of:
– brain
– spinal cord
– nerves
– neurons
– sense organs

The Neuron

The Brain

Functions of the Nervous System
• Your nervous system is a communications network
– Receiving information
– Responding to stimuli
– Maintaining homeostasis

Receiving Information
• Because of your nervous system, you are aware of what is happening in the environment around you
• Your brain is also aware of your internal conditions like temperature and glucose level

Responding to Stimuli
• After receiving information, your nervous system analyzes the data and causes a response
– Putting your hand in front of your face if a ball is coming at you
– Increasing your heart rate when exercising

Maintaining Homeostasis
• The nervous system maintains homeostasis by directing the body to respond correctly to the information it receives
– When you are hungry, your brain tells you to eat

Central Nervous System
• The control center of the body
• Composed of your:
– Brain – controls most functions
– Spinal Cord – thick column of nerve tissue that links the brain to nerves in the peripheral nervous system

Brain
• The brain contains 100 million neurons
• The skull, layers of connective tissue, and fluid protect the brain from injury
• The brain is composed of three main parts
– Cerebrum
– Cerebellum
– Brain stem

Cerebrum
• Largest part of the brain
– reads input from the senses
– controls skeletal muscles
– In charge of learning, remembering and making judgments

Cerebrum
• Right side
– controls left side of body
– controls creativity and artistic ability
• Left side
– controls right side of body
– Controls math, speech, writing, and logic

Cerebellum
• Second largest part of your brain
• Coordinates actions of your muscles
• Helps you keep your balance

Brain Stem
• Lies between the cerebellum and spinal cord
• Controls involuntary actions
– Breathing
– Heartbeat

Spinal Cord
• The link between your brain and peripheral nervous system
• Protected by bone, connective tissue and fluid

Peripheral Nervous System
• Consists of a network of nerves that branch out from the central nervous system
• Made up of 43 pairs of nerves
– 12 begin in the brain
– 31 begin in the spinal cord
• One nerve in each pair goes to the right side and one to the left

The Neuron
• Neurons are cells that carry information around your body
• Nerve impulse - The message a neuron carries

The Neuron
• The cell body of the neuron has two extensions
– Dendrite – carries impulses to the cell body
– Axon – carries impulses away from the cell body
• The nerve impulse begins in the dendrite, moves to the cell body then moves down the axon

The Neuron signal goes from axon to dendrite

Kinds of Neurons
• Different kinds of neurons perform different functions
– Sensory neurons
– Interneurons
– Motor neurons

Sensory Neuron
• Picks up stimuli from the internal or external environment and converts each stimulus into a nerve impulse
• The impulse travels along the sensory neuron until it reaches an interneuron in the brain or spinal cord
• sensory impulse travels at 76.2 m/s

Interneuron
• Neuron that carries nerve impulses from one neuron to another
• Can pass stimuli from sensory neuron to motor neuron

Motor Neuron
• Send an impulse to a muscle and the muscle contracts in response
• Motor impulse travels at 119 m/s

How a Nerve Impulse Travels
• Millions of nerve impulses travel your body each day
• The nerve impulse travels along the neuron in the form of electrical and chemical signals

How a Nerve Impulse Travels
• There are tiny spaces or synapses between a neuron and the next structure
• A nerve impulse must jump this gap
• Axon tips release a neurotransmitter that allows the impulse to travel the gap

How a Nerve Impulse Travels
Drugs and alcohol can affect the neurotransmitters
• alcohol increases reaction time
• depressants, like marijuana also increase reaction time
• stimulants, like meth, decrease reaction time

The Path of a Nerve Impulse

Reflex
• A reflex is an automatic response that occurs very rapidly and without conscious control
• Reflexes protect us from pain and injury

Reflexes

Body systems that work with the nervous system;
• The nervous system works with every system in the body

Comparing Cells to the Body
• The cell part that controls the cell is the nucleus