The Nervous System
WHAT IS THE MAIN ORGAN FOR THIS?
Stimuli
 Any change inside or outside your body that brings
about a response-reaction
 The nervous system plays a MAJOR part in this
 Each day you experience thousands of these
 Your body’s goal is to maintain homeostasis (a
balance)
 Your internal control systems-will work with
breathing rate, heartbeat rate, digestion, etc.
Neurons
 These are nerves
 This is the working unit of the nervous system
 A neuron consists of a body and branches—dendrites
and axons
 Dendrites
= receives messages—send to
body
 Axon = carries message away from the
body
 These messages are called impulses
Types of Neurons
 Receptors-respond to various stimulus
 Have 3 different types
 Sensory

Receive information and send impulses from the brain and spinal
cord
Motor
 Conduct impulses from the brain and spinal cord to
muscle and glands
 Interneuron
 Relay the impulses from the sensory to motor neurons
 You have more of these than the other 2 neurons

Synapse
 This is the space in-between 2 neurons
 Neurons DON’T TOUCH each OTHER
 Have chemicals that travel across the synapse to
send the messages-impulse
Nervous System
 Have 2 major divisions
 Central nervous system


Made up of the brain and spinal cord
Peripheral nervous system
All the nerves not in the central nervous system
 These nerves connect the brain and spinal cord
to the rest of the body

Brain
 Has about 100 billion neurons
 The 3 major parts = cerebrum, cerebellum, and brain
stem
 The grooves/folds in the brain = cortex
Spinal Cord
 This is really an extension of the brain stem
 Made up of bundles of neurons carrying impulses
from all parts of brain and from the brain to all parts
of the body
 About as thick as your thumb
 Protected by vertebrae
Peripheral Nervous System
 Connects brain + Spinal cord to the rest of the body
 12 pairs of cranial nerves-from your brain
 31 pairs of spinal nerves—from your spinal cord
 Made up of sensory and motor neurons
 Can have several impulses going at the same time
2 divisions of the peripheral nervous system

Somatic


These go to the muscles
Autonomic

Controls heartbeat, breathing, digestion, gland functions
Reflexes
 An involuntary and automatic response to a stimulus
 Occur before you really know what happened
 Really controlled by your SPINAL CORD not the
brain
 Reflex arc is a simple nerve pathway
 For something hot

Sensory receptor responds to heat-sends impulse to spinal cord—
impulse goes to interneuron in spinal cord—sends impulse to
motor neuron—impulse from motor neuron goes to muscle—pull
away from hot thing
 After reflex has occurred your brain will then step in
and deal with the pain
 Also the brain will be making a memory
Affect of Drugs
 Alcohol
 Is a depressant = slows down the activities done by the central
nervous system
 Will impair judgment, reasoning, memory, and concentration
 Will destroy brain cells and liver cells
Caffeine


Is a Stimulant = drug that speeds up the activity of the central
nervous system
Increases heartbeat rate—causing restlessness, tremors,
insomnia, production of urine increases,
 For any of these drugs your body can become
addicted
 When on any drugs/medicine—your body has to
work harder to maintain homeostasis
 Keeping homeostasis is more difficult when your
body must cope with the effects of drugs.
Parts of the Brain
Spinal Cord
 Superhighway of the body
 Carries information up to
the brain
 Carries instructions back down
from the brain
Medulla Oblongata
 Controls the body’s autonomic functions
 Things you don’t think about to perform

Respiration, digestion, heart rate
 Relay station for nerve signals going to/from the
brain
Pons
 Level or consciousness and sleep
 Helps control autonomic body functions
Cerebellum
 Regulates and coordinates movement, posture, and
balance
 Helps in learning movement
Hypothalamus
 Monitors and controls your :
 circadian rhythms = your daily sleep/wake cycle
 Homeostasis- making sure your body is running smoothly
 Appetite
 Thirst
 Emotions
 Motor functions
 Autonomic functions
Thalamus
 THE RELAY station in the brain
 Helps in processing
 Sensory signals
 Sound
 Visual
 Skin and internal organ messages
 Motor control
Cerebrum
 Takes up 2/3 of the brain
 Develop= language, abstract thought, consciousness,
and imagination
 Have 2 hemispheres-left and right




Left controls the right side of the body
Right controls the left side of the body
Left is concerned with colder-linear-rational- verbal aspects
Right is concerned with artistic-spatial-musical aspects
 Divided into different parts based on what kid of
though it process/produces
Frontal Lobe
 Command and control in your body
 Reasoning, problem solving, judgment, impulses is
done here
 Higher emotions-empathy and altruism id done her
 Helps with memory and motor control
 Is the last to develop—not full developed tell late 20s
Parietal Lobe
 Process pain and touch sensation
 Calculate location and speed of things
 Helps with movement, orientation, recognition, and
speech
Temporal Lobe
 Sound and language recognitions
 Also involved in emotions, memory, and speech
Occipital Lobe
 Visual sensation and processing
Broca’s Area
 Controls speech, language recognition , and facial
nerves
Facts about the Brain
 Width = 5.5 in
 Length 6.5 in
 Height = 36. in.
 At birth weights =4/5 lbs, Adult 3 lbs
Composition of the brain
 78% =water
 11% Fat
 8% protein
 1% carbs
 2% organic salts
Composition of Brain
 Cerebellum contain half of all the neurons in the
brain but is only 10% of the actual brain
 Cerebrum is 85% of the brain—fontal lobe 41%,
temporal- 22%, partial 19%, occipital 18%
 There are about 100 billion neurons in the human
brain-the same number of stars in our galaxy
 Left hemisphere of the brain has 186 million more
neurons than the right hemisphere
 1000mL of blood is pump to the brain every min.
(about 3 pop cans)
 In 1 minute the brain will consume 1/5 c of oxygen
from the blood
Times of the Brain
 The brain can stay alive for 4-6 minutes without
oxygen-after this cells begin to die
 You will go unconscious after just 10 seconds of no
blood getting to the brain
 After 40-110 seconds of no blood to the brain the
reflexes won’t work
 During early pregnancy-1st term the neurons are
growing 250,000 per minute
Other facts about the Brain
 Is 2% of the total body weight and uses 20% of the




body’s energy
More electrical impulses are generated in 1 day by
your brain that all the telephones in the world
70,000 thoughts are processed in 1 day
After age 30, the brain shrinks a .25% in mass each
year.
Albert Einstein’s brain weighed 2.71 lbs (average is 3
lbs)
The End