The Nervous System

http://www.brightstorm.com/science/biology/the-human-body/nervous-system/

The Nervous System

• A complex network of nervous tissue that carries electrical messages throughout the body

• Includes– Brain and Spinal cord• Central Nervous System

– Nerves that run throughout the body• Peripheral Nervous System

Nerve Cells

• Two basic types of nerve cells– Neurons• The structural and functional units of the nervous

system– Transmit electrical signals called nerve impulses

– Glial Cells• Support the neurons• Provide neurons with nutrients and other materials

Neurons• Cell body – contains the

nucleus and other cell organelles

• Dendrites – extend from the cell body and receive nerve impulses from other neurons

• Axon – long extension of the cell body that transmits nerve impulses to other cells http://www.youtube.com/watch?v=o

b5U8zPbAX4&lr=1

The Myelin Sheath

• The outer layer of many neurons– Myelin is a lipid produced by a type of glial cell

known as a Schwann cell– Acts like a layer of insulation– Regularly spaced nodes, or gaps, in the myelin

sheath allow nerve impulses to skip along the axon very rapidly

Types of Neurons

• Classified based on the direction in which they carry nerve impulses– Sensory neurons – carry nerve impulses away

from tissues and organs to the spinal cord and brain

– Motor neurons – carry nerve impulses from the brain and spinal cord to muscles and glands

– Interneurons – carry nerve impulses back and forth between sensory and motor neurons

Motor Neurons

Nerve Impulses

• These are electrical in nature• Come from a difference in electrical charge

across the plasma membrane of a neuron– Ions are involved in this process• Remember that these are electrically charged atoms or

molecules

Resting Potential

• Not actively transmitting a nerve impulse

• Maintained by the sodium-potassium pump– Maintains a charge

differential across the membrane

Uses ATP to pump Na+ ions out of the cells and K- ions into the cellThe inside of the neuron is negatively charge with the fluid surrounding the neuron is positively chargeThe difference is called the resting potential

Action Potential• A nerve impulse causes a

sudden reversal of the electrical charge across the membrane of a resting neuron– This reversal is called the action

potential• Begins with a chemical signal

from another cell– Gates to the Na/K pump open

allowing Na+ ions to rush back into the cell

– Charges are now reverse

The reversed charges causes a ripple effect down the axon as a very rapid electrical currentIf a myelin sheath is there these ions can only flow where there is a node

Sodium Potassium Pumps and Action Potential

• http://www.youtube.com/watch?v=C_H-ONQFjpQ&lr=1

• http://www.youtube.com/watch?v=gkQtRec2464&lr=1

The Synapse• The place where an axon

terminal meets another cell is called a synapse– Separated by a narrow

space known as the synaptic cleft

– When an action potential reaches the axon terminal, a molecule called a neurotransmitter is released

– http://outreach.mcb.harvard.edu/animations/synaptic.swf

Central Nervous System

• CNS – brain and spinal cord– The Brain• The most complex organ of the human body• The control center of the CNS• 100 billion neurons• Reasoning• Imagination• Memory• Language• Breathing and Heartbeat

The CNShttp://www.pbs.org/wnet/brain/3d/index.html

Parts of the Brain

Parts of the Brain

• Cerebrum – largest part of the brain– Conscious functions• Reasoning, language, sight, touch, hearing• Two hemispheres

– Similar but not identical– Connected by a thick bundle of axons deep within the brain– 4 Lobes

» Frontal lobe – reasoning» Parietal lobe – touch» Temporal lobe – hearing» Occipital lobe - sight

Parts of the Brain

• Cerebellum– Just below the cerebrum– Coordinates body movements– Many nerve pathways link the cerebellum with

motor neurons throughout the body• Brain Stem– The lowest part of the brain– Connects the rest of the brain to the spinal cord– Controls unconscious functions

Spinal Cord

• A thin, tubular bundle of nerves running from the brain stem and down through the center of the body to the pelvis– Protected by the vertebrae

Peripheral Nervous Systems - PNS

• All the nervous tissue outside of the CNS

• Connected to the CNS by nerves– Longest nerve in the

body is the sciatic nerve• From lower back all the

way to the toes

PNS

• Sensory and Motor portions• Somatic nervous system– Controls mainly voluntary activities that are under

conscious control• Attached to skeletal muscles

– Also controls unconscious activities like reflexes

Autonomic Nervous System - ANS

• All other involuntary activities• Connected to glands and internal organs– Heart Rate– Breathing– Digestion– Sweat Production– http://www.garyfisk.com/anim/autonomicns.swf

ANS

• Sympathetic division– Deals with emergency situations– “Fight or flight”

• Parasympathetic division– Controls involuntary activities that are not

emergencies• Organs of the digestive system

The Senses

• Part of the PNS sensory division– Eyes– Ears– Mouth– Nose– Skin• All have special cells called sensory receptors• http://www.brightstorm.com/science/biology/the-hum

an-body/sensory-system/

Sight

• http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP14304

Hearing

• Translating sound ways into an understandable sound

Balance

• Our ears are responsible for our sense of balance

• Any movement sends impulses to the brain and then the bran sends out impulses triggering contractions of skeletal muscles as needed to restore balance

Taste and Smell

• Both are involve the ability to sense chemicals• http://www.bbc.co.uk/science/humanbody/b

ody/factfiles/taste/taste_ani_f5.swf

Touch

• The ability to sense pressure– Pressure receptors are found mainly in the skin• Concentrated on the tongue, lips, face, palms of the

hands, and soles of the feet• http://www.youtube.com/watch?v=xRkPNwqm0mM

The Flavor of Food: Smell + Taste + Touch

• http://science.kqed.org/quest/video/science-of-taste/

Drugs and the Nervous System

• Psychoactive – affects the CNS– Influence the transmission of nerve impulses– http://www.thirteen.org/closetohome/animation/

neuron-main.html– Examples• Caffeine – a stimulant that makes you feel more awake

and alert• Alcohol – a depressant

Drug Abuse and Addiction

• Drug abuse – using a drug without the advice of a medical professional or more reasons not originally intended

• Drug addiction – continued used where you are unable to stop– Usually leads to needing more of the drug to get

the same effect• Can lead to overdose and death

Disorders of the Nervous System

• Vascular disorders – causing death of brain cells• Infections of the nervous tissue– Meningitis

• Brain or spinal cord injuries• Abnormal brain functioning– Headaches, epilepsy

• Breakdown of nervous tissues– Alzheimer’s, ALS, Consussions

Autism

• http://science.kqed.org/quest/video/autism-searching-for-causes/

Alzheimer’s Disease

• http://science.kqed.org/quest/video/alzheimers-is-the-cure-in-the-genes/