Nervous System

Nerves

•Hold out your hand in front of you•Now wave at yourself•Now, tap your head

•Put your arms down•Say out loud to “Move Arm”…Just tell it to

move▫Did it move?▫Why not?

Nerves

•How does our arm know when you want it to move?

•Our experiment shows that your arm does not understand spoken commands.

•So what does it understand? •What tells it to move. If you think it is

your brain, you are correct.

Nerves

•But wait a moment. Your brain is clear up in your head, while your arm is clear down on your body.

•How does your brain talk to your arm? Somehow they must be connected.

•The connection between your brain and your arm, as well as every other part of your body is known as your nervous system.

Nervous System

•How are messages transmitted along your nervous system? Interestingly enough, messages travel from your brain to your various body parts via electricity, in much the same way cable television signals travel from the cable company to your house, or in the same way that this web page traveled from our web servers to your computer.

Are your Synapses Firing?

•Remember that the cells making up your nervous system are called neurons.

•Neurons are connected to other neurons, as well as to other tissues within the body via synapses.

•The location where a neuron connects to another cell is called a synapse.

Brain neurons firing• When a message is transferred

through a neuron it passes to the next neuron via an amazing fast chemical and electrical reaction.

• Because of its lightning speed, it is often said that a person’s synapses are firing when they are in deep thought.

• Regardless of whether you are solving a problem, or taking a nap, your synapses are always busy transporting messages.

The Central Nervous System (CNS)•The Central Nervous

System is made up of your brain, and your spinal cord.

• It is the main control center of your body, and the center of thought. Your Central Nervous System controls most of the actions within your body.

Brain

•Your mind is a powerful and amazing organ. Its ability to calculate, control and think exceeds that of every computer on Earth put together.

•Your brain has three main parts. ▫Cerebrum▫Cerebellum▫Brain Stem.

Cerebrum

•Largest portion of the brain•Your cerebrum is responsible for all the

voluntary processes that you do each day, including thought.

•Voluntary means that you want to do something, or that you decide to do something, like hold your hand in the air, wave to yourself, and tap yourself on the head.

Cerebrum

•As you do these actions, your cerebrum sends electrical messages out to your body using the neurons of your nervous system.

•When the message reaches your arm, your muscles obey, and do as they are instructed.

Corpus Callosum

•What happens when the corpus callosum is cut?

•Sensory inputs are still crossed•Motor outputs are still crossed•Hemispheres can’t exchange data

•Epileptic

The ‘Split Brain’ studies

•Surgery for epilepsy : cut the corpus callosum

•Roger Sperry, 1960’s

•Special apparatus▫ picture input to just one

side of brain▫ screen blocks objects on

table from view

Nonverbalrighthemisphere

Verballefthemisphere

Nonverbalrighthemisphere

Verballeft

hemisphere

??

“What didyou see?”

•Picture to left brain▫can name the object▫left hand cannot

identify by touch

Picture to right brain can’t name the object left hand can identify

by touch

“Using your left hand,Pick up what you saw.”

The ‘Split Brain’ studies

I saw anapple.

“What didyou see?”

Nonverbalrighthemisphere

Verballeft

hemisphere

Cerebellum

•Your cerebellum aids your cerebrum in the task of moving your muscles.

•It helps to maintain balance, moving the muscles you don’t think to move, as you make your arm wiggle around. This allows you to move about smoothly, with little effort.

Brain Stem•Your brain stem sites at the

base of the brain, and connects it to the spinal cord.

•The brain stem controls the flow of information between the brain and the rest of the body, and also controls many of the involuntary movements that your body does, every single day.

Super Highway• Like a powerful broadband Internet connection,

your spinal cord can move a lot of data very quickly. Its job is to carry messages to and from the body to the brain.

• There are 32 different nerves that connect directly into the spinal cord, and that branch outward towards the rest of the body.

• Reflexes are processed directly in the spinal cord, allowing you to respond very quickly to danger, without wasting time thinking about what you should do.

Addictive Drugs Act on Chemical Synapses•Emotional states (mood, pleasure, pain,

etc.) are determined by particular groups of neurons that use special sets of neurotransmitters and neuromodulators▫many researchers think that depression

results from a shortage of serotonin▫Prozac, an anti-depressant, inhibits the

reabsorption of serotonin

Drugs alter transmission of impulses across the synapse

Addictive Drugs Act on Chemical Synapses•Nerve cells are particularly prone to the

loss of sensitivity when exposed to a chemical signal for a long time

▫if receptor proteins within synapses are exposed to high levels of neurotransmitters for prolonged periods, the nerve cell often responds by inserting fewer receptor proteins into the membrane

Addictive Drugs Act on Chemical Synapses•Cocaine acts a neuromodulator, causing

abnormal amounts of neurotransmitters to remain in the synapse for long periods▫it affect neurons in the brain’s pleasure

pathways these cells transmit pleasure messages using the

neurotransmitter dopamine

▫cocaine works by blocking transporter proteins on the presynaptic membrane that normally reabsorb dopamine because dopamine cannot bind to a transporter, it

remains in the synapse and continues to stimulate

Addictive Drugs Act on Chemical Synapses•When receptor proteins in the pleasure

pathways of the brain are exposed to high levels of dopamine due to cocaine, the nerve cells respond by lowering the number of receptor proteins▫with so few receptors, the drug user needs

the drug to maintain even normal nerve activity levels

▫this is addiction, the physiological adaptation of the nervous system due to drug abuse

How drug addiction works

Addictive Drugs Act on Chemical Synapses•Nicotine, also an addictive drug, binds to

postsynaptic receptors in the brain that normally bind to Ach

•The brain responds by▫making fewer receptors to which nicotine can

bind▫altering the pattern of activation of the nicotine

receptors (i.e., their sensitivity to neurotransmitters)

•This leads to profound changes in the patterns of release of many neurotransmitters, and addiction results

How the Brain Works

•The cerebrum is the center for thought and association and makes up about 85% of the weight of the brain▫the cerebrum is divided into right and left

halves, called cerebral hemispheres

•Much of the neural activity of the cerebrum occurs within a thin, gray outer layer called the cerebral cortex

Senses• We use our senses to get information about the

world around us into our brains. • There are five main senses that most of us use each

day. ▫Sight▫Hearing▫Touch▫Taste▫smell

• Without senses, your brain would have no way of knowing what was going on around you. Life would be a very lonely, dark, and quiet place.

Eyes•The human eye is an amazing

and powerful organ. As you read the words on this screen, your eyes see the shapes of the letters, and transmit the information back to your brain.

• Light travels from the computer screen to your eyes, entering them through a transparent layer of tissue called the cornea.

Eyes• The light of your computer screen then travels

onward through the lens. The lens of your eye focuses the light onto a special tissue called the retina.

• The retina is lined with special photoreceptors called rods and cones.

• Rods are more sensitive to light, but cannot distinguish between colors.

• While cones are less sensitive, but can differentiate the different colors, giving us color vision.

• Not all animals have cones. What does this mean? It means that many animals see in black and white.

Eyes

•As light lands on the rods and cones it is converted into electrical impulses and is transmitted to the brain, where it is interpreted as the beautiful images all around us.

Sensing Light: Vision

•Color blindness occurs when individuals are not able to perceive all three colors▫it typically occurs due to an inherited lack

of one or more types of cones▫it is a sex-linked trait, so men are more

likely to be colorblind than women

Test for color blindness

Sometimes your eyes can play tricks on you…

Optical Illusion•The brain also uses information learned in

the past to help it perceive the images that the eyes send

•the brain can have a tendency to “force” an image into something that the image is not, just so the image looks more familiar. These are called cognitive illusions

•optical illusion isn’t “real,” although the brain interprets the illusion as being true

Hearing

•How do we hear?•As objects move, or interact with other

objects, they cause the air to vibrate. Think of a swimming pool.

•What happens if you jump in? •First you make a big splash, followed by a

series of ripples. The harder you jump, the bigger your ripples will be.

Hearing

•The air of our atmosphere works in much the same way as a swimming pool.

•Even though we cannot see the ripples, every time, we move they go traveling through the air.

•Some of these ripples, or vibrations reach our ears. Inside of your ear is a thin tissue known as the tympanum, or eardrum.

Hearing

•The vibrations in the air cause your eardrum to begin vibrating.

•Behind your eardrum are three tiny bones called

•Hammer•Anvil•Stirrup

Hearing•As your eardrum begins to vibrate, so do

these tiny bones. •The last of these bones, the stirrup transmits

these vibrations into the fluid filled cochlea. •This causes tiny hairs within the cochlea to

vibrate. •The vibration of these hairs is converted into

electrical impulses, which are then transmitted to the brain for interpretation.

Taste and Smell

•The senses of taste and smell are interpreted from tiny objects on your tongue, and in your nose.

•Receptors within your nose detect and transmit smells to your brain, while your taste buds detect and transmit flavors to your brain

Taste and Smell

•Much of what we think we are tasting is actually smell.

•Try an experiment. Next time you are eating something, plug your nose. What happens?

•Much of the flavor disappears.

Touch

•The senses we have discussed so far have been located in one specific location, such as the eye, or nose.

•However, your sense of touch is not restricted to one small area, but covers your entire body.

•Your skin is sensitive to heat, to pressure, and to pain.

•Within your body, there are also many nerve endings that are sensitive to touch.