Module 3

Brain’s Building Blocks

DEVELOPMENT OF THE BRAIN

• fact that your brain does not develop into a nose is because of instructions contained in your genes

• Genes– chains of chemicals that are arranged like rungs on a

twisting ladder– there are about 20,000-25,000 genes that contain

chemical instructions that equal about 300,000 pages of written instructions

– genes program the development of individual parts into a complex body & brain

DEVELOPMENT OF THE BRAIN (CONT.)

STRUCTURE OF THE BRAIN

• Human brain:– is shaped like a small wrinkled melon– 1,350 grams (less than 3 pounds)– pinkish-white color– consistency of firm Jell-O– Fueled by sugar (glucose)– 1 trillion plus cells divided into

• glial cells• neurons

STRUCTURE OF THE BRAIN (CONT.)

• Glial cells• 1 trillion in the human brain• 3 Functions:

– guide the growth of developing neurons– wrap around neurons and form an insulation to

prevent interference from other electrical signals– release chemicals that influence a neuron’s growth

and function

STRUCTURE OF THE BRAIN (CONT.)

STRUCTURE OF THE BRAIN (CONT.)

• Neuron – a brain cell with 2 specialized extensions– one extension is for receiving electrical signals– the other extension is for transmitting electrical

signals

STRUCTURE OF THE BRAIN (CONT.)

GROWTH OF NEW NEURONS

• Can a brain grow new neurons?– primate and human brain

• researchers conclude that adult monkey and human brains are capable of growing relatively limited numbers of neurons throughout adulthood

• Some new neurons play important role in continuing to learn and remember new things (hippocampus) Area related to learning and memory

GROWTH OF NEW NEURONS (CONT.)

• Repairing the Brain– advances in stem cell research suggest the human

brain may be able to grow more neurons– repair damages:

• accident• disease• Alzheimer’s

PARTS OF THE NEURON

• Cell Body

– large egg-shaped structure that provides fuel, manufactures chemicals, and maintains the entire neuron in working order

• Dendrite

– branchlike extensions that arise from the cell body

– receive signals from other neurons, muscles, or sense organs

– pass these signals onto the cell body

PARTS OF THE NEURON (CONT.)

• Axon– a single threadlike structure that extends from and

carries signals away from the cell body to neighboring neurons, organs, or muscles

• Myelin Sheath– looks like separate tubelike segments composed of

fatty material that wraps around and insulates an axon

– prevents interference from electrical signals generated in adjacent axons

PARTS OF THE NEURON (CONT.)

• End bulbs or Terminal bulbs– located at extreme ends of the axon’s branches– miniature container that stores chemicals called

neurotransmitters (used to communicate with neighboring cells)

• Synapse– infinitely small space (20-30 billionths of a meter)– exists between an end bulb and its adjacent body

organ, heart, muscles, or cell body

ALZHEIMER’S DISEASE AND NEURONS

• Alzheimer’s disease– excessive buildup of gluelike substances– gradually destroy neurons

• Researchers recently discovered an experimental vaccine that may help stop the buildup of these gluelike, killer substances and they continue to search for other interventions

NERUONS VERSUS NERVES

• Reattaching Limbs– John Thomas

• lost arms in farming accident• Transplanting a Face

– Isabelle• face severely disfigured by a dog• received

– new nose– lips– chin

SENDING INFORMATION: ACTION POTENTIAL SEQUENCE

– axon membrane has chemical gates that can open to allow electrically charged particles to enter or can close to keep out these particles

– ions are chemical particles that have electrical charges

– opposite charges attract and like charges repel

SENDING INFORMATION: ACTION POTENTIAL SEQUENCE (CONT.)

SENDING INFORMATION: ACTION POTENTIAL SEQUENCE (CONT.)

• Resting state– the axon has a charge– the charge results from the axon membrane

separating positive ions on the outside from negative ions on the inside

SENDING INFORMATION: ACTION POTENTIAL SEQUENCE (CONT.)

• Action potential– tiny electric current that is generated when the

positive sodium ions rush inside the axon– enormous increase of sodium ions inside the axon

causes the inside of the axon to reverse its charge– inside becomes positive and outside becomes

negative

SENDING INFORMATION: ACTION POTENTIAL SEQUENCE (CONT.)

SENDING INFORMATION: NERVE IMPULSE

• Sending information– action potential is a tiny electrical current that is

generated when the positive sodium ions rush inside the axon

– the enormous increase of Na ions inside the axon causes the inside to reverse its charge

– the inside becomes positive & the outside becomes negative

SENDING INFORMATION: NERVE IMPULSE (CONT.)

• All-or-None law– if an action potential starts at the beginning of the

axon, the action potential will continue at the same speed segment to segment to the very end of the axon

• Nerve impulse– nerve impulse is made up of 6 action potentials, with

the first occurring at the beginning of the axon

SENDING INFORMATION: NERVE IMPULSE (CONT.)

TRANSMITTERS

• A transmitter is a chemical messenger that transmits information between nerves and body organs, such as muscles and heart

• Excitatory and Inhibitory– excitatory transmitters

• open chemical locks and turn on neurons– inhibitory transmitters

• block chemical locks and turn off neurons

NEUROTRANSMITTER

• Neurotransmitters– dozens of different chemicals that are made by

neurons and then used for communication between neurons during the performance of mental or physical activities

ALCOHOL

• Alcohol (ethyl alcohol)– A psychoactive drug that is classified as a

depressant, which means that it depresses the activity of the central nervous system

ALCOHOL

WHAT DOES ALCOHOL DO?

• Alcohol affects the brain by imitating a naturally occurring neurotransmitter, GABA

• GABA Neurons– GABA neurons have chemical locks that can be

opened by chemical keys in the form of the neurotransmitter GABA

• GABA Keys– alcohol molecules so closely resemble those of the

GABA neurotransmitter that alcohol can function like GABA keys and open GABA receptors

– when GABA neurons are excited, they decrease neural activity

03p55c.jpg

WHAT DOES ALCOHOL DO? (CONT.)

• many people drink alcohol to feel less anxious and more relaxed

• appears to be a biological link between alcohol and anxiety

• deficiency in a specific brain protein is associated with high anxiety and excessive alcohol use

NEW TRANSMITTERS• Number of well-known neurotransmitters, such as

– Acetylcholine = Aids in memory, learning and cognitive function

– GABA = Regulates impulsivity, inhibition, and anxiety– Norepinephrine = relaxes the body after stress– Epinephrine = prepares emotional & physical arousal to

stress (adrenaline)– Dopamine = allows fluid muscle movement, focus, &

attention– Serotonin = regulates mood, emotion, sleep, and appetite

NEW TRANSMITTERS (CONT.)

• New– Endorphins (1970’s)

• painkiller similar to morphine• decreases effects of pain during great bodily stress

– Anandamide (1990’s)• similar to THC (active ingredient in marijuana)

– involved with» memory» motorcoordination» emotions

NEW TRANSMITTERS (CONT.)

• Anandamide may help people regulate emotions, which would help them to better deal with anxiety and stress

– Nitric oxide (mid-1990’s)• may be involved in regulating aggressive and

impulsive behaviors

REFLEX

• Reflex– unlearned, involuntary reaction to some stimulus– neural connections underlying a reflex are prewired

by genetic instructions

REFLEX (CONT.)

• Reflex sequence– sensors

• sensors trigger neurons that start the withdrawal effect

– afferent neurons• carry information from the senses to the spinal

cord

REFLEX (CONT.)

– Interneuron• relatively short neuron whose primary task

is making connections between other neurons

– Efferent neuron• carry information away from the spinal cord

to produce responses in various muscles and organs throughout the body

REFLEX (CONT.)

PARKINSON’S DISEASE

• Parkinson’s Disease– includes symptoms of tremors and shakes in the

limbs, a slowing of voluntary movements, muscle stiffness, problems with balance and coordination and feelings of depression

– as the disease progresses, patients develop a shuffling walk and may suddenly freeze in space for minutes or hours at a time

– Michael J. Fox

PARKINSON’S DISEASE (CONT.)

• Parkinson’s Disease– it is caused by destruction of neurons that produce

dopamine– L-dopa is a medication that boosts the levels of

dopamine in the brain – eventually the drug causes involuntary jerky

movements – after prolonged use, L-dopa’s beneficial effect may be

replaced by unwanted jerky movements

EXPERIMENTAL TREATMENTS

• Sterotaxic procedure– fixing a patient’s head in a holder and drilling a small

hole through the skull– the holder has a syringe that can be precisely guided

into a predetermined location in the brain & transplant stem cells

EXPERIMENTAL TREATMENTS

EXPERIMENTAL TREATMENTS

EXPERIMENTAL TREATMENTS

• Removing part of the brain– Thalamotomy (Michael J. Fox)

• Brain Stimulation– electrodes placed into thalamus– patient controls amount of stimulus– helps reduce tremors

EXPERIMENTAL TREATMENTS