Anatomy of the Central Nervous System New technology and advances in science have led to a better understanding of the relationship of the brain, biological basis of behavior, and mental disorders

Student Objective I can identify parts and functions of the Central Nervous System (CNS)

Cells of the Nervous System The cells are known as Neurons. – Neurons- the basic building block of the nervous system that specialize in transmitting information throughout the body Unusual shape Nerve fibers extend from body cell (soma) – Dendrites- branched fibers that receive neural impulses – Axons- transmits neural messages from cell body towards another neuron

Two principal divisions of the nervous system Central Nervous System (CNS) Peripheral Nervous System (PNS)

Central Nervous System (CNS) – Brain and spinal cord Serve as control center for entire organism Integrated incoming information and determines appropriate responses

Peripheral Nervous System – Made up of nerves outside of CNS Acts a communication lines to and from CNS – Made up of sense organs- eyes, ears, taste buds, olfactory receptors, and touch receptors

Mental Health Link Understanding of mental disorders most often involves understanding the structure and function of the CNS

The Brain Part II Neurophysiology-Chemical Events at the Synapse Each structure and each chemical produced and used by the brain has a specific function. Disease may cause alteration in the function of the brain. An understanding of the chemical events occurring at the synapse is fundamental to biological psychology. Objective: – Student will identify the neurotransmitters and name disorders that can result when there is neurotransmitter dysfunction.

Neurons Nerve cells that make up the brain and peripheral nerves – Communicate with each other at the synapses Synapse is a functional (not physical) contact between to neurons About 100 billion neurons in human brain – Each neuron has about 10,00 synaptic contacts with other neurons.

Parts of a Neuron Cell body or soma – Contains the nucleus of the cell (DNA) – Soma constitutes “receiving” surface of the neuron – If the soma is damages, a neuron will not recover

Parts of a Neuron Dendrite – Multiple branches come off the coma – Branches receive nerve impulses from other neurons – Dendrite branching is influences by environment during development, both pre and post natal The more branches, the more receiving sites for a neuron Dendrites are few and sparsely branched in certain conditions such as Downs Syndrome and Fetal Alcohol Syndrome Lab animals who have received stimulations as infants shoe more dendritic branching

Axon Single fiber that is thicker and longer than dendrites Axon may have many branches at it end Axons may be very short (1 micron) to very long (1 meter) depending on their destinations in the nervous system Damaged neurons may show sprouting of new terminals to fill in spaces vacated by damaged axons Mature neurons may not have an axon Axon terminals in brain may be represented by these organizations

Myelin Sheath The lipid and protein sheath surrounding the axon Purpose to insulate neuron The more heavily mylinated the neuron the faster the electrical pulse can travel down the axon to other neurons Multiple Sclerosis (MS) condition where the myelin of the brain and spinal cord degenerate – Nerve impulses unable to travel smoothly and efficiently

The Synapse A dynamic region between neurons consisting of: – Axon terminal (carries electrical impulses away from soma) – Synaptic cleft (a space between terminal axon and receiving neuron) – Dendrite (or adjacent neuron body) REMEMBER that both SOMA and DENDRITES constitutes the RECEIVING surface of a neuron – Synapse Graphic Synapse Graphic

Neurotransmitters: The Chemical Messengers Chemicals (hormones) that are made in soma and stored in small synaptic vesicles (“packages”) at the tip of the axon As electrical pulses travel from soma to axon, neurotransmitters are released into synapse Neurotransmitters stick to receptors proteins in neighboring dendrite and trigger nerve impulse that travel down dendrite, across soma, down axon, etc. Our behavior is consequence of millions of cells “talking” to each other via these electrochemical processes Neurotransmitter Graphic

Inactivation of Neurotransmitters The action of neurotransmitters can be stopped by four different mechanisms: – Diffusion: the neurotransmitter drifts away, out of the synaptic cleft where it can no longer act on a receptor. – Enzymatic degradation (deactivation): a specific enzyme changes the structure of the neurotransmitter so it is not recognized by the receptor. For example, acetylcholinesterase is the enzyme that breaks acetylcholine into choline and acetate. Neurotransmitter Graphic

Inactivation of Neurotransmitters – Glial cells: astrocytes remove neurotransmitters from the synaptic cleft – Reuptake: the whole neurotransmitter molecule is taken back into the axon terminal that released it. This is a common way the action of norepinephrine, dopamine and serotonin is stopped...these neurotransmitters are removed from the synaptic cleft so they cannot bind to receptors

Some of the Well Known Neurotransmitters Acetylcholine (Ach) Dopamine (DA) Serotonin and Norepinephrine Gamma Aminobutyric Acid (GABA)\ Endorphines (“endegenous morphine)

IFA What is the synapse composed of?

Acetylcholine (Ach) Contributes to movement, learning, memory processes and REM sleep Only transmitter between motor neurons and voluntary muscles EXCESS: muscle paralysis or convulsions, sometimes death DEFICIT: memory impairment (Alzheimer’s disease)

Dopamine (DA) Used by neurons control voluntary movement Also used by neurons that are important for learning, attention, thought, and emotion EXCESS: irrational thought, delusion, and/or hallucinations (Schizophrenia) DEFICIT: tremors, muscular rigidity (Parkinson’s disease)

Serotonin and Norepinephrine Serotonin play prominent role in regulation of mood, sleep impulsivity, aggression, and appetite. Norepinephrine plays role in eating, sleep, and mood Lower level of activity in serotonin and norephinephrine is related to depression DEFICIT serotonin: may lead to increased aggressive behavior and suicide Some antidepressants drugs act to block reuptake of serotonin or norepinephrine

Gamma-Aminobutyric Acid (GABA) – i. Appears to have inhibitory effects at synapses – ii. contributes to regulation of anxiety – iii. lower levels of activity related to anxiety – iv. antianxiety drugs (tranquilizers such as Valium) facilitate GABA synapses and thereby reduce anxiety – v. abnormality in GABA neurons may cause epilepsy

Endorphins (“endogenous morphine”) – opiate-like substances produced in the body – provide relief from pain and produce feelings of pleasure and well-being – drugs such as opium, morphine, and heroin bind with receptors for endorphins – endorphins may explain “runners-high” experienced by long-distance runners