NEURON AND NEURAL TRAMSMISSION: ANATOMY OF A NEURON
NEURON AND NEURAL TRAMSMISSION: MICROSCOPIC VIEW OF NEURONS A photograph taken through a light microscope (500x) of neurons in the spinal cord.
NEURON AND NEURAL TRAMSMISSION: RESTING POTENTIAL When a neuron is at rest, the inside of the neuron has a slight negative electrical charge compared to the outside.
NEURON AND NEURAL TRAMSMISSION: ACTION POTENTIAL When a neuron is stimulated, more positively charged particles (sodium ions) flow into the cell, making the inside suddenly positive compared to the outside of the cell. This sudden reversal of the electrical charge is called the action potential.
NEURON AND NEURAL TRAMSMISSION: RESTING POTENTIAL AND ACTION POTENTIAL
NEURON AND NEURAL TRAMSMISSION: BIOCHEMICAL BASIS OF THE ACTION POTENTIAL (a) An action potential occurs when sodium gates in the membrane of a neuron open, permitting sodium ions to flow into the axon (blue arrows). (b) After an action potential occurs, the sodium gates close at that point, but similar gates open at the next point along the axon, allowing the action potential to flow along the axon. (3) In the wake of the action potential, potassium gates open to let positively charged potassium ions flow outward (purple arrows), thus reestablishing a negative charge inside.
NEURON AND NEURAL TRAMSMISSION: THE SYNAPSE (1)Release: When action potential reaches the axon terminal, neurotransmitter molecules stored in synaptic vesicles will be released into synaptic cleft. (2) Binding: Some neurotransmitter molecules will then bind with the matching receptor sites on the next neuron. (3) Inactivation or Clearing- Out : Neurotransmitter molecules will be removed from the receptor site after binding.
NEURON AND NEURAL TRAMSMISSION: THE SYNAPSE (SLIDE 2) INACTIVATION OR CLEARING-OUT OF NEUROTRANSMITTERS After the binding at the receptor sites, neurotransmitter molecules will be removed from the receptor sites in one of the three ways: Some neurotransmitters will be destroyed by the enzymes in the synaptic cleft. Some neurotransmitters will be broken down into its component molecules which will be reclaimed by the axon terminal. Some neurotransmitters will be reabsorbed by the axon terminal as a whole, a process called reuptake.
Afferent or Sensory Neurons: relay messages from the sensory organs and receptors (eyes, ear, nose, skin, etc.) to the brain and spinal cord. Interneurons or Association Neurons: carry information between neurons (most in the central nervous system) Efferent or Motor Neurons: convey signals from the central nervous system to the muscles and glands.
ACTION POTENTIAL: THE ALL-OR-NONE LAW The All-or-None Law: A single neuron is either fires or does not fire. If fires, it always fires at full speed and intensity. Strength of a message is determined by: the number of neurons firing the rate of firing (number of times per second)
GLIAL CELLS: The Neurons Helper Cells Glial cells are specialized cells found throughout the nervous system that provide structural support and insulation for neurons. Glial ( glue ) cells hold the nervous system together. They are smaller than neurons but outnumber neurons about nine to one. They guide the formation of the nervous system during the prenatal development. They provide nutritional and housekeeping functions for neurons. They are involved in the formation of the myelin sheath.
NEUROTRANSMITTERS: TYPES THREE TYPES OF NEUROTRANSMITTERS: EXCITATORY: influence neurons to fire. INHIBITORY: affect neurons not to fire. EXCITATORY OR INHIBITORY: depend on the receptors.
NEUROTRANSMITTERS: EXAMPLES SOME KNOWN NEUROTRANSMITTERS: Acetylcholine (Ach) Dopamine (DA) Serotonin Norepinephrine (NE) Gammaaminobutyric acid (GABA) Endorphins
ACETYLCHOLINE Acetylcholine (Ach) contributes to movement, learning, memory precsses, and REM sleep. It is the only transmitter between motor neurons and voluntary muscles. Excess: Muscle paralysis or convulsions, sometimes death. Deficit: Memory impairment, Alzheimer s disease.
DOPAMINE Dopamine (DA) is used by neurons that control voluntary movements. It is also used by neurons that are important for learning, attention, thought and emotion. Excess: Schizophrenia (irrational thought, delusion, and/or hallucinations) Deficit: Parkinson s disease (tremors, muscular rigidity)
DOPAMINE HYPOTHESIS FOR SCHIZOPHRENIA
SEROTONIN AND NOREPINEPHRINE Serotonin plays a prominent role in the regulation of mood, sleep, impulsivity, aggression and appetite. Norepinephrine plays a role in eating, sleep, and mood. Lower level of activity in serotonin and norepinephrine is related to depression. Deficit in serotonin may lead to increased aggressive behavior and suicide. Some antidepressant drugs act to block the reuptake of serotonin or norepinephrine.
GABA gamma-aminobutyric acid GABA appears to have inhibitory effects at synapses. It contributes to the regulation of anxiety in humans. Lower levels of activity in GABA activity is related to anxiety. Antianxiety drugs (tranquilizers such as Valium) facilitate GABA synapses and thereby reduce anxiety. An abnormality in GABA neurons may cause epilepsy.
ENDORPHINS Endorphins ( endogenous morphine ) are opiatelike substances produced in the human body itself. They provide relief from pain and produce feelings of pleasure and well-being. Drugs such as opium, morphine, and heroin bind with the receptors for endorphins. Endorphins may explain the runner s high experienced by long-distance ruunners.
Psychoactive drugs work on the nervous system in following ways: Some affect the release of neurotransmitters: Amphetamines ( Speed ) increase the release of dopamine, norepinephrine, and perhaps serotonin. Some bind with the receptor sites (acting like pretenders ): The opiates (opium, morphine, and heroin) bind with endorphins receptors. Tranquilizers such as Valium bind with GABA receptors. LSD binds to a specific subtype of serotonin receptor. Marijuana (THC) attaches to anandamide receptors. Some block out the receptor sites to make them ineffective: Antipsychotic drugs used to treat schizophrenis block out dopamine receptors. Some disrupt the reuptake or clearing process: Cocaine and Amphetamine slow the reuptake of dopamine and created norepinephrine. by Dr. Joanne Hsu