Physiological Psychology Chapter 2 PDF

Two types of cells in the NS 1) Neurons 2) Supporting cells CHAPTER 2 CELLS OF THE NERVOUS SYSTEM 1) The Neuron The st...

Two types of cells in the NS 1) Neurons 2) Supporting cells CHAPTER 2 CELLS OF THE NERVOUS SYSTEM 1) The Neuron The structures of a neuron The neuron (nerve cell) is the information‐ processing and information‐transmitting Soma/cell body: Dendrites: tree branch like, receive message Axon: long slender like; carries/sends message Terminal Buttons: little knobs or buds; contain neurotransmitters 1  Internal structures of a neuron Internal structures of a neuron Membrane: defines the boundary of the cell Cytoplasm: jellylike substance that fills the inside of the cell Mitochondria: extract energy from nutrients; produce ATP Nucleus: central structure of cells; contains chromosomes Types of neurons ‐ functionally Types of neurons‐ physical structure Sensory neurons – carry messages from sense Unipolar neuron: one receptors to the brain or spinal cord axon attached to soma Motor Neurons – carry messages from the & divides into receiving brain or spinal cord to muscles and organs & sending parts. Interneurons –They transmit information between sensory neurons and motor Neurons. Found in CNS 2  Multipolar neurons: the soma gives rise to one axon and to the trunks of many dendritic trees. Found in CNS Bipolar neurons: give rise to one axon and one dendritic tree, at opposite ends of the soma. Supporting cells /glial cells/neuroglia Astrocyte (Astroglia): physical support, provide nutrients, clean up brain debris Microglia: protect from harmful microorganisms Oligodendroglia: provide myelin sheath in CNS Schwann Cells: provide myelin sheath in PNS Satellite Cells: physical support in PNS 3 Blood‐brain barrier (BBB)‐ a semipermeable barrier b/n blood and brain produced by the cells in the walls of the brain’s capillaries Neural Communication 4  Neural Communication Neural Communication A)Activity with in neuron A) Activity with in neuron neuron as a tiny battery B)Activity between neurons The electric signals of neurons arise from the (synaptic communication) movement of charges – in the form of ions across the membrane. The charged molecules (ions) are found in the intracellular and extracellular fluid. But, their concentration in the intracellular and extracellular fluid is different This difference in the concentration of the ions across the cell membrane creates an electrical charge Membrane Potential 5  Resting Membrane potential Neurons have a selectively permeable membrane During resting conditions membrane is: – permeable to potassium (K+) (channels are open) – impermeable to sodium (Na+) (channels are closed) Diffusion force pushes K+ out (concentration gradient) This creates a positively charged extra‐cellular space. Electrostatic force pushes K+ in sodium‐potassium pumps /transporters embeded in the membrane exchange Na+ for K+, pushing three sodium ions out for every two potassium ions they push in Thus, there is a ‘dynamic equilibrium’ with zero net movement of ions. The resting membrane potential is negative (‐ 70mv) Steps during AP Action Potential – 1: stimulus depolarizes the inside of neuron to threshold potential level Action potential: The brief electrical impulse – 2: Na+ channels open, Na+ diffuses in that provides the basis for conduction of Polarity briefly reversed, to +40 mV information along an axon. – 3: Na+ channels close – 3: K+ channels open, K+ diffuses out, Potential returns to During AP, a brief reversal of the electrical zero charge difference occurs b/n the inside and – 4: All channels closed, Na‐K pump moves Na+ back out & K+ back in outside of cell. – Hyperpolarization – Resting potential restored 6  Voltage‐dependent ion channel: An ion channel that opens or closes according to the value of the membrane potential. Threshold of excitation: The value of the membrane potential that must be reached to produce an action potential. Depolarization: Reduction (toward zero) of the membrane potential of a cell from its normal resting potential and result from opening of Na+ channels. Refractory periods: There are two types of Characteristics of AP refractory period: Absolute Refractory Period – Na+ channels are All‐or‐none law: The principle that once an inactivated and no matter what stimulus is action potential is triggered in an axon, it is applied they will not re‐open to allow Na+ in & propagated without decrement to the end of depolarise the membrane to the threshold of an the fiber. action potential. Rate law: The principle that variations in the Relative Refractory Period ‐ Some of the Na+ intensity of a stimulus or other information channels have re‐opened but the threshold is being transmitted in an axon are represented higher than normal making it more difficult for by variations in the rate at which that axon the activated Na+ channels to raise the fires. membrane potential to the threshold of excitation. 7  Conduction of AP Synaptic Transmission ‐ Communication Between Neurons Two types of conduction Synapse is the physical gap between pre‐ and 1_The passive conduction of electrical current, post‐synaptic membranes. The gap is also in a decremental fashion, down the length of an known as synaptic clef, and it is filled by axon. extracellular fluids 2_Saltatory conduction; Conduction of action Presynaptic cell‐ message sending neuron potentials by myelinated axons. The action Presynaptic membrane is typically an axon potential appears to jump from one node of terminal Ranvier to the next. The axon terminal contains synaptic vesicles (round objects) that contain neurotransmitter Postsynaptic membrane can be: – A dendrite (axodendritic synapse) – A cell body (axosomatic synapse) – Another axon (axoaxonic synapse) Postsynaptic thickening/density contains receptors for transmitters 8  Chemical Events at the Synapse The major sequence of events allowing communication between neurons across the synapse: 1. The neuron synthesizes chemicals that serve as neurotransmitters. 2. Neurons store neurotransmitters in axon terminals or transport them there. 3. An action potential triggers the release of neurotransmitters into the synaptic cleft. 2 types of receptors 1) An ionotropic receptor‐ refers to when a 4. The neurotransmitters travel across the cleft and attach to receptors on the postsynaptic neurotransmitter attaches to receptors and neuron. immediately opens ion channels. 5. The neurotransmitters separate from the receptors. Most effects occur very quickly and are very 6. The neurotransmitters are taken back into short lasting. the presynaptic neuron, diffuse away, or are inactivated by chemicals. Most ionotropic effects rely on glutamate or 7. The postsynaptic cell may send negative GABA. feedback to slow the release of further neurotransmitters. 9 2) Metabotropic receptor‐ when Excitatory postsynaptic potential (EPSP) is a graded potential that decays over time and space. neurotransmitters attach to a receptor and The cumulative effect of EPSPs are the basis for initiates a sequence of slower and longer lasting temporal and spatial summation. metabolic reactions. inhibitory postsynaptic potential or the temporary G protein activation – second mesenger hyperpolarization of a membrane. production ‐ The second messenger An ISPS occurs when synaptic input selectively opens communicates to areas within the cell. the gates for positively charged potassium ions to leave the cell or negatively charged chloride ions to enter the – May open or close ion channels, alter production cells. of activating proteins, or activate chromosomes. Serves as an active “brake”, that suppresses excitation. Neural Integration spatial summation ‐ synaptic input from several locations can have a cumulative effect and trigger a nerve impulse. temporal summation ‐ repeated stimuli can have a cumulative effect and can produce a nerve impulse when a single stimuli is too weak. 10  Drug effects on synapses Psychopharmacology – major concepts – Pharmacokinetics – Routes of administration – Drug effectiveness – Drug response curve – Therapeutic index – Drug tolerance & sensitization – Withdrawal symptom – Placebo effect Sites of drug action Production of NTs, storage of NTs EFFECTS OF DRUGS Release of NTs – AGONIST Effects on receptors – ANTAGONIST – Direct agonist – Indirect agonist – Direct antagonist – Indirect antagonist Reuptake or deactivation of NTs 11  Neurotransmitter Function Effects of Deficit Effects of surplus Excitatory: It produces Paralysis; muscle contractions and is A factor associated with Violent muscle Acetylcholine found in the motor neurons; Alzheimer’s disease: levels of contractions (ACh) in the hippocampus, it is acetylcholine are severely involved in memory reduced associated with formation, learning and memory general intellectual function. impairment. Excitatory: involved in Muscle rigidity; One factor associated voluntary muscle A factor associated with with schizophrenia‐like Dopamine movements, attention, Parkinson’s disease: symptoms such as learning, memory, and degeneration of neurons in the hallucinations and emotional arousal and substantia nigra that produce perceptual disorders, rewarding sensations dopamine. addiction Inhibitory or excitatory: Anxiety, mood disorders, involved in mood, sexual insomnia; Autism Serotonin behavior, pain perception, One factor associated with sleep, eating behavior, obsessive‐compulsive disorder maintaining a normal body and depression temperature and hormonal state Inhibitory: regulates pain Endorphins perception and involved in Body experiences pain Body may not give sexuality, pregnancy, labor, adequate and positive emotions warning about pain associated with aerobic exercise—the brains natural opiates. Neurotransm Drugs and their effects Stimulants itters Nicotine: increases the release of acetycholine Curare: blocks the receptor sites of acetycholine Caffeine – Adenosine ANT Acetylcholine Botulin: poisons found in improperly canned food, blocks the release of acetylcholine resulting in paralysis of the muscles Nicotine – Acetylcholine AGO Nerve gas: continual release of acetylcholine Scopolamine: blocks ACh receptors and impairs learning and even at low doses causes drowsiness, amnesia and confusion Cocaine – Dopamine, Noradrenaline AGO Dopamine L‐dopa: converts into dopamine in the brain Pheneothaizine: reduces dopamine in the brain Amphetamines ‐ Dopamine, Noradrenaline AGO Amphetamines: Increases dopamine and norepinehrine, and to some extent serotonin and activates the sympathetic nervous system. Chat – Epinephrine, Nor epinephrine AGO LSD: Impairs the reuptake of serotonin, making more serotonin available. Prozac: Prevents the reuptake of serotonin, making more serotonin available Serotonin MDMA (ecstasy): Destroys serotonin nerve cells in animals with moderate and large doses. Cocaine: Affects norepinephrine and serotonin, and prevents the reuptake of dopamine in the synapse and activate the sympathetic nervous system. Endorphins Opiates: Increases the production of endorphins Naloxone: blocks endorphin receptor sites Caffeine: Reduces the ability of the brain to produce adenosine, the “brakes” of the brain and CNS. Doses of 700 mg can contribute to panic attacks (200 mg is two strong cups of coffee Mountain 12  Depressants Opiates Alcohol– GABA AGO Heroin– Endorphines AGO Barbiturates– GABA AGO Morphine– Endorphines AGO Benzodiazepines– GABA AGO Hallucinogens LSD– Noradrenaline AGO Marijuana– Amandamide AGO 13