Neurons and Synapses PDF

NEURONS AND SYNAPSES By: Elida Dominique L. Morona THE NERVOUS SYSTEM: AN OVERVIEW  Central Nervous system Brain and Spinal Cord recieves sensory signals, stores memories, and carries...

NEURONS AND SYNAPSES By: Elida Dominique L. Morona THE NERVOUS SYSTEM: AN OVERVIEW  Central Nervous system Brain and Spinal Cord recieves sensory signals, stores memories, and carries thoughts DIVISIONS OF THE NERVOUS SYSTEM Peripheral Nervous system Nerves, neurons, and sensory organs outside of the CNS send signals to CNS. stimulates effectors PERIPHERAL NERVOUS Somatic Autonomic interacts with external Regulates the body’s SYSTEM (PNS) enviornments internal enviornment. Affarent nerves - Affarent nerves - sensory signals from sensory signals from the senses to the CNS the senses to the CNS Efferent Nerves - Efferent Nerves - Motor signals from the Motor signals from the CNS to the skeletal CNS to the skeletal muscles. muscles. AUTONOMIC NERVOUS Sympathetic SYSTEM (PNS) Fight or Flight response also known as “Adrenergic nervous system” Secretion of Epinephrine through the stimulation of sweat glands aroused body to expend energy Parasympathetic Rest and Digest also known as “Cholinergic nervous system” no effect on sweat glands. calms body to conserve and maintain energy  WHICH OF THE FOLLOWING IS TRUE? 1. the brain and the cranium complete the CNS 2.The brain and the spinal cord comprise the PNS A. 1 ONLY C. BOTH B. 2 ONLY D. NONE  QUESTION 2 You are being chased by a dog, and were able to escape. you were able to reach your home immediately...as you reach your house, what is the response of your body? A. Sympathetic B. Parasympathetic CELLS OF THE NERVOUS SYSTEM Neurons and Glia (Neuroglia) NEURON “Nerve Cell” Basic Building block of the nervous system Cells that are specialized for the reception, conduction 03 - SOCIAL MEDIA and transmission of electrochemical signals 03 - SOCIAL MEDIA Presynaptic Terminal end bulb or bouton CLASSES OF NEURONS NEURON CELL MEMBRANE lipid bilayer some membrane protein serve as a channel protein 03 - SOCIAL and MEDIA some are signal protein NEUROTRANSMITTER NEUROTRANSMITTER A chemical released from a neuron following an action potential. travels across the synapse to excite or inhibit the target neuron. Different types of neurons use different neurotransmitters 03 - SOCIAL MEDIA and therefore have different effects on their targets.  Excitatory CLASSIFICATION OF NEUROTRANSMITTER They increase the likelihood that the neuron will fire an action potential. Inhibitory They decrease the likelihood that the neuron will fire an action potential. TYPES OF NEUROTRANSMITTER TYPES OF NEUROTRANSMITTER TYPES OF NEUROTRANSMITTER  TO BE CONTINUED... ACTION VS RESTING POTENTIAL I GLIAL CELLS ! NERVE CELLS SYNAPSES GLIAL CELLS FORGOTTEN CELLS NEURONS VS Neurons Glial Generate and GLIAL Modulate neuron propagate electrical function and signaling. and chemical signals Has no dendrites and Has dendrites and axons axons smaller than neurons bigger than Glial cells ARE THERE MORE GLIAL CELLS THAN NEURONS? TYPES OF GLIAL CELLS astrocytes, oligodendrocytes, microglia ASTROCYTE Largest Glial cell means “star cell” provide physical support to neurons and clean up debris within the brain by producing and releasing chemicals. involve in providing nourishment to neurons regulate synaptic release of neurotransmitter and reuptake and inactivation of neurotransmitter (e.g., GABA and Glutamate) OLIGODENDROCYTES provide support to axons and produce myelin sheath (80% lipids and 20% protein) in CNS Bare axon - Node of Ranvier SCHWANN CELLS perform as similar function as oligodendrocytes in the PNS 1 =1 ratio as oppose to 1 = many of oligodendrocytes Only one who can guide axonal regenration (regrowth) MICROGLIA smallest of the glial cells respond to injury or disease by by multiplying, engulfing cellular debris, or even an entire cell (scavenger cell) responsible for the inflammatory reaction NERVE IMPULSE membrane potential and resting potential, MEMBRANE POTENTIAL Difference in electrical charge between the inside and the outside of a cell Action potential - -When a neuron sends a signal down it's axon to communicate with another neuron (-65 mV Threshold) -”All or nothing law/response” Resting potential - amount of power that is available to a cell to maintain its homeostatic state (-70 millivolts (mV) as the resting potential) hence, polarized SODIUM POTASSIUM PUMP IONIC BASIS OF THE RESTING Potential positively and negatively charged ions and ions can pass through ion channels electro static pressure and concentration gradient GENERATION AND Conduction of Postsynaptic Potentials GENERATION AND Conduction of Postsynaptic Potentials Excitatory postsynaptic potential (EPSPs)- Sodium channels open - Depolarization Inhibitory postsynaptic potential (IPSPs) - Chloride/ Potassium channels open - Hyperpolarization STAGES OF ACTION POTENTIAL ACTION POTENTIAL Threshold of excitation is usually about -65 mV Action potential (AP) as a massive but momentary reversal of the membrane potential from about-70 to about +50 MV All or none response/law Two types of summation: spatial and temporal. CONDUCTION OF ACTION POTENTIALS Voltage-activated ion channels open or close in response to changes in the level of the membrane potential STAGES OF ACTION POTENTIALS Depolarization “upswing” Positively charged sodium ions rush into a nerve cell Sodium channels open the membrane of the stimulated cell reverses its polarity so that the outside of the membrane is negative relative to the inside STAGES OF ACTION POTENTIALS Repolarization “Downswing” – once reached threshold Sodium ion channels close and potassium ion channels open restore the localized negative membrane potential of the cell, bringing it back to its normal voltage. STAGES OF ACTION POTENTIALS Refractory Phase The neuron cannot reach action potential during this “rest period.” The sodium-potassium pump returns sodium ions to the outside and potassium ions to the inside. Absolute vs relative refractory period. Depends on two things: The sodium channels are closed, and potassium is flowing out of the cell at a faster than-usual rate. AXONAL CONDUCTION OF ACTION POTENTIALS Nondecremental Slower conduction than postsynaptic potentials Antidromic conduction vs Orthodromic conduction CONDUCTION IN MYELINATED AXONS Ions can pass through the axonal membrane only at the nodes of Ranvier Rapid and decremental Saltatory conduction - “to leap” SYNAPTIC TRANSMISSION Chemical Transmissions of Signals Among Neurons STRUCTURE OF SYNAPSES Axodendritic synapse - Axon to dendrite Axosomatic synapse - Axon to Soma Axoaxonic synapse - Axon to axon ------------------------ Directed vs non directed synapse  HOW DO NEUROTRANSMITTERS TRAVEL? SYNTHESIS, PACKAGING, AND TRANSPORT OF NEUROTRANSMITTER MOLECULES several types of neurotransmitters large neurotransmitters are all neuropeptides (small chains of amino acids that are synthesized and released by neurons.) Co-existence in many neurons SYNTHESIS, PACKAGING, AND TRANSPORT OF NEUROTRANSMITTER MOLECULES Storage of Transmitters - The presynaptic terminal stores high concentrations of neurotransmitter molecules in vesicles. RELEASE OF NEUROTRANSMITTER MOLECULES Exocytosis bursts of release of neurotransmitter from the presynaptic neuron. ACTIVATION OF RECEPTORS BY NEUROTRANSMITTER MOLECULES neurotransmitters bind to receptors in the postsynaptic membrane (Ligand) ionotropic receptors - ligand-gated ion channels (Glutamate and GABA) metabotropic receptors - require G proteins and second messengers to indirectly modulate ionic activity in neurons Ionotropic synapse VS Metabotropic synapse REUPTAKE, ENZYMATIC DEGRADATION, AND RECYCLING message terminating system enzymatic degradation in the process of reuptake, excess neurotransmitters are returned to the presynaptic neuron. THANK YOU