Neurophysiology Summer 2023 Past Paper PDF

The Nervous System Neurophysiology VP Summer 2023 Clara Camargo, DVM Neurophysiology Study Guide The Nervous System 1. Explain: a) The difference between the Central Nervous System and the Peripheral Nervous System b) The difference between a neuron and a neuroglial cell c) The components of th...

The Nervous System Neurophysiology VP Summer 2023 Clara Camargo, DVM Neurophysiology Study Guide The Nervous System 1. Explain: a) The difference between the Central Nervous System and the Peripheral Nervous System b) The difference between a neuron and a neuroglial cell c) The components of the neuron and their function 2. What are the classifications of neurons as described functionally? 3. Explain the different types of neurons and their location in the body 4. What is myelin and where does myelin originate? 5. Explain the correlation between an unmyelinated cell vs myelinated cell 6. Explain the function of the nodes of Ranvier and saltatory conduction 7. Explain resting membrane potential? What are the major factors of RMP? 8. Explain action potential? 9. List the components to the Action Potential Graph and the Ions impacting each stage 10. Explain EPSP or IPSP and how does this influence membrane potential changes? 11. How is Calcium involved with the synapse as the action potential travels down the axon? 12. List 6 major classes of Neurotransmitters The Mammalian Nervous System The Nervous System 2 major subdivisions: CENTRAL NERVOUS SYSTEM PERIPHERAL NERVOUS SYSTEM Lateral views of several vertebrate brains showing evolutionary relationships. (Copyright © McGraw Hill). The Nervous System 2 Categories of Cells in the Nervous System Neurons (Greek neuron=nerve)  MAJOR Functional Units of the Nervous System  Electrically excitable (action potential)  Specialized in information processing  Do not divide once they reach maturity  Injury leading to neuronal death will permanently change the structure & functions of the affected areas Neuroglia/ glial cells (Greek glia= glue)  The Helper Cells, The Support System  Involved in the nutrition & maintenance of the nerve cells  Astrocytes, Oligodendrocytes, Schwann cells The Nervous System NEURON COMPOSITION The Nervous System • DENDRITES – information- receiving area of the cell membrane, detect stimuli • CELL BODY, SOMA or PERIKARYON – contains organelles • AXON HILLOCK or TRIGGER ZONE – axon origin; originates Action Potential (AP) • AXON – information-carrying extension of the cell membrane • PRESYNAPTIC TERMINAL – end of axon; transmit information (neurotransmiters) • MYELIN SHEATH – enhances speed of information transfer • NODE OF RANVIER – gaps in the insulating myelin sheath AXON HILLOCK The Nervous System Parts of a Neuron. The axon neuron is wrapped by Schwann cells, which form a myelin sheath. NEURONS-classified according to their function SENSORY or AFFERENT • Send (INPUT) information from receptors towards the brain/spinal cord • Somatic (skin or skeletal muscles) and visceral (internal organs) INTERNEURONS or ASSOCIATION NEURONS • Found in the brain/spinal cord, connecting motor & sensory neurons MOTOR or EFFERENT • Send information from the brain/spinal cord to muscle/glands (effectors, command) • Somatic (voluntary) and autonomic (involuntary) The Nervous System The Nervous System The Nervous System NEURONS-classified according to their structure The Nervous System https://www.interactive-biology.com/3247/the-neuron-external-structure-and-classification/#peusdounipolar Bipolar Neuron  Have 2 processes that connect to the cell body • 1 axon & 1 dendrite • Found in specific areas of the nervous system (retina and nose - olfactory epithelium)  INTERNEURONS The Nervous System The Nervous System Pseudounipolar Neurons  1 single stem axonal process that branches to form 2 processes • Peripheral and central NS (sensory ganglia and cranial nerves) • Do not have dendrites, axonal processes will receive and transmit information  SENSORY NEURONS • Send information from receptors in sensory organs towards the brain/spinal cord Multipolar Neuron o 1 axon & many dendrites o Most common type o Found throughout the body MOTOR NEURONS & INTERNEURONS Send information from the brain/spinal cord to muscle/glands. The Nervous System THE NEURON Dendrites: receive signals from presynaptic terminals of other neurons Cell body: contains organelles such as: • Nucleus • Free ribosomes • Rough Endoplasmic Reticulum (rER) • Golgi apparatus • Mitochondria  these are contained everywhere in neurons in large quantities as nerve cells require large amounts of ATP Axon hillock and Initial axon segment: • Integrates different signals (often opposing each other) & • Generates and shape the AP before it is propagated along the axon Axon: can be very long, is the conducting unit, adult axons often don’t contain ribosomes and depend on proteins from cell body. Presynaptic Terminals: signaling to adjacent cells The Nervous System The Nervous System NEURON AND SYNAPSE Neurons communicate via Synapses • Greek Synapsis = connection • Specialized contact areas with other neurons, muscle fibers or glands • Synapses are formed by:  The presynaptic terminal of one cell  The receptive surface of the adjacent cell (post synaptic cell)  Synaptic Cleft ( space b/t the 2 cells)  Action potentials travel along the axon  Speed varies from 0.5 to 120 meters per second  Larger axons are myelinated  Smaller ones (< 1 μm in diameter) are not myelinated Electrical activity of neurons https://media.hhmi.org/biointeractive/click/Neuron_Activity/01-vid.html Myelin Sheath The myelin sheath is a greatly modified plasma membrane  Wrapped around the axon in a spiral fashion  Originate from and are part of the: • Schwann cells in PNS • Oligodendrocytes in the CNS  Each myelin-generating cell furnishes myelin for only one segment of the axon  The periodic interruptions are the NODES OF RANVIER • Critical to the functioning of myelin The Nervous System The Nervous System Schwann cell Schwann cell cytoplasm forms a ring inside and outside of the sheath NEURON AND SYNAPSE The Nervous System The Myelin Sheath Facilitates  Conduction  “Electrical Insulation”  Saltatory Conduction of the impulse • Latin Saltare = to “Jump” • Action Potentials “jumps” from node to node • Depolarization occurs more rapidly in myelinated axons MYELIN & CONDUCTION VELOCITY The Nervous System Conduction velocity in myelinated fibers is proportional to the diameter of the fiber  Larger the axon, longer the internode, faster the conduction velocities (up to 150m/s) Unmyelinated fibers conduction is proportional to the square root of the diameter (0.5 to 10m/s) Myelin facilitates conduction while conserving space & energy THE NEURON INFORMATION CONDUCTION Dendrites: receive signals from presynaptic terminals of other neurons Dendritic spines: small protrusions of the dendritic membrane, they greatly increase the receptive surface of the postsynaptic cell  Contain specialized receptors to recognize the chemical transmitters released from the presynaptic terminal The Nervous System NEURAL COMMUNICATION AND SIGNALING 1. Receptors (usually dendritic) receive neurochemical signals from presynaptic terminals of many other neurons 2. Receptors convert neurochemical signals into small voltage changes 3. All different signals are integrated at axon hillock initial axon segment (IPSPs and EPSPs) 4. Depending on results of this integration, an action potential AP may be generated 5. AP travels rapidly along axon, to the presynaptic terminals and causes release of chemical neurotransmitters onto another neuron or muscle cell The Nervous System RESTING MEMBRANE POTENTIAL The Nervous System The resting membrane potential is determined by the uneven distribution of ions (charged particles) between the inside & the outside of the cell and by the different permeability of the membrane to different types of ions. → Especially sodium (Na⁺) and potassium (K⁺) Although net concentration of + and - charges is similar in both intraand extracellular fluids: • Excess positive charges accumulates just outside the cell membrane, & excess of negative charges immediately inside the cell membrane • This makes the inside of cell (-) charged compared to outside of cell • This electrical difference (voltage) across membrane: varies with cells, in mammalian neurons: ~ -70mV (average) THE ACTION POTENTIAL The Nervous System Resting membrane potential Neurons (as all cells) have an electrical potential (voltage) across their cell membrane Electrical membrane potential of neurons and muscle cells is special: its magnitude and sign can be changed in response to: • Synaptic signaling from other cells • Transduction of environmental energy (sensory organs) When change in membrane potential (neuron/muscle cells) reaches a threshold value, this causes a dramatic change in the membrane potential:  an ACTION POTENTIAL (AP) Neuron resting potential https://youtu.be/YP_P6bYvEjE RESTING MEMBRANE POTENTIAL Resting membrane potential is a result of 3 major factors: 1. The concentration of ions on the inside and outside of the cell. An ion species will move toward a dynamic equilibrium if it can flow across the membrane. • the concentration difference across the membrane creates a chemical driving force, creating an electrical driving force leading to a charge imbalance across membrane = voltage This is called the equilibrium potential for that ion. Ions always flow towards it! 2. Na+, K+ pump (ATPase): this energy-dependent pump in cell membranes pumps Na+ ions out of the cell and draws K+ ions into the cell against their concentration gradients, 3 Na+ ions out for each 2 K+ ions in 3. Differential permeability of the membrane to diffusion of ions: the resting membrane is much more permeable to K + than to Na+ ions because it has many more K+ leak channels than Na+ leak channels The Nervous System MEMBRANE POTENTIAL CHANGES Resting membrane potential can be changed by synaptic signals • neurons and muscle cells are unique, their membrane potential can be changed by a synaptic signal from another cell • Neurotransmitters (released from presynaptic axon terminal) bind to receptors on postsynaptic membrane:  open or close ion selective channels and change the membrane potential of the postsynaptic cell  Can change it in 2 ways: make more negative (–) or more positive (+)  This depends on which receptors are activated  Creating postsynaptic potential The Nervous System MEMBRANE POTENTIAL CHANGES • If postsynaptic potential: more positive than RP (-70 mV) → excitatory postsynaptic potential (EPSP) → increases the chances for reaching the threshold and triggering an AP • Depolarization (more positive), caused by: Na+ channels open, Na+ ions flow inside the cell • Chemical transmitter is quickly removed from synapse: change only lasts milliseconds as channels close again The Nervous System • If postsynaptic potential more negative than RP (-90mV) → inhibitory postsynaptic potential (IPSP) → decreases the chance for triggering an AP • Hyperpolarization (more negative), caused by: opening of K+ channels, K+ ions move out ACTION POTENTIALS: The Nervous System • APs begin at the axon’s initial segment (hillock or trigger zone) and spread down the entire length of the axon • They result from the integration of the various EPSPs and IPSPs that the postsynaptic cell receives • If membrane potential becomes positive enough to reach threshold potential: AP is triggered • APs are the result of sequential opening and closing of voltage-gated ion channels: First to Na+, then to K+ • Triggering an AP causes explosive changes in membrane potential: 1. Depolarization: Na+ channels open: Na+ flows in 2. Repolarization: Na+ channels close, K+ channels open: K+ flows out 3. Hyperpolarization: K+ flows out through leak channels as well as voltage-gated channels 4. Return to resting potential as voltage-gated K+ channels gradually close Membrane Potential Changes & Ion Movements during an Action Potential The Nervous System The Nervous System ACTION POTENTIALS • APs propagate from their origin down the axon • Positive charges passively spread to adjacent resting segments of the membrane and trigger an action potential there • In this way, the AP spreads from the axon’s initial segment down to the presynaptic terminal at the axon’s far end ACTION POTENTIALS - CONDUCTION VELOCITY • The speed of AP conduction varies → diameter of axon and degree of myelination • In smaller, unmyelinated axons: conduction velocity is slow (i.e. 0.5 m/s) • Larger size and myelination can speed up velocity to > 90 m/s • The current travels faster in wider axons • In myelinated axons, the current can ‘jump’ from one node to another (saltatory conduction) • Flows very rapidly under the myelin The Nervous System THE SYNAPSE • The action potential travels down the axon • It ultimately causes the opening of other voltage-gated ion channels at the axon terminal: Ca2+ channels • High levels of intracellular Ca2+ cause fusion of vesicles with the membrane • Neurotransmitters contained in those synaptic vesicles are released into the synaptic cleft by exocytosis and can bind to receptors of the postsynaptic cell  cellular response The Nervous System NEUROTRANSMITTERS Major classes of neurotransmitters: • Amino acids: glutamate, glycine, γ-aminobutyric acid (GABA) • Amines: acetylcholine, serotonin, histamine • Catecholamines: dopamine, norepinephrine, epinephrine • Peptides: substance P, vasopressin, somatostatin • Opioids: Leu-encephalin, met-encephalin, βendorphin • Purines: adenosine, adenosine triphosphate (ATP) • And other atypical ones The Nervous System https://www.youtube.com/watch?v=z0M7_HPSi14 HOW A SYNAPSE WORKS https://www.youtube.com/watch?v=OvVl8rOEncE https://www.youtube.com/watch?v=mItV4rC57kM Supplemental Images/Videos ACTION POTENTIAL https://www.youtube.com/watch?v=oa6rvUJlg7o Supplemental Images The Nervous System HAPPY STUDYING Clara Camargo, DVM [email protected] ©2021 Ross University School of Veterinary Medicine. All rights reserved.