Neurophysiology Lecture Oct 2024 HBS1.2 PDF

Official (Closed) - Non Sensitive Neurophysiology Oct 2024 HBS1.2  Official (Closed) - Non Sensitive Lesson Objectives At the end of...

Official (Closed) - Non Sensitive Neurophysiology Oct 2024 HBS1.2  Official (Closed) - Non Sensitive Lesson Objectives At the end of this lecture, students should be able to:​ ​Describe the anatomical and functional divisions of the nervous system. Describe the structure of the neuron Recall the structural and functional types of neurons Recall the functions of neuroglia Understand the events involved in the generation and propagation of an action potential. Describe the structure and mechanism of a synapse ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Integration and Coordination The nervous system and endocrine system coordinate other organ systems to maintain homeostasis. NERVOUS SYSTEM ENDOCRINE SYSTEM Faster to respond Response is slower Action lasts for short time Action lasts longer Specific targets Multiple targets Neurotransmitters are Hormones are involved involved ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Functions of the Nervous System Monitors the body's internal and external environments Integrates sensory information Coordinates voluntary and involuntary responses ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive LO: DESCRIBE THE ANATOMICAL AND FUNCTIONAL DIVISIONS OF THE NERVOUS SYSTEM.  Official (Closed) - Non Sensitive Anatomic divisions of the nervous system Made up of the All the neural brain and spinal tissues outside of cord the CNS Integrates and The connection coordinates between the CNS input and and the organs output ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive A Functional Overview of the Nervous System ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive LO: DESCRIBE THE STRUCTURE OF THE NEURON.  Official (Closed) - Non Building blocks of nervous Sensitive system Nervous tissue is made up of two types of cells – Neurons: – basic unit – Transmits nerve impulse – Neuroglia: – Protects, supports and regulate the environment around the neurons ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non The structure of a Neuron. Sensitive ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Neuron Sensitive Cells that communicate and carry information Basic structure of a neuron: Dendrites: Receive signals Cell body: Contains the nucleus and organelles Axon hillock: Where electrical signal begins Axons: Carry signals to the next cell Axon Bulb-shaped endings that form a terminals: synapse with the next cell Have a very limited ability to regenerate when damaged or destroyed ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Anatomy of a myelinated neuron. Sensitive Myelin Sheath: A lipid covering on long axons that acts to increase the speed of nerve impulse conduction, insulation, and regeneration of the neurons (mainly in PNS) Nodes of Ranvier – gaps between myelination on the axons ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive LO: RECALL THE STRUCTURAL AND FUNCTIONAL TYPES OF NEURONS.  Structural Classification of Official (Closed) - Non Sensitive Neurons Multipolar neuron Unipolar neuron ©Ngee Ann Polytechnic_ Oct 2024_1HBS12 Bipolar neuron  Official (Closed) - Non Sensitive Structural Classification of Neurons Based on the relationship of the dendrites to the cell body Multipolar Most common in the CNS and efferent neurons neurons Have two or more dendrites and one axon Unipolar Most abundant in the afferent division/ neurons sensory neurons Cell body off to one side Bipolar Found in special sensory organs neurons Have one dendrite and one axon with the cell body in the middle ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Functional Classification of Neurons Sensory Afferent neurons Neurons Receive information from sensory receptors Interneuron Receives information in the CNS and sends it to a motor neuron Motor Efferent neurons Neurons Carry information to peripheral targets called effectors ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive LO: RECALL THE FUNCTIONS OF NEUROGLIA.  Official (Closed) - Non Neuroglial Cells Sensitive Are supportive cells and make up about half of all neural tissue Able to divide and regenerate ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Glial cell found in Functions Clinical notes CNS Astrocytes Star-shaped cells that provide One of the common cell physical and nutritional support group causing of CNS for neurons and maintains the tumors - Astrocytoma blood-brain barrier Ependymal cells Related to cerebrospinal fluid Dysfunctional ependymal (CSF) production and circulation cells can alter the circulation of CSF and lead to hydrocephalus Microglia Microglia are the resident Microglial cells increase in Phagocytic cells derived from number during CNS white blood cells and provide a infections to protect the first line of defence against brain. invading pathogens. Altered neuroprotective ability and age related functional changes of microglia has a strong association with Alzheimer’s disease Oligodendrocytes Produce an insulating Demyelination of CNS & membranous wrapping around optic nerve: Multiple axons called myelin sclerosis ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Glial cell found Functions Clinical notes in PNS Satellite cells Surround and support neuron cell bodies Schwann cells Produce an insulating Autoimmune disorder membranous wrapping around characterized by axons called myelin demyelination of PNS - Guillain-Barré Syndrome ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Neuroglia ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Neuroglia – Clinical Notes Demyelination: A condition that results in damage to the protective covering (myelin sheath) that surrounds neurons. The nerve impulses slow or even stop, causing neurological problems. – Multiple sclerosis Demyelination of CNS & optic nerve – Guillain - Barré Syndrome Autoimmune disorder characterized by demyelination of PNS – Chronic exposure to heavy metallic ions – arsenic, lead and mercury ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Neurophysiology LO: Understand the events involved in the generation and propagation of an action potential.  Official (Closed) - Non Information Transmission Sensitive In the nervous system, message moves from one location to another in the form of action potential(nerve impulse) along the axon of a neuron - electrical Transferring of information from one cell to another takes place at synapse - chemical ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Understanding neurophysiology Plasma membrane of a neuron is selectively permeable. The membrane contains many transport proteins Specific – ion channels – Some ion channels are permanently open vs some have gates – Potassium ions pass through the membrane more readily than do sodium ions Na+ K+ pumps (ATP) – Ejects 3 Na+ out of the cell and brings in 2 K+ inside the cell. ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Membrane ion channels ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non An undisturbed cell has a resting Sensitive membrane potential Excessive positive ionic charges on the outside of the cell – Extracellular fluid (ECF) is high in Na+ and CI– Excessive negative charges on the inside, – Intracellular fluid (ICF) is high in K+ and negatively charged proteins (Pr –) The resting membrane potential of neurons is –70 mV ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Changes in Membrane Potential Stimulation of a membrane can locally affect its resting potential. When the membrane potential becomes less negative, the membrane is depolarized. If sufficiently strong depolarization occurs, a threshold potential is achieved as ion channels open. Graded Potential - Local changes in the membrane that fade over distance Action Potential - A change in the membrane that travels the entire length of neurons ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Action potential – nerve impulse Initiated when graded potentials reach a certain threshold (triggering point) Depolarization: Voltage-sensitive Na channels open, Na moves into the axon (this reverses the voltage across the membrane, interior becomes ) Repolarization: Na channels close, K channels open, K moves out of the axon (this restores the initial polarity, actually becomes temporarily hyperpolarized) Reestablishment of the resting potential: K channels close, the normal activity of the sodium-potassium pump restores resting potential ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Figure 8-8 The Generation of an Action Potential Sodium channels close, voltage- gated potassium channels open, and potassium ions move out of the cell. Repolarization begins. +30 3 D E P O L A R I Z AT I O N R E P O L A R I Z AT I O N 0 Membrane potential (mV) Resting 2 Resting potential Voltage-gated sodium Potassium channels potential –40 close, and both sodium channels open and and potassium chan- sodium ions move into –60 Threshold the cell. The membrane nels return to their normal states. 1 potential rises to +30 –70 mV. A graded 4 depolarization brings H Y P E R P O L A R I Z AT I O N an area of excitable membrane to thresh- old (–60 mV). REFRACTORY PERIOD During the refractory period, the membrane cannot respond to further stimulation. 0 Time (msec) 1 2 ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Action Potentials – Nerve impulse Are all-or-none and will propagate down the length of the neuron From the time the voltage-gated channels open until repolarization is finished The membrane cannot respond to further stimulation This period of time is the refractory period – And limits the rate of response by neurons ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Propagation of an Action Potential Wave of membrane potential changes along the axon Continuous propagation – Occurs in unmyelinated fibers and is relatively slow Saltatory propagation – Is in myelinated axons and is faster ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Neurophysiology: The Synapse LO: Describe the structure and mechanism of a synapse  Official (Closed) - Non Sensitive The Synapse A functional junction between a neuron and another cell (target) Involves release and diffusion of chemical messengers – The neurotransmitter Communication happens in one direction. The target cells can be neurons muscles glands ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive A Synapse between Two Neurons Synapse – Between the axon terminals of the presynaptic neuron – Across the synaptic cleft – To the dendrite or cell body of the postsynaptic neuron Neurotransmitters – Stored in vesicles of the axon terminals – Released into the cleft and bind to receptors on the postsynaptic membrane ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non The Structure of a Typical Synapse. Sensitive Axon terminal Synaptic cleft Postsynaptic membrane Mitochondrion Axon of presynaptic cell Presynaptic membrane Synaptic vesicles ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Cholinergic synapses Synapse that release Acetyl Choline (Ach) is known as cholinergic synapses The cholinergic synapses can be found at: – Neuromuscular junction - Junction between a nerve and muscle – Many synapses in CNS – All Synapses in PNS ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive An action potential arrives at an axon terminal. Calcium ions enter and synaptic vesicles fuse with the plasma membrane of the pre synaptic neuron. Neurotransmitter molecules are released into the synaptic cleft. Neurotransmitters bind to receptors on the membrane of the receiving or post synaptic neuron. Sodium diffuses into the post synaptic neuron through an ion channel in the receptor, and an action potential begins. ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive An action potential arrives presynaptic ACh binds to receptors and depolarizes neuron and the postsynaptic membrane. Na channels depolarizes the axon terminal activated & initiated AP if threshold is Presynaptic Action potential reached. neuron Synaptic EXTRACELLULAR vesicles FLUID Initiation of Axon action potential terminal if threshold is reached AChE POSTSYNAPTIC NEURON AP Propagated & depolarization of Extracellular Ca2+ enters the axon postsynaptic membrane ends as ACH is terminal, triggering the exocytosis/release broken down by an enzyme AChE of ACh (acetylcholinesterase) ACh Propagation of action potential (if generated) Ca2+ Ca2+ Synaptic cleft Chemically regulated sodium ion channels ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Important Neurotransmitters Excitatory Neurotransmitters: Facilitates the information transmission to the post synaptic cell. acetylcholine, glutamate, dopamine, norepinephrine Inhibitory Neurotransmitters: Inhibit the information transmission to the post synaptic cell. Gamma-aminobutyric acid (GABA) and glycine ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Clinical notes Botulism  The botulin toxin binds to the presynaptic membranes and prevents the release of acetylcholine from motor neurons  preventing synaptic transmission and muscle contraction. Myasthenia gravis  An antibody-mediated immunological attack directed at proteins in the postsynaptic membrane of the neuromuscular junction  Preventing synaptic transmission leading to muscle weakness ©Ngee Ann Polytechnic_ Oct 2024_1HBS12  Official (Closed) - Non Sensitive Clinical notes Neuromuscular blocking drugs – Binds to the ACh receptors in the post synaptic membrane and prevent synaptic transmission Produce muscle paralysis, Used to relax the laryngeal muscles to facilitate intubation Sodium channel blocker (local anaesthetic drug e.g lidocaine) - Block influx of Na+ into the membrane of neuron - Prevents initiation and conduction of impulses Inhibitory neurotransmitters as medications – Anti-epileptic drugs Mimic or potentiate GABA action (drug binds to receptors) Decreases the impulse firing and controls epilepsy ©Ngee Ann Polytechnic_ Oct 2024_1HBS12