SN2016 Anatomy and Physiology Lecture 4 PDF

SN2016 Anatomy and Physiology Lecture 4 Nervous system Part 1 Neural tissue  Learning Outcomes At the end of this session, students should be able to –Describe the anatomical and functional divisions of the nervous system. –Sketch and lab...

SN2016 Anatomy and Physiology Lecture 4 Nervous system Part 1 Neural tissue  Learning Outcomes At the end of this session, students should be able to –Describe the anatomical and functional divisions of the nervous system. –Sketch and label the structure of a typical neuron, describe the functions of each component, and classify neurons on the basis of their structure and function. –Describe the locations and functions of the various types of neuroglia. –Describe the generation of action potentials. –Understand the function of synapses and neurotransmitter  (CNS) © 2018 Pearson Education, Inc.  Central nervous system (CNS) Consists of the spinal cord and brain ① C Contains neural tissue, connective tissues, and ③ blood vessels ① Functions of the CNS are to process and coordinate sensory data from inside and outside body, and ② motor commands control activities of peripheral organs ① Higher functions of brain include intelligence, ⑤ ⑰ ① memory, learning, emotion  Peripheral Nervous System (PNS) All neural tissue outside the CNS Deliver sensory information to the CNS, and carry motor commands to peripheral tissues and systems Nerves (also called peripheral nerves) are bundles of axons with connective tissues and blood vessels to carry sensory information and motor commands in PNS – Cranial nerves : 12 pairs, directly connect to brain – Spinal nerves attach to spinal cord  PNS Afferent division Carries sensory information From PNS sensory receptors to CNS Sensory receptors are neurons and specialized cells that o detect changes or respond to stimuli – Special sensory organs (e.g., eyes, ears) Efferent division Carries motor commands From CNS to PNS to muscles and glands  PNS ⑪ Somatic nervous system (SNS) controls voluntary and ② involuntary (reflexes) skeletal muscle contractions ① Autonomic nervous system (ANS) controls subconscious ② ③ actions, contractions of smooth muscle and cardiac muscle, ⑭ and glandular secretions – Sympathetic division has a stimulating effect – Parasympathetic division has a relaxing effect Effector organs (e.g. muscles, glands) respond to efferent signals Figure 12-1 A Functional Overview of the Nervous System. Organization of the Nervous System Central Nervous System (CNS) Integrate, process, and coordinate sensory (brain and spinal cord) data and motor commands Sensory information Motor commands within within afferent division efferent division Peripheral Nervous System (PNS) (neural includes tissue outside the CNS) Somatic nervous Autonomic system (SNS) nervous system (ANS) Parasympathetic Sympathetic division division Receptors Effectors Smooth muscle Special sensory Visceral sensory Somatic sensory Cardiac receptors receptors receptors muscle monitor smell, taste, vision, monitor internal organs monitor skeletal Glands balance, and hearing muscles, joints, and Skeletal Adipose tissue skin surface muscle © 2015 Pearson Education, Inc.  Nervous Tissue Neurons – Cells that send and receive signals ① – Neurons perform all communication, information ⑯ ③ processing, and control functions of the nervous system – Function types: sensory neuron, motor neuron, interneurons Neuroglia Neuron difficult - replace to – Cells that support and protect neurons.. need time to recover/ permanent damage – Neuroglia are essential to survival and function of neurons – CNS neuroglia include astrocytes, microglia, ependymal cells, oligodendrocytes – PNS neuroglia include Schwann cells and Satellite cells  Neurons The basic functional units of the nervous system Typical neurons contain – Cell body (soma) – Short, branched dendrites – Long, single axon ↳ to make sure the decision X distrected Figure 12-2a The Anatomy of a Multipolar Neuron. probably touch other dendrites Dendrites Perikaryon ↓ Cell body Telodendria Nucleus & Axon white M a This color-coded figure shows the four general regions of a neuron. well body T gray © 2015 Pearson Education, Inc.  Cell body of neurons Contains large nucleus and nucleolus Mitochondria produce energy [messengers to pass signals) RER and ribosomes produce neurotransmitters > Nissl bodies are the dense areas of RER and ribosomes that make neural tissue appear gray (gray matter of the brain and spinal cord) Cytoskeleton  Dendrites – Highly branched with many fine processes – Receive information from other neurons – Cover 80–90% of neuron surface area Axon carries electrical signal (action potential) to target – Each neuron has only one axon - – Arises from the axon hillock  Types of neurons Multipolar neuron has several dendrites and axons extending from the cell body, the most common type Bipolar neuron has one dendrite and one axon extending from the cell body, only in receptor cells of some special - sense organs eg eyes. Unipolar neuron has one peripheral process and one central process, only => in sensory neurons in PNS ganglia © 2018 Pearson Education, Inc. Figure 12-2b The Anatomy of a Multipolar Neuron. it makes M gray Nissl bodies (RER and free Dendritic branches ribosomes) Mitochondrion makes white Axon hillock A Initial segment of Axolemma Axon Telodendria axon Direction of action potential Golgi apparatus Axon terminals Neurofilament Nucleolus Nucleus Dendrite See Figure 12–3 Presynaptic cell b An understanding of neuron function requires knowing its structural components. Postsynaptic cell © 2015 Pearson Education, Inc.  Sensory Neurons Structures of Sensory Neurons – Cell bodies grouped in sensory ganglia – Processes (afferent fibers) extend from sensory chemical (smell) receptors to CNS g e. Physical (pressure). Function classifications Internal – Visceral sensory neurons: monitor internal - & organ environment Chugry) – Somatic sensory neurons: monitor effects of external environment 1 external eart hot cold noisy ) , , ,... coutside body)  Motor Neurons – Carry instructions from CNS to peripheral effectors via efferent fibers (axons) – Two major efferent systems Somatic nervous system (SNS): All somatic motor E neurons that innervate skeletal muscles (involuntary part) Autonomic (visceral) nervous system (ANS): Visceral motor neurons innervate all other peripheral effectors (smooth muscle, cardiac muscle, glands, adipose tissue)  Interneurons – Most are located between sensory and motor neurons in brain, spinal cord, and autonomic ganglia – Responsible for distribution of sensory information and coordination of motor activity – Involved in higher functions, such as memory, planning, learning  The brain Half of the volume of the nervous system White matter are the regions with many myelinated nerves – Myelination of axons increases speed of action potentials – Myelin insulates myelinated axons, makes nerves appear white Gray matter are the unmyelinated areas of CNS (no blood except stroke)  Neuroglia in the CNS (insulator ( CNS PNS Ensure referently Protect < partof triple BS © 2018 Pearson Education, Inc. (Block RBBL/WBC)  Neuroglia in the PNS – Satellite cells Surround ganglia (Masses of neuron cell bodies) Regulate environment around neuron – Schwann cells Form myelin sheath around peripheral axons One Schwann cell sheaths one segment of axon There are many Schwann cells that sheath entire axon Figure 12-7a Schwann Cells, Peripheral Axons, and Formation of the Myelin Sheath (Part 1 of 2). Axon hillock Nucleus Myelinated internode Initial Dendrite segment (unmyelinated) Nodes Axon Axolemma Myelin covering internode a A myelinated axon, showing the organization of Schwann cells along the length of the axon. © 2015 Pearson Education, Inc. Figure 12-7b Schwann Cells, Peripheral Axons, and Formation of the Myelin Sheath (Part 1 of 2). Schwann cell #1 Schwann cell Schwann Schwann cell #2 cell nucleus > - form bundles Neurilemma to enhance the Axons signals Schwann cell #3 nucleus Axons b The enclosing of a group of unmyelinated axons by a single Schwann cell. A series of Schwann cells is required to cover the axons along their entire length. © 2015 Pearson Education, Inc. (signal) Y X Nat in , K + out - Save ATP > - faster transmission  Neural Responses to Injuries Axon distal to injury degenerates Schwann cells form path for new growth and wrap new axon in myelin Nerve regeneration in CNS is limited by chemicals that block growth and produce scar tissue  Membrane potential The flow of ions across cell membranes general electrical currents Different numbers of cation (+) and anion (-) on the two sides of cell membranes result in a membrane potential Membrane potential is regulated by ion channels (membrane proteins)  Membrane potential When gated ion channels open, ion diffusions occur from high to low concentrations, and move to the area of opposite charge Types of ion channels – Leakage channels: always open – Chemically gated (ligand-gated) channels: open when certain chemicals bind – Voltage-gated channels: open and close when membrane potential changes – Mechanically gated channels: open when the receptor receives physical pressure Active (ATP) * - Resting Membrane Potential (consuming ATP) Caused by Na+–K+ ATPase (ion exchange pump) Active forces across the membrane powered by ATP Carries 3 Na+ out and 2 K+ in Balances passive forces of diffusion The cell membrane is highly permeable to K+ (more leakage channels), but much less permeable to Na+ Maintains resting potential ( 70 mV) (X action potential Figure 12-14 Generation of an Action Potential (Part 3 of 9). RESTING POTENTIAL –70 mV + + + + + + + – – – – – + + + + + + The axolemma contains both voltage- gated sodium channels and voltage- gated potassium channels that are closed when the membrane is at the resting potential. KEY + = Sodium ion + = Potassium ion © 2015 Pearson Education, Inc. Resting membrane potential  * spected what kind of channel Action Potential in short question Propagated changes in membrane potential Affect an entire excitable membrane Link graded potentials at cell body with motor end plate actions Four steps in the generation of action potentials – Step 1: Depolarization to threshold – Step 2: Activation of Na channels – Step 3: Inactivation of Na channels and activation of K channels – Step 4: Return to normal permeability Step 1: Depolarization to threshold -e > - less-re – A graded depolarization of axon hillock large enough (10 to 15 mV) to change resting potential ( 70 mV) to threshold level of voltage-gated sodium channels ( 60 to 55 mV) – This initial stimulus follows the all-or-none principle If a stimulus exceeds threshold amount, action potential is either triggered, or not The action potential is the same, no matter how large the initial stimulus is Step 2: Activation of Na Channels Rapid depolarization – Na+ ions rush into cytoplasm (diffusion) – Inner membrane changes from negative to positive Step 3: Inactivation of Na Channels and Activation of K Channels At 30 mV – Inactivation gates close, Na channel is inactivated – K channels open – Repolarization begins crush out to bring diffusion ? more-ve) Step 4: Return to Normal Permeability – K channels begin to close when membrane reaches normal resting potential ( 70 mV) – When K channels finish closing, membrane is hyperpolarized to 90 mV – Then membrane potential returns to resting level – Action potential is over Figure 12-14 Generation of an Action Potential (Part 4 of 9). 1 Depolarization to Threshold –60 mV + + + + + + + Local – – + – current + + + + + + + The stimulus that initiates an action potential is a graded depolarization large enough to open voltage-gated sodium channels. The opening of the channels occurs at the membrane potential known as the threshold. KEY + = Sodium ion + = Potassium ion © 2015 Pearson Education, Inc. Figure 12-14 Generation of an Action Potential (Part 5 of 9). 2 Activation of Sodium Channels and Rapid Depolarization +10 mV + + + + – + + – + + + + + + + + + When the sodium channel activation gates open, the plasma membrane becomes much more permeable to Na+. Driven by the large electrochemical gradient, sodium ions rush into the cytoplasm, and rapid depolarization occurs. The inner membrane surface now contains more positive ions than negative ones, and the membrane potential has changed from –60 mV to a positive value. KEY + = Sodium ion © 2015 Pearson Education, Inc. + = Potassium ion Figure 12-14 Generation of an Action Potential (Part 6 of 9). 3 Inactivation of Sodium Channels and Activation of Potassium Channels +30 mV + + + + + + + + + + + + + + + + As the membrane potential approaches +30 mV, the inactivation gates of the voltage- gated sodium channels close. This step is known as sodium channel inactivation, and it coincides with the opening of voltage-gated potassium channels. Positively charged potassium ions move out of the cytosol, shifting the membrane potential back toward resting levels. Repolarization now begins. KEY + = Sodium ion © 2015 Pearson Education, Inc. + = Potassium ion Figure 12-14 Generation of an Action Potential (Part 7 of 9). 4 Closing of Potassium Channels + + –90 mV + + + + + + – – – – – – + + + + + + The voltage-gated sodium channels remain inactivated until the membrane has repolarized to near threshold levels. At this time, they regain their normal status: closed but capable of opening. The voltage-gated potassium channels begin closing as the membrane reaches the normal resting potential (about –70 mV). Until all these potassium channels have closed, potassium ions continue to leave the cell. This produces a brief hyperpolarization. KEY + = Sodium ion © 2015 Pearson Education, Inc. + = Potassium ion * & D *  Generation of an Action Potential © 2015 Pearson Education, Inc. Propagation of action potential  Refractory Period – The time period from beginning of action potential to return to resting state, during which membrane will not respond normally to additional stimuli – Absolute refractory period From Na+ channel opening to inactivation To ensure that AP is all-or-none and one-way transmission – Relative refractory period After absolute refractory period Raise threshold for AP generation http://yourkamagraguide.com/  Synapse – Area where a neuron communicates with another cell (neuron, muscle or gland) – Presynaptic cell: Neuron that sends message – Postsynaptic cell: Cell that receives message – Synaptic cleft: The small gap that separates the presynaptic membrane and the postsynaptic membrane – Synaptic terminal is the expanded area of axon of presynaptic neuron which contains synaptic vesicles of neurotransmitters – Neuromuscular junction: Synapse between neuron and muscle – Neuroglandular junction: Synapse between neuron and gland  Two Types of Synapses – Electrical synapses: Direct physical contact between cells – Chemical synapses (more common): Signal transmitted across a gap by chemical neurotransmitters Figure 12-3 The Structure of a Typical Synapse. Telodendrion Axon terminal Mitochondrion Synaptic vesicles Presynaptic membrane Postsynaptic Synaptic membrane cleft © 2015 Pearson Education, Inc. Synapses  Neurotransmitters – Chemical messengers – Released at presynaptic membrane – Affect receptors of postsynaptic membrane – Broken down by enzymes – Reassembled at axon terminal – There are at least 50 neurotransmitters  Acetylcholine (ACh) Neurotransmitters at cholinergic synapses, including: 1. All neuromuscular junctions with skeletal muscle fibers 2. Many synapses in CNS 3. All neuron-to-neuron synapses in PNS 4. All neuromuscular and neuroglandular junctions of ANS parasympathetic division Events at a Cholinergic Synapse 1. Action potential arrives, depolarizes synaptic terminal 2. Calcium ions enter synaptic terminal, trigger exocytosis of ACh 3. ACh binds to receptors, depolarizes postsynaptic membrane 4. ACh is broken into acetate and choline by AChE Recall the events occurring at the neuromuscular junction (3-1) © 2018 Pearson Education, Inc. Recall the events occurring at the neuromuscular junction (3-2) © 2018 Pearson Education, Inc. Recall the events occurring at the neuromuscular junction (3-3) © 2018 Pearson Education, Inc.  Summary Vocabulary: neurons, neuroglia, CNS, PNS, white and gray matter, synapse, neurotransmitter Structures of neuron cells Synapse structure Membrane potential and generation of action potential