Overview of the Nervous System - Spring 2023

Overview of the Nervous System Learning Outcome: 1. Distinguish between the central nervous system and the peripheral nervous system with regard to location and function 2. List the three types of neurons and provide a function for each 3. Summarize the activities that generate and propagate an act...

Overview of the Nervous System Learning Outcome: 1. Distinguish between the central nervous system and the peripheral nervous system with regard to location and function 2. List the three types of neurons and provide a function for each 3. Summarize the activities that generate and propagate an action potential 4. Explain the role of neurotransmitters and the process of synaptic integration Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 1  Overview of the Nervous System, continued Nervous system – Has two major divisions: Central nervous system (CNS) – consists of the brain and spinal cord Peripheral nervous system (PNS) – consists of nerves, which lie outside the CNS Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 2 3  Overview of the Nervous System, cont. The nervous system has three functions: 1. Sensory – sensory receptors respond to stimuli by generating nerve signals that travel via the PNS to the CNS 2. Integration – the CNS sums up the input it receives from all over the body, stores memories, and creates motor responses 3. Motor – generates motor output, which travels from the CNS via the PNS to muscles, glands, and organs Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 4  Nervous Tissue Contains two types of cells: neurons and neuroglia – Neurons – transmit nerve impulses – Neuroglia – support and nourish neurons Greatly outnumber neurons Neuroglia in the CNS that form myelin sheaths: oligodendrocytes Neuroglia in the PNS that form myelin sheaths: Schwann cells Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 5  Anatomy of a Neuron Three types of neurons, based on function: sensory neurons, interneurons, motor neurons – Sensory neuron – carries nerve signals from a sensory receptor to the CNS Sensory receptors – detect changes in the environment Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 6  Anatomy of a Neuron, continued Three types of neurons, cont. – Interneuron – found only within the CNS Receive input from sensory neurons and other interneurons Sum up signals received from other neurons, then communicate with motor neurons Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 7  Anatomy of a Neuron, cont. Three types of neurons, cont. – Motor neuron – carries nerve impulses away from the CNS to an effector (muscle fiber, organ, or gland), which carries out the response to the environmental change Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 8  Anatomy of a Neuron, cont. Neurons have three structures: cell body, dendrites, and an axon – Cell body – contains the nucleus, other organelles – Dendrites – short extensions off the cell body that receive signals from sensory receptors or other neurons Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 9 10 11 12  Anatomy of a Neuron, cont. Neurons, cont. – Axon – the portion of a neuron that conducts nerve impulses Individual axons are termed nerve fibers, and collectively they form a nerve Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 13  Myelin Sheath Myelin sheath – Covers some axons – Formed when Schwann cells (PNS) or oligodendrocytes (CNS) wrap around an axon many times – Node of Ranvier – space between myelin sheaths Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 14 15  Myelin Sheath, continued Myelin sheath, cont. – Gray matter of the CNS is gray because it contains no myelinated axons; white matter is white because it does – Multiple sclerosis (MS) – myelin breaks down Neurons can’t transmit information Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 16  Physiology of a Neuron Physiology of a neuron – Nerve signals – electrical signals that convey information within the nervous system – Resting potential – the potential energy of a neuron at rest Exists because the plasma membrane is polarized: there is a more positive charge outside the cell, more negative charge inside It is measured in millivolts (mV) Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 17  Physiology of a Neuron, continued Resting potential, cont. – Neurons must maintain their resting potential to be able to send nerve signals To do this, they have a protein carrier called the sodium-potassium pump that pumps Na+ out and K+ into the neuron Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 18  Action Potential Nerve signals are also called action potentials – Occur only in axons – A stimulus is a change that activates the neuron E.g., a stimulus for pain neurons in the skin would be the prick of a sharp pin Threshold – the minimum voltage that must be reached in order for an action potential to occur – Equal to -55 mV Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 19  Action Potential, continued Action potentials are ‘all-or-nothing’ – Once threshold is reached, the action potential happens completely; it doesn’t vary in size Increasing the strength of a stimulus does not change the size of an action potential Action potentials don’t come in different sizes; there are no small, medium or large AP’s Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 20  Action Potential, cont. Depolarization – The first part of an action potential – Protein channels open and Na+ rushes into the cell – Adding positively charged Na+ causes the inside of the axon to become positive compared to the outside Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 21  Action Potential, cont. Repolarization – The second part of an action potential – Na+ channels close and K+ channels open K+ flows out of the cell – The inside of the cell becomes negative again – Finally, the sodium-potassium pump completes the action potential K+ are returned to the inside of the cell and Na+ to the outside; resting potential is restored Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 22  Propagation of an Action Potential Propagation of an action potential – In unmyelinated axons, action potentials stimulate adjacent parts of the axon membrane to produce an action potential Conduction can be slow because each section of the axon must be stimulated Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 23  Propagation of an Action Potential, continued Propagation of an action potential, cont. – In myelinated fibers, action potentials only occur at nodes of Ranvier This is called saltatory conduction and is much faster Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 24  Saltatory Conduction Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 25  The Synapse Synapse – Junction between two neurons – Synaptic cleft – a small gap that separates the presynaptic neuron from the postsynaptic neuron – Neurotransmitter – transmits action potentials across a synapse Stored in synaptic vesicles in the axon terminals Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 26  The Synapse, cont. The events at a synapse: 1. Nerve signals travel along an axon and reach an axon terminal 2. Exocytosis of the synaptic vesicles occurs 3. Neurotransmitter is released into the synaptic cleft and diffuses across to the postsynaptic membrane Binds to receptor proteins Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 27 28 29  Synaptic Integration Integration – summing up of multiple incoming signals – If a neuron receives enough signals, threshold will be met, and its axon will transmit a signal Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 30 31  Check Your Progress 1. Describe the three types of neurons, and list the three main parts of a neuron 2. Describe how a nerve impulse is propagated 3. Summarize how a nerve impulse is transmitted from one neuron to the next Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 32  The Central Nervous System Learning Outcomes: 1. Identify the structures of the spinal cord and provide a function for each 2. Identify the structures of the brain and provide a function for each 3. Identify the lobes and major areas of the human brain 4. Distinguish between the functions of the primary motor and the primary somatosensory areas of the brain Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 33  The Central Nervous System, continued CNS – the spinal cord and the brain – Receives sensory information and initiates motor control – Both the spinal cord and the brain are protected by bone (vertebrae and skull) – Also, both the spinal cord and the brain are wrapped in membranes known as meninges – Meningitis – infection of the meninges; may be caused by bacteria or viruses Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 34  Cerebrospinal Fluid Cerebrospinal fluid – found between the meninges; cushions and protects the CNS Cerebrospinal fluid is also in the four ventricles of the brain and in the central canal of the spinal cord Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 35 36  Gray and White Matter The CNS is composed of two types of nervous tissue—gray matter and white matter – Gray matter contains cell bodies, dendrites and short, unmyelinated axons – White matter contains myelinated axons Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 37  Structure of the Spinal Cord Structure of the spinal cord – A cross section of the spinal cord shows a central canal, gray matter, and white matter – The spinal nerves project from the cord Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 38 39 40  Structure of the Spinal Cord, cont. Structure of the spinal cord, cont. – White matter surrounds the gray matter – White matter carries information to and from the brain Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 41  Functions of the Spinal Cord Functions of the spinal cord – Paralysis – a loss of sensation and voluntary control Paraplegia – if damage is in the thoracic region of the spinal cord, the lower body and legs are paralyzed Quadriplegia – if damage is in the neck region, all four limbs are affected Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 42  The Brain Brain – Made up of the cerebrum, diencephalon, cerebellum, and brain stem – Cerebrum The largest part of the brain Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 43 44  The Brain, continued Cerebral hemispheres – Left and right cerebral hemispheres communicate via the corpus callosum – Gyri (sing., gyrus) – thick folds separated by shallow grooves called sulci (sing., sulcus) Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 45  The Brain, cont. Cerebral hemispheres, cont. – Divided into lobes: Frontal lobe – the most anterior Parietal lobe – posterior to the frontal lobe Occipital lobe – posterior to the parietal lobe Temporal lobe – inferior to the frontal and parietal lobes Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 46 47  The Cerebral Cortex Cerebral cortex – Thin, highly convoluted outer layer of gray matter; covers the cerebral hemispheres – Responsible for sensation, voluntary movement, thought processes and consciousness Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 48  Primary Motor and Sensory Areas of the Cortex Primary motor area – in the frontal lobe – Voluntary signals to skeletal muscles begin here – Muscles that control facial movements (swallowing, salivation, expression) take up an especially large portion Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 49 50  Primary Motor and Sensory Areas of the Cortex, continued Primary somatosensory area – in the parietal lobe – Sensory information from the skin and skeletal muscles arrives here – Large areas are dedicated to those body areas with acute sensation E.g., the face and hands occupy the largest portion Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 51  The Diencephalon Diencephalon – includes the hypothalamus and thalamus – Hypothalamus – integrating center Regulates hunger, heart rate, breathing, and thirst Controls the endocrine system Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 52  The Diencephalon, continued Diencephalon, cont. – Thalamus Receives all sensory input except the sense of smell Sends it on to the appropriate areas of the cerebrum Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 53  The Cerebellum Cerebellum – under the occipital lobe – Maintains posture and balance – Produces smooth, coordinated, voluntary movements Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 54  The Brain Stem The brain stem – Contains the midbrain, pons, medulla oblongata – Midbrain Has reflex centers for visual, auditory, tactile – Pons – communicates between the cerebellum and the rest of the CNS Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 55  The Brain Stem, continued The brain stem, cont. – Medulla oblongata Contains reflex centers for regulating heart rate, breathing, and blood pressure Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 56  Check Your Progress 1. List the functions of the spinal cord 2. Summarize the major regions of the brain, and describe the general function of each Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 57  The Limbic System and Higher Mental Functions, continued Limbic system – Handles emotions and memory – Isn’t just one area of the brain; includes several areas Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 58  The Peripheral Nervous System Learning Outcomes: 1. Describe the series of events during a spinal reflex 2. Distinguish between the somatic and autonomic divisions of the peripheral nervous system 3. Distinguish between the sympathetic and parasympathetic divisions of the autonomic division Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 59  The Peripheral Nervous System, continued The peripheral nervous system – Cranial nerves – arise from the brain – Spinal nerves – arise from the spinal cord Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 60 61  Cranial Nerves Cranial nerves – the 12 pairs of nerves attached to the brain – Concerned with the head, neck, and facial regions Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 62 63  Spinal Nerves Spinal nerves – emerge from either side of the spinal cord – There are 31 pairs of spinal nerves Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 64  Somatic System The nervous system is divided anatomically into the CNS and PNS – The PNS is divided functionally into the somatic and autonomic nervous systems Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 65  Somatic System, cont. Somatic system – Serves the skin and skeletal muscles – Not all somatic motor actions are voluntary; some are automatic Reflexes – automatic responses to a stimulus Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 66  Reflex Arc Reflex arc – Sensory neurons enter the cord and stimulate interneurons – Interneurons synapse with motor neurons – Nerve signals then travel in these motor fibers to an effector (brings about a response to the stimulus) – Some of the interneurons involved carry nerve signals to the brain for perception Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 67 68  Autonomic System Autonomic system – regulates cardiac and smooth muscles, organs, and glands – Divided into the sympathetic and parasympathetic divisions These two systems create opposite responses Are involuntary Innervate all internal organs Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 69  Sympathetic Division Sympathetic division – Active during emergency situations when you might be required to fight or take flight – Increases the heartbeat and dilates the airways for a ready supply of glucose and oxygen – Inhibits the digestive and urinary organs Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 70  Parasympathetic Division Parasympathetic division – Promotes responses associated with a relaxed state E.g., promotes digestion of food, slows heart rate Can be called the ‘rest-and-digest’ system Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 71  Check Your Progress 1. Contrast cranial and spinal nerves 2. Detail the fastest way for you to react to a stimulus 3. Predict what could happen to homeostasis if the autonomic nervous system failed Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 72  Drug Therapy and Substance Use Disorders Learning Outcomes: 1. Explain the ways that drugs interact with the nervous system 2. Classify drugs as to whether they have a depressant, stimulant, or psychoactive effect on the nervous system 3. List the long-term effects of drug use on the body Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 73  Drug Mode of Action Common modes of action of drugs: – Increasing the amount of neurotransmitter at a synapse – Decrease the action of a neurotransmitter – Replace or mimic a neurotransmitter Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 74  Substance Use Disorders Substance Use Disorders – Dopamine is a neurotransmitter that is important in the brain’s reward circuit – Some drugs artificially stimulate the reward circuit to the point that abusers neglect basic physical needs in favor of drug use Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 75  Substance Use Disorders, continued Substance Use Disorders, cont. – Abusers display a psychological and/or physical dependence on the drug Psychological dependence – cravings Physical dependence – they have become tolerant to it (more is needed to get the same effect, and withdrawal symptoms occur when they stop taking it) Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 76  Alcohol Alcohol – Acts as a depressant on the brain – Depending on the amount consumed, can lead to a feeling of relaxation, lowered inhibitions, impaired concentration and coordination, slurred speech, and vomiting – If blood levels of alcohol become too high, coma or death can occur Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 77  Nicotine Nicotine – Whether chewed, smoked or vaped, it raises blood sugar When that wears off, blood sugar falls, causing depression and fatigue – user then craves nicotine – Stimulates neurons to release the neurotransmitter dopamine in the pleasure centers, which causes a temporary feeling of pleasure This reinforces dependence on the drug 78  Nicotine, continued Nicotine, continued – 70% of people who try using nicotine become addicted Once addicted, only 10-20% can quit – Smoking causes serious diseases of the cardiovascular and respiratory systems 79  Cocaine and Crack Cocaine and crack – A powerful stimulant The result is a sense of well-being that lasts from 5 to 30 minutes This is followed by fatigue, depression, irritability Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 80  Methamphetamine and Ecstasy Methamphetamine and ecstasy – Powerful stimulant – Often produced in home laboratories – Causes a rush of euphoria, energy, alertness, and elevated mood Typically followed by a state of agitation and sometimes violent behavior Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 81  Heroin Heroin – Derived from the opium poppy plant Drugs derived from opium are called opiates (includes morphine and codeine) – Causes feelings of euphoria, along with relief of pain – Addiction is common Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 82  Marijuana and K2 Marijuana and K2 – The names ‘cannabis’ and ‘marijuana’ apply to either the plant or THC, the active ingredient – The user experiences mild euphoria, along with alterations in vision and judgment Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 83  Check Your Progress 1. Contrast drug therapy and drug abuse 2. List how the abuse of drugs, including alcohol, affects the nervous system 3. Detail several modes of action of pharmaceutical and illegal drugs Copyright © 2018 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. 84