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Essentials of Human Anatomy & Physiology Elaine N. Marieb Seventh Edition Chapter 9 The Nervous System Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Functions of the Nervous System • Maintain homeostasis with electrical signals • Provide for sensation • Provide for higher mental functions and emotions • Activate muscles and glands Roles of the Nervous System 1. Sensory input – gathering information To monitor changes occurring inside and outside the body (changes = stimuli) 2. Integration – to process and interpret sensory input and decide if action is needed. 3. Motor output A response to integrated stimuli The response activates muscles or glands Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.1a Structural Classification of the Nervous System Central nervous system (CNS) Brain & spinal cord Dorsal cavity Command center Takes in info & give instruction Peripheral nervous system (PNS) Nerves outside the brain and spinal cord Communication lines Slide 7.2 Functional Classification of the Peripheral Nervous System Sensory (afferent) division Nerve fibers that carry information to the central nervous system Figure 7.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.3a Functional Classification of the Peripheral Nervous System Motor (efferent) division Nerve fibers that carry impulses away from the central nervous system Figure 7.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.3b Functional Classification of the Peripheral Nervous System Motor (efferent) division Two subdivisions Somatic nervous system = voluntary Autonomic nervous system = involuntary Figure 7.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.3c Organization of the Nervous System Figure 7.2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.4 Neuroglia vs. Neurons • • • • Neuroglia divide. Neurons do not. Most brain tumors are “gliomas.” Most brain tumors involve the neuroglia cells, not the neurons. • Consider the role of cell division in cancer! Support Cells of the PNS Schwann cells Form myelin sheath in the peripheral nervous system Figure 7.3e Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.7b Nervous Tissue: Neurons Neurons = nerve cells Cells specialized to transmit messages Major regions of neurons Cell body – nucleus and metabolic center of the cell Processes – fibers that extend from the cell body (dendrites and axons) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.8 Neuron Anatomy Cell body Nucleus Large nucleolus Figure 7.4a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.9b Neuron Anatomy Extensions outside the cell body Dendrites – conduct impulses toward the cell body Axons – conduct impulses away from the cell body (only 1!) Figure 7.4a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.10 Axons and Nerve Impulses Axons end in axonal terminals Axonal terminals contain vesicles with neurotransmitters Axonal terminals are separated from the next neuron by a gap Synaptic cleft – gap between adjacent neurons Synapse – junction between nerves Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.11 Nerve Fiber Coverings Schwann cells – produce myelin sheaths in jelly-roll like fashion Nodes of Ranvier – gaps in myelin sheath along the axon Figure 7.5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.12 Application • In Multiple Scleroses the myelin sheath is destroyed. • The myelin sheath hardens to a tissue called the scleroses. • This is considered an autoimmune disease. • Why does MS appear to affect the muscles? Neuron Cell Body Location Most are found in the central nervous system Gray matter – cell bodies and unmylenated fibers Nuclei – clusters of cell bodies within the white matter of the central nervous system Ganglia – collections of cell bodies outside the central nervous system Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.13 Classification of Neurons (based on fxn. Sensory (afferent) neurons Carry impulses from the sensory receptors Motor (efferent) neurons Carry impulses from the central nervous system to muscles and glands Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Functional Classification of Neurons Interneurons (association neurons) Found in neural pathways in the central nervous system Connect sensory and motor neurons Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Neuron Classification Figure 7.6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.15 How Neurons Function (Physiology) Irritability – ability to respond to stimuli Conductivity – ability to transmit an impulse The plasma membrane at rest is polarized Fewer positive ions are inside the cell than outside the cell Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.17 Starting a Nerve Impulse Depolarization – a stimulus depolarizes the neuron’s membrane A depolarized membrane allows sodium (Na+) to flow inside the membrane The exchange of ions initiates an action potential in the neuron Figure 7.9a–c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.18 The Action Potential If the action potential (nerve impulse) starts, it is propagated over the entire axon Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane The sodium-potassium pump restores the original configuration This action requires ATP Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.19 Nerve Impulse Propagation The impulse continues to move toward the cell body Impulses travel faster when fibers have a myelin sheath Figure 7.9c–e Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.20 All-or-None Response • Greater intensity of the stimulation does not produce a stronger impulse but rather more impulses are sent • Remember this from the muscular system?? Continuation of the Nerve Impulse btwn. Neurons (Conductivity) Impulses are able to cross the synapse to another nerve (electrochemical event) Neurotransmitter is released from a nerve’s axon terminal The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter An action potential is started in the dendrite Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.21 How Neurons Communicate at Synapses Figure 7.10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.22 Ways to slow conduction • • • • • Alcohol Sedatives Anesthetics Cold Continuous pressure The Reflex Arc Reflex – rapid, predictable, and involuntary responses to stimuli Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector Figure 7.11a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.23 Simple Reflex Arc Figure 7.11b, c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.24 • The knee-jerk reflex is an example of a 2neuron reflex arc (sensory receptor, afferent neuron, efferent neuron, efferent organ) • What would be the componeets of a 3neuron reflex arc? Types of Reflexes and Regulation Autonomic reflexes Smooth muscle regulation Heart and blood pressure regulation Regulation of glands Digestive system regulation Somatic reflexes Activation of skeletal muscles Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.25 Central Nervous System (CNS) CNS develops from the embryonic neural tube The neural tube becomes the brain and spinal cord The opening of the neural tube becomes the ventricles Four chambers within the brain Filled with cerebrospinal fluid Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.26 Regions of the Brain Cerebral hemispheres Diencephalon Brain stem Cerebellum Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.12 Slide 7.27 Cerebral Hemispheres (Cerebrum) Paired (lf & rt) superior parts of the brain= hemispheres Include more than half of the brain mass Largest & most complex area of the brain Figure 7.13a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Cerebral Hemispheres (Cerebrum) The surface is made of ridges (gyri) and grooves (sulci) Figure 7.13a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Lobes of the Cerebrum Fissures (deep grooves) divide the cerebrum into lobes Longitudinal fissure – separates hemispheres Lobes of the cerebrum Frontal lobe Parietal lobe Occipital lobe Temporal lobe Slide Lobes of the Cerebrum Figure 7.15a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Lobes of the brain Frontal Lobe Primary motor area – sends impulses to skeletal muscles Broca’s area – involved in our ability to speak Intellectual and psychic functions Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.30 Sensory and Motor Areas of the Cerebral Cortex Figure 7.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.31 Temporal Lobe Gustatory, auditory, olfactory area Occipital Lobe Visual areas Parietal Lobe Sensations; pain; hot & cold; touch; speech & reading Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Specialized Area of the Cerebrum Interpretation areas of the cerebrum Speech/language region Language comprehension region General interpretation area Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Specialized Area of the Cerebrum Figure 7.13c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Layers of the Cerebrum Gray matter Outer layer Composed mostly of neuron cell bodies Initiates thoughts & voluntary actions Figure 7.13a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Layers of the Cerebrum White matter Fiber tracts inside the gray matter Example: corpus callosum connects hemispheres Figure 7.13a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Diencephalon Sits on top of the brain stem Enclosed by the cerebral heispheres Made of three parts Thalamus Hypothalamus Epithalamus Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Thalamus The relay station for sensory impulses Transfers impulses to the correct part of the cortex for localization and interpretation Ability to concentrate Degree of wakefulness Pleasantness & unpleasantness Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.35 Hypothalamus Helps regulate body temperature Controls water balance Regulates metabolism Appetite and thirst An important part of the limbic system (emotions) The pituitary gland is attached to the hypothalamus Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Epithalamus Houses the pineal body (an endocrine gland) – sexual maturity and growth Includes the choroid plexus – forms cerebrospinal fluid Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.37 Brain Stem Attaches to the spinal cord Parts of the brain stem Midbrain Pons Medulla oblongata Size your thumb (~ 3 inches) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Midbrain Mostly composed of tracts of nerve fibers Reflex centers for vision and hearing Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.39 Pons The bulging center part of the brain stem Mostly composed of fiber tracts Includes nuclei involved in the control of breathing Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.40 Medulla Oblongata The lowest part of the brain stem Merges into the spinal cord Contains important control centers Heart rate control Blood pressure regulation Breathing Swallowing Vomiting Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.41 Cerebellum Two hemispheres with convoluted surfaces Functions in balance and coordination Provides involuntary coordination of body movements Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Cerebellum Figure 7.15a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Protection of the Central Nervous System Scalp and skin Skull and vertebral column Meninges Figure 7.16a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Protection of the Central Nervous System Cerebrospinal fluid Blood brain barrier Figure 7.16a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Meninges Dura mater Double-layered external covering Periosteum – attached to surface of the skull Meningeal layer – outer covering of the brain Folds inward in several areas Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Meninges Arachnoid layer Middle layer Web-like Pia mater Internal layer Clings to the surface of the brain Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Cerebrospinal Fluid Similar to blood plasma composition Forms a watery cushion to protect the brain Circulated in arachnoid space, ventricles, and central canal of the spinal cord Changes in composition help diagnose disorders Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.46 Nervous System disorders • Meningitis – inflammation of the meninges; serious threat to the brain b/c of bacterial or viral types may spread into central nervous tissue • Encephalitis – inflammation of the brain • Hydrocephalus – “water on the brain;” CSF cannot drain and pressure is exerted on the brain Blood Brain Barrier Includes the least permeable capillaries of the body Excludes many potentially harmful substances Useless against some substances Fats and fat soluble molecules Respiratory gases Alcohol Nicotine Anesthesia Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.48 Traumatic Brain Injuries (TBI) Concussion Slight or mild brain injury Bleeding & tearing of nerve fibers happened Recovery likely with some memory loss Contusion A more severe TBI Nervous tissue destruction occurs Nervous tissue does not regenerate Cerebral edema Swelling from the inflammatory response May compress and kill brain tissue Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.49 Cerebrovascular Accident (CVA) Commonly called a stroke The result of a ruptured blood vessel supplying a region of the brain Brain tissue supplied with oxygen from that blood source dies Loss of some functions or death may result Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.50 Alzheimer’s Disease Progressive degenerative brain disease Mostly seen in the elderly, but may begin in middle age Structural changes in the brain include abnormal protein deposits and twisted fibers within neurons Victims experience memory loss, irritability, confusion and ultimately, hallucinations and death Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.51 Spinal Cord Extends from medulla oblongata to T12 region 31 pairs of nerves Fxn is to conduct nerve impulses& serve for spinal reflex centers Spinal tap – withdrawal of CSF (2-3 ml); decreases pressure and can diagnose problems Peripheral Nervous System Nerves and ganglia outside the central nervous system Nerve = bundle of neuron fibers Neuron fibers are bundled by connective tissue Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.55 Classification of Nerves (PNS) Mixed nerves – both sensory and motor fibers Afferent (sensory) nerves – carry impulses toward the CNS Efferent (motor) nerves – carry impulses away from the CNS Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.57 PNS Structure 1. Sensory (afferent) division – nerve fibers that convey impulses to the CNS from sensory receptors a. Somatic sensory fibers – impulses from skin, skeletal muscles, and joints b. Visceral sensory fibers – impulses from visceral organs PNS structure (cont.) 2. Motor (efferent) division – caries impulses from the CNS to organs, muscles and glands; causes a response a. (somatic ( voluntary) nervous system – allows voluntary contraction of skeletal muscles b. Autonomic ( involuntary ) nervous system – regulates involuntary actions, such as glands, cardiac, and muscles Autonomic Nervous System The involuntary branch of the nervous system Consists of only motor nerves Divided into two divisions Sympathetic division Parasympathetic division Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.67 Comparison of Somatic and Autonomic Nervous Systems Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.24 Slide 7.69 Anatomy of the Autonomic Nervous System Figure 7.25 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.73 Autonomic Functioning Sympathetic – “fight-or-flight” Response to unusual stimulus Takes over to increase activities Remember as the “E” division = exercise, excitement, emergency, and embarrassment Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Autonomic Functioning Parasympathetic – housekeeping activities Conserves energy Maintains daily necessary body functions Remember as the “D” division - digestion, defecation, and diuresis Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Development Aspects of the Nervous System The nervous system is formed during the first month of embryonic development Any maternal infection can have extremely harmful effects The hypothalamus is one of the last areas of the brain to develop Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Development Aspects of the Nervous System No more neurons are formed after birth, but growth and maturation continues for several years (new evidence!) The brain reaches maximum weight as a young adult However, we can always grow dendrites! Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Nervous System Disorders 1. Cerebral palsy – neuromuscular disability where voluntary muscles are poorly controlled; causes by a temporary lack of oxygen to motor areas of the brain during delivery 2. Spina bifada – results when vertebrae from incompletely; part of the spinal cord is functionless 3. Parkinson’s disease – disorder in the ganglia characterized by shaking Nervous System Disorders 4. Orthostatic hypertension – type of low blood pressure resulting from changes in body position (sympathetic) 5. Brain shrinkage – common but sped up in boxers and alcoholics (both groups exhibit signs of dementia unrelated to aging) 6. Epilepsy – characterized by seizures – caused by sudden bursts of irregular electrical activity in the brain