Nervous System Part 1 PDF

The Nervous System Functions of the Nervous System Maintain homeostasis with electrical signals Provide for sensation Provide for higher mental functions and emotions Control and activate muscles and glands  Roles of the Nervous System 1. Sensory input – gathering information...

The Nervous System Functions of the Nervous System Maintain homeostasis with electrical signals Provide for sensation Provide for higher mental functions and emotions Control and 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 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 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 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 Slide 7.3c Organization of the Nervous System Figure 7.2 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 CNS Astrocytes Provide structural support Regulate neuronal signaling Help with neural tissue repair Slide 7.7b  Support Cells of the CNS Ependymal cells Lines the ventricles of brain and central canal of spinal cord Circulates and produces CSF Slide 7.7b  Support Cells of the CNS Microglia Protect CNS from infection By becoming phagocytic in response to inflammation Slide 7.7b  Support Cells of the CNS Oligodendrocytes Form myelin sheath in the central nervous system Slide 7.7b  Support Cells of the PNS Schwann cells Form myelin sheath in the peripheral nervous system Figure 7.3e Slide 7.7b  Support Cells of the PNS Satellite cells Provide support and nutrition to neurons Protect neurons from heavy metal poisons 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) Slide 7.8 Neuron Anatomy Cell body Nucleus Large nucleolus Figure 7.4a 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 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 Slide 7.12  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 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 Slide 7.14a  Functional Classification of Neurons Interneurons (association neurons): Found in neural pathways in the central nervous system Connect sensory and motor neurons Slide 7.14b Neuron Classification Figure 7.6 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 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 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 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 Slide 7.20  Continuation of the Nerve Impulse between 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 Slide 7.21 How Neurons Communicate at Synapses Figure 7.10 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 Slide 7.23 Simple Reflex Arc Figure 7.11b, c Slide 7.24  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 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 Slide 7.26  Regions of the Brain Cerebral hemispheres Diencephalon Brain stem Cerebellum Figure 7.12 Slide 7.27 Cerebral Hemispheres (Cerebrum) Paired (left & right), superior parts of the brain Include more than half of the brain mass Largest & most complex area of the brain Figure 7.13a Slide Cerebral Hemispheres (Cerebrum) The surface is made of ridges (gyri) and grooves (sulci) Figure 7.13a 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 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 Slide 7.30 Sensory and Motor Areas of the Cerebral Cortex Figure 7.14 Slide 7.31  Temporal Lobe Gustatory, auditory, olfactory area Occipital Lobe Visual areas Parietal Lobe Sensations; pain; hot & cold; touch; speech & reading Slide  Specialized Area of the Cerebrum Interpretation areas of the cerebrum Speech/language region Language comprehension region General interpretation area Slide Specialized Area of the Cerebrum Figure 7.13c Slide  Layers of the Cerebrum Gray matter Outer layer Composed mostly of neuron cell bodies and their dendrites Initiates thoughts & voluntary actions Figure 7.13a Slide  Layers of the Cerebrum White matter Bundles of parallel axons with myelin sheaths Forms conduction pathways which propagate action potentials 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 hemispheres Made of three parts: Thalamus Hypothalamus Epithalamus 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 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 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) Slide Midbrain Mostly composed of tracts of nerve fibers Reflex centers for vision and hearing 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 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 Slide 7.41 Cerebellum Two hemispheres with convoluted surfaces Functions in balance and coordination Provides involuntary coordination of body movements Slide Cerebellum Figure 7.15a Slide Protection of the Central Nervous System Scalp and skin Skull and vertebral column Meninges Figure 7.16a Slide Protection of the Central Nervous System Cerebrospinal fluid Blood brain barrier Figure 7.16a 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 Slide Meninges Arachnoid layer Middle layer Web-like Pia mater Internal layer Clings to the surface of the brain 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 Slide 7.46 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 Slide 7.48 Spinal Cord Extends from medulla oblongata to T12 region 31 pairs of nerves Function is to conduct nerve impulses & serve for spinal reflex centers Spinal tap – withdrawal of CSF (2-3 ml); decreases pressure and can diagnose problems