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The Nervous System Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Nervous System Passage of information occurs in 2 ways: Nerves :process and send information fast (eg. Stepping on a tack) Hormones: process & send information slowly (eg. Growth hormone) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Neurons (Nerve Cells) Conduct messages in the form of nerve impulses They number in the billions (much higher in anatomy teachers) Have extreme longevity Most cannot divide (hippocampus is a rare exception; it is involved in memory). Have a high metabolic rate; require mucho oxygen and glucose 3 basic regions: dendrites, cell body, and axons Impulses travel from dendrites to cell body to axons Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Neurons (Nerve Cells) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.4b Neuroglial Cells Nervous tissue cells that aid and protect components of nervous system by functioning like connective tissue. Various types of neuroglial cells in the CNS: 1. Microglia- function as phagocytes by engulfing foreign invaders. 2. Oligodendrocytes- connect thick neuronal fibers and produce an important insulating material called the myelin sheath. 3. Astrocytes-star shaped cells that connect neurons together and to their blood supply. 4. Ependymal- (epithelial-like) provide a barrier between brain and spinal fluid. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Nervous System The master controlling and communicating system of the body Functions Sensory input – monitoring stimuli Integration – interpretation of sensory input Motor output – response to stimuli Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Nervous System Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.1 Organization of the Nervous System Central nervous system (CNS) Brain and spinal cord Integration and command center Peripheral nervous system (PNS) Paired spinal and cranial nerves Carries messages to and from the spinal cord and brain Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Involuntary Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Voluntary Motor Division: Two Main Parts Somatic nervous system Conscious control of skeletal muscles Autonomic nervous system (ANS) Regulates smooth muscle, cardiac muscle, and glands Divisions – sympathetic and parasympathetic Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Differences Between Sympathetic & Parasympathetic Systems Parasympathetic- “resting and digesting system” Most active in nonstressful situations Keeps energy use low and maintains vital housekeeping activities running. Sympathetic division- “fight or flight” division Exercise, excitement, emergency, and embarrassment division Prepares the body for action Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Differences Between Sympathetic & Parasympathetic Systems Characteristic Sympathetic Parasympathetic When functioning? Emergencies Normal/Everyday Digestive System Inhibits/slows Promotes Pupil Dialates Constricts Heartbeat/breathing rate Accelerates Retards Neurotransmitter Norepinephrine Acetylcholine Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Concept Check What is the difference between peripheral and central nervous systems? Explain the difference between somatic and autonomic nervous systems… What are the two divisions of the PNS? Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Neurons A neuron has a cell body with mitochondria, lysosomes, golgi apparatus, rough endoplasmic reticulum, and neurofibrils. Nerve fibers include a solitary axon and numerous dendrites Brnaching dendrites carry impulses from other neurons (or from receptors) toward the cell body. The axon transmits the impulse away from the cell body and may give off side branches Larger axons are enclosed by sheaths of myelin provided by Schwann cells and are myelinated fibers. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Neurons Continued. . . The outer layer of myelin is surrounded by a sheath made up of the cytoplasm and nuclei of the Schwann cell. Narrow gaps in the myelin sheath between Schwann cells are called Nodes of Ranvier. The smallest axons lack a myelin sheath. White matter vs. gray matter White brain matter in the CNS is myelinated. Gray brain matter in the CNS is unmylinated Meniges are membranse that wrap & protect the CNS (brain & spinal cord) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Myelin Sheath Whitish, fatty (protein-lipoid), segmented sheath around most long axons It functions to: Increase the speed of nerve impulse transmission because the nerve impulse jumps from one Node of Ranvier to the next. Protect the axon by insulating to prevent the nerve impulse form “shorting” out. Electrically insulate fibers from one another Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Histology of Nerve Tissue The two principal cell types of the nervous system are: Neurons – excitable cells that transmit electrical signals Supporting cells – cells that surround and wrap neurons Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Microglia and Ependymal Cells Microglia – small, ovoid cells with spiny processes Phagocytes that monitor the health of neurons Ependymal cells – range in shape from squamous to columnar They line the central cavities of the brain and spinal column Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Microglia and Ependymal Cells Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.3b, c Oligodendrocytes, Schwann Cells, and Satellite Cells Oligodendrocytes – branched cells that wrap CNS nerve fibers Schwann cells (neurolemmocytes) – surround fibers of the PNS Satellite cells surround neuron cell bodies with ganglia Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Oligodendrocytes, Schwann Cells, and Satellite Cells Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.3d, e Concept Check What is the difference between Schwann Cells and Oligodendrocytes? Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Dendrites of Motor Neurons Short, tapering, and diffusely branched processes They are the receptive, or input, regions of the neuron Electrical signals are conveyed as graded potentials (not action potentials) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Axons: Function Generate and transmit action potentials Secrete neurotransmitters from the axonal terminals Movement along axons occurs in two ways Anterograde — toward axonal terminal Retrograde — away from axonal terminal Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Myelin Sheath and Neurilemma: Formation Formed by Schwann cells in the PNS A Schwann cell: Envelopes an axon in a trough Encloses the axon with its plasma membrane Has concentric layers of membrane that make up the myelin sheath Neurilemma – remaining nucleus and cytoplasm of a Schwann cell Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Myelin Sheath and Neurilemma: Formation PLAY InterActive Physiology ®: Nervous System I, Anatomy Review, page 10 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.5a–c Nodes of Ranvier (Neurofibral Nodes) Gaps in the myelin sheath between adjacent Schwann cells They are the sites where axon collaterals can emerge PLAY InterActive Physiology ®: Nervous System I, Anatomy Review, page 11 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Unmyelinated Axons A Schwann cell surrounds nerve fibers but coiling does not take place Schwann cells partially enclose 15 or more axons Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Axons of the CNS Both myelinated and unmyelinated fibers are present Myelin sheaths are formed by oligodendrocytes Nodes of Ranvier are widely spaced There is no neurilemma Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Regions of the Brain and Spinal Cord White matter – dense collections of myelinated fibers Gray matter – mostly soma (body) and unmyelinated fibers Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Concept Check Why would there be unmyelinated neurons in the brain? Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Neuron Classification Functional: Sensory (afferent) — transmit impulses toward the CNS Motor (efferent) — carry impulses away from the CNS Interneurons (association neurons) — shuttle signals through CNS pathways Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Neurophysiology Neurons are highly irritable Action potentials, or nerve impulses, are: Electrical impulses carried along the length of axons Always the same regardless of stimulus The underlying functional feature of the nervous system Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Electricity Definitions Voltage (V) – measure of potential energy generated by separated charge Potential difference – voltage measured between two points Current (I) – the flow of electrical charge between two points Resistance (R) – hindrance to charge flow Insulator – substance with high electrical resistance Conductor – substance with low electrical resistance Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Concept Check Use the following in a sentence to explain what they mean: Resistance, current, insulator Voltage, potential difference Conductor, current, voltage Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Electrical Current and the Body Reflects the flow of ions rather than electrons There is a potential on either side of membranes when: The number of ions is different across the membrane The membrane provides a resistance to ion flow Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Role of Ion Channels Types of plasma membrane ion channels: PLAY Passive, or leakage, channels – always open Chemically gated channels – open with binding of a specific neurotransmitter Voltage-gated channels – open and close in response to membrane potential Mechanically gated channels – open and close in response to physical deformation of receptors InterActive Physiology ®: Nervous System I: Ion Channels Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Operation of a Gated Channel Example: Na+-K+ gated channel Closed when a neurotransmitter is not bound to the extracellular receptor Na+ cannot enter the cell and K+ cannot exit the cell Open when a neurotransmitter is attached to the receptor Na+ enters the cell and K+ exits the cell Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Operation of a Gated Channel Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.6a Operation of a Voltage-Gated Channel Example: Na+ channel Closed when the intracellular environment is negative Na+ cannot enter the cell Open when the intracellular environment is positive Na+ can enter the cell Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Operation of a Voltage-Gated Channel Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.6b Gated Channels When gated channels are open: Ions move quickly across the membrane Movement is along their electrochemical gradients An electrical current is created Voltage changes across the membrane Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Electrochemical Gradient Ions flow along their chemical gradient when they move from an area of high concentration to an area of low concentration Ions flow along their electrical gradient when they move toward an area of opposite charge Electrochemical gradient – the electrical and chemical gradients taken together Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Resting Membrane Potential (Vr) The potential difference (–70 mV) across the membrane of a resting neuron It is generated by different concentrations of Na+, K+, Cl, and protein anions (A) Ionic differences are the consequence of: Differential permeability of the neurilemma to Na+ and K+ Operation of the sodium-potassium pump PLAY InterActive Physiology ®: Nervous System I: Membrane Potential Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Measuring Mebrane Potential Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.7 Resting Membrane Potential (Vr) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.8 Membrane Potentials: Signals Used to integrate, send, and receive information Membrane potential changes are produced by: Changes in membrane permeability to ions Alterations of ion concentrations across the membrane Types of signals – graded potentials and action potentials Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Changes in Membrane Potential Changes are caused by three events Depolarization – the inside of the membrane becomes less negative Repolarization – the membrane returns to its resting membrane potential Hyperpolarization – the inside of the membrane becomes more negative than the resting potential Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Changes in Membrane Potential Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.9 Action Potential: Role of the Sodium-Potassium Pump Repolarization Restores the resting electrical conditions of the neuron Does not restore the resting ionic conditions Ionic redistribution back to resting conditions is restored by the sodium-potassium pump Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Phases of the Action Potential 1 – resting state 2 – depolarization phase 3 – repolarization phase 4 – hyperpolarization Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.12 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Saltatory Conduction Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.16 Synapses A junction that mediates information transfer from one neuron: To another neuron To an effector cell Presynaptic neuron – conducts impulses toward the synapse Postsynaptic neuron – transmits impulses away from the synapse Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Synapses Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.17 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Chemical Synapses Specialized for the release and reception of neurotransmitters Typically composed of two parts: Axonal terminal of the presynaptic neuron, which contains synaptic vesicles Receptor region on the dendrite(s) or soma of the postsynaptic neuron PLAY InterActive Physiology ®: Nervous System II: Anatomy Review, page 7 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Synaptic Cleft Fluid-filled space separating the presynaptic and postsynaptic neurons Prevents nerve impulses from directly passing from one neuron to the next Transmission across the synaptic cleft: Is a chemical event (as opposed to an electrical one) Ensures unidirectional communication between neurons PLAY InterActive Physiology ®: Nervous System II: Anatomy Review, page 8 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Synaptic Cleft: Information Transfer Nerve impulses reach the axonal terminal of the presynaptic neuron and open Ca2+ channels Neurotransmitter is released into the synaptic cleft via exocytosis in response to synaptotagmin Neurotransmitter crosses the synaptic cleft and binds to receptors on the postsynaptic neuron Postsynaptic membrane permeability changes, causing an excitatory or inhibitory effect PLAY InterActive Physiology ®: Nervous System II: Synaptic Transmission, pages 3–6 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Neurotransmitters Chemicals used for neuronal communication with the body and the brain 50 different neurotransmitters have been identified Classified chemically and functionally Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Synaptic Cleft: Information Transfer Ca2+ 1 Neurotransmitter Axon terminal of presynaptic neuron Postsynaptic membrane Mitochondrion Axon of presynaptic neuron Na+ Receptor Postsynaptic membrane Ion channel open Synaptic vesicles containing neurotransmitter molecules 5 Degraded neurotransmitter 2 Synaptic cleft Ion channel (closed) 3 4 Ion channel closed Ion channel (open) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.18 Synaptic Cleft: Information Transfer Ca2+ 1 Axon terminal of presynaptic neuron Axon of presynaptic neuron Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.18 Synaptic Cleft: Information Transfer Ca2+ 1 Axon terminal of presynaptic neuron Mitochondrion Axon of presynaptic neuron Synaptic vesicles containing neurotransmitter molecules 2 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.18 Synaptic Cleft: Information Transfer Ca2+ 1 Axon terminal of presynaptic neuron Mitochondrion Postsynaptic membrane Axon of presynaptic neuron Synaptic vesicles containing neurotransmitter molecules 2 Synaptic cleft Ion channel (closed) 3 Ion channel (open) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.18 Synaptic Cleft: Information Transfer Ca2+ 1 Neurotransmitter Axon terminal of presynaptic neuron Postsynaptic membrane Mitochondrion Axon of presynaptic neuron Na+ Receptor Postsynaptic membrane Ion channel open Synaptic vesicles containing neurotransmitter molecules 2 Synaptic cleft Ion channel (closed) 3 4 Ion channel (open) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.18 Synaptic Cleft: Information Transfer Ca2+ 1 Neurotransmitter Axon terminal of presynaptic neuron Postsynaptic membrane Mitochondrion Axon of presynaptic neuron Na+ Receptor Postsynaptic membrane Ion channel open Synaptic vesicles containing neurotransmitter molecules 5 Degraded neurotransmitter 2 Synaptic cleft Ion channel (closed) 3 4 Ion channel closed Ion channel (open) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 11.18 Basic Pattern of the Central Nervous System Spinal Cord Central cavity surrounded by a gray matter core External to which is white matter composed of myelinated fiber tracts Brain Similar to spinal cord but with additional areas of gray matter Cerebellum has gray matter in nuclei Cerebrum has nuclei and additional gray matter in the cortex Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Functional Areas of the Cerebral Cortex The three types of functional areas are: Motor areas – control voluntary movement Sensory areas – conscious awareness of sensation Association areas – integrate diverse information Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Functional Areas of the Cerebral Cortex Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.8a Functional Areas of the Cerebral Cortex Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.8b Lateralization of Cortical Function Lateralization – each hemisphere has abilities not shared with its partner Cerebral dominance – designates the hemisphere dominant for language Left hemisphere – controls language, math, and logic Right hemisphere – controls visual-spatial skills, emotion, and artistic skills Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Cerebral White Matter Consists of deep myelinated fibers and their tracts It is responsible for communication between: The cerebral cortex and lower CNS center, and areas of the cerebrum Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Cerebral White Matter Types include: Commissures – connect corresponding gray areas of the two hemispheres Association fibers – connect different parts of the same hemisphere Projection fibers – enter the hemispheres from lower brain or cord centers Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Fiber Tracts in White Matter Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.10a Fiber Tracts in White Matter Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.10b Brain Stem Consists of three regions – midbrain, pons, and medulla oblongata Similar to spinal cord but contains embedded nuclei Controls automatic behaviors necessary for survival Provides the pathway for tracts between higher and lower brain centers Associated with 10 of the 12 pairs of cranial nerves Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Brain Stem Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12.15a Peripheral Nervous System (PNS) PNS – all neural structures outside the brain and spinal cord Includes sensory receptors, peripheral nerves, associated ganglia, and motor endings Provides links to and from the external environment Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings PNS in the Nervous System Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.1 Sensory Receptors Structures specialized to respond to stimuli Activation of sensory receptors results in depolarizations that trigger impulses to the CNS The realization of these stimuli, sensation and perception, occur in the brain Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Receptor Classification by Stimulus Type Mechanoreceptors – respond to touch, pressure, vibration, stretch, and itch Thermoreceptors – sensitive to changes in temperature Photoreceptors – respond to light energy (e.g., retina) Chemoreceptors – respond to chemicals (e.g., smell, taste, changes in blood chemistry) Nociceptors – sensitive to pain-causing stimuli Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.2 Main Aspects of Sensory Perception Perceptual detection – detecting that a stimulus has occurred and requires summation Magnitude estimation – how much of a stimulus is acting Spatial discrimination – identifying the site or pattern of the stimulus Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Main Aspects of Sensory Perception Feature abstraction – used to identify a substance that has specific texture or shape Quality discrimination – the ability to identify submodalities of a sensation (e.g., sweet or sour tastes) Pattern recognition – ability to recognize patterns in stimuli (e.g., melody, familiar face) Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Structure of a Nerve Nerve – cordlike organ of the PNS consisting of peripheral axons enclosed by connective tissue Connective tissue coverings include: Endoneurium – loose connective tissue that surrounds axons Perineurium – coarse connective tissue that bundles fibers into fascicles Epineurium – tough fibrous sheath around a nerve Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Structure of a Nerve Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.3b Classification of Nerves Sensory and motor divisions Sensory (afferent) – carry impulse to the CNS Motor (efferent) – carry impulses from CNS Mixed – sensory and motor fibers carry impulses to and from CNS; most common type of nerve Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Peripheral Nerves Mixed nerves – carry somatic and autonomic (visceral) impulses The four types of mixed nerves are: Somatic afferent and somatic efferent Visceral afferent and visceral efferent Peripheral nerves originate from the brain or spinal column Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Regeneration of Nerve Fibers Damage to nerve tissue is serious because mature neurons are amitotic If the soma of a damaged nerve remains intact, damage can be repaired Regeneration involves coordinated activity among: Macrophages – remove debris Schwann cells – form regeneration tube and secrete growth factors Axons – regenerate damaged part Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Regeneration of Nerve Fibers Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.4 Regeneration of Nerve Fibers Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.4 Cranial Nerves Twelve pairs of cranial nerves arise from the brain They have sensory, motor, or both sensory and motor functions Each nerve is identified by a number (I through XII) and a name Four cranial nerves carry parasympathetic fibers that serve muscles and glands Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Cranial Nerves Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.5a Summary of Function of Cranial Nerves Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.5b Cranial Nerve I: Olfactory Arises from the olfactory epithelium Passes through the cribriform plate of the ethmoid bone Fibers run through the olfactory bulb and terminate in the primary olfactory cortex Functions solely by carrying afferent impulses for the sense of smell Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Cranial Nerve I: Olfactory Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure I from Table 13.2 Cranial Nerve II: Optic Arises from the retina of the eye Optic nerves pass through the optic canals and converge at the optic chiasm They continue to the thalamus where they synapse From there, the optic radiation fibers run to the visual cortex Functions solely by carrying afferent impulses for vision Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Cranial Nerve II: Optic Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure II from Table 13.2 Cranial Nerve III: Oculomotor Fibers extend from the ventral midbrain, pass through the superior orbital fissure, and go to the extrinsic eye muscles Functions in raising the eyelid, directing the eyeball, constricting the iris, and controlling lens shape Parasympathetic cell bodies are in the ciliary ganglia Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Cranial Nerve III: Oculomotor Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure III from Table 13.2 Cranial Nerve IV: Trochlear Fibers emerge from the dorsal midbrain and enter the orbits via the superior orbital fissures; innervate the superior oblique muscle Primarily a motor nerve that directs the eyeball Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Cranial Nerve IV: Trochlear Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure IV from Table 13.2