The Nervous System PDF

THE NERVOUS SYSTEM Eric B. Panopio, M.D.  Nervous System 2 types of cells in the nervous system: – Neurons. – Supporting cells. Nervous system is divided into: – Central nervous system (CNS): Brain. Spinal cord. – Peripheral nervous system (PNS): Cranial...

THE NERVOUS SYSTEM Eric B. Panopio, M.D.  Nervous System 2 types of cells in the nervous system: – Neurons. – Supporting cells. Nervous system is divided into: – Central nervous system (CNS): Brain. Spinal cord. – Peripheral nervous system (PNS): Cranial nerves. Spinal nerves.  Neurons Basic structural and functional units of the nervous system. – Cannot divide by mitosis. Respond to physical and chemical stimuli. Produce and conduct electrochemical impulses. Release chemical regulators. Nerve: – Bundle of axons located outside CNS. Most composed of both motor and sensory fibers.  THE NEURON The Neuron is the Basic Functional Unit of the Nervous System. Whatever their specific function, all neurons have the same physical parts: The Cell Body, Dendrites and One Axon. Neurons can be classified into THREE TYPES: SENSORY (RECEPTOR) NEURONS (AFFERENT) - Carry impulses from the SENSE ORGANS (RECEPTORS) to the Brain and Spinal Cord. Receptors detect external or internal changes and send the information to the Central Nervous System in the form of impulses by way of the Afferent Neurons. MOTOR NEURONS (EFFERENT) - Carry impulses from the Brain and Spinal Cord to MUSCLES or GLANDS. Muscles and Glands are Two Types of Effectors. In response to impulses, Muscles Contract and Glands Secrete. INTERNEURONS - Connect Sensory and Motor neurons and carry impulses between them. They are found entirely within the Central Nervous System  CELL BODY - The largest part, contains the nucleus and much of the cytoplasm (area between the nucleus and the cell membrane), most of the metabolic activity of the cell, including the generation of ATP (Adenine Triphosphate Compound that Stores Energy) and synthesis of protein. DENDRITES - Short branch extensions spreading out from the cell body. Dendrites Receive STIMULUS (Action Potentials) and carry IMPULSES from the environment or from other NEURONS and carry them toward the cell body AXON - A Long Fiber that carries impulses away from the cell body. Each neuron has only ONE AXON. The Axon Ends in a series of small swellings called AXON TERMINALS.  covered with a Lipid Layer known as the MYELIN SHEATH which insulates & speeds up transmission of nerve impulses through the axon  In the Peripheral Nervous System, Myelin is produced by SCHWANN CELLS, which surround the Axon.  GAPS (NODES) in the Myelin Sheath along the length of the Axon are known as the NODES OF RANVIER  Neuron Axon Dendrites Synapse Neurotransmitters Myelin sheath Types of Neurons  Neurons (continued) Cell body (perikaryon): – “Nutrition center.” – Cell bodies within CNS clustered into nuclei, and in PNS in ganglia. Dendrites: – Provide receptive area. – Transmit electrical impulses to cell body. Axon: – Conducts impulses away from cell body. – Axoplasmic flow: Proteins and other molecules are transported by rhythmic contractions to nerve endings. – Axonal transport: Employs microtubules for transport. May occur in orthograde or retrograde direction.  NERVE TISSUE & NERVOUS SYSTEM Central nervous system Brain & spinal cord Peripheral nervous system Spinal, cranial & peripheral nerves ganglia Nerve cells (neuron) Glial cell (supporting cells)  STRUCTURE OF NEURON Cell body Axon dendrite  GLIAL CELLS CNS Oligodendrocytes Ependymal cells Astrocytes Microglial cells PNS Neurolemmocytes (Schwann cells)  Cellular Organization of Neural Tissue Two cell types: 1. Neurons 2. Neuroglia – Schwann cells – Satellite cells – Astrocytes – Oligodendrocytes – Microglial cells – Ependymal cells Neuroglia Neuroglia (Neuroglial (Neuroglial Cells) Cells) Central Neuroglia Peripheral Neuroglia Astrocyte Schwann Cell protoplasmic astrocyte fibrous astrocyte in peripheral nerve Oligodendrocyte and ganglion perineuronal satellite cell Capsular (Satellite) Cell interfascicular cell in ganglion Microglia Ependymal Cell Types of Neurogli a  General Neuron Structure Cell body or Soma with Perikaryon Dendrites Axon with axon hillock Synaptic terminals Neurons (continued)  Functional Classification of Neurons Based upon direction impulses conducted. Sensory or afferent: – Conduct impulses from sensory receptors into CNS. Motor or efferent: – Conduct impulses out of CNS to effector organs. Association or interneurons: – Located entirely within the CNS. – Serve an integrative function.  Structural Classification of Neurons Based on the # of processes that extend from cell body. – Pseudounipolar: Short single process that branches like a T. – Sensory neurons. – Bipolar neurons: Have 2 processes. – Retina of the eye. – Multipolar: Have several dendrites and 1 axon. – Motor neuron.  PNS Supporting Cells Schwann cells: – Successive wrapping of the cell membrane. – Outer surface encased in glycoprotein basement membrane. – Provide insulation. Nodes of Ranvier: – Unmyelinated areas between adjacent Schwann cells that produce nerve impulses. Satellite cells: – Support neuron cell bodies within ganglia.  CNS Supporting Cells Oligodendrocytes: – Process occurs mostly postnatally. – Each has extensions that form myelin sheaths around several axons. Insulation. Oligodendrocyte Smaller than astrocyte Produce myelin in CNS (white matter vs. gray matter!) Myelin = ?  Nerve Regeneration Schwann cells: – Act as phagocytes, as the distal neuronal portion degenerates. – Surrounded by basement membrane, form regeneration tube: Serve as guide for axon. Send out chemicals that attract the growing axon. Axon tip connected to cell body begins to grow towards destination. Schwann Cells Responsible for and Peripheral Axonsmyelination, but surround all peripheral axons! Involved in repair mechanism after injury Wallerian Degeneration myelinated  CNS Supporting Cells (continued) Astrocytes: – Most abundant glial cell. – Vascular processes terminate in end-feet that surround the capillaries. – Stimulate tight junctions, contributing to blood- brain barrier. – Regulate external environment of K+ and pH. – Take up K+ from ECF, NTs released from axons, and lactic acid (convert for ATP production). Other extensions adjacent to synapses.  Astrocytes: largest & most numerous Function: BBB structural framework & repairs regulation of ions, nutrients, gases  CNS Supporting Cells (continued) Microglia: – Phagocytes, migratory. Ependymal cells: – Secrete CSF. – Line ventricles. – Function as neural stem cells. – Can divide and progeny differentiate. Microglia cells Smallest Phagocytosis of ?  # during infection or injury  Ependym al cells Lining of ventricles & central canal Some regions ciliated Some specialized to produce CSF MENINGES  The system of membranes which envelops the central nervous system. The meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater. The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system. Meningeal Coverings of the Brain  Pia Mater A very delicate membrane which firmly adheres to the surface of the brain and spinal cord. As such it follows all the minor contours of the brain (gyri and sulci). Pierced by blood vessels which travel to the brain and spinal cord, and its capillaries are responsible for nourishing the brain.  Joins with the ependyma which lines the ventricles to form choroid plexuses that produce cerebrospinal fluid. In the spinal cord, the Pia mater attaches to the Dura mater by the denticular ligaments through the arachnoid membrane. The pia mater is a neural crest derivative.  Arachnoid Membrane The middle element of the meninges which exists as a thin, transparent membrane. Has a spider web-like appearance. Provides a cushioning effect for the CNS. The arachnoid and pia mater are sometimes together called the leptomeninges.  Dura Mater A thick, durable membrane, closest to the skull. Consists of two layers, the periosteal layer, closest to the calvaria and the inner meningeal layer. Contains larger blood vessels which split into the capillaries in the pia mater. Surrounds and supports the large venous channels (dural sinuses) carrying blood from the brain toward the heart. separates into two layers at dural reflections, places where the inner dural layer is reflected as sheet-like protrusions into the cranial cavity.  Separates into two layers at dural reflections, places where the inner dural layer is reflected as sheet-like protrusions into the cranial cavity. There are two main dural reflections: – The tentorium cerebelli exists between and separates the cerebellum and brainstem from the occipital lobes of the cerebrum – The falx cerebri, which separates the two hemispheres of the brain, is located in the longitudinal cerebral fissure between the hemispheres  Normally, the dura mater is attached to the skull, or to the bones of the vertebral canal in the spinal cord. The arachnoid is attached to the dura mater, and the pia mater is attached to the central nervous system tissue. When the dura mater and the arachnoid separate through injury or illness, the space between them is the subdural space.  Subarachnoid Space The space which exists between the arachnoid and the pia mater Filled with cerebrospinal fluid. 3 principal openings: – Pontine cistern – Interpeduncular cistern – Cisterna magna  Pontine Cistern Opening at the ventral aspect of pons Contains the basilar artery Continuous behind with the subarachnoid cavity of the medulla spinalis, and with the cisterna cerebellomedullaris; and in front of the pons with the cisterna interpeduncularis.  Interpeduncular Cistern A wide cavity where the arachnoid extends across between the two temporal lobes It encloses the cerebral peduncles and the structures contained in the interpeduncular fossa, and contains the arterial circle of Willis  Cisterna Magna Opening in the subarachnoid space between the arachnoid and pia mater Located between the cerebellum and the dorsal surface of the medulla oblongata. CSF produced in the 4th ventricle drains into the cisterna magna via the lateral apertures and median aperture CEREBROSPIN AL FLUID  A clear bodily fluid that occupies the subarachnoid space and the ventricular system around and inside the brain. Essentially, the brain "floats" in it. More specifically, the CSF occupies the space between the arachnoid mater (the middle layer of the brain cover, meninges) and the pia mater (the layer of the meninges closest to the brain). It is produced in the brain by modified ependymal cells in the choroid plexus (approx. 50-70%), and the remainder is formed around blood vessels and along ventricular walls. A Graphic Presented where the CSF is Produced  It circulates from the choroid plexus through the interventricular foramina (foramen of Monro) into the third ventricle, and then through the cerebral aqueduct (aqueduct of Sylvius) into the fourth ventricle, where it exits through two lateral apertures (foramina of Luschka) and one median aperture (foramen of Magendie). It then flows through the cerebellomedullary cistern down the spinal cord and over the cerebral hemispheres.  Circulation of Cerebrospinal Fluid (CSF) LATERAL VENTRICLE’S LATERAL CHORIOD PLEXUSES CSF VENTRICLES THROUGH INTERVENTRICULAR FORAMINA THIRD VENTRICLE’S THIRD VENTRICLES CHORIOD PLEXUS CSF THROUGH CEREBRAL AQUEDUCT FOURTH VENTRICLE’S FOURTH CHORIOD PLEXUS CSF VENTRICLES THROUGH LATERAL & MEDIAN APERTURES SUBARACHNOID SPACE ARACHNOID VILLI OF DURAL VENOUS SINUSES Arterial Blood VENOUS BLOOD HEART AND LUNGS  CLINICAL APPLICATION Hydrocephalus The term hydrocephalus is derived from the Greek words "hydro" meaning water and "cephalus" meaning head. It is excessive accumulation of fluid in the brain.  Name the Organ: Sliced Brain at the Coronal Plane; Give the Pathology of the Organ: Flattened Gyri ABSENT SULCI Dilated Lateral & Third Ventricle of the BRAIN. Give Your Impression on this Figure: HYDROCEPHALUS A Case of HYDROCEPHALUS  Treatment of Hydrocephalus Ventriculo-Auricular Shunt Ventriculo-Peritoneal Shunt Hydrocephalus Types of Neurogli a  Neuron (Nerve Cell) Unit of structure and function Consists of 3 parts: 1. Cell Bodies – Contain nucleus, nucleolus and cytoplasm – Vesicular nucleus with a fish eye nucleus 2. Dendrites – Receptive portion; proximal segment with Niss l’s granules 3. Axons – Conducting portion – Long processes with collaterals – Devoid of Nissl’s granules  Types of Neurons Anaxonic neurons – Neurons with no axons & are found in the CNS; – With unknown function Unipolar neurons – Have their cell body off to the side & the axon & dendrite are continuous Bipolar neurons – Have a single dendrite & axon with the cell body in between Multiple neurons – Have several dendrites and a single axon with one or more branches 1. unipolar neuron 2. bipolar neuron 3. pseudounipolar neuron 4. multipolar neuron a. axon d. dendrite  Neuroglia Supporting cells of the nervous system 3 kinds: Astrocytes – provide structural support to the neurons & help maintain blood brain barrier Oligodendrocytes – extensions of these cells wrap themselves around axons in parts of the CNS & provide a structural framework Microglia – formation in phagocytosis to remove cell debris and waste  Synapse Functional connection between a neuron and another neuron or effector cell. Transmission in one direction only. Axon of first (presynaptic) to second (postsynaptic) neuron. Synaptic transmission is through a chemical gated channel. Presynaptic terminal (bouton) releases a neurotransmitter (NT).  I. CNS Neuroglial Cells – Astrocytes: most numerous glial cells – Oligodendrocytes: precursor of myelin sheath in CNS – Microglia: phagocytic cell in CNS Ependymal Cells – Lines the central canal of the SC and ventricles of the brain  II. PNS Schwann cells – Precursor of the myelin sheath in the PNS Satellite cells – Found in ganglia  Nervous System consists of the: Central Nervous System Peripheral Nervous System Autonomic Nervous System  The Central Nervous System (CNS) consist of the Brain and the Spinal Cord. The Spinal Cord carries messages from the body to the Brain, where they are analyzed and interpreted. Response Messages are then passed from the Brain through the Spinal Cord and to the rest of the Body. The Peripheral Nervous System (PNS) consists of the neurons NOT Included in the Brain and Spinal Cord. Some Peripheral Neurons Collect Information from the Body and Transmit it TOWARD the CNS. These are called AFFERENT NEURONS. Other Peripheral Neurons Transmit Information AWAY from the CNS. These are called EFFERENT NEURONS. The Autonomic Nervous System (ANS), also known as the "involuntary" nervous system controls activities of the body unconsciously. It includes all the nerve cells, or neurons, located outside the spinal cord and the brain stem. The Sympathetic division sends impulses that speed up or enhance (as in running) whereas the Parasympathetic division slows down (digestion). These two systems combined regulate the majority of the body's involuntary functions.  Nervous System Peripheral Central Autonomic Nervous Nervous Nervous System System System  Central Nervous System Spinal Cord Brain  Brain Cerebrum Brainstem Cerebellum  Cerebrum Telencephalon Diencephalon  Telencephalon Cerebral Basal Subcortical Cortex Ganglia White Matter  Basal Ganglia Caudate Globus Putamen Nucleus Pallidus  Brainstem Midbrain Pons Medulla Oblongata  Midbrain Quadrigeminal Plate Basis  Basis Cerebral Substantia Peduncle Nigra  Divisions of the Brain Primary Subdivision Derivative Division Cerebral cortex, basal Telencephalo ganglia n (Endbrain) Prosencephalon Subcortical white matter (Forebrain) Diencephalo Thalamus, Epithalamus n (Between Subthalamus, Hypothalamus brn) Mesencephalon Mesencephal Quadrigeminal plate (Midbrain) on Tegmentum, Basis Metencephal Pons Rhombencephal on Cerebellum on (Hindbrain) Myelencepha Medulla oblongata lon Embryonic Embryonic (developmental) (developmental) divisions divisions of of the the Brain Brain Primary Primary vesicle vesicle Secondary Secondary vesicle vesicle Derivatives Derivatives Cerebral Cerebral cortex cortex telencephalon telencephalon Cerebral Cerebral white white matter matter Basal Basal ganglia ganglia Prosencephalon Prosencephalon Thalamus Thalamus Hypothalamus Hypothalamus diencephalon diencephalon Subthalamus Subthalamus Epithalamus Epithalamus Mesencephalon Mesencephalon mesencephalon mesencephalon Midbrain Midbrain Cerebellum Cerebellum Rhombencephalo Rhombencephalo metencephalon metencephalon Pons Pons nn myelencephalon myelencephalon Medulla Medulla oblongata oblongata  The CNS The Central Nervous System consists of the Brain and Spinal Cord. It contains millions of neurons (nerve cells). The white matter consists of axons, it appears white because it contains a lot of fatty material called myelin. The myelin sheath insulates an axon from its neighbors. This means that nerve cells can conduct electrical messages without interfering with one another. The grey matter consists of cell bodies and the branched dendrites which effectively connect them together.  White Matter vs. Gray Matter Both the spinal cord and the brain consist of white matter = bundles of axons each coated with a sheath of myelin gray matter = masses of the cell bodies and dendrites — each covered with synapses. In the spinal cord, the white matter is at the surface, the gray matter inside  Cerebrum The cerebrum, which develops from the front portion of the forebrain, is the largest part of the mature brain. It consists of two large masses, called "cerebral hemispheres", which are almost mirror images of each other. They are connected by a deep bridge of nerve fibers called the "corpus callosum" and are separated by a layer called the "falx cerebri". The surface of the cerebrum is marked by numerous ridges or "convolutions", called "gyri", which are also separated by grooves. A shallow groove is called a "sulcus", and a very deep one is a "fissure". A "longitudinal" fissure separates the right and left hemispheres of the cerebrum, and a "transverse" fissure separates the cerebrum from the cerebellum. The lobes are named for the skull bones under which they rest and are: (1) the frontal lobe, (2) the parietal lobe, (3) the temporal lobe, (4) the occipital lobe  Cerebrum Frontal Lobe Temporal Lobe  Voluntary  Speech  Intelligence  Hearing  Cognitive function  Language  Speech Parietal Lobe  Emotion  Proprioceptive  Affective  Tactile  Motor Occipital Lobe  Vision Cerebrum – Cerebral Hemisphere Telencephalic structure –lateral ventricles 1. Cerebral Cortex - lobes, gyrus & sulcus 2. Cerebral White Matter (medullary center) 3. Basal Ganglia Cerebral Cortex Lobes of the Cerebral Cortex (lateral surface) 1. Frontal lobe 2. Parietal lobe 3. Temporal Lobe 4. Occipital lobe 5. Limbic lobe Lobes of the Cerebral Cortex (medial surface) 1. Frontal lobe 2. Parietal lobe 3. Temporal Lobe 4. Occipital lobe 5. Limbic lobe Lobes of the Cerebral Cortex (basal surface) 1. Frontal lobe 2. Parietal lobe 3. Temporal Lobe 4. Occipital lobe 5. Limbic lobe Brain  FRONTAL LOBE Located in front of the central sulcus. The largest lobe Concerned with abstract thought, concentration, memory and motor function. Concerned with reasoning, planning, parts of speech and movement (motor cortex), emotions, and problem-solving.  PARIETAL LOBE Located behind the central sulcus. Concerned with perception of stimuli related to touch, pressure, temperature and pain. Sensory lobe Analyzes sensory information and relays the interpretation of this information to the thalamus and other cortical areas Individual’s awareness of the body in space as well as orientation in space and spatial relation  TEMPORAL LOBE Located below the lateral fissure. Concerned with perception and recognition of auditory stimuli (hearing) and memory (hippocampus). Auditory cortex  OCCIPITAL LOBE Located at the back of the brain, behind the parietal lobe and temporal lobe. Concerned with many aspects of vision Visual cortex Cortical Functional Regions Hemisphere of the Brain The hemispheres Left Hemisphere communicate with Language each other through a thick band of 200-250 Math million nerve fibers Logic called the corpus callosum. Right Hemisphere A smaller band of Spatial abilities nerve fibers called the Face recognition anterior commissure also connects parts of Visual imagery the cerebral Music hemispheres.  Brainstem The lower extension of the brain where it connects to the spinal cord. Neurological functions located in the brainstem include those necessary for survival (breathing, digestion, heart rate, blood pressure) and for arousal (being awake and alert). Most of the cranial nerves come from the brainstem. The brainstem is the pathway for all fiber tracts passing up and down from peripheral nerves and spinal cord to the highest parts of the brain. Brain Stem  Brainstem Midbrain  Carry sensory impulses from the SC to the thalamus & motor impulses from the cortex back to the SC Pons  Carry signals between various regions of the brain Medulla  Cardiac center: regulates heart rate  Respiratory center: regulates breathing rate & depth  Midbrain The midbrain serves as the nerve pathway of the cerebral hemispheres and contains auditory and visual reflex centers.  Medulla Oblongata The medulla oblongata functions primarily as a relay station for the crossing of motor tracts between the spinal cord and the brain. It also contains the respiratory, vasomotor and cardiac centers, as well as many mechanisms for controlling reflex activities such as coughing, gagging, swallowing and vomiting.  Pons The pons is a bridge-like structure which links different parts of the brain and serves as a relay station from the medulla to the higher cortical structures of the brain. Cranial nerves V, VI, VII and VIII take origin at the border of the pons.  Thalamus Lies on the other side of the third ventricle and acts primarily as a relay center  Hypothalamus The main function of the hypothalamus is homeostasis, or maintaining the body's status quo. Factors such as blood pressure, body temperature, fluid and electrolyte balance, and body weight are held to a precise value called the set-point. The Hypothalamus is the control center of all autonomic regulatory activities of the body. It is the hub for automatic and endocrine homeostatic systems such as cardiovascular, temperature, and abdominal visceral regulation. It manages all endocrine hormonal levels, sensory processing, and organizing body metabolism, as well as behaviors.  Functions of the Hypothalamus Pituitary gland Hormonal regulation regulation Ovarian function Blood pressure Testicular regulation function Feeding & thirst Mood & Reflexes behavioral function Body temp Behavior functions regulation Sleep & Heart rate wakefulness Bladder function Energy levels  Cerebellum The cerebellum (literally "little brain") is a brain region important for a number of motor and cognitive functions, including motor learning, movement planning, motor timing, posture maintenance, and some cognitive/attentive functions. Tree of life/ cauliflower The portion of the brain (located at the back) which helps coordinate movement (balance and muscle coordination). Damage may result in ataxia which is a problem of muscle coordination. This can interfere with a person's ability to walk, talk, eat, and to perform other self care tasks.  Cerebellum Paleocerebellum or Anterior Lobe  For propulsive stereotyped movements like swimming and walking  Concerned for regulation of muscle tone Neocerebellum or Posterior Lobe  Concerned with muscle coordination Archicerebellum or Flocculonodular Lobe  Concerned with equilibrium Spinal Cord  Dorsal Column System: Ascendin g Pathway Descendin g Pathway: Pyramidal System Meningeal Coverings of the Spinal Cord  Posterior or Dorsal Portion Ascending Tracts: Consists of axons that conduct action potentials or Impulses towards Anterior or Ventral Portion the brain. Posterior or Dorsal Portion Descending Tracts: Consist of axons that conduct action potentials or Anterior or Ventral Portion  Ascending Tracts Lateral & Anterior Spinothalamic Tracts  pain & temperature sensation and crude touch Dorsal Column  fine touch, proprioception, two-point discrimination Dorsal & Ventral Spinocerebellar Tracts  proprioceptive and exteroceptive stimuli for movement and position sense Spinoreticular Tract  deep and chronic pain  Descending Tracts Anterior Corticospinal (Direct Pyramidal Tract) Pathway for control of voluntary motion Lateral Corticospinal (Crossed Pyramidal Tract) Pathway for control of voluntary motion Vestibulospinal Tract For postural reflexes Rubrospinal Tract Serves as motor junction  Reticulospinal Tract For modulation of sensory transmission esp. pain; spinal reflexes Tectospinal Tract For reflex head turning Medial Longitudinal Fissure For coordination of head and eye movements PERIPHERAL NERVOUS SYSTEM  Division of the PNS Sensory Division  Visceral sensory nerves: impulses from body organs  Somatic sensory nerves: impulses from body surface Motor Division  Somatic division: impulses from CNS to skeletal ms  Autonomic division: sympathetic parasympathetic PNS consists of: nerves, plexuses, ganglia  Spinal Nerves Arise from the spinal cord within the vertebral canal 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal The dorsal roots are sensory and transmit sensory impulses from specific areas of the body known as dermatomes The ventral roots are motor and transmit impulses from the spinal cord to the body Spinal Nerves  Plexuses Cervical Plexus formed from the ventral rami of C1 to C4 spinal nerves supply cutaneous nerve for the ventrolateral portions of the back of the head Brachial Plexus derived from the ventral rami of C4 to T1 spinal nerves  Cranial Nerves 12 pairs of cranial nerves the olfactory and optic nerves are the only one connected directly to the brain Classified into General  arise from roots of the cranial & spinal dorsal roots Special  arise from specific roots of cranial nerves Cranial Nerves  CN I – Olfactory Nerve The olfactory nerve has only a special sensory component. Special sensory (special afferent)- Functions in the special sense of smell or olfaction. The olfactory system consists of the olfactory epithelium, bulbs and tracts along with olfactory areas of the brain collectively known as the rhinencephalon.  CN II - Optic Nerve The optic nerve has only a special sensory component Special sensory conveys visual information from the retina (special afferent). Visual information enters the eye in the form of photons of light which are converted to electrical signals in the retina. These signals are carried via the optic nerves, chiasm, and tract to the lateral geniculate nucleus of each thalamus and then to the visual centers of the brain for interpretation  CN III - Oculomotor Nerve Consists of two components with distinct functions: Somatic motor (general somatic efferent) Supplies four of the six extraocular muscles of the eye and the levator palpebrae superioris muscle of the upper eyelid. The somatic motor component of CN III plays a major role in controlling the muscles responsible for the precise movement of the eyes for visual tracking or fixation on an object. Visceral motor (general visceral efferent) Parasympathetic innervation of the constrictor pupillae and ciliary muscles. The visceral motor component is involved in the pupillary light and accommodation reflexes.  CN IV - Trochlear Nerve The trochlear nerve has only a somatic motor component: Somatic motor (general somatic efferent) Somatic motor innervates the superior oblique muscle of the contralateral orbit. CN V – Trigeminal Nerve Mixed Facial sensation, corneal reflex, mastication  CN VI – Abducens Nerve Has only a somatic motor (general somatic efferent) component. Somatic motor: innervates the lateral rectus muscle of the ipsilateral orbit. The lateral rectus muscle is one of the six extraocular muscles responsible for the precise movement of the eye for visual tracking or fixation on an object.  CN VII - Facial Nerve The facial nerve has four components with distinct functions: Branchial motor (special visceral efferent) Supplies the muscles of facial expression; posterior belly of digastric muscle; stylohyoid, and stapedius. Largest portion of the facial nerve Visceral motor (general visceral efferent) Parasympathetic innervation of the lacrimal, submandibular, and sublingual glands, as well as mucous membranes of nasopharynx, hard and soft palate. Special sensory (special afferent) Taste sensation from the anterior 2/3 of tongue; hard and soft palates. General sensory (general somatic afferent) General sensation from the skin of the concha of the auricle and from a small area behind the ear. CN VIII – Auditory Nerve Acoustic Sensory Hearing and equilibrium  CN IX – Glossopharyngeal Nerve The glossopharyngeal nerve consists of five components with distinct functions: Branchial motor Supplies the stylopharyngeus muscle. Visceral motor (Parasympathetic innervation of the smooth muscle and glands of the pharynx, larynx, and viscera of the thorax and abdomen. Visceral sensory Carries visceral sensory information from the carotid sinus and body. General sensory Provides general sensory information from the skin of the external ear, internal surface of the tympanic membrane, upper pharynx, and the posterior one-third of the tongue. Special sensory Provides taste sensation from the posterior one-third of the tongue.  CN X – Vagus Nerve The vagus nerve consists of five components with distinct functions: Branchial motor Supplies the voluntary muscles of the pharynx and most of the larynx, as well as one extrinsic muscle of the tongue. Visceral motor Parasympathetic innervation of the smooth muscle and glands of the pharynx, larynx, and viscera of the thorax and abdomen. Visceral sensory Provides visceral sensory information from the larynx, esophagus, trachea, and abdominal and thoracic viscera, as well as the stretch receptors of the aortic arch and chemoreceptors of the aortic bodies. General sensory Provides general sensory information from the skin of the back of the ear and external auditory meatus, parts of the external surface of the tympanic membrane, and the pharynx. Special sensory A very minor component of CN X. Provides taste sensation from the epiglottic region. This component will not be discussed further  CN XI - Accessory Nerve The accessory nerve has a cranial root and a spinal root, both of which consist of branchial motor fibers. Branchial motor - cranial root (special visceral efferent) Innervates muscles of larynx and pharynx. Branchial motor - spinal root (special visceral efferent) Innervates the trapezius and sternocleidomastoid muscles.  CN XII – Hypoglossal Nerve Hypoglossal Motor Movement of the tongue AUTONOMIC NERVOUS SYSTEM  Sympathetic Nervous System Regulates visceral functions not usually subject to conscious control These fibers arise from the thoracic and spinal nerves Parasympathetic Nervous System Supplied by 4 cranial nerves: CN III, CN VII, CN IX, CN X Supplied by 3 sacral nerves S2, S3, S4: forms the pelvic splanchnic nerves These fibers arise from the cranial & sacral nerves Innervati ons by ANS NEUROLOGICAL ASSESSMENT  1. Cranial Nerves CN I – Olfactory Nerve (Sensory) CN II – Optic Nerve (Sensory) CN III – Oculomotor (Motor) CN IV – Trochlear Nerve (Motor) CN V – Trigeminal Nerve (Mixed) CN VI – Abducens Nerve (Motor) CN VII – Facial Nerve (Mixed) CN VIII – Auditory Nerve (Sensory) CN IX – Glossopharyngeal Nerve (Mixed) CN X – Vagus Nerve (Mixed) CN XI – Accessory Nerve (Motor) CN XII – Hypoglossal Nerve (Motor)  2. Motor System Muscle size a. bilaterally symmetrical b. atrophy c. hypertrophy Muscle Strength a. paresis b. paralysis Tone a. flaccidity b. spasticity c. rigidity d. involuntary movements  Cerebellar Function A. Balance Tests a. Gait - Normal gait - Tandem walking b. Romberg Test c. Shallow Knee bend B. Coordinating and Skilled Movements a. Rapid alternating movement (RAM) b. Finger to finger test c. Finger to nose test d. Heel to shin test  3. Sensory System Spinothalamic tract a. pain b. temperature c. light touch Posterior column tract a. Vibration b. Proprioception & Kinesthesia c. Tactile Discrimination (Fine touch) d. Stereognosis e. Graphesthesia f. Two point discrimination: normal 4 -5 mm h. Point location  4. Reflexes Stretch, or Deep Tendon Reflex a. Biceps/Brachioradialis reflex (C5 to C6) b. Triceps reflex (C7 to C8) c. Quadriceps reflex “knee jerk” (L2 to L4) d. Achilles reflex “ankle jerk” (L5 to S2) f. Abdominal reflexes - upper (T8 to T10) - lower (T10 to T12) g. Cremasteric reflex (L1 to L2) h. Plantar reflex (L4 to S2)  5. Neurologic Reflex LOC Motor Function Pupillary Response VS GCS  End: Nervous System Overview Prepared by: Eric B. Panopio, M.D.