Nervous System I PDF

Central Nervous System (CNS) brain spinal cord Peripheral Nervous System (PNS) cranial nerves spinal nerves CNS PNS  sensory input motor input sensory receptor effector integration  dendrite cell body Myelin sheath...

Central Nervous System (CNS) brain spinal cord Peripheral Nervous System (PNS) cranial nerves spinal nerves CNS PNS  sensory input motor input sensory receptor effector integration  dendrite cell body Myelin sheath axon Synapse  unipolar bipolar multipolar Dorsal root eye, ear, & olfactory most abundant type in CNS ganglion cells  Na+ Outside cell -70mV K+ Inside cell Schwann Cells Nodes of Ranvier Axon  Whenever, positive and negative ions are held apart, a potential difference (PD) exists The size of the PD is measured in volts (V ) or millivolts (mV) On average, the PD is -70mV for many cells including neurons at rest  Membrane Channels Passive/leak channels – Always open Active/gated channels – Open/close in response to specific stimuli Three types of gated channels – Chemically regulated e.g. Receptor that bind ACh – Voltage-regulated e.g. A membrane capable of generating and conducting an action potential – Mechanically regulated e.g. Physical distortion of membrane surface.  An action potential is propagated changes in the transmembrane potential. Once initiated, affect an entire excitable membrane Summary: Action Potentials STEP 1- Depolarization to threshold STEP 2-Activation of Na+ channels and rapid depolarization STEP 3- Inactivation of Na+ channels and activation of K+ channels STEP 4-Return to normal permeability  Ca2+ Presynaptic neuron Postsynaptic membrane Synaptic vesicles containing neurotransmitters  Acetylcholine- slows heart rate; PNS Glutamate- most prevalent neurotransmitter in the brain Aspartate- in CNS GABA- inhibitory neurotransmitter Glycine- inhibitory neurotransmitter Norepinephrine- awakening from deep sleep tyrosine Epinephrine- increase heart rate Dopamine- movement of skeletal muscles Seratonin- sensory perception, temp regulation, mood, sleep Nitric oxide- may play a role in memory and learning Enkephalin- inhibit pain impulses by suppressing release of substance P Substance P- enhances perception of pain CNS & PNS  Outline CNS PNS – Basic CNS Pattern – ANS – Spinal Cord Sympathetic Anatomy Parasympathetic Reflexes Neurotransmitters Trauma – Somatic – Meninges & CSF Cranial Nerves Spinal Nerves – Blood Brain Barrier – Brain Basic Pattern of the Central Nervous System Figure 12.5 Central Nervous System – Spinal Cord  Spinal Cord Functional Areas – Dorsal Root – Ventral Root – Spinal Tracts Ascending Tracts – Dorsal column tract – Anterolateral System Descending Tracts – Corticospinal Tract  Reflexes A reflex is a rapid, predictable motor response to a stimulus Reflexes may: – Be inborn or learned (acquired) – Involve only peripheral nerves and the spinal cord – Involve higher brain centers as well  Reflex Arc There are five components of a reflex arc – Receptor – Sensory neuron – Integration center – Motor neuron – Effector Reflex Arc Figure 13.12  Reflex Classification Classified Functionally Somatic Reflexes Autonomic reflexes  Reflexes in Adult Humans Accommodation reflex Mammalian diving reflex Achilles reflex Patellar reflex (knee-jerk reflex) Biceps stretch reflex Photic sneeze reflex Brachioradialis reflex Plantar reflex (Babinski reflex) Corneal reflex (also known as the blink Pupillary reflex reflex) Quadriceps reflex Gag reflex Salivation Scratch reflex Sneeze Tendon reflex Triceps stretch reflex Vestibulo-ocular reflex Withdrawal reflex Yawn  Mammalian Diving Reflex Submerging the face into water causes the mammalian diving reflex Includes three factors: – Bradycardia – Peripheral vasoconstriction – Blood shift When the face is submerged, receptors that are sensitive to water within the nasal cavity and other areas of the face supplied by cranial nerve V (trigeminal) relays the information to the brain and then innervates cranial nerve X (vagus).  Photic Sneeze Reflex A medical condition by which people exposed to bright light sneeze. – Occurs in 17% to 25% of humans The probable cause is a congenital malfunction in nerve signals in the trigeminal nerve nucleus. – Overstimulation of the optic nerve triggers the trigeminal nerve, and this causes the photic sneeze reflex.  Yawn A reflex of deep inhalation and exhalation associated with being tired, with a need to sleep, or from lack of stimulation. Pandiculation It is claimed to help increase the state of alertness of a person. It could possibly be from lack of oxygen. The exact causes of yawning are still unknown.  Spinal Cord Trauma: Paralysis Paralysis – loss of motor function Flaccid paralysis – severe damage to the ventral root or anterior horn cells Spastic paralysis – only upper motor neurons of the primary motor cortex are damaged  Spinal Cord Trauma: Transection Cross sectioning of the spinal cord at any level results in total motor and sensory loss in regions inferior to the cut Paraplegia – transection between T1 and L1 Quadriplegia – transection in the cervical region  Poliomyelitis Destruction of the anterior horn motor neurons by the poliovirus Early symptoms – fever, headache, muscle pain and weakness, and loss of somatic reflexes  Amyotrophic Lateral Sclerosis (ALS) Lou Gehrig’s disease Symptoms – loss of the ability to speak, swallow, and breathe  The Brain Composed of wrinkled, pinkish gray tissue Surface anatomy includes cerebral hemispheres, cerebellum, and brain stem Adult Neural Canal Regions Figure 12.3a, b Adult Neural Canal Regions Figure 12.3c Adult Neural Canal Regions Adult Neural Canal Regions Figure 12.3c, e Ventricles of the Brain Figure 12.6  Protection of the Brain The brain is protected by bone, meninges, and cerebrospinal fluid Harmful substances are shielded from the brain by the blood-brain barrier  Meninges Three connective tissue membranes that lie external to the CNS – dura mater, arachnoid mater, and pia mater Functions of the meninges include: – Cover – Protect – Contain – Form Meninges Figure 12.20a  Dura Mater Leathery, strong meninx composed of two fibrous connective tissue layers The two layers separate in certain areas and form dural sinuses Three dural septa extend inward and limit excessive movement of the brain – Falx cerebri – Falx cerebelli – Tentorium cerebelli Dura Mater Figure 12.21  Arachnoid Mater The middle meninx, which forms a loose brain covering It is separated from the dura mater by the subdural space Arachnoid Mater Figure 12.20a  Pia Mater Deep meninx composed of delicate connective tissue that clings tightly to the brain  Cerebrospinal Fluid (CSF) Watery solution similar in composition to blood plasma Contains less protein and different ion concentrations than plasma Forms a liquid cushion that gives buoyancy to the CNS organs  Cerebrospinal Fluid (CSF) Circulates through the ventricle system of the brain to the brainstem Aided by circulatory, respiratory and postural changes Barrier between the blood in the capillaries of the choroids plexus and the  Choroid Plexuses Clusters of capillaries that form tissue fluid filters, which hang from the roof of each ventricle Have ion pumps that allow them to alter ion concentrations of the CSF Help cleanse CSF by removing wastes Choroid Plexuses Figure 12.22a  Blood-Brain Barrier Protective mechanism that helps maintain a stable environment for the brain Bloodborne substances are separated from neurons by: – Continuous endothelium of capillary walls – Relatively thick basal lamina – Bulbous feet of astrocytes  Blood-Brain Barrier: Functions Selective barrier Absent in some areas Responds to stress  Blood-Brain Barrier: Functions – Reduce the immune systems access to the brain – Comprised of the cells that make up the smallest blood vessels of the brain Anatomical structures Physiological transport systems - Accounts for some drug actions » Morphine vs. heroin – Many substances are not lipid soluble » Glucose and other important brain substrates  Brain Brainstem – Midbrain – Pons – Medulla Oblongata Cerebellum Forebrain – Diencephalon – Cerebrum Limbic System Brain Stem Figure 12.15  Midbrain Located between the diencephalon and the pons Midbrain structures include: – Cerebral peduncles – Cerebral aqueduct – Various nuclei Midbrain Nuclei Figure 12.16a  Midbrain Nuclei Nuclei that control cranial nerves III (oculomotor) and IV (trochlear) Corpora quadrigemina – Superior colliculi – Inferior colliculi Substantia nigra Red nucleus – largest nucleus of the reticular formation Pons Figure 12.6b  Pons Bulging brainstem region between the midbrain and the medulla oblongata Forms part of the anterior wall of the fourth ventricle Fibers of the pons: – Connect higher brain centers and the spinal cord – Relay impulses between the motor cortex and the cerebellum Origin of cranial nerves V (trigeminal), VI (abducens), and VII (facial) Contains nuclei of the reticular formation Reticular Formation Figure 12.19  Reticular Formation: RAS and Motor Function RAS – reticular activating system – Sends impulses to the cerebral cortex to keep it conscious and alert – Filters out repetitive and weak stimuli Motor function – Helps control coarse motor movements – Autonomic centers regulate visceral motor functions  Medulla Oblongata Most inferior part of the brain stem Contains a choroid plexus on the ventral wall of the fourth ventricle Pyramids – two longitudinal ridges formed by corticospinal tracts Medulla Oblongata Figure 12.16c  Medulla Nuclei Inferior olivary nuclei – gray matter that relays sensory information Cranial nerves X, XI, and XII are associated with the medulla Vestibular nuclear complex Cardiovascular control center – adjusts force and rate of heart contraction Respiratory centers – control rate and depth of breathing Cerebellum  Cerebellum Proprioceptors and visual signals “inform” the cerebellum of the body’s condition Cerebellar cortex calculates the best way to perform a movement Plays a role in language and problem solving Recognizes and predicts sequences of events  Forebrain Two Regions – Cerebrum – Diencephalon  Forebrain Cerebrum – Right and left cerebral hemispheres Cerebral cortex an outer shell of gray matter White matter Cell clusters called subcortical nuclei – Fiber tract carry information out & in and form connections within a hemisphere – Hemispheres connected via the corpus callosum Left hemisphere Right hemisphere Cerebrum  Forebrain – Cortex Divided into four lobes – Frontal – Temporal – Parietal – Occipital – Subcortical Nuclei Heterogenous groups of gray matter than lie within the cerebral hemispheres Basal ganglia Cerebral Cortex – Functional Areas – Sensorimotor cortex = all of the parts of the cerebral cortex that act together in the control of muscle movement Primary motor cortex Premotor area Supplementary motor cortex Parietal-lobe association cortex Somatosensory cortex Functional Areas: Left Cerebral Cortex Figure 12.8a Primary Motor Cortex Figure 12.9.1  Sensorimotor Cortex Premotor cortex – the part of the brain responsible for planning, selection and execution of actions Supplementary motor cortex – responsible for planning and coordination of complex movements Parietal-lobe association cortex – responsible for transforming visual information to motor commands Somatosensory Cortex Diencephalon  Forebrain Diencephalon – Three major parts Thalamus Hypothalamus Epithalamus Limbic System Figure 12.18  Limbic System Structures located on the medial aspects of cerebral hemispheres and diencephalon Includes the rhinencephalon, amygdala, hypothalamus, hippocampus, cingulate gyrus, and anterior nucleus of the thalamus Hypocampal structures Parts especially important in emotions: – Amygdala – Cingulate gyrus  Cerebrovascular Accidents (Strokes) Caused when blood circulation to the brain is blocked and brain tissue dies Transient ischemic attacks (TIAs) – temporary episodes of reversible cerebral ischemia  Alzheimers Disease Neurogenerative disease Progressive loss of higher function Caused by neuronal loss and atrophy  Huntingtons Disease Genetic disorder – HD gene located on chromosome 4 – Extra CAG repeat on the end of the gene Caused by degeneration of neuronal cells – Frontal lobes – Basal ganglia – Caudate nucleus Symptoms – Jerky uncoordinated movements which become progressively worse – Excecutive function, abstract thinking, speech and perceptual and spatial function are all affected  Blood Supply Glucose is the only energy source that the brain uses for energy production (under normal circumstances) Brains glycogen stores are minimal so dependent of a continuous blood supply for oxygen and sugar Adult brain makes up only 2% of the body weight, it receive 12 – 15% of the total blood supply Deprivation of either oxygen or glucose can lead to brain death  Peripheral Nervous System (PNS) PNS – all neural structures outside the brain and spinal cord Includes: sensory receptors, peripheral nerves, associated ganglia, and motor endings Can be divided into: – Autonomic Nervous System – Somatic Nervous System Provides links to and from the external environment  Autonomic Nervous System Efferent innervation of all tissues other than skeletal muscle Parallel chains of two neurons connect the CNS and effector cells – Preganglionic Neuron – Preganglionic Fibers – Autonomic ganglia – Postganglionic Neuron – Postganglionic Fibers  Autonomic Nervous System Two Divisions – Many glands and muscle are innervated by both the parasympathetic and sympathetic nervous system called dual innervation – Two divisions usually activated reciprocally – Autonomic responses usually occur without conscious control – Distinguished by Their unique origin sites Relative fiber lengths Location of their ganglia Degree of fiber branching Functional role Neurotransmitters  Anatomy of ANS Division Origin of Fibers Length of Fibers Location of Ganglia Sympathetic Thoracolumbar region Short preganglionic and Close to the spinal of the spinal cord long postganglionic cord Parasympathetic Brain and sacral spinal Long preganglionic and In the visceral cord short postganglionic effector organs Figure 6.44  Anatomy of ANS Division Origin of Fibers Length of Fibers Location of Ganglia Sympathetic Thoracolumbar region Short preganglionic and Close to the spinal of the spinal cord long postganglionic cord Parasympathetic Brain and sacral spinal Long preganglionic and In the visceral cord short postganglionic effector organs  Sympathetic Nervous System Extensive branching of the preganglionic fibers Innervates visceral organs in the internal body cavities and in the superficial part of the body – Sweat glands and arrector pilli muscles – All arteries and veins (smooth muscle) Anatomy ties the entire system together so that it can act as a single unit – Small segments of the system can be regulated independently Usually increases its response under conditions of physiological stress  Role of the Sympathetic Division The sympathetic division is the “fight-or-flight” system Involves E activities – exercise, excitement, emergency, and embarrassment Promotes adjustments during exercise – blood flow to organs is reduced, flow to muscles is increased Its activity is illustrated by a person who is threatened – Heart rate increases, and breathing is rapid and deep – The skin is cold and sweaty, and the pupils dilate  Sympathetic Nervous System Fibers leave from the thoracic and lumbar regions of the spinal cord (T1-L2) Preganglionic fibers form the lateral horn of the gray matter in the spinal column Ganglia lie close to the spinal cord and form two chains of ganglia one on each side of the cord called sympathetic trunks  Unique Roles of the Sympathetic Division Regulates many functions not subject to parasympathetic influence These include the activity of the adrenal medulla, sweat glands, arrector pili muscles, kidneys, and most blood vessels The sympathetic division controls: – Thermoregulatory responses to heat – Release of renin from the kidneys – Metabolic effects  Thermoregulatory Responses to Heat Applying heat to the skin causes reflex dilation of blood vessels Systemic body temperature elevation results in widespread dilation of blood vessels This dilation brings warm blood to the surface and activates sweat glands to cool the body When temperature falls, blood vessels constrict and blood is retained in deeper vital organs  Metabolic Effects The sympathetic division promotes metabolic effects that are not reversed by the parasympathetic division – Increases the metabolic rate of body cells – Raises blood glucose levels – Mobilizes fat as a food source – Stimulates the reticular activating system (RAS) of the brain, increasing mental alertness  Effects of Sympathetic Activation Sympathetic activation is long-lasting because NE: – Is inactivated more slowly than ACh – Is an indirectly acting neurotransmitter, using a second-messenger system – NE and epinephrine are released into the blood and remain there until destroyed by the liver  Parasympathetic Nervous System Fibers leave from the brain and the sacral portion of the spinal cord Preganglionic axons extend from the CNS nearly all the way to the structures to be innervated Terminal ganglia lie within the organs innervated by the postganglionic neurons or very close to the organs Short postganglionic axons issue from the terminal ganglia and synapse with the effector organ  Parasympathetic Division Outflow Cranial Output – Run in the oculomotor, facial, glossopharyngeal and vagus nerves – Oculomotor Nerve III (preganglionic fibers) Innervate smooth muscles in the eyes that cause the pupils to constrict and lens to bulge (so that you can focus on objects close up) – Facial Nerve VII (preganglionic fibers) Stimulate many large glands in the head Nasal glands and lacriminal glands Submandibular and sublingual salivary glands  Parasympathetic Division Outflow Cranial Output – Glossopharyngeal Nerve IX (preganglionic fibers) Activate the parotid salivary glands anterior to the ear – Distal ends of the preganglionic fibers from nerve III, VII and IX jump over to branches of the trigeminal nerve to synapse with postganglionic fibers in the trigeminal nerve (V), they travel down the trigeminal nerve tract to reach the face  Parasympathetic Division Outflow Cranial Output – Vagus Nerve (X) Account for about 90% of all preganglionic parasympathetic fibers Serve virtually every organ in the thoracic and abdominal cavities Have branches that go to the cardiac plexus that slow heart rate Have branches that go to the pulmonary plexus and esophageal plexus Have branches from the aortic plexus that go to the abdominal viscera Parasympathetic Division Outflow Figure 14.4  Parasympathetic Division Outflow Sacral Output – Branch of the spinal cord to form the pelvic nerves that pass through the inferior hypogastric plexus – Have synapses in the distal half of the large intestine, urinary bladder, ureters and reproduction organs Made up of relatively independent components – Responses can be quite variable and are tailored to the demands of the situation  Interactions of the Autonomic Divisions Most visceral organs are innervated by both sympathetic and parasympathetic fibers This results in dynamic antagonisms that precisely control visceral activity Sympathetic fibers increase heart and respiratory rates, and inhibit digestion and elimination Parasympathetic fibers decrease heart and respiratory rates, and allow for digestion and the discarding of wastes  Neurotransmitters and Receptors Acetylcholine (ACh) and norepinephrine (NE) are the two major neurotransmitters of the ANS Cholinergic fibers – ACh-releasing fibers Adrenergic fibers – sympathetic postganglionic axons that release NE  Nicotinic Receptors Nicotinic receptors are found on: – Motor end plates (somatic targets) – All ganglionic neurons of both sympathetic and parasympathetic divisions – The hormone-producing cells of the adrenal medulla The effect of ACh binding to nicotinic receptors is always stimulatory  Effects of Drugs Atropine – blocks parasympathetic effects Neostigmine – inhibits acetylcholinesterase and is used to treat myasthenia gravis Tricyclic antidepressants – prolong the activity of NE on postsynaptic membranes Beta-blockers – attach mainly to 1 receptors and reduce heart rate and prevent arrhythmias  Homeostatic Imbalances Hypertension – Can be caused by an overactive sympathetic vasoconstrictor response promoted by continuous high levels of stress – Increases the work load on the heart, which may precipitate heart disease, and increases wear and tear on the arteries Somatic Nervous System  Cranial Nerves Twelve pairs of cranial nerves arise from the brain – Two arise from the forebrain and the rest originate from the brainstem – With the exception of the vagus nerve all serve regions in the head or neck – Oh Once One Takes The Anatomy Final A Good Vacation Seems Heavenly They have sensory, motor, or both sensory and motor functions. Cranial Nerves Figure 13.4a Summary of Function of Cranial Nerves Figure 13.4b  Cranial Nerve I: Olfactory Arises from the olfactory epithelium Fibers run through the olfactory bulb and terminate in the primary olfactory cortex Functions solely by carrying afferent impulses for the sense of smell Anosmia – fracture of the ethmoid bone or lesions of the olfactory fibers may lead to a loss either total or partial of smell Cranial Nerve I: Olfactory Table 13.2(I)  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  Cranial Nerve II: Optic Functions solely by carrying afferent impulses for vision Anopsias – damage to the optic nerve or to the vision pathway beyond the optic chiasm can lead to total or complete loss of sight in that eye Cranial Nerve II: Optic Table 13.2(II)  Cranial Nerve III: Oculomotor Supplies four of the extrinsic eye muscles that move the eyeball in its orbit Has – Somatic motor fibers – Parasympathetic fibers – Sensory afferents Testing – Pupils examined for size, shape and equality (concussion pupils of uneven size) – Pupillary reflex is tested – Convergence for near vision External Strabismus – oculomotor nerve is paralyzed, Cranial Nerve III: Oculomotor Table 13.2(III)  Cranial Nerve IV: Trochlear Fibers emerge from the dorsal midbrain and travel ventrally around the midbrain to enter orbits via the superior orbital fissure Innervates an intrinsic eye muscle Supply somatic fibers to and carry proprioceptor fibers Trauma to this nerve results in double vision and reduced ability to rotate the eye inferolaterally Cranial Nerve IV: Trochlear Table 13.2(IV)  Cranial Nerve V: Trigeminal Supplies sensory fibers to the face and motor fibers to the chewing muscles Largest of the cranial nerves  Cranial Nerve V: Trigeminal Fibers extend from the pons to the face to form three divisions – Ophthalmic division – Maxillary division – Mandibular division  Cranial Nerve V: Trigeminal Trigeminal neuralgia – caused by inflammation of the trigeminal nerve – Extreme pain – Treated via analgesics, carbamazepine and in severe cases nerve is cut proximally to the trigeminal ganglia Cranial Nerve V: Trigeminal Table 13.2(V)  Cranial Nerve VI: Abducens Controls the extrinsic eye muscle Supplies somatic motor fibers to the lateral rectus muscle an brings back proprioceptive impulses to the brain Table 13.2(VI)  Cranial Nerve VII: Facial Innervates muscles of facial expression Fibers issue from the pons and enter the temporal bone via the internal acoustic meatus Mixed nerve with fiber major branches – Temporal – Zygomatic – Buccal – Mandibular – Cervical  Cranial Nerve VII: Facial Convey motor impulses skeletal muscles of the face and proprioioceptor impulses to the brain Transmit parasympathetic motor impulses to the lacriminal, nasal, palatine, submandibular and sublingual glands Convey sensory impulses from the taste buds on the anterior 2/3’s of the tongue Bell’s Palsy – Characterized by paralysis of facial muscles on the affected side of the face. – Caused by herpes simplex I viral infection which causes swelling and inflammation of the facial nerve Cranial Nerve VII: Facial Table 13.2(VII)  Cranial Nerve VIII: Vestibulocochlear Sensory nerve for hearing and balance Fibers arise from hearing and equilibrium apparatus of the inner ear and pass through the internal acoustic meatus to enter the brain at the pons-medulla border  Cranial Nerve VIII: Vestibulocochlear Two branches – Cochlear – Vestibular Lesions of cochlear nerve Damage to the vestibular division Cranial Nerve VIII: Vestibulocochlear Table 13.2(VIII)  Cranial Nerve IX: Glossopharyngeal Innervates the tongue and pharynx Provide motor fibers to and carry proprioceptors from the stylopharngeus, which elevates the pharynx during swallowing. Provides parasympathetic motor fibers to the parotid salivary gland  Cranial Nerve IX: Glossopharyngeal Sensory fibers conduct taste and general sensory impulses from the pharynx and posterior tongue, from chemoreceptors in the carotid body, and from pressure receptors of the carotid sinus Damage impairs swallowing and taste, particularly for sour and bitter substances Cranial Nerve IX: Glossopharyngeal Table 13.2(IX)  Cranial Nerve X: Vagus Extends into the thorax and abdomen Almost all are parasympathetic efferents – Supply the heart, lungs and abdominal viscera – Are involved in regulation of heart rate, breathing and digestive system activity  Cranial Nerve X: Vagus Transmit sensory impulses from the thoracic and abdominal viscera, from the carotid sinus, the carotid and aortic bodies, and taste buds of the posterior tongue and pharynx. Paralysis can lead to hoarseness and loss of voice, difficulty swallowing and impaired digestive motility. Cranial Nerve X: Vagus Table 13.2(X)  Cranial Nerve XI: Accessory Considered and accessory part of the vagus nerve Cranial root emerges from the lateral aspect of the medulla – primarily motor in function – joins with the vagus nerve to innervate the larynx, pharynx and soft palate Cranial Nerve XI: Accessory Table 13.2(XI)  Cranial Nerve XII: Hypoglossal Runs inferior to the tongue and innervates some of the tongue moving muscles Fibers arise from a series of roots from the medulla and exit the skull via the hypoglossal canal to travel to the tongue Primarily motor in function  Cranial Nerve XII: Hypoglossal Carry impulses to intrinsic and extrinsic muscles of the tongue, and proprioceptors fibers from these muscles to the brain Allows food mixing and manipulation of the tongue Damage to the hypoglossal nerve causes difficulties in speech and swallowing Cranial Nerve XII: Hypoglossal Table 13.2(XII)  Spinal Nerves Thirty-one pairs of mixed nerves They are named according to their point of issue – 8 cervical (C1-C8) – 12 thoracic (T1-T12) – 5 Lumbar (L1-L5) – 5 Sacral (S1-S5) – 1 Coccygeal (C0) Figure 13.5  Spinal Nerves Each spinal nerve connects to the spinal cord by a dorsal root and ventral root Spinal nerves are short because after emerging it divides in three parts – Dorsal ramus – Ventral ramus – Meningeal branch – reenters the spinal cord to innervate the meninges and the blood vessels in the CNS  Innervation of Specific Body Regions The spinal nerve rami and their main branches supply the entire somatic region of the body from the neck down Dorsal Rami – Supply the posterior body trunk Ventral Rami – Supply the rest of the trunk and limbs  Innervation of the Back Innervation follows a neat segmented plan Each dorsal ramus innervates a narrow strip of muscle and skin in line with its emergence point from the spinal column Innervation of the Anterolateral Thorax and Abdominal Wall Ventral rami are arranged in a simple segmental pattern Form the intercostals nerves and have cutaneous branches to the skin Spinal Nerve Innervation: Back, Anterolateral Thorax, and Abdominal Wall Figure 13.6b  Cervical Plexus Formed by the ventral rami of the first four cervical nerves Most branches are cutaneous nerves Figure 13.7  Cervical Plexus Branches also innervate the muscles of the anterior neck Phrenic nerve – diaphragm - hiccups Figure 13.7  Brachial Plexus Gives rise to almost all the nerves that innervate the upper limb Plexus formed from intermixing of ventral rami from C5-C8 and most of the T1 ramus Injuries are common when the upper limb is pulled hard or receives a blow to the top of the shoulder  Brachial Plexus Five important nerves – Axillary nerve – runs posterior to the surgical neck of the humerus – Musculotaneous nerve – travels inferiorly in the anterior arm – Median nerve – Ulnar nerve – Radial nerve Brachial Plexus: Distribution of Nerves Figure 13.8c Brachial Plexus: Distribution of Nerves Figure 13.8c  Lumbar Plexus Arises from L1-L4 and innervates the thigh, abdominal wall, and psoas muscle The major nerves are the femoral and the obturator Femoral nerve Obturator Nerve Figure 13.9 Lumbar Plexus Figure 13.9  Sacral Plexus Arises from spinal nerves L4-S4 Has nerves that serve the buttock and lower limb Sciatic nerve – Sciatica Sacral Plexus Figure 13.10  Skin Innervation - Dermatomes Dermatomes: A dermatome is an area of skin supplied by sensory neurons that arise from a spinal nerve ganglion Every spinal nerve except C1 innervates dermatomes Some overlap between innervation regions Dermatomes Figure 13.11