Nervous system

Peripheral nervous systemNervous systemPeripheral nervous systemNerves that branch from CNS and connect it to other body partsCranial nervesArise from the brainSpinal nervesArise from the spinal cordPeripheral branchesSomatic nervous systemConsist of cranial nerve fibersConnect CNS to skin and skeletal musclesOversees conscious activitiesAutonomic nervous systemFibers that connect CNS to visceraControls unconscious activities

Cranial nerves 12 pairs of cranial nerves11 of the twelve originate from the brain stemThe first pair arises within the cerebrumMost are mixed nervesExcept those associated with special senses will be sensoryCranial nerves that only affect effectors are primarily motor fibersCranial Nerves cont.Numbers and names are associated with cranial nervesNumber= order in which nerves arise from front to back of brainNames= primary functions or the general distribution of the fibers

Olfactory nerves (I)Associated with the sense of smellOnly sensory neuronsBipolar neuronsTravel along olfactory tracts from olfactory bulbs to cerebral centersInterpretation results in the sense of smell

Optic nerves (II)Arise from the retina to form the optic nerveForm the optic chiasma from the partial crossing over of the fibersPurely sensorySensory impulses are interpreted as visionOculomotor (III)Arise from the midbrain and pass into the orbits of the eyesPrimarily motorConnects to voluntary muscles that raise the eyelids and four of the six muscles for eye movementSuperior, inferior, medial rectus, and inferior obliqueSecond component is part of the ANSSupplies involuntary muscles within the eyesMuscles that control lens shape and pupil sizeTrochlear (IV)Smallest cranial nerve and arises from the midbrain to the eyeSupplies motor fibers to external eye muscle (superior oblique)Aids in the ability to follow moving objectsTrigeminal (V)Largest cranial nervesArise from the ponsMixed nerves with predominantly sensory portionsEach sensory component includes three large branches Ophthalmic, maxillary, and mandibular divisionsOphthalmic divisionSensory fibers bring impulses to the brain from the surface of the eyes, tear glands, and the skin of the anterior scalp, forehead, and upper eyelidsTrigeminal (V) cont.Maxillary divisionCarry sensory impulse from the upper teeth, upper gum, and upper lipAlso from the mucous lining of the palate and the skin of the faceMandibular divisionIncludes both sensory and motor fibersSensory impulses transmit impulses from the scalp behind the ears, the skin of the jaw, the lower teeth, the lower gum, and the lower lipMotor branches supply muscles of mastication and muscles of the floor of the mouthAbducens (VI)Small and originate from the pons Each nerve enters the orbit of the eye and supplies motor impulses to the lateral rectusRolls the eye laterallyFacial nerves (VII)Arise from the lower part of the pons and emerge on the sides of the faceSensory branches associated with taste receptors on the anterior 2/3 of the tongueMotor fibers transmit impulses to muscles of facial expressionOther motor fibers function in the ANS and stimulate secretions from tear glands and salivary glands Vestibulocochlear nerves (VIII)Sensory nerves that arise from the medulla oblongataTwo distinct parts1. vestibular branchcontain receptors involved in maintaining equilibrium2. cochlear branchfibers located in parts of the inner ear and house hearing receptorsImpulses from these branches pass through the pons and medulla to the temporal lobe for interpretation

Glossopharyngeal nerves (IX)Associated with the tongue and pharynxMixed nerves that arise from the medulla, but predominantly sensorySensory impulses from lining of pharynx, tonsils, and posterior 1/3 of the tongueMotor fibers innervate muscles of the pharynx for swallowing and salivary glands

Vagus nerve (X)Originate in the medulla oblongata Extends down through the neck, into the chest and abdomenMixed nerves with both somatic and autonomic branchesSomatic- impulses to muscles of the larynx associated with speech and swallowingAutonomic- heart and smooth muscles and glands of the thorax and abdomenPromotes digestionAccessory (XI)Originate in the medulla oblongata and spinal cordBoth cranial and spinal branchesCranial branchJoins vagus nerve and carries impulses to muscles of the soft palate, pharynx, and larynxSpinal branchDescends into the neck and supplies motor fibers to the trapezius and sternocleidomastoid muscles

Hypoglossal (XII)Arise from the medulla oblongataPass into the tongueMotor fibers that carry impulses to muscles that move the tongue in speaking, chewing, and swallowingSpinal nerves31 pairs that originate from the spinal cordNamed based on the level from which they arise8 cervical pairs12 thoracic pairs5 lumbar pairs5 sacral pairs1 coccygealCauda equina- formed from the lumbar, sacral, and coccygeal nerves

Mixed nerves that provide two way communication between the spinal cord and the rest of the bodyThe adult spinal cord ends at the level between the 1 and 2nd lumbar vertebraeThe lumbar, sacral, and coccygeal nerves descend beyond the end of the spinal cord19Spinal nervesEmerge by two short branches or rootsDorsal root- posterior or sensory rootContains the cell bodies of the sensory neurons whose dendrites conduct impulses inward Ventral root- anterior or motor rootConsist of axons from the motor neurons whose cell bodies are located in the gray matter of the spinal cord

Ventral root and dorsal root combine to form a spinal nerve, which extends out from the vertebral canal

20Spinal nerves The main portions of the nerves combine to form complex networks called plexusesThe fibers are sorted and recombined so fibers that innervate a particular peripheral body part reach it in the same nerve

Plexuses Cervical plexusForm from the branches of the 1st four cervical nervesSupply the muscles and the skin of the neckFibers from 4th,5th, and 6th nerves pass into the phrenic nerve to conduct impulses to the diaphragmBrachial plexusBranches of the lower 4 cervical and 1st thoracic nerveSupplies the muscles and skin of the arm, forearm, and handIncludes the musculocutaneous, ulnar, radial, and axillary nerves

22Plexus cont.LumbosacralFormed on either side of the last thoracic nerve and the lumbar, sacral, and coccygeal nervesAssociated with muscles of the skin of the lower abdominal wall, external genitalia, buttocks, thighs, legs, and feetIncludes the obturator, femoral, and sciatic nervesAnterior branches of thoracic nerves do not enter a plexusInstead enter spaces between ribs and become intercostal nervesSupply motor impulses to the intercostal muscles and the upper abdominal wall musclesSensory impulses from the skin of the thorax and abdomen

Autonomic nervous system Functions independently and continuously without conscious effortControls visceral functionsRespond to emotional stress and prepare the body to meet the demands of strenuous physical activity Regulating smooth muscles, cardiac muscles, and glandsRegulates heart rate, blood pressure, breathing rrate, body telmperature, and other visceral activities that control homestasis

24ANS general characteristicsPeripheral nerve fibers lead to ganglia outside of the CNSImpulses they carry are integrated within the gangliaThis function provides the ANS with a degree of independence from the CNSDivided into two divisionsSympathetic divisionPrepares the body for energy-expending, stressful, or emergency situationsParasympatheticMost active under ordinary, restful conditionsCounterbalances thesympathetic and restores to resting stateSome viscera have nerve fibers on each branchDivisions may act antagonistically, alternately activating, or inhibiting the actions of some viscera25Autonomic nerve fibersMotor nerve fibersTwo neurons between the CNS and skeletal musclePreganglionic fiber leaves the CNS and synapses with one or more neurons whose cell bodies are within the autonomic ganglionPostganglionic fiber- the axon of the second neuron, and extends to a visceral effector

Sympathetic divisionAlso called the thoracolumbar division1st neurons are in the gray matter of the spinal cord between T1 and L2Preganglion fibers are shortMost of the postganglion fibers are longExtensive divergence and can control a variety of visceral effectors and can produce a complex and coordinated responsePreganglion fibers- AcetylcholineAlways excitatoryPostganglion fibers- NorepinephrineShort because the ganglia are relatively close to the spinal cord27Sympathetic activationWhen full activiated produces the fight or flight response and readies the body for a crisis Increased alertnessA feeling of energy and euphoria, can be associated with disregard for danger and a temporary insensitivity to painful stimuliIncreased activity in the cardiovascular and respiratory centers of the pons and medulla oblongataLeads to increased blood pressure, heart rate, breathing rate, and depth of respiration

Via stimulation of the reticular activating system, causes a person to feel on edge28Sympathetic cont.General elevation of muscle tone through stimulation of the medial and lateral pathways The person looks tense and may begin to shiverThe mobilization of energy reserves through the accelerated breakdown of glycogen in muscles cells and liver cells and the release of lipids by adipose tissue

Parasympathetic division Ganglionic neurons are located in the same ganglion and their postganglionic fibers influence the same target organMore specific and localized than the sympathetic divisionPreganglion fibers arise from the brain stem and sacral region of the spinal cordShort postganglion fibersLocated within or next to target organsThe effects of parasympathetic stimulation are generally brief and restricted to specific organ sitesParasympathetic activationThese functions center on relaxation, food processing, and energy absorptionCalled the anabolic system because its stimulation leads to increase of nutrients in bloodConstriction of pupils and focusing of the lensRestricts the amount of light that enters the pupilSecretion by digestive glands,The secretion of hormones that promote the absorption and utilization of nutrients by cellsChanges in blood flow and glandular activity associated with sexual arousal Parasympathetic activation cont.An increase in smooth muscle activity along the digestive tractThe stimulation and coordination of defecationContraction of the urinary bladder during urinationConstriction of the respiratory passagewaysA reduction in heart rateAnd in the force of contraction Sexual arousal and the stimulation of sexual glands in both sexes