2 IX. The Nervous System A. Overall function of the Nervous System 1. Connects to the body via nerves conducting nerveimpulses.2. Sensory input - senses change both within andoutside the body3. Integration – interprets the sensory input(brain and spinal cord).4. Motor output – causes a response (musclescontract, glands secrete).B. Divisions of the Nervous System1. Anatomical Classificationa. Central Nervous System (CNS) – brain andspinal cord.
3 b. Peripheral Nervous System (PNS). 1.) Sensory (afferent)2.) Motor (efferent)2. Functional classification of the PNS.a. Somatic (voluntary) – skeletal muscle.b. Autonomic ( involuntary) – smooth, cardiacmuscle, glands.1.) Sympathetic – “fight or flight”2.) Parasympathetic – normal activity,“rest and digest”.
5 C. Cells of the Nervous System 1. Neuroglia – most numerous, wrap around, nurtureneurons.2. Neurons – cells that conduct nerve impulses tosensory areas of the brain and from motorbrain areas. They compose the brain andspinal cord.
6 a. Structure1.) Cell body – contains nucleus and typicalorganelles.2.) Dendrites – (branches) conduct impulses towardthe cell body.3.) Axons – conduct impulse away from the cellbody.4.) Coverings of neuron cell processes.a.) CNS axons – myelinated (covered by a white fatty sheath fromoligodendrocytes.Myelinated = faster conduction.Unmyelinated = slower conduction.
8 b.) PNS axons – myelinated covered by Schwann Cells wrapped in concentric rings( myelin sheath) over theneurilemma (looks white).Unmyelinated lacks the myelinsheath covering the neurilemma.
9 b. Classification of Neurons 1.) Anatomicala.) Unipolar – a single process from the cell bodythat divides like a T. Are“sensory” neurons.b.) Bipolar – two process (axon & dendrite) fromopposite ends of the cell body.Rare, in retina and nose.c.) Multipolar – have three or more processes.99% of all neurons, major typein the CNS (motor).
10 2.) Functional classification of neurons a.) Sensory – carries impulses to the CNS fromthe external and internal(proprioception).b.) Motor – carry impulses from the CNS tomuscles and glands for action.somatic division= sk muscleautonomic division=smooth, cardiac glandsc.) Association – carry impulses from oneneuron to another(interneurons).
11 D. Physiology of Neuron1. Membrane charges (potentials) – sodium (Na+)and potassium (K+).a. Resting potential -70mV. > Na+ outside, < K+ inside2. Nerve impulse – “action potential”a. A change in charge on the neurilemma
13 b. Na+ moves in and depolarizes the cell from -70mV to +30mV. c. The impulse (action potential) will speed to the end of the axon, if to a muscle = contraction, gland = secrete, another neuron = affects the next neuron (stimulate or inhibit)3. Synapses – junctions between two neuronsa. Definition – point of close contact between two neurons or a neuron and an effector cell.
14 b. Excitatory synapse – transmitter substances neurotransmitters are chemical substancesreleased across the synapse that make the nextneuron more permible to Na+ (Cell membrane more +).1. Acetylcholine (ACh) active in the PNS.2. Norepinephrine acts in the CNS and PNS.c. Inhibitory synapse – transmitter substancesmake post synaptic neurons less permible to Na+ (cell membrane more negative)1. Dopamine acts in the CNS2. Serotonin acts in the CNS3. GABA (gamma-aminobutyric acid) active in CNS
15 E. Central Nervous System 1. The braina. Cerebral hemispheres1.) Cortex – outer thin layer of gray matter.2.) Medulla – inner white matter with gray matter.
16 4.) Serves as an area for reasoning, judgments, moral conduct, emotional responses, sensoryinterpretation, initiation of muscle activity.5.) Has the primary motor areas and sensory areas.6.) Consists of lobes - each with their primaryfunctions.a.) frontal - primary motor for voluntary musclecontraction.b.) parietal - primary sensory areas from theskin.c.) occipital - primary vision area.d.) temporal – primary auditory and gustatoryareas.
18 7.) Two of the four ventricles are in the cerebrum. a.) The lateral ventricles form, contain andcirculate cerebrospinal fluid (CSF).b.) CSF is secreted by the vascular choroidplexus found in each ventricle.c.) CSF functions to nourish the brain and spinalcord while protecting them by making thembuoyant.
20 b. Diencephalon – (interbrain) area between the cerebral hemispheres and the brainstem. 1.) Thalamus – sensory relay center, encloses the third ventricle.2.) Hypothalamus – the floor of the third ventricle and the brain’s automatic control center.a.) Regulates water balance – thirstb.) Regulates metabolism – body temperaturec.) Regulates pituitary hormones – produces two hormones.c. Brainstem1.) Midbrain – contains cerebral peduncles “little feet” (white fiber tracts) and corpora quadrigemina involved in eye and ear reflexes.
21 2.) Pons – connecting “bridge” for other brain divisions. It contains secondarycenters that help regulate breathing.3.) Medulla oblongata – ascending (sensory)from the parietal lobe and descending(motor) pathways from the frontal lobe gothrough this part. Motor nerve fibers“cross over” to the opposite side(decussation of the pyramids) beforeentering the spinal cord.a.) Primary control of heart rate.b.) Controls blood vessels, arterioles.c.) Primary control of breathing.d.) Non-vital control centers – sneezing,coughing, vomiting.
22 Descending Tracts= motor Ascending tracts=sensory Commissuralfibers (corpuscallosum)Longitudinal fissureSuperiorLateralventricleAssociationfibersBasal nuclei• CaudateCorona radiata• Putamen• Globus pallidusFornixInternalcapsuleThalamusGray matterThirdventricleWhite matterProjectionfibersPonsDecussationof pyramidsMedulla oblongata(a)Information and motor commands from the right side go to the left side of the bodyvia decussation below medulla
23 d. Cerebellum1.) Controls coordination of skeletal muscleactivity.2.) Maintains muscle tone.3.) Helps coordinate balance or equilibrium.2. The spinal cord – stops at L1 or L2 (in adults)a. Structure1.) H or butterfly shaped gray matter horns (cellbodies) surrounded by white matter (myelinatedfibers).a.) A central canal circulates CSF.
24 2.) Contains ascending posterior (sensory columns) to the brain and descending anterior (motorcolumns) or tracts to muscles and organs.3.) 31 vertebrae segments give rise to 31 pairs ofspinal nerves.
25 4.) Covered by 3 meningeal layers (as in the brain) a.) Outer most dura mater “tough mother”b.) Arachnoid mater with a CSF filled spacebeneath called the subarachnoid space.c.) Innermost delicate pia mater on the spinalcord surface.5.) Surrounded by CSF just like the brain.CSF circulates in SubA
26 3. Reflex arcs – structural and functional units of nervous behavior. Involve cranial (brain) andspinal (spinal cord) nerves.a. A rapid, predictable response to a stimulus.b. typical reflex arcs contain a receptor, sensoryneuron, one or more interneurons, a motor neuron,and an effector (muscle or gland).
30 4. Sensory and motor pathways (tracts) in the spinal cord.a. Nerve processes in the white matter are organizedinto three columns. The anterior, lateral andposterior white columns. Smaller bundles of fibersin each column are organized into sensory of motor“tracts”.1.) Sensory tracts conduct impulses up to brain.2.) Motor tracts conduct impulses down to effector.a.) Descending motor tracts “decussate” in thelower medulla. Left cerebral motor areacontrols the right side of the body and visaversa.
32 F. Peripheral Nervous System 1. Cranial nervesa. 12 pairs connect brain to organs in the head, neckand shoulders (vagus to thorax and abdomen).b. Names tend to identify functions or generalinnervations.
33 c. Names and types of cranial nerves. (handout 23B) 1.) I. Olfactory – sensory (smell).2.) II. Optic – sensory (vision).3.) III. Oculomotor – motor (controls external eyemuscles for movement of theeye).4.) IV. Trochlear – motor (external eye muscles)5.) V. Trigeminal – Mixed nerve (motor – chewing)(sensory – sensation from forehead,eyebrows, eyelids, nose, lips,cheeks, gums and teeth).6.) VI. Abducens – motor (external eye muscles formovement).
34 7.) VII. Facial – mixed (sensory – taste) (motor – facial expressions,tear glands, salivary glands).8.) VIII. Vestibulocochlear – sensory (cochlear branch– hearing).(vestibularbranch –balance orequilibrium).10.) X. Vagus – mixed (parasympathetic nerve).motor – organs in the thoracic,sensory abdominal, and pelviccavities
35 2. Spinal nerves – 31 pairs originate from the spinal cord. a. Mixed nerves connecting spinal cord to arms, legs, neck and trunk.b. Named by spinal area1.) C1 - C8 (cervical)2.) T1 - T (Thoracic)3.) L1 - L (Lumbar)4.) S1 - S (Sacral)5.) C (Coccygeal)c. Nerve Plexuses are 4 areas where spinal nerves from different spinal regions comingle and give rise to nerve trunks to internal organs and muscles of the appendages. The plexuses are: cervical, brachial, lumbar, and sacral. Spinal nerves T2 – T11 do not form plexuses.
37 F. Peripheral Nervous System (PNS) 1. Cranial Nervesa. 12 Pairs connect the brain to parts in the head,neck, shoulders, while the vagus nerve “wanders”into many organs in the thorax and abdomen.b. Names tend to identify their functions orinnervations. Know handout 23 B!2. Spinal Nerves – 31 pairs originate from the spinal cord.a. Spinal nerves are mixed nerves, Why?b. They are named according to the spinal area of theirorigin.c. Spinal nerves T2 – T11 do not form plexuses.d. Spinal nerves in the neck, shoulder, lumbar, andpelvic area give rise to plexuses.
38 1.) Plexus – means a redistribution of nerve fibers forming major peripheral nerves.2.) Cervical plexus – phrenic nerve to diaphragm forbreathing.3.) Brachial plexus – forms nerves to shoulder andarm.a.) Radial nerve – innervates extensors of fingersand wrist.b.) Median nerve – innervates flexors of fingersc.) Ulnar nerve – same as the median.
39 4.) Lumbar plexus – supplies nerves to the lower abdomen and front of the thigh.a.) Femoral nerve innervates the quadraceps.(Rectus femoris, Vastus medialis,Vastus lateralis).b.) The saphenous nerve innervates the skin ofthe medial foot and toes.5.) Sacral plexus – supplies nerves to the back ofthe thigh and lower leg.a.) Sciatic nerve innervates the hamstrings,(Biceps femoris, Semitendinosus,Semimembranosus).b.) Tibial nerve innervates the calf muscles.
42 6.) Dermatome – is an area of skin innervated by spinal nerves. 7.) Myotome – is an area of muscle innervated by spinal nerves.3. Covering of Peripheral nervesa. Endoneurium – connective tissue covering surrounding one (each) nerve fiber (axon).b. Perineurium – covers groups of fibers (fascicles).c. Epineurium – tough fibrous sheath covering all fascicles to form the “nerve”.
45 G. Autonomic nervous system , ANS (involuntary control) 1. The autonomic system is a part of the PNS.2. It functions to maintain homeostasis by controllingthe heart, blood vessels and glands.a. The somatic system is one neuron from the brainor spinal cord to skeletal muscles.
46 b. The autonomic system is two neurons (a preganglionic & postganglionic neuron), to smooth, cardiac muscle or glands.
47 3. Two Divisions – sympathetic and parasympathetic a. Sympathetic – “fight or flight”.1.) Emerges from thoracic and lumbar spinal cordregions forms the “sympathetic trunk andganglia” near the spinal column.2.) The preganglionic neuron is short while thepostganglionic neuron is long.3.) Functions to meet stressful conditions, releasesnorepinephrine (NE) and epinephrine (E).
49 b. Parasympathetic – “rest and digest” 1.) Emerges from cranial nerves and sacral spinalnerves from the spinal cord.2.) The preganglionic neuron is long while thepostganglionic neuron is short.3.) Functions in quieter periods to restore energyand is dominant during periods of relaxation.It releases acetylcholine (ACh) neurotransmitter.4.) *NOTE – ACh excites skeletal muscle,but NOT smooth, cardiac muscle andglands!