G03 - ANS, CNS, PNS Dr. Morton G03: ANS, CNS, PNS Reading: GAFS 62-88 Objectives: •Familiarize students with the structure and organization of the nervous system Nervous System Definitions and Overview •Structural Divisions • Central nervous system (CNS)- the portion of the nervous system consisting of the brain and spinal cord. Command center that integrates and processes nervous system information. • Peripheral nervous system (PNS)- the part of the vertebrate nervous system constituting the nerves outside the central nervous system (nerves and gan- glia) • Upper motor neuron (UPN)- a motor neuron whose cell body is located in the motor area of the cerebral cortex and whose processes connect with motor nuclei in the brainstem or the anterior horn of the spinal cord. • Lower motor neuron (LMN)- a motor neuron whose cell body is located in the brainstem or the spinal cord and whose axon innervates skeletal muscle fi- bers. Also called final motor neuron. • Functional Divisions • Sensory (afferent = back to the CNS) • General afferent (touch, temperature, pain, etc) • Visceral afferent (viscera = internal organ) • Special afferent (sight, taste, sound) • Motor (efferent= away from the CNS) • Somatic efferent- innervates skeletal muscles derived from somites (body wall) • Branchial efferent- innervates skeletal muscles derived from the pha- ryngeal arches • Visceral efferent (viscera = internal organ) •Functional Organization •Receive stimuli •Receptors (e.g., pain, temperature) •Transmit responses •Conductors (e.g., muscle contraction) •Process input •Brain (interpretation) 26 G03 - ANS, CNS, PNS CNS PNS Sensory Motor General Visceral Special Somatic Branchial Visceral Afferent Afferent Afferent Efferent Efferent Efferent Skeletal mus- Skeletal mus- Smooth mus- cle of the body cle derived cle, glands, wall from pharyn- and modified geal arches cardiac muscle Touch Return information Sight, Pain (reflexes, pain) con- Taste, Sympathetic Parasympathetic Temperature cerning hollow or- Sound T1-L2 CN 3,7,9,10 Vibration gans and blood ves- S2-S4 Proprioception sels Organ, Tract, or System Sympathetic Parasympathetic Pupil •Dilates •Constricts Skin •Arrector pili muscle contraction •No effect •Vessels- vasoconstriction •Sweat glands- sweating Lacrimal and salivary glands •Decreases secretion •Increase secretion Heart •↑ rate and strength of contrac- •↓ rate and strength of contrac- tion tion •Dilates coronary vessels •Constricts coronary vessels Lung •Bronchodilation •Bronchoconstriction Digestive tract •Inhibits peristalsis •Stimulates peristalsis •Constricts blood vessels Genital system •Ejaculation •Erection Suprarenal medulla •Release of adrenaline •No effect Overview •Fight or Flight (E) •Rest and Digest (D) •Exercise •Digestion •Excitement •Defecation •Emergency •Diuresis 27 G03 - ANS, CNS, PNS CNS •Organization •Brain and spinal cord •Gray matter •Contains nerve cells •White matter •Contains nerve fibers •Meninges (membranes) •Dura mater (dur = tough, mater = mother) •Arachnoid mater (arachnoid = spi- der, i.e., spider web-like) •Pia mater 28 G03 - ANS, CNS, PNS CNS (continued) •Spinal Cord •Located in the vertebral column (spinal canal) •Length •Embryo: fills the column length •At birth: extends caudally to L2 - L3 •Adult: extends caudally to L1 - L2 •Why is this distinction clinically important? •Enlargements (2) •Cervical (upper limbs) •Lumbar (lower limbs) Regions of the Spinal Cord and Verterbral Column Region Number of Spinal Number of Vertebrae Nerves Cervical 8 7 Thoracic 12 12 Lumbar 5 5 Sacral 5 5 Coccygeal 1 4 29 G03 - ANS, CNS, PNS CNS (continued) •Spinal cord components •Dentate (denticulate) ligaments •Conus medullaris •Cauda equina •Filum terminale PNS •Organization •Ganglia (cell bodies) •Sensory •Dorsal root ganglia •Cranial nerve ganglia •Nerves (fibers) •Sensory and motor •Peripheral nerves (31 pairs) 30 G03 - ANS, CNS, PNS PNS (continued) •Typical Spinal Nerve and Its Peripheral Distribution •Components •Dorsal roots (sensory) •Cell bodies located in the dorsal root ganglia •Ventral roots (motor) •Cell bodies located in the CNS •Formed by fusion of segmental ventral and dorsal roots (2-4 mm long) •Exit intervertebral foramen •Divide into dorsal and ventral primary rami •Plexuses •Cervical (neck) •Brachial (upper limb) •Lumbar (distal thoracic region, abdomen, pelvis and lower limb) •Sacral (pelvis and lower limb) 31 G03 - ANS, CNS, PNS Pathways • Somatic afferent (sensory) • Sensory fibers carry sensor (afferent information from the tissues of the limbs and back through the ventral and dorsal rami respec- tively, to the dorsal root to the spinal cord (Note: the collection of sensory cell bodies in the dorsal root forming the dorsal root gan- glion (DRG)) • Somatic efferent (motor) • Motor neurons carry so- matic motor information from the spinal cord to the skeletal muscles of the limbs and back 32 G03 - ANS, CNS, PNS Sympathetic system • “Thoracolumbar” nervous system • T1 to L2 • Function: fight, fright, flight 33 G03 - ANS, CNS, PNS • Visceral efferents (sympathetic) • Preganglionic fibers from spinal levels T1-L2 course out the ventral root and exit the spinal nerve through a white rami communicantes to synapse in the paraverte- bral ganglion • Postganglionic sympathetic neurons exit through a gray rami communicantes to course to the blood vessels, erector pili muscles and sweat glands of the upper and lower limbs • Visceral efferents (sympathetics) • Preganglionic fibers from spinal levels T1-L2 course out the ven- tral root and exit the spinal nerve through a white rami communi- cantes to synapse in a higher or lower paravertebral ganglion • Postganglionic sympathetic neu- rons exit through a gray rami communicantes to course to the blood vessels, erector pili mus- cles and sweat glands of the up- per and lower limbs 34 G03 - ANS, CNS, PNS • Visceral efferents (sympathetics) • Preganglionic fibers course through a splanchnic nerve to synapse in a pre-vertebral ganglion (i.e. celiac ganglion) • Postganglionic fibers go to intestines, kidneys, liver, pancreas, etc. 35 G03 - ANS, CNS, PNS • Visceral efferents (sympathetics) • Preganglionic fibers from spinal levels T1-T4 course up the sympathetic trunk to synapse in a more superior sympathetic ganglion (i.e. superior cervical ganglion) • Postganglionic fibers go from superior sympathetic ganglion go to heart, lung, eye, lacrimal gland, salivary glands, cranial vessels • Visceral efferents (sympathetics) • Preganglionic fibers from spinal levels T12-L2 course down the sympathetic trunk to synapse in a more infe- rior sympathetic ganglion (inferior mesenteric) • Postganglionic fibers go to colon, rectum, and genitalia 36 G03 - ANS, CNS, PNS • Visceral afferents (on sympathetic fibers) • Return information from internal organs and smooth muscle of large blood vessel walls in the limbs 37 G03 - ANS, CNS, PNS Parasympathetic system • “Cranio-caudal” nervous system • Cranial nerves 3, 7, 9, 10; S2-S4 • Function: homeostasis 38 G03 - ANS, CNS, PNS Comparison of Pre- versus Postganglionic Neurons of the ANS Sympathetic Parasympathetic Short preganglionic fibers Long preganglionic fibers Long postganglionic fibers Short postganglionic fibers Ganglia located relatively far Ganglia located on or near their from their target organ target organ Sympathetic Parasympathetic Preganglionic cell bodies: T1 Preganglionic cell bodies: to L2 brainstem and S2-S4 Postganglionic cell bodies: Postganglionic cell bodies: chain or collateral ganglia cranial or enteric ganglia Ganglia run entire length of Ganglia are at one end or the spinal cord other of spinal cord 39 .