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Autonomic Nervous System Autonomic Nervous System Autonomic = self governing Responsible for visceral motor func9on Two parts: • sympathe)c and parasympathe)c • nerve antagonists • one s9mulates/one inhibits CNS PNS Afferent Efferent Sensory division Motor division Afferent • carry nerve impulses from receptors or sense organs towards the CNS visceral efferent somac efferent Efferent •carry nerve impulses away from the CNS to effectors such as muscles or glands CNS PNS Afferent Efferent Sensory division Motor division Visceral= Somac Autonomic voluntary involuntary Somac skeletal 1 muscle voluntary Autonomic peripheral ganglion smooth 1 2 muscle, cardiac muscle, PREganglionic POSTganglionic glands CNS outside CNS INvoluntary Structure Funcon Somac 1 cell in pathway voluntary 1. spinal cord (ventral horn) or brain skeletal muscle Visceral/ 2 cells in pathway involuntary Autonomic 1. spinal cord or brain smooth muscle 2. peripheral ganglion* cardiac muscle glands *The autonomic system is a two neuron system vs. the one neuron used in connec9ng the PNS to the CNS (motor and sensory) . ANS divisions must then use a "ganglion" where the preganglionic fiber synapses with the postganglionic cell body. There are various types of ganglia (accumulaons of nerve cell bodies outside the CNS) associated with these synapse sites: paravertebral ganglia (sympathe*c trunk ganglion), that lie on either side of the vertebral column. They are used only for synapses of the sympathe9c division of the ANS prevertebral ganglia (“collateral ganglia”) that lie anterior to the vertebral column, close to major abdominal arteries from which they get their name (i.e. celiac, superior mesenteric, inferior mesenteric ganglion). For the synapse of fibers from the sympathe*c division intramural ganglia (terminal ganglia) located at the end ohe visceral efferent pathway, close to, or within the effector organ. These are sites of parasympathe*c synapse. CNS PNS Afferent Efferent Sensory division Motor division Visceral= Somac Autonomic voluntary involuntary Sympathe9c Parasympathe9c “fight or flight” “rest and digest” Sympathe9c “Fight or Flight” • heart rate speeds up • breathes faster • pupils dilate • digeson slows • cold, sweaty skin • liver releases sugars into the blood Parasympathe9c “Rest and Digest” • heart rate slows • breathing slows • blood flow to diges9ve system increases • pupils constricted Sympathe9c sympathe:c chain ganglia near spinal cord short preganglionic long postganglionic Parasympathe9c ganglia near target long preganglionic short postganglionic Sympathe9c Parasympathe9c Sympathe9c Parasympathe9c thoracolumbar craniosacral Parasympathetic Division Cell bodies for the parasympathetic division of the ANS are localized in the nuclei of the brain stem (cranial nn.) and in spinal cord segments S2-4 (i.e. craniosacral distribution) The preganglionic parasympathetic fiber travels out via cranial nerves (from the brain stem nuclei), and by pelvic splanchnic nn. from the sacral cord levels. Cranial nerves may then contain motor, sensory and parasympathetic fibers, or any combination of these - but never contain sympathetic fibers. 4 cranial nerves with parasympathetic fibers: CN III (oculomotor n.) CN VII (facial n.) CN IX (glossopharyngeal n.) CN X (vagus n.) There are 4 parasympathetic ganglia in the head (COPS) associated with the cranial nerves but only 3 of the parasympathetic nn. are associated (synapse) in them: ciliary (CN III) submandibular (CN VII) otic (CN IX) pterygopalatine (CN VII) The parasympathetic fibers in the vagus n. (CN X) are not confined to the head but spread parasympathetic innervation to 2/3 of the body (thorax and abdomen). The vagus uses intramural ganglia exclusively. Sympathe9c chain ganglia – 22 – 24 cervical – 3 thoracic – 11 lumbar – 4 sacral – 4 coccygeal - 1 The sympathetic chain extends from the base of the skull to the base of the coccyx. Its function is to distribute sympathetic innervation throughout the body since it is only found in the spinal cord segments Tl-L2. An example of this is the sympathe9c innervaon for the head and neck. It arises from the spinal cord segments T1-T4. The preganglionic fibers enter the sympathe9c trunk via the white rami communicans at these levels and ascends to synapse in the superior cervical ganglion at the base of the skull before extending onto the face as a postganglionic sympathe9c fiber. Gray rami are found at every vertebral level that exhibits a sympathetic ganglion. This extends from the base of the skull through to the tip of the coccyx. Gray rami communicans are output fibers for the sympathetic division of the ANS. There are more gray rami than white as white rami input sympathetic innervation and are restricted to TI-L2 where the sympathetic cell bodies are located. Sympathetic Division Cell bodies for the sympathetic division of the ANS are localized in the intermediolateral grey horn of the spinal cord from segments TI-L2 only. It is referred to as being thoracolumbar in distribution. The preganglionic sympathetic fiber travels out into the spinal nerve along the ventral root in company with the motor fiber. Once in the ventral ramus the preganglionic fiber enters a sympathetic ganglion (paravertebral autonomic ganglion) via the white ramus communicans. In the thorax and abdomen there is one sympathetic ganglion per vertebral level (i.e. 12 thoracic and 5 lumbar sympathetic ganglia). The ramus is termed "white" because the preganglionic fiber that traverses it is myelinated having arrived there from the spinal cord. White rami input sympathetic impulse into the sympathetic chain from T1-L2. Once in the sympathetic trunk, one of three things can happen… 1. The preganglionic fiber synapses in the sympathetic (paravertebral autonomic) ganglion and the postganglionic fiber re- enters the ventral (and dorsal) ramus via the grey (non-myelinated) ramus communicans to supply sympathetic innervation to the body wall. 2. The preganglionic fiber ascends or descends within the sympathetic trunk to synapse in a sympathetic (paravertebral autonomic) ganglion at a level other than that at which it entered the trunk. The post- ganglionic fiber re-enters the ventral (and dorsal) ramus via the grey (nomnyelinated) ramus communicans. These fibers may be directed to viscera or the body wall. Once in the sympathetic trunk, one of three things can happen… 3. The preganglionic fiber passes through the sympathetic (paravertebral autonomic) ganglion via a splanchnic nerve to a prevertebral autonomic ganglion where it synapses. The postganglionic fiber then passes out along to the target organ - usually a visceral organ in this instance. Structure Funcon • short preganglionic, long “fight or flight:” postganglionic increase heart rate Sympathe9c • 2nd cell body in increase respiraon sympathe9c chain dilate pupils • thoracolumbar inhibit blood to gut • branch profusely • long preganglionic, short “rest and digest:” postganglionic decrease heart rate Para- • 2nd cell body in ganglia slow respiraon sympathe9c near target increase blood flow to • craniosacral diges9ve tract • do not branch much ANA 611/811 Autonomic Nervous System 20 Schematic for Sympathetic Autonomic Distribution Somatomotor Visceromotor Somatosensory Visceral sensory ??? CNS PNS Afferent Efferent Sensory division Motor division Visceral= Somac Autonomic voluntary involuntary Sympathe9c Parasympathe9c “fight or flight” “rest and digest” Functional Aspects of the Afferent/Efferent Divisions Each spinal nerve contains two types of afferent (sensory) and efferent (motor) fibers: i) somatic afferent/efferent fibers that relay information to and from the body wall • somatic efferents: motor to skeletal muscle • somatic afferents: peripheral sensory receptors feeding the CNS Functional Aspects of the Afferent/Efferent Divisions Each spinal nerve contains two types of afferent (sensory) and efferent (motor) fibers: ii) visceral afferent/efferent fibers that relay information to and from the viscera of the body • visceral efferents (MOTOR): preganglionic visceral (sympathetic) fibers (TI-L2) that enter the sympathetic trunk via the white rami communicans. These fibers synapse in prevertebral ganglia and the postganglionic fibers go to the target organ. Parasympathetic viscerals (S2-4) leave the ventral rami and synapse in the target organ • visceral afferents (SENSORY): come back from the viscera via the white rami communicans and can travel up or down the sympathetic trunk prior to synapsing in the spinal cord Splanchnic (visceral) nerves Splanchnic nerves extend from the paravertebral (sympathetic) ganglia out to the prevertebral ganglia (celiac, superior and inferior mesenteric). They carry sympathetic pre- and postganglionic fibers to this ganglion as well as visceral afferent (sensory) fibers back from the visceral to the CNS. The preganglionic sympathetic fibers synapse in the prevertebral ganglion, the postganglionic sympathetic fibers simply pass through. In addition, preganglionic parasympathetic fibers access the prevertebral ganglion and also pass through. Referred pain: A term used to describe the phenomenon of pain perceived at a site adjacent to or at a distance from the site of an injury's origin Concepts Involved in Referred Pain 1. Proximal - Distal Where the injury is proximal and pain is felt distally. One example is a herniated disc. Herniation of the intervertebral disc between L4 and L5 involves the protrusion of the nucleus pulposus (center of disc) posteriorly into the vertebral foramen. Lumbar spinal nerves pass down the
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