HB23_HB24 Organization of SNS & ANS - Saleha PDF

SOMATIC NERVOUS SYSTEM & AUTONOMIC NERVOUS SYSTEM DR. SITI SALEHA MASRUDIN DEPARTMENT OF HUMAN ANATOMY FACULTY OF MEDICINE AND HEALTH SCIENCES UNIVERSITI PUTRA MALAYSIA ...

SOMATIC NERVOUS SYSTEM & AUTONOMIC NERVOUS SYSTEM DR. SITI SALEHA MASRUDIN DEPARTMENT OF HUMAN ANATOMY FACULTY OF MEDICINE AND HEALTH SCIENCES UNIVERSITI PUTRA MALAYSIA  At the end of the session, the students should understand and able to define and describe the OBJECTIVES basic concepts of the somatic nervous system & autonomic nervous system. SOMATIC NERVOUS SYSTEM - is a component of the peripheral nervous system associated with the VOLUNTARY control of the body movements and reflex action via skeletal muscles. - It is responsible for all the functions we are aware of and can consciously influence, including the movement of our arms, legs, and other body parts.  SOMATIC NERVOUS SYSTEM Component of peripheral nervous system is 43 different segments of nerves 12 pairs of cranial nerve 31 pairs of spinal nerve pairs: 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal Consists of both afferent (sensory) and efferent (motor) nerves.  SOMATIC NERVOUS SYSTEM Components of SNS: Dorsal roots: Carry sensory information Afferent fibers Ventral roots: Carry motor information Efferent fibers Dorsal root ganglia: location of sensory neurons (cell bodies) Interneurons Mechanoreceptors SOMATIC NERVOUS SYSTEM It is responsible for the reflex arc, which involves skeletal muscle and the use of interneurons to perform reflexive actions. Somatic reflex arc Reflex arcs are neural pathways that produce involuntary movements. A reflex involving only 2 neurons and 1 synapse is known as a monosynaptic reflex arc (knee jerk) Affect the skeletal muscle AUTONOMIC NERVOUS SYSTEM - Autonomic nervous system is a component of the peripheral nervous system that regulates INVOLUNTARY physiologic processes. - E.g.: heart rate, blood pressure, respiration, digestion, and sexual arousal. - It contains three anatomically distinct divisions: sympathetic, parasympathetic, & enteric. Division of Autonomic Nervous System  AUTONOMIC NERVOUS SYSTEM It is distributed throughout the central and peripheral nervous system. The ANS consists of two parts: Sympathetic nervous system Parasympathetic nervous system Autonomic nervous system (ANS):  Functional Classification of Nervous System Motor division consists of TWO parts: 1. SOMATIC NERVOUS SYSTEM Voluntary, control of skeletal muscle, tendon & joints 2. AUTONOMIC NERVOUS SYSTEM Involuntary, control of smooth muscle + cardiac muscle + glands 2 division: sympathetic and parasympathetic Functional Classification of Nervous System  Somatic Nervous System vs Autonomic Nervous System SOMATIC NERVOUS SYSTEM AUTONOMIC NERVOUS SYSTEM (SNS) (ANS) Definition A part of peripheral nervous system that A part of peripheral nervous system that regulates voluntary movements of skeletal regulates involuntary movements of internal muscles. organs / smooth muscles. Nature of the Can be voluntarily manageable. Involuntary. movements that regulate Components Cranial nerves & spinal nerves. Sympathetic & parasympathetic nervous system. Nature of the Functions are less complex that the ANS. Functions of ANS are more complex (signalling functions pathway). Neurotransmitter Involves excitatory neurotransmitter. Involves both excitatory & inhibitor neurotransmitters. Type of muscles Acts on skeletal muscle. Acts on smooth muscle, cardiac muscles, and glands. Neuron (to transmit One efferent neuron. Two efferent neurons & one signals) ganglia to transmit signal. 10 The sympathetic system: The sympathetic activities prepare/stimulates the body for an emergency/stress situation (i.e, fight, fright and flight situations) The parasympathetic system: The parasympathetic activities conserve and restore energy. PNS SNS During urgent, nervous condition Both systems PNS SNS counter- balance each other SN S PNS During relaxing & quiescence stage Somatic vs autonomic (sympathetic) : I I II II III III I.– Sensory neuron (afferent) II.– Connector neuron III.– Motor neuron (efferent) III Reflex arc a neural pathway that controls an action reflex. there are 2 types of reflex arcs: Autonomic reflex arc (visceral reflex) that affects the inner organs. Somatic reflex arc that affects muscles. Autonomic reflex arc (visceral reflex) Stimulus Receptor in viscera Visceral sensory neuron Integration centre (3 possible locations): - Preganglionic neuron - Dorsal horn interneuron - Within walls of viscera Motor neuron (2- neuronchain): - Preganglionic neuron - Postganglionic neuron Response Visceral effector Autonomic reflex arc (visceral reflex) The afferent impulses: Originate in visceral receptors Travel via an afferent pathway to CNS Integrated through connector neurons at different levels Leave via an efferent pathway to visceral effector organs Vasomotor: - refers to actions upon a blood vessel which alter its diameter. - vasodilator action and vasoconstrictor action. Sudomotor: -from Latin sudor, 'sweat' and motor. -describes anything that stimulates the sweat glands. Pilomotor: reflex n. contraction of the smooth muscle of the skin. caused by mild application of a tactile stimulus or by local cooling. resulting in goose bumps.  Differences between SNS & ANS Somatic Nervous System Autonomic Nervous System 1. Motor neurones have cell bodies in the Motor neurones are cells of the autonomic anterior horn of the spinal cord. ganglia situated outside the CNS. 2. Motor endings are motor end Motor endings are a composite plexus between plates of the striated muscle fibres. and around all the smooth muscle fibres and glands = autonomic ground plexus. 3. The connector neurone is wholly situated The connector neurone is the preganglionic inside the CNS. neurone with its cell body in the lateral horn of the spinal cord (Sympathetic) or in the nuclei of III, VII, IX & X cranial nerves (Parasympathetic). The neurone lies partly in the CNS and partly in the PNS. What is the great difference between the somatic motor and autonomic motor systems? Somatic motor system organization Somatic motor neuron Cell body Target spinal cord organ The somatic motor fibres leave the CNS run uninterruptedly to the effector. Autonomic motor system organization Autonomic ganglion Preganglionic Postganglionic Cell body in neurone neurone Target brainstem or organ spinal cord The pathway of the autonomic motor fibres from CNS to target organ is interrupted by synapses in a ganglion 2 sets of neurones What is the great difference between the somatic motor and autonomic motor systems? 1. The somatic motor fibres leave the CNS run uninterruptedly to the effector. 2. The pathway of the autonomic motor fibres from CNS to target organ is interrupted by synapses in a ganglion, 2 sets of neurones. AUTONOMIC NERVOUS SYSTEM: SYMPATHETIC Division of Autonomic Nervous System  Division of Autonomic Nervous System Sympathetic Parasympathetic Enteric Nervous system system System Activation leads to a Activation leads to a Involved in the regulation of state of overall elevated state of overall digestive processes function depressed function Capable of functioning independently of the Responsible for the Responsible for the remainder of the nervous “fight-or-flight” “rest-and-digest” system response response Made up primarily of 2 Connections to most Parasympathetic complex bundles of nerves: tissues of the body dominance → ↓ HR, ↓ The myenteric (Auerbach) Sympathetic dominance blood pressure, plexus → ↑ HR, ↑ blood promotion of GI The submucosal (Meissner) pressure, cessation of peristalsis, glycogenesis plexus GI peristalsis, Exception to the 2-neuron glycogenolysis innervation rule of the ANS Division of Autonomic Nervous System Sympathetic nervous system What are the 3 keywords to represent SNS? FRIGHT, FIGHT, FLIGHT! Sympathetic nervous system Function : prepares the body to deal with the emergency situations carry vasomotor, pilomotor, secretory fibres to sweat glands, visceral pain *Vasomotor refers to actions upon a blood vessel which alter its diameter. More specifically, it can refer to vasodilator action and vasoconstrictor action. *Pilomotor pertaining to the arrector muscles, the contraction of which produces cutis anserina (goose flesh / goose bumps) and piloerection. Sympathetic nervous system Cell bodies of preganglionic neurons are located in the spinal cord Emerge from thoraco- Cervical lumbar region (T1 to L2) Thoracic Lumbar Sacral Sympathetic nervous system 2 sets of neurones : Preganglionic neurones cell bodies of Preganglionic neurones is located in CNS (in the lateral horn cells of T1-L2 segment of spinal cord). Postganglionic neurones cell bodies of Postganglionic neurones is located in sympathetic trunk OR in autonomic plexuses in the abdomen and pelvis. Sympathetic trunk - also known as paravertebral ganglia. - lying on both side of the vertebral column (extending along its whole length; from C1 to coccyx). Sympathetic trunk 22 Pairs of sympathetic ganglia 3 cervical ganglia 11 thoracic ganglia 4 lumbar ganglia 4 sacral ganglia Terminal ganglion: ganglion impar → fusion of two sympathetic trunks in front of the coccyx. Prevertebral ganglia also known as collateral ganglia / peripheral ganglia. Consist of 3 ganglia: a. Celiac ganglion b. Superior mesenteric ganglion c. Inferior mesenteric ganglion situated in front of the origin of coeliac trunk (T12), superior mesenteric artery (L1) and inferior mesenteric artery (L3) of the abdominal aorta. What is the sympathetic trunk? What is the sympathetic trunk? Also known as sympathetic chain are a paired bundle of nerve fibers that run from the base of the skull to the coccyx. The sympathetic trunk travels in a downward direction from the skull, just lateral to the vertebral bodies. It interacts with the spinal nerves or their ventral rami by way of rami communicantes. The superior end of it is continued upward through the carotid canal into the skull. What is the sympathetic trunk? The inferior part travels in front of the coccyx, where it converges with the other trunk at a structure known as the ganglion impar. Along the length of the sympathetic trunk are ganglia known as paravertebral ganglia. The sympathetic trunk is a fundamental part of the sympathetic division of the autonomic nervous system. What is the sympathetic trunk? It allows nerve fibers to travel to spinal nerves that are superior and inferior to the one in which they originated. A number of nerves (such as most of the splanchnic nerves) arise directly from the trunks. What is the sympathetic trunk? Autonomic Nervous System Schematic diagram to show the craniosacral outflow (parasympathetic) and thoracolumbar outflow (sympathetic). Why is the Sympathetic nervous system also known as thoracolumbar outflow? * PreGGL neurons exit the CNS from T1-L2 spinal segments Chromaffin cells – neural crest cells in origin; form the SNS trunk & preaortic ganglia; migrated into adrenal medulla; Sympathetic pathway 1. Cell bodies located in CNS (lateral horn cells of spinal cord of T1-L2) 2. Preganglionic nerve fibres leaves the CNS (known as thoracolumbar outflowT1→ L2) Sympathetic pathway 3. Reached at sympathetic trunk a. synapse with cell bodies in trunk ganglion or run up or down the trunk to reach to other ganglion b. leave the trunk without synapse; synapse at the ganglion in an autonomic plexus c. leave the trunk without synapse; synapse at the modified ganglion cells in the suprarenal gland (adrenal gland) Sympathetic pathway Sympathetic pathway There is NO sympathetic outflow from the cervical, lower lumbar and coccygeal segments of the spinal cord The Preganglionic fibres that : run with cervical nerves must ascend in the sympathetic trunk to cervical ganglia. run with lumbar & sacral nerves descend in the trunk to lower lumbar and sacral ganglia. The white ramus communicans & The gray ramus communicans  White ramus communicans ramus means branch (plural:rami communicantes) is the preganglionic sympathetic outflow nerve tract from the spinal cord. Each of the thoracic, and the first and second lumbar nerves contribute a white ramus communicans to the adjoining sympathetic ganglion. contain both myelinated and unmyelinated preganglionic sympathetic fibres. appears white because they are more myelinated than unmyelinated fibers, unlike the gray rami. Gray ramus communicans Each spinal nerve receives a branch called a gray ramus communicans from the adjacent paravertebral ganglion of the sympathetic trunk. contain both preganglionic and postganglionic nerve fibres of the sympathetic nervous system. Sympathetic ganglia: a. Cervical sympathetic ganglia (3) b. Thoracic sympathetic ganglia (11) c. Lumbar sympathetic ganglia (4) d. Sacral sympathetic ganglia (4) (a) 3 cervical sympathetic ganglia Extends from the base of skull to the neck of 1st rib 3 ganglia → superior, middle and inferior a. Superior cervical ganglion b. Middle cervical ganglion c. Inferior cervical ganglion Inferior cervical ganglion often fuses with T1 ganglion → cervicothoracic ganglion (stellate ganglion). Cervical Sympathetic Ganglia - Pathway Grey rami Superior cervical ganglion communicantes Is there any white rami communicantes to the Middle cervical ganglion cervical ganglion? grey rami Inferior cervical ganglion communicantes Lateral horn cells Dorsal ramus Ventral ramus 1st thoracic white rami ganglion communicantes (b) 11 Thoracic sympathetic ganglia 11 thoracic symp. ganglia Don’t forget that we have 12 pairs of thoracic spinal nerves! T1-T4 ganglia → postGGL fibers to heart, lung, oesophagus (through cardiac, pulmonary and oesophageal plexuses) (cardiopulmonary splanchnic n) T5-T11 ganglia → preGGL fibers form 3 splanchnic nerves that end in coeliac and superior mesenteries plexuses and ganglia on abdominal aorta (abdominopelvic splanchnic n). a. greater splanchnic n. : T5 – T9 ganglia b. lesser splanchnic n. : T10-T11 ganglia c. least splanchnic n. : T11 ganglion T5-T12 sympathetic ganglia - pathway (T12) 3 prevertebral ganglia (L2) located IN FRONT of vertebral column in the abdominal (L1) cavity (L3) situated close to ORIGIN of superior, middle & inferior mesenteric arteries (c) 4 lumbar sympathetic ganglia 4 lumbar ganglia associated with VL1 to VL4 (known as paravertebral ganglia) are postganglionic neurons that synapse with preganglionic sympathetic axon from thoracic nerve level via white rami communicans Only L1 & L2 paravertebral ganglia connected to spinal nerves by a white rami communicans The L3 and L4 paravertebral ganglia receive presynaptic sympathetic axons that descended from higher level via gray rami communicans. (d) 4 sacral sympathetic ganglia 4 sacral ganglia, anterior to sacral foramina (known as sacral paravertebral ganglia) are postganglionic sympathetic neurons that synapse with preganglionic sympathetic axon from thoracic+L1+L2 nerve level via white rami communicans Since sacral ganglia are below the origin, none sacral paravertebral ganglia are directly connected to the sacral spinal cord Postganglionic axon leave sacral ganglia via gray communicants, joining S1 to S4 nerve to target Forming sacral splanchnic nerve  Functions of sympathetic nervous system System Sympathetic effect Eye Dilatation of pupil Respiratory system Relaxation smooth muscle of the bronchial wall → widen bronchial tube Cardiovascular system Increases heart rate Gastrointestinal tract Inhibition of GIT motility Constriction of anal sphincter Genitourinary system Relaxation of urinary bladder wall & constriction of sphincter Ejaculation of penis Body wall Contraction of arrector pili → erection of hair muscles Stimulate secretion from sweat gland Vasoconstriction of peripheral blood vessel  Clinical anatomy Raynaud’s disease or phenomenon An exaggerated sympathetic response causes blood vessels in the fingers and toes to constrict, usually in response to cold or stress. Pathology: Vasospasm (abnormal vasoconstriction of small arteries) causes decreased blood flow to the fingers and toes due to sympathetic overactivity Management: Keep warm, manage stress, nerve block/sympathectomy (stellate ganglion may be cut)  Clinical anatomy Horner’s syndrome Horner's syndrome (Bernard- Horner syndrome/ oculosympathetic palsy) is a combination of symptoms that arises when a group of nerves known as the sympathetic trunk supply eye & facial muscles are damaged. (Ipsilateral) Eg: traction of cervical rib (extra rib arises from the seventh cervical vertebra) on stellate ganglion/carotid artery injury/tumors Typical signs : sunken eyeballs (enophthalmos) partial ptosis (drooping or falling of the upper or lower eyelid) anhydrosis (deficiency or absence of perspiration/ unable to generate sweat) miosis (constriction of the pupil) PARASYMPATHETIC NERVOUS SYSTEM  Parasympathetic nervous system Function : aims to reserve and restore energy 2 sets of neurones : i. Preganglionic neurones ii. Postganglionic neurones Parasympathetic ganglia Cell body in Postganglionic cranial nerve Preganglionic neurone neurone Target ganglia and S2-4 spinal organ segment (i) Preganglionic neurones: cell bodies in CNS cranial nerve nuclei lateral horn cells of sacral segment of spinal cord (ii) Postganglionic neurones: cell bodies in PNS in the walls of the viscera concerned 4 ganglia located some distance from the structures innervated in the head: i. Ciliary ganglia ii. Pterygopalatine ganglia iii. Submandibular ganglia iv. Otic ganglia Why parasympathetic nervous system also known as craniosacral outflow? Preganglionic neurons exit the CNS from the cranial nerve nuclei and lateral horn cells of S2-S4 spinal segments. Parasympathetic pathway (cranial outflow) Cranial outflow Parasympathetic component of Cranial nerves III, VII, IX, X Parasympathetic pathway (cranial outflow)  Parasympathetic pathway (cranial outflow) Cranial outflow 1. Cell bodies located in CNS Midbrain: Edinger-Westphal nucleus (nucleus of the Oculomotor cranial n). Pons & Medulla: Salivatory nuclei (Facial & glossopharyngeal nerves) Medulla: Dorsal vagal nucleus (Vagus n) 2. Preganglionic nerve fibres leaves the CNS through cranial nerves (CN III, VII, IX, X) Parasympathetic pathway (cranial outflow) Cranial outflow 3) Reached at parasympathetic ganglia: 4 parasympathetic ganglia (in the head & neck) Pterygopalatine, Ciliary, Submandibular & Otic ganglia. autonomic nerve plexuses (in the thorax & abdomen) Parasympathetic pathway (sacral outflow) Sacral outflow 1. Cell bodies located in spinal cord (grey matter of S2-S4 spinal segments) 2. Preganglionic nerve fibres pass along with anterior nerve roots of the corresponding sacral spinal nerves to form pelvic splanchnic nerves 3. Reached at parasympathetic ganglia located near or within the walls of pelvic organs Sacral parasympathetic outflow Cell bodies of preganglionic originate from lateral horn of the S2-4 spinal segment preganglionic axons forms pelvic splanchnic nerves synapse around the ganglia located near or within the wall Sacral parasympathetic outflow  Functions of parasympathetic nervous system System Parasympathetic effect Eye Constriction of pupil Respiratory system Contraction of smooth muscle of the bronchial wall ➔ narrowing of the bronchial tube Cardiovascular system Decreases heart rate Gastrointestinal tract Increases GIT motility Relaxation of anal sphincter Stimulate secretion from mucosal glands Genitourinary system Contraction of urinary bladder wall & relaxation of sphincter Erection of penis Body wall No effect on arrector pili, sweat gland & peripheral blood vessel Comparison of the sympathetic and parasympathetic pathways sympathetic division ❖ preGGL axon → shorter; postGGL axon → longer Sympathetic ganglia Preganglionic neurone Postganglionic Cell body in neurone T1-L2 spinal Target segments CHOLINERGIC ADRENERGIC organ (Acetylcholine) (Noradrenaline) ** Except fibers supplying the sweat gland and arrector pili → CHOLINERGIC Comparison of the sympathetic and parasympathetic pathways parasympathetic division ❖ pre GGL axon → longer; postGGL axon → shorter Parasympathetic ganglia Preganglionic Postganglionic Cell body in neurone neurone brainstem and Target S2-4 spinal CHOLINERGIC organ segment CHOLINERGIC (Acetylcholine) (Acetylcholine)  ENTERIC NERVOUS SYSTEM  Enteric nervous system - A network of intrinsic neurones and ganglia located IN the wall of the GIT - Derived from neural crest cells (INDEPENDENT of sympathetic & parasympathetic) - Regulates GIT motility, secretory activity, vascular activity - Eg : Meissner’s plexus (submucosa plexus) ; Auerbach’s plexus (myenteric plexus) Enteric nervous system Enteric nervous system Clinical anatomy: Hirschsprung's disease Neural crest cells fail to migrate to descending colon → lack of parasympathetic ganglia in myenteric plexus Megacolon → faecal accumulation at the region proximal to the aganglionic intestinal wall.  Differences between Sympathetic & Parasympathetic systems Sympathetic Parasympathetic 1. Thoraco-lumbar outflow 1. Cranio-sacral outflow (T1 to L2) (CN:3,7,9 & 10 and S 2,3,4) 2. Preganglionic neurone → 2. Preganglionic neurone → lateral horn brainstem & sacral segment of S/cord 3. Preganglionic fiber →short 3. Preganglionic fiber → long 4. Ganglion → near vertebral 4. Ganglion → near target column organ 5. Postganglionic fiber → long 5. Postganglionic fiber → short  Differences between Sympathetic & Parasympathetic systems Sympathetic Parasympathetic 6. Neurotransmitter at pre-ganglionic 6. Acetylcholine ending → Acetylcholine (Ach) 7. Neurotransmitter at post-ganglionic 7. Acetylcholine at all endings ending → norepinephrine 8. Action → Prepares body for 8. Conserves & restores energy emergency 9. Widespread due to many 9. Discrete action with few postganglionic fibers postganglionic fibers PARASYMPATHETIC DIVISION SYMPATHETIC DIVISION AUTONOMIC NERVOUS SYSTEM Actions of sympathetic and parasympathetic systems Organ Sympathetic Parasympathetic Visceral sphincter Constriction Dilatation Visceral wall m/s Relaxation Contraction Blood vessel Constriction Relaxation Pupil Dilatation Constriction Heart rate Increase Diminish Blood pressure Increase Diminish Bronchial m/s Dilatation Constriction Urinary bladder Relaxation Micturition Rectum and anal Continence Defecation canal AUTONOMIC NERVOUS SYSTEM Actions of sympathetic and parasympathetic systems Organ Sympathetic Parasympathetic Uterus Variable ** Variable ** Male reproductive Contraction of smooth Vasodilatation of organs muscles of - arteries and greatly Seminal vesicle increases blood flow Prostate and to erectile tissue Vas deferans producing erection. producing ejaculation ***Action depends on the stage of esterous cycle