Biology 141 The Autonomic Nervous System Chapter 15

Overview The CNS The CNS spinal cord spinal cord brain brain The peripheral nervous system The peripheral nervous system sensory-somatic nervous system Responds to the external environment 12 pairs of cranial nerves and 31 pairs of spinal nerves. autonomic nervous system Responds to the internal environment Parasympathetic nervous system Sympathetic nervous system

Divisions of the Nervous System

ANS Function: Function: operates without conscious control. operates without conscious control. Regulation: Regulation: Control: Control: hypothalamus and brain stem. hypothalamus and brain stem. receives input from limbic system and other regions of the cerebrum receives input from limbic system and other regions of the cerebrum Regulate activity of Regulate activity of smooth muscle, cardiac muscle & certain glands smooth muscle, cardiac muscle & certain glands

ANS Sensory receptors associated with interoceptors (receptors that monitor internal environments) Sensory receptors associated with interoceptors (receptors that monitor internal environments) Located in blood vessels, viscera, smooth muscle Located in blood vessels, viscera, smooth muscle Chemoreceptors Chemoreceptors Baroreceptors monitor BP Baroreceptors monitor BP Internal pain - angina Internal pain - angina Mechanoreceptors Mechanoreceptors Monitor vessel stretch Monitor vessel stretch

Comparison SOMATIC vs. ANS Somatic Somatic contains both sensory and motor neurons. contains both sensory and motor neurons. input from the special and somatic senses. input from the special and somatic senses. sensations are consciously perceived. sensations are consciously perceived. innervate skeletal muscle to produce conscious, voluntary movements. effect of a motor neuron is always excitation.

Comparison SOMATIC vs. ANS ANS ANS contains both sensory and motor neurons. contains both sensory and motor neurons. Input from interoceptors. Input from interoceptors. input not consciously perceived. input not consciously perceived. may receive input from somatic senses and special sensory neurons. may receive input from somatic senses and special sensory neurons. regulate visceral activities Effect: exciting or inhibiting activities of cardiac muscle, smooth muscle, and glands.

Comparison SOMATIC vs. ANS Somatic motor pathways consist of a single motor neuron Somatic motor pathways consist of a single motor neuron Autonomic motor pathways consists of two motor neurons in series Autonomic motor pathways consists of two motor neurons in series

Motor Neurons in Series first autonomic first autonomic cell body in the CNS cell body in the CNS myelinated axon extends to an autonomic ganglion or adrenal medullae myelinated axon extends to an autonomic ganglion or adrenal medullae second autonomic second autonomic cell body in an autonomic ganglion cell body in an autonomic ganglion nonmyelinated axon extends to an effector. nonmyelinated axon extends to an effector.

Somatic has 1 motor neuron ANS has 2 motor neurons in series

First motor neuron: preganglionic Preganglionic neuron Preganglionic neuron cell body in brain or spinal cord axon is myelinated extends to autonomic ganglion

Second motor neuron: postganglionic Postganglionic neuron Postganglionic neuron cell body lies outside the CNS in an autonomic ganglion cell body lies outside the CNS in an autonomic ganglion axon is unmyelinated fiber that terminates in a visceral effector axon is unmyelinated fiber that terminates in a visceral effector

First Neuron terminates in a ganglion or adrenal medulla Can use either NE or ACh as the neurotransmitter Can use either NE or ACh as the neurotransmitter

ANS Efferent Branches The output (efferent) part of the ANS is divided into two principal parts: The output (efferent) part of the ANS is divided into two principal parts: the sympathetic division the sympathetic division the parasympathetic division the parasympathetic division Organs that receive impulses from both sympathetic and parasympathetic fibers are said to have dual innervation. Organs that receive impulses from both sympathetic and parasympathetic fibers are said to have dual innervation.

Parasympathetic and Sympathetic Parasympathetic Parasympathetic Sympathetic Sympathetic

Dual innervation Dual innervation Dual innervation one speeds up organ one slows down organ Sympathetic NS increases heart rate Parasympathetic NS decreases heart rate

Anatomy of Autonomic Motor Pathways Components Components Preganglionic neuron Preganglionic neuron Sympathetic Sympathetic Parasympathetic Parasympathetic Autonomic ganglia Autonomic ganglia Postganglionic neuron Postganglionic neuron Autonomic Plexus Autonomic Plexus

Preganglionic Neurons Sympathetic Also called thoracolumbar division Also called thoracolumbar division Cell bodies in the lateral horns of the gray matter in segments T1-T12 and L1- L2 Cell bodies in the lateral horns of the gray matter in segments T1-T12 and L1- L2 Axons are called the thoracolumbar outflow Axons are called the thoracolumbar outflowParasympathetic Also called craniosacral division Also called craniosacral division Cell bodies in the brain stem cranial nerve nuclei III, VII, IX, and X Cell bodies in the lateral gray horns of segments S2- S4 Axons are called craniosacral outflow

Autonomic Ganglia Sympathetic 2 groups 2 groups Sympathetic trunk ganglia (Vertebral chain ganglia) Sympathetic trunk ganglia (Vertebral chain ganglia) lie in a vertical row on either side of the vertebral column lie in a vertical row on either side of the vertebral column Innervate above the diaphragm Innervate above the diaphragm Prevertebral ganglia (collateral) Prevertebral ganglia (collateral) Anterior to vertebral column close to large arteries Anterior to vertebral column close to large arteries Innervate below the diaphragm Innervate below the diaphragm

Autonomic Ganglia Parasympathetic 1 group: terminal ganglia 1 group: terminal ganglia Located near or in viscera

Postganglionic Neurons postganglionic neuron can be branched to receive signals from multiple ganglionic locations. postganglionic neuron can be branched to receive signals from multiple ganglionic locations.

Autonomic Plexuses: Tangled neural networks that lie along major arteries. Major autonomic plexuses Major autonomic plexuses Cardiac: supplies the heart, Cardiac: supplies the heart, Pulmonary: supplies the lung, Pulmonary: supplies the lung, Celiac (solar): liver, gallbladder, stomach, pancreas, spleen, kidney, reproductive organs Celiac (solar): liver, gallbladder, stomach, pancreas, spleen, kidney, reproductive organs

Major autonomic plexuses Major autonomic plexuses superior mesenteric: small and large intestines inferior mesenteric: large intestines Renal: kidneys and ureters Hypogastric: pelvic viscera

Structure of the Sympathetic Division Preganglionic – leave spinal cord through ventral root Preganglionic – leave spinal cord through ventral root Enter the ganglion via the white ramus Enter the ganglion via the white ramus Synapse with postganglionic Synapse with postganglionic Leave via gray ramus Leave via gray ramus Terminates on visceral effectors Terminates on visceral effectors

3 Pathways of Sympathetic Fibers Spinal nerve route Spinal nerve route out same level Sympathetic chain route Sympathetic chain route up chain & out spinal nerve Collateral ganglion route Collateral ganglion route out splanchnic nerve to collateral ganglion

Divergence of Sympathetic Neurons Divergence: Divergence: 1 preganglionic cell synapses on many postganglionic cells 1 preganglionic cell synapses on many postganglionic cells Mass activation due to divergence Mass activation due to divergence multiple target organs multiple target organs fight or flight response explained fight or flight response explained Adrenal gland Adrenal gland modified cluster of postganglionic cell bodies that release epinephrine & norepinephrine into blood modified cluster of postganglionic cell bodies that release epinephrine & norepinephrine into blood

Horner’s Syndrome Sympathetic innervation to one side of the face is lost (mutation, injury, or disease). Sympathetic innervation to one side of the face is lost (mutation, injury, or disease). Affects outflow Affects outflow Drooping of eyelid Drooping of eyelid Constricted pupil Constricted pupil Lack of sweating Lack of sweating

Structure of the parasympathetic division Preganglionic Preganglionic Cranial Cranial As part of a cranial nerve As part of a cranial nerve Sacral Sacral From ventral root of spinal nerve From ventral root of spinal nerve Terminal ganglia Terminal ganglia In the walls of viscera In the walls of viscera Postganglionic Postganglionic Innervate smooth muscle and glands of the visceral walls Innervate smooth muscle and glands of the visceral walls

Parasympathetic Cranial Nerves Oculomotor nerve Oculomotor nerve ciliary ganglion in orbit ciliary ganglion in orbit iris iris Facial nerve Facial nerve pterygopalatine and submandibular ganglions pterygopalatine and submandibular ganglions supply tears, salivary & nasal secretions supply tears, salivary & nasal secretions Glossopharyngeal Glossopharyngeal otic ganglion supplies parotid salivary gland otic ganglion supplies parotid salivary gland Vagus nerve Vagus nerve supply heart, pulmonary and GI tract as far as the midpoint of the colon supply heart, pulmonary and GI tract as far as the midpoint of the colon

Parasympathetic Sacral Nerve Form pelvic splanchnic nerves Form pelvic splanchnic nerves

ANS Neurotransmitters Classified as either cholinergic or adrenergic neurons based upon the neurotransmitter released Classified as either cholinergic or adrenergic neurons based upon the neurotransmitter released Adrenergic Adrenergic Cholinergic Cholinergic

ANS NEUROTRANSMITTERS Cholinergic Cholinergic Produce and release acetylcholine (ACh) Produce and release acetylcholine (ACh) All sympathetic and parasympathetic preganglionic All sympathetic and parasympathetic preganglionic All parasympathetic postganglionic All parasympathetic postganglionic Only sweat gland sympathetic postganglionic Only sweat gland sympathetic postganglionic Adrenergic Adrenergic Produce and release norepinephrin (NE) Produce and release norepinephrin (NE) Most sympathetic postganglionic neurons(noradrenalin) Most sympathetic postganglionic neurons(noradrenalin)

Cholinergic Neurons Excitation or inhibition depending upon receptor subtype and organ involved. Excitation or inhibition depending upon receptor subtype and organ involved.

Cholinergic Receptors Cholinergic receptors Cholinergic receptors integral membrane proteins in the postsynaptic plasma membrane. 2 types: Nicotinic and muscarinic integral membrane proteins in the postsynaptic plasma membrane. 2 types: Nicotinic and muscarinic Activation of muscarinic receptors excitation or inhibition Muscarinic receptors are found on plasma membranes of all parasympathetic effectors (viscera, smooth muscle) Activation of nicotinic receptors Activation of nicotinic receptors excitation excitation Nicotinic receptors are found on postsynaptic cells of ANS cells and at NMJ Nicotinic receptors are found on postsynaptic cells of ANS cells and at NMJ

Adrenergic Neurons Adrenergic neurons release norepinephrine (NE) ) Adrenergic neurons release norepinephrine (NE) ) from postganglionic sympathetic neurons only from postganglionic sympathetic neurons only Excites or inhibits organs Excites or inhibits organs NE lingers at the synapse until enzymatically inactivated NE lingers at the synapse until enzymatically inactivated Effects triggered by adrenergic neurons typically are longer lasting than those triggered by cholinergic neurons. Effects triggered by adrenergic neurons typically are longer lasting than those triggered by cholinergic neurons.

Physiological Effects of the ANS Autonomic Tone Autonomic Tone balance between sympathetic and parasympathetic activity balance between sympathetic and parasympathetic activity regulated by the hypothalamus regulated by the hypothalamus Sympathetic Response Sympathetic Response Supports rigorous functions and rapid ATP production Supports rigorous functions and rapid ATP production Fight or flight response Fight or flight response Parasympathetic Response Parasympathetic Response Enhances rest and digestive functions, storage of ATP Enhances rest and digestive functions, storage of ATP

Fight or Flight Alarm reaction Alarm reaction dilation of pupils dilation of pupils Increase Increase heart rate heart rate respirations respirations BP BP Blood flow to skeletal muscles Blood flow to skeletal muscles Blood sugar Blood sugar decrease in blood flow to nonessential organs decrease in blood flow to nonessential organs Long lasting Long lasting lingering NE in synaptic gap lingering NE in synaptic gap

Pathway Autonomic Reflexes Autonomic Reflexes Receptor Receptor Responds to stimuli Responds to stimuli Transduce stimuli to action potential Transduce stimuli to action potential Sensory neuron Sensory neuron Action potential travels to CNS Action potential travels to CNS Integrating center (CNS) Integrating center (CNS) Interneurons relay sensory info to motor neurons Interneurons relay sensory info to motor neurons Hypothalamus Hypothalamus Brain stem Brain stem Spinal cord Spinal cord 2 Motor neurons (pre and post ganglionic) 2 Motor neurons (pre and post ganglionic) Carries action potential from the CNS to an effector Carries action potential from the CNS to an effector Effector Effector Smooth or cardiac muscle, glands Smooth or cardiac muscle, glands

Autonomic Control by Higher Centers Major control and integration center: hypothalamus Major control and integration center: hypothalamus Output to Output to Brain stem Heart Blood vessels Salivary glands swallowing Spinal cord Intestines bladder Receives input from Receives input from Viscera Viscera Olfaction Olfaction Gustation Gustation Changes in temp Changes in temp Osmolarity Osmolarity Blood chemistry levels Blood chemistry levels Limbic system Limbic system

DISORDERS Raynaud’s phenomenon Raynaud’s phenomenon excessive sympathetic stimulation of smooth muscle in the arterioles of the digits excessive sympathetic stimulation of smooth muscle in the arterioles of the digits Result - vasoconstriction Result - vasoconstriction the digits (fingers and toes) become ischemic (lack blood) after exposure to cold or with emotional stress. the digits (fingers and toes) become ischemic (lack blood) after exposure to cold or with emotional stress. Digits may become necrotic Digits may become necrotic

Autonomic Dysreflexia Exaggerated response of sympathetic NS in cases of spinal cord injury above T6 Exaggerated response of sympathetic NS in cases of spinal cord injury above T6 Sensory impulses from below the injury are unable to ascend to the brain Sensory impulses from below the injury are unable to ascend to the brain Causes mass stimulation of sympathetic nerves below the injury Causes mass stimulation of sympathetic nerves below the injury Result Result vasoconstriction which elevates blood pressure vasoconstriction which elevates blood pressure parasympathetic NS tries to compensate parasympathetic NS tries to compensate slows heart rate, dilates blood vessels above the injury slows heart rate, dilates blood vessels above the injury Produces a pounding headache, hypertension, flushed skin, profuse sweating above the injury and cool dry skin below Produces a pounding headache, hypertension, flushed skin, profuse sweating above the injury and cool dry skin below can lead to seizure, stroke or heart attack can lead to seizure, stroke or heart attack