A&P II Chapter 16 Autonomic Nervous System PDF

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Dr. Regan Chapter 16 lecture notes...

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BSC 251 — Chapter 16 Notes : Autonomic Nervous System 16.1 Overview of the Autonomic Nervous System Autonomic Nervous System (ANS): maintains homeostasis, directs the activities of cardiac muscle, smooth muscle and glands. 16.2 Contrasting the Somatic and Autonomic Nervous Systems Differences

Somatic Nervous System

Autonomic Nervous System

Effectors

Skeletal Muscle

Cardiac Muscle, Smooth Muscle, Glands

Headquarter in Brain

Primary Motor Cortex of Cerebrum

Hypothalamus

PNS Neurons

Upper and Lower Motor Neurons

Preganglionic and Postganglionic Neurons

16.3 Anatomy of the Autonomic Nervous System Sympathetic: fight or flight, mobile in extreme situations - origin at CNS — Spinal Cord - types of nerves involved — Spinal Nerves - neurotransmitter released at ganglion (preganglionic) — Acetylcholine (ACh) - neurotransmitter received at target (postganglionic) — Norepinephrine (NE) and Epinephrine (E) Parasympathetic: rest and repose, maintenance activities and conserve energy - origin at CNS — Brain Stem and Sacral Region of Spinal Cord - types of nerves involved — Pelvic and Spinal Nerves - neurotransmitter released at ganglion (preganglionic) — Acetylcholine (ACh) - neurotransmitter received at target (postganglionic) — Acetylcholine (ACh) Dual Innervation: most of the organs and tissues associated with the ANS are innervated by both the Sympathetic and Parasympathetic divisions - The divisions usually have opposing effects. - allows for a range of activity of these organs and tissues, where one division may increase the level of activity and the other division decreases it - EX: the heart, where the Sympathetic Division increases HR, and the Parasympathetic Division decreases HR Enteric Nervous System: (ENS, once considered part of the ANS) is associated with the digestive tract. Referred to as the “second brain”. - collection of neural tissue of the digestive tract - Autonomous: it does not have to receive signals from the CNS to function, but the CNS can regulate the ENS activity by increasing or decreasing it through the PNS Page 1

BSC 251 — Chapter 16 Notes : Autonomic Nervous System Sympathetic Division of The Autonomic Nervous System Sympathetic Division: (thoracolumnar) preganglionic fibers of the thoracic and lumbar and ganglionic neurons - fight or flight division, active under times of stress - also called the thoracolumbar - stimulation of this division results in increases metabolism and alertness - consists of preganglionic fibers of the thoracic and lumbar region of the spinal cord and ganglionic neurons - three different pathways - Ganglionic Neurons of the Sympathetic Division are located in the: 1. Sympathetic Chain Ganglia: paired ganglia in close proximity to the spinal cord; these neurons innervate structures in the head, body wall and limbs 2. Collateral Ganglion: innervates tissues and organs in the abdominopelvic cavity 3. Adrenal Medullae: center of the adrenal gland, releases neurotransmitters into blood The Three Pathways of The Sympathetic Division 1. Sympathetic Chain (Paravertebral or Lateral Ganglia): - Preganglionic Fibers - located in the ventral root - extend from spinal cord to chain ganglia - each ganglion of the chain innervate a segment of the body - Site of Synapse with Postganglionic Neuron — on the neurons of the chain ganglia - Neuron to Neuron Synapse - Postganglionic Fibers - has two possible pathways A) pass through the spinal nerves and innervate structures of the head, neck, and body wall - Nerve Type — Spinal Nerves - Effectors — body wall, head and neck B) that form sympathetic nerves and innervate structures of the thoracic cavity - Nerve Type — Sympathetic Nerves - Effectors — Thoracic Cavity

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BSC 251 — Chapter 16 Notes : Autonomic Nervous System 2. Collateral Ganglia (Prevertebral Ganglia): - innervates organs of the abdominopelvic cavity - Site of Synapse with Postganglionic Neuron — within the Collateral Ganglion - Effectors — Abdominopelvic Cavity - Nerve Type — Splanchnic Nerves - Effects: reduce blood flow to certain regions of the body as well as release stored energy reserves - Preganglionic Fibers - extend through the chain ganglion to form splanchnic nerves and synapse within the collateral ganglion - Neuron to Neuron synapse - innervate organs and tissues of the abdominopelvic cavity - Celiac Ganglion: innervates stomach, liver, gall bladder, pancreas, spleen - innervates structures in the upper abdominopelvic cavity - Superior Mesenteric Ganglion: innervates small intestine and proximal 2/3 of large intestine - innervates structures in the mid abdominopelvic cavity - Inferior Mesenteric Ganglion: innervates terminal portions of large intestine, kidney, urinary bladder, and sex organs - innervates structures in the lower abdominopelvic cavity 3. Adrenal Medullae (Suprarenal Medullae): - adrenal gland sits on top the kidneys - medullae refers to the center of the organ - Preganglionic Fibers - extend from the spinal cord to the adrenal glands - synapse with neuroendocrine cells****************** - enter the adrenal gland and synapse of neuroendocrine cells that release epinephrine (75-80%) and norepinephrine into the circulation (hormones) - Neuron to cell synapse - Site of Synapse with Postganglionic Neuron — Adrenal Medullae - Effectors — structures throughout the body - Nerve Type — Splanchnic Nerves

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BSC 251 — Chapter 16 Notes : Autonomic Nervous System Parasympathetic Division (Craniosacral) - rest and digest; most active during resting conditions - allows for housekeeping activities of the body - cleaning blood, maintaining the nutrient levels in the blood stream, etc. - a pathway for almost every structure innervated - Craniosacral because the Preganglionic Fibers extend from the Brainstem and the Sacral Region of the spinal cord - neurons extending from the brainstem innervate structures throughout the entire body - Preganglionic Fibers - in the brain stem (cranial nerves III, VII, IX, and X) and sacral segments of the spinal cord - ganglionic neurons located within (intramural) or adjacent (terminal) to target organs - preganglionic fibers that leave brainstem as components of the cranial nerves innervate structures of the head, thoracic cavity and abdominopelvic cavity - III (oculomotor), VII (facial), IX (glossopharyngeal) innervate structures of head - X (vagus) innervate structures of the neck, thoracic cavity and abdominopelvic cavity (75% of parasympathetic (fibers) neurons) ** - preganglionic fibers that extend from the sacral region of the spinal cord form pelvic splanchnic nerves innervate the kidneys, bladder, sex organs and large intestines 16.4 Physiology of the Autonomic Nervous System Parasympathetic and Sympathetic usually have antagonistic effects Effects of the Sympathetic Activation - increased alertness - increase heart rate and blood pressure - increase respiratory rate and dilation of respiratory pathways - increase metabolic rate - activation of sweat glands - activation of energy reserves - pupils dilate - decrease in digestive and urinary functions

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BSC 251 — Chapter 16 Notes : Autonomic Nervous System Effects of Parasympathetic activation - increased digestive gland secretion - increase motility of the digestive tract - increase blood flow to digestive tract - hormone secretion regulating nutrient uptake - defecation and urination stimulation - constriction of pupils - constriction of respiratory tract - decrease heart rate and blood pressure - decrease metabolic rate - sexual arousal and sex gland stimulation Neurotransmitters of The Sympathetic Division - Preganglionic Fibers: release Acetylcholine (ACh) at the ganglion, that effects the postganglionic neuron - Postganglionic Fibers: release primarily Norepinephrine (NE) at the synapse with the target tissue - except for the Neuroendocrine Cells of the Adrenal Medullae, they release Epinephrine as well as some Norepinephrine (NE) into the bloodstream > Effect of the neurotransmitter depends on the receptor - in some cases there is an increase in activity - in other cases, like the small intestine, the release of Norepinephrine may be an inhibitor and slow down the activity - Adrenergic (NE) Receptors: are all G proteins, membrane proteins that produce second messengers in the target cell that alter cell activity.

- Two types of Sympathetic Receptors: 1. Alpha: activate enzymes in the target cell a. α1 cause the release of Ca2+ in target cell; always excitatory b. α2 lead to the release of cAMP; usually inhibitory 2. Beta: change metabolic activity of target cell by increasing cAMP; three types Neurotransmitters of The Parasympathetic Division - Both Preganglionic and Postganglionic Fibers — release ACh (cholinergic synapse)

> Effect of the neurotransmitter depends on the type of cholinergic receptor is present - Two types of cholinergic receptors 1. Nicotinic: always excitatory; opens ion channels 2. Muscarinic: G protein; alters enzyme activity of target cell Page 5

BSC 251 — Chapter 16 Notes : Autonomic Nervous System Terms for Autonomic Activity Autonomic Tone: background level of neural activity in structures that are ONLY innervated with the Sympathetic Division (blood vessels) ; with dual innervation different division can alter the level of activity For example, parasympathetic neurons of the heart release ACh to decrease heart rate, and sympathetic neurons release norepinephrine to increase heart rate In the absence of dual innervation, background level of sympathetic tone keeps the blood vessels partially constricted. Increasing or decreasing the level of sympathetic activity will alter vessel diameter.

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