9.13.11+-+Autonomic+Nervous+System

=Autonomic Nervous System=


 * 1) Define the Following terms and describe their function**
 * **adrenergic fiber** - a neuron for which the neurotransmitter is either adrenaline (epinephrine), noradranaline or dopamine. Includes 95% of sympathetic postganglionic fibers.
 * **Cardiac Plexus** - Plexus of nerves situated at the base of the heart that innervate the heard. Divided into superficial arch (in the concavity of the aortic arch) and deep part (between aortic arch and trachea).
 * **Dorsal Root Ganglion** - A nodule on the dorsal root containing cell bodies of neurons in afferent spinal nerves. Composed of pseudounipolar neuronal bodies. Develops from neural crest cells not neural tube.
 * **Parasympathetic division** - One of two main divisions of the autonomic nervous system (ANS). ANS is responsible for regulation of internal organs and glands, which occur unconsciously. The parasympathetic system is responsible for "rest-and-digest" activities, as opposed to the sympathetic nervous system, which is responsible for "fight-or-flight" activities. Physically, the preganglionic neurons are located in the brain stem (CN III, CN XII, CN IX and CN X) and the sacrum (S2, S3 and S4) and the ganglionic neurons are in hundreds of ganglia that are located within the wall of the innervated organ.
 * **Pilae erector muscles** - tiny smooth muscles in the dermis which cause body hairs to stand erect. Innervated by autonomic efferent fibers
 * **Preganglionic Nerve Fibers -** In the Autonomic Nervous System, there are 2 neurons involved, one in CNS (preganglionic) and one in a ganglion in the periphery somewhere (ganglionic). Both these neurons are multipolar. For Sympathetic Nervous System, preganglionic nerve fibers are located within the intermediolateral cell column from T1 to L2. For Parasympathetic Nervous System, preganglionic fibers are located within the brain stem or the sacral spinal cord. There are NO pre-ganglionic neurons in cervical spinal or the lower lumbar spinal cord.
 * **Pulmonary Plexus** - Autonomic Plexus formed from pulmonary branches of vagus nerve and the sympathetic trunk. Supplies bronchial tree and visceral pleura
 * **Somatic Efferents** - Motor neuron cell bodies are located in the ventral horns of the gray matter in the spinal cord, exit through the ventral roots and carry motor impulses to the skeletal muscle.
 * **Sympathetic Chain** - The set of ganglionic neurons in the Sympathetic Division of the ANS. ganglia located lateral to the vertebral bodies of the vertebral column. Approximately 24 pairs, typically 3 cervical, 12 thoracic, 5 lumbar and 4 sacral or coccygeal ganglia.
 * **Sympathetic Trunk -** Axons from pre-ganglionic neurons which accompany the sympathetic chain.
 * **Visceral Efferents** - Two neurons involved in efferent portion of autonomic nervous system. One in the CNS (pre-ganglionic) and one in a ganglion in the periphery somewhere (ganglionic). Neurons are multipolar. For the Sympathetic Division, the pre-ganglionic neuron cell bodies are in the intermediolateral cell column from T1-L2. For the Parasympathetic Division, the preganglionic neuron cell bodies are in the brain stem or in the intermediolateral cell column from the Sacral spinal cord. Autonomic ganglia are divided into sympathetic, parasympathetic and enteric catagories. These ganglia are sites of synapses between pre-ganglionic fibers and ganglionic neurons. All autonomic ganglia are efferent in function and have NO intrinsic sensory function
 * **Autonomic nervous system** - Visceral Nervous System contains sensory and efferent components. Visceral Efferent components are referred to as the Autonomic Nervous System (ANS). The ANS controls involuntary activities of glandular epithelia, smooth muscle or cardiac muscles. Divided into Sympathetic Division (fight-or-flight), Parasympathetic Division (rest-or-digest) and Enteric Division (gastrointestinal system).
 * **Cholinergic Fiber** - Any synaptic terminals releasing acetylcholine as their neurotransmitter. Includes sympathetic and parasympathetic preganglionic fibers, the ~5% of sympathetic postganglionic fibers which innervate sweat glands in the skin and postganglionic parasympathetic fibers.
 * **Intramural ganglion -** The nerve cell bodies that make up the parasympathetic division of the ANS. Nerve cell bodies can be located in hundreds of ganglia within the wall of the organ being innervated (intramural ganglia) or nearby the walls of the organ (terminal ganglia).
 * **Sympathetic Nervous System -** One of two main divisions of the Autonomic Nervous System. The SNS is the portion of the autonomic nervous system associated with "fight-or-flight". Physically the preganglionic nerve cell bodies are located in the intermediolateral gray columb of the spinal cord from T1 - L2. Ganglionic neurons can be in either paravertebral (~24 pairs of ganglia lateral to vertebral bodies in "sympathetic chain") or prevertebral ganglia (small sympathetic ganglia anterior to abdominal aorta which innervate smooth muscle in the abdomen, adrenal medulla gland and blood vessels in the abdomen).
 * **Paravertebral sympathetic ganglion** - Set of 24 pairs of ganglia located lateral to the vertebral bodies of the vertebral column. Full set referred to as the "sympathetic chain"**.** Except for neck, correspond closely to number of vertebrae (3 cervical, 12 thoracic, 5 lumbar, 4 sacral)
 * **Postganglionic fiber** - One of two types of nerves associated with the Parasympathetic Nervous System. As their ganglia are located either in the wall of their organ or very nearby, these are short and difficult to see.
 * **Prevertebral sympathetic ganglion -** One of two types of ganglionic neurons of sympathetic division, located anterior to abdominal aorta at junction with large blood vessels. Responsible for innervating smooth muscle structures in the abdomen (celiac ganglion, aorticorenal ganglia, super mesenteric ganglion, inferior mesenteric ganglion and diffuse sets of very small ganglia making up superior and inferior hypogastric plexi).
 * **Somatic Afferents** - Single neuron involved, cell body is pseudounipolar and located in dorsal root ganglia
 * **Splanchnic Nerves (greater, lesser, least)** - Splanchnic Nerves (of the thorax) carry preganglionic sympathetic fibers into the spinal cord, pass through thoracic sympathetic ganglia without making synapses and ultimately make synaptic contact with prevertebral ganglia of the abdomen. Includes Greater Splanchnic Nerve (T5-T9), Lesser Splanchnic Nerve (T10 and T11) and Least Splanchnic Nerve (T12).
 * **Terminal Ganglia** - Parasympathetic nerve cell bodies located nearby the walls of organs
 * **Visceral Sensory Afferents** - Single neuron involved in sensory portion of Visceral Nervous System. Cell body is pseudounipolar and located within a dorsal root ganglion. Can sense pain or distension only and is both poorly localized and very unpleasant. Can be conscious (full bladder) or unconscious (such as organs in blood vessels regulating blood pressure).
 * **White Rami Communicantes** - Myelinated nerves in the Sympathetic Nervous System which connect spinal nerves with sympathetic ganglia. Since they carry pre-ganglionic axons, they are only associated with T1-L2 spinal nerves.
 * **Grey Rami Communicantes** - Unmyelinated nerves connecting sympathetic ganglia with spinal nerves. Since they carry post-ganglionic axons, they are associated with all spinal nerves (C1-Co1). In general, grey rami carries post-ganglionic nerve fibers to the anterior and posterior rami of spinal nerves to innervate structures in the skin. Carry away from the ganglia

Somatic NS controls voluntary movements. Somatic NS has efferent innervation to skeletal muscle. One neuron is involved. Cell body is multipolar and located in the ventral horn grey matter. Somatic NS has afferent innervation to the 5 somatic tissues: skin (except blood vessels and other smooth muscle), skeletal muscle, bone (periosteum), joints and dura mater. Cell body is pseudounipolar and located in Dorsal Root Ganglia. Localized type of pain, often "burning" quality. Visceral Nervous System controls involuntary activities of glandular epithelia, smooth muscle or cardiac muscle. Visceral NS afferent nerves involve only one pseudounipolar neuron located in a dorsal root ganglion (or equivalent in vagus nerve) and can sense pain or distension only. Poorly localized and very unpleasant. Can be conscious or unconscious. Visceral NS efferent nerves (called Autonomic Nervous System [ANS]) has TWO neurons involved - one in CNS ("pre-ganglionic") and one in a ganglion in periphery ("ganglionic"). Both are multipolar. Divided into 3 systems - Sympathetic, Parasympathetic and Entric.
 * 2) Compare and Contrast the anatomical and functional differences between the somatic and autonomic nervous systems, and contrast the types of tissue innervated by each.**

Sympathetic, Parasympathetic and Entric. Parasympathetic and sympathetic fibers connect the central nervous system directly with the digestive tract. Through these cross connections, the gut can provide sensory information to the CNS, and the CNS can affect gastrointestinal function. Connection to the central nervous system also means that signals from outside of the digestive system can be relayed to the digestive system: for instance, the sight of appealing food stimulates secretion in the stomach.
 * 3) Name the 3 major divisions of the autonomic nervous system.**
 * Explain how the sympathetic and parasympathetic divisions of the autonomic nervous system affect the enteric nervous system.**

Sympathetic nerves contain pre-ganglionic cell bodies in the intermediolateral gray column of the spinal cord from T1-L2. Parasympathetic nerves contain pre-ganglionic cell bodies in the brain stem ("cranial parasympathetic outflow") and the intermediolateral gray column of spinal cord from S2, S3 and S4 ("sacral parasympathetic outflow").
 * 4) Name the 3 regions of the CNS containing pre-ganglionic neuron cell bodies. Identify which of these regions contain sympathetic pre-ganglionic neurons and which contain parasympathetic pre-ganglion neurons.**

All preganglionic neuron cell bodies travel from the ventral root, to the spinal nerve, then to the white rami communicantes and into the sympathetic ganglia. From here, neuron cell bodies split to innervate different parts of the body:
 * 5) Describe the Pathways taken by pre-ganglionic and postganglionic fibers of the sympathetic division of the autonomic nervous system as they innervate the following structures**

Preganglionic neurons can ascend, descend or exit from the sympathetic ganglia at it's current level. Before it leaves the sympathetic ganglia it makes synaptic contact with a postganglionic neuron which exits out via the grey ramus communicantes and the ventral/dorsal rami depending on the target area.
 * Smooth muscle of hair follicles, blood vessels and sweat glands of trunk and limbs**

Preganglionic neurons can either ascend or synapse in the sympathetic ganglia with the cardiopulmonary splanchnic, part of the cardiopulmonary plexus.
 * Smooth muscle, cardiac muscle and lungs of the thorax**

Preganglionic neurons typically enter the sympathetic ganglia and exit via the thoracic splanchnic nerves. They synapse with prevertebral ganglia which then go to their ultimate destination.
 * Smooth muscle of the abdomen**

Preganglionic neurons typically descend from their level of entry via the sympathetic ganglia. They make synaptic contact with postganglionic neurons at the level of their exit. Postganglionic neurons exit out of the sympathetic ganglia via the grey ramus communicantes and exit via vental/dorsal rami to their destinations.
 * Smooth muscle of the pelvis**

Prevertebral exist anterior to the abdominal aorta at its junction with the large blood vessels of the abdomen. They include: Celiac ganglion- near the celiac trunk (around the level of T8) Aorticorenal ganglia- near the renal arteries (around the level of T9) Superior mesenteric ganglion- near the superior mesenteric artery (around the level of T12) Inferior mesenteric ganglion- near the inferior mesenteric artery (around the level of L2) Superior/inferior hypogastric plexi- diffuse (around the level of S1-4)
 * 6) Name the prevertebral sympathetic ganglia, and describe their anatomical locations**

White rami communicantes are myelinated nerves that connect spinal nerves with sympathetic ganglia (preganglionic axons). Associated with T1-L2 spinal nerves. Gray rami communicantes are unmyelinated nerves connecting sympathetic ganglia with spinal nerves (postganglionic). Associated with all spinal nerves (C1-Co1). Typically innervate structures in the skin through ventral and dorsal rami.
 * 7) Describe the white and gray rami communicantes. Name the type of fibers that form each ramus. Name the spinal cord levels associated with white rami communicantes and gray rami communicantes. Explain the difference between the two**

Preganglionic neurons begin in the brain stem or from the intermediolateral gray column of the spinal cord from S2-4 and follow the ventral roots and join with other sets of nerves (ex: neurons from S2-4 will follow ventral roots to the pelvic splanchnic nerves then meet up with the sacral splanchnic nerves before joining the inferior hypogastric plexus). The preganglionic neuron will eventually meet up with the postganglionic neuron in the wall of the organ it is innervating.
 * 8) Describe the pathways taken by preganglionic and postganglionic fibers of the parasympathetic division of the autonomic nervous system from the CNS to the parasympathetic ganglion to the effector organ**

The preganglionic neuron will exit out of the intermediolateral column through the ventral root and travel along the spinal nerve through the white rami communicantes and into the sympathetic ganglion. From here, it will travel along the thoracic splanchnic nerves until it reaches the prevertebral ganglia. Depending on its final destination it will travel along one of three routes: - Neurons from T5-9 will travel along the greater splanchnic nerve to the celiac ganglion - Neurons from T10-11 will travel along the lesser splanchnic nerve to one of the other prevertebral ganglia - Neurons from T12 will travel along the least splanchnic nerve to the other prevertebral ganglia
 * 9) Describe the source of preganglionic parasympathetic axons that innervate the thoracic viscera, abdominal viscera and pelvic viscera.**

Sympathetic- increases strength and rate of heart beat Parasympathetic- inhibits cardiac muscle contraction to reduce heart rate
 * 10) Describe the effects of sympathetic nervous system and parasympathetic nervous system activation on the following structures**
 * Heart**

Sympathetic- decreases blood flow, diverting more blood to skeletal muscles Parasympathetic- None
 * Blood Vessels**

Sympathetic- inhibits smooth muscle contraction in walls, dilates airway Parasympathetic- constricts smooth muscles, increases lung secretions
 * Bronchi**

Sympathetic- stimulates smooth muscle, decreases blood flow, diverting more blood to skeletal muscles Parasympathetic- stimulation of smooth muscles, increases motility
 * Gut**

Sympathetic- constricts sphincter and relaxes bladder Parasympathetic- tenses bladder and relaxes sphincter to release urine
 * Urinary Bladder**

Sympathetic- stimulates secretion and release of epinephrine Parasympathetic- None
 * Adrenal Medulla**

Sympathetic- stimulation of smooth muscle, initiates ejaculation and orgasm Parasympathetic- increases blood supply
 * Erectile Tissue**

The sympathetic nervous system stimulates sweat glands of the skin and dilates airway to to help decrease body temperature.
 * 11) Explain how sympathetic nervous system participates in body thermoregulation**