Autonomic_nervous_system_DSA.txt

Responsible for the integrative functions of the nervous system

• Brain and spinal cord (CNS)
• * responsible for integrative functions of the nervous system
• * composed solely of blood vessels and nervous tissue

• Brain
• 1) cell bodies (gray matter) outside, the myelinated axons (white matter) inside
• 2) interprets info> make decisions on info>and responds with info that is shipped down the spinal cord and back out to the periphery
• 3)Forms motor responses to the information that reaches the brain, the brain also uses the information to perform our most complicated human functions:
• *intellect
• * emotion
• * behavior
• * memory
• * learning, etc.

• The spinal cord
• 1)cell bodies (gray matter) inside, the myelinated axons (white matter) outside
• 2)highway for information from the brain to the periphery
• 3)performs basic integrative functions such as reflexes.

• *Very long-can run from the spinal cord to the big toe, or very short, staying within a spinal cord segment.
• *Only the axon is capable of transmitting a signal to another neuron or to a cell of an effector organ through its neurotransmitter.
• *axon terminals usually end on other neurons, most commonly on the dendrites of another neuron, but also on the cell body and rarely on an axon

. This complexity gives us the ability to do everything from walk, to feel emotion, to learn, to constrict blood vessels, make us breathe and all of the other things that make us huma

• *myelinated-Neurons or processes with myelin sheaths
• *unmyelinated-Neurons have processes with cellular sheath but lack myelin

*vast majority of axons are myelinated and accumulations of them appear whitish.

* Cell bodies never have myelin and accumulations of them have a grayish appearance.

Signals that travel along axons are essentially electrical and consequently processes and neurons have to be insulated from one another like electrical wires. This is accomplished by supporting cells that encapsulate the neurons (except at synapses and axon terminals) or form sheaths around the processes. The sheath cells around some processes produce a lipid and protein material that is whitish in appearance called myelin. The myelin insulates the processes and greatly increases the speed of signal transmission.

• 1)cell body with nucleus and organelles to provide for general metabolism and cellular maintenance
• 2)dendrites(one to many)- receive signals some of which have special endings,for specific types of stimuli, such as pressure or temperature. Other dendrites may receive signals from other neurons.
• 3)axons(one process)-transmit signals, one to several terminal endings that release neurotransmitters.
• 4)synapse-the contact point between the neurons.
• 5)The nervous system is composed of billions of neurons that make billions of connections

"business cell in the nervous system"-passes messages from one part of the body to another

*Connects the central nervous system (CNS) to the limbs and organs.

"A system of sensory and motor nerve cell bodies and their respective processes which connect the central nervous system with peripheral structures through the incorporation of twelve cranial nerves and thirty-one pairs of spinal nerves."

• Composed of:
• *nerves and ganglia outside of the brain and the spinal cord
• *not protected by bone of spine /skull, or by the blood-brain barrier, leaving it exposed to toxins and mechanical injuries

• Classified:
• By direction
• There are two types of neurons, carrying nerve impulses in different directions. These two groups of neurons are:

• *sensory neurons(afferent neurons) to CNS
• *motor neurons (efferent neurons) Away from CNS
• By function
• The peripheral nervous system is functionally as well as structurally divided into
• *somatic nervous system
• *autonomic nervous system

• Definition: That portion of the CNS and PNS that is
• responsible for unconscious control of visceral function, i.e. heart rate, respiratory rate, vascular diameter, gut motility, pupillary diameter, sexual preparedness, etc. This is accomplished through the direct innervation of cardiac muscle fibers, the smooth muscle fibers of bronchioles, arterioles and hollow organs (viscous) and the sudomotor cells (secretory) of glands.

2. Divisions

a. Parasympathetic division (‘craniosacral’; cranial: motor nuclei of cranial nerves III, VII, IX, X and sacral: lateral horn *(I.M.L.C.C.) of spinal cord levels S2,3,4): Responsible for constant control of visceral function (vegetative state) i.e., decreased heart rate, decreased rate and depth of respiration, increased gut motility, shunting of blood toward the gut away from skeletal muscle, etc.

b. Sympathetic division (thoracolumbar: *(I.M.L.C.C.) lateral horn of spinal cord levels T1-L2): Responsible for control of visceral reaction in response to immediate stress (fight or flight), i.e. increased heart rate, increased rate and depth of respiration, decreased gut motility, shunting of blood from gut to skeletal muscle, etc.

• NOTE: Although the A.N.S. is classically described as a motor system (GVE),
• visceral afferents (GVA) parallel the course of the sympathetic subdivision, while
• visceral afferents can be found within branches of CNs VII, IX & X. In general,
• afferents paralleling sympathetic fibers carry visceral pain, while the para-
• sympathetic afferents (mostly vagal) are responsible for the modality of distention
• (feeling of fullness).

• a. White matter ‑ composed of ascending and descending fiber tracts grouped in funiculi (fiber bundles), composed of smaller fasiculi
• b. Gray matter ‑ seat of neurons (cell bodies) within the spinal cord

Lateral horn (INTERMEDIOLATERAL CELL COLUMN - I.M.L.C.C.) ‑ contains autonomic pre‑ganglionic neurons that: *innervate smooth muscle c

• Ventral horn ‑ contains neurons whose fibers:
• *innervate skeletal muscle

• a) Dorsal horn ‑
• 1)composed of neurons that give rise to fibers that:
• * complete simple reflex arcs
• * decussate (cross to the opposite side) or
• * ascend to other sensory substations in the C.N.S.

Ventral Root ‑ for the most part transmits efferent (motor) fibers to somatic and visceral structures

Dorsal Root ‑ for the most part, transmits afferent (sensory) fibers of somatic and visceral origins

NOTE: A ganglion (collection of cell bodies outside the CNS) exists on the dorsal root, which contains the cell bodies of ALL the afferent (sensory) fibers, except for vagal afferents, below the level of the head.

• a)31 pairs of spinal nerves exist:
• 8 cervical,
• 12 thoracic,
• 5 lumbar,
• 5 sacral
• 1 coccygeal

b)The first spinal nerve exits between the skull and CV1; all others exit inter- vertebral foramina and, except for in the cervical region, are numbered in reference to the vertebra from which they exit beneath.

Spinal (segmental) Nerves (Figs. 2, 3, 4)

Definition: a mixed nerve (motor and sensory) formed at the junction of a dorsal and a ventral root.

• From Wiki:
• The Ventral rami, including the sinuvertebral nerve branches, supply structures anterior to the facet joint, including the vertebral bodies, the discs and their ligaments, and joins other spinal nerves to form the lumbo-sacral plexus.

Because each spinal nerve carries both sensory and motor information.

• Shortly after a spinal nerve exits the intervertebral foramen, it branches into the
• dorsal ramus >ventral ramus>rami communicantes

Each of these latter three structures carries both sensory and motor information.

The posterior (or dorsal) branches (or divisions) of the spinal nerves are as a rule smaller than the anterior divisions. They are also referred to as the dorsal rami.

*remain distinct from each other

• *each innervates a narrow strip of skin and muscle along the back, more or less at the level from which the ramus leaves the spinal nerve,except (C1,S4,5,Coccygeal)
• * carry visceral motor, somatic motor, and sensory

• dorsal branch of a spinal nerve containing fibers of all types (sensory, motor, somatic, visceral) which innervate cutaneous and subcutaneous areas of the dorsal surface of:
• 1)head
• 2) neck
• 3)trunk
• 4)deep back muscles
• 5) joints of the spine

A nerve plexus is a network of intersecting nerves. They combine sets of spinal nerves that serve the same area of the body into one large grouped nerve.

• 1)Cervical plexus - serves the head, neck and shoulders
• 2)Brachial plexus - serves the chest, shoulders, arms and hands
• 3)Lumbar plexus - serves the back, abdomen, groin, thighs, knees, and calves
• 4)Sacral plexus - serves the pelvis, buttocks, genitals, thighs, calves, and feet

*Lumbosacral plexus-Lumbar and Sacral plexus are interconnected and sometimes identified as one.

• 5)Solar plexus - serves internal organs
• 6)Coccygeal plexus - Same as Solar Plexus

*intercostal nerves that give the chest and parts of the abdominal wall efferent (motor) innervation and the pleura and peritoneum afferent innervation[1] are the only ones that do not originate from a plexus.

• ventral branch of a spinal nerve containing fibers of all types which innervate the limbs and ventral torso
• *form all somatic nerve plexuses of the body, i.e., cervical, brachial, and lumbosacral.

autonomic fibers, which innervate smooth muscle, cardiac muscle and glands

‑ fibers, which innervate skeletal muscle

‑ fibers, which carry information (distension, some pain) from internal structures (interoceptive)

‑ fibers, which carry information from skeletal muscles, tendons and joint capsules (proprioceptive) and from the outside of the body concerning pain, touch, and temperature (exteroceptive).

Fibers (functional components) found within spinal nerves (Refer to Fig.1)

• a. General Somatic Afferent
• b. General Visceral Afferent
• c. General Somatic Efferent
• d. General Visceral Efferent

The term "myotome" is used to describe the muscles served by a single nerve root. It is the motor equivalent of a dermatome.

• Extra info:
• In vertebrate embryonic development, a myotome is a group of tissues formed from somites that develop into the body wall muscle.

• Each myotome divides into a dorsal epaxial part and a ventral hypaxial part.
• The myoblasts from the hypaxial division form the muscles of the thoracic and anterior abdominal walls.

• Each muscle in the body is supplied by a particular level or segment of the spinal cord and by its correspoding spinal nerve. The muscle and its nerve make up a myotome.[2]
• The epaxial muscle mass loses its segmental character to form the extensor muscles of the neck and trunk of mammals

• If a spinal nerve is severed, it cannot ablate an entire dermatome or paralyze an entire muscle. Since most muscles are derived from components of several myotomes each muscle is innervated by 2, 3 or 4 ventral roots (one for each myotome represented).
• Likewise, considerable overlap in the innervation of dermatomes exists, such that fibers of up to 3 or 4 dorsal roots supply each dermatome

Any of the plexuses of nerves in relation to blood vessels and viscera, whose component fibers are sympathetic, parasympathetic, and sensory

a collection of neuron cell bodies is called a nucleus, CNS

(plural: ganglia). a collection of neuron cell bodies is called a ganglion

*basal ganglia in the brain is exception. Indeed, the basal ganglia technically should be called the basal nuclei, but they were named prior to the terms being defined and the name has stuck.

• 1)Cervical plexus - serves the head, neck and shoulders
• 2)Brachial plexus - serves the chest, shoulders, arms and hands
• 3)Lumbar plexus - serves the back, abdomen, groin, thighs, knees, and calves
• 4)Sacral plexus - serves the pelvis, buttocks, genitals, thighs, calves, and feet
• *Lumbosacral plexus-Lumbar and Sacral plexus are interconnected and sometimes identified as one.
• 5)Solar plexus - serves internal organs
• 6)Coccygeal plexus - Same as Solar Plexus

*intercostal nerves that give the chest and parts of the abdominal wall efferent (motor) innervation and the pleura and peritoneum afferent innervation[1] are the only ones that do not originate from a plexus

*exists on the dorsal root, which contains the cell bodies of ALL the afferent (sensory) fibers, except for vagal afferents, below the level of the head.

In a nutshell, referred pain happens when nerve fibers from regions of high sensory input (such as the skin) and nerve fibers from regions of normally low sensory input (such as the internal organs) happen to converge on the same levels of the spinal cord.

The best known example is pain experienced during a heart attack. Nerves from damaged heart tissue convey pain signals to spinal cord levels T1-T4 on the left side, which happen to be the same levels that receive sensation from the left side of the chest and part of the left arm. The brain isn't used to receiving such strong signals from the heart, so it interprets them as pain in the chest and left arm.

The diaphragm is innervated by two phrenic nerves (left and right), which emerge from spinal cord levels C3, C4, and C5 (medical students remember these spinal cord levels using the mnemonic, "C3, 4, 5 keeps the diaphragm alive"). The phrenic nerves carry both motor and sensory impulses, so they make the diaphragm move and they convey sensation from the diaphragm to the central nervous system.Most of the time there isn't any sensation to convey from the diaphragm, at least at the conscious level. But if a nearby organ gets sick, it may irritate the diaphragm, and the sensory fibers of one of the phrenic nerves are flooded with pain signals that travel to the spinal cord (at C3-C5). It turns out that C3 and C4 don't just keep the diaphragm alive; neurons at these two spinal cord levels also receive sensation from the shoulders (via the supraclavicular nerves). So when pain neurons at C3 and C4 sound the alarm, the brain assumes (quite reasonably) that the shoulder is to blame. Usually that's a good assumption, but sometimes it's wrong.

"localized visceral stimuli producing patterns of reflex response in segmentally related somatic structures"

• Visceral afferent fibers entering the spinal cord synapse not only on ascending tract neurons, but also on interneurons that synapse on cells of the lateral and ventral horns. These interneurons therefore, have the ability to stimulate contraction of vascular smooth muscle (preganglionic sympathetic stimulation) as well as contraction of paraspinal musculature (ventral motor horn cell stimulation).
• b. Recall that increased firing of visceral afferents due to underlying visceral disease results in increased firing of ascending tract neurons resulting in referred pain. Increased firing of visceral afferents also results in an excess of neurotransmitter substances being available to stimulate the aforementioned interneurons. These interneurons become irritable, their threshold decreases, thereby increasing their excitability and firing rate.

a segment of spinal cord that has facilitated somatic changes due to visceral input. The importance of these to osteopathic manipulative medicine is such that areas of somatic dysfunction(those that display the effects of viscerosomatic reflexes)can lead to the identification and localization of visceral disease.

• Specific osteopathic manipulation applied to areas of somatic dysfunction, through stimulation of somatic afferent fibers and spinal interneurons, can help to ‘tone’ down the effects of visceral afferents stimulated by the underlying disease process.
• Identification of facilitated segments can lead to the identification and localization of visceral disease.