Download The Autonomic Nervous System

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Infarction, seborrhea, hyperglycemia, anastomosis, auscultation, chelation, hyperkalemia, hyponatremia, ileus
The Autonomic Nervous System
p. 420 - 437, CH. 13
Introduction (p. 420-423)
KNOW THE ANSWERS TO APPENDIX 10 – IT WILL HELP ON THE TEST
The ANS controls the function of smooth muscle tissue, glandular epithelium, and cardiac muscle. The ANS maintains
homeostasis by increasing or decreasing the activity of these various organs in response to changes in the internal and
external environment.
Organization of the ANS
Neuro Effector tissues
–
–
–
Cardiac muscle - ANS controls rate of contraction
Smooth muscle - arranged in circular layers around the walls of blood vessels, bronchioles, sphincter muscles of
the GIT and urinary tract, and in visceral organs.
• Single unit - connected by gap junctions, act as a unit
• multi unit - contract individually
Glandular epithelium - secretion is controlled by ANS
effector organs
presence of ganglia
number of neurons from CNS to
effector tissue
effect of nerve impulse
types of nerve fibers
effect of denervation (cutting nerve )
•
ANS
sm. mm, cardiac, glands
in motor side
2
versus
contraction/relaxation
secretion/ no secretion
Type B and C
Nothing or something: controls are
gone system may speed up or slow
down (Car is running, but accelerator
and brake are gone)
Somatic Nervous System
skeletal muscles
ventral horn of spinal cord
1
contraction
Type A
atrophy
Preganglionic ( in spinal cord ) versus postganglionic
Structure of the ANS
p. 429, Tables 13.3, 13.4, 13.5
The ANS is structurally divided into two divisions by the location of the origin of the preganglionic neurons.
1. Sympathetic - Thoracolumbar – Preganglionic nerve cell body in lateral horn T1-L2
2. Parasympathetic - Craniosacral – Preganglionic nerve cell body in brain stem and sacral segments S2,3,4
There are basic functional differences between the two divisions also.
1. Sympathetic Nervous System – the thoracolumbar or “Fight or Flight” system – helps prepare the body cope
with crises situation
Origin - lateral horn of the spinal cord, segments T1-L2
Connection to spinal nerves – allows for communication
• white rami (=branch) communicantes - have more myelin, connect GVE neuron from spinal nerve to the
paravertebral chain of ganglia. Found on spinal nerves T1-L2. Type B fibers.
• gray rami communicantes - have less myelin, connect paravertebral chain to the spinal nerve, where
postganglionic GVE neuron re-enters the spinal nerve for distribution to peripheral structures. Associated with
all spinal nerves. Type C fibers.
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Peripheral ganglia are a collection of neuron cell bodies outside of the CNS. Contain the axon terminus of the
preganglionic neuron, the dendrites, soma, and axon hillock of the postganglionic neuron.
Types of Sympathetic peripheral ganglia:
1. Paravertebral ganglia – sympathetic chain ganglia
These contain ascending and descending preganglionic sympathetic fibers, GVA fibers, and the cell bodies (soma) of
sympathetic postganglionic neurons. They are located parallel to the vertebral column from C1 to S3.
2. Prevertebral ganglia
are associated with major vascular branches off of the abdominal aorta.
Many preganglionic neurons that exit the spinal cord below the level of the diaphragm pass through the sympathetic
trunk without synapsing. They form the splanchnic nerves and synapse in the prevertebral ganglia.
Prevertebral Ganglia are located anteriorly to the vertebral column
A. Celiac ganglion
N300
– innervated by the greater splanchnic nerve, arises from sympathetic neurons from spinal segments T4-T9. Also
contribute to the formation of the celiac (solar) plexus. Postganglionic neurons innervate the stomach, spleen,
pancreas, liver, small intestines and kidney.
B. Superior mesenteric ganglion
– innervated by the lesser splanchnic nerve ( from the thoracic segments), postganglionic fibers innervate the
small intestines and colon.
C. Inferior mesenteric ganglion
– innervated by the lower splanchnic nerve ( from lower thoracic, upper lumbar segments ), postganglionic fibers
innervate the distal colon, rectum, urinary bladder and genital organs
•
Course of a Typical Preganglionic Neuron Fiber
GVE sympathetic
N 154
–
Myelinated axons leave the lateral horn of the spinal cord in the ventral rootlets, then form roots to continue on in
the spinal nerve. They exit the spinal n. via the white rami to enter the paravertebral chain, then 1 of 4 things
happens:
1) they synapse in the sympathetic chain ganglia at the level of entrance
} postganglionic fibers reenter spinal
2) ascend or descend the chain and synapse
} nerves via gray rami
3) pass through the chain in the thoracic portion of the trunk without synapsing, form the splanchnic nerves
4) pass through the sympathetic chain and synapse in the adrenal medulla (T10, 11) ( SPECIAL!)
–
•
•
1) and 2) re-enter the spinal nerve via the gray rami
The Adrenal Gland - suprarenal gland is located superior to the kidneys. It consists of the cortex (3 zones: Zona
glomerulosa, zona fasciculata, and zona reticularis) and the medulla (modified postganglionic neuron cell bodies,
also called Chromaphin cells). The adrenals release epinephrine ( 80%) and norepinephrine (20%) which function
as hormones and neurotransmitters in the body. They are only produced here.
Spinal origin of sympathetic preganglionic neurons and the tissues they innervate:
T1-T2 - head
T3-T4 - heart and lungs
T3-T6 - upper limbs
T4-T9 - abdominal viscera
T10-T11 - adrenal gland
T12- L2 - pelvic viscera and reproductive organs
T7-L1 - lower limbs
Effects of Sympathetic Stimulation – gets the body ready for fight or flight
1. Mydriasis
2. Increase rate and force of contraction of heart
3. Elevation of blood glucose
4. Bronchodilation
5. Increase blood flow to skeletal muscle
6. Cutaneous vasoconstriction
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7. Pilo erection
8. Diaphoresis
2. Parasympathetic nervous system is also called the craniosacral or “Rest and Digest system”
GVE
Origin - brain stem (carried in CN 3,7,9 and 10) and sacral spinal segments, S2-S4
Synapse occurs in a ganglia called terminal ganglia ( at the end of the 2 neuron chain), located close to or in the wall
of the organ innervated.
Most parasympathetic neurons do not travel in spinal nerves.
There is no parasympathetic input to sweat glands, arrector pili muscles, smooth muscle in the walls of blood
vessels of the skin or skeletal muscle – these are all sympathetic.
Parasympathetic nuclei in the brain stem (=cranial)
N111
– GVE cell column is located lateral to the GSE column in the brain stem, contain 4 nuclei which give rise to GVE
parasympathetic fibers
1. Edinger Westphall Nucleus – gives rise to the GVE fibers carried in CN III - located in the midbrain,
N 115
dorsal to the oculomotor nucleus at the level of the superior colliculus in the pretectal area,
innervates the eye ultimately
2. Superior Salivatory Nucleus – gives rise to the GVE fibers carried in CN VII - in the pons
3. Inferior Salivatory Nucleus – gives rise to the GVE fibers carried in CN IX - in the medulla at the
N 119
pontomedullary junction
4. Dorsal Motor Nucleus of the Vagus – gives rise to the GVE fibers carried in CN X - beneath the
N 120
floor of the fourth ventricle in the dorsal medulla
Sacral segments giving rise to parasympathetic GVE neurons - S2,3,4 – no rami communicantes associated with
these.
– pelvic splanchnic nerves - nervi erigentes - only splanchnic nerve which carries parasympathetic fibers,
innervates descending colon, sigmoid colon, bladder, reproductive organs, etc. ( tissues of the pelvis )
Peripheral Ganglia - Terminal Ganglia
– ciliary ganglion- CN III- to intrinsic muscles of the eye
– pterygopalatine ganglion or sphenopalatine g. - CN VII - lacrimal gland
– submandibular ganglion - CN VII - submandibular and sublingual salivary glands
– otic ganglion - CN IX - parotid salivary gland
Effects of Parasympathetic Stimulation
1. Miosis
2. Salivation
3. Increased peristalsis and GIT secretions
4. Bronchoconstriction
5. Erection ( the exception to the “rest”, ejaculation is sympathetic )
4-1-99
Enuresis – bedwetting
Pathognomonic - Characteristic or indicative of a disease
Pruritis – itching
Genu varum – bow-legged
Genu valgum – knock knees
Teleology - the doctrine that goals or end states have a causal influence on present events and that the future as well as
the past
affect the present
Alopecia, Dystocia, polycythemia, Aneurism
Functions of the ANS ( p. 429 - 433, Table 13.6) APPENDIX 7
Actions of the ANS
–
–
sympathetic nervous system - “fight or flight”, prepares the body to cope with intense physical activity
parasympathetic nervous system - “resting and digesting”, provides finite control of visceral function
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Neurotransmitters of the ANS
1. Acetylcholine (ACH) - released from all preganglionic neurons and all postganglionic parasympathetic neurons
–
–
Cholinergic - relating to nerve cells that release or receptors which respond to ACH
Cholinergic axons: all preganglionic autonomic fibers, all postganglionic parasympathetic fibers, postganglionic
sympathetic fibers which innervate eccrine sweat glands and blood vessels in skeletal muscles which produce
vasodilatation, somatic neurons to skeletal muscle (not part of the ANS).
Acetylcholinesterase - an enzyme that breaks down ACH, stopping its effects on the postsynaptic tissue.
Nerve gases ( Toban, Soman, … ) and organophosphates block ACHase
Antidote – Atropine prevents toxic effects from being manifested
2. Norepinephrine
–
–
–
–
tyrosine - DOPA  dopamine  norepinephrine  epinephrine (this last step is in the adrenal medulla)
dopamine, norepinephrine and epinephrine are called catecholamines
Adrenergic - neurons which release or receptors which respond to norepinephrine or epinephrine
Release and re-uptake of adrenergic neurotransmitters
• 80% of norepi released is re-uptaked back into the axon and broken down by MAO then remade. That which
remains in the synaptic space is broken down by COMT.
Enzymes that break down catecholamines
1. Monoamine oxidase - MAO
– intracellular on the outer surface of the mitochondria, inactivate catecholamines by oxidation, found in many
cells throughout the body including gut epithelium
2. Catechol-O-methyl transferase - COMT
– in the synaptic space - extracellular, inactivates catecholamines by methylation
Catecholamine metabolites
– 3,4 Dihydroxymandelic acid (DOMA) is broken down into 3 methoxy 4 hydroxymandelic acid vanillylmandelic acid (VMA) - excreted in the urine at a rate of 770ug/day
Aminita muscarina – a mushroom that kills flies ( musca = fly)
Autonomic Receptors
Cholinergic receptors
•
•
Muscarinic receptors - located on neuroeffector tissues innervated by autonomic postganglionic cholinergic fibers
(smooth muscle, cardiac muscle, glands)
Nicotinic receptors - located on the postganglionic neurons located in the autonomic ganglia and on skeletal muscle
motor end plate (NOT a part of the ANS)  that explains the sympathetic and parasympathetic response to nicotine.
Adrenergic receptors
1. alpha
 alpha 1 - on blood vessels – vasoconstriction – smooth muscle contraction, pupils of eye
 alpha 2 – presynaptic( on the axon) – autoinhibitory – negative feedback for NE
2. beta
APPENDIX 9
 beta 1 - excitatory to the heart, + chronotrope ( affects HR) and + inotrope ( force of contraction); release Renin;
relax smooth muscle in the gut
 beta 2 - relax smooth muscle, bronchodilate the lungs
Organs with Dual Innervation
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•
many organs receive dual innervation from the sympathetic and the parasympathetic divisions of the ANS.
1. Antagonistic effects, i.e.. heart, pupil of the eye, intestinal motility.
2. Complementary effects - salivary secretions - parasympathetic stimulation produces watery secretions whereas
sympathetic stimulation decreases blood flow and results in prod. of thick viscous secretions.
3. Cooperative effects - urinary and reproductive systems. Erection is parasympathetic and ejaculation is
sympathetic, urinary bladder contraction is enhanced by parasympathetic, sphincter is sympathetic
Organs without Dual Innervation
3. adrenal medulla - sympathetic only ( LAB)
4. arrector pili muscles - sympathetic only
5. sweat glands - sympathetic only
6. most blood vessels - mostly sympathetic
7. control is achieved by increasing or decreasing the tone (firing rate) of the sympathetic neurons.
The ANS can be controlled by the cerebrum/cortex
Control of the ANS by Higher Brain Centers
8. Medulla oblongata – respiratory and cardiac control centers
9. Hypothalamus – overall control and integration for the pituitary
10. Limbic System
–
a group of fiber tracts which form a ring around the brain stem. Several nuclei. Houses the centers for primordial
instincts: hunger, thirst, anger, fear, sex drive.
You can be so angry that you are totally controlled by the limbic system. BUT: you can still choose to take cerebral
control!
Marie Paas
59
Anatomy Tri1
06/29/17