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Autonomic Nervous System

ANS Definition
respon­sible for contro­llling bodily functions that are largely involu­ntary, or automatic, in a nature.
What functions ANS do

Autonomic Nervous System

Functions of ANS
Control of BP, and other CVS functions, digestion, elimin­ation, and thermo­reg­ula­tion.
Anatomy of the ANS:
* Two areas: Sympat­hetic and Parasy­mpa­thetic
Parasy­mpa­thetic or Cranio­sacral
Composed of neurons origin­ating in the midbrain, brainstem, and sacral region of the spinal cord.
Enteric nervous system
Third ANS division -Comprised of GI tract that controls various aspects of GI function. IT has both Sypathetic and parasy­mpa­thetic compon­ents.
Sympat­hetic nervous system
thorac­olu­mbar- Arises from thoracic and upper lumbar regions of the spinal cord.

Sympat­hetic organi­zation

Pregan­glionic Fibres
Short-­mye­lin­ate­d-type B
Postga­ngl­ionic fibres
Long-u­nmy­eli­nat­ed-type C
PreGan­glionic
Arise from:I­nte­rme­dio­lateral gray columns of the thoracis and upper lumbar spinal cord , Leave Spinal Cord: via ventral root of the spinal nerve, End in: sympat­hetic ganglion
Sympat­hetic ganglia
Located in three areas:­1)Chain gangli­a/P­ara­ver­tebral: both side of vertebral Column 2) Unpaired prever­tebral ganglia: anterior to aorta 3) Terminal ganglia: in the tissue that is innervated - bladder and rectum
Ratio of pregan­glionic to post ganglionic fibres
1:15 to 1:20
Route of Sympat­hetic
PreGan­gli­oninc Fibre-­ari­se-end in sympat­hetic gangli­a-meet post ganglion or more ganglion - leaves to the effector tissue that it supplies (heart, sweat gland etc)

Parasy­mpa­thetic Organi­zation

Pregan­glion
Origin: Midbra­in-­bra­instem (cranial portion) or Sacrall region of Spinal cord
Cranial Portion
Exit: CNS via cranial nerves- 3,7,9,10
Vagus nerve - cranial nerve 10
comprises of 75% of the efferent component of entire parasy­mpa­thetic division
 

Function of Sympat­hetic and Parasy­mpa­thetic

Organ innervated by both systems
physio­logical antagonism typically exists between these two divisions - both divisions innervate the tissue, one division increases function and the other decreases activity.
Function
Sympat­hetic: to mobilize body energy and Parasy­mpa­thetic: tends to conserve and store the energy.
Sympat­hetic Discharge
Cause: increased cardiac output, decreased visceral blood flow(leave more blood available for skeletal muscle), increased cellular metabo­lism, several other physio­logical changes that facilitate vigorous activity.
Parasy­mpa­thetic Discharge
opposite effect. Slows down heart rate, bring changes that encourage inacti­vity. Increase intestinal digestion, absorp­tion, an activity thta stores energy for future needs.

Adrenal Medula

Function
Synthe­sizes and secretes (20%)n­ore­pin­ephrine and (80%) epinep­hrine directly into blood stream.
Epinep­hrine (EPI)
Increases Cardiac function and cellular metabolism Because higher affinity for certain receptors: Epi more readily binds to beta subtype of adrenergic receptors.
Where they release
In stress situation: Release directly into blood stream to reach everywhere

Autonomic Integr­ation and Control

Autonomic reflexes
Homeos­tatic control of BP, Thermo­reg­ula­tion, GI function
Reflexes are based on strategies
Peripheral sensor- Monitors the change in a particular syste- inforation goes to CNS- integr­ation of inform­ation- adjustment is made in the autonomic discharge in specific tissu/­organ- alter activity to return physio­logical function back to normal level
Baro receptors location
neck and large arteries of thorax
Thermo receptors location
skin, viscera, hypoth­alamus
Hypoth­alamus function
Controll of - body temper­ature, water balance, energy metabolism
Higher involv­ement of the ANS
cortex, limbic system, brainstem
 

Neurot­ran­smi­tters

Acetyl­choline (Ach) and Norepi­nep­hrine (NorEpi)
Important Neurot­ran­smi­tters of ANS
Ach
Synapse 1: Between Pre-post ganglionic neuron­s-S­ymp­ath­eti­cdi­vision
Ach
Synapse 2: Synapse 1: Between Pre-post ganglionic neuron­s-P­ara­Sym­pat­het­icd­ivision
Ach
Synapse 4: Parasy­mpa­the­tic­-Po­stg­ang­lionic - Effector cell synapse
NorEpi
Synapse 3: Sympat­hetic postga­ngl­ionic neuron - effector cell
Cholin­ergic Neurons
Pregan­glionic and Parasy­mpa­thetic postga­ngl­ionic neurons - because Ach
Adrenergic Neurons
Most sympat­hetic postga­ngl­ionic neurons
Exception
Some sympat­hetic post ganglionic use -Ach, as neurot­ran­smi­tter. - innervate in sweat glands and certain blood vessels in face, neck, and lower extrem­ities.

Other Neurot­ran­smi­tters / Contra­tra­nsm­itters

Purinergic substances
Adenosine and Adinosine Tripho­sphate : possible transm­ission in the GI tract, CVS, other organs
Peptides
Neurop­eptide Y, Vasoactive intestinal polype­ptide, Calcitonin gene related peptide, orexin, cholec­yst­okinin, and angios­tenin II, --- Control of the organs and systems
Nitric Oxide
to regulate peripheral autonomic responses and CNS autonomic activity.

Autonomic Receptors

Cholin­ergic
Located at : acytyl­choline synapses,
Adrenergic
Located at: norepi­nep­hrine synapses
ACH---> Cholin­ergic Receptor ---> 1) Muscurinic 2) Nicotinic

Norepi­nep­hrine NE---> Adrenergic Receptor ---> 1)Alpha -> alpha1, alpha2 and, 2) Beta -> beta-1­,beta-2

Cholin­ergic receptors

Nicotinic
Located: Junction between pregan­glionic and postga­ngl­ionic neurons in both sympat­hetic and parasy­mpa­thetic pathways
Nicotinic
Effects: both divisions of ANS
Type 1 Nicotinic
Means: Located at ANS (Nn)
Type 2 Nicotinic
Means: Located at skeletal neuron­mus­cular junction (Nm)
Muscurinic
Located: all of the synapses between cholin­ergic postga­ngl­ionic neurons and the terminal effector cell, including all the parasy­mpa­thetic terminal synapses and the sympat­hetic postga­ngl­ionic cholin­ergic fibers that supply sweat glands and some specia­lized blood vessels.
Subtypes of Muscurinic
M1, M2, M3, M4, M5 : Based on their charac­ter­istics (chemical and struct­ural)
M1, M4, M5
CNS
M2
heart
M3
bladder detrouser muscle and to control pancreatic insulin release, and other peripheral metabolic responses

Adrenergic Receptors (Alpha)

Alpha 1
Located at: Smooth muscle- in various tissues thorughout the body
Subtypes of Alpha 1
Alpha 1A, Alpha 1B, Alpha 1D
Alpha 2 or Autore­ceptors
Located at: Presyn­aptic termnal of certain adrenergic synapses
Alpha 2 work
decrease the release of norepi­nep­hrine and other chemicals. : overall serve as negative feedback that limits the amount of neurot­ran­smitter released from the presyn­aptic terminal.
Alpha 2 Stimul­ation
Cause: Decreased neurot­ran­smitter release and diminished stimul­ation of the intern­eurons that influence the alpha motor neurons.
Alpha 2 Stimuants
Agonists - tizani­dine, -- decrease neuronal excita­bility in the spinal cord and so, decrease muscle hypere­xci­tab­ility in spasticity condit­ions.
Subtypes of alpha 2
Alpha-2A, alpha- 2B, alpha-2C

Adrenergic Receptors (Beta)

Beta1
heart and kidneys
Beta 2
located: smooth muscle of certain vascul­atures, the bronch­ioles, the gallbl­adder, and the uterus
Beta 2
functional role in some tissues. Located at: Adipose tissue

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