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 |
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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 |
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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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