Download Autonomic Nervous System

Autonomic Nervous System
Touqeer Ahmed PhD
3rd March, 2017
Atta-ur-Rahman School of Applied Biosciences
National University of Sciences and Technology
Nervous System Divisions
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The peripheral nervous system is subdivided into
– afferent division: bring information from the
periphery to the CNS. Afferent neurons provide
sensory input to modulate the function of the
efferent division
– efferent division: carry signals away from the brain
and spinal cord to the peripheral tissues
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The efferent portion of the peripheral nervous system is
further divided into two major functional subdivisions
– Somatic: involved in the voluntary control of
functions such as contraction of the skeletal muscles
essential for locomotion
– Autonomic systems: Regulates everyday
requirements of vital bodily functions without the
conscious participation of the mind
Autonomic Nervous System
Role of the CNS in the control of autonomic functions:
ANS is a motor system but it does require sensory input from
peripheral structures to provide information on the state of affairs in
the body.
This feedback is provided by streams of afferent impulses, originating
in the viscera and other autonomically innervated structures that
travel to integrating centers in the CNS, such as the hypothalamus,
medulla oblongata, and spinal cord. These centers respond to the
stimuli by sending out efferent reflex impulses via the ANS
Autonomic Nervous System
Autonomic Nervous System
Anatomy of the ANS
1.
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Efferent neurons: The ANS carries nerve impulses
from the CNS to the effector organs by way of two
types of efferent neurons.
The first neuron is called a preganglionic neuron,
and its cell body is located within the CNS.
Preganglionic neurons emerge from the brainstem
or spinal cord and make a synaptic connection in
ganglia (an aggregation of nerve cell bodies located
in the peripheral nervous system and functions as
relay stations).
The postganglionic euron has a cell body originating
in the ganglion. It is generally nonmyelinated and
terminates on effector organs, such as smooth
muscles of the viscera, cardiac muscle, and the
exocrine glands.
Anatomy of the ANS
2. Afferent neurons:
The afferent neurons (fibers) of the ANS are important in the reflex regulation of
system (for example, by sensing pressure in the carotid sinus and aortic arch) and
in signaling the CNS to influence the efferent branch of the system to respond.
Anatomy of the ANS
5. Enteric neurons:
The enteric nervous system is the third division of the ANS. It is a collection
of nerve fibers that innervate the gastrointestinal (GI) tract, pancreas, and
gallbladder, and it constitutes the “brain of the gut.”
This system functions independently of the CNS and controls the motility,
exocrine and endocrine secretions, and microcirculation of the GI tract.
It is modulated by both the sympathetic and parasympathetic nervous
systems.
Autonomic Nervous System
Autonomic Nervous System
Sympathetic Nervous System
Parasympathetic Nervous System
Functions of the sympathetic nervous system
Although continually active to some degree (for example, in
maintaining the tone of vascular beds), the sympathetic division has
the property of adjusting in response to stressful situations, such as
– trauma
– Fear
– Hypoglycemia
– Cold and exercise.
Effects of stimulation of the sympathetic division:
– increase heart rate and blood pressure
– mobilize energy stores of the body
– increase blood flow to skeletal muscles and the heart while
diverting flow from the skin and internal organs.
– sympathetic stimulation results in dilation of the pupils and the
bronchioles
– it also affects GI motility and the function of the bladder
Functions of the Parasympathetic nervous system
• The parasympathetic division is involved with maintaining homeostasis
within the body. To accomplish this, it maintains essential bodily
functions, such as digestive processes and elimination of wastes.
• The parasympathetic division is required for life. It usually acts to
oppose or balance the actions of the sympathetic division and is
generally dominant over the sympathetic system in “rest and digest”
situations.
• The parasympathetic never discharges as a complete system. If it will, it
will produce massive, undesirable, and unpleasant symptoms, such as
involuntary urination and defecation.
• Discrete parasympathetic fibers are activated separately and the
system functions to affect specific organs, such as the stomach or eye.
Autonomic Nervous System Neurotransmitters
Muscarinic and Nicotinic Receptors
Autonomic Nervous System (Receptors)
Muscarinic receptors:
M1 – M5
•M2 is present in heart
•M3 is present in glands, smooth muscles and
endothelium
•Nicotinic receptors (present in NMJ and CNS)
Adrenergic receptors:
α and β Receptors
•α are mainly present in blood vessels
• β are present in heart and lungs
Differences between sympathetic and
parasympathetic nervous systems.
Somatic Nervous System
Somatic nervous system:
– The efferent somatic nervous system differs from the
autonomic system in that a single myelinated motor
neuron, originating in the CNS, travels directly to
skeletal muscle without the mediation of ganglia.
– Somatic nervous system is under voluntary control,
whereas the autonomic system is involuntary.
– Responses in the somatic division are generally faster
than those in the ANS.
Drugs Acting on The Autonomic Nervous System
Drugs Acting on The Autonomic Nervous System
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Antimuscarinic drugs (e.g. Atropine and scopolamine)
Cholinergic blockers are beneficial in a variety of clinical situations such as, dilation of pupil,
antispasmodic in GIT, antidote for the overdoses of cholinesterase inhibitor insecticides and
antisecretory. Used as antisecretory agent to block secretions in the upper and lower respiratory tracts
prior to surgery. Because they do not block nicotinic receptors, the antimuscarinic drugs have little or
no action at skeletal neuromuscular junctions.
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Ganglionic blockers (e.g. Mecamylamine):
The drugs produce complex and unpredictable responses, making it impossible to achieve selective
actions. Therefore, ganglionic blockade is rarely used therapeutically. However, ganglionic blockers
often serve as tools in experimental pharmacology. Mecamylamine is primarily used to lower blood
pressure in emergency situations.
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Neuromuscular Blocking Drugs: (Tubocurarine)
Neuromuscular blockers are clinically useful during surgery for producing complete muscle relaxation,
without having to employ higher anesthetic doses to achieve comparable muscular relaxation.
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Adrenergic Blocking Drugs (Propanolol and atenolol)
Drugs that block adrenoceptors profoundly affect blood pressure. Blockade of these receptors reduces
the sympathetic tone of the blood vessels, resulting in decreased peripheral vascular resistance.