Touqeer Ahmed Ph.D.

Atta-ur-Rahman School of Applied Biosciences

National University of Sciences and Technology

Autonomic Nervous System

6th March, 2015&

19th March, 2015

Role of the CNS in the control of autonomic functions:

ANS is a motor system but it does require sensory input fromperipheral structures to provide information on the state of affairsin the body.

This feedback is provided by streams of afferent impulses,originating in the viscera and other autonomically innervatedstructures that travel to integrating centers in the CNS, such as thehypothalamus, medulla oblongata, and spinal cord. These centersrespond to the stimuli by sending out efferent reflex impulses viathe ANS

Autonomic Nervous System

Autonomic Nervous System

Autonomic Nervous System

Anatomy of the ANS

1. 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 latter neuron 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

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

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

Sympathetic Nervous System Parasympathetic Nervous System

Autonomic Nervous System

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:

– 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.

Somatic Nervous System

Drugs Acting on The Autonomic Nervous System

• 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.

• 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.

• 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.

• 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. Propanolol is non specific blocker and atenolol is selective beta 1 bolcker

Drugs Acting on Autonomic Nervous System