Autonomic Nervous System Overview

The autonomic nervous system (ANS) controls involuntary bodily functions like heart rate, breathing, digestion, and sweating.

The ANS operates independently of conscious control, unlike the somatic nervous system which controls voluntary movements.

The ANS is divided into two branches: the sympathetic and parasympathetic nervous systems, which have opposing effects to maintain homeostasis.

The sympathetic nervous system prepares the body for action, increasing heart rate, blood pressure, and respiration for fight or flight responses.

The parasympathetic nervous system promotes relaxation and digestion, slowing heart rate, lowering blood pressure, and diverting energy to digestive processes.

The nervous system is the body's communication network, made up of nerves and cells that transmit signals.

The central nervous system (CNS) is composed of the brain and spinal cord, responsible for processing information and coordinating activities.

The peripheral nervous system (PNS) extends throughout the body, carrying signals between the CNS and organs, muscles, and sensory receptors.

The sympathetic nervous system prepares the body for action, often called the 'fight-or-flight' response, increasing heart rate and blood pressure.

The parasympathetic nervous system promotes relaxation and conserves energy, slowing heart rate and lowering blood pressure, often called the 'rest and digest' response.

Neurotransmitters are chemical messengers that carry signals across gaps between neurons called synapses.

Drugs can interact with the nervous system by influencing neurotransmitter activity, either increasing or decreasing their effects.

A cluster of nerve cell bodies (ganglia) in the autonomic nervous system where the first autonomic neuron (preganglionic neuron) synapses with the second autonomic neuron (postganglionic neuron).

The Autonomic Nervous System (ANS) controls involuntary bodily functions like heartbeat, breathing, digestion, and sweating.

The preganglionic neuron in the sympathetic nervous system is short and synapses close to the spinal cord, while the postganglionic neuron is long and extends to the target organ.

The preganglionic neuron in the parasympathetic nervous system is long and extends far from the spinal cord, while the postganglionic neuron is short and synapses close to the target organ.

The vagus nerve is a major parasympathetic nerve that projects from the brainstem and innervates many organs in the thorax and abdomen, controlling functions like heart rate, digestion, and respiration.

The sympathetic trunk (also known as the sympathetic chain) is a series of interconnected ganglia located on both sides of the spinal cord, containing the postganglionic neurons of the sympathetic nervous system.

Noradrenaline, a neurotransmitter released by sympathetic nerves, increases heart rate by activating beta (β) adrenergic receptors on the heart.

Acetylcholine released by parasympathetic nerves, slows down heart rate by activating muscarinic acetylcholine receptors (mAChR).

Drugs that block muscarinic acetylcholine receptors (mAChR) increase heart rate. For example, atropine is used in emergencies to revive a slow heartbeat.

Drugs can either stimulate or inhibit sympathetic and parasympathetic nervous system activity by targeting receptors on organs or ganglia.

Sympathomimetic drugs stimulate the sympathetic nervous system, while sympatholytic drugs inhibit it. Similarly, parasympathomimetic drugs stimulate the parasympathetic system, while parasympatholytic drugs inhibit it.

The ANS is divided into two main branches, each with opposing effects to maintain balance: the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS).

The two main neurotransmitters in the ANS are noradrenaline and acetylcholine.

Drugs that mimic the effects of neurotransmitters are called agonists. Drugs that block the effects of neurotransmitters are called antagonists.

Sympathomimetics mimic the effects of the sympathetic nervous system, while sympatholytics block the effects of the sympathetic nervous system.

Noradrenaline and Acetylcholine are the key neurotransmitters in the autonomic nervous system (ANS). These neurotransmitters are responsible for controlling involuntary bodily functions like heart rate and digestion.

Noradrenaline, also known as norepinephrine, binds to adrenergic receptors, specifically alpha (α) and beta (β) receptors. These receptors mediate the effects of noradrenaline on various tissues and organs.

Acetylcholine binds to cholinergic receptors, specifically muscarinic (m) and nicotinic (n) receptors. These receptors are involved in the transmission of signals throughout the ANS.

All preganglionic neurons, which are the first neurons in the ANS pathway, release acetylcholine and bind to nicotinic receptors on postganglionic neurons. This ensures that the signal is passed on to the next neuron in the chain.

Postganglionic neurons, the second neurons in the ANS pathway, release either noradrenaline or acetylcholine depending on the branch of the ANS and the target tissue. They bind to adrenergic or muscarinic receptors, respectively.

The sympathetic nervous system is responsible for the 'fight or flight' response. It prepares the body for action by accelerating heart rate, increasing blood pressure, and diverting energy to muscles.

The parasympathetic nervous system is responsible for the 'rest and digest' response. It promotes relaxation and digestion, slowing heart rate, lowering blood pressure, and directing energy to digestive processes.

Pharmacological intervention of adrenergic and cholinergic receptors can alter the activity of visceral organs like the heart, lungs, and intestines. This is a key principle in the treatment of various diseases.