Autonomic Nervous System Pharmacology

Lecture 1The Autonomic Nervous System: Introduction

Dr. Mohit Kulmi

CENTRAL NERVOUS SYSTEM (CNS)• Brain and spinal cord: • receives and processes incoming sensory information and

responds by sending out signals that initiate or modify a process

PERIPHERAL NERVOUS SYSTEM OR PNSIncludes all the neurons and ganglia found outside the CNSAfferent: sensory input to CNS• Afferent neurons carry sensory input from the periphery to the

CNS and modify motor output through the reflex arc. Efferent: motor output from CNS• Efferent neurons carry motor signals from the CNS to the

peripheral areas of the body.

Efferent Division

The efferent portion of the PNS is further divided into two major functional subdivisions,

1. Somatic (SNS): • one motor neuron innervates the skeletal muscles and control

voluntary (consciously) functions; movement, respiration and posture.

2. Autonomous nervous system (ANS):• The ANS is the major involuntary portion of the NS• is responsible for automatic, unconscious bodily function, such as • control of HR and BP and both GIT and GUT functions.

Nervous System

Two main divisionsI. CNS• Brain & spinal

cord

II. PNS1. Afferent (sensory)2. Efferent (motor)• Somatic & ANS

Key steps in neurotransmission

Cholinergic Neurotransmission

Synthesis

Storage

Release

Binding

Degradation

Recycling of choline

Central roots of originParasympathetic Division– also called

the craniosacral division• The preganglionic fibers arise

from the cranial nerve nuclei III, VII, IX, and X and sacral region (usually S2-S4) of the spinal cord, and synapse in ganglia close to the effector organ.

• Thus, in contrast to the sympathetic system, the preganglionic fibers are long, and the postganglionic ones are short.

Sympathetic Division – also called the thoracolumbar division

• The preganglionic fibers arise from the thoracic (T1-T12) and lumbar (L1-L5) regions of the spinal cord, and they synapse in paravertebral ganglia close and parallel to the vertebral column. Postganglionic axons lead to an effector organ.

DIFFERENCES BETWEEN SYMPATHETIC AND PARASYMPATHETIC NERVOUS SYSTEM

Location of Ganglia

• Both the PANS and SANS have relay station, or ganglia, between the CNS and the end organ, but the somatic system does not;

• The ANS, carries nerve impulses by

• a preganglionic fiber that leaves the CNS,

• a postganglionic fiber that innervates the effector.

GENERAL OUTLAY OF EFFERENT NERVOUS SYSTEM :

Adrenal medulla

the adrenal medulla, • like the sympathetic ganglia, receives preganglionic fibers

from the sympathetic system. • Lacking the axons, • in response to stimulation by Ach, influences other organs by

secreting the epinephrine and lesser amounts of nor-epinepherine into the blood.

Functions of the Sympathetic Nervous System

• Is normally active, even at rest; however, it assumes a dominant role when the body becomes stressed (trauma, fear, hypoglycemia cold or exercise).

• Fight or Flight – Protective mechanisms designed to help person cope with the stress or get away from it.

• For example, if you sense danger: Your heart rate increase, BP rises, eyes dilates, blood sugar rises, bronchioles expand, and blood flow shift from skin to skeletal muscles.

Functions of the Parasympathetic Nervous System

1. Rest and digest: maintains essential body functions; digestive process and elimination of wastes.

2. Save energy. 3. Dilation of blood vessels in skin. 4. Decrease heart rate (bradycardia).5. Increase secretion of digestive enzymes.6. Constriction of smooth muscle of bronchi. 7. Increase in sweat glands. 8. Contraction of smooth muscles of urinary bladder.

The cholinergic neuron

• All preganglionic fibers of both sympathetic and parasympathetic divisions.

• All parasympathetic postganglionic.• Few sympathetic postganglionic fibers (sweat gland).• All Somatic (non autonomic) fibers to skeletal muscle

The adrenergic neuron

• Most sympathetic postganglionic fibers release norepinephrine; are noradrenergic or simply adrenergic.

• Some peripheral sympathetic fibers release dopamine (dopaminergic).

• The adrenal medulla, a modified sympathetic ganglion, receives sympathetic preganglionic fibers and releases epinephrine (~85%) and to a lesser amount norepinephrine (15%) into the blood.

Receptor types• Parasympathetic – cholinergic receptors: – muscarinic (M1 to M5) – and nicotinic receptors

• Sympathetic – adrenergic receptors: – alpha (α1, α 2), – beta (β1 to β 3), – and dopamine (D1 to D5) receptors.

SYMPATHETIC AND PARASYMPATHETIC NS & EFFECTOR ORGANS

Thank you!