Autonomic Nervous System

Prepared by: ANAM KHAN

Brain and spinal cord:

Receives and processes incoming sensory information and responds by sending out signals that initiate or modify a process.

Includes all the neurons and ganglia found outside the CNS-any nerve that enters or leaves the CNS

The main function of the PNS is to connect the CNS to the limbs and organs, essentially

serving as a communication relay going back and forth between the brain and the extremities.

It is subdivided into:

Efferent Division – the neurons of which carry signals away from the brain and spinal cord to peripheral tissues.

= Afferent division – the neurons of which bring info from the periphery to the CNS.They provide sensory input to modulate the function of efferent division.

Efferent

Somatic Autonomic

Somatic efferent neurons are Involved in the voluntary control of functions

Autonomic Efferent Regulates everyday requirement of vital bodily functions without the conscious participation of the mind.

Preganglionic neurons

Cell body is located within the CNS

Postganglionic neurons

Cell body originating in the ganglion

preganglionic postganglionic

Either unmyelinated or myelinated

Emerge from brainstem or spinal cord and make synaptic connection in ganglia

Generally Nonmyelinated

Terminates on effector organs

These fibers arise from the cranium (from cranial nerves III,VII,IX and X) and from the sacral region(S2-4) of spinal cord.

Efferent nerve fibers originate from nerve cells in the lateral gray column of the spinal cord between first thoracic and second lumbar segments( thoracic outflow)

Two types of acetylcholine receptors exists

Acetylcholine has the ability to bind with both of these receptors.

In preganglionic neurons, both parasympathetic and sympathetic, the release of acetylcholine binds

predominantly with nicotinic receptors on the postganglionic neurons

Sympathetic system:

•At the synapses within the ganglia, preganglionic neurons release acetylcholine.

•In response to this stimulus postganglionic neurons - with two important exceptions - release nor epinephrine.

•Activates adrenergic receptors on the peripheral target tissues.

The activation of target tissue receptors causes the effects associated with the sympathetic system.

The two exceptions mentioned above are:

• postganglionic neurons of

sweat glands and

• chromaffin cells of the adrenal medulla.

Parasympathetic system The parasympathetic nervous system uses chiefly acetylcholine (ACh) as its neurotransmitter.

Most transmissions occur in two stages:

•When stimulated, the preganglionic nerve releases ACh at the ganglion.

•which acts on nicotinic receptors of postganglionic neurons.

•The postganglionic nerve then releases ACh to stimulate the muscarinic receptors of the target organ.

Both always present in the blood.

Nor epinephrine varies

Epinephrine is a constant

3rd division of ANS

Works independently of CNS

Brain of Gut ( as it is the collection of nerve fibers that innervate the gastrointestinal tract , pancreas and gall bladder)

Modulated by both the parasympathetic and sympathetic nervous system

Exocrine/endocrine secretions and microcirculation of gastrointestinal tract

Continually active to some degree

Diffused distribution of postganglionic Fibers.

The changes experienced by the body during emergencies have been referred to as the “fight or flight” response.

Maintains essential bodily functions

Generally dominant over sympathetic

system in “Rest and Digest” situations.

It usually acts to oppose or balance the actions of sympathetic division.

Eye

P-constricts pupils ( III occulomotor)

S-dilates pupils

Heart muscles P-decreases rate; slows and steadies

heart(bradycardia)

S-Increases rate and force of heartbeat

Blood vessels P-vasoconstriction

S- vasodilation

Glands (nasal, lacrimal, salivary, gastric, pancreas)

P-stimulates secretary activity

S-inhibits secretary activity

Lungs

P-constricts bronchioles

S-Dilates bronchioles and mildly constricts blood vessels

Digestive Tract Organs:

P-increases motility and amount of secretions by digestive organs' relaxes sphincters and allow movement of food along tract

S-decreases activity of glands and muscles of digestive system and constricts sphincter; causes vasoconstriction

Sweat Glands S-stimulates sweating

Arrector pili muscles attached to hair follicle S-stimulates to contract—Goosebumps

LiverS-Epinephrine stimulates liver to release

glucose to blood

Adrenal Medulla S-Stimulates medulla cells to secrete epinephrine and noreponephrine into bloodstream

Kidney

S- causes vasoconstriction; decreases urine output

Gallbladder

P-stimulates activity; gallbladder contracts to expel bile

S-gallbladder relaxed

Bladder, Urethra

P-contraction smooth muscle of bladder wall

S-relaxation of smooth muscle of bladder wall

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Summary