the topic contain ANS effect, function and other related information

1. AUTONOMIC NERVOUS SYSTEM (ANS)
Ravish Yadav

2. AUTONOMIC NERVOUS SYSTEM (ANS)
• Operates via reflex arcs.
• Structurally, the ANS includes
• Autonomic sensory neurons,
• Integrating centers in the CNS
• Autonomic motor neurons.
• A continual flow of nerve impulses from
• (1) Autonomic sensory neurons in visceral organs and blood vessels propagate into
• (2) Integrating centers in the central nervous system (CNS).
• Then, impulses in (3) Autonomic motor neurons propagate to various effector tissues,
• Thereby regulating the activity of
• Smooth muscle, cardiac muscle, and many glands.
• The ANS usually operates without conscious control.
• The system was originally named autonomic because
• It was thought to function autonomously or in a self-governing manner, without
control by the CNS.
• However, centers in the hypothalamus and brain stem do regulate ANS reflexes.

3. AUTONOMIC SENSORY NEURONS
• The main input to the ANS
• Comes from autonomic sensory neurons.
• Mostly, these neurons are associated with interoceptors ,
• Which are sensory receptors located in
• Blood vessels, visceral organs, muscles, and the nervous system
• That monitor conditions in the internal environment.
• Examples of interoceptors are
• Chemoreceptors and mechanoreceptors.
• Input that influences the ANS also includes some sensations monitored by
• Somatic sensory and special sensory neurons.

4. AUTONOMIC MOTOR NEURONS
• Regulate visceral activities by
• Either increasing (exciting) or decreasing (inhibiting) ongoing activities in their effector
tissues (cardiac muscle, smooth muscle, and glands).
• Examples of autonomic motor responses:-
• Changes in the diameter of the pupils, dilation and constriction of blood vessels, and
adjustment of the rate and force of the heartbeat
• The efferent (motor) nerves of the autonomic nervous system
• Arise from nerve cells in the brain and
• Emerge at various levels between the midbrain and the sacral region of the spinal
cord.
• Many of them travel within the same nerve sheath as the peripheral nerves
of the central nervous system
• To reach the organs which they innervate.

6. EFFECTS OF AUTONOMIC CONTROL
• Rapid and essential for homeostasis.
• The effector organs are:
• Smooth muscle
• Cardiac muscle
• Glands
• Effects of autonomic stimulation include:
• Changes in rate and force of the heartbeat
• Stimulation or depression of secretion of glands
• Vasoconstriction or vasodilatation
• Bronchoconstriction or bronchodilation
• Changes in size of the pupils of the eyes

7. Divisions OF ANS
• The autonomic nervous system is divided into two divisions:
• sympathetic (thoracolumbar outflow)
• parasympathetic (craniosacral outflow).
• The two divisions have both structural and functional differences.
• They normally work in an opposing manner,
enabling or restoring balance of involuntary functions, maintaining
homeostasis.
• Sympathetic activity tends to predominate in stressful situations and
parasympathetic
activity during rest.

9. • Each division has two efferent neurones in its peripheral pathways between
the central nervous system and
effector organs.
• These are:
• The preganglionic neurone
• The postganglionic neurone.
• The cell body of the preganglionic neurone is in
• The brain or spinal cord.
• Its axon terminals synapse with the cell body of the postganglionic neurone
in an autonomic ganglion outside the central nervous system.
• The postganglionic neurone conducts impulses to the effector organ.

10. SYMPATHETIC NERVOUS SYSTEM
• Neurones convey impulses from their origin in the hypothalamus, reticular
formation and medulla oblongata to effector organs and tissues.
• The first neurone has its cell body in the brain and its fibre extends into the
spinal cord.
The preganglionic neurone.
• This has its cell body in the lateral column of grey matter in the spinal cord
between the levels of the 1st thoracic and 2nd or 3rd lumbar vertebrae.
• The nerve fibre of this cell leaves the cord by the
anterior root and terminates in one of the ganglia either
in the lateral chain of sympathetic ganglia or passes through it to one of
the prevertebral ganglia.
• Acetylcholine is the neurotransmitter.
The postganglionic neurone.
• This has its cell body in a ganglion and terminates in the organ or tissue
supplied.
• Noradrenaline is usually the neurotransmitter.

12. SYMPATHETIC GANGLIA
• The lateral chains of sympathetic ganglia.
• These are chains of ganglia which extend from the upper cervical level to the
sacrum, one chain lying on each side of the bodies of the vertebrae.
• The ganglia are attached to each other by nerve fibres.
• Preganglionic neurones that emerge from the cord may synapse with the cell
body of the postganglionic neurone at the same level or they may
pass up or down the chain through one or more ganglia before synapsing.
• For example, the nerve which dilates the pupil of the eye leaves the cord at
the level of the 1st thoracic vertebra and passes up the chain to the superior
cervical ganglion before it synapses with the cell body of the postsynaptic
neurone.
• The postganglionic neurones then pass to the eyes.
• The major exception is that there is no parasympathetic supply to the sweat
glands, the skin and blood vessels of skeletal muscles.
• These structures are supplied by only sympathetic fibres, some of which
have acetylcholine and some adrenaline and noradrenaline as their
neurotransmitter.
• They have, therefore, the effects of both sympathetic and parasympathetic
nerve supply.

13. Prevertebral ganglia
• There are three prevertebral ganglia situated in the abdominal cavity close
to the origins of arteries of the same names:
• Coeliac ganglion
• superior mesenteric ganglion
• inferior mesenteric ganglion.
• The ganglia consist of nerve cell bodies rather diffusely distributed among
a network of nerve fibres which form plexuses. Preganglionic sympathetic
fibres pass through the lateral chain to reach these ganglia.

14. Parasympathetic nervous system
• Two neurones (preganglionic and postganglionic) are involved in the
transmission of impulses from their source to the effector organ.
• The neurotransmitter at both synapses is acetylcholine.
The preganglionic neurone.
• This has its cell body either in the brain or in the spinal cord. Those
originating in the brain are the cranial nerves III, VII, IX and X, arising from
nuclei in the midbrain and brain stem, and their nerve fibres terminate
outside the brain.
• The cell bodies of the sacral outflow are in the lateral columns of grey
matter at the distal end of the spinal cord.
• Their fibres leave the cord in sacral segments 2, 3 and 4 and synapse with
postganglionic neurones in the walls of pelvic organs.
The postganglionic neurone.
• This has its cell body either in a ganglion or in the wall of the organ
supplied.

16. FUNCTIONS OF THE AUTONOMIC NERVOUS SYSTEM
• The autonomic nervous system is involved in a complex
of reflex activities which, like the reflexes described
previously, depend on sensory input to the brain or spinal
cord, and on motor output.
• In this case the reflex action is rapid contraction, or inhibition of contraction,
of involuntary (smooth and cardiac) muscle or glandular secretion.
• These reflexes are coordinated subconsciously in the brain,
i.e. below the level of the cerebrum.
• Some sensory input does reach consciousness and may result in temporary
inhibition of the reflex action, e.g. reflex micturition can be inhibited
temporarily.

17. • The majority of the organs of the body are supplied by both sympathetic and
parasympathetic nerves which have opposite effects that are finely balanced
to ensure the optimum functioning of the organ.
• Sympathetic stimulation prepares the body to deal with exciting and
stressful situations, e.g. strengthening its defences in danger and in extremes
of environmental temperature.
• The adrenal glands are stimulated to secrete the hormones adrenaline and
noradrenaline into the bloodstream.
• These hormones potentiate and sustain the effects of sympathetic
stimulation.
• It is sometimes said that sympathetic stimulation mobilises the body for
'fight or flight'.
•

18. • Parasympathetic stimulation has a tendency to slow
down body processes except digestion and absorption of food and
the functions of the genitourinary systems.
• Its general effect is that of a 'peace maker' allowing restoration
processes to occur quietly and peacefully.
• Normally the two systems function together maintaining a regular
heartbeat, normal temperature and an internal environment
compatible with the immediate external surroundings.

19. EFFECTS OF AUTONOMIC STIMULATION
• Cardiovascular system
• Sympathetic stimulation
• Exerts an accelerating effect upon the sinoatrial node in the heart,
increasing the rate and force of the heartbeat.
• Causes dilatation of the coronary arteries, increasing the blood supply to
cardiac muscle.
• Causes dilatation of theblood vessels supplying skeletal muscle, increasing
the supply of oxygen and nutritional materials and the removal of metabolic
waste products, thus increasing the capacity of the muscle to work.
• Raises peripheral resistance and blood pressure by constricting the small
arteries and arterioles in the skin.
• In this way an increased blood supply is available for highly active tissue,
such as skeletal muscle, heart, brain.
• Constricts the blood vessels in the secretory glands of the digestive
system, reducing the flow of digestive juices.
• This raises the volume of blood available for circulation in dilated blood
vessels.
• Blood coagulation occurs more quickly because of vasoconstriction.

20. • Parasympathetic stimulation
• Decreases the rate and force of the heartbeat.
• Causes constriction of the coronary arteries reducing the blood
supply to cardiac muscle.
• The parasympathetic nervous system exerts little or no effect on
blood vessels except the coronary arteries.

21. RESPIRATORY SYSTEM
Sympathetic stimulation
• This causes dilatation of the airways, especially the bronchioles, allowing a
greater amount of air to enter the lungs at each inspiration and increases the
respiratory rate.
• In conjunction with the increased heart rate, the
oxygen intake and carbon dioxide output of the body are increased.
Parasympathetic stimulation
• Produces constriction of the bronchi.

22. Digestive and urinary systems
• Sympathetic stimulation
• The liver converts an increased amount of glycogen to glucose, making more
carbohydrate immediately available to provide energy.
• The adrenal (suprarenal) glands are stimulated to secrete
adrenaline and noradrenaline which potentiate and sustain the effects of
sympathetic stimulation.
• The stomach and small intestine. Smooth muscle contraction and secretion
of digestive juices are inhibited, delaying digestion, onward movement and
absorption of food and the tone of sphincter muscles is increased.
• Urethral and anal sphincters. The muscle tone of the sphincters is increased,
inhibiting micturition and defecation.
• The bladder wall relaxes.
• The metabolic rate is greatly increased.

23. Parasympathetic stimulation
• The stomach and small intestine. The rate of digestion
and absorption of food is increased.
• The pancreas. There is an increase in the secretion of
pancreatic juice and the hormone insulin.
• Urethral and anal sphincters. Relaxation of the internal
urethral sphincter is accompanied by contraction of
the muscle of the bladder wall and micturitionoccurs.
• Similar relaxation of the internal anal sphincter is
accompanied by contraction of the muscle of the
rectum and defecation occurs.
• In both cases there is voluntary relaxation of the external sphincters.

24. Eye
• Sympathetic stimulation
• This causes contraction of the radiating muscle fibres of the iris,
dilating the pupil.
• Retraction of the levator palpebral muscles occurs, opening the eyes
wide and giving the appearance of alertness and excitement. The
ciliary muscle that adjusts the thickness of the lens is slightly relaxed.
• Parasympathetic stimulation
This causes contraction of the circular muscle fibres of
the iris, constricting the pupil. The eyelids tend to close,
giving the appearance of sleepiness.

25. SKIN
• Sympathetic stimulation
• Causes increased secretion ofsweat, leading to
increased heat loss from the body.
• Produces contraction of the arrectores pilorum (the muscles in the hair
follicles of the skin),
• Causes constriction ofthe blood vessels preventing
heat loss.
There is no parasympathetic nerve supply to the skin.
Some sympathetic fibres are adrenergic, causing vasoconstriction, and some
are cholinergic, causing vasodilatation