The part of nervous system which controls somatic/voluntary structures of the body. Its target structures are skeletal muscle and skin.
Autonomic nervous system -
The part of nervous system which controls involuntary structures of the body. Its target structures are smooth muscle, cardiac muscle, glands (exocrine) and mucus membrane of viscera.
Autonomic vs. Somatic NS
Somatic nervous system
excitation of skeletal muscle
consciously perceived sensations
one neuron connects CNS to organ
Autonomic nervous system
involuntary inhibition or excitation of smooth muscle, cardiac muscle or glandular secretion
unconsciously perceived visceral sensations
two neurons needed to connect CNS to organ
Effector remains functional but not able to quickly respond to the changing needs of the body. Paralysis and muscle wastage (atrophy) Effect of nerve damage on the effector Acetylcholine, adrenaline, noradrenaline Acetylcholine Neurotransmitter Chain ganglia, collateral ganglia or terminal ganglia 0 Ganglia outside the CNS 2 1 Number of neurons from CNS to effector Adjustment within the internal environment (homeostasis) Adjustment to external environment. General function Smooth muscle, Cardiac Muscle, Glands Voluntary (skeletal) muscle Effectors Autonomic Nervous System Somatic Nervous System Characteristic
Autonomic vs. Somatic
Somatic NS motor pathway only contains one neuron.
Autonomic NS motor pathway is a 2 neuron pathway
Endocrine system and autonomic nervous system control internal environment of the body. They bring about fine internal adjustments necessary for the optimal internal environment ( milieu interior of Claude Bernard/homeostasis of Canon ) of the body.
These control effect is extremely rapid, widespread and occurs at subconscious level.
Distribution of autonomic nervous system occurs through somatic nervous system.
ANS is controlled by hypothalamus and it receives input from limbic system.
Autonomic nervous system has 3 subdivisions-
Sympathetic nervous system
Parasympathetic nervous system
Enteric nervous system
Sympathetic and parasympathetic division of ANS produce opposite effects in most organs, thus considered as physiological antagonists . However they operate in conjunction with one another and it is the balance in activities that maintains a stable internal environment. Exception: Both sympathetic and parasympathetic increase salivation. Enteric nervous system Enteric neurons form plexuses that surround and extend along the length of the gut, including stomach, small and large intestines. Enteric system activate coordinated contraction of smooth muscles to cause peristaltic constriction of the gut. Most of enteric nervous system functions independently of higher CNS control.
ANS has motor/efferent component and sensory/afferent components.
They represent GVE functional components.
2 sets of neuron which synapse at ganglion.
Preganglionic neuron/1st set/primary neuron
Postganglionic neuron/2nd set/secondary neuron
Cell body in brain or spinal cord
Axon is myelinated type B fiber that extends to autonomic ganglion
Sympathetic preganglionic neurons are located in lateral horn of T1-L2/L3 spinal segments------ THORACOLUMBAR OUTFLOW
Parasympathetic preganglionic neurons are located partly in the brain stem in connection 3 rd , 7 th , 9 th and 10 th cranial nerves and partly in S2, 3, 4 spinal segments--------------------- CRANIOSACRAL OUTFLOW
Cell body lies outside the CNS in an autonomic ganglion
Axon is unmyelinated type C fiber that terminates in a visceral effector
Structure of autonomic ganglion
Connective tissue capsule
Cell bodies of post ganglionic neurons
Interneurons – SIF cells
Nerve fibers-Pre- and postganglionic fibers
and fibers traversing the ganglion without synapse
Structures having only sympathetic supply- no parasympathetic supply :
JG cells of nephron
Follicular cells of thyroid gland
Efferent nerve fiber (sympathetic outflow)
Cell bodies of primary neuron in lateral gray horn of T1-L2/3 segment of spinal cord
Myelinated axon in anterior root………spinal nerve trunk……anterior ramus……..ganglionated sympathetic trunk through white rami communicantes (14/15 in number)
Fate of preganglionic fibers in the ganglion of sympathetic trunk-
Some fibers make synapse with (cell bodies of postganglionic) neurons of corresponding ganglion. Post ganglionic fibers enter ventral ramus of spinal nerve through gray rami communicantes (31 in number). Distributed through spinal nerves to cutaneous viscera as vasomotor, pilomotor and sudomotor branches.
Some fibers leave the corresponding ganglion without making synapse as medial branch and synapse in subsidiary ganglia. These long preganglionic fibers are called splanchnic nerve. Postganglionic fibers from these subsidiary ganglia supply deep seated viscera.
Some fibers travel upward to reach upper ganglia. Here they synapse. Some postganglionic fibers return back to corresponding spinal nerve through gray rami communicantes and distributed to skin viscera. Some postganglionic fibers are distributed along blood vessels to important structures of head-neck region.
Some fibers travel downward to reach lower ganglia. Here they may synapse. Some postganglionic fibers return back to corresponding spinal nerve through gray rami communicantes and distributed to skin viscera. Some postganglionic fibers are distributed along splanchnic nerve. Some preganglionic fibers leave the ganglion as medial branch of the ganglion called lumber or sacral splanchnic nerve which synapse with subsidiary ganglia and distributed to viscera.
SHORT CILIARY NERVE CILIARY GANGLION C3: OCCULOMOTOR NERVE EDINGER WESTPHAL NUCLEUS TARGET THROUGH GANGLION CRANIAL NERVE NUCLEUS
For vagus nerve
Preganglionic myelinated fibers synapse in neurons of terminal ganglia lying close to or within organ wall.
Terminal ganglia are located in-
Postganglionic unmyelinated fibers supply heart, lung, foregut and midgut portion of alimentary tract.
Cell bodies of preganglionic neurons lie in the gray matter of S2, 3, 4 spinal segments.
Myelinated preganglionic fibers….enter anterior root…sacral nerve trunk……leave sacral nerve and form pelvic splanchnic nerve (nervi erigentes).
Pelvic splanchnic nerve ultimately synapse in ganglia in the hypogastric plexuses (close to target structure). Post ganglionic unmyelinated fibers supplies pelvic viscera and hindgut part of alimentary tract.
Classified as either cholinergic or adrenergic neurons based upon the neurotransmitter released
Ach Ach Ach Ach Ach Ach Epinephrine Norepinephrine Neurotransmitters Everywhere Adrenal medulla Sweat gland Everywhere Sympathetic Parasympathetic M receptor N receptor N receptor N receptor A>B receptor B>A receptor M receptor N receptor
Alpha (A) receptor-
Beta (B) receptor-
Muscarinic (M) receptor-
Nicotinic (N) receptor-
Functions of ANS
Physiological Effects of the ANS
Some organs have only sympathetic innervation
sweat glands, adrenal medulla, arrector pili mm & many blood vessels
controlled by regulation of the “tone” of the sympathetic system
Most body organs receive dual innervation
innervation by both sympathetic & parasympathetic
Hypothalamus regulates balance (tone) between sympathetic and parasympathetic activity levels
Sympathetic nervous system
Parasympathetic nervous system
Difference between sympathetic and parasympathetic nervous system
Central control Afferents
Anatomical entity Para Sym
Vasodilatation of skin arteriole
Loss of ciliospinal/ pupillary skin reflex
Cause: due to interruption of sympathetic nerve supply to