• Nervous system
• The central
nervous system is
comprised of the
brain and spinal
• The peripheral
• Central nervous system
• Peripheral nervous system
– Sympathetic, parasympathetic, enteric nervous
• sympathetic & parasympathetic provide a link
between CNS and peripheral organs (except
motor innervation to skeletal muscle)
• ANS is largely outside of voluntary control
• Enteric nervous system – intrinsic nerve plexus
of GIT (interconnected with sym & parasym)
• Autonomic nervous system (ANS)
• Functions largely below the level of consciousness
and controls visceral functions.
• Like the somatic nervous system, the ANS
consists of afferents, centre and efferents.
• Most visceral nerves – (mixed nerves) –
– carry non myelinated visceral afferent fibres.
• The cell bodies - in the dorsal root ganglion of
• They mediate visceral pain as well as
cardiovascular, respiratory and other visceral
Central autonomic connections
• no exclusively autonomic areas in the CNS
• considerable intermixing and integration of somatic
and autonomic innervation occurs.
• Many autonomic centres (pupillary, vagal, respiratory,
etc.) are located in the mid-brain and the medulla in
relation to the cranial nerves.
• The lateral column in the thoracic spinal cord contains
cells which give rise to the sympathetic outflow.
• The motor limb of ANS is anatomically divided into
sympathetic and parasympathetic.
• functionally antagonistic
• and most organs receive both
sympathetic and parasympathetic innervation.
• ANS – efferent – two neurons arranged in
series (preganglionic & post ganglionic)
• Somatic – efferent – single motor neuron
connects CNS to skeletal muscle fibre
• Between pre and post ganglionic neurones –
there is autonomic ganglia
– Situated outside CNS
• Cell bodies of
preganglionic neurones –
lateral horns of the spinal
cord (thoraco-lumbar) -
• In parasympathetic pathways,
– Post ganglionic cells are + in target organs
• Two outflow
– Oculomotor (eye)
– Facial & glossopharyngeal (salivary gland &
– Vagus nerve (thoracic and abdominal viscera)
• Ganglias exist close to target organs
• Post ganglionic neurones – very short
• Sacral outflow
• Neurohumoral transmission implies that
nerves transmit their message across synapses
and neuroeffector junctions by the release of
humoral (chemical) messengers.
1. should be present in the presynaptic neurone
2. should be released after nerve stimulation
3. It’s application should produce responses identical to
those produced by nerve stimulation
4. Its effects should be antagonized or potentiated by other
substances which similarly alter effects of nerve
• RMP 70 mV (negative inside) High K+ & low
• Stimulation or arrival of impulse
• Sudden increase in Na+ entry
• Depolarization & overshoot (+20mV)
• AP is propragated
• The transmitter (excitatory or inhibitory) is stored in
prejunctional nerve endings within synaptic vesicles
• Nerve impulse promotes fusion of vesicular
and axonal membranes through Ca2+ entry
which utilizes membranes
• All contents of the vesicle - transmitter, enzymes
and other proteins) are extruded (exocytosis) in the
• The release process can be modulated by the
transmitter itself and by other agents through
activation of specific receptors located on the pre
– e.g. noradrenaline (NA) release is inhibited by NA ( α2
• The released transmitter combines with specific
receptors on the post-junctional membrane and
depending on its nature induces an
excitatory postsynaptic potential (EPSP) or an
inhibitory postsynaptic potential (IPSP).
• A suprathreshold EPSP generates a
propagated postjunctional AP which results in
nerve impulse (in neurone), contraction (in
muscle) or secretion (in gland).
• An IPSP stabilizes the postjunctional
membrane and resists depolarizing stimuli.
• Following its combination with the receptor, the
transmitter is either locally degraded (e.g. ACh)
or is taken back into the prejunctional neurone
by active uptake or diffuses away (e.g. NA,
• In the ANS,
• besides the primary transmitters ACh and NA,
• neurones have been found to elaborate
– purines (ATP, adenosine),
– peptides (vasoactive intestinal peptide or VIP,
neuropeptide-Y or NPY, substance P, enkephalins,
– nitric oxide
– and prostaglandins as co-transmitters.
• Mainly classified into α and β subtypes
• 2 main α adrenoreceptor subtypes – α1 & α2
• 3 β adrenoreceptor subtypes – β1, β2, β3
• Contraction and relaxation of vascular and visceral
• All excocrine and certain endocrine secretions
• The heartbeat
• Energy metabolism, particularly in liver and skeletal
• Other system
– Kidney, immune, somatosensory
• The level of activity of innervated organ at a given moment is
the algebric sum of sympathetic and parasympathetic tone:
• Most blood vessels, spleen, sweat glands and hair follicles
receive only sympathetic,
• while ciliary muscle, gastric and pancreatic glands receive
only parasympathetic innervation.
• The enteric plexus of nerves receives input from both
sympathetic and parasympathetic divisions, but in addition
functions independently to integrate bowel movements as
well as regulate: secretion and absorption labelled as a
distinct 'enteric nervous system'.
• Rang, HP, Dale, MM, Ritter, JM, Flower, RJ,
Henderson, G (2012). Rang and Dale's
Pharmacology. 7th ed. London: Elsevier
Churchill Livingstone. 139-149.
• Tripathi, KD. 2008. Essentials of Medical
Pharmacology. 6th Edition. India: Jaypee
Brothers Medical Publishers (P) Ltd.