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• Afferent (Sensory)

  Nerves that convey flow of impulse from peripheral to CNS
• Parasympathetic Nervous System

  • Cholinergic Nervous System
• Nerves transmit their impulses across synapses and neuroeffector junctions using specific chemicals called neurohumoural transmitters or neurotransmitters
• The Autonomic Nervous System modulates the involuntary activity of secretory glands, smooth muscles, and visceral organs
• Differences between Autonomic and Somatic Nervous System

  • Efferent nerves of A.N.S. supply all innervated structures of the body except skeletal muscles
  • The most distal synaptic junction in A.N.S. occurs in ganglia that are entirely outside the cerebrospinal axis
  • Many autonomic fibres form extensive peripheral plexuses
  • When cut, organ supplied generally show some level of spontaneous activity independent of intact innervations
  • Pre-ganglionic and post-ganglionic fibres are present
  • Post-ganglionic autonomic nerve fibres are generally non-myelinated (slow conduction of impulse), whereas pre-ganglionic fibres are myelinated (fast conduction of nerve impulse)
  • Somatic nerves supply skeletal muscles
  • Somatic nerves contain no peripheral ganglia, and synapses are located entirely within the cerebrospinal axis
  • No peripheral plexus is present in somatic nerve fibres
  • When cut, skeletal muscles supplied become paralyzed and undergo atrophy
  • Most fibres of skeletal muscles are myelinated
• Autonomic drugs exert their actions on smooth muscles, cardiac muscles, glands, and visceral organs by mimicking or modifying the action of neurotransmitters released by autonomic fibres
• Most autonomic fibres are non-myelinated for slow conduction of impulse, while most somatic fibres are myelinated for fast conduction of nerve impulse
• Neuroeffector junction

  The junction of a post-ganglionic axonal terminal with its effector cell
• Nerve plexus

  A network of nerve fibres
• The Autonomic Nervous System sustains homeostatic conditions during periods of reduced physical and emotional activity and assists in internal bodily reactions to stressful circumstances
• Figure: 'The Autonomic Nervous System Schematic representation of the autonomic nerves and effector organs based on chemical mediation of nerve impulses. Yellow (cholinergic), red (adrenergic), dotted blue (visceral afferent), solid lines (preganglionic), broken lines (postganglionic). The rectangle at right shows the finer details of the ramifications of adrenergic fibers at any one segment of the spinal cord, the path of the visceral afferent nerves, the cholinergic nature of somatic motor nerves to skeletal muscle, and the presumed cholinergic nature of the vasodilator fibers in the dorsal roots of the spinal nerve'
• Sympathetic Nervous System

  • Adrenergic Nervous System
• Differences between Autonomic and Somatic Nervous System:
• Efferent (Motor)

  Nerves that convey impulses from the brain and spinal cord (CNS) to muscles, glands and other effector organs
• It is not known whether the vasodilator fibers are motor or sensory or where their cell bodies are situated
• Parasympathetic Nervous System Characteristics

  • Arises as a craniosacral outflow
  • Ganglia are away from the C.N.S. and on or close to the organs
  • Distribution is much more limited
  • Neurotransmitter is acetylcholine in both ganglia and at neuroeffector junctions
  • Function involves modulating body functions towards the needs of a period of inactivity and repair of energy deficits
  • Activity predominates during rest
  • Endowed with the medullary functions
  • Function is usually normal if taken out, but the animal will not survive long due to conservation of energy
• Parasympathetic-mediated responses

  • General inhibition
  • Decrease heart rate
  • Decrease contractile force
  • Decrease conduction velocity; AV block
  • Decrease contract
• Details of the ramifications of adrenergic fibers at any one segment of the spinal cord, the path of the visceral afferent nerves, the cholinergic nature of somatic motor nerves to skeletal muscle, and the presumed cholinergic nature of the vasodilator fibers in the dorsal roots of the spinal nerves are shown in the rectangle at right
• Sympathetic Nervous System Characteristics

  • Arises as thoraco-lumbar outflow (T1 to L3)
  • Ganglia are nearer to the C.N.S.
  • Distributed to effector organs throughout the body
  • Neurotransmitters are acetylcholine (in ganglia) and norepinephrine (at neuroeffector junctions)
  • Function involves changes in the body for a period of activity and energy expenditure
  • Activity increases in stress and emergency
  • Responsible for providing continuous stimulus to the organs and parts supplied
  • Animal can survive with some physiological changes if nerve is cut
• Sympathetic-mediated responses


  • General excitation
  • β1 – increase heart rate
  • β1 – increase contractile force, conduction velocity
  • β1 – increase automaticity, conduction velocity
  • β1 – increase automaticity, conduction velocity
  • β1 – increase contractile force, conduction velocity, irritability
• Effector tissues

  • Heart
  • Sinoatrial (SA) node
  • Atria
  • Atrioventricular (AV) node
  • His-Purkinje system
  • Ventricles
• Effects of General inhibition

  • Decrease heart rate
  • Decrease contractile force
  • Decrease conduction velocity
  • AV block
• α1 stimulation


  Constriction
• β2 stimulation

  Relaxation
• β2 stimulation


  Secretion
• Effects of α2 stimulation

  • Dilation
• α2 stimulation

  Decrease release of norepinephrine
• Superscript numbers are defined as follows: (1) α and β designate the principal adrenoceptor type subserving a tissue response. α1, α2, β1 and β2 designate the receptor subtype. The usual receptor types are presented; considerable interspecies variation exists, particularly with reference to subtypes. (2) Except when otherwise designated (e.g. ganglia), parasympathetic responses are subserved by muscarinic receptors. (3) Catecholamine-induced irritability of the myocardium may be associated with β1 and α receptors, systemic pressor response may contribute. (4) Muscarinic receptors subserving decreased contractility are demonstrable in ventricular muscle, but the significance is not definitely known. (5) In small coronary arteries, β receptors are more numerous, more sensitive, and/or more responsive than α receptors. In large coronary arteries, α receptors can be demonstrated. β1 and β2 subtypes differ depending upon species. (6) Depending upon experimental conditions, cholinergic effects on coronary blood vessels have been reported as both constriction and dilation. (7) Arterial smooth muscle generally is not innervated by the parasympathetic nervous system (exceptions include blood vessels in genitalia). Thus cholinergic receptors in most arterial beds are not associated with parasympathetic nerves. In certa
• Effects of β2 stimulation

  • Dilation
• Decrease (usually)

  Relaxation
• α1 stimulation

  Contraction
• α2 stimulation

  Aggregation
• Effects of β1 stimulation

  • Increase automaticity
  • Conduction velocity
  • Increase contractile force
• Effects on Blood vessels

  • Coronary
  • Cutaneous, mucosal
  • Cerebral
  • Skeletal muscle
  • Splanchnic
  • Renal
  • Genital
  • Veins
  • Endothelium
• α1 stimulation

  Scant, viscous secretion
• α stimulation

  Contraction
• β2 stimulation

  Increase release of norepinephrine
• Effects of α1 stimulation

  • Constriction
• Parasympathetic-induced dilation of genital blood vessels (which contributes to erection) is not mediated by ACh: the neurotransmitter is believed to be nitric oxide
• Energetic effects on coronary blood vessels

  Reported as both constriction and dilation