autonomic nervous system

• The autonomic nervous system consists of the sympathetic and parasympathetic systems.
• The parasympathetic division is responsible for rest and digestion.
• The parasympathetic nervous system is responsible for restoration and vegetative functions of the body when there are no stressors present.
• The sympathetic nervous system is responsible for the fight or flight response in threatening situations.
• The Autonomic Nervous System (ANS) controls all vegetative (involuntary) functions such as heart rate, blood pressure, GI motility, and iris diameter
• The ANS is separate from the voluntary (somatic) motor system
• The ANS is entirely efferent but is regulated by afferent inputs
• The ANS has two divisions:

  • Parasympathetic division
  • Sympathetic division
• The sympathetic nervous system responds to stressful situations with a "fight or flight" response, increasing heart rate, force of contraction, and blood pressure
• The parasympathetic nervous system regulates basal activities like basal heart rate, promoting a "rest and digest" state
• The principal neurotransmitters in the ANS are acetylcholine (ACh) and noradrenaline (NA)
• All pre-ganglionic neurons in the ANS are cholinergic, using ACh as their neurotransmitter
• Parasympathetic and sympathetic pre-ganglionic release of ACh results in the activation of post-ganglionic nicotinic ACh receptors
• Parasympathetic post-ganglionic neurons are cholinergic and release ACh, acting on muscarinic ACh receptors in the target tissue
• Most sympathetic post-ganglionic neurons are noradrenergic, using noradrenaline (NA) as the principal neurotransmitter
• Noradrenaline interacts with two major classes of adrenoceptors: α-adrenoceptors and β-adrenoceptors
• Some sympathetic post-ganglionic neurons are cholinergic and innervate sweat glands, hair follicles, releasing ACh that acts at muscarinic ACh receptors
• Other transmitters in the ANS include non-adrenergic, non-cholinergic (NANC) transmitters like ATP, nitric oxide (NO), serotonin, and neuropeptides
• Sympathetic postganglionic neurons in the adrenal glands differentiate to form neurosecretory chromaffin cells that release adrenaline into the bloodstream
• Parasympathetic stimulation causes bradycardia, reduced cardiac conduction velocity, bronchial contraction, increased intestinal mobility, bladder contraction, penile erection, and increased glandular secretion
• Sympathetic stimulation causes tachycardia, positive inotropy, arteriolar contraction, bronchiolar/intestinal/uterine relaxation, bladder sphincter contraction, radial muscle contraction, and increased glandular secretion
• Different organs/tissues/cells express different subtypes of adrenoceptors to coordinate appropriate responses to autonomic control
• The ANS is also modulated by sensory neurons monitoring blood levels of CO2, O2, nutrients, arterial pressure, and GI tract content and composition
• The enteric nervous system, a third division of the ANS, controls the gastrointestinal system independently of the CNS
• The Autonomic Nervous System (ANS) consists of two main divisions:

  • Parasympathetic division
  • Sympathetic division
• The ANS innervates peripheral tissues
• The pre-ganglionic neurons of the ANS are located in the central nervous system (CNS) and the post-ganglionic neurons are in the peripheral nervous system (PNS)
• Key neurotransmitters involved in the ANS are acetylcholine (ACh) and norepinephrine (NA)
• Cholinergic function can be manipulated by altering acetylcholine levels
• Cholinergic transmission involves the synthesis, release, and interaction of acetylcholine with receptors
• There are muscarinic ACh receptors and nicotinic ACh receptors in the ANS
• Drugs can selectively target muscarinic ACh receptors for therapeutic interventions
• Cholinergic drugs can have non-selective effects leading to unwanted side effects
• Adrenergic function in the ANS involves the release and interaction of noradrenaline with adrenoceptors
• Noradrenergic transmission includes synthesis, release, and re-uptake of noradrenaline
• Adrenoceptor pharmacology includes subtype-selective agonists and antagonists for clinical use
• Beta-2 adrenoceptor-selective agonists like salbutamol are used in asthma to reverse bronchoconstriction
• Alpha-1 adrenoceptor-selective antagonists and beta-1 adrenoceptor-selective antagonists are used to treat cardiovascular disorders like hypertension
• the anatomical divisions of brain stem and spinal chord are :

  M=cranial/medullary

  C=cervical

  T=thoracic

  L=lumbar

  S=sacral
• the sympathetic system originates in the thoracic and lumbar region of the spinal chord