autonomic nervous system agents

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  • Autonomic Nervous System Agents Ma. Tosca Cybil A. Torres, RN, MAN
    • Central Nervous System(CNS)- the bodys primary nervous system which is composed of the brain and spinal cord.
    • Peripheral Nervous System(PNS)- located outside the brain and spinal cord.
      • Two divisions:
        • Autonomic
        • Somatic
    • After the interpretation of the CNS, the PNS receives stimuli and initiates responses to those stimuli
  • Nervous system
    • Autonomic Nervous system (ANS)
      • also called the visceral system- ---innervates (acts on) smooth muscles and glands
      • An involuntary nervous system
      • Functions: Control and regulation of the heart, respiratory system, GIT, bladder, eyes, and glands
      • Two sets of neurons:
        • Afferent (sensory) neurons - send impulses to the CNS, where they are interpreted
        • Efferent (motor) neurons - receive the impulses from the brain and transmit those impulse through the spinal cord to the effector organ cells
    • The efferent pathways in the ANS are divided into two branches:
    • 1. Sympathetic nervous system
      • Also known as the adrenergic system
      • Smooth muscle innervated by the neurotransmitter norepinephrine
        • Norepinephrine - released from the terminal nerve ending and stimulates the cell receptors to produce a response
    • 2. Parasympathetic nervous system
      • Also called the cholinergic system
      • Muscles innervated by the neurotransmitter acetylcholine
    • Acetylcholine (ACh) is a neurotransmitter substance that is found in both the CNS and in the PNS.
    • In the PNS, it is the NT released at synapses on skeletal muscles and is also found in the cell bodies of the autonomic nervous system.
    • In the brain, it appears to be involved in learning/memory, attention as well as sleeping and dreaming.
  • Body Tissue/Organ Sympathetic Response Parasympathetic Response Eye Dilates pupils Constricts pupils Lungs Dilates bronchioles Constricts bronchioles and increase secretions Heart Increases heart rate Decreases heart rate Blood vessels Constricts Dilates GI Relaxes smooth muscles of GIT Increases peristalsis Bladder Relaxes bladder muscle Constricts bladder Uterus Relaxes uterine muscles Salivary gland Increases salivation
  • Autonomic Nervous System: Sympathetic and Parasympathetic Sympathetic Stimulants Sympathomimetics ( adrenergics, adrenomimetics, or adrenergic agonists ) Parasympathetic Stimulants Direct-Acting Parasympathomimetics (cholinergics or cholinergic agonists) Action: Increase BP Increase PR Relax bronchioles Dilates pupils Relax uterine muscles Increase blood sugar Action: Decrease blood pressure Decrease pulse rate Constrict bronchioles Constrict pupils Increase urinary contraction Increase peristalsis Indirect-Acting Cholinesterase inhibitors (anticholinesterase) Action: Increase muscle tone Sympathetic Depressants Sympatholytics( adrenergic blockers, adrenolytics, or adrenergic antagonists ) Parasympathetic Depressants Parasympatholytics (anticholinergics, cholinergics antagonists, or antispasmodics) Action: Decrease PR Decrease BP Constrict Bronchioles Action: Increase PR Decrease mucous secretions Decrease GI motility Increase urinary retention Dilate pupils
  • Cholinergic Agents and Cholinergic Blocking Agents
  • Cholinergic Agents
  • Cholinergic Agents
    • Also called cholinomimetics, cholinergic stimulants, cholinergic agonists
    • Drugs that stimulate the parasympathetic nervous system (PSNS)
    • Mimic the effects of the PSNS neurotransmitter
    • Acetylcholine (ACh)
  • Cholinergic Receptors
    • Two types, determined by:
    • Location
    • Action once stimulated
    • Nicotinic receptors and Muscarinic receptors
  • Nicotinic Receptors
    • Located in the ganglia of both the PSNS and SNS
    • Affects the skeletal muscle
    • Named nicotinic because can be stimulated by the alkaloid nicotine
  • Nicotinic receptor sites
  • Muscle contraction
  • Muscarinic Receptors
    • Located postsynaptically:
      • Smooth muscle
      • Cardiac muscle
      • Glands of parasympathetic fibers
      • Effector organs of cholinergic sympathetic fibers
    • Named muscarinic because can be stimulated by the alkaloid muscarine
  • Cholinergic Agents: Mechanism of Action
    • Direct-acting (agonist)
      • Bind to cholinergic receptors, causing stimulation
      • Acts on the receptor sites to activate a tissue response
    • Direct-Acting Cholinergic Drugs
    • Ex:
    • bethanechol chloride(Urecholine)- used to increase urination
    • metoclopramide HCL(Plasil)- usually used to treat GERD---increases gastric emptying time
  • Cholinergic Agents: Mechanism of Action
    • Indirect-acting
      • Inhibit the enzyme cholinesterase (chE) (acetylcholinesterase)
      • Cholinesterase- destroys acetylcholine before it reaches the receptor or after it has attached to the receptor site
      • Result: more ACh is available
      • at the receptors
    • Indirect Acting cholinergic drugs
    • Ex:
    • demecarium bromide(Humorsol)-reduces IOP in glaucoma, long acting miotic
    • ambenonium Cl (Mytelase)- to increase muscle strength in MG, long acting
    • edrophonium Cl(Tensilon)- to diagnose MG, very short acting
  • Indirect-Acting Cholinergic Agents (Cholinesterase Inhibitors)
    • Reversible
      • Bind to cholinesterase for a period of minutes to hours
    • Irreversible
      • Bind to cholinesterase and form a permanent covalent bond
      • The body must make new cholinesterase
  • Drug Effects of Cholinergic Agents
    • Effects seen when the PSNS is stimulated.
    • The PSNS is the rest and digest system.
  • Drug Effects of Cholinergic Agents
    • SLUDGE
    • S alivation
    • L acrimation
    • U rinary incontinence
    • D iarrhea
    • G astrointestinal cramps
    • E mesis
  • Drug Effects of Cholinergic Agents
    • Stimulate intestine and bladder
      • Increased gastric secretions
      • Increased gastrointestinal motility
      • Increased urinary frequency
    • Stimulate pupil
      • Constriction (miosis)
      • Reduced intraocular pressure
    • Increased salivation and sweating
  • Drug Effects of Cholinergic Agents
    • Cardiovascular effects
      • Decreased heart rate
      • Vasodilation
    • Respiratory effects
      • Bronchial constriction, narrowed airways
  • Drug Effects of Cholinergic Agents
    • At recommended doses, the cholinergics primarily affect the MUSCARINIC receptors.
    • At high doses, cholinergics stimulate the NICOTINIC receptors.
  • Cholinergic Agents: Therapeutic Uses
    • Direct-Acting Agents
    • Reduce intraocular pressure
    • Useful for glaucoma and intraocular surgery
    • Examples: acetylcholine, carbachol, pilocarpine
    • -Topical application due to poor oral absorption