Drugs Affecting the Nervous System

Drugs Affecting the Nervous System

• Neurons: Basic units of the nervous system, act as message carriers. Three types:
  • Sensory: Carry impulses to the central nervous system (CNS).
  • Associative: Carry impulses between neurons.
  • Motor: Carry impulses away from the CNS.

Nervous System Function

• Direction of Message (Action Potential):

  • Dendrites: Receive & transmit impulses to the cell body.
  • Cell Body: Contains the nucleus, maintaining the cell's life.
  • Axon: Carries impulses away from the cell body to muscle cells, organs, or other nerves.
  • Myelin Sheath: Speeds impulse conduction.
  • Terminal End Fibres: Transmit the message to the synapse.

• Synapse: The space between neurons or a neuron and a muscle/gland. Neurotransmitters (NTs) carry the message across the synapse.

Physiology & Function

• Purpose of the Nervous System: To receive stimuli and transmit information to initiate an appropriate response.

• Components:

  • Central Nervous System (CNS): Brain and spinal cord.
  • Peripheral Nervous System (PNS):
    • Cranial Nerves: Originate from the brain.
    • Spinal Nerves: Originate from the spinal cord; include sensory and motor nerves (voluntary).
    • Somatic Nervous System (SoNS): Controls voluntary muscle responses.
    • Autonomic Nervous System (ANS): Controls involuntary responses (smooth and cardiac muscles, glands).
      • Sympathetic (SNS) and Parasympathetic (PSNS) divisions.

• CNS: Encased in meninges (3 layers), contains the cerebral spinal fluid (CSF) for cushioning and nourishment.

Peripheral Nervous System Info

• Cranial Nerves: How many? Sensory and motor functions.
• Spinal Nerves: Paired;
  • Dorsal: Sensory impulses from periphery.
  • Ventral: Motor impulses from the spinal cord to muscle, gland, or neuron.
• Sympathetic Nervous System: Sympathetic trunk between T1-T3.
  • Pathway: Neurotransmitter (NT) > ganglion (short) > next NT > effector organ/gland (long).
  • Key Neurotransmitters: Preganglionic - acetylcholine, Postganglionic - norepinephrine, epinephrine.
• Sympathetic Nervous System Continued: Fight/flight/freeze/fret response, including effects on eyes and lungs.
• Cranial/Sacral origins: pathway: NT > Ganglion (long) > Next NT > effector organ/gland (short). Key Neurotransmitter = Acetylcholine

Neurotransmitter Action and Drug Effects

• NTs and Receptor Effects: Neurotransmitters act on specific receptors, causing various effects in target tissues. Examples include effects on blood vessels, the heart, and the respiratory system.

• Drug Effects at Receptors: Drugs can act as agonists (mimicking natural neurotransmitters) or antagonists (blocking natural neurotransmitters) by binding to receptors. Effectiveness depends on drug affinity and receptor number.

  • Alpha 1 and 2 agonists → effects on skeletal/smooth muscle
  • Beta 1 and 2 agonists → effects on the heart
  • Dopaminergic agonists → effects on the coronary, renal, and mesenteric blood vessels.

Parasympathetic Nervous System

• Organization: Cranial-sacral origins. Pathway: NT > ganglion (long) > next NT > effector organ/gland (short).

• Key Neurotransmitter: Acetylcholine.

Drugs Affecting ANS

• Sympathomimetics (adrenergic drugs) - mimic effects of sympathetic NTs.
• Sympatholytics (adrenergic blocking drugs) - block sympathetic NTs
• Parasympathomimetics (cholinergic drugs) - mimic effects of parasympathetic NTs.
• Parasympatholytics (anti-cholinergic drugs) - block parasympathetic NTs

Specific Drugs and Their Uses/Effects

• Numerous specific drugs (e.g., epinephrine, norepinephrine, dopamine, acetylcholine, etc.) and their effects are discussed in detail.

Adverse Side Effects

• Adrenergics/ Sympathomimetics: Tachycardia, hypertension, nervousness, cardiac arrhythmia, and pulmonary edema.
• Adrenergic Blocking/ Sympatholytics: Bradycardia, hypotension, worsening heart failure, and bronchoconstriction.
• Parasympathomimetics: Bradycardia, hypotension, heart block, lacrimation, diarrhea, vomiting, increased GI activity, and intestinal rupture.
• Parasympatholytics: Drowsiness, disorientation, tachycardia, photophobia, constipation, anxiety, and burning at injection site.

CNS Drug Classes

• Anticonvulsants (AEDs): Reduce seizure frequency and severity.

  • Phenobarbital: Drug blood levels monitored regularly.
  • Diazepam: Short acting; used for status epilepticus.

• Tranquilizers, Sedatives, & Anti-anxiety: Effects involve sedation, anti-emetic action, or reduced excitation in animals.

• Stimulants: Primarily used for respiratory depression/arrest (e.g., Doxapram)

• Euthanasia Agents: Controlled drugs that induce unconsciousness and cessation of vital functions (e.g., pentobarbital).

Additional Information

• Bethanechol, pilocarpine, atropine, glycopyrrolate, and other drugs and their uses for different conditions.
• Drug interactions, dosages, and monitoring.
• Different types of nervous system drugs are mentioned, with cautions/warnings on some.