Week 3

Autonomic Nervous System Overview

• Sympathetic effects activate "fight or flight" response; increases heart rate, bronchodilation, glycogenolysis, and sweating.
• Parasympathetic effects promote "rest and digest" response; decreases heart rate, promotes digestion, and conserves energy.

Neurotransmitter Functions

• Noradrenaline:

  • Released from presynaptic receptors; promotes heart activity and bronchodilation.
  • Causes pupil dilation and secretion reduction in some organs (α receptors).
  • Enhances glycogenolysis and renin secretion (β receptors).

• Acetylcholine:

  • Found in two main types of receptors: Nicotinic (muscle contraction) and Muscarinic (parasympathetic response).
  • Involved in many parasympathetic responses such as lacrimation and detrusor contraction.

Integration in the Nervous System

• Integration is the process of combining information for quick response generation.
• Neurons receive both excitatory and inhibitory inputs determining action potential generation.

Reflex Arcs

• Reflexes involve sensory neurons detecting stimuli, interneurons integrating information, and motor neurons reacting.
• The stretch reflex serves as a fundamental example.

Neurological Disorders and Neurotransmitters

• Conditions like depression, schizophrenia, and Parkinson’s are linked to neurotransmitter imbalances.
• Treatment often involves drugs modifying neurotransmitter activity, such as SSRIs, SNRIs, and MAOIs.

Receptor Types

• Adrenoceptors:

  • Types include α (constriction of blood vessels) and β (various effects including fat mobilization).
  • β3 found in fat cells, promoting fat mobilization.

• Cholinergic Receptors:

  • Nicotinic receptors involved in muscle contraction, while Muscarinic receptors mediate parasympathetic responses.

Stress and Pain Modulation

• Stress-induced analgesia involves endogenous opioids dampening pain signals during extreme stress.
• Pain perception is a complex interaction of sensory inputs and emotional responses.

Pharmacology and Neurotransmitter Interaction

• Targeting neurotransmitters for treatment must consider potential side effects due to shared pathways affecting various systems.
• Drug therapies aim to either block reuptake of neurotransmitters or inhibit their breakdown for prolonged effects.

Autonomic Receptors & Neurotransmitters

• Drugs targeting the autonomic nervous system manage blood flow and blood pressure.
• The sympathetic division affects blood vessel constriction and heart rate.
• During sympathetic activation, tissues receive less blood flow, redirecting it to vital organs.
• Adrenergic receptors can mediate both vasoconstriction and vasodilation depending on the receptor subtype and location.

Drug Actions on Autonomic Receptors

• Bronchodilation during an asthma attack can be treated using adrenergic agonists to activate β2-adrenergic receptors.
• Cholinergic agonists can relieve bronchoconstriction by increasing airway secretions.
• Adrenergic beta blockers can help to reduce blood pressure and manage cardiac arrhythmias by lowering heart rate.
• Adrenergic agonists, like decongestants, relieve nasal congestion through vasoconstriction.
• Epinephrine, an adrenergic agonist, counteracts anaphylaxis by reversing histamine-induced vasodilation and bronchoconstriction.

Case 1 – Sarin Gas Poisoning

• Sarin is an organophosphate and potent acetylcholinesterase inhibitor.
• Excess acetylcholine occurs due to inhibition of its breakdown, leading to overstimulation of receptors.
• Symptoms of poisoning include respiratory distress, muscle twitching, and excessive secretions.
• Respiratory failure is the likely cause of death following exposure to such poisons.

Case 2 – Arnold's Back Pain and Symptoms

• Arnold experiences severe lumbar pain, hard and tense muscles, and weak stretch reflexes.
• Pins and needles sensation indicates potential nerve compression or injury.
• An MRI would reveal abnormalities like herniated discs or spinal impingements.
• Identified abnormalities could compress spinal nerves leading to muscle weakness and sensory disturbances.
• Affected neurons include lower motor neurons, evident from reflex testing revealing weakness.

Integrating Information

• Neurons release only one specific neurotransmitter; effects depend on receptor interactions on the post-synaptic neuron.
• Diagram of synapse: Include structures such as presynaptic terminal, synaptic cleft, and postsynaptic membrane.
• Excitatory neurotransmitter release typically causes depolarization in the postsynaptic neuron.
• Inhibitory neurotransmitters can lead to hyperpolarization, decreasing neuronal firing likelihood.
• Simultaneous activation of excitatory and inhibitory inputs leads to integration of responses in the postsynaptic cell.
• Prolonged inhibition can dominate postsynaptic effects even if excitatory input is present briefly.

Moro Reflex

• Present until approximately 4-5 months of age.

Reflex Arc Activation

• First step involves the activation of a sensory receptor.
• Last step is the response of a muscle.

Reflex Types

• Touching a hot burner elicits a withdrawal reflex.
• The stretch reflex is crucial for regulating posture and involves sensory organs in the tendon.

Reflex Organization

• Simplest reflexes are organized at the level of the spinal cord.
• Reflexes maintain homeostasis by facilitating rapid organ or system adjustments.

Beta-2 Adrenergic Receptors

• Stimulation leads to relaxation of uterine smooth muscle.
• Clinical applications include treating bronchial asthma and potentially hypertension.

Effects of Increased Sympathetic Activity

• Results in vasoconstriction in gut vessels, leading to decreased blood flow to the gastrointestinal tract.

Muscarinic Receptors

• Blocking muscarinic receptors can reverse bradycardia.

Asthma Treatment Effects

• Activating beta receptors may cause increased blood flow to skeletal muscles if the drug enters the bloodstream.

Depression Treatment Strategies

• Potential treatments include adding drugs that cross the blood-brain barrier or increasing neurotransmitter levels at synapses.

Antihistamines and Sedation

• Non-sedating antihistamines reduce drowsiness by preventing passage through the blood-brain barrier.

Organophosphate Toxicity

• Inhibition of acetylcholinesterase leads to increased acetylcholine levels causing excessive parasympathetic stimulation, potentially resulting in dehydration and respiratory paralysis.

Analgesia Techniques

• Achieved by disrupting signaling in nociceptors, the spinal cord, or the brain.

Caution in Asthmatics

• Medications blocking beta-receptors should be used cautiously due to potential adverse effects on airways.

Transmitter Functions

• Acetylcholine is key for parasympathetic actions, memory formation, and muscle activation.

Parasympathetic Activity Effects

• Stimulation results in decreased heart rate, relaxation of the urinary bladder muscle, and vasodilation of skeletal muscle vessels.

Inhibitory Neurotransmitter

• Gamma-aminobutyric acid (GABA) is an essential inhibitory neurotransmitter in the brain.

Nicotinic Receptor Blockade Effects

• Blocking nicotinic receptors can cause skeletal muscle weakness and paralysis.

Beta-1 Receptors

• Activation leads to tachycardia and increased blood pressure.

Withdrawal Reflex

• Effector muscles help remove the body from the painful stimulus; involves multiple neurons and both stimulation and inhibition.

Reflex Testing and Neuron Function

• Reflex testing provides insights into the central nervous system, motor neurons, and sensory neurons involved in the reflex.
• Concurrent inhibitory and excitatory neurotransmitter activity affects the neuron in various ways; the outcome depends on the relative strength and duration of each signal.
• A positive Babinski sign in adults indicates potential damage to the corticospinal motor tract; the plantar reflex is normally negative in adults but positive in infants.

Spinal Reflex Arc

• The typical sequence for a simple spinal reflex arc is: receptor → afferent neuron → integration center → efferent neuron → effector.

Acetylcholinesterase Inhibitor Effects

• Symptoms of a cholinergic crisis due to acetylcholinesterase inhibitors include increased salivation, diarrhea, abdominal cramps, bronchoconstriction, and skeletal muscle paralysis.

Autonomic System Management

• Activating α receptors is beneficial for managing hypertension and nasal congestion.
• For a drug to cause pupillary dilation, increased blood pressure, urinary retention, and constipation, it must activate α1 receptors.
• To treat bradycardia effectively, a drug should activate beta-1 receptors or block muscarinic receptors to increase heart rate.

Explore the functions of the sympathetic and parasympathetic nervous systems with this quiz. Test your knowledge on how these systems influence heart rate, bronchial dilation, and other critical physiological responses. Dive into the intricate workings of autonomic regulation in the human body.