automatic nervous system werk

Target Organs and Exceptions

  • Introduction to exceptions in the sympathetic division concerning target organs.

    • Target Organs: Sweat glands, blood vessels, and skeletal muscles.

    • In the sympathetic division, postganglionic neurons mainly release norepinephrine.

    • Exception: In sweat glands and blood vessels of skeletal muscle, postganglionic neurons release acetylcholine instead of norepinephrine.

Receptors

  • Muscarinic Receptors: Present in sweat glands and blood vessels, and located in skeletal muscle.

    • These receptors bind to acetylcholine.

    • Muscarinic receptors are categorized based on their sensitivity to

    • Toxin: Muscarine (a toxic compound derived from mushrooms).

  • Cholinergic Receptors: Two main types include nicotinic and muscarinic.

    • Nicotinic Receptors:

    • A category of cholinergic receptors that respond to nicotine.

    • Found in all ganglionic neurons and adrenal medulla.

    • When acetylcholine binds, it increases sodium influx leading to an excitatory postsynaptic potential.

      • Example: Neuromuscular junction physiology.

    • Muscarinic Receptors:

    • Found in all target membranes in the parasympathetic division.

    • Functions:

      • Different effects based on binding. They can either stimulate or inhibit functions in the body.

      • Example: Binding in GI tract enhances motility (stimulation). In cardiac muscle, it decreases heart rate (inhibition).

Norepinephrine and Adrenergic Receptors

  • Norepinephrine: A catecholamine.

    • Equally Related Catecholamines: Includes epinephrine.

    • Adrenergic Receptors: Main types include alpha and beta receptors.

    • Alpha Receptors:

    • Generally stimulated by norepinephrine.

    • Alpha 1: Stimulatory (various localizations).

    • Alpha 2: Primarily inhibitory.

    • Beta Receptors:

    • Can be both stimulatory or inhibitory.

    • Beta 1: Mainly stimulatory.

    • Beta 2: Primarily inhibitory.

    • Beta 3: Can be both.

Referred Pain

  • Definition and explanation of referred pain.

    • Concept: Strong visceral sensations perceived in unexpected areas due to neural pathways.

    • Example: Heart pain felt in the left shoulder and arm (especially in males).

    • Mechanism: Visceral sensory fibers and somatosensory fibers synapse at the same spinal cord level, causing misinterpretation by the brain.

Dual Innervation and Autonomic Control

  • Dual Innervation: The interaction between sympathetic and parasympathetic nervous systems maintaining homeostasis.

    • Example: Control of pupillary size.

    • Sympathetic pathway:

      • Preganglionic neuron stimulates the cervical vertebrae; postganglionic neurons release norepinephrine to dilate pupils.

    • Parasympathetic pathway:

      • Preganglionic neurons stimulate ganglions in the brainstem that release acetylcholine, causing pupil constriction.

Autonomic Tone

  • Definition: The balance of sympathetic and parasympathetic activity in organ systems.

    • No system is entirely dominant; both work together to maintain homeostasis.

    • Organ System Example:

    • Heart: Considered to have parasympathetic tone (resting heart rate lowers from intrinsic rate of 100 bpm to around 60 bpm).

    • Blood Pressure:

      • Regulated by sympathetic tone via smooth muscle contraction in blood vessels (maintained near 120/80 mmHg).

      • No significant input from the parasympathetic division in this case.

Central Control of the Autonomic Nervous System

  • The autonomic nervous system is influenced by various brain regions including:

    • Cerebrum: Affects conscious activities and responses; stress response aids preparedness.

    • Hypothalamus: Central hub for autonomic and endocrine function integration.

    • Amygdala: Regulates emotional states and triggers the sympathetic "fight or flight" response.

    • Hippocampus: Involved in learning and memory.

  • The Brainstem: Controls reflex changes (heart rate, blood pressure, digestion); has nuclei for autonomic reflexes.

  • Spinal Cord: Involvement in autonomic responses such as urination and defecation; these can be influenced by higher brain centers (e.g., cerebrum for inhibition).

Conclusion

  • The autonomous interactions of the two divisions, sympathetic and parasympathetic, play crucial roles in maintaining homeostasis and responding to changes in internal and external environments.