Peripheral Nervous System (PNS) and Autonomic Nervous System

Overview of the Nervous System

• The Nervous System consists of:

  • Peripheral Nervous System (PNS):

  • Sensory division: Sends information to the CNS via afferent neurons.

  • Efferent division: Comprises autonomic and somatic nervous systems, carrying commands from the CNS to effector cells.

  • Central Nervous System (CNS): Composed of the brain and spinal cord, serving as the central integrating center.

Peripheral Nervous System (PNS)

• Efferent Division:

  • Somatic Nervous System:

  • Composed of sensory neurons (touch, pain, temperature, proprioception).

  • Motor neurons control skeletal muscles, primarily under voluntary control.

  • Autonomic Nervous System (ANS):

  • Uses sensory input from blood vessels, visceral organs, and muscles (interoceptors).

  • Regulates involuntary processes (smooth and cardiac muscle, glands).

  • Divided into:

    • Sympathetic Division: Activates fight-or-flight reactions.

    • Parasympathetic Division: Activates rest-and-digest responses.

Sympathetic vs Parasympathetic Division

• Sympathetic Division:

  • Known for "fight or flight" responses.

  • Mobilizes energy, increases heart rate, inhibits digestion, dilates bronchioles.

  • Preganglionic neurons originate from thoracolumbar regions (T1-L3).

• Parasympathetic Division:

  • Known for "rest and digest" functions.

  • Minimizes energy use, aids digestion, manages waste elimination.

  • Preganglionic neurons originate craniosacral (brain stem and sacral levels 2-4).

Neurotransmission

• Key Neurotransmitters:

  • Acetylcholine (ACh) used primarily in parasympathetic functions.

  • Norepinephrine (NE) used in sympathetic functions.

  • Sympathetic postganglionic neurons can be adrenergic using NE or epinephrine.

• Receptor Types:

  • Cholinergic Receptors: Bind ACh, include muscarinic and nicotinic types.

  • Adrenergic Receptors: Bind NE and epinephrine, with alpha (α) and beta (β) subtypes.

Comparison of Autonomic and Somatic Nervous Systems

• Effector Organs:

  • Somatic: Skeletal muscles (voluntary control).

  • Autonomic: Cardiac, smooth muscles, glands (involuntary control).

• Structure:

  • Somatic: Directly innervate muscles; single neuron path.

  • Autonomic: Two neuron chains (preganglionic and postganglionic).

Reflex Arcs and Control

• Components of Autonomic Reflex Arc:

  • Receptor → Sensory Neuron → Integrating Center → Motor Neuron → Effector.

• Control Centers:

  • Located in the hypothalamus, brain stem, and spinal cord, managing blood pressure, heart rate, digestion, and more.

Unique Features of the Autonomic Nervous System

• Sympathetic:

  • Controls adrenal medulla (epinephrine release), thermoregulation, and metabolic effects.

  • Longer-lasting and diffuse effects compared to parasympathetic.

• Parasympathetic:

  • Short-lived, localized effects due to rapid breakdown of ACh by acetylcholinesterase (AChE).

Disorders of the Autonomic Nervous System

• Conditions like Autonomic Dysreflexia and Raynaud's Phenomenon illustrate dysfunction in autonomic regulation, impacting vital bodily functions.

Contributions of the ANS to Various Body Systems

• Integrates functions across systems:

  • Cardiovascular: Regulates heart rate, blood pressure.

  • Endocrine: Influences hormone secretion from glands.

  • Respiratory: Adjusts airway diameter, respiration rate.

  • Digestive: Regulates digestion through enteric functions.

  • Reproductive: Controls various reproductive activities.

This study material is aimed at providing comprehensive notes on the organization and functionality of the Autonomic Nervous System (ANS) and its interactions with other body systems to maintain homeostasis.