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BIOL5_Ch9_NervousSys_III (1)

Chapter 9: The Autonomic Nervous System

Overview

  • Autonomic Nervous System (ANS) manages physiology; primarily a motor system (efferent).

  • Regulates visceral activities: smooth muscle, cardiac muscle, and glands.

  • Functions without conscious control, regulated by brain centers (cerebral cortex, hypothalamus, medulla oblongata).

Anatomy Review

Structure of ANS

  • Comprised of two neurons; preganglionic neuron (from CNS) and postganglionic neuron (from autonomic ganglion).

  • Target tissues: smooth muscle, cardiac muscle, and glands.

Comparison with Peripheral Nervous System (PNS)

Central Nervous System (CNS) and Sensory Division

  • Sensory (Afferent) Division:

    • Somatic sensory: touch, pain, pressure, temperature.

    • Visceral sensory: stretch, pain, irritation in viscera; taste and smell.

Motor (Efferent) Division

  • Somatic motor: innervation of skeletal muscles.

  • Visceral motor: autonomic division—innervation of smooth muscle, cardiac muscle, and glands.

Divisions of the ANS

  • Sympathetic Division (Thoracolumbar):

    • Coordinates 'fight or flight' response.

    • Increases alertness and metabolism during emergencies; active during stress and exercise.

  • Parasympathetic Division (Craniosacral):

    • Coordinates 'rest and digest' response.

    • Slows down activities; active during rest and digestion (SLUDD effects: Salivation, Lacrimation, Urination, Digestion, Defecation).

Autonomic Neurons

  • Consist of preganglionic and postganglionic neurons.

  • First neuron has its cell body in the brain or spinal cord; synapses in an autonomic ganglion.

  • Postganglionic neuron extends to target tissue.

Neurotransmitters in ANS

Types of Neurons

  • Cholinergic Neurons: Release acetylcholine (ACh).

  • Adrenergic Neurons: Release norepinephrine (NE).

  • Effects of norepinephrine last longer than ACh due to slower breakdown by enzymes.

Synapses

  • Both sympathetic and parasympathetic preganglionic neurons release ACh.

  • Sympathetic postganglionic neurons predominantly release NE, but some (e.g., sweat glands) release ACh.

Receptors in the ANS

  • Cholinergic Receptors: Include nicotinic and muscarinic.

  • Adrenergic Receptors: Include alpha (α1, α2) and beta (β1, β2) receptors.

  • Example: Nicotinic receptors lead to muscle contraction; adrenergic receptors vary effects based on type (sympathetic/parasympathetic).

Control by Higher Brain Centers

  • Medulla Oblongata: Controls cardiovascular, pulmonary, and digestive systems.

  • Hypothalamus: Regulates temperature, hunger, thirst; influences medulla.

  • Limbic System: Links emotional states to visceral responses.

  • Cerebral Cortex & Cerebellum: Also influence ANS.

Disorders of the ANS

  • Autonomic Dysreflexia:

    • Common in individuals with spinal cord injury above T6.

    • Symptoms: mass stimulation of sympathetic nerves causes severe hypertension, risk of stroke or heart attack.

  • Raynaud Phenomenon:

    • Caused by excessive sympathetic stimulation; leads to vasoconstriction of digits.

    • Symptoms: digits appear white, can progress to cyanosis and necrosis if untreated.