Nervous System Overview

Study Notes

The nervous system is comprised of the central nervous system (CNS) and the peripheral nervous system (PNS).
The CNS comprises the brain and spinal cord, acting as the control center for bodily functions.
The PNS comprises nerves originating from the CNS, connecting it to the rest of the body.
The PNS further divides into the somatic nervous system, responsible for voluntary control of skeletal muscles, and the autonomic nervous system (ANS), controlling involuntary functions of organs and glands.

The ANS maintains homeostasis by responding to internal and external changes.
It comprises the sympathetic, parasympathetic, and enteric nervous systems.
The sympathetic nervous system is responsible for the fight-or-flight response, increasing alertness, metabolism, and physical activity.
The parasympathetic nervous system promotes the rest-and-digest state, conserving energy and maintaining normal bodily functions during rest.
The enteric nervous system controls gastrointestinal functions, regulating motility, secretion, and blood flow.

Ganglia are neuronal cell clusters found outside the CNS, acting as junctions between preganglionic (originating from the CNS) and postganglionic (innervating target organs) neurons.
Ganglia are categorized into sympathetic and parasympathetic, with further location-based classification:
- Lateral (paravertebral) ganglia: Located along the vertebral column, responsible for sympathetic pre- and postganglionic neuron synapse.
- Collateral ganglia: Located near major abdominal arteries, relaying preganglionic fibers for postganglionic neuron synapse.
- Terminal ganglia: Found on the effector organ wall, relaying parasympathetic preganglionic fibers to target tissues.

Relay station: Regulating autonomic nervous system function.
Distributing center: Divergence of signals, where each preganglionic fiber connects with multiple postganglionic neurons.

The sympathetic nervous system originates from the thoracolumbar region of the spinal cord (T1 to L2-L3).
It prepares the body for stressful situations, triggering a cascade of effects, including:
- Heart: Increases heart rate and contraction strength.
- Blood Vessels: Vasoconstriction in most blood vessels, increasing blood pressure.
- Lungs: Bronchodilation, increasing airflow.
- Metabolism: Glucose release from the liver for quick energy.
- Adrenal Glands: Epinephrine and norepinephrine secretion.
- Pupils: Dilation, enhancing vision.
- Digestive System: Inhibition of digestion and digestive functions.

The parasympathetic nervous system originates from the craniosacral region, involving cranial nerves and pelvic splanchnic nerves.
It promotes the "rest and digest" state, controlling various processes:
- Heart: Decreases heart rate and contraction strength.
- Blood Vessels: Vasodilation in specific areas.
- Lungs: Bronchoconstriction, decreasing airflow.
- Metabolism: Stimulates digestive activities and nutrient absorption.
- Glands: Stimulation of salivary, lacrimal, and digestive glands.
- Pupils: Constriction, reducing light intake.
- Digestive System: Stimulation of digestion and peristalsis, promoting gastrointestinal functions.

The enteric nervous system functions independently but is influenced by the sympathetic and parasympathetic divisions.
It regulates various gastrointestinal processes:
- Gastrointestinal Motility: Regulates peristalsis and segmentation.
- Secretion: Controls digestive enzyme, acid, and other substance secretion.
- Blood Flow: Regulates blood flow to the gut, ensuring nutrient absorption and waste removal.