Nervous System Overview

Introduction to the Nervous System

• The nervous system is the master controlling and communicating system of the body.
• It transmits impulses to every organ in the body controlling its activity.
• The nervous system is divided into the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

General Organization of the Nervous System

• Central Nervous System (CNS): Includes the brain and spinal cord.
• Peripheral Nervous System (PNS): Comprised of the somatic and autonomic nervous systems.
  • Somatic Nervous System: Controls voluntary movement; effector organ is skeletal muscle.
  • Autonomic Nervous System (ANS): Controls involuntary functions; effector organs are smooth muscle and glands. The ANS is further divided into the sympathetic and parasympathetic divisions.
    • Sympathetic Nervous System (SNS): "Fight or flight" response; activated during physical or psychological stress. Increased heart rate, blood pressure, and blood flow to the heart. The liver releases glucose. Pupils dilate and GI activity decreases.
    • Parasympathetic Nervous System (PNS): "Rest and digest" response; activated when a person is resting. Digestion, defecation, and diuresis are increased.

Overview of Structural and Functional Organization

• Central Nervous System (CNS): Composed of the brain and spinal cord.
• Afferent Division (Sensory): Carries signals towards the CNS. - Somatic sensory: Sensory information from skin, muscles, and joints. - Visceral sensory: Sensory information from organs. - Special sensory: Sensory information from the special senses (sight, smell, etc.).
• Efferent Division (Motor): Carries signals away from the CNS. - Somatic motor: Voluntary movement; involves motor neurons that stimulate skeletal muscle cells. - Autonomic motor: Involuntary control of organs; involves two-neuron chains. - Sympathetic: "Fight or flight"; preganglionic neurons release acetylcholine, postganglionic neurons release norepinephrine or epinephrine. - Parasympathetic: "Rest or digest"; preganglionic and postganglionic neurons release acetylcholine.

Divisions of the Peripheral Nervous System

• The peripheral nervous system is divided into somatic and autonomic divisions.
  • Somatic division: Controls voluntary movement using a single neuron. Skeletal muscles are the effector organ.
  • Autonomic division: Controls involuntary functions (smooth muscle, cardiac muscle, and glands) using two neurons. Sympathetic and parasympathetic divisions.

Somatic vs Autonomic Nervous System

• Somatic: Single neuron, innervates skeletal muscle, only leads to muscle excitation.
• Autonomic: Two neurons, innervates smooth and cardiac muscle, glands, etc., can be excitatory or inhibitory.

Autonomic Ganglia

• The ANS is composed of two neurons.
• Preganglionic neurons: The neurons that connect the CNS to a ganglion.
• Postganglionic neurons: The neurons that connect the ganglion to the effector organ (smooth muscle, cardiac muscle, or gland).
• The synapse between these two neurons is called an autonomic ganglion.

Types of Ganglia

• Sympathetic: Lateral ganglia, close to the spinal cord, and collateral ganglia in the abdominal cavity.
• Parasympathetic: Terminal ganglia, very close to the effector organs.

Neurotransmitters

• Neurotransmitters are chemicals used for neuronal communication.
• They bind to specific receptors to perform their action.

Neurotransmitters in ANS

• At ganglia: Acetylcholine (ACh) is the neurotransmitter for both sympathetic and parasympathetic divisions.
• Postganglionic Sympathetic: Norepinephrine (NE) or epinephrine (EPI)
• Postganglionic Parasympathetic: Acetylcholine (ACh)

Adrenergic Receptors

• Receptors in organs innervated by the sympathetic division.
• Activated by norepinephrine and epinephrine.

Cholinergic Receptors

• Receptors present in organs innervated by the parasympathetic division.
• Activated by acetylcholine.

Effects of Sympathetic and Parasympathetic Stimulation

• Summarizes the different effects of the sympathetic and parasympathetic nervous systems on various organs (e.g., heart rate, blood pressure, digestion).

Other Key Concepts

• Homeostasis: The dynamic balance between the sympathetic and parasympathetic branches.
• Fight or Flight: Physiological responses triggered by the sympathetic nervous system during stressful situations.
• Rest and Digest: The physiological responses triggered by the parasympathetic nervous system during relaxation.

This quiz covers the fundamental aspects of the nervous system, including its organization into the Central Nervous System and Peripheral Nervous System. It explores the roles of the somatic and autonomic nervous systems, as well as the sympathetic and parasympathetic divisions. Test your understanding of the master control system of the body!