Nervous and Endocrine Systems: Structure and Function

Nervous System Structure

Spinal Cord Organization

The spinal cord is a central part of the nervous system, responsible for transmitting signals between the brain and the rest of the body. Its structure is divided into two main regions based on appearance and function.

• Grey Matter: The central region of the spinal cord, composed mainly of nerve cell bodies. This area appears grey due to the absence of myelin and is involved in processing and integrating information.

• White Matter: The outer region of the spinal cord, consisting primarily of axons covered with fatty myelin sheaths. This area appears white and is responsible for transmitting nerve impulses over long distances.

Example: Sensory information entering the spinal cord is processed in the grey matter before being relayed through the white matter to the brain.

Synapses

Synapses are specialized junctions between nerve cells (neurons) that enable communication within the nervous system. They play a crucial role in the transmission of nerve impulses.

• Definition: A synapse is a gap between two neurons, across which chemical messengers (neurotransmitters) are released.

• Function: Neurotransmitters diffuse across the synaptic gap and bind to receptors on the membrane of the receiving neuron, initiating a new nerve impulse.

• Scale: Each neuron can form thousands of synapses, resulting in an estimated 100 to 1000 trillion synapses in the human brain.

Example: The neurotransmitter acetylcholine is released at neuromuscular junctions to stimulate muscle contraction.

Chemical Coordination

Glands and Hormones

Chemical coordination in the body is achieved through glands that secrete substances, including hormones, which regulate various physiological processes.

• Gland: An organ that produces and releases a chemical substance.

• Exocrine Glands: Secrete their products through ducts to specific locations (e.g., sweat glands, salivary glands).

• Endocrine Glands: Release hormones directly into the bloodstream, allowing them to reach target organs throughout the body.

• Hormones: Chemical messengers that affect only tissues or organs with specific receptors for that hormone.

Example: The hormone insulin is secreted by the pancreas and acts on liver cells that possess insulin receptors to regulate blood glucose levels.

Major Endocrine Glands

The endocrine system consists of several glands that secrete hormones to regulate bodily functions.

• Pituitary Gland: Located at the base of the brain, it produces hormones such as antidiuretic hormone (ADH), which controls water balance in the kidneys, and hormones that regulate reproduction.

• Hypothalamus: A region of the brain situated above the pituitary gland, involved in controlling the release of pituitary hormones.

• Other Major Glands: Thyroid, pancreas, and others (see table below).

Example: The pituitary gland releases growth hormone, which stimulates growth and cell reproduction.

Comparison of Nervous and Endocrine Systems

The nervous and endocrine systems both coordinate body functions but differ in their mechanisms and effects. The following table summarizes their main differences:

Feature	Nervous System	Endocrine System
Type of Signal	Electrical impulses	Chemical messengers (hormones)
Speed of Response	Very rapid	Slower
Duration of Response	Usually short-lived	Usually longer-lasting
Area of Effect	Localized (specific tissues)	Can be widespread (if cells have correct receptors)

Example: Reflex actions are mediated by the nervous system for immediate response, while hormonal regulation of metabolism is slower and sustained.

Summary of Main Endocrine Glands

Gland	Location	Main Hormones	Function
Pituitary	Base of brain	ADH, growth hormone, reproductive hormones	Controls other glands, water balance, growth, reproduction
Thyroid	Neck	Thyroxine	Regulates metabolism
Pancreas	Abdomen	Insulin, glucagon	Regulates blood glucose
Additional info: Other glands include adrenal glands (stress response), ovaries/testes (sex hormones).

Additional info:

• The notes infer the presence of other major endocrine glands (adrenal, ovaries, testes) based on standard biology curriculum.

• Scientific names and terms (e.g., insulin, thyroxine) are italicized for clarity.