Nervous System

Definition:

• The nervous system is vital to the human body as it controls all bodily functions and activities.
• It gathers information from the five senses.
• It analyzes the received information through stimuli and responds appropriately to maintain bodily balance and homeostasis.

Structures of the Nervous System:

• The Nervous System comprises three main components:

  • The Nerves
  • The Spinal Column
  • The Brain

Nerves or Neurons (Nerve Cells):

• Neurons are the fundamental structural and functional units of the nervous system.
• They consist of a cell body with dendrites and axons.
• Some axons are surrounded by a myelin sheath, composed of lipids and proteins, to enhance the speed of nerve impulses.
• Neurons communicate with each other at synapses through the release of neurotransmitters.
• Neuroglia are non-excitable cells that provide support and protection to neurons.

Unique Features of Nerves:

• Nerves are cylindrical bundles of fibers originating from the brain and central cord, extending throughout the entire body.
• Neurons transmit signals to other cells through thin fibers called axons, leading to the release of neurotransmitters at synapses.
• A synapse rapidly commands the target cell, with the entire communication process typically taking just a fraction of a millisecond.
• Signals can travel along an alpha motor neuron in the spinal cord at a remarkable speed of 268 mph (431 km/h), making it the fastest transmission in the human body.
• The average human brain contains over 100 trillion neural connections, although the number and location of these connections can vary.
• Notably, neurons lack the ability to regenerate once damaged or lost.

Types of Neurons:

• Sensory Neurons: Relay messages from the sensory organs to the brain via the spinal column.
• Motor Neurons: Relay messages from the brain and spinal column to the muscles or glands, resulting in muscle contractions or hormone secretion based on the impulses.
• Interneurons: Exclusively found in the central nervous system (CNS), they connect motor neurons to sensory neurons, facilitating the relay of messages between them.

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The spinal column

The Spinal or Vertebral Column - The vertebral column’s most important physiologic function is protecting the spinal cord, which is the main avenue for communication between the brain and the rest of the body.

Spine Nerves Anatomy, Diagram & Function | Body Maps

The vertebral column's most important physiologic function is protecting the spinal cord, which is the main avenue for communication between the brain and the rest of the body. The spinal cord is nestled in a cavity called the vertebral foramen inside of the vertebrae.

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The Brain

The human brain stands as the most intricate organ within our body. It serves as the center of consciousness and oversees both voluntary and involuntary movements and bodily functions. Through the nervous system, a complex network of channels transmitting electrochemical signals, the brain communicates with every part of the body, facilitating seamless coordination and control.

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Function of the Nervous System

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Relaying Messages

1. Messages are electrical signals called IMPULSES
2. Impulses travel in ONE direction
3. Messages are transmitted CHEMICALLY between two neurons – this space is the SYNAPSE
4. Axon terminals connect to Dendrites of the second Neuron to transmit impulses.

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Divisions of the Nervous System

Structurally, the nervous system has two components:

1. CNS - the Central Nervous System and
2. PNS - the Peripheral Nervous System.

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Central Nervous System

1. Consists of the brain and spinal cord Nucleus is a collection of nerve cell bodies Tract is a bundle of axons connecting neighboring or distant nuclei
2. Nerve cell bodies lie within the gray matter of the brain and spinal cord (H- shaped) Right and left dorsal and ventral horns
3. Fiber tracts constitute white matter in which the gray matter is embedded

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Peripheral Nervous System

1. Nerve fibers and cell bodies that lie outside the CNS but are continuous with it
2. Function to connect the CNS with peripheral structures (especially in the limbs)

SENSORY NERVOUS SYSTEM -

Afferent (sensory) fibers convey impulses from sense organs (e.g., eyes) and skin receptors to the CNS

MOTOR NERVOUS SYSTEM -

Efferent (motor) fibers convey impulses from the CNS to the muscles and glands The Motor Nervous System is further subdivided into –

1. Voluntary Nervous System
2. Involuntary Nervous System

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Central + Peripheral Nervous System

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The signal chain of Nerves Basic

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Signal chain of nerves complex

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Video

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