What Is Nervous System?

Definition

Nervous system is a complex system that refers to the network of specialized cells, tissues, and organs that coordinate and control the body's functions, as first described by Galen in the 2nd century.

How It Works

The nervous system operates through a combination of electrical and chemical signals, allowing it to transmit and process information. The neurons, which are the core components of the nervous system, have an average of 7,000 synapses per neuron (Koch, 1999), enabling them to communicate with each other and with other cells. This complex network of neurons and synapses allows the nervous system to control voluntary movements, such as walking and talking, as well as involuntary movements, such as breathing and heart rate.

The nervous system is divided into two main parts: the central nervous system (CNS), which consists of the brain and spinal cord, and the peripheral nervous system (PNS), which includes the nerves that connect the CNS to the rest of the body. The CNS processes information and sends signals to the PNS, which then transmits these signals to muscles and glands throughout the body. For example, the autonomic nervous system, a subset of the PNS, regulates the body's automatic functions, such as heart rate and blood pressure, with the sympathetic nervous system responsible for the "fight or flight" response and the parasympathetic nervous system responsible for the "rest and digest" response.

The nervous system also relies on neurotransmitters, such as dopamine and serotonin, to transmit signals between neurons. These neurotransmitters bind to specific receptors on the surface of neurons, triggering a response that can either excite or inhibit the neuron. The balance of these neurotransmitters is crucial for maintaining proper nervous system function, with imbalances contributing to conditions such as depression and anxiety. The blood-brain barrier, a specialized network of blood vessels that supplies the brain with oxygen and nutrients, also plays a critical role in maintaining the health of the nervous system, with approximately 100 billion neurons relying on it for survival (Boyd, 2018).

Key Components

• Sensory receptors: detect changes in the environment, such as light, sound, and touch, and transmit this information to the CNS, where it is processed and interpreted.
• Motor neurons: transmit signals from the CNS to muscles and glands, allowing for voluntary and involuntary movements.
• Neuroglia: provide support and protection for neurons, with approximately 10-50 neuroglia cells for every neuron (Azevedo, 2009).
• Synapses: the gaps between neurons where chemical signals are transmitted, with an estimated 100 trillion synapses in the human brain (Drachman, 2005).
• Myelin: a fatty substance that surrounds and insulates nerve fibers, allowing for faster transmission of electrical signals, with demyelination contributing to conditions such as multiple sclerosis.
• Cerebrospinal fluid: a clear fluid that surrounds the brain and spinal cord, providing cushioning and protection, with approximately 500 milliliters produced daily (Fishman, 1992).

Common Misconceptions

• Myth: The brain uses 10% of its capacity — Fact: This myth has been debunked, with the brain using almost all of its neurons and synapses, even when at rest (Raichle, 2006).
• Myth: Humans only have five senses — Fact: Humans have at least nine senses, including balance, proprioception, and nociception (Sherrington, 1906).
• Myth: The nervous system is fully formed at birth — Fact: The nervous system continues to develop and mature throughout childhood and adolescence, with significant changes in brain structure and function occurring during this time (Giedd, 1999).
• Myth: Nervous system function declines with age — Fact: While some decline in nervous system function is inevitable, many older adults remain cognitively and physically active, with lifestyle factors such as exercise and social engagement contributing to healthy aging (Colcombe, 2006).

In Practice

The nervous system plays a critical role in many real-world scenarios, such as the development of prosthetic limbs. For example, the Luke Arm, a prosthetic limb developed by the Defense Advanced Research Projects Agency (DARPA), uses electrodes to detect signals from the nervous system, allowing users to control the limb with precision and accuracy. This technology has the potential to revolutionize the field of prosthetics, with approximately 1.6 million Americans living with amputations (Ziegler-Graham, 2008). The development of such technologies relies on a deep understanding of the nervous system and its many complex components.