Journal of Clinical & Experimental Neuroimmunology
Open Access

What is the peripheral nervous system?

The peripheral nervous system consists of all the nerves that lie outside the brain and spinal cord, collectively known as the central nervous system (CNS). The PNS acts as a communication highway, relaying information from the CNS to the rest of the body and vice versa. It is responsible for receiving sensory inputs, controlling voluntary muscle movements, and managing involuntary functions such as heart rate and digestion.

The PNS is divided into two major subsystems:

• Somatic nervous system (SNS): This system is responsible for controlling voluntary movements and relaying sensory information to the brain. It connects to skeletal muscles, allowing us to perform activities like walking, talking, and picking up objects.
• Autonomic nervous system (ANS): This system regulates involuntary functions such as heart rate, blood pressure, digestion, and respiratory rate. The autonomic nervous system is further divided into two branches:
• Sympathetic nervous system (SNS): Known as the "fight or flight" system, it prepares the body to respond to stressful or dangerous situations.
• Parasympathetic nervous system (PNS): Often referred to as the "rest and digest" system, it helps the body conserve energy and perform routine maintenance activities.

Key functions of the peripheral nervous system

The peripheral nervous system’s broad range of functions makes it critical to nearly every aspect of our physical well-being. Here’s how it works in various areas of the body:

• Sensory input

The PNS enables us to sense the world around us. Through sensory nerves, it gathers information from receptors in the skin, muscles, and organs [1-3]. These signals are sent to the CNS, where they are processed, allowing us to feel touch, pain, temperature, and more. For instance, when you touch a hot surface, sensory neurons in your skin send a message through the PNS to your spinal cord and brain, triggering the immediate reflex to pull your hand away.

• Motor control

The motor neurons of the PNS transmit signals from the CNS to skeletal muscles, controlling voluntary movement. This process allows us to perform complex physical tasks such as running, typing, or playing a musical instrument. Each movement we make is a result of intricate communication between motor neurons and muscle fibers.

• Involuntary functions

While the somatic nervous system governs voluntary movements, the autonomic nervous system (a part of the PNS) oversees involuntary activities like heart rate, digestion, and respiratory function. The sympathetic and parasympathetic systems work together to maintain homeostasis, ensuring the body responds appropriately to various conditions. For instance, during exercise, the sympathetic system increases heart rate and respiration, while the parasympathetic system works to slow these functions down afterward.

• Homeostasis and Balance

The PNS is key in maintaining the body’s internal equilibrium, known as homeostasis. Through a delicate balance between the sympathetic and parasympathetic systems, the PNS helps regulate blood pressure, body temperature, and metabolic processes, allowing us to adapt to changing environments or stressors without conscious thought.

The importance of the peripheral nervous system in health

Given its role in movement, sensation, and essential bodily functions, the peripheral nervous system is integral to our overall health [4-6]. However, damage to the PNS can lead to a range of disorders and complications.

Common PNS disorders

Peripheral neuropathy: This is a condition where nerves in the PNS are damaged, often causing symptoms like numbness, tingling, and weakness, especially in the hands and feet. It can result from diabetes, infections, traumatic injuries, or even exposure to toxins.

Guillain-barré syndrome: This is a rare autoimmune disorder where the body’s immune system attacks the PNS, leading to muscle weakness and, in severe cases, paralysis. Early diagnosis and treatment are crucial for recovery.

Nerve compression syndromes: Conditions like carpal tunnel syndrome occur when peripheral nerves are compressed, leading to pain, numbness, and limited mobility. These can be caused by repetitive motions, injury, or inflammation.

Nerve regeneration and healing

Unlike the central nervous system, where nerve damage is often permanent, the peripheral nervous system has a limited ability to regenerate after injury. Peripheral nerves can sometimes regrow if the damage isn’t too severe, particularly if the nerve fibers are still intact. This regenerative capacity offers hope for recovery in certain injuries, but it remains a challenging process that can take months or even years.

Conclusion

While the brain and spinal cord often take center stage in discussions about the nervous system, the peripheral nervous system is equally vital to our survival and daily functioning. It allows us to move, sense, and perform both voluntary and involuntary actions. Its role in maintaining homeostasis keeps our bodies functioning smoothly under various conditions [7-9]. Damage to the PNS can have profound effects, leading to sensory loss, impaired movement, and disruptions in essential bodily functions. Therefore, understanding the PNS’s structure, functions, and the potential risks to its health is crucial for maintaining overall well-being and preventing long-term complications. In essence, the peripheral nervous system is the body's unsung hero, operating behind the scenes to ensure that life continues seamlessly beyond the brain.

1. Robine J M, Paccaud F (2005)Nonagenarians and centenarians in Switzerland, 1860–2001: a demographic analysis. J Epidemiol Community Health 59: 31–37.

Google Scholar, Crossref, Indexed at

2. Ankri J, Poupard M (2003)Prevalence and incidence of dementia among the very old. Review of the literature. Rev Epidemiol Sante Publique 51: 349–360.

Google Scholar, Indexed at

3. Wilkinson TJ, Sainsbury R (1998)The association between mortality, morbidity and age in New Zealand’s oldest old. Int J Aging Hum Dev 46: 333–343.

Google Scholar, Crossref, Indexed at

4. Miles TP, Bernard MA (1992)Morbidity, disability, and health status of black American elderly: a new look at the oldest-old. J Am Geriatr Soc 40: 1047–1054.

Google Scholar, Crossref, Indexed at

5. Gueresi P, Troiano L, Minicuci N, Bonafé M, Pini G, et al. (2003)The MALVA (MAntova LongeVA) study: an investigation on people 98 years of age and over in a province of Northern Italy. Exp Gerontol 38: 1189–1197.

Google Scholar, Crossref, Indexed at

6. Nybo H, Petersen HC, Gaist D, Jeune B, Andersen K, et al. (2003)Predictors of mortality in 2,249 nonagenarians—the Danish 1905-Cohort Survey. J Am Geriatr Soc 51: 1365–1373.

Google Scholar, Crossref, Indexed at

7. Silver MH, Newell K, Brady C, Hedley-White ET, Perls TT (2002)Distinguishing between neurodegenerative disease and disease-free aging: correlating neuropsychological evaluations and neuropathological studies in centenarians. Psychosom Med 64: 493–501.

Google Scholar, Crossref, Indexed at

8. Stek ML, Gussekloo J, Beekman ATF, Van Tilburg W, Westendorp RGJ (2004)Prevalence, correlates and recognition of depression in the oldest old: the Leiden 85-plus study. J Affect Disord 78: 193–200.

Google Scholar, Crossref, Indexed at

9. von Heideken Wågert P, Rönnmark B, Rosendahl E, Lundin-Olsson L, M C Gustavsson J, et al. (2005)Morale in the oldest old: the Umeå 85+ study. Age Ageing 34: 249–255.

Google Scholar, Crossref, Indexed at