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A Brief Overview of the Nervous System and Its Functions

The nervous system is a complex network that controls and coordinates the various functions of the human body. It can be divided into two main parts: the central nervous system and the peripheral nervous system.1,2

Central Nervous System (CNS)

The CNS comprises the brain and the spinal cord. The brain is the command center of the nervous system. It controls thoughts, memory, emotions, and most bodily functions. The spinal cord is a long, thin bundle of nerves that extends from the brain down the back. It acts as a pathway for signals between the brain and the rest of the body.1,2 

Brain. The brain is a highly complex organ with various regions that control different functions in the body. These regions include the frontal lobe (associated with reasoning and planning), parietal lobe (responsible for sensory information), temporal lobe (involved in auditory processing and memory), and occipital lobe (center for visual processing), among others.

The brain is responsible for coordinating and regulating virtually all bodily activities. It processes sensory information, initiates motor responses, controls emotions, and houses cognitive functions, such as thinking, learning, and memory. The brain is protected by the skull, which provides a sturdy, bony enclosure; cerebrospinal fluid, which acts as a cushion; and three layers of protective tissue called meninges. The key components of the human brain include neurons, glial cells, cerebral cortex, white matter, gray matter, brain stem, cerebellum, hippocampus, thalamus, hypothalamus, and pituitary gland.

Neurons. Neurons—nerve cells that transmit signals through electrical and chemical impulses—are the fundamental building blocks of the brain. They consist of a cell body, dendrites (which receive signals from other neurons), and an axon (which transmits signals to other neurons). Neurons communicate with each other through synapses, which are tiny gaps between the axon of one neuron and the dendrites of another.

Glial cells. Glial cells, or neuroglia, are non-neuronal cells that provide support and protection to neurons. They help maintain the structural integrity of the nervous system, regulate the extracellular environment, and play a role in the immune defense of the brain.

Cerebral cortex. The cerebral cortex is the outermost layer of the brain and is responsible for higher cognitive functions, such as thinking, reasoning, language, and sensory perception. It is highly folded and convoluted, forming gyri (ridges) and sulci (grooves).

White matter and gray matter. The brain is divided into white matter and gray matter. Gray matter consists of cell bodies and is found on the outer layer of the cerebral cortex and in subcortical nuclei. White matter is composed of myelinated axons, forming the internal part of the brain. Myelin is a fatty substance that insulates and speeds up the transmission of nerve impulses.

Brain stem. The brain stem is the lower part of the brain that connects to the spinal cord. It includes the medulla oblongata, pons, and midbrain. The brain stem controls basic functions, such as breathing, heart rate, and digestion.

Cerebellum. The cerebellum is located at the back of the brain and is involved in the coordination of voluntary movements, balance, and posture.

Hippocampus. The hippocampus is a seahorse-shaped structure located within the temporal lobe and is involved in the formation of new memories and spatial navigation.

Thalamus. The thalamus acts as a relay station for sensory information, directing signals to the appropriate areas of the cerebral cortex.

Hypothalamus. The hypothalamus plays a crucial role in regulating functions such as body temperature, hunger, thirst, and the sleep-wake cycle. It also controls the release of hormones from the pituitary gland.

Pituitary gland. Although part of the endocrine system, the pituitary gland is closely connected to the brain. It releases hormones that regulate various bodily functions.

These components all work together to enable the intricate functions of the human brain, allowing for complex thought processes, emotions, and the coordination of bodily activities. The brain is an incredibly dynamic and adaptable organ, capable of reshaping itself in response to learning, experience, and environmental factors throughout life.1,2

Spinal cord. The human spinal cord is a cylindrical bundle of nerves that extends from the base of the brain (brainstem) down the vertebral column, enclosed and protected by the spinal column. Like the brain, the spinal cord is additionally protected by a layer of cerebrospinal fluid and layers of meninges. The spinal cord plays a crucial role in relaying information between the brain and the peripheral nerves, coordinating voluntary and involuntary movements, and facilitating reflex actions. Reflexes are quick, automatic responses to stimuli that don’t require conscious thought. For example, the knee-jerk reflex is an automatic response initiated by the spinal cord without input from the brain. The sensory and motor pathways within the spinal cord allow for rapid communication and response to stimuli without direct involvement of the brain. The spinal cord comprises various tissues and structures, including gray matter, white matter, nerve roots, spinal canal, and meninges.1,2

Gray matter. The central region of the spinal cord contains gray matter, which consists mainly of nerve cell bodies, dendrites, and unmyelinated axons. The gray matter is organized into butterfly-shaped structures known as the dorsal (posterior) and ventral (anterior) horns. These horns contain different types of neurons involved in sensory and motor functions.

White matter. Surrounding the gray matter, the spinal cord has white matter, which primarily consists of myelinated axons. The white matter is organized into ascending and descending tracts that carry sensory information to the brain (ascending) and motor commands from the brain to the body (descending).

Nerve roots. The spinal cord has pairs of spinal nerves that emerge from the spinal cord through openings between the vertebrae. Each spinal nerve has two roots: dorsal (posterior) roots and ventral (anterior) roots. Dorsal roots carry sensory information from the body to the spinal cord. The dorsal root ganglion, located just outside the spinal cord, contains cell bodies of sensory neurons. The ventral root contains motor neurons that send signals from the spinal cord to muscles and glands.

Spinal canal. The spinal cord runs through the spinal canal, a bony canal formed by the vertebrae of the spine. The spinal canal protects the delicate spinal cord from external damage.

Meninges. The spinal cord is surrounded and protected by three layers of membranes known as the meninges. These layers are the dura mater (outer layer), arachnoid mater (middle layer), and pia mater (inner layer). The meninges provide additional protection and support for the spinal cord.1,2

Peripheral Nervous System (PNS)

The PNS is a crucial component of the human nervous system, working in conjunction with the CNS. The PNS consists of nerves and ganglia (clusters of nerve cell bodies) that extend outside the CNS, connecting it to various parts of the body. The PNS is further divided into two main components: the somatic nervous system and the autonomic nervous system.

Somatic nervous system (SNS). This part of the PNS is responsible for voluntary movements and sensory information. The SNS allows us to interact with our environment on a conscious level. It enables conscious control over skeletal muscles, allowing us to perform activities such as walking, talking, and reaching. Cranial nerves arise from the brain and are responsible for functions such as facial movement, hearing, and vision. Spinal nerves emerge from the spinal cord and connect to specific regions of the body. They include sensory and motor fibers, which facilitate communication between the CNS and the rest of the body. Sensory neurons carry information from sensory receptors, such as the skin, eyes, and ears, to the CNS. Motor neurons transmit signals from the CNS to muscles, facilitating movement.1,2

Autonomic nervous system (ANS). The ANS regulates involuntary bodily functions, such as those of the heart, digestive system, respiratory system, and other bodily systems.

The ANS is further divided into the sympathetic and parasympathetic nervous systems. The sympathetic nervous system is activated during the “fight or flight” response, preparing the body for stressful situations by increasing heart rate, dilating pupils, and redirecting blood flow. The parasympathetic nervous system promotes a “rest and digest” state, slowing the heart rate, relaxing muscles, and enhancing digestion.1,2

Nutrition and the Nervous System

The human brain depends on glucose as its primary source of energy. Glucose metabolism is a critical and complex process that is closely involved in brain physiology and function, and a full description of its role in relation to the human nervous system is outside the scope of this article. However, in a nut shell, glucose metabolism supplies the energy needed for physiological brain functioning through the generation of adenosine triphosphate (ATP), a nucleic acid that serves as the foundation for neuronal and non-neuronal cellular maintenance and neurotransmitter production.3 However, a balanced intake of a variety of nutrients is important to proper nerve functioning, signal transmission, and overall neural health. Some key nutrients that support a healthy human nervous system include the following:4

Omega-3 fatty acids. Omega-3 fatty acids are found in fatty fish (e.g., salmon, mackerel), flaxseeds, and walnuts. They are essential for the structure and function of cell membranes, including those of nerve cells.

B Vitamins. B1 (thiamine) is found in whole grains, beans, and nuts, and is essential for nerve function and energy metabolism. B6 (pyridoxine) is present in poultry, fish, bananas, and potatoes and is important for neurotransmitter synthesis. B9 (folate) is abundant in leafy greens, legumes, and fortified grains and supports deoxyribonucleic acid (DNA) synthesis and repair in nerve cells. B12 (cobalamin) is found in animal products and is essential for nerve function and the production of myelin, a protective coating for nerves.

Vitamin D. Vitamin D is obtained through sunlight exposure, fatty fish, and fortified foods and supports nerve growth and function. Deficiency has been linked to neurological disorders. 

Antioxidants (vitamins C and E). Vitamin C is found in citrus fruits, berries, and vegetables and acts as an antioxidant, protecting nerve cells from oxidative stress. Vitamin E is present in nuts, seeds, and vegetable oils and protects cell membranes, including those of nerves, from damage.

Minerals. Calcium is found in dairy products, leafy greens, and fortified foods and is essential for nerve signal transmission and muscle contraction. Iron is found in red meat, poultry, fish, and plant sources, like lentils and spinach, and is Important for oxygen transport, and iron deficiency can lead to cognitive impairment. Magnesium is present in nuts, seeds, whole grains, and leafy greens and supports nerve function and relaxation of muscles. Zinc is found in meat, dairy, and legumes and is important for nerve signaling and neurotransmitter function. 

Protein. Protein is found in meat, dairy, eggs, and plant sources and is essential for the synthesis of neurotransmitters and the maintenance of the overall structure and function of nerve cells.

Amino acids. Tryptophan is found in protein sources, such as turkey, chicken, and dairy, and is a precursor to serotonin, a neurotransmitter involved in mood regulation. Tyrosine is present in protein-rich foods and is a precursor to dopamine, a neurotransmitter involved in motivation and pleasure.

A well-balanced and varied diet that includes these nutrients supports the health and function of the nervous system, contributing to optimal cognitive function and overall wellbeing. Always consult with a healthcare professional or a registered dietitian for personalized dietary advice.

Sources

  1. Thau L, Reddy V, Singh P. Anatomy: central nervous system. Last Update: 10 Oct 2022. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. https://www.ncbi.nlm.nih.gov/books/NBK542179/. Accessed 13 Nov 2023.
  2. Haines DE, Rudge P, Noback C. Human nervous system. Last update: 1 Apr 2023. Britannica website. https://www.britannica.com/science/human-nervous-system/Brainstem. Accessed 13 Nov 2023.
  3. Mergenthaler P, Lindauer U, Dienel GA, Meisel A. Sugar for the brain: the role of glucose in physiological and pathological brain function. Trends Neurosci. 2013;36(10):587–597. 
  4. Gibson GE, Blass JP. Nutrition and functional neurochemistry. In: Siegel GJ, Agranoff BW, Albers RW, et al (eds). Basic Neurochemistry: Molecular, Cellular and Medical Aspects. 6th edition. Philadelphia: Lippincott-Raven; 1999. https://www.ncbi.nlm.nih.gov/books/NBK28242/. Accessed 13 Nov 2023.  

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