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The Body & Its Systems

The human body is a complex and fascinating machine composed of interconnected systems that work together seamlessly to maintain life and support overall function. We'll start with an overview of these key systems, providing a glimpse into their individual roles and how they collaborate. Then, we'll delve deeper into the intricate world of the nervous system, the command center of the body, where Functional Neurological Disorder (FND) takes center stage.

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The Body's Systems

body systems

​Cardiovascular System:

  • Function: Transports blood, oxygen, nutrients, and hormones throughout the body, while also removing waste products.  

  • Key organs: Heart, blood vessels (arteries, veins, capillaries). 

 

Respiratory System:

  • Function: Responsible for gas exchange, taking in oxygen and expelling carbon dioxide.  

  • Key organs: Lungs, airways (trachea, bronchi).  

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Digestive System:

  • Function: Breaks down food into nutrients the body can absorb and use for energy, growth, and repair.  

  • Key organs: Mouth, esophagus, stomach, small intestine, large intestine, liver, pancreas, gallbladder.  

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Nervous System:

  • Function: Controls and coordinates bodily functions, both voluntary and involuntary, and transmits signals throughout the body.  

  • Key organs: Brain, spinal cord, nerves.  

 

Musculoskeletal System:

  • Function: Provides support, structure, and movement to the body.  

  • Key organs: Bones, muscles, joints, tendons, ligaments.  

 

Endocrine System:

  • Function: Produces and secretes hormones that regulate various bodily functions, such as growth, metabolism, and reproduction.  

  • Key organs: Pituitary gland, thyroid gland, adrenal glands, pancreas, ovaries, testes.

 

Urinary System:

  • Function: Filters waste products from the blood and eliminates them from the body as urine.  

  • Key organs: Kidneys, ureters, bladder, urethra.  

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Integumentary System:

  • Function: Protects the body from external damage, regulates temperature, and provides sensory input.

  • Key organs: Skin, hair, nails.  

 

Lymphatic System:

  • Function: Helps maintain fluid balance, defends against infection, and absorbs fats from the digestive system.

  • Key organs: Lymph nodes, lymph vessels, spleen, thymus.

 

Reproductive System:

  • Function: Enables reproduction and the production of sex hormones.  

  • Key organs:

    • Male: Testes, prostate gland, penis.

  • Female: Ovaries, fallopian tubes, uterus, vagina.

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These systems work interdependently, relying on each other to maintain overall health and well-being. For example, the respiratory system provides oxygen to the cardiovascular system, which then transports it to the rest of the body. The digestive system provides nutrients, and the urinary system removes waste products. The nervous system and endocrine system coordinate and regulate the functions of all the other systems.​

The Nervous System

nervous system

The nervous system is your body's command center. It is a complex network that can be divided into different branches based on structure and function. It's responsible for everything you think, feel, and do – from reading these words to taking a breath to feeling a touch.

Main Components:

  • Neurons: The fundamental units of the nervous system, specialized cells that transmit electrical and chemical signals. They allow communication between your brain, skin, organs, glands, and muscles, enabling you to move, feel sensations, and perform complex behaviors. Learn more about neurons here. 

  • Glial Cells: Support cells that provide essential functions for neurons, including making myelin (which insulates nerve fibers), modulating synapse formation and function, regulating blood flow and metabolism, and maintaining the proper chemical environment for neuronal signaling.

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Structural Divisions:

  • Central Nervous System (CNS):

    • Brain: The control center for the entire nervous system. It reads signals from your nerves to regulate how you think, move, and feel.​

    • Spinal Cord: A long bundle of nerves that extends from the brain down the back, transmitting signals between the brain and the peripheral nervous system.  

  • Peripheral Nervous System (PNS): The network of nerves that branch out from your spinal cord. It relays information from the CNS to the rest of your body.

    • Cranial Nerves: 12 pairs of nerves originating from the brain. Learn more about cranial nerves here.

    • Spinal Nerves: 31 pairs of nerves branching from the spinal cord.

 

Functional Divisions:

  • Sensory (Afferent) Division: Transmits sensory information from receptors throughout the body to the CNS. This includes information about touch, pain, temperature, sight, hearing, smell, taste, and body position.

  • Motor (Efferent) Division: Transmits signals from the CNS to muscles and glands, initiating actions and responses.

    • Somatic Nervous System (SNS): Guides your voluntary movements, like walking or reaching for an object.

    • Autonomic Nervous System (ANS): Regulates involuntary and automatic movements, such as heart rate, breathing, digestion, and glandular activity.

      • Sympathetic Nervous System: "Fight or flight" response, preparing the body for action in stressful situations.

      • Parasympathetic Nervous System: "Rest and digest" response, promoting relaxation and conserving energy.

  • Enteric Nervous System (ENS):

    • Often referred to as the "second brain," the ENS is embedded in the lining of the gastrointestinal system. 

Enteric Nervous System (ENS) 

ENS

The enteric nervous system (ENS) is often called our "second brain" and for good reason! It's an extensive network of neurons and glia embedded within the walls of the gastrointestinal tract, from the esophagus to the anus. It has a remarkable degree of autonomy, meaning it can control many aspects of digestion independently of the brain.  

Key Features of the ENS:

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  • Independent Operator: The ENS is unique in its ability to operate somewhat independently from your brain and central nervous system (CNS). It can gather information about conditions inside your GI tract, process that information locally, and generate a response without needing instructions from the brain. This autonomy is why it's called the "second brain."

  • Digestive Maestro: The ENS plays a vital role in controlling digestion, influencing every stage of the process:

    • Swallowing: Initiating the movement of food down the esophagus.

    • Enzyme Release: Triggering the release of enzymes that break down food into absorbable nutrients.

    • Blood Flow Control: Regulating blood flow to the digestive organs to aid in nutrient absorption.

    • Elimination: Controlling the movement of waste products through the intestines and their elimination from the body.

  • Neurotransmitter Powerhouse: The ENS utilizes a wide range of neurotransmitters, many of which are the same ones found in the brain. These chemical messengers allow the nerve cells within the ENS to communicate with each other and with other parts of the body. Some key neurotransmitters in the ENS include:

    • Serotonin: Plays a crucial role in regulating mood, sleep, and appetite. Interestingly, the majority of the body's serotonin is actually produced in the gut!

    • Dopamine: Involved in motivation, reward, and movement.

    • Norepinephrine: Important for alertness, focus, and the stress response.

  • Gut Feeling: The ENS is responsible for those "gut feelings" you experience, like the butterflies in your stomach when you're nervous or the instinct to "go with your gut" when making a decision. It sends signals to the brain that can influence your emotions and even your decision-making.

  • Key Connections:

    • Vagus Nerve: A crucial communication pathway between the ENS and the brain, allowing them to exchange information and influence each other.

    • ​Endocrine System: The ENS interacts with hormones that regulate hunger, fullness, and stress, further connecting digestion with your overall well-being.

    • Immune System: The ENS works closely with the immune system in the gut to respond to injury or disease, protecting your digestive health.

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The ENS and the GBA:

The gut-brain axis (GBA) is a complex system of communication involving the ENS, the central nervous system, and the endocrine (hormone) system. Here's how the ENS contributes:  

  • Sensing the Gut Environment: The ENS monitors the internal environment of the gut, detecting changes in nutrient levels, the presence of harmful substances, and the composition of the gut microbiome.  

  • Sending Signals to the Brain: It relays this information to the brain via the vagus nerve and other pathways, influencing brain function and behavior. 

  • Responding to Brain Signals: The ENS also receives signals from the brain, allowing the brain to influence gut function in response to stress, emotions, and other factors.

The Limbic System

The limbic system is a fascinating and complex network of structures nestled deep within the brain. Often referred to as the "emotional brain," it plays a central role in our behavioral and emotional responses, particularly those related to survival instincts. 

limbic system

Key Functions:

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  • Emotional Regulation: The limbic system is responsible for generating and processing a wide range of emotions, including fear, anger, happiness, and sadness. It helps us to recognize and respond appropriately to emotional cues in ourselves and others.  

  • Survival Instincts: This system is deeply involved in driving essential survival behaviors, such as:

    • Feeding: Motivating us to seek out food and water.  

    • Reproduction: Driving sexual behavior and ensuring the continuation of our species.  

    • Caring for Young: Promoting nurturing and protective behaviors towards offspring.  

    • Fight-or-Flight Response: Preparing the body to respond to threats by either fighting or fleeing.  

  • Motivation and Reward: The limbic system plays a crucial role in motivation, reward-seeking behavior, and the experience of pleasure. It helps us to learn from our experiences and repeat behaviors that lead to positive outcomes.  

  • Olfactory Processing: The sense of smell is closely linked to the limbic system, which is why certain scents can evoke strong emotional memories.  

  • Memory Formation: The limbic system, particularly the hippocampus, is essential for the formation of long-term memories, especially those with strong emotional content.  

 

Components of the Limbic System:

Due to the complex interconnectedness of the limbic system with other brain regions, there's some debate about its precise boundaries. However, key structures generally considered part of the limbic system include:

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  • Amygdala: Almond-shaped structures involved in processing emotions, particularly fear and aggression.  

  • Hippocampus: Seahorse-shaped structures crucial for forming new memories.  

  • Thalamus: A relay station for sensory information, including emotions.  

  • Hypothalamus: Regulates vital bodily functions and plays a role in emotional responses.  

  • Cingulate Gyrus: Involved in processing emotions and regulating behavior.  

  • Basal Ganglia: Contributes to motor control, habit formation, and reward processing.  

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