Presented by the Anatomy & Physiology Club  

Why the Nervous System? 

Have you ever wondered what controls and coordinates how we move our legs, blink our eyes, and respond to someone’s questions? Have you ever wondered about the purpose of the billions of nerve cells in our bodies? The nervous system, a complex and beautiful system within each of our bodies and in the bodies of all vertebrates, provides all the answers. 

Neuron Structure & Function 

Neurons consist of three essential components: the axon terminal, dendrites, and the cell body.  

The axon terminal serves as the conduit for electrical signals, facilitating their transmission to other neurons within the intricate neural network. This specialized region also features nodes of Ranvier and myelin sheaths, which play a crucial role in accelerating the propagation of electrical signals along the axon terminal. 

  Dendrites, on the other hand, function as the primary receivers of signals from neighboring neurons, acting as messengers that convey information to the cell body. Within the neuron’s cell body, intricate processing occurs, and it assumes the responsibility of regulating the operations of both the dendrites and the axon terminal, further contributing to the complex interplay of neural communication.  

Glial cells, or glia or neuroglia, are cells in the nervous system that provide physical and chemical support to neurons, nervous cells, and maintain an optimal environment for their function and survival. Glia is a classification of the variety of cells that provide specialized functions to support neurons. The following is a collection of the major glial cells in our nervous system:  

• Astrocytes: support neurons with nutrition such as cellular fuel, aid in the repair and regeneration of neurons, and can release and take up neurotransmitters. Astrocytes contribute to the blood-brain barrier, a semipermeable border that shields the brain from toxic substances within the blood, supplies proper nutrients to the brain, tissues, and filters waste and harmful compounds in the brain back into the bloodstream. 

• Oligodendrocytes: attach to the neurons in the central nervous system (brain and spinal cord) and produce an insulating membrane and myelin that wrap the neuron’s axons, allowing the axons to conduct signals faster.  
• Schwann Cells: perform similar functions as the oligodendrocytes, but these cells wrap around neurons of the peripheral nervous systems – neurons that are outside of the central nervous system (away from the brain and the spinal cord)  
• Microglia: phagocytic cells that ingest and breakdown waste products and pathogens in the CNS and carry out associated immune functions to protect the neurons  

Central & Peripheral Nervous System 

The nervous system consists of two parts: the central nervous system which connects the brain and the spinal cord, and the peripheral nervous system, which transmits information between the body’s tissues and the central nervous system.  

The somatic nervous system is a subdivision of the peripheral nervous system, a system consisting of nerves running throughout the body. The somatic nervous system consists largely of voluntary actions, allowing one to move and control their own muscles.  

The Autonomic Nervous System (ANS) is made up of two main branches, the sympathetic and parasympathetic nervous systems. The sympathetic system is the “fight or flight” response, activating in stressful situations to increase heart rate and alertness. The parasympathetic system, often called the “rest and digest” mode, promotes relaxation and recovery, slowing heart rate and aiding in digestion. These two systems maintain the body’s equilibrium by responding to different environmental cues. 

The Brain 

The brain can be divided into three main divisions: the forebrain, the midbrain, and the hindbrain. 

The forebrain consists of the cerebral cortex, the thalamus, and the hypothalamus. The cerebrum is responsible for complex cognitive functions, including conscious thought and voluntary movement. It makes up the largest portion of the human brain and consists of two hemispheres: the left hemisphere and the right hemisphere. Both hemispheres can be divided into four lobes, each with different cognitive functions. The frontal lobe is associated with problem-solving, motor control, and personality. The parietal lobe processes sensory information and spatial awareness. The temporal lobe has a major role in processing auditory information and memory formation. Finally, the occipital lobe is responsible for processing visual information. 

The Thalamus serves as a relay station for processing different information from the senses in the cerebral cortex. It is also involved in the limbic system, the circuits in the brain that control and connect emotions, memory, and motivation. The hypothalamus is part of the endocrine system and regulates physiological processes like body temperature. 

The midbrain is at the center of the brain, containing structures involved in the processing and response to sensory stimuli and associated with reflexes and sleep-wake cycles. 

The hindbrain consists of the medulla oblongata, the pons, and the cerebellum. These three structures are all involved in regulating basic bodily functions such as breathing, heart rate, and sleep. They also coordinate movements and are associated with some cognitive functions related to learning and memory. 

Neural Diseases & Drugs  

Neural diseases encompass a spectrum of disorders affecting both the central and peripheral nervous systems, giving rise to conditions such as epilepsy, learning disabilities, neuromuscular disorders, autism, strokes, brain tumors, and cerebral palsy. These ailments have multifaceted causes, including bacterial infections, immune responses to infections, genetic disorders, brain injuries, and unhealthy lifestyles. 

Among the types of strokes, three stand out: ischemic stroke, hemorrhagic stroke, and transient ischemic attack. Ischemic stroke transpires when blood flow to the brain is interrupted, depriving brain tissue of vital oxygen and nutrients, resulting in damage to brain cells. This interruption occurs through two primary mechanisms: cerebral thrombosis, wherein a blood clot forms at the site of fatty deposits, obstructing blood flow, and cerebral embolism, which transpires when a portion of an existing blood clot dislodges and becomes lodged within a brain vessel. In the contemporary world, approximately 15 million individuals endure strokes globally, with 5 million succumbing to this condition. 

In the realm of pharmaceuticals, drugs are categorized as agonists and antagonists, each eliciting distinct impacts on our nervous system. These effects encompass a range of consequences. In the central nervous system, drugs can precipitate a decline in cognitive functions, including memory and decision-making. Moreover, they have the potential to influence neurotransmitter activity, thereby altering mood and emotions, sometimes resulting in anxiety and depression. In the peripheral nervous system, drug use can lead to nerve damage, manifesting as numbness in various body parts and weakened muscles. Additionally, drugs can interfere with the Autonomic Nervous System (ANS), which regulates critical functions like blood pressure, digestion, and heart rate. For instance, opioids may trigger abnormally fast heart rates and elevated blood pressure. Notably, a long-term consequence of drug use is increased tolerance, necessitating higher drug consumption to achieve the same desired effect and potentially leading to severe addiction. Recognizing a problem and seeking professional help are essential steps in addressing drug-related challenges. 

Citations:  

Most Common Neurological Disorders. Centro Medico abc, 15 July 2020, centromedicoabc.com/en/digital-magazine/most-common-neurological-disorders/#:~:text=Some%20of%20the%20most%20common,and%20disorders%20caused%20by%20malnutrition. Accessed 8 Oct. 2023. 

“Neurological Disorders.” Montana, dphhs.mt.gov/schoolhealth/chronichealth/neurologicaldisorders#:~:text=Neurological%20disabilities%20include%20a%20wide,are%20congenital%2C%20emerging%20before%20birth. Accessed 9 Oct. 2023. 

“What Causes Stroke.” Think Ahead, www.think-ahead.org.uk/what-causes-stroke?gclid=Cj0KCQjw4bipBhCyARIsAFsieCwWofyZlM6j_EvVM1HmaQD-kPvb1ssdoqFErIwD6r4OFoHVOyw-oEQaAtbdEALw_wcB. Accessed 6 Oct. 2023. 

Rye, Connie, et al. “35.1 Neurons and Glial Cells – Biology | OpenStax.” Openstax.org, OpenStax, 2016, openstax.org/books/biology/pages/35-1-neurons-and-glial-cells. Accessed 27 Sept. 2023.  

Stangor, Charles, and Jennifer Walinga. “4.2 Our Brains Control Our Thoughts, Feelings, and Behaviour.” Opentextbc.ca, BCcampus, 17 Oct. 2014, opentextbc.ca/introductiontopsychology/chapter/3-2-our-brains-control-our-thou ghts-feelings-and-behavior/. Accessed 1 Oct. 2023.  

Clinic, Cleveland. “Neurotransmitters: What They Are, Functions & Types.” Cleveland Clinic, 2022, my.clevelandclinic.org/health/articles/22513-neurotransmitters. Accessed 27 Sept. 2023.