Nervous System

The human body contains a remarkable diversity of specialized cells, each adapted to perform unique functions. Parietal cells in the stomach produce stomach acid for digestion, while mast cells in the immune system release histamine crucial for inflammation. Skeletal muscle fibers are cylindrical with multiple nuclei and contain filaments essential for contraction. These structural differences highlight how various cell types are uniquely tailored to their roles within different systems.

The nervous system, a complex network responsible for communication within the body, is introduced with neurons as its key specialized cells. The structure of this system can be broadly divided into two main regions: central and peripheral components. This foundational overview sets up further exploration into specific cell types and processes like action potentials.

The nervous system is divided into the central nervous system (CNS) and peripheral nervous system (PNS). The CNS, comprising the brain and spinal cord, acts as a command center that processes sensory information. Meanwhile, the PNS includes nerves throughout the body that relay sensory data to the CNS. Together they enable motor responses or regulate bodily functions based on processed information.

The human brain, part of the central nervous system (CNS), is divided into three main regions: hindbrain, midbrain, and forebrain. The hindbrain includes the medulla (regulates breathing, blood pressure, heart rate), pons (coordinates signals to other brain areas), and cerebellum (controls balance and movement coordination). The midbrain handles alertness, sleep/wake cycles, motor activity; together with parts like the medulla and pons it forms what’s known as the "brainstem." Lastly in the forebrain lies structures such as cerebrum—responsible for speech, reasoning emotions—and thalamus/hypothalamus which manage sensory-motor info or endocrine control respectively.

The peripheral nervous system (PNS) is divided into the somatic nervous system (SNS) and autonomic nervous system (ANS). The SNS manages motor functions of skeletal muscles, including voluntary actions under conscious control and somatic reflexes. In contrast, the ANS regulates internal processes involving gastrointestinal, excretory, endocrine systems as well as smooth and cardiac muscle activities through autonomic reflexes.

The autonomic nervous system (ANS) is divided into sympathetic and parasympathetic systems, each with distinct roles. The sympathetic system triggers the fight or flight response during stress, increasing heart rate and breathing while suppressing non-essential functions like digestion. For example, facing a stressful situation such as malfunctioning machinery can activate this response to prioritize survival actions. Conversely, the parasympathetic system promotes rest and digest activities by slowing down heart rate and facilitating digestion when at ease. These two systems often have opposing effects on organs to maintain balance.

The nervous system comprises two primary cell types: neurons and glial cells. Neurons, found in both the central and peripheral systems, consist of a cell body housing the nucleus, dendrites for receiving signals, an axon to transmit signals away from the neuron, and synapses where communication with other cells occurs. Glial cells play essential roles beyond structural support; they regulate chemical balance between neurons for signaling efficiency, maintain the blood-brain barrier to protect neural tissue from harmful substances, produce myelin sheaths that insulate axons for signal transmission speed enhancement, generate cerebrospinal fluid crucial for brain protection and homeostasis maintenance while also performing critical immune functions within the nervous system.

Understanding Resting Potential in Neurons Neurons communicate by receiving signals at dendrites and transmitting them down the axon, a process enabled by action potentials. At rest, neurons maintain a resting potential of around -70 millivolts due to ion distribution: sodium (Na+) is concentrated outside while potassium (K+) resides inside. This negative internal charge is maintained through mechanisms like the sodium-potassium pump.

Mechanism and Characteristics of Action Potentials When stimulated, an action potential occurs as Na+ floods into the neuron via ion channels causing depolarization—making the interior more positive—which propagates along the axon. The signal resets behind it through processes involving specific channel activities such as refractory periods or undershoots. Myelinated neurons allow faster transmission with signals jumping between nodes of Ranvier; importantly, this phenomenon operates on an all-or-none principle where it either fully activates or doesn’t occur at all.

When an action potential reaches the axon terminals, it triggers synaptic vesicles to release neurotransmitters into the synapse. These chemical messengers can be derived from various substances like amino acids or gases such as nitric oxide. The released neurotransmitters travel across a small gap called the synaptic cleft and bind to specific receptors on the next neuron, facilitating communication between neurons.

The nervous system is divided into the peripheral (PNS) and central nervous systems (CNS), with the CNS comprising the brain and spinal cord. The PNS splits further into somatic (SNS) and autonomic systems, which include sympathetic and parasympathetic divisions. Key cell types in this system are glial cells and neurons; neurons communicate via action potentials that trigger neurotransmitter release at synapses to signal neighboring neurons. This intricate network continues to be a focus for research aimed at addressing neurological diseases, offering numerous career opportunities in neurology.