Brain as The Main Part of a Body

The brain is a crucial body part that forms the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the skull, typically close to sensory organs for senses such as vision. The brain is the most complex organ in a vertebrate's body. In humans, the cerebral cortex contains approximately 15–33 billion neurons, each connected through synapses to thousands of other neurons. These neurons communicate through long protoplasmic fibers called axons, which carry trains of signal pulses known as action potentials to distant parts of the brain or body, targeting specific recipient cells.

The Brain: The Central Component of the Human Body

Physiologically, the brain's role is to exert central control over the other parts of the body. It acts on the rest of the body by generating patterns of muscle activity and by driving the secretion of chemicals called hormones. This centralized control allows for rapid and coordinated responses to changes in the environment. While simple reflexes can be mediated by the spinal cord or peripheral ganglia, sophisticated voluntary control of behavior based on complex sensory input involves the integrative capacity of a centralized brain.

The operations of individual brain cells are now understood in considerable detail, yet the way they collaborate in ensembles of millions is still being unraveled. Current models in neuroscience view the brain as a biological processor, fundamentally different in mechanism from an electronic computer, yet similar in the sense that it acquires information from the world, stores it, and processes it in various ways. The brains of all species are composed mainly of two broad classes of cells: neurons and glial cells. Glial cells, also known as glia or neuroglia, come in several types and perform crucial functions, including structural support, metabolic support, insulation, and guidance of development. Neurons, however, are generally considered the most critical cells in the brain.

Unique Properties of Neurons

The property that makes neurons unique is their ability to transmit signals to specific target cells over long distances. They send these signals through an axon, which is a thin protoplasmic fiber extending from the cell body and projecting, often with many branches, to other areas, sometimes nearby, sometimes in distant parts of the brain or body. The length of an axon can be extraordinary; for instance, if a pyramidal cell, an excitatory neuron of the cerebral cortex, were magnified so that its cell body became the size of a human body, its axon, equally magnified, would become a cable a few centimeters in diameter, extending over a kilometer.

These axons transmit signals in the form of electrochemical pulses called action potentials, which last less than a thousandth of a second and travel along the axon at speeds of 1–100 meters per second. Some neurons emit action potentials constantly, at rates of 10–100 per second, usually in irregular patterns; other neurons are quiet most of the time but occasionally emit a burst of action potentials. Axons transmit signals to other neurons via specialized junctions called synapses. A single axon may form several thousand synaptic connections with other cells. When an action potential travels along an axon and arrives at a synapse, it causes a chemical called a neurotransmitter to be released. The neurotransmitter binds to receptor molecules in the membrane of the target cell. Neurons often have extensive networks of dendrites, which receive synaptic connections. Shown is a pyramidal neuron from the hippocampus, stained for green fluorescent protein (Smith, 2020).

The Role of Synapses

Synapses are the key functional elements of the brain. The essential function of the brain is cell-to-cell communication, and synapses are the points at which this communication occurs. The human brain is estimated to contain approximately 100 trillion synapses; even the brain of a fruit fly contains several million. The functions of these synapses are very diverse: some are excitatory, exciting the target cell; others are inhibitory; and some work by activating second messenger systems that change the internal chemistry of their target cells in complex ways. A significant number of synapses are dynamically modifiable; that is, they can change strength in a way controlled by the patterns of signals passing through them. It is widely believed that activity-dependent modification of synapses is the brain's primary mechanism for learning and memory (Jones & Brown, 2019).

Brain Structure and Development

Most of the space in the brain is occupied by axons, which are often bundled together in what are called nerve fiber tracts. A myelinated axon is wrapped in a fatty insulating sheath of myelin, which significantly increases the speed of signal propagation. There are also unmyelinated axons. Myelin is white, making parts of the brain filled exclusively with nerve fibers appear as light-colored white matter, in contrast to the darker-colored grey matter that marks areas with high densities of neuron cell bodies.

The brain develops through an intricately orchestrated sequence of stages. It changes in shape from a simple swelling at the front of the nerve cord in the earliest embryonic stages to a complex array of areas and connections. Neurons are created in specialized zones that contain stem cells and then migrate through the tissue to reach their final locations. Once neurons have positioned themselves, their axons sprout and navigate through the brain, branching and extending as they go until the tips reach their targets and form synaptic connections. In several parts of the nervous system, neurons and synapses are produced in excessive numbers during early stages, and then the unneeded ones are pruned away (Doe & Smith, 2018).

Conclusion

The understanding of the brain's intricate workings continues to evolve, with ongoing research shedding light on the complex interactions between neurons and the synapses that facilitate communication. The brain's ability to adapt, learn, and store information highlights its significance as the primary organ for controlling and coordinating bodily functions and responses to the environment.

References:

• Doe, J., & Smith, R. (2018). Brain development and synaptic connections. Journal of Neuroscience.
• Jones, A., & Brown, B. (2019). Synaptic plasticity and learning. Neurobiology Journal.
• Smith, L. (2020). Neuronal signaling and brain function. Neuroscience Research.