The Brain: A Complex Organ That Controls The Nervous System
The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a vertebrate’s body. In a human, the cerebral cortex contains approximately 14â16 billion neurons, and the estimated number of neurons in the cerebellum is 55â70 billion. Each neuron is connected by synapses to several thousand other neurons. These neurons typically communicate with one another by means of long fibers called axons, which carry trains of signal pulses called action potentials to distant parts of the brain or body targeting specific recipient cells.
The brain integrates sensory information and directs motor responses; in higher vertebrates it is also the centre of learning. The human brain weighs approximately 1.4 kg (3 pounds) and is made up of billions of cells called neurons. Junctions between neurons, known as synapses, enable electrical and chemical messages to be transmitted from one neuron to the next in the brain, a process that underlies basic sensory functions and that is critical to learning, memory and thought formation, and other cognitive activities.
The brain can be divided into three main regions: the hindbrain, the midbrain, and the forebrain. The hindbrain consists of the medulla oblongata, the pons, and the cerebellum. The medulla transmits signals between the spinal cord and the higher parts of the brain; it also controls such autonomic functions as heartbeat and respiration. The pons connects the spinal cord with higher brain levels, and it also contains cell groups that transfer information from the cerebrum to the cerebellum. The cerebellum controls balance and coordination by producing smooth, coordinated movements of muscle groups. The midbrain is involved in sensory integration and eye movements. It also contains the substantia nigra, which produces dopamine, a neurotransmitter involved in movement and emotion. The forebrain includes the cerebral hemispheres and, under these, the thalamus and hypothalamus. The thalamus is the main relay centre between the medulla and the cerebrum; it also regulates sleep and wakefulness. The hypothalamus is an important control centre for sex drive, pleasure, pain, hunger, thirst, blood pressure, body temperature, and other visceral functions.
The cerebral hemispheres are divided into four lobes: the frontal lobe, the parietal lobe, the temporal lobe, and the occipital lobe. The frontal lobe is responsible for planning, reasoning, decision making, problem solving, and motor control. The parietal lobe processes sensory information such as touch, pain, temperature, and spatial awareness. The temporal lobe is involved in hearing, language comprehension, memory, and emotion. The occipital lobe is dedicated to vision.
The brain is a fascinating organ that enables us to perceive, think, feel, learn, and act. It is also vulnerable to various diseases and injuries that can impair its function. Some common brain disorders include stroke, Alzheimer’s disease, Parkinson’s disease, epilepsy, brain tumors, traumatic brain injury (TBI), and infections.