Major Brain Structures and Their Functions

The brain is divided into two cerebral hemispheres by the longitudinal fissure. The surface is characterized by sulci (fissures) and gyri (ridges), formed by the folding of the cerebral cortex. The cortex is essential for sensory processing, movement, and higher-level cognitive functions. It is typically divided into four lobes: frontal, parietal, occipital, and temporal.

The frontal lobe contains the motor cortex, crucial for voluntary movement, and the prefrontal cortex, involved in decision-making, planning, impulse control, and long-term goal pursuit. Broca's area, found in the left hemisphere for most people, is important for language production.

The parietal lobe processes language, spatial orientation, attention, and bodily sensations through the primary somatosensory cortex. The occipital lobe is at the back of the brain and is primarily associated with visual processing, including the primary visual cortex. The temporal lobe is involved in higher-order visual processing, learning, memory, and hearing, containing the primary auditory cortex. Wernicke's area, near the temporal and parietal lobes, is associated with language comprehension.

The cerebellum, located at the back and bottom of the brain, is best known for its roles in movement, including motor coordination and control, balance, posture, fine-tuning of voluntary movements, and movement-related learning.

The brain stem connects the brain to the spinal cord and is vital for many functions. The medulla oblongata regulates vital functions like cardiovascular and respiratory activity. The pons contains pathways to and from the cerebellum and nuclei for cranial nerves. The midbrain is the uppermost part and contains the substantia nigra and ventral tegmental area (VTA), both significant for dopamine production. Substantia nigra dopamine neurons are critical for movement, and their degeneration causes Parkinson's disease. VTA dopamine neurons project to areas like the nucleus accumbens, crucial for reward experiences and addiction.

The substantia nigra and nucleus accumbens are part of the basal ganglia, which are involved in movement, habit formation, and reward processing. Above the brain stem, the thalamus acts as a relay station for most sensory information (except smell) to the cerebral cortex. Posterior to the thalamus, the pineal gland secretes melatonin, regulating circadian rhythms.

The hypothalamus, located below the thalamus, is crucial for maintaining homeostasis, regulating thirst, hunger, body temperature, stress responses, and circadian rhythms. It controls many of these functions through its connection with the pituitary gland, a hormone-secreting gland that releases hormones like growth hormone, thyroid stimulating hormone, and also stores oxytocin and vasopressin produced by the hypothalamus.

The hippocampus, found within the temporal lobe, is vital for memory, particularly in converting short-term memories into long-term memories. Adjacent to the hippocampus is the amygdala, an almond-shaped structure primarily known for its role in processing emotions, especially fear and responses to threats, but also involved in positive emotions.

The corpus callosum is the largest bundle of axons in the brain, connecting the left and right cerebral hemispheres and enabling communication between them. The brain also contains a system of cavities called ventricles, which produce cerebrospinal fluid (CSF). CSF protects the brain by cushioning it, reducing the effects of gravity, and removing waste products, while also regulating the extracellular environment of neurons.