The brain is the most complex organ in the human body. It consists of four main parts: the cerebrum, diencephalon, cerebellum, and brainstem.

The cerebrum is the largest section of the brain and divides into left and right hemispheres, separated by a deep fissure. The cerebral outer layer of grey matter — the cerebral cortex — comprises elevations called gyri and shallow groves called sulci. The inner portion of white matter includes long nerve fibers known as axons, which connect various areas of grey matter throughout both hemispheres.

The cerebellum is the second most prominent part of the brain, located at the back of the skull. An arbor vitae — a network of white fibers — connects its two hemispheres. The cerebellum separates into three lobes on each side — anterior, posterior & flocculonodular lobes. It aids in coordinating activities like fine-tuning skeletal muscle movements, equilibrium, and balance.

The diencephalon is a region that lies between the cerebrum and midbrain and houses vital structures such as the thalamus and hypothalamus. The thalamus acts as a relay station for sensory signals from all over the body to reach specific areas in the cortex. Concurrently, the hypothalamus helps regulate basic needs such as hunger or thirst by releasing hormones into other parts of the body.

The brainstem, located between the diencephalon and the spinal cord, consists mainly of the medulla oblongata, pons, and midbrain. It is responsible for vital functions such as respiration, heart rate, and digestion.

Protective brain coverings include the meninges and three membrane layers. Between the dura mater and arachnoid membranes is a space filled with cerebrospinal fluid, which helps cushion the brain from any mechanical forces and serves as a medium for exchanging nutrition and waste products.

The overall shape of the human brain can be divided into three parts: the cerebrum, cerebellum & brainstem. The average cranial capacity for male adults is about 1300 cubic centimeters (cc) and 1150 cc for females. White matter constitutes most of the volume, whereas 10-15% is grey matter with neurons that send signals throughout the body.

In conclusion, the human brain has multiple complex parts that are intertwined with one another to form a single unit responsible for various vital functions like breathing or movement coordination.