The complex human brain controls who we are: how we think, feel, and act. It gives meaning to our world and our place in it. The brain also controls all major body functions.

The brain is housed in the skull, which protects it from injury. Averaging a pound at birth, the brain grows to approximately three pounds by adulthood. The brain, along with the spinal cord is a crucial component of the central nervous system (CNS).

Two types of cells exist in the brain. Neurons send and receive signals to and from your brain and the rest of the body. Glial cells, sometimes called neuroglia or glia, form myelin, a fatty, insulating layer around nerve fibers. The cells maintain stability, and provide nutrition and support.

Each part of the brain performs a particular function and is linked to other parts of the brain.

In between the skull and brain are three layers of tissue, called meninges. They protect the brain. The strong, outermost layer is named the dura mater. The middle layer, the arachnoid mater, is a thin membrane made of blood vessels and elastic tissue. It covers the entire brain. The pia mater is the innermost layer, with blood vessels that run deep into the brain.

CerebrumForebrain, largest part of the brain divided into two halvesPerforms higher functioning processes such as vision, hearing, speech, emotion, and movement
Left hemisphereLeft side of cerebrumResponsible for language in most right-handed people and about 50 percent of left-handed people; controls analytical reasoning and calculations; processes motor and sensory signals for the right side of the body
Right hemisphereRight side of cerebrumInterprets visual cues and spatial processing, including emotional, artistic, and visual reasoning; processes motor and sensory signals for left side of the body
Corpus callosumBetween the two hemispheresConnects the left and right hemispheres
Frontal lobeLargest section of brain, front of the headHelps form reasoning, emotions, movement
Parietal lobeMiddle part of brainHelps us understand our spatial relation to other people and objects; interprets touch and pain
Occipital lobeBack of the brainHelps process visual information
Temporal lobesOn each side of the brainHelps with memory, language, smell, the ability to recognize faces; interprets emotions
CerebellumHindbrain Controls fine motor movements, balance, and posture
BrainstemIn front of the cerebellum, connected to the spinal cordControls basic bodily functions that are necessary for survival
MidbrainTop section of the brainstemControls eye movements, facial sensation, balance, and hearing
PonsMiddle section of the brainstemControls sensory analysis, motor skills, sleep, and consciousness
Medulla oblongataLowest section of brainstemControls respiratory drive, swallowing, coughing, gag reflex; helps to regulate circulation, blood pressure, and heart rate
Limbic systemSet of structures above the brainstemResponsible for emotions
ThalamusFound under the cerebrumResponsible for integrating all of the sensory signals coming from the spinal cord and limbic system
HypothalamusSits right below the thalamusSends messages to pituitary gland and helps to regulate temperature, thirst, water balance, sleep, hormone production, and appetite
AmygdalaStructure in limbic systemProcesses aggressive behavior and fear
HippocampusStructure in limbic systemHelps us remember new information
Pituitary glandBase of the brainSecretes hormones
Basal gangliaWithin the deep part of the cerebrumCoordinates steady movements

The cerebrum, or forebrain, forms the biggest part of the brain and is divided in two halves. The left hemisphere is largely responsible for language. The right hemisphere is important for interpreting visual cues and spatial processing. The cerebrum controls coordination, temperature, sight, sound, reasoning, learning, and emotions.

The space between the two hemispheres is called the great longitudinal fissure. The corpus callosum connects the two sides and transfers signals from one side of the brain to the other.

The cerebrum has billions of neurons and glia that form the cerebral cortex, its outermost layer. This is commonly known as gray matter. Connection fibers between neurons beneath the surface of the brain are called white matter.

The cerebellum, or hindbrain, handles fine motor movements, balance, and posture. It helps us to perform quick and repetitive movements.

The brainstem is in front of the cerebellum and is connected to the spinal cord. Its job is to pass signals between the cerebral cortex and the rest of the body. It helps to control our most basic functions and is made up of three parts.

The midbrain controls eye movements, facial sensation, balance, and hearing. Signals from the cortex to the spinal cord and nerves move through the pons, which controls sensory analysis, motor skills, sleep, and consciousness. The lowest part of the brainstem is the medulla oblongata, which helps controls heart and lung functions, among other functions.

The frontal lobe is the largest part of the brain, located in the front of the head. It helps to form reasoning, emotions, and movement. The parietal lobe is the middle part of the brain. It helps us to understand our place in relation to other people and things. It also helps us to interpret touch and pain. The occipital lobe is the back of the brain and helps us process visual information.

The temporal lobes are located on each side of the brain. They help with memory, language, and our sense of smell. They also help us to recognize faces and objects and interpret the reactions of other people.

The limbic system is responsible for emotions. The thalamus is the hub for information coming and going to the cortex. It deals with the sensation of pain and alertness. The hypothalamus is a tiny structure that sends messages to the pituitary gland. It also helps to control sexual behavior, eating, sleeping, body temperature, and movement. The amygdala is involved in processing aggressive behavior and fear. The hippocampus helps us to remember new information.

The brain has four ventricles connected by cavities and tubes. The two lateral ventricles in the cerebral hemispheres communicate with a third located in the center of the brain. It communicates with the fourth at the base of the brain through a tube called the cerebral aqueduct.

Cerebrospinal fluid flows through the fourth ventricle and around the brain. This is a clear, watery liquid produced in the ventricles. It cushions the brain and spinal cord, and is continually absorbed and replenished.

The pineal gland is an outgrowth at the back of the third ventricle. Its purpose isn’t fully understood, but is thought to play a part in sexual maturation.

The pituitary is a small gland at the base of the brain that secretes hormones. It plays a key role in the function of other glands, organs, sexual development, and growth.