Brain

The human brain enclosed in cranium is a highly complex organ and is the center of the nervous system.

It weighs about 3 pounds and has the texture of a firm jelly. The brain contains estimated 50-100 billion neurons which are about 10 billion cortical pyramidal cells. These types of cells transmit signals to one another in 1000 trillion synaptic connections.

Generally, it has the same structure with the brains of other mammals. It is just larger in relation to body size. Measuring using the encephalization quotient (ratio of brain to body size), a human brain is thrice as large as the brain of a chimpanzee. The expansion greatly comes from the cerebral cortex in its frontal lobes. This part is associated with reasoning, self-control, planning and abstract thought. And the part for vision is also enlarged.

Structure
An adult human brain has an average weight of 3 pounds or 1.5 kilograms. In men, the average volume is about 1260 cubic centimeters and in women, its 1130 cubic centimeters. Though men’s brain are 100 grams heavier than women’s, the difference do not correlate with IQ or other cognitive performance.

A living brain has a consistency of a jelly or tofu. Though the live cortex is usually called as the grey matter, it is actually in pinkish-beige color and has an off-white interior. The cerebral portion of the brain is covered with a cortical layer with a complex topography.

The brain has 3 main structures: cerebrum, cerebellum, and brainstem

Below the cerebrum is the brainstem which looks like a stalk where the cerebrum is attached. Beneath the cerebrum and behind the brainstem lies the cerebellum.

The Cerebrum
The cerebrum is composed of 3 sub-regions: cerebral cortex, basal ganglia, and limbic system. It is involved in remembering, thinking, problem solving, feeling and movement. The thick-layered neural tissue called cerebral cortex covers majority of the brain. The cerebral cortex is divided into 4 lobes- frontal lobe, temporal lobe, parietal lobe, and occipital lobe.

The frontal lobe is linked with planning, reasoning, parts of speech, emotions, movement, and problem solving.

The temporal lobe is linked with auditory stimuli recognition and perception, memory, and speech.

The parietal lobe is linked with recognition, orientation, stimuli perception and movement.

The occipital lobe is linked with visual processing.

A deep crease divided the cerebrum into two halves called the left and right hemispheres. The left and right regions are similar in shape. Though some areas have lateralization especially areas involved in language, many cortical areas are duplicated on each side. They may differ in function such as the left hemisphere is connected to logic abilities and controls the body’s movement on the right side while the right hemisphere is on creativity and controls the body’s left side movement.

A bundle of axons called corpus callosum connects the two halves.

Cerebral Cortex
The cerebral cortex is the wrinkled surface outer layer of the cerebrum. Scientists mapped the regions of the cortex according to these certain functions:

-interpreting sensations like sights, sounds and smell

-generating ideas, making plans and solving problems

-forming and storing memories

-controlling voluntary movements

The six-layered neocortex found in this structure is present only in highly evolved mammals such as humans, dolphins and primates. It is responsible for higher thinking functions like language, sensory perception, spatial reasoning and conscious thought.

Basal Ganglia
The basal ganglia are a set of nuclei with varied origins in the brain which act as a whole functional unit. It is located below the forebrain and connected with cortex, thalamus and other regions.

It is associated with many functions such as controlling cognition and voluntary motor, movement coordination, procedural learning, and eye movements.

Limbic system
The limbic system is a group of brain structures located on both sides of thalamus under the cerebrum. The group includes hippocampus, anterior thalamic nuclei, amygdale, septum, habenula, fornic and limbic cortex.

It is linked to behavior, emotion, motivation, olfaction and long-term memory. It seems to be responsible for the emotional aspect and formation of memories.

The Cerebellum
The cerebellum is located under cerebrum, at the back of head. Similar to the cerebrum, it has highly folded cortex and has two hemispheres. The “little brain” controls posture, balance, and regulation and coordination of movement.

The Brain Stem
The brain stem connecting the brain to the spinal cord is located beneath the cerebrum and front of the cerebellum. It is associated with the basic life functions like breathing, blood pressure, heart rate and digestion.

It is made up of the midbrain, pons and medulla.

Scientists considered this structure as the "simplest" part of human brain. Other animals like the reptiles, their entire brain is similar to our brain stem.

Brain Divisions
The forebrain or prosencephalon is consists of the diencephalon and telencephalon. The thalamus and hypothalamus are found in the diencephalon. They are associated in controlling motor and autonomic functions and delivering sensory information. The cerebrum is found in the telencephalon. The forebrain is also involved in thinking, perceiving, making and understanding language.

The midbrain or mesencephalon together with the hindbrain comprises the brainstem. The midbrain is associated in body’s motor function, auditory and visual responses. It is the part of the brainstem that connects the forebrain and hindbrain.

The hindbrain or rhombencephalon is consists of the metencephalon and myelencephalon. The pons and cerebellum are part of the metencephalon which aids in maintaining body balance, equilibrium, and movement coordination. The medulla oblongata is part of the myelencephalon which controls autonomic functions like digestion, heart rate and breathing.