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Central Nervous System

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Structure of Human Brain

The human brain is the central organ of the human nervous system, and with the spinal cord makes up the central nervous system.
The human brain is the largest brain of all vertebrates relative to body size.
It weight about 1.5 kilograms (3Ibs) and brain volume is 1.5-1.8 cubic centimeters.
The average male and female has a volume of 1,274 and 1,131 cubic centimeters.
The brain makes up 2 percent of a human’s body weight.
The cerebrum makes up 85 percent of the brain weight.
It contains about 86 billion nerve cells( neurons)- the gray matter.
It contains billions of nerve fibers(axon and dendrites)- the white matter.
These neurons are connected by trillions of connections, or synapses.

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Main parts of the Brain

The main parts of the brain
Forebrain
Midbrain
Hindbrain
Brainstem
The cortex

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Forebrain(Prosencephalon)

The forebrain is the rostral (forward-most) portion of the brain. At the five-vesicle stage ,the forebrain separates into the diencephalon (thalamus, hypothalamus. Subthalamus, epithalamiums, and pretectum) and the telencephalon which develops into the cerebrum. The cerebrum consists of the cerebral cortex, underlying white matter, and the basal ganglia.

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Cerebrum

Cerebrum is the largest part of the brain and its composed of right and left hemispheres. The cerebral hemispheres are centrally connected by thick bundles of white brain substance, where the transverse fibers of the “corpus callosum”.The cerebral cortex is an outer layer of grey matter, covering the core of white matter. The cortex is split into the neocortex and the much smaller allocortex. The neocortex is made up of six neuronal layers, while the allocortex has three of four. Each hemisphere is conventionally divided into four lobes- the frontal , temporal, perietal, and occipital lobes. The surface of the cerebrum, i.e. its core is abundantly furrowed so that by numerous shallower and deeper furrows it is divided into a large number of curls. Among the deep fissures, the most prominent is the lateral Sylvian fissure, which lies between the frontal and temporal lobe.The cortex is outer part of the brain surface that is 1.5 to 4.5mm thick. It represents the gray brain substance, with 12 to 18 billion neurons. Its ares approximately measures 2300 cm2. It is the most complicated part of the nervous system.

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Functions of lobes

Frontal lobe

Personality, behavior, emotions
Judgment, planning, problem solving
Speech: speaking and writing (Broca’s area)
Body movement (motor strip)
Intelligence, concentration, self awareness

Parietal lobe

Interprets language, words
Sense of touch, pain, temperature (sensory strip)
Interprets signals from vision, hearing, motor, sensory and memory
Spatial and visual perception

Occipital lobe

Interprets vision (color, light, movement)

Temporal lobe

Understanding language (Wernicke’s area)
Memory
Hearing
Sequencing and organization

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Cortex�

The surface of the cerebrum is called the cortex. It has a folded appearance with hills and valleys. The cortex contains 16 billion neurons (the cerebellum has 70 billion = 86 billion total) that are arranged in specific layers. The nerve cell bodies color the cortex grey-brown giving it its name – gray matter. Beneath the cortex are long nerve fibers (axons) that connect brain areas to each other — called white matter.

The cortex contains neurons (grey matter), which are interconnected to other brain areas by axons (white matter). The cortex has a folded appearance. A fold is called a gyrus and the valleybetween is a sulcus. The folding of the cortex increases the brain’s surface area allowing more neurons to fit inside the skull and enabling higher functions. Each fold is called a gyrus, and each groove between folds is called a sulcus. There are names for the folds and grooves that help define specific brain regions.

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Deep structures�

Pathways called white matter tracts connect areas of the cortex to each other. Messages can travel from one gyrus to another, from one lobe to another, from one side of the brain to the other, and to structures deep in

the brain .

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Thalamus and hypothalamus

The thalamus is an olive shaped structure about one inch in length. It serves as a relay station for impulses traveling to and from the spinal cord, brain stem, cerebellum and cerebrum. It has an important function in directing sensory input to the appropriate place in the cerebral cortex. Sensory input from the body, the eyes, ears and other senses (except for smell) pass through the thalamus.

serves as a relay station for almost all information that comes and goes to the cortex. It plays a role in pain sensation, attention, alertness and memory.

Hypothalamus: is located in the floor of the third ventricle and is the master control of the autonomic system. The hypothalamus is located below the thalamus. The hypothalamus is an important center for many critical internal body functions. The hypothalamus monitors water concentration, hormone concentrations and body temperature. It is associated with feelings of rage, aggression, hunger and thirst.

It plays a role in controlling behaviors such as hunger, thirst, sleep, and sexual response. It also regulates body temperature, blood pressure, emotions, and secretion of hormones.

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Midbrain

The midbrain is located below the cerebral cortex, and above the hindbrain placing it near the center of the brain. It is comprised of the tectum, tegmentum, cerebral aqueduct, cerebral peduncles and several nuclei and fasciculi. The primary role of the midbrain is to act as a sort of relay station for our visual and auditory systems. Portions of the midbrain called the red nucleus and the substantia nigra are involved in the control of body movement, and contain a large number of dopamine-producing neurons. The degeneration of neurons in the substantia nigra is associated with Parkinson’s disease. The midbrain is the smallest region of the brain, and is located most centrally within the cranial cavity.

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Functions of Midbrain

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Hindbrain

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Functions of Hindbrain