Neuroscience of sex differences The adult human brain weighs on average about 1. Each hemisphere is divided into four main lobes although Terminologia Anatomica and Terminologia Neuroanatomica also include a limbic lobe and treat the insular cortex as a lobe.
Neurulation is the formation of the neural tube from the ectoderm of the embryo. It follows gastrulation in all vertebrates. During gastrulation cells migrate to the interior of embryo, forming three germ layers — the endoderm the deepest layermesoderm and ectoderm the surface layer —from which all tissues and organs will arise.
In a simplified way, it can be said that the ectoderm gives rise to skin and nervous system, the endoderm to the guts and the mesoderm to the rest of the organs. After gastrulation the notochord —a flexible, rod-shaped body that runs along the back of the embryo—has been formed from the mesoderm.
During the third week of gestation the notochord sends chemical signals to the overlying ectoderm, inducing it to become neuroectoderm.
This results in a strip of neuronal stem cells that runs along the back of the embryo. This strip is called the neural plateand is the origin of the entire nervous system.
The neural plate folds outwards to form the neural groove. Beginning in the future neck region, the neural folds of this groove close to create the neural tube this form of neurulation is called primary neurulation.
The ventral front part of the neural tube is called the basal plate ; the dorsal rear part is called the alar plate. The hollow interior is called the neural canal.
By the end of the fourth week of gestation, the open ends of the neural tube the neuropores close off. The spinal cord forms from the lower part of the neural tube. The wall of the neural tube consists of neuroepithelial cells, which differentiate into neuroblasts, forming the mantle layer the gray matter.
Nerve fibers emerge from these neuroblasts to form the marginal layer the white matter. The ventral part of the mantle layer the basal plates forms the motor areas of the spinal cord, whilst the dorsal part the alar plates forms the sensory areas.
Between the basal and alar plates is an intermediate layer that contains neurons of the autonomic nervous system. Late in the fourth week, the superior part of the neural tube flexes at the level of the future midbrain—the mesencephalon.
Above the mesencephalon is the prosencephalon future forebrain and beneath it is the rhombencephalon future hindbrain. The optical vesicle which will eventually become the optic nerve, retina and iris forms at the basal plate of the prosencephalon. The embryo's nervous system at six weeks.
In the fifth week, the alar plate of the prosencephalon expands to form the cerebral hemispheres the telencephalon. The basal plate becomes the diencephalon. The diencephalon, mesencephalon and rhombencephalon constitute the brain stem of the embryo.
It continues to flex at the mesencephalon. The rhombencephalon folds posteriorly, which causes its alar plate to flare and form the fourth ventricle of the brain.
The pons and the cerebellum form in the upper part of the rhombencephalon, whilst the medulla oblongata forms in the lower part.
Human brain development[ edit ].The reticular formation is a cluster of nerves within the brainstem that relay sensory and motor signals to and from the spinal cord and the brain.
It aids in the control of autonomic and endocrine functions, as well as muscle reflexes and sleep and awake states. The human brain is the central organ of the human nervous system, and with the spinal cord makes up the central nervous system. The brain consists of the cerebrum, the brainstem and the cerebellum.
Finally, the brain reaches its peak power around age 22 and lasts for 5 more years. Afterwards, it’s a downhill pattern. Last to mature and the first to go are the brain functionality of executive control occurring in the prefrontal and temporal cortices.
Facial features (like eyes and nostrils) are beginning to form, and little buds appear where arms and legs will develop.
8 weeks Arms and legs are growing, and your baby now has little fingers, as . The brain constitutes only about 2 percent of the human body, yet it is responsible for all of the body's functions. Learn about the parts of the human brain, as well as its unique defenses, like. The healthy human brain contains tens of billions of neurons—specialized cells that process and transmit information via electrical and chemical signals.
They send messages between different parts of the brain, and from the brain to the muscles and organs of the body. Alzheimer’s disease.