The neural tube, also known as the neural layer, is the embryonic structure that gives rise to the nervous system. The nervous system includes neurons, glial cells, and other supporting structures.
Neurons are cell bodies with long processes called axons and dendrites that carry electrical impulses and receive them, respectively.
Glial cells include astrocytes, oligodentrocytes, and ependymal cells. Astrocytes are supportive cells that provide nutrients and structural support for neurons; oligodendrocytes form the myelin sheath around neurons; and ependymal cells are lining cells of the central nervous system.
During neurogenesis (the process of development of the brain and spinal cord), a portion of the neural tube converts into a placode. A placode is a group of embryonic epithelial cell layers that thickens and bumps out into a dome-like structure. There are two main types of placodes: dorsal (on top) and ventral (on bottom).
Cortical layer
The next layer you should search for is the cortical layer. This layer contains both a single-celled pigmented layer and a neural (nerve) layer.
The single-celled pigment epithelial (skin) layer lies just beneath the neuroectoderm and is what gives the cortex its color. The larger nerve cells lie just below this superficial skin and give the cortex its texture.
This is one of the easier layers to identify, as you can see both structures through the skin. The hardest part is determining if what you see is actually nerve cells or if it is part of the underlying ectoderm.
Ventricular layer
The next layer is called the ventricular layer. This is also referred to as the inner neuroectodermal layer. This layer contains both an embryonic neural tube and a single-celled pigment cell layer.
The neural tube later develops into the spinal cord and some parts of the brain and nervous system. The pigment cells later develop into the melanocytes that are located in the skin, hair, and eyelid.
This layer is located underneath the cortical layer and above the basal metabolic cell layer. As mentioned before, all of these layers combine to form the developing embryo structure known as the limb bud.
The limb bud is what will eventually develop into either arm or leg bones, hands or feet, depending on its shape. The different shapes are due to different levels of hormones in your mother’s pregnancy blood stream. These hormones cause different developmental changes in your body.
Deep neural layer
The deep neural layer is the last layer of the epidermis. This layer contains all of the nerve endings that sense touch, temperature, and pain.
The deeper layers of the epidermis contain melanocytes, cells that produce melanin. Melanin is the pigment that gives your skin its color. It also helps protect your skin from the sun’s UV rays.
Just below the deep neural layer is the papillary dermis, a very thin region with fibrous tissue and vascular channels. Below that is the reticular dermis, a thicker region with more collagen and fewer vascular channels. Both of these regions are part of the dermis and contribute to skin strength and elasticity.
Finally, the hypodermis is underneath the dermis. It consists of adipose (fat) tissue and fibers that connect to muscles elsewhere on your body.
Paleostriatum
The next level of the brain ladder is called the paleostriatum. This part of the brain controls emotional responses such as fear and aggression.
It also controls balance and posture, including coordination of movements. The paleostriatum is a collection of nerve cells organized into two layers: an inner layer of gray matter (cell bodies and dendrites) and an outer layer of white matter (axons).
The gray matter contains cell bodies and dendrites, while the white matter contains nerve fibers. Connecting these two layers are nerve cells called synapses. These synapses are where one neuron sends a signal to another neuron via a chemical message ( neurotransmitter ).
The paleostriatum is located in an interior part of the brain, beneath the corpus callosum that connects the left and right hemispheres. Like other parts of thebrain, it undergoes changes during development that shape its structure.
Neostriatum
The neostriatum is a layer of the cerebral cortex located in the dorsal part of the telencephalon. This area is also referred to as the basal ganglia.
This region contains structures that control movements. These include the corpus striatum (nucleus caudatus and nucleus lentiformis), globus pallidus, and subthalamic nucleus.
These areas are responsible for regulating voluntary movements. For example, the corpus striatum regulates voluntary movement via muscular activity, whereas the globus pallidus regulates bodily movements such as posture and balance. The subthalamic nucleus modulates activity in other parts of the brain that control movement.
Lesions (or traumatic injury) to these areas can result in movement disorders such as Parkinson’s disease or dystonia. Due to the importance of this region in controlling movement, these lesions must be surgically removed to treat patients.
Lentiform nucleus
The lentiform nucleus is a midbrain structure that contains the corpora quadrigemina (four chambers) and the dorsal colexus. The lentiform nucleus functions to control eye movements, coordinate head and eye movements, and integrate sensory information from the upper half of the body (above the neck).
The four chambers of the corpora quadrigemina are the mesodermic ventral lateral canal, dorsal canal, vertical canal, and horizontal canal. These contain neurons that project to different areas in the brain.
The dorsal colexus is located in between the cerebral hemispheres and controls motor function in the limbs (arms and legs). It coordinates muscle contractions to produce coordinated movements such as walking or running.
Identify this layer on an animal with a well-developed midbrain and examine how it functions to control motor function in limbs.
Substantia innominata
The next layer in the nervous system is called the substantia innominata. This layer is a thin, single-celled pigment cell layer that contains neurons.
This layer lies just beneath the white matter of the spinal cord. So, this layer consists of a single-celled pigment cell membrane and the neurons that it contains, which are surrounded by fibrous material.
The substantia innominata receives sensory information from the skin and muscles via its neurons and passes this information on to the spinal cord. It also sends motor information from the spinal cord to the skin and muscles to control bodily functions.
The substantia innominata receives its blood supply from arteries that enter from the back of the brain. These arteries then divide into small vessels that supply blood to the substantia innominata.
Thalamus
The next layer of the brain is the thalamus. The thalamus is a smaller nucleus that sits inside of the midbrain.
This area performs a number of functions that relate to our senses. For example, it collects sensory information from the dorsal posterior nucleus, which is responsible for relaying information from the skin to the brain.
The thalamus also projects to other areas of the brain that process sensory information. For example, it projects to the somatosensory cortex, which processes touch and where it locates it.
In addition, it projects to the part of the brain that regulates sleep, known as the lateral geniculate nucleus (LGN). The LGN controls how light is processed in the retina and sent to other parts of the brain. These functions help keep us awake and aware during light hours and asleep during dark hours.
