Upon CNS injury astrocytes will proliferate, causing gliosis , a form of neuronal scar tissue, lacking in functional neurons. The brain cerebrum as well as midbrain and hindbrain consists of a cortex , composed of neuron-bodies constituting gray matter, while internally there is more white matter that form tracts and commissures. Apart from cortical gray matter there is also subcortical gray matter making up a large number of different nuclei. From and to the spinal cord are projections of the peripheral nervous system in the form of spinal nerves sometimes segmental nerves .
The nerves connect the spinal cord to skin, joints, muscles etc. All in all 31 spinal nerves project from the brain stem,  some forming plexa as they branch out, such as the brachial plexa , sacral plexa etc. The spinal cord relays information up to the brain through spinal tracts through the "final common pathway"  to the thalamus and ultimately to the cortex.
Reflexes may also occur without engaging more than one neuron of the CNS as in the below example of a short reflex. Apart from the spinal cord, there are also peripheral nerves of the PNS that synapse through intermediaries or ganglia directly on the CNS. These 12 nerves exist in the head and neck region and are called cranial nerves. Cranial nerves bring information to the CNS to and from the face, as well as to certain muscles such as the trapezius muscle , which is innervated by accessory nerves  as well as certain cervical spinal nerves.
Two pairs of cranial nerves; the olfactory nerves and the optic nerves  are often considered structures of the CNS. This is because they do not synapse first on peripheral ganglia, but directly on CNS neurons.
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The olfactory epithelium is significant in that it consists of CNS tissue expressed in direct contact to the environment, allowing for administration of certain pharmaceuticals and drugs. Rostrally to the spinal cord lies the brain. It is often the main structure referred to when speaking of the nervous system in general.
Basic Structure and Function of the Nervous System | Anatomy and Physiology I
The brain is the major functional unit of the CNS. While the spinal cord has certain processing ability such as that of spinal locomotion and can process reflexes , the brain is the major processing unit of the nervous system. The brainstem consists of the medulla , the pons and the midbrain. The medulla can be referred to as an extension of the spinal cord, which both have similar organization and functional properties.
Regulatory functions of the medulla nuclei include control of blood pressure and breathing.
Overview of neuron structure and function
Other nuclei are involved in balance , taste , hearing , and control of muscles of the face and neck. The next structure rostral to the medulla is the pons, which lies on the ventral anterior side of the brainstem. Nuclei in the pons include pontine nuclei which work with the cerebellum and transmit information between the cerebellum and the cerebral cortex. The midbrain, or mesencephalon, is situated above and rostral to the pons. It includes nuclei linking distinct parts of the motor system, including the cerebellum, the basal ganglia and both cerebral hemispheres , among others.
Additionally, parts of the visual and auditory systems are located in the midbrain, including control of automatic eye movements. The brainstem at large provides entry and exit to the brain for a number of pathways for motor and autonomic control of the face and neck through cranial nerves,  Autonomic control of the organs is mediated by the tenth cranial nerve.
Such functions may engage the heart , blood vessels , and pupils , among others. The brainstem also holds the reticular formation , a group of nuclei involved in both arousal and alertness. The cerebellum lies behind the pons. The cerebellum is composed of several dividing fissures and lobes. Its function includes the control of posture and the coordination of movements of parts of the body, including the eyes and head, as well as the limbs.
Further, it is involved in motion that has been learned and perfected though practice, and it will adapt to new learned movements. These connections have been shown by the use of medical imaging techniques, such as functional MRI and Positron emission tomography. The body of the cerebellum holds more neurons than any other structure of the brain, including that of the larger cerebrum , but is also more extensively understood than other structures of the brain, as it includes fewer types of different neurons.
The two structures of the diencephalon worth noting are the thalamus and the hypothalamus. The thalamus acts as a linkage between incoming pathways from the peripheral nervous system as well as the optical nerve though it does not receive input from the olfactory nerve to the cerebral hemispheres. Previously it was considered only a "relay station", but it is engaged in the sorting of information that will reach cerebral hemispheres neocortex.
Apart from its function of sorting information from the periphery, the thalamus also connects the cerebellum and basal ganglia with the cerebrum. In common with the aforementioned reticular system the thalamus is involved in wakefullness and consciousness, such as though the SCN. The hypothalamus engages in functions of a number of primitive emotions or feelings such as hunger , thirst and maternal bonding.
This is regulated partly through control of secretion of hormones from the pituitary gland. Additionally the hypothalamus plays a role in motivation and many other behaviors of the individual. The cerebrum of cerebral hemispheres make up the largest visual portion of the human brain. Various structures combine to form the cerebral hemispheres, among others: the cortex, basal ganglia, amygdala and hippocampus.
The hemispheres together control a large portion of the functions of the human brain such as emotion, memory, perception and motor functions. Apart from this the cerebral hemispheres stand for the cognitive capabilities of the brain. Connecting each of the hemispheres is the corpus callosum as well as several additional commissures.
Functionally, the cerebral cortex is involved in planning and carrying out of everyday tasks. The hippocampus is involved in storage of memories, the amygdala plays a role in perception and communication of emotion, while the basal ganglia play a major role in the coordination of voluntary movement.
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Both act to add myelin sheaths to the axons, which acts as a form of insulation allowing for better and faster proliferation of electrical signals along the nerves. Axons in the CNS are often very short, barely a few millimeters, and do not need the same degree of isolation as peripheral nerves. Some peripheral nerves can be over 1 meter in length, such as the nerves to the big toe.
To ensure signals move at sufficient speed, myelination is needed. The way in which the Schwann cells and oligodendrocytes myelinate nerves differ. A Schwann cell usually myelinates a single axon, completely surrounding it. Sometimes, they may myelinate many axons, especially when in areas of short axons. They do this by sending out thin projections of their cell membrane , which envelop and enclose the axon. During early development of the vertebrate embryo, a longitudinal groove on the neural plate gradually deepens and the ridges on either side of the groove the neural folds become elevated, and ultimately meet, transforming the groove into a closed tube called the neural tube.
The neuron and nervous system
At this stage, the walls of the neural tube contain proliferating neural stem cells in a region called the ventricular zone. The somatic system consists of nerves that connect the brain and spinal cord with muscles and sensory receptors in the skin. There are over trillion neural connections in the average human brain, though the number and location can vary. A synapse gives a command to the cell and the entire communication process typically takes only a fraction of a millisecond. Motor neurons, located in the central nervous system or in peripheral ganglia, transmit signals to activate the muscles or glands.
The brain's connections and thinking ability grew over thousands of years of evolution. This code packages up genetic information and sends it from nerve cells to other nearby nerve cells, a very important process in the brain. There are a number of tests and procedures to diagnose conditions involving the nervous system. In addition to the traditional X-ray, a specialized X-ray called a fluoroscopy examines the body in motion, such as blood flowing through arteries, according to the NIH.
The trajectory of the ball and its speed will need to be considered. Maybe the count is three balls and one strike, and the batter wants to let this pitch go by in the hope of getting a walk to first base. The nervous system can be divided into two parts mostly on the basis of a functional difference in responses.
The somatic nervous system SNS is responsible for conscious perception and voluntary motor responses. Voluntary motor response means the contraction of skeletal muscle, but those contractions are not always voluntary in the sense that you have to want to perform them. Some somatic motor responses are reflexes, and often happen without a conscious decision to perform them. The autonomic nervous system ANS is responsible for involuntary control of the body, usually for the sake of homeostasis regulation of the internal environment.
Sensory input for autonomic functions can be from sensory structures tuned to external or internal environmental stimuli. The motor output extends to smooth and cardiac muscle as well as glandular tissue. The role of the autonomic system is to regulate the organ systems of the body, which usually means to control homeostasis. Sweat glands, for example, are controlled by the autonomic system. When you are hot, sweating helps cool your body down. That is a homeostatic mechanism. But when you are nervous, you might start sweating also.
That is not homeostatic, it is the physiological response to an emotional state. There is another division of the nervous system that describes functional responses. The enteric nervous system ENS is responsible for controlling the smooth muscle and glandular tissue in your digestive system. It is sometimes valid, however, to consider the enteric system to be a part of the autonomic system because the neural structures that make up the enteric system are a component of the autonomic output that regulates digestion.
There are some differences between the two, but for our purposes here there will be a good bit of overlap. See Figure 5 for examples of where these divisions of the nervous system can be found. Visit this site to read about a woman that notices that her daughter is having trouble walking up the stairs. This leads to the discovery of a hereditary condition that affects the brain and spinal cord.
The electromyography and MRI tests indicated deficiencies in the spinal cord and cerebellum, both of which are responsible for controlling coordinated movements. To what functional division of the nervous system would these structures belong? Have you ever heard the claim that humans only use 10 percent of their brains? Maybe you have seen an advertisement on a website saying that there is a secret to unlocking the full potential of your mind—as if there were 90 percent of your brain sitting idle, just waiting for you to use it.
An easy way to see how much of the brain a person uses is to take measurements of brain activity while performing a task. An example of this kind of measurement is functional magnetic resonance imaging fMRI , which generates a map of the most active areas and can be generated and presented in three dimensions Figure 6. This procedure is different from the standard MRI technique because it is measuring changes in the tissue in time with an experimental condition or event.
The underlying assumption is that active nervous tissue will have greater blood flow. By having the subject perform a visual task, activity all over the brain can be measured. Consider this possible experiment: the subject is told to look at a screen with a black dot in the middle a fixation point. A photograph of a face is projected on the screen away from the center. The subject has to look at the photograph and decipher what it is. The subject has been instructed to push a button if the photograph is of someone they recognize.
The photograph might be of a celebrity, so the subject would press the button, or it might be of a random person unknown to the subject, so the subject would not press the button. In this task, visual sensory areas would be active, integrating areas would be active, motor areas responsible for moving the eyes would be active, and motor areas for pressing the button with a finger would be active. Those areas are distributed all around the brain and the fMRI images would show activity in more than just 10 percent of the brain some evidence suggests that about 80 percent of the brain is using energy—based on blood flow to the tissue—during well-defined tasks similar to the one suggested above.
This task does not even include all of the functions the brain performs. There is no language response, the body is mostly lying still in the MRI machine, and it does not consider the autonomic functions that would be ongoing in the background. The nervous system can be separated into divisions on the basis of anatomy and physiology.
The anatomical divisions are the central and peripheral nervous systems. The CNS is the brain and spinal cord. The PNS is everything else. Functionally, the nervous system can be divided into those regions that are responsible for sensation, those that are responsible for integration, and those that are responsible for generating responses.
The Central and Peripheral Nervous Systems
All of these functional areas are found in both the central and peripheral anatomy. Considering the anatomical regions of the nervous system, there are specific names for the structures within each division. Whereas nuclei and ganglia are specifically in the central or peripheral divisions, axons can cross the boundary between the two. A single axon can be part of a nerve and a tract. The name for that specific structure depends on its location. Nervous tissue can also be described as gray matter and white matter on the basis of its appearance in unstained tissue.
These descriptions are more often used in the CNS. Gray matter is where nuclei are found and white matter is where tracts are found. In the PNS, ganglia are basically gray matter and nerves are white matter. The nervous system can also be divided on the basis of how it controls the body.
The somatic nervous system SNS is responsible for functions that result in moving skeletal muscles.