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A neuron can be broken down into three key structures; the cell body, one axon, and dendrites. Neurons are nerve cells that transmits impulses to and from the nervous system. The cell body of a neuron contains the nucleus and cytoplasm. The axon in a neuron extends from the cell body and transmits impulses away from the cell body. Neurons have dendrites that branch out from the cell body in multiple locations. Dendrites transmit impulses towards the cell body.
Neuroglia are the other main type of cell in the nervous system but they do not transmit impulses. Neuroglia assist in phagocytosis, digesting unwanted material. There are three structures of neuroglia; astrocytes, microglia, and oligodendrocytes. Astrocytes are star-shaped cells that wrap themselves around the brain's capillaries forming the blood-brain barrier. These cells are the largest and most numerous. Next, the microglia are phagocytic and during time of injury their numbers increase dramatically. These cells travel to places of injury or damage. Lastly, the oligodendrocytes fan out from the cell body and wrap themselves around axons of numerous neurons forming myelin sheaths. These myelin sheaths protect and increase the speed of nerve impulses.
The peripheral nervous system is made up of nerves and ganglia. It contains afferent and efferent nerves. The afferent nerves carry impulses from the body to the central nervous system. The efferent nerves carry impulses from the central nervous system to the muscles and glands. These nerves cause responses in the targeted organs and muscles.
The peripheral nervous system can be divided into two parts; the somatic nervous system and the autonomic nervous system. The somatic nervous system controls voluntary control over skeletal muscle. The autonomic nervous system controls involuntary control over smooth muscle, cardiac muscle, and glandular activities. The autonomic nervous system contains two types of nerves; sympathetic and parasympathetic. The sympathetic nerves regulate involuntary body functions such as increasing the heart rate whereas, the parasympathetic nerves regulate the involuntary body functions back to a more restful state.
The Central Nervous System
The CNS contains the brain and spinal cord. The brain and spinal cord are protected by bone, connective tissue (called meninges), and cerebrospinal fluid (CSF). There are three layers of meninges the first one being the dura mater. The dura mater is the most outer layer of the meninges and is tough, white connective tissue. Above the dura mater is the epidural space and it contains cushioning fat and connective tissue. Under the dura mater, there is the subdural space. This space is filled with serous fluid. The middle meninge layer is called the arachnoid membrane. This membrane has numerous threadlike strands that attach to the innermost layer of meninges and resembles a spider wed. The inner most layer of the meninges is called the pia mater. This layer is tightly bound to the brain and spinal cord.
Within the central nervous system are two main nerves called the afferent and efferent nerves. The afferent nerves (sensory) carry impulses from the body to the central nervous system (brain and spinal cord) whereas, the efferent nerves (motor nerves) carry impulses from the central nervous system to muscles and glands causing a response. Interneurons are connecting neurons that carry impulses from afferent nerves to efferent nerves.
Structures of the Brain
The brain can be divided into four major regions consisting of the cerebrum, the cerebellum, the diencephalon, and the brain stem.
The cerebrum is the largest part of the brain and makes up the upper portion. There is a left and right hemisphere that's divided by a longitudinal fissure. The cerebrum controls voluntary movement, memory, sensations, and consciousness. It is recognized by its many grooves (sulci) and elevations (gyri).
The cerebellum is in the back lower portion of the brain and is attached to the brain stem. It is responsible for maintaining muscle tone and coordinating normal movement and balance.
The diencephalon consists of the thalamus (sensory stimuli), the hypothalamus (activates, controls, and integrates many systems, processes, and sensory functions), and the pineal body (regulates the biological clock). The diencephalon is located between the cerebrum and the midbrain.
Lastly, the brain stem is between the spinal cord and the diencephalon. The brain stem consists of the midbrain, pons, and the medulla oblongata. The brain stem provides a pathway for nerve impulses between the brain and spinal cord. It is responsible for respiration, blood pressure, and heart rate.
10 Pathological Conditions
Among the countless conditions affecting the nervous system, I have chosen the ten that best stood out to me. The first one is anencephaly. This condition is characterized by the absence of the brain and spinal cord at birth. There is no way of survival or treatment for this condition.
Next, cerebral palsy is congenital brain damage that is permanent but not progressive. Symptoms include lack of control over the child's voluntary muscles. There are four types of cerebral palsy; spastic, ataxic, athetoid, and mixed. There is no cure and treatment consists of symptom control.
Also, carpal tunnel syndrome is a very common disorder characterized by pain in the fingers, hands and wrists that worsens at night. Inflammation in the tendons of the hands is caused usually by repetitious overuse. Treatment involves stopping the repetitious overuse, splints, anti-inflammatory medications, and physical therapy.
Epilepsy is a pathological condition that may occur in a diseased or normal central nervous system. Its symptoms are recurring seizures. These seizures can vary between partial (mild) seizures to generalized (moderate-severe) seizures. Treatment includes anticonvulsant medications and detailed testing to confirm a diagnosis.
Also, headaches (cephalalgia) can result from disease or be totally benign. They very from mild to severe and can be chronic or acute. Most headaches are mild and treatment is a mild analgesic. Headaches can be categorized into three categories; migraine, tension, and clusters.
A epidural hematoma develops rapidly and can be fatal. It is defined as a collection of blood above the dura mater and below the skull. Symptoms include loss of consciousness, seizures, with a state of worsening over time. It is vital that treatment begin immediately. Treatment involves burr holes to remove the clot and also a craniotomy to repair damaged vessels and remove pooled blood.
A subdural hematoma is a collection of blood between the dura mater and the arachnoid layer of the meninges. It is often the result of a head injury. Treatment includes diuretic medications and surgical evacuation.
Another disorder is intracranial tumors. These tumors can be benign or malignant. Treatment is usually surgical removal but sometimes chemotherapy and radiation depending on location and type of tumor.
Multiple sclerosis is a incurable, inflammatory disease that attacks the myelin sheath in the spinal cord and brain. This interrupts impulses and leads to debilitating symptoms including blindness, unsteady balance, and numbness. Treatment is a process of controlling the symptoms and minimizing any pain.
Lastly, narcolepsy is very rare and characterized by sudden, uncontrolled sleep attacks. Cataplexy (sudden paralysis) is also common in people with narcolepsy. Treatment may include medications that would promote alertness.