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Explain the different structures and functions of the two main types of cells in the nervous system.
Neurons are the functional unit that transmits impulses in the nervous system. They are made up of three basic parts; the cell body, one or more dendrites, and one axon. The cell body is the structure that contains the nucleus, cytoplasm, mitochondria and other organelles typical of eukaryotic cells. The dendrites receive information from other cells and transmits them to the cell body while the axon conducts impulses and information away from the cell body.
The neuroglia provide a support system for the neurons. Their purpose is not to transmit impulses but instead to protect the nervous system. Through phagocytosis, neuroglia engulf and digest unwanted substances. There are three types of neuroglia cells; astrocytes, microglia, and oligodendrocytes. Astrocytes are the most numerous and largest of the three neuroglia. They form a sheath around brain capillaries forming a blood-brain barrier that prevents harmful substances from coming into the bloodstream, brain or cerebrospinal fluid. Microglia engulf cellular debris, waste products, and pathogens within the nerve tissue. These cells increase in number and migrate to damaged or infected areas when needed. Oligodendrocytes are smaller than astrocytes with fewer processes. They are the cells that coil around axons and create a protective cover called the myelin sheath.
Describe the structures and functions of the peripheral nervous system (PNS). Be sure to include the nerves associated with the PNS, and contrast the functions of the somatic and autonomic nervous systems.
The peripheral nervous system (PNS) contains two types of nerves; afferent (sensory) nerves, and efferent (motor) nerves. Sensory nerves carry impulses from the body to the central nervous system (CNS) while motor nerves carry impulses from the CNS to the muscles and glands. The motor nervous system can be divided into the somatic nervous system (SNS) and the autonomic nervous system (ANS). The SNS controls voluntary skeletal muscle movement while the ANS controls involuntary smooth and cardiac muscle as well as glandular activity and secretions. The ANS has two types of nerves; parasympathetic and sympathetic. Parasympathetic nerves control functions including slowing down the heart rate, constricting pupils, and increasing glandular secretions while sympathetic nerves often have the opposite effect in the same organs. Sympathetic nerves control functions that include speeding up heart rate, raising blood pressure by constricting blood vessels, and dilating the pupils. The Sympathetic nervous system prepares our body to deal with threats to the environment, known as the "fight-or-flight response."
Name the two primary components of the central nervous system (CNS). Describe the protective membranes associated with the CNS. Differentiate between afferent and efferent nerve structure and function.
The brain and the spinal cord are the two primary components of the CNS. They are both surrounded by bone for protection; the brain has the cranium, also known as the skull, while the spinal cord has vertebrae for protection. The meninges also offer the brain and spinal cord protection. The meninges consist of three layers of protective membranes. The first layer is called the dura mater. This is a strong white connective tissue under which there are two cavities called the subdural space and the epidural space. The subdural space is filled with serous fluid and the epidural space contains a supporting cushion of fat and other connective tissues. The second layer is called the arachnoid membrane. Below this spider web-like membrane is the subarachnoid space containing cerebrospinal fluid which serves as a shock absorber. The pia mater is the third layer of the meninges. It is the delicate innermost membrane protecting the brain and spinal cord.
Afferent (sensory) nerves carry impulses from the body to the central nervous system (CNS) while efferent (motor) nerves carry impulses from the CNS to the muscles and glands.
Name and give a brief description of the structures of the brain. Include the functions of these structures.
The brain has four main divisions; cerebrum, cerebellum, diencephalon, and the brain stem. The cerebrum is the largest and uppermost portion of the brain. This portion of the brain is what controls higher brain functions such as thought, memory, emotions, and voluntary movements. The cerebrum's surface, the cerebral cortex, is characterized by elevations and grooves known as gyri and culci. The cerebellum is attached to the brain stem. It is similar to the cerebrum in appearance, though smaller, and is associated with regulation and coordination of movement, posture, and balance.
The diencephalon is part of the limbic system and is located between the cerebrum and the midbrain. This part of the brain is made up of several structures including the thalamus, hypothalamus, and the pineal gland. The thalamus relays sensory stimuli, with the exception of smell, to the cerebral cortex. The hypothalamus is ventral to the thalamus and is involved in the control of the autonomic nervous system as well as functions including emotion, thirst, hunger, body temperature, and circadian rhythms. The pineal gland's main purpose is to produce melatonin which is a hormone believed to regulate day/night cycles as well as the onset of puberty.
The brain stem is located between the diencephalon and the spinal cord and consists of the midbrain, pons, and medulla oblongata. The midbrain makes up the upper part of the brain stem and is involved in functions such as vision, hearing, eye movement, and body movement. The pons is between the midbrain and the medulla and is involved in motor control and sensory analysis. The medulla oblongata makes up the lowest part of the brain stem and is responsible for maintaining vital body functions, such as breathing and heart rate.
Choose 10 pathological conditions affecting the nervous system; describe each including diagnosis and treatment, if applicable.
Alzheimer's disease (AD) - an irreversible, progressive brain disease that leads to loss of mental, emotional, and physical functioning. Diagnosis is based on physical, psychological, neurological, and psychiatric exams along with lab tests. Treatment includes a mixture of memory enhancing drugs, antidepressants, and tranquilizers.
carpal tunnel syndrome- the pinching or compression of the carpal tunnel, a narrow passage in the wrist that houses blood vessels, tendons, and the median nerve. Inflammation or numbness usually occur and it is treated through anti-inflammatory medications, splints, physical therapy, and stopping the repetitive overuse that caused it.
cerebral palsy (CP)- lack of voluntary muscle control due to injuries to the cerebrum occurring before, during or up to the first 3-5 years after birth. There is no cure, but treatments include therapy (physical, speech, etc.) and seizure and muscle medications.
epilepsy- involuntary muscle spasms and seizures due to excessive electrical activity in the brain. It can be diagnosed through MRI and CT scans. Treatments include anticonvulsant medications.
headache (cephalalgia)- pain in the cranial cavity that can be treated through a mild analgesic such as aspirin.
narcolepsy- chronic neurological sleep disorder characterized by bouts of excessive daytime sleepiness, sudden attacks of sleep, or cataplexy. Medications are used to treat this disorder.
Parkinson's disease- a degenerative disorder of the CNS characterized by progressive deterioration of nerves in the brain stem impairing motor skills, speech, and other functions. It can be diagnosed through neurological examination and while there is no cure, it can be treated through drug and physical therapy.
spina bifida occulta- the mildest form of spina bifida, this is a birth defect where the outer part of some of the vertebrae are not completely closed. It can be diagnosed through X-ray image and with no symptoms, no treatment is recommended.
paraplegia- paralysis of the lower extremities caused by an injury to the thoracic or lumbar region of the spinal cord. Treatment includes physiotherapy and surgery in some cases.
Tay-Sachs disease- a congenital disorder that causes progressive neurological deterioration of the brain due to an accumulation of fatty substances in the brain's tissues and nerve cells. It is diagnosed in utero through amniocentesis. Treatment is symptomatic as there is no specific therapy for this condition.