![]() ![]() Symptoms of ALS include fasciculations, weakness, spasticity, muscle cramps, and difficulty speaking, swallowing, and breathing. The disease includes the destruction of motor neurons in the motor cortex, the brainstem, and the spinal cord. Some of these include neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) or Lou Gehrig disease, some dementias, Huntington disease, spinal and bulbar muscular atrophies, as well as lesions of the motor neurons.ĪLS is characterized by the clinical presentation of both upper and lower motor neuron lesion symptoms. Many conditions can affect neurons and their transmission. Somatic innervation to the external urethral sphincter is also involved in the process. Sympathetic innervation in the pelvic region inhibits the functions of the parasympathetic innervation with the relaxation of the detrusor muscle and constriction of the internal urethral sphincter. A notable example of autonomic innervation is the parasympathetic innervation of the detrusor muscle of the bladder and the internal urethral sphincter to accommodate micturition. Somatic innervation is the cause of voluntary muscle function, whereas, autonomic innervation controls the involuntary muscle contraction and relaxation, and glandular secretion that enables the body to function and adapt without conscious thought. Somatic nerves and autonomic nerves both act on muscles. Acetylcholine molecules then bind their receptors on the sarcolemma to cause the opening of sodium channels which results in the production of an action potential and its propagation to the myofibril to cause muscle contraction. This permits the fusion of neurotransmitter vesicles with the axon terminal membrane to cause acetylcholine release into the junction. When an action potential reaches the axon terminal of the motor neuron, voltage-dependent calcium channels open and accommodate the influx of calcium. Motor neurons in vertebrates secrete acetylcholine into the neuromuscular junction. Muscles require innervation to contract and to maintain tone. There is a continuing interest in potential therapeutic uses for neural progenitor cells following injury. However, neural progenitors that are capable of participation in neurogenesis are present in certain regions such as the dentate gyrus of the rat, and in the subependymal of rodents. Mature neurons are unable to divide, so their destruction may lead to a neurological deficit. The variety of interactions among neurons enables the transmission of impulses to perpetrate diverse functions within the body. Graded potentials are also important to note as they vary in strength, and lose amplitude throughout their transmission. As a depolarizing threshold stimulus occurs, an action potential that is consistent in amplitude is generated and travels down the axon to the terminal. The resting membrane potential of typical neurons is around -70 mV. Potassium, sodium, and chloride ions are the greatest contributors to the membrane potential of the common neuron. Neurons propagate their potentials by ion movement through voltage-gated ion channels (though calcium channels are largely voltage-independent) across their membranes. Axonal transport is carried out by proteins such as kinesin and dynein. Axons typically end in an axon terminal at which neurotransmitters, neuromodulators, or neurohormones are released in the conversion of the electrical signal to a chemical signal which can cross the synapse or neuromuscular junction. In addition to afferent signaling, dendrites can be involved in protein synthesis and independent signaling functions with other neurons. ![]() There may be one or many dendrites associated with a single neuron depending on its function and location. The soma contains the nucleus and other organelles necessary for neuronal function. Neurons exist in a variety of forms including multipolar, bipolar, pseudounipolar, and anaxonic which differ primarily in their number and arrangement of axons and dendrites. Neurons are characterized by the long processes which extend out from the cell body or soma. Neurons are unique in their ability to receive and transmit information.
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