2/19/2023 0 Comments Somatic nervous system examples![]() These dendrites contain ion channels that open in response to mechanical forces in the cell. The afferent neurons of the somatic nervous system have their sensory dendrites in this area. These small sensory organs have specialized muscle fibers with a non-contractile central segment. In addition to typical extrafusal muscle fibers, a muscle body also contains muscle spindles. Sensory neuronsĪfferent sensory neurons of the somatic nervous system provide information to the CNS about joint angle, muscle length, muscle tension, and the presence of noxious stimuli. While botulinum toxin produces flaccid paralysis, tetanus toxin produces spastic or rigid paralysis. When tetanus toxin enters the presynaptic nerve terminal, it prevents the release of neurotransmitters at the neuromuscular junction. The only other toxin of this potency is the tetanus toxin, which works similarly. It is among the most potent neurotoxins known, with a lethal dose of 1 microgram for an adult. Thus, it leads to paralysis, initially of the facial muscles and, in severe cases, even the smooth muscles of the diaphragm. The toxin interferes with the fusion of synaptic vesicles with the neuronal plasma membrane, thus preventing acetylcholine’s release at the neuromuscular junction. This is particularly true for improperly prepared canned foods, as the warm, humid, and anaerobic environment inside food containers can provide a fertile environment for bacteria to grow. Both chemicals are produced by bacteria: the first by a bacterium called Clostridium botulinum and the second by Clostridium tetani.īotulism can affect humans through inhalation or ingestion of the toxin or bacterial spores from contaminated food. These receptors are ion channels that open upon ligand binding, leading to a cascade of ions within the muscle fiber, leading to muscle contraction.īotulinum toxin and tetanus toxin are two potent toxins that affect the neuromuscular junction. These ions induce the fusion of synaptic vesicles with the plasma membrane, resulting in the release of acetylcholine at the neuromuscular junction.Īcetylcholine then binds to nicotinic receptors on muscle cells. When an action potential reaches the axon end of the alpha motor neuron, a voltage-gated ion channel allows calcium ions to enter the neuron. The axon terminus of an alpha motor neuron forms a neuromuscular junction with striated muscle fibers, where acetylcholine is released as a neurotransmitter. Therefore, the muscles of a finger will have substantially more alpha motor neurons associated with them than the thigh or upper arm muscles. The number of alpha motor neurons that innervate a single muscle depends on the extent of fine motor control required at the site. Alpha motor neurons can receive signals from higher motor neurons for voluntary muscle movement.Īt the same time, they can also receive information from sensory neurons and interneurons to initiate reflex actions. Gam motor neurons support alpha motor neuron activity by keeping muscle spindles taut. Alpha motor neurons are thick, myelinated, multipolar nerve fibers involved in the innervation of most skeletal muscle fibers and cause them to contract. There are three types of lower motor neurons: alpha, beta, and gamma. The depolymerization of the lower motor neuron results in the transmission of the action potential to the skeletal muscles. Upper motor neurons synapse with lower motor neurons in the spinal cord and release glutamate in the synaptic cleft. The primary function of these neurons is to connect the brain with the spinal cord. The origin of the upper motor neurons is from the precentral gyrus, moving through the midbrain and medulla to form the lateral and anterior corticospinal tracts.
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