![]() 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 towards skeletal muscles. At the spinal cord, upper motor neurons form synapses with lower motor neurons, and release glutamate into the synaptic cleft. The primary function of these neurons is to connect the brain with the spinal cord. The image shows the origin of upper motor neurons from the precentral gyrus, moving through the midbrain and medulla to form the lateral and anterior corticospinal tracts. The axons of other upper motor neurons travel along the corticospinal tract, passing the medulla oblongata and reaching the ventral horns of the spinal cord. The image shows upper motor neurons emerging from the precentral gyrus and traveling along the corticobulbar tract towards the brainstem. The axons of these lower motor neurons form cranial nerves such as the oculomotor, trochlear or trigeminal nerves that are involved with the contraction of skeletal muscles in the face, neck, jaw and tongue. Neurons whose axons travel along the corticobulbar tract synapse with lower motor neurons in the brain stem. The axons of upper motor neurons related to voluntary muscle movement travel along the CNS in two pathways – the corticospinal and corticobulbar tracts. ![]() This region is located towards the posterior end of the frontal lobe in the cerebral cortex and is associated with the primary motor cortex. Upper motor neurons have their cell bodies in the precentral gyrus of the brain. They innervate muscle fibers and directly cause their contraction. Lower motor neurons can be a part of cranial or spinal nerves. The neural pathway that results in skeletal muscle contraction can be functionally divided into two main types of neurons – the upper motor neurons in the central nervous system and the lower motor neurons of the somatic nervous system. From the still readiness of her body before the music begins till the last bow and smile, the neurons of the SoNS signal every large and small striated muscle group in the body based on the directions of the CNS. For example, a dancer on stage is integrating her memory of the music and choreography in the CNS to direct the movement of her skeletal muscles through the SoNS. Similar events are occurring within the nervous system in vastly varied activities. Gross and fine motor skills are used to sprinkle a pinch of salt on the leech to ensure that it falls off. On finding a leech, the CNS, through memory and learning, directs skeletal muscles of the arms and fingers through the SoNS to reach for some salt. Skeletal muscles act to alter your position so that the area can be visually inspected. At the same time, if a leech is stuck to your calf muscle, sensory neurons indicate the presence of a persistent damp feeling on your leg. As the CNS constantly receives visual input, it sends messages to the peripheral nervous system, particularly the SoNS, to alter posture and contractility of skeletal muscle, and accommodate changes to the surface of the forest floor. For instance, while walking in a tropical forest, you watch the forest floor for fallen twigs, insects or undergrowth. Striated skeletal muscles under voluntary control receive signals to contract on the basis of stimuli relayed to the CNS. The somatic nervous system is intricately linked to the central nervous system with the sensory and motor neurons of the SoNS communicating with the brain and spinal cord. Examples of the Somatic Nervous System Response Other examples include the immediate withdrawal of a hand on touching a hot stove or a quick change in posture when the foot is placed on a sharp stone. The knee-jerk response to the stimulation of the patellar ligament in the knee is an example of a reflex response. The motor response is practically ‘hard-wired’ for a particular stimulus. ![]() While the impulse for most voluntary muscle contraction originates in the brain or brainstem, a reflex action can be brought about with just a single sensory and motor neuron that synapse in the spinal cord. A reflex arc results in an extremely quick muscle contraction in response to a stimulus, with minimal intervention from the brain. Therefore, the primary function of the somatic nervous system is to connect the CNS with organs and striated muscles in order to enable complex movements and behavior.Īdditionally, the SoNS also mediates a subset of involuntary muscle responses called reflex arcs. This response determines the location and strength of muscle contraction across different parts of the body. The brain and spinal cord process the input from a variety of sources and integrate them before devising a response. The SoNS contains both afferent nerves traveling towards the CNS and efferent nerves responsible for sending signals from the CNS towards the rest of the body.
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