Upper Motor Neurons
Upper motor neurons and lower motor neurons act to carry nerve impulses from the brain out to the muscles in the body.
Upper motor neurons supply input to the lower motor neurons. They do this by either synapsing directly to lower motor neurons, or by synapsing with a local circuit neuron, which then synapses with a lower motor neuron. The upper motor neurons originate in the motor region of the cerebral cortex or brainstem. The neurons from the cerebral cortex are important for planning, initiating, and directing voluntary movements. Neurons from the brainstem help to regulate muscle tone, control postural muscles, and help maintain balance and orientation of the head and body. Upper motor neurons connect the brain to the proper point of …show more content…
They have their cell bodies in the brain stem and the spinal cord, and their axons extend from the motor nuclei of the cranial nerves to skeletal muscles. These motor neurons synapse with the upper motor neurons, carrying on the nerve impulses that the upper motor neurons are carrying.
Motor neurons descend the spinal cord in tracts. These tracts are for the conduction of nerve impulses. The sensory tracts ascend towards the brain, and the motor tracts descend, to the rest of the body. The tracts are named for their position and their direction of signal. Examples of motor tracts are the pyramidal (corticospinal) tract, and the extrapyramidal tract.
An example of an upper motor neuron is the corticospinal tract. The corticospinal tract originates in the cortex of the cerebral hemisphere. This tract is the largest descending pathway. From the cortex, the corticospinal tract descends through the medullary pyramids and 80% of the fibres decussate. This tract contains both sensory and motor axons. The sensory axons go into the dorsal horns of grey matter. This pathway primarily controls voluntary motor control of the limbs, and voluntary posture …show more content…
If the cranial nerve motor nuclei in the brain stem are only affected, the symptoms appear as facial weakness, dysphagia, and dysarthria. When a motor neuron is damaged, the results are very different, depending on which motor neuron was damaged. In an upper motor neuron lesion, reflexes are hyperactive, atrophy is absent, fasciculations are absent, and tone is increased. When the lower motor neuron lesion occurs, the results are the opposite. Reflexes are diminished (or absent), atrophy is present, fasciculations are present, and tone is decreased (or
Upper motor neurons supply input to the lower motor neurons. They do this by either synapsing directly to lower motor neurons, or by synapsing with a local circuit neuron, which then synapses with a lower motor neuron. The upper motor neurons originate in the motor region of the cerebral cortex or brainstem. The neurons from the cerebral cortex are important for planning, initiating, and directing voluntary movements. Neurons from the brainstem help to regulate muscle tone, control postural muscles, and help maintain balance and orientation of the head and body. Upper motor neurons connect the brain to the proper point of …show more content…
They have their cell bodies in the brain stem and the spinal cord, and their axons extend from the motor nuclei of the cranial nerves to skeletal muscles. These motor neurons synapse with the upper motor neurons, carrying on the nerve impulses that the upper motor neurons are carrying.
Motor neurons descend the spinal cord in tracts. These tracts are for the conduction of nerve impulses. The sensory tracts ascend towards the brain, and the motor tracts descend, to the rest of the body. The tracts are named for their position and their direction of signal. Examples of motor tracts are the pyramidal (corticospinal) tract, and the extrapyramidal tract.
An example of an upper motor neuron is the corticospinal tract. The corticospinal tract originates in the cortex of the cerebral hemisphere. This tract is the largest descending pathway. From the cortex, the corticospinal tract descends through the medullary pyramids and 80% of the fibres decussate. This tract contains both sensory and motor axons. The sensory axons go into the dorsal horns of grey matter. This pathway primarily controls voluntary motor control of the limbs, and voluntary posture …show more content…
If the cranial nerve motor nuclei in the brain stem are only affected, the symptoms appear as facial weakness, dysphagia, and dysarthria. When a motor neuron is damaged, the results are very different, depending on which motor neuron was damaged. In an upper motor neuron lesion, reflexes are hyperactive, atrophy is absent, fasciculations are absent, and tone is increased. When the lower motor neuron lesion occurs, the results are the opposite. Reflexes are diminished (or absent), atrophy is present, fasciculations are present, and tone is decreased (or