Somatic Sensory and Motor Tracts
The name says it all! Ventral Corticospinal Tract: located in the ventral white column begins in the cerebral cortex ends in the spinal cord. The location of the terminals is the last part of the name. Since it is FROM the brain to the cord, it is a motor (descending) tract. Nerve impulses from sensory receptors propagate up the spinal cord to the brain along 4 main routes:
Dorsal Column Tract Gracile Fasciculus & Cuneate Fasciculus
Lateral Column Tract Ventral, Dorsal, Rostral & Cuneo Spinocerebellar Tracts
Spinothalamic Tract Ventral & Lateral
Trigeminothalmic Tract CN V
Sensory information is processed by interneurons in the spinal cord and brain and responses to integrative decisions are in the form of motor responses.
Motor output from the brain travels down the spinal cord in two types of descending pathways:
Pyramidal/Direct Pathways: Corticospinal and Corticobulbar Tracts convey impulses originating in the cortex and are destined for fine, isolated, precise, specific voluntary movements of skeletal muscles. Extrapyramidal/Indirect Pathways: Ventral Column Tract Rubrospinal, Tectospinal, Vestibulospinal and Reticulospinal convey impulses from the brain stem to cause the automatic movements that regulate muscle tone, posture, balance, and orientation of the head and body.
Somatic Sensory Pathways
These pathways relay information from the somatic sensory receptors described above to the primary somatosensory area in the cerebral cortex and to the cerebellum. These pathways consist of thousands of sets of 3 neurons: first-order neuron, second-order neuron, third-order neuron. First-Order Neurons : conduct impulses from somatic receptors into the brain stem or spinal cord. For the face, mouth, teeth, and eyes, somatic sensory impulses propagate along cranial nerves into the brain stem. For neck, trunk and limbs somatic sensory impulses propagate along spinal nerves into the spinal cord. Second-Order Neurons : conduct impulses from the spinal cord or brain stem to the thalamus. Second-order neurons decussate (cross over to the opposite side) in the brain stem or spinal cord before ascending to the thalamus. Thus, all somatic sensory information from one side of the body, reaches the thalamus on the opposite side.
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