![]() These neurons are usually stimulated by interneurons within the spinal cord but are sometimes directly stimulated by sensory neurons. Motor neurons have cell bodies in the ventral gray matter of the spinal cord that project to muscle through the ventral root. The sensory neuron cell bodies are grouped in structures called dorsal root ganglia and are shown in Figure 2.Įach sensory neuron has one projection-with a sensory receptor ending in skin, muscle, or sensory organs-and another that synapses with a neuron in the dorsal spinal cord. Each of the 31 spinal nerves (in humans) contains both sensory and motor axons. Spinal nerves transmit sensory and motor information between the spinal cord and the rest of the body. For example, the glossopharyngeal nerve has a role in both taste (sensory) and swallowing (motor). Other cranial nerves contain a mix of sensory and motor fibers. For example, the oculomotor nerve controls the opening and closing of the eyelid and some eye movements. Other cranial nerves transmit almost solely motor information. For example, the olfactory nerve transmits information about smells from the nose to the brainstem. Some cranial nerves transmit only sensory information. The somas of motor neurons are found in the ventral portion of the gray matter of the spinal cord. ![]() The somas of sensory neurons are located in dorsal root ganglia. Each cranial nerve is accorded a name, which are detailed in Figure 1.įigure 2. Spinal nerves contain both sensory and motor axons. Humans have 12 cranial nerves, nerves that emerge from or enter the skull (cranium), as opposed to the spinal nerves, which emerge from the vertebral column. Acetylcholine is the main neurotransmitter released at these synapses. Unlike the autonomic nervous system, which has two synapses between the CNS and the target organ, sensory and motor neurons have only one synapse-one ending of the neuron is at the organ and the other directly contacts a CNS neuron. Without its sensory-somatic nervous system, an animal would be unable to process any information about its environment (what it sees, feels, hears, and so on) and could not control motor movements. Motor neurons transmit messages about desired movement from the CNS to the muscles to make them contract. Sensory neurons transmit sensory information from the skin, skeletal muscle, and sensory organs to the CNS. It controls voluntary and involuntary activities, including movements, breathing, thinking, digestion, etc. ![]() The sensory-somatic nervous system is made up of cranial and spinal nerves and contains both sensory and motor neurons. The human nervous system functions as the control center for everything our body does.
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