Figure 16.26. In the autonomic worried system, a preganglionic neuron of the CNS synapses with a postganglionic neuron of the PNS. The postganglionic neuron, in turn, acts upon a target organ. Autonomic responses are mediated by the sympathetic and also the parasympathetic systems, which room antagonistic come one another. The sympathetic device activates the “fight or flight” response, if the parasympathetic mechanism activates the “rest and also digest” response.

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The sympathetic nervous mechanism is responsible for the “fight or flight” response that occurs when an animal encounters a attention situation. One way to remember this is to think of the surprise a person feels when encountering a line (“snake” and also “sympathetic” both start with “s”). Instances of functions controlled by the sympathetic worried system encompass an sped up heart rate and inhibited digestion. This functions aid prepare an organism’s body for the physics strain required to escape a perhaps dangerous situation or come fend turn off a predator.

Figure 16.27. The sympathetic and also parasympathetic nervous systems frequently have opposing effects on target organs.

The sensory-somatic nervous device is made up of cranial and also spinal nerves and also contains both sensory and motor neurons. Sensory neurons transmit sensory information from the skin, skeleton muscle, and also sensory organs to the CNS. Motor neurons transmit messages about desired motion from the CNS to the muscles to do them contract. There is no its sensory-somatic nervous system, an pet would be unable to procedure any information around its setting (what the sees, feels, hears, and also so on) and also could not control motor movements. Unequal the autonomic concerned system, which has two synapses in between the CNS and the target organ, sensory and also motor neurons have actually only one synapse—one ending of the neuron is in ~ the organ and the other straight contacts a CNS neuron. Acetylcholine is the main neurotransmitter exit at these synapses.

Humans have actually 12 cranial nerves, nerves that emerge from or get in the skull (cranium), together opposed come the spinal nerves, which emerge from the vertebral column. Every cranial nerve is accorded a name, which are comprehensive in number 16.28. Part cranial nerves transmit only sensory information. For example, the olfactory nerve transmits information about smells indigenous the nose to the brainstem. Various other cranial nerves transmit virtually solely engine information. Because that example, the oculomotor nerve controls the opening and closing the the eyelid and also some eye movements. Other cranial nerves contain a mix of sensory and motor fibers. Because that example, the glossopharyngeal nerve has actually a role in both taste (sensory) and also swallowing (motor).

Figure 16.28. The human mind contains 12 cranial nerves that receive sensory input and also control motor output for the head and also neck.

Spinal nerves transmit sensory and motor information in between the spinal cord and also the rest of the body. Every of the 31 spinal nerves (in humans) contains both sensory and motor axons. The sensory neuron cell bodies room grouped in structures referred to as dorsal root ganglia and also are presented in figure 16.29. Each sensory neuron has one projection—with a sensory receptor ending in skin, muscle, or sensory organs—and one more that synapses v a neuron in the dorsal spinal cord. Engine neurons have cell bodies in the ventral gray matter of the spinal cord that task to muscle through the ventral root. These neurons are usually stimulated by interneurons in ~ the spinal cord yet are sometimes directly stimulated through sensory neurons.

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Figure 16.29. Spinal nerves save on computer both sensory and also motor axons. The somas of sensory neurons are situated in dorsal root ganglia. The somas of engine neurons are discovered in the ventral part of the gray issue of the spinal cord.