Cross-sectioned, the spinal cord reveals a structure in H shape which corresponds to the gray matter and where neuron cell bodies are located. Outside this medullary H, is the white matter, composed of myelinated fibers that carry information to the upper parts of the CNS and others that bring the responses to the motor organs.
Note that the internal disposition of the gray matter and the external disposition of the white matter is the opposite of that found in the brain.
Along the marrow there are 31 pairs of nerves. Each nerve is connected to the medulla as a "Y", ie it has two roots: as a dorsal root in which there is a ganglion (dilation), which contains the cell bodies of sensory neurons from the periphery of the body, and a ventral root. by which axon beams of motor neurons emerge, whose cell bodies are located in the gray matter of the medulla. These two roots come together to form the unique "Y" "cable", traversed by both the sensory and motor beams.
Peripheral Nervous System
The peripheral nervous system consists of the nerves and by nerve ganglia, and its function is to connect the central nervous system to various parts of the animal's body.
Nerves and nerve ganglia
Nerves They are bundles of nerve fibers surrounded by a layer of connective tissue. In the nerves, there are blood vessels responsible for the nutrition of nerve fibers.
At fibers present in the nerves can be either dendrites or axons, which lead, respectively, nerve impulses from various regions of the body to the central nervous system. The ganglia appear as small dilations in certain nerves.
Sensory nerves, motors and mixed
According to the type of nerve fibers they present, the nerves can be classified into sensitive (or afferent), motor (or efferent) and mixed.
- Sensory Nerves they contain only sensory fibers, ie, they drive impulses from the sense organs to the central nervous system.
- Motor nerves they contain only motor fibers that drive impulses from the central nervous system to the effector organs (muscles or glands).
- Already the mixed nerves They contain both sensory and motor fibers and drive two-way impulses from the various regions of the body to the central nervous system and vice versa.