The gray commissure is the crossbar of the H. Gray matter appears in the center of the spinal cord in the form of the letter H (or a pair of butterfly wings) when viewed in cross section: Dorsal roots contain sensory nerve fibers, transmitting nerve impulses from peripheral regions to the spinal cord.Ī dorsal root ganglion is a cluster of cell bodies of a sensory nerve. Ventral roots contain motor nerve axons, transmitting nerve impulses from the spinal cord to skeletal muscles.Ī dorsal root (posterior or sensory root) is the branch of a nerve that enters the dorsal side of the spinal cord. Two major roots form the following:Ī ventral root (anterior or motor root) is the branch of the nerve that enters the ventral side of the spinal cord. Roots are branches of the spinal nerve that connect to the spinal cord. External features of the spinal cord.Ī cross section of the spinal cord reveals the following features, shown in Figure 2: There are four plexus groups: cervical, brachial, lumbar, and sacral.The thoracic nerves do not form a plexus.įigure 1. The cauda equina are nerves that attach to the end of the spinal cord and continue to run downward before turning laterally to other parts of the body. The anterior median fissure and the posterior median sulcus are two grooves that run the length of the spinal cord on its anterior and posterior surfaces, respectively. Nerves that extend into the lower limbs originate or terminate here. (Top left) An axial cross section of the spinal cord (right) the same cross section. The lumbar enlargement is a widening in the lower part of the spinal cord (T 9–T 12). FIGURE 8.2 Cross sections at C6 taken using mUS probe with central. Nerves that extend into the upper limbs originate or terminate here. The cervical enlargement is a widening in the upper part of the spinal cord (C 4–T 1).
The cervical nerves form a plexus (a complex interwoven network of nerves-nerves converge and branch). Spinal nerves emerge in pairs, one from each side of the spinal cord along its length. The following are external features of the spinal cord (see Figure 1): Along its length, the spinal cord is held within the vertebral canal by denticulate ligaments, lateral extensions of the pia mater that attach to the dural sheath. The spinal cord is held in position at its inferior end by the filum terminale, an extension of the pia mater that attaches to the coccyx. Here, the spinal cord comes to a tapering point, the conus medullaris. The spinal cord is an extension of the brainstem that begins at the foramen magnum and continues down through the vertebral canal to the first lumbar vertebra (L 1). Spinal reflexes. Neurons in the gray matter of the spinal cord integrate incoming sensory information and respond with motor impulses that control muscles (skeletal, smooth, or cardiac) or glands. Transmission of nerve impulses. Neurons in the white matter of the spinal cord transmit sensory signals from peripheral regions to the brain and transmit motor signals from the brain to peripheral regions. Quiz: Regulation of Urine Concentration.Quiz: Structure of the Digestive Tract Wall.Quiz: Function of the Respiratory System.Quiz: Structure of the Respiratory System.Quiz: Supplements to the Immune Response.Quiz: Humoral and Cell-Mediated Immune Responses.Humoral and Cell-Mediated Immune Responses.Quiz: Specific Defense (The Immune System).The Immune System and Other Body Defenses.Quiz: Functions of the Cardiovascular System.Quiz: The Hypothalamus and Pituitary Glands.Quiz: The Ventricles and Cerebrospinal Fluid.The spinal cord is composed of neurons that send and receive signals. A component of the central nervous system, it sends and receives information between the brain and the rest of the body. Quiz: Muscle Size and Arrangement of Muscle Fascicles The spinal cord is a bundle of nerve fibers that extend from the brain stem down the spinal column to the lower back.Muscle Size and Arrangement of Muscle Fascicles.Quiz: Structure of Cardiac and Smooth Muscle.Quiz: Connective Tissue Associated with Muscle Tissue.Connective Tissue Associated with Muscle Tissue.
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