The spinal cord develops as 31 segments buy calan 240 mg low price, each of which gives rise to a pair of spinal nerves that emerge from the spinal cord through the intervertebral foramina buy generic calan 80mg line. Two grooves 120 mg calan visa, an ante- rior median fissure and a posterior median sulcus, extend the SPINAL CORD length of the spinal cord and partially divide it into right and left portions. Like the brain, the spinal cord is protected by three dis- The spinal cord consists of centrally located gray matter, involved tinct meninges and is cushioned by cerebrospinal fluid. The pia in reflexes, and peripherally located ascending and descending mater contains an extensive vascular network. The gray matter of the spinal cord is centrally located and Objective 25 Describe the structure of the spinal cord. It is composed of nerve cell bodies, neuroglia, and unmyelinated association neurons (interneurons). Objective 26 Describe the arrangement of ascending and The white matter consists of bundles, or tracts, of myelinated descending tracts within the spinal cord. The relative size and shape of the gray and white matter The spinal cord is the portion of the CNS that extends through varies throughout the spinal cord. The amount of white matter the vertebral canal of the vertebral column (fig. It is con- increases toward the brain as the nerve tracts become thicker. It provides a means of neural com- The core of gray matter roughly resembles the letter H munication to and from the brain through tracts of white (fig. Ascending tracts conduct impulses from the pe- cord are called horns, and are named according to the direction ripheral sensory receptors of the body to the brain.
The audio- uals in some instances may beneﬁt from gram is a method of recording the softest ampliﬁcation purchase calan 120mg fast delivery. Normal hear- loss experienced with mixed hearing im- ing sensitivity ranges from –10 to +20 pairments and the success of intervention decibels buy discount calan 240 mg. A general guide for describing the depend on the degree and type of sen- degrees of hearing loss associated with sorineural damage quality calan 120 mg. Duration of Loss or Age of Onset Another classiﬁcation of hearing loss is Table 5–1 Functional Implications of Degrees based on when the hearing loss occurred: of Decibel Loss • Prelingual hearing loss occurs before 26–40 Mild hearing loss. In ideal listening the individual acquires language, usu- conditions, hearing is minimally ally before the age of 3. Degree of Hearing Loss Hears loud conversational speech that is close by. Has difﬁculty Hearing loss can also be classified hearing in group situations. Conversational • Hard of hearing refers to individuals speech severely affected. May hear (or feel from usually have difﬁculty understanding than 90 vibrations) only very loud sounds. Hearing loss may be congenital or The type and degree of hearing loss ex- acquired. Congenital hearing loss is present perienced by individuals, regardless of the at birth. Hearing loss usually hearing loss are genetic transmission (inheri- involves more than a reduction in the ted hearing loss), caused by the mother’s loudness of sound.