The last portion of the brain stem the myelencephalon

This preview shows page 5 - 6 out of 11 pages.

The last portion of the brain stem, themyelencephalon, consists of the medulla oblongata, which is a conduitfor ascending and descending nerve fiber tracts that connect the spinal cord to the rest of the brain. The medullacontains the 'vital centers', which are important for autonomic control of the heart andperipheral blood vessels, respiratory rate and depth and sneezing (along with centers in thepons), swallowing, coughing and vomiting reflexes. It also contains a diffuse neuronalnetwork system called the reticular formation. The reticular formation connects variousareas of the brain together and processes a great deal of neuronal information. An ascendingtract of the reticular formation determines consciousness and is termed the reticularactivity system (RAS). The RAS can filter out sensory information during sleep, but triggerconsciousness when asleep or alertness if drowsy.Figure 10.11:Schematic of the brain divisionThe Spinal CordThe spinal cord is a continuation of the medulla caudally as it leaves the skull through a large opening termedthe magnum foramen. It is protected from damage by the bony vertebral column, the meninges and cerebrospinal fluid(CSF). The vertebral column is composed of seven cervical vertebrae, twelve thoracic vertebrae, five lumbar vertebrae,the sacrum (part of pelvis, 5 fused vertebrae) and the coccyx (four fused rudimentary vertebrae). Due to differences ingrowth rate between the spinal cord and vertebral column, the spinal cord terminates at the level of the second lumbarvertebrae and is termed the conus medullaris. Afferent nerves that enter the spinal cordbranch into the dorsal root, whereas efferent fibers that leave the spinal cord leave bythe ventral root. The ventral and dorsal roots combine before leaving the vertebralcolumn forming a peripheral spinal nerve. Thus, peripheral nerves are mixed nerves thatcontain both efferent and afferent information. The spinal cord in cross section revealsan outer white matter and inner grey matter configuration (opposite to the cerebrum).The grey matter consists of cell bodies whereas the white is composed of myelinatednerve axons. The meninges of the brain continue down the vertebral column andsurround and protect the spinal cord. From the outermost layer to the innermost is thedura, arachnoid and pia maters. The spinal cord arises from the primitive neural tubeand as a result contains a central canal, which is continuous with the ventricular systemof the brain. Cerebrospinal fluid provides nutrition and shock-absorbing protection andislocated in the central canal and subarachnoid space.Figure 10:12Vertebrae in the spinal cordThe spinal cord acts as a large conduit connecting spinal nerves to the brain. Ascending tracts convey sensoryinformation from the body to the brain and descending tracts transmit efferent information from the brain to targettissues. These communicating tracts are often labeled by the area where the nerve impulse arise and terminates; the

Upload your study docs or become a

Course Hero member to access this document

Upload your study docs or become a

Course Hero member to access this document

End of preview. Want to read all 11 pages?

Upload your study docs or become a

Course Hero member to access this document

Term
Winter
Professor
N/A
Tags

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture