Histology Practical Neuropsychiatry Block Histology of Spinal Cord Dr. Einas Yousef 2018/2019 einas.m@dau.edu.sa

Objectives By the end of practical session, the students should be able to: Describe the organization and understand some of the basic functions of regions of the spinal cord (e.g. dorsal horn, ventral horn and lateral extension of the ventral horn), Be able to identify tissues in the nervous system (nerves, cell bodies, and white vs. gray matter in the spinal cord). Observe neuroglial cell such as astrocytes and ependymal cells of the choroid plexus.

Introduction The spinal cord is enclosed in vertebral column extending from foramen magnum in the skull to intervertebral disc between Lumbar 1 and 2 (L1 &2). It is continuous above with medulla oblongata, while it lower end in conical in shape and is called conus medullaris. It has two enlargements: cervical and lumbar 5/15/2019

Organization of spinal cord It is formed of two identical halves, made of central H shaped grey matter, surrounded by white matter.

Organization of spinal cord Spinal cord at all level is made of anterior and posterior horns. The thoracic and upper two lumbar segments, show lateral horns (having sympathetic nuclei). The two sides are connected by grey matter commissure, which contains the central canal of the spinal cord

Organization of spinal cord 7 1 2 3 6 5 4 Posterior Anterior This picture shows the following structures in the spinal cord: 1- White matter (blue) 2- Grey matter (Brown) 3- Central canal 4- ventral (anterior) horn 5- dorsal horn 6- anterior median sulcus 7- posterior median fissure

Histology of spinal cord A- Grey matter: Spinal cord at all level is made of anterior and posterior horns. The thoracic and upper two lumbar segments, show lateral horns (having sympathetic nuclei). The grey matter is composed of nerve cell bodies, non-myelinated nerve fibers and neuroglial cells. B- White matter It is made of dorsal, lateral and ventral columns The white matter consists of bundles of myelinated and few unmyelinated nerve fibers (Axons). It also contains neuroglial cell bodies (mostly oligodendrocytes that produce myelin in CNS) and few blood capillaries. It lack: nerve cell bodies and dendrites Nucleus in CNS means a group of nerve cells lying very close to each other and having the same function. A tract in CNS means a group of nerve fibers (axons) which arise from the same origin and terminate at the same termination and they have the same function. A bundle: is a group of nerve fibers, some of them are ascending (sensory) and some are descending (motor)

Microscopic structure of spinal cord (Motor neurons) The motor neuron in the ventral horn is easily identifiable by its large size, polygonal shape and extension from the cell body. Compare the size of the nucleolus in the motor neuron with the nuclei in the surrounding support cells. The above pictures showing part of grey matter: Motor neuron (in these pictures we can see the nerve cell body which contains nucleus and Nissl bodies). Nissl bodies: are patches of rER and free ribosomes which appear as blue granules in the cytoplasm of motor neuron cells.

Microscopic structure of spinal cord (Motor neurons and Nissl bodies) اسم ورقم المقرر – Course Name and No. 5/15/2019

Microscopic structure of spinal cord (Motor neurons and Neuroglial cells) اسم ورقم المقرر – Course Name and No. 5/15/2019

Microscopic structure of spinal cord (Neuroglial cells (Astrocytes) Astrocytes in contact with blood vessels Functions: Supportive and nutritive functions to the neurons Participate in “blood-brain barrier” Stimulate the formation of scar tissue secondary to CNS injury

Microscopic structure of spinal cord (Neuroglial cells (Ependymal cells) Functions: Line ventricles of brain & central canal of spinal cord (Choroid plexus) Produce, monitor & help circulate CSF (cerebrospinal fluid)

Relative amount of gray and white matter at each level of the spinal cord. In the cervical segment, there is a relatively large amount of white matter. This pattern is caused by the many axons going up to the brain from all levels of the spinal cord AND there are many axons traveling from the brain down to different segments of the spinal cord. In lower segments of the spinal cord, there is less white matter because there are fewer axons traveling to and from the brain. Gray Matter There are also differences in the gray matter. In the cervical segment, the ventral horn (the lower half of the segment) is enlarged. Also in the lumbar segment that is illustrated, the ventral horn is large. These segments are those that contain motor neurons that control movement of the arms (cervical segment) and legs (lumbar segment). Compare the relative amount of gray and white matter at each level of the spinal cord. اسم ورقم المقرر – Course Name and No. 5/15/2019

Human Can you guess which animal goes with each of these spinal cords? Pay attention to the cervical and lumbar enlargements for hints to which spinal cord goes with which animal. Human Animal Choice The first one from left: Notice the cervical and lumbar enlargements. The enlargement in the cervical part of the spinal cord is due to the many axons that are necessary to control the muscles of the wings. The lumbar enlargement is due to many axons that control the limbs. Also notice the thin thoracic section of the spinal cord. This is because movement of the wings and limbs do NOT need to be coordinated. When birds fly, their legs are tucked under their bodies. The Middle one: Notice that the snake does NOT have a cervical or lumbar enlargement of the spinal cord. This is because the snake has no limbs. The third one from left: Notice the enlargements in the cervical and lumbar parts of the spinal cord. This is the typical pattern found in mammals. The enlargements are necessary for the many neurons required to control limb movement. Spinal cord Choice اسم ورقم المقرر – Course Name and No. 5/15/2019

For more slides and picture Please review Atlas of Human Histology (Nervous tissue) http://www.histologyguide.com/slidebox/06- nervous-tissue.html Michigan Histology and virtual microscopy learning resources. (CNS) http://histology.medicine.umich.edu/medical- schedule اسم ورقم المقرر – Course Name and No. 5/15/2019