October 8 - Spinal Cord.docx

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Department
Anatomy and Cell Biology
Course
Anatomy and Cell Biology 3319
Professor
guestlecture
Semester
Fall

Description
October 8, 2013 Spinal Cord Pp. 374-379, 360-362, 439-442 The Spinal Cord - Function: - Through the spinal nerves that attach to it, the spinal cord is involved in the sensory and motor innervation of the entire body inferior to the head - Provides a two-way conduction pathway for signals between the body and the brain - It is a major center for reflexes - Runs through the vertebral canal of vertebral column - Spinal cord extends from foramen magnum at the base of the skull’s occipital bone - At inferior end it tapers into the conus medullaris (cone of the spinal cord) - This cone in turn tapers into a long filament of connective tissue, the filum terminale (end terminal)  which attaches to the coccyx inferiorly - 31 pairs of spinal nerves (PNS structures) attach to the spinal cord - Spinal nerves lie in the intervertebral foramina, from which they send lateral branches throughout the body - Divided into groups:  Cervical (8)  Thoracic (12)  Lumbar (5)  Sacral (5)  Coccygeal (1) - In cervical and lumbar regions, nerves to upper and lower limbs arise, the spinal cord shows enlargements called cervical and lumbar enlargements - Cauda equina: nerve roots at the inferior end of vertebral canal (horse’s tail) - Spinal cord forms from neuroectoderm - Its segmented appearance reflects the pattern of the adjacent somites - Spinal cord segment: indicate the region of the spinal cord from which the nerve fibers that form a given spinal nerve emerge  Each spinal cord segment is designated by the spinal nerve that issues from it - Spinal cord does not extend to the end of the spinal column - Spinal cord segments are located superior to where their corresponding spinal nerves emerge through the intervertebral foramina - Spinal cord is wider laterally than anteroposteriorly - Two grooves:  Dorsal (posterior) median sulcus  Ventral (anterior) median fissure – wider one  These 2 grooves run the length of the cord and partly divide it into right and left halves - White matter of the spinal cord - Ascending: most ascending fibers in spinal cord carry sensory info from sensory neurons of body up to the brain - Descending: most descending fiber carry motor instructions from brain to spinal cord, to stimulate contraction of body’s muscles and secretion from glands - Commissural: a commissure is a bundle of axons that crosses from one side of the CNS to the other, and commissural fibers are white- matter fibers that carry info from one side of spinal cord to the other - White matter on each side of spinal cord is divided into 3 funiculi (long ropes):  Dorsal (posterior) funiculus  Ventral (anterior) funiculus  Lateral funiculus  Ventral and lateral funiculi are continuous with each other  Contain many fiber tracts – composed of axons that all have similar destinations and functions - Gray matter of spinal cord and spinal roots - Consists of a mixture of neuron cell bodies, short unmyelinated axons and dendrites and neuroglia - Gray commissure: crossbar of gray matter  Composed of unmyelinated axons that cross from one side of the CNS to the other  Contains the central canal: narrow cavity of spinal cord - The 2 posterior arms of the H are the dorsal (posterior) horns –  Interneuron’s  receive info from sensory neurons whose cell bodies lie outside the spinal cord in dorsal root ganglia and whose axons reach the spinal cord via the dorsal roots - The 2 anterior arms of the H are the ventral (anterior) horns –  Motor neurons  send their axons out of spinal cord via the ventral roots to supply muscles and glands  Ventral horns are largest in the cervical and lumbar segments because they innervate the upper and lower limbs (more skeletal musculature) - Lateral horns: small lateral gray matter columns present in the thoracic and superior lumbar segments - 4 zones of spinal cord gray matter:  Somatic sensory (SS)  Visceral sensory (VS)  Visceral motor (VM)  Somatic motor (SM) - Damage to spinal cord or spinal roots: - Can cause paralysis (loss of motor function) or parasthesia (abnormal or lost sensation) - Severe damage to ventral horn or to ventral motor roots destroys the somatic motor neurons in the region of injury and results in complete, or flaccid paralysis  Because muscles are no longer stimulated by neurons, they shrink and waste away, and spinal reflexes are absent - Damage of only the descending fiber tracts in the white matter of the spinal cord leaves the spinal cord motor neurons and spinal reflexes intact  Muscles remain healthy, but their movements are no longer under voluntary control because their connection to the brain has been lost – spastic paralysis - Protection of the spinal cord - Neural tissue is protected by vertebrae, meninges, and by watery cushion of cerebrospinal fluid - Meninges  Function: (1) cover and protect the CNS, (2) enclose and protect the blood vessels that supply the CNS, and (3) contain the cerebrospinal fluid  Dura Mater (most external)  Leathery “tough mother” – strongest of meninges  Composed of dense fibrous connective tissue and forms a tough protective covering  Spinal dural mater: dura mater around spinal cord  Epidural space: just external to spinal dura; filled with cushioning fat and a network of veins o Anesthetics are often injected here  Arachnoid Mater  Subdural space: space between arachnoid and dura o Contains only a film of fluid o Potential space because it has potential to
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