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The Spinal Cord
General Overview: Function and Location
- 1. attachment of spinal nerves; involved in sensory and motor innervation of the entire body inferior to the head
- 2. provides a two way conduction pathway for signals between the body and the brain
- 3. it is a major center for reflexes
- Extends from foramen magnum to the level of the first or second lumbar vertebra (L1 or L2)
Gross Anatomy of the Spinal Cord
- Conus Medullaris: tapered inferior end, "cone of the spinal cord"
- Filum Terminale: long filament of connective tissue tapering from the conus medullaris; attaches inferiorly to the coccyx and anchors the spinal cord
- Cervical and Lumbar Enlargements: enlarged sections of the spinal cord where the nerves of the upper and lower limbs arise
- Cauda equina: collection of nerve roots at the inferior end of the vertebral canal; descending lumbar and sacral nerve roots
White Matter of the Spinal Cord
Composed of myelinated and unmyelinated axons that allow communication between different parts of the spinal cord and between the spinal cord and brain.
- Three fiber types:
- 1. Ascending: carry sensory information from sensory neurons on the body to the brain
- 2. Descending: carry motor instructions from the brain to the spinal cord; stimulates contraction of muscles and secretion of glands
- 3. Commissural: a bundle of axons that crosses from one side of the CNS to the other, carrying information from one side of the spinal cord to the other.
- White matter in the spinal cord is divided into three funiculi:
- 1. dorsal (posterior) funiculus2. ventral (anterior) funiculus3. lateral funiculusThe ventral and lateral funiculi are continuous; divided by the end of the ventral horns.
- Contain fiber tracts composed of axons that have similar functions and destinations
Gray Matter of the Spinal Cord and Spinal Roots
Consists of a mixture of neuron cell bodies, short, unmyelinated axons and dendrites, and neuroglia.
- H-shaped (or butterfly); crossbar of "H" is the gray commissure composed of unmyelinated axons that cross from one side of the CNS to the other.
- Central canal: narrow central cavity of the spinal cord
- Dorsal (posterior) horns: two posterior arms of the "H"; consists entirely of interneurons that receive information from the sensory neurons whose cell bodies lie in the dorsal root ganglion
- Ventral (anterior) horns: two anterior arms of the "H"; contain cell bodies of motor neurons that send their axons out of the spinal cord via ventral roots to supply muscles and glands (also contains interneurons, but not emphasized); size reflects degree of muscle innervation (largest in cervical and lumbar regions: upper and lower limb innervation)
- Lateral horns: small lateral gray matter columns; present in thoracic and superior lumbar segments of the spinal cord
Can further be classified into Visceral/Somatic Sensory/Motor regions; (visceral regions are more central, somatic regions more superficial)
Flaccid vs Spastic Paralysis
Flaccid paralysis: damage to ventral horn destroys motor neurons results in paralysis of motor neurons served. Muscles atrophy from lack of stimulation/contraction; no reflexes present
Spastic paralysis: damage to fiber tracts in white matter of spinal cord; motor neurons and reflexes intact, but no longer under voluntary control.
Protection of the Spinal Cord
: three connective tissue membranes that lie external to the brain and spinal cord; function to cover and protect the CNS, enclose and protect blood vessels supplying the CNS, and contain the cerebral spinal fluid (CSF)
: outermost layer, strongest of the meninges; composed of dense fibrous connective tissue. epidural space
: lies just external to dura mater; filled with fat and blood veins that cushion the spinal cord; site of epidural injections
: separated from dura mater by the subdural (potential) space
that contains only a thin film of fluid
lies just deep to the arachnoid mater; spanned by weblike threads that attach the arachnoid mater to the pia mater; filled with CSF and contains large blood vessels that supply neural tissue.
- Pia mater: innermost later of delicate connective tissue richly vascularized by fine blood vessels; clings tightly to spinal cord surface; extends to the coccyx, covering filum terminale; lateral extensions are called denticulate ligaments
- Cerebral Spinal Fluid: fills hollow cavities of CNS; provides liquid cushion and bouyancy (reducing weight of CNS by 97%). Also helps nourish the brain and spinal cord, remove waste produced by neurons, carry hormones through the CNS
- *composition is similar to blood plasma, but contains more sodium and chloride ions and less protein.
- **100-160mls present in body
= inflammation of meninges; can lead to encephalitis; diagnosed through spinal tap (lumbar puncture)
Spinal Cord Injuries
Paraplegia: damage between the T1 and L2 segments of the spinal cord, affecting lower limbs, but not upper limbs
Quadriplegia: damage in the cervical region of the spinal cord, affecting all four limbs
Spinal cord damage superior to the midneck destroys motor neurons to the diaphragm, resulting in an inability to breathe.