Spinal Cord Notes
Gross Anatomy:
Position: Adult: stretches from the foramen magnum to L1, L2. Dura ends at the level of S1 in sacral canal. Embryo: spinal cord fills the whole vertebral canal.
Features/Components of a Cross Section:
1. Posterior median septum; anterior median fissure.
2. Central canal.
3. Grey and white matter (latter for ascending and descending pathways).
4. Anterior and posterior grey horns.
5. Anterior, posterior and lateral funiculi (white matter).
Enlargements: Cervical and lumbar.
Caudal aspect: Conus medullaris is the tapered part and filum terminale the termination. Inserts on the first-coccygeal vertebra, via the coccygeal ligament.
Meninges: coverings of spinal cord.
1. Spinal dura (the extradural space is used for epidural anaesthesia.
2. Spinal arachnoid matter.
3. Spinal pia mater. The CCF is found in the subarachnoid space found between the pia and the arachnoid. Distally, spinal roots are found in the lumbar cistern.
Cord Supports: Denticulate ligaments i.e. pia is attached to the dura at regular intervals by the serrated ligamentum denticulatum.
Cord Indentations:
1. Ventral median fissure.
2. Dorsal median sulcus.
Spinal Nerve Attachments: (31 bilaterally paired).
1. Cervical (8).
2. Thoracic (12).
3. Lumbar (5).
4. Sacral (5).
5. Coccygeal (1).
SPINAL NERVES:
Composition: Fusion of a dorsal root (sensory fibres) and ventral root (motory fibres). A series of rootlets join to form each root. Each dorsal root bears a swelling called the spinal or dorsal root ganglion. Initially, these rootlets are covered by meninges and dural extensions. The cervical nerves exit the vertebral canal via the intervertebral foramen above the corresponding vertebra. The thoracic and lumbar nerves leave the intervertebral foramen below the corresponding vertebra. The roots of nerves L1 - S5 run caudally and form a leash around the filum terminale termed the cauda equina. A typical spinal nerve contain 4 components ie innervation of skeletal muscle (motor), sensory to muscle, skin and joints, autonomic motor innervation and sensory to visceral structures (see later).
CROSS SECTIONAL STRUCTURE OF THE CORD:
Components:
1. White matter and ventral white commissure. Divided into dorsal, lateral and ventral columns.
2. Grey matter (H-shaped), with central canal and grey commissure: Dorsal and ventral horns visible and lateral horn in the thoracic zone (for sympathetic outflow).
Function of Spinal Cord:
1. Relay of sensory information and transmission to brain.
2. Motor innervation of somatic and visceral structures. Under central control.
White Matter:
Nature: Composed of ascending and descendig tracts.
Ascending Spinal Tracts:
1. Gracile fasciculus: terminate in the gracile nucleus (dorsal column).
2. Cuneate fasciculus: terminate in the cuneate nucleus (dorsal column). The two fasciculi are also termed the posterior column - medial lemniscal pathway. Both the fasciculus gracilis and cuneatus relay in the gracile and cuneate nuclei in the medulla oblongata respectively. The function of the posterior columns are directed at conscious proprioception and discriminative touch. Three orders of afferents carry the information from the sensory receptors to the somatic sensory cortex.
a. First order afferents: Information from the lower limb, hand and trunk are relayed from the sensory receptors (Meissner, Pacinian, Ruffini, Merkel Cell, Golgi tendon organs) is the two fasciculi. Fibres from the lower leg and trunk pass in the gracile fasciculi and upper limb in the cuneate fasciculus, respectively.
b. Second order neurons pass from the two nuclei (in medulla oblongata) cross over to the opposite side, enter the medial lemniscus, transverse the tegmentum (pons and midbrain), relay in the ventral posterolateral nucleus of the thalamus.
c. Third order neurons pass from the thalamus to the somatic sensory cortex of the cerebrum.
3. Anterior and posterior spinocerebellar tracts: cuneo-cerebellar and rostral spinocerebellar. Functions include relay of unconscious proprioception fibres.
4. Anterior and lateral spinothalamic tracts: The latter is called the spinal lemniscus as it traversus the brainstem. The tracts carry fibres for temperature, touch and pain sensation.
5. Spinoreticular, spinotectal, spino-olivary tracts.
Descending Spinal Tracts:
1. Lateral and ventral corticospinal tracts. At the level of the medulla the fibres cross over to the opposite side in the pyramid decussation.
2. Reticulospinal tract.
3. Rubrospinal tract (rudimentary in man).
4. Raphespinal tract.
5. Tectospinal tract.
6. Vestibulospinal tract.
7. Aminergic.
8. Autonomic.
The anterior grey horn is divided roughly into a medial third and lateral two thirds. The medial axons supply the flexors and extensors muscles of the trunk. Axons or nuclei are sited in the lateral division as follows:
1. Retrodorsal - supply flexors and extensors of hand and foot.
2. Dorsolateral - supply flexors and extensors of the forearm and leg.
3. Ventrolateral - supply flexors and extensors of the arm and thigh.
4. Central - supplies the diaphragm.
Origin of Fibres Entering the Corticospinal Tracts:
1. Premotor area.
2. Motor cortex (precentral gyrus - area 4).
3. Somatic sensory cortex.
4. Superior region of parietal lobule.
Passage of Corticospinal Tracts: From the somato-motory cortex (Betz cells) through the corona radiata and internal capsule, via the brainstem, crus of the midbrain and pons to the medulla oblongata. In the medulla oblongata the fibres are termed the pyramidal tract.
Function of corticospinal or pyramidal tract
The chief function is control of fine voluntary movements (i.e. writing and doing up a button).
Connections and Divisions of the Corticospinal Tracts:
1. Cortico-nuclear branches to cranial nuclei (affecting face, jaw, tongue).
2. At the pyramidal decussation 80% if the fibres pass in the lateral corticospinal tract and about 15% in the anterior corticospinal tract.
3. About 5% of fibres remain uncrossed and descend in the ipsilateral corticospinal tract.
4. High damage to the corticospinal tracts results in Upper Motor Neuron Disease (i.e. stroke).
Other Functions of the Descending Tracts:
1. Reticulospinal: Locomotion and postural control. Control of the proximal parts of the limbs and trunk and in walking and running.
2. Tectospinal: Function uncertain in man but is postulated to be associated with head and trunk orientation following visual and auditory stimuli.
3. Vestibulospinal: Maintenance of centre of gravity between the feet. Reflexes that alter body position in relation to movements of the head.
4. Raphespinal: Modulation of sensory transmission.
5. Aminergic: Inhibit sensory and facilitate motor neurons.
6. Central Autonomic Pathways: Sympathetic pathways are associated with baroreceptor - reflexes, and the parasympathetic pathways, bladder and rectal function.
Grey Matter of the Spinal Cord:
Dorsal Horn: Composition - dorsal horn nuclei or columns.
1. Substantia gelatinosa.
2. Dorsolateral fasciculus.
3. Nucleus proprius (principal sensory nucleus).
4. Nucleus dorsalis (Clarke’s column).
5. Besides the nuclei, the dorsal horn contains 10 laminae of Rexed (integrate somatic motor information, act as reflex centres and associated with spinocerebellar fibres).
Lateral Horn: Composition.
Autonomic nucleus.
Ventral Horn: Composition.
Motor nucleus (in the upper cervical region is termed the spinal accessory nucleus). Contains lower motor neurons which innervate striated muscles.
Divided into:
a. Medial and lateral motor columns.
b. Intermedio-lateral and intermedio-medial cell columns.
Blood Supply of the Spinal Cord:
Arterial Supply:
1. Anterior spinal arteries: Supply cord anterior to the posterior grey columns.
2. Posterior spinal arteries: Supply posterior columns.
3. Anastomotic radiculospinal reinforcements at the level of TI and TII (arteries of Adamkiewicz).
Venous drainage:
1. Anterior and posterior spinal veins empty into segmental or radicular veins (vertebral, azygous, lumbar and lateral sacral veins).
Labels: Basic Science: Neuroanatomy
2 Comments:
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At 11/04/2008,
jaydeep said...
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GOOD NEURO ANATOMY NOTES BUT IT LACKS IMAGES, IT LL BE BETTER WITH PICS,
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At 11/04/2008,
said...
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good notes
