09 Control and Coordination - part 08 - Spinal Cord

 

09 Control and Coordination - part 08 - Spinal Cord

Spinal Cord :

• Part of central nervous system and forms the lower extension of the medulla oblongata of the brain. 
• Covered and protected by bony covering and membranes. 
• Lies within the neural canal of the vertebral column.
• Surrounded by three meninges - 

1. Dura mater
2. Arachnoid mater and 
3. Pia mater. 

• The Cerebro Spinal Fluid (CSF) secreted by pia mater, forms a fluid cushion around the spinal cord and within it inside the central canal.

Externally -

• Spinal cord appears as long cylindrical rod.
• 42 to 45 cm long and 2.0 to 2.5 cm broad. 
• Broadest at its anterior end gradually tapers into conus medullaris (L1 to L2) and continues as a thread like filum terminale end posteriorly.
• Shows two swellings along its length called cervical and lumbar swelling.
• 31 pairs of spinal nerves arise from lateral sides.
• These nerves are concentrated in the region of cervical and lumbar swelling and around the conus medullaris. 
• The bunch of nerves in the hind part of the spinal cord, along with the filum terminale, appear like a horse’s tail, so called cauda equina.

T. S. of spinal cord

• Dorsoventrally flattened due to the presence of deep, narrow posterior fissure and shallow, broad anterior fissure. 
• A central canal can be seen in the centre. 
• Fissures divide the spinal cord incompletely into a right and left side. 
• Grey matter is somewhat H-shaped or butterfly shaped and is on the inner side.
• White matter is on the outer side. 
• The fissures divide the grey matter into six horns, namely dorsal, lateral and ventral horns, 
• White matter is divisible into 6 columns or funiculi, namely dorsal, lateral and ventral funiculi. 
• The dorsal and ventral horns extend out of the spinal cord as dorsal root and ventral root of spinal cord respectively. 
• Dorsal root is connected to the dorsal root ganglion. (It lies just outside and lateral to the spinal cord). 
• It has an aggregation/collection of unipolar sensory neurons.
• Association or inter-neurons lie inside the grey matter. 
• The receive signal from the sensory nerve, integrate it and direct the response towards motor neurons lying towards the ventral horn. 
• The lateral horns have neurons of autonomic nervous system (ANS).
• Nerves arising from these neurons, emerge out from the ventral root of spinal nerve.
• White matter consists mainly of bundles of myelinated nerve fibre called ascending and descending tracts. 
• The ascending tracts conduct sensory impulses from spinal cord to the brain and these lie in the dorsal column/funiculi.
• The descending tracts conduct motor impulses from brain to the lateral and ventral funiculi of spinal cord.

Functions of Spinal Cord : 

• Main centre for the most reflex actions. 
• Provides pathway for conduction of sensory and motor impulses to and from the brain. 
• Provides nervous connection to many parts of the body.