ANATOMY OF SPINAL CORD

 INTRODUCTION 

the spinal cord is a part of the central nervous system. 

it contains the pathways that carry information from and to the brain.

tracts that carry sensory  information to the brain are called ascending tracts

tracks that carry motor information from the brain to muscles are known as descending tracts 

FEATURES 

lies in the vertebral canal. 

it extends from the foramen magnum to the lower border of the first lumbar vertebrae 

it is covered by bone, meninges ( dura matter, arachnoid matter, pia mater ), cerebrospinal fluid.

the space between the spinal cord and the spinal dural sheet is called Epidural space 

cauda equina - a collection of  long descending nerve roots present in the lower portion of the vertebral canal  (filum terminal)  

the spinal cord has 2 enlargements 

• cervical enlargement 
• innervates upper extreme areas 
• lumbar enlargement 
• innervates lower extreme areas 

cerebrospinal fluid is collected in the 3rd lumbar vertebra for testing

 

COMPONENTS OF SPINAL CORD 

SEGMENTS AND NERVES 

It is made of 31 segments 

• cervical        8 
• thoracic        12 
• lumbar          5
• sacral            5 
• coccygeal      1

segments of the spinal cord corresponding to their pairs of spinal cord 

 

NERVE ROOT 

each spinal nerve is formed by an

    - anterior (ventral ) root 

    - posterior (dorsal) root

 

FISSURES

the spinal cord is flattened from the front to the back with two grooves on its surface 

• Anterior median fissure 
• Posterior median sulcus 

they divide the spinal cord into right and left halves

the depth is about 3mm 

• anterolateral sulcus 
• lateral to the anterior median fissure 
• exit for anterior nerve root 
• posterior median septum 
• posterior intermediate septum 
• posterolateral sulcus 

NEURAL SUBSTANCE 

the neural substance in the spinal cord is divided into grey matter and white matter 

a section of the spinal cord shows grey matter and white matter 

WHITE MATTER 

white matter is a collection of nerve cell fibres 

they are formed by both myelinated and non-myelinated nerve fibres

(predominantly myelinated ) 

anterior median fissure and posterior medial septum divides the white matter into 2 lateral halves 

a band of the white matter lying in front of the anterior grey commissure is called anterior white commissure 

They are organized based on their direction  

• anterior funiculus 
• contains the anterior spinothalamic tract 
• posterior funiculus 
•  contains the fasciculus gracilis and fasciculus cutnaeous 
• lateral funiculus
• contains lateral spinothalamic tract 

the fibres are organized into tracts based on their function and direction 

• Ascending tracts - carries the sensory impulse to the brain 
• descending tracts - carries motor impulse to the motor units  
• transverse tract - communication between the one side of the spinal cord and the other side 

GRAY MATTER 

Gray matter is a collection of the nerve cell body 

it forms the central portion of the spinal cord 

it has anterior, lateral and posterior horn 

• Anterior (ventral) horn 
• contains cell bodies of somatic motor neuron
• alpha motor neurons - supplies the skeletal muscle 
• gamma motor neuron - supplies proprioceptors (position) in muscle
•  interneurons regulate the activity of the alpha motor neuron 
• they are the largest at cervical and lumbar region 

• Lateral horn 
• preganglionic fibres of  the sympathetic division (internal organ) of ANS


• prominent in the thoracic, lumbar and sacral segments 
• they supply visceral organs 
• axons leave the spinal cord through the anterior (ventral) root 
• the ventral root contains both somatic and autonomic fibres 

• posterior (dorsal) horn 

• contains fibres of afferent track neurons that carry the sensory impulse 

• the cell bodies of the sensory neuron are present in the enlarged region of the dorsal root called   dorsal root ganglion

• the axons entering the posterior horn can ascend or synapse with interneuron in the posterior horn 
• 
  
•  posterior horn has several layers 
• substantial gelatinosa of rolando
• nucleus of proprius 
• clarke's column 
• visceral afferent nucleus