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 fibers
they are formed by both myelinated and non-myelinated nerve fibers
(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 cutaneous
lateral funiculus
contains lateral spinothalamic tract
the fibers 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 fibers 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 fibers
posterior (dorsal) horn
contains fibers 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
Komentáře