SPINAL CORD
S
LOCATION OF THE SPINAL CORD
The cord runs about 45 cm
downwards from the brain
via a canal in the spine,
tapering at its lower end.
It is covered by meninges,
which are continuous with
the covering of the brain.
Structure of the spinal cord
The grey matter contains nerve cell bodies,
whereas the white matter consists of tracts
of nerve fibres. Spinal nerves join the cord
at regular intervals.
ANATOMY OF THE SPINAL NERVES
The 31 pairs of nerves are divided into
groups - cervical, thoracic, lumbar,
and sacral - according to the section
of spine from which they emerge.
Those emerging from the middle of
the spinal cord encircle the body,
branching to supply a fairly distinct
segment of trunk. Those emerging
from the top and bottom of the spine
join to form networks, called plexuses,
from which branches arise to supply
the arms and legs.
Nerve twig
Dorsal root
Spinal cord
Spinous process
o f vertebra
Brain
Cervical nerves
Thoracic nerves
Spinal cord
Lumbar nerves
Sacral nerves
— Cauda equina
Distribution
The branches of each
nerve divide asthey
travel further from
the spinal cord. As a
result, all parts ofthe
trunk, arms, and legs
are supplied with a
network of nerve twigs.
Spinal nerve
Nerve bundle
Nerve axon
Vertebra
Intervertebral discs
Structure
Each nerve consists of bundles ofthe
axons, or fibres, of individual nerve
cells that have their cell bodies in or
close to the spinal cord.
STRUCTURE
A t t h e c o r e o f t h e s p i n a l c o r d i s
g r e y
m a t t e r , w h i c h c o n t a i n s t h e c e l l b o d i e s
o f n e r v e c e l l s , a l o n g w i t h v a r i o u s s u p -
p o r t i n g c e l l s . S o m e o f t h e n e r v e c e l l s a r e
m o t o r n e u r o n s f r o m w h i c h l o n g p r o -
j e c t i n g f i b r e s ( c a l l e d a x o n s ) p a s s o u t o f
t h e
s p i n a l
c o r d
i n
b u n d l e s
w i t h
t h e
s p in a l n e rv e s
a n d
e x t e n d
t o
g l a n d s
o r
m u s c l e s i n t h e t r u n k a n d l i m b s . S u r -
r o u n d i n g t h e g r e y m a t t e r a r e a r e a s o f
w h i t e m a t t e r , w
h i c h c o n s i s t o f b u n d l e s
o f n e r v e c e l l a x o n s r u n n i n g l e n g t h w i s e
t h r o u g h t h e c o r d .
S p r o u t i n g f r o m
e a c h s i d e a t r e g u l a r
i n t e r v a l s
a r e
t h e
s e n s o r y
a n d
m o t o r
s p i n a l
n e r v e
r o o t s . T h e s e
c o m
b i n e
t o
f o r m t h e s p i n a l n e r v e s , w h i c h l i n k t h e
c o r d t o a l l a r e a s o f t h e t r u n k a n d l i m b s .
T h e c o r d i s b a t h e d i n
c e r e b r o s p in a l f lu id
a n d
s u r r o u n d e d
b y
t h r e e
p r o t e c t i v e
m e m b r a n e s k n o w n a s t h e
m e n in g e s .
FUNCTION
T h e
n e r v e
t r a c t s
i n
t h e
w h i t e
m a t t e r
a c t
m a i n l y
a s
h i g h w a y s
f o r
s e n s o r y
i n f o r m a t i o n
p a s s i n g
u p
t o
t h e
b r a i n
o r m
o t o r s i g n a l s p a s s i n g d o w n ; h o w e v -
e r ,
t h e
c o r d
p r o c e s s e s
s o m e
s e n s o r y
i n f o r m a t i o n ,
a n d
p r o v i d e s
m o t o r
r e s -
p o n s e s , w i t h o u t a n y i n v o l v e m e n t o f t h e
b r a i n .
M a n y
r e f l e x
a c t i o n s
a r e
c o n -
t r o l l e d i n t h i s w a y .
DISORDERS
T h e
s p i n a l
c o r d
m a y
b e
i n j u r e d
b y
t r a u m a t o t h e s p i n e ( s e e
s p in a l in ju r y ) .
S e v e r i n g
o f
n e r v e
t r a c t s
i n t e r r u p t s
c o m
m
u n i c a t i o n b e t w e e n t h e b r a i n a n d
t h e p a r t s o f t h e b o d y s e r v e d f r o m t h e
s e c t i o n o f t h e
c o r d b e l o w t h e i n j u r y .
T h i s c a n l e a d t o v a r i o u s t y p e s o f p a r a l -
y s i s
a n d / o r
l o s s
o f s e n s a t i o n ,
w h i c h
a r e
u s u a l l y
p e r m
a n e n t
b e c a u s e
n e r v e
c e l l s a n d f i b r e s w i t h i n t h e c o r d a r e n o t
a b l e t o r e g e n e r a t e . H o w e v e r , t h e r e f l e x e s
t h a t a r e
c o n t r o l l e d b y t h e s p i n a l c o r d
a r e u s u a l l y m a i n t a i n e d . P r e s s u r e o n t h e
c o r d , w h i c h m a y b e c a u s e d b y a b l o o d
c l o t o r a t u m o u r , f o r e x a m p l e , c a n a l s o
706
previous page 705 BMA A Z Family Medical Encyclopedia   2004 read online next page 707 BMA A Z Family Medical Encyclopedia   2004 read online Home Toggle text on/off