spinal cord Flashcards
introduction
- what is a spinal cord?
a spinal cord is a long cylindrical, lower part of the CNS. - it is the main pathway for information connecting the brain and the PNS.
- it occupies 2/3 part of the vertebral canal
- it is enclosed in 3 menninges
- length- 45cm in males and 42cm in females
it weighs 30g - it gives rise to 31 pairs of spinal nerves.
7 it extends from upper border of atlas to the lower border of L1 (ADULTS) and L2(CHILDREN)
- it is related as it is superiorly continuous by medulla oblongata and inferiorly terminates in conus medularis .
meninges and spaces
- the spinal cord is covered by 3 meninges they are -
the outermost- durameter
middle- arachnoid mater
innermost- pia meter
spaces present in spinal cord are
1, subdural space
2. subarachnoid space ( contains CSF
CLINICAL- in lumbar puncture use take the csf from this space)
- epidural space
it is the space between the endosteum of the vertebral canal and dura meter
it is filled with adipose tissue and blood vessels
CLINICAL- in this space we give the epidural anesthesia .
PARTS of the spinal cord
- LIGA-MENTA DENTI-CULATA
-21 pairs of teeth like projections
- fuse laterally with dura and arachnoid between the exits of the roots of the adjacent spinal nerves
- keeps the spinal cord n position. - LINE-A SP-LEN-DENS
it is the thickening of the anterior median sulcus of the lower spinal cord - FI-LUM TER-MIN-ALE
-the fibrous cord part of pia meter that extends below the conus medullaris.
-20cm
-attached to CO1
- has two divisions
-INTERNUM
upper part 15cm
extends to lower border of S2
-EXTERNUM
lower part 5cm
extends between the L1-S2 - cau-da equina
- dorsal and ventral nerve roots of left and right sides of L2-L5 S1-S5 C01
joins at the intervertebral foramen and exits as a spinal nerve
- lies vertically around filum terminale
-resembles horsetail
- at the beginning we have 40 nerve roots dorsal and ventral of right and left of each segment
ech segment has 4 nerve roots
so, if we calculate 4X4-16
4X5-20
4X1-4 so total of 40 nerve roots
structure
outside - white matter
inside - grey matter
centre- central canal
GREY MATTER
- it forms an Hshaped mass
- divided into
ANTERIOR/VENTRAL GREY COLUMN
POSTERIOR/DORSAL GREY COLUMN
LATERAL GREY COLUMN(between dorsal and ventral grey columns)
the grey matter of right and left sides of spinal cord is connected in the midline by a GREY COMMISURE , which is transversed by
CENTRAL CANAL
CENTRAL CANAL
-the lower end of central canal expands to form the TERMINAL VENTRICLE which lies in the conius medullaries
-the central canal contains CSF
-and is lined by the ependimal cells
WHITE MATTER
-it is divided into he
ANTERIOR MEDIAN FISSURE
POSTERIOR MEDIAN SEPTUM
- the white matter medial to the dorsal grey column forms the
POSTERIOR FUNICULUS(posterior white column)
-the white column medial and ventral to the ventral grey column forms the ANTERIOR FUNICULUS (anterior grey column) - the white column lateral to the both forms the LATERAL FUNICULUS
- the white matter is continous in the midline through the VENTRAL WHITE COMMISSURE
which lies anterior to the grey commissure
-the myelinated fibres that run transversely through the grey commissure, posterior to the central canal are called the DORSAL WHITE COMMISSURE
spinal nerves and spinal segments
what -
it is a segment/part of spinal cord to which a pair of dorsal / ventral nerve root is attached,
each roots is aggregated to form a number of rootlet.
The length of the spinal cord gives origin to the rootlet of one spinal nerve constituets one spinal segment.
the spinal cord is made up of 31 spinal segments
8C 5L 5S 1CO
the rootlets of the dorsal nerve root are attached to a POSTERIOLATERAL SULCUS
and the rootlets of the ventral nerve roots are attached to the ANTEROLATERAL SULCUS
THE DORSAL AND VENTRAL NERVE ROOTS JOIN EACH OTHER TO FORM A SPINAL NERVE
just proximal to their joining the dorsal nerve root is marked by a swelling known as the DORSAL NERVE ROOT GANGLION OR SPINAL GANGLION
the spinal segments do not lie opposite to their corrosponding vertebral canal
(table)
the spinal segments that contribute to the nerves of the upper limb are enlarged to form the CERVICAL ENLAREGMENTS
simialry the segments innervating the lower limbs forms the LUMBAR ENLARGEMENTS.
Dorsal root ganglion/spinal ganglion
What✓
FUNCTION
To house the cell bodies of sensory neurones
TYPE
Pseudounipolar
BRANCHES
1. dorsal ramus
Supple the 1/3 body wall
2. Ventral ramus
Supply 2/3 bw
Including limbs
Herpes Zoster
The dorsal nerve root ganglia (and the sensory ganglia of
cranial nerves) can be infected with a virus.
This leads to the
condition called herpes zoster. Vesicles appear on the skin over
the area of distribution of the nerve. The condition is highly
painful.
Segmental innervation
DERMATOMES
Areas of skin supplied by individual spinal nerves are
called dermatomes
The following dermatomes are of clinical significance:
• Spinal nerve C1 does not supply any area of skin (C1
has no dermatome).
• Spinal nerve C4 supplies the tip of shoulder.
• Spinal nerves C6, C7, C8 supplies the skin of the hand.
• Spinal nerve T4 supplies the skin over the nipple.
• Spinal nerve T10 supplies the skin over the umbilicus.
• Spinal nerves L5, S1 supplies the skin of the sole.
Referred pain:
The pain of an internal organ or structure
is projected (referred) to that part of the body wall that is
innervated by the same spinal segment (dermatome).
Examples are:
• Heart: T1 to T5 (referred over precordium and inner border
of upper limb)
• Diaphragm: C3, C4, C5 (referred to tip of shoulder)
• Appendix: T10 (referred to umbilicus)
MYOTOMES
Myotomes
Group of muscles supplied by a single spinal nerve is
called myotomes.
Some significant features of myotomes
are as follows:
• It is rare for a muscle to be supplied only by one segment.
Some exceptions are shoulder abductor (deltoid), C5;
intrinsic muscles of the hand, T1; invertor of foot, L4.
• The segment supplying muscles acting on a joint,
supply the joint itself and also the skin over the joint
(Hilton’s law).
• Muscles having a common action are usually supplied
by the same spinal segments.
CLINICAL
Injury of spinal cord above C3 causes paralysis of all
respiratory muscles and death due to paralysis of diaphragm.
• Injury of spinal cord at C4–C5 level paralyses all four limbs—
quadriplegia
.
• Injury to spinal nerves C5 and C6 (Erb’s paralysis) causes
loss of abduction of shoulder, loss of flexion of elbow, loss of
supination and loss of extension of wrist. Unopposed action
of antagonists produces policeman’s tip deformity.
• Injury to spinal nerves C8 and T1 (Klumpke’s paralysis) causes
paralysis of intrinsic muscles of the hand causing claw hand.
• Injury of spinal cord between T2 and L1 paralyses both the
lower limbs—paraplegia.
Nuclei of the spinal cord
- ANTERIOR GREY COLUMN
-MEDIAL GROUP
-dorsomedial & -ventromedial
-afferent connection -
Corticospinal, spinal interneurons and muscle spindle.
Efferent connection -Ventral muscles of trunk
-afferent connection -
Corticospinal, spinal interneurons and muscle spindle.
-efferent connection - Dorsal muscles of trunk
______________________________________
-LATERAL GROUP
-Dorsolateral & -ventrolateral&
- Retrodorsolateral
afferent connection -
Corticospinal, spinal interneurons and muscle spindle.
Efferent connection-
1. Ventral muscles of limb
2. Dorsal muscle of limb
3. Muscles of hand and foot
_______________________________________
-CENTRAL GROUP
-Phrenic &
-spinal accessory
- lumbosacral nucleus
- spinal border nucleus
afferent connection -
Corticospinal, spinal interneurons and muscle spindle.
Efferent connection
1. Diaphragm
2. SCM, TRAPEZIUS
______________________________
- POSTERIOR GREY COLUMN
- POSTERIOMARGINAL NUCLEUS
- SUBSATNTIA GELATINOSA
- NUCLEUS
PROPRIUS - DORSAL NUCLEUS(CLARK COLUMN)
-Afferent connection
1. Fast pin pricking pain from Dorsolateral tract of lassanuer
- Stimulation from large diameter
sensory fibres;
inhibitory from pain
fibreS -
sensation of crude
touch, pressure,
thermal and “slow”
burning pain - Proprioception from lower limbs
-efferent connection
1. Gives origin to lateral spinothalamic tract of opposite side
- Presynaptic
inhibition
to nucleus
proprius - Gives origin to
anterolateral
spinothalamic
tracts of the
opposite side -
Gives origin to posterior spinocerebellar tract of
same side
_______________________________ - LATERAL GREY COLUMN
-INTERMEDIOMEDIAL NUCLEUS
- INTERMEDIOLATERAL NUCLEUS
DESCENDING TRACTS -END IN SPINAL CORD- CORTICOSPINAL TRACT
DESCENDING TRACTS
The grey matter of lamina IX of Rexed (alpha and gamma
motor neurons) sends axons that innervate skeletal
muscles through the anterior root of spinal cord
This
pathway is called as final common pathway or Lower
Motor Neuron (LMN) pathway.
The LMN can
be activated by:
• Pyramidal tract or corticospinal tract or upper motor
neuron (UMN) starting from cerebral cortex for
voluntary movements
Extrapyramidal tracts starting from brainstem for
postural control of proximal muscles and controlling
the output of autonomic nervous system
• Spinal reflexes (monosynaptic stretch reflex or
polysynaptic reflexes) through intersegmental tracts
CORTICOSPINAL TRACT OR PYRAMIDAL TRACT
-ORIGIN
-they are predominantly made up of axons of neurons that lie in motor area of cerebral cortex.
-they also arises from the
-premotor area
-somatosensory area
-parietal cortex
-COURSE
-The fibres passes through the corona radiata to enter the internal capsule where they lie posterior limb, then the fibres enter crush cereberi occupying the middle 2/3rd, the fibres then descend through ventral part of pons to enter the pyramids in upper part of medulla.
At the lower end of medulla The fibres cross and constitutes pyramidal dicussation
-they fibres that cross-
enter lateral funiculus and descend as lateral corticospinal tract
Where they
TERMINATE -
-indirectly through internuncial neurons then to ventral horn cells
OR
-directly to ventral horn cells
-they fibres that do not cross enter anterior funiculus to form anterior corticospinal tract
And terminate similarly
FUNCTIONS
-they cerebral cortex controls involuntary movements through corticospinal tract
-they are facilitatory to flexors and inhibitory to extensors
DESCENDING TRACTS -END IN SPINAL CORD- RUBROSPINAL TRACT
-ORIGIN
This tract is made up of axons lying in the red nucleus present in the upper part of midbrain
COURSE
-The fibres cross to opposite side in the lower part of midbrain and constitutes ventral tegmental dicussation
This tract descends through pons and medulla to enter lateral funiculus of spinal cord
Here the tract lie just in front of lateral corticospinal tract
TERMINATION
the fibres of this tract end by synapsing with the ventral horn cells through internuncial neurons
FUNCTION
facilities flexors
Inhibition extensors
Reflexes
Spinal segments responsible for deep or stretch reflex
- Reflex- Knee jerk L3, L4
- **Ankle jerk S1, S2 **
or Achilles
tendon reflex - **Biceps
tendon reflex
C5, C6**
- **Triceps
tendon reflex
C7, C8**
- **Supinator jerk
C6, C7**
Spinal segments responsible for superficial reflexes
- Abdominal
reflexes:
• Upper T7, T8
•Middle T9, T10
• Lower T11, T12
**Cremasteric
reflex
L2**
**Gluteal reflex
L4 to S1**
**Plantar reflex
L5, S1**
**Anal reflex
S4, S5, Co**
TECTOSPINAL TRACTS
ARISE- SUPERIOR COLLICULUS
COURSE
cross the opposite side of upper part of tegmentum of midbrain
And constitutesdorsal tegmental dicussation
Descends to pons and medulla into the anterior funiculus os SP
TERMINATION
same as before
VESTIBULOSOINAL TRACTS
- LATERAL
ARISE-
LATERAL VESTIBULAR NUCLEUS
UNCROSSED
LIE- ANTERIOR FUNICULUS
TERMINATION - VENTRAL GREY COLUMN
IMPORTANCE - EQUILIBRIUM
facilities motor neuronal, supplying extensors muscles
- MEDIAL
ARISE-
Medial VESTIBULAR NUCLEUS
They are partly crossed and partly UNCROSSED
DESEND TO - ANTERIOR FUNICULUS
END
**CERVICAL SEGMENTS OF LAMINA 7&8
Inhibitiory to muscles of neck and back
OLIVOSPINAL
arise- inferior olivary nucleus (medulla)
Termination - ventral horn
RETICULOSPINAL TRACT
** the reticular formation is connected to spinal grey matter through medial and lateral reticulospinaltract**
- MEDIAL
arise - medial part of reticular formation of both pons and medulla
The fibres that cross or uncross enter- anterior funiculus
They end- directly through INTERNEURONS / alpha or gamma neurons
Facilitory - muscles of trunk and limbs
Concerned with- postural adjustments
- LATERAL
arise ventrolateral part of reticular formation of pons
Fibre cross and enter - lateral funiculus
