Spinal cord at a glance

Spinal Cord & Nerves

This is the viscera of spinal cord and spinal meninges

1.         Anatomical points:

             I.         anteriror median fissure lies anteriorly

          II.      cauda equine lies inferiorly

2.         length : 45cm                    wide 2.5 cm

3.          Extension of spinal cord:

   Adult: at the level of foramen magnum to lower border of 1^st lumbar vertebra

   Children: at the level of the foramen magnum to the 3^rd lumber vertebra

4.         Terminal part of sub-arachnoid space of the spinal cord : lower border of 2^nd sacral vertebra

5.         termination of filum terminalis: at the 1^st coccyx

External feature of spinal cord :

i)                    anteriorly : anterior median fissure

ii)                  posteriorly : posterior median septum

iii)                inferiorly : filum terminalis and cauda equine

iv)                two enlargement in cervical and lumbar region

v)                  external surface is covered by spinal meninges : outer meningeal dura mater, middle arachnoid mater and  inner pia mater

vi)                ventral roots, dorsal roots and dorsal root ganglia and spinal nerve

6.         How many enlargement present within the spinal cord and why?

i)                    Cervical enlargement: extend from the foramen magnum to 1^st thoracic vertebra. Supply upper limb

ii)                  Lumbar enlargement: extend from thoracic 10^th to 12^th vertebra. Supply lower limb.

7.         What is spinal segment?

 Ans: Part of the spinal cord to which one pairs of spinal nerve is attached.

8.         How many spinal segments present in the spinal cord? – 31 spinal segments

9.         What is conus medullaris? – cone shaped terminal part of spinal cord

 1.         What is filum terminalis ? – it is the prolongation of pia mater which extend from the cunus medullaris to 1^st coccyx

2.         What is cauda equine: the lumbar and sacral roots below the termination of spinal cord continue as a leash of nerve roots known as cauda equine.

3.         What is legamentum denticulate: it is the thickening of pia mater situated on either side of spinal cord between nerve roots. (Figure ellis 364)

Spinal nerve

How many Spinal nerves present in our body? Number: 31 pairs. 8 cervical spinal nerve, 12 thoracic spinal nerve, 5 lumbar spinal nerve, 5 sacral spinal nerve and 1 coccygeal spinal nerve

How a spinal nerve is formed? :  Spinal nerve form by union of ventral and dorsal nerve roots

Location of spinal nerve: within the intervertebral foramen

Exit : C1-C7 spinal nerves exit ABOVE C1-C7 vertebrae

                         C8 spinal nerve projects below C7 vertebra

                         T1-S5 spinal nerves project BELOW T1-S5 vertebrae

 Branches of a Spinal Nerve:

                        1. dorsal ramus – supply deep muscles and skin of back

                        2. ventral ramus – supply upper and lower extremities, ventrolateral trunk

                        3. meningeal branch - back into the spinal column

                        4. rami communicantes - for autonomic nerve fibers

Type of spinal nerves: they are mixed nerve (both sensory and motor ).

Component: GSA (general somatic afferent –carry impulse from periphery to CNS) and GSE( general somatic efferent- impulse goes from CNS to skeletal muscle)

Plexus of spinal nerve: plexus of spinal nerve is formed by ventral rami of different spinal nerves. There are four spinal nerve plexus  present within the body.

Name of plexus	Formation	Supplied area	Important nerve of the plexus
1. cervical plexus	ventral rami of C1-C4 with some C5	a. muscles/skin of head, neck, some shoulder b. phrenic nerve - diaphragm muscle (breathing)	phrenic nerve -
2. brachial plexus	ventral rami of C5-C8 and T1	Upper limb and shoulder	Axillary N, musculocutanous  N, Radial N, median N, Ulnar N
3. lumbar plexus	- ventral rami of L1-L4	a. abdominal wall, genitals, part of lower limb	Femoral N, Obturator N
4. sacral plexus	ventral rami of L4-L5 and S1-S4	a. buttocks, perineum, part of lower limb b. sciatic nerve	Sacral n- largest nerve of body,  pudendal n, Sup and inf Gluteal n

                       

 Dermatomes: area of skin is supplied by single spinal nerve

           

Internal feature of spinal cord:

Inner grey matter contains a central canal. Parts of grey matter, ant horn and pos horn and lateral horn only in thoracic and lumbar region

Grey matter contain motor and internuncial neuron

Parts of outer white matter: 1. anterior (ventral) column

                        2. posterior (dorsal) column

                        3. lateral (intermediate) column

white matter contain ascending and descending tracts:

fasciculi/tracts –they are collection  axon bundles within the CNS. They are two types:                                a. ascending tracts – carry sensory impulse to the brain. Spinothalamic tract

            b. descending tracts – carry motor impulse from brain to the effector organ (skeletal muscle). corticospinal tract

Important tract within the spinal cord :

ASCENDING TRACTS (SENSORY)
anterior (ventral) spinothalamic	touch and pressure to thalamus
lateral spinothalamic tract	pain & temperature to thalamus
fasciculus gracilis	touch, 2-pt. discrimination,
fasciculus cuneatus	conscious proprioception,      vibration
posterior spinocerebellar                                  anterior spinocerebellar	subconscious proprioception

DESCENDING TRACTS (MOTOR)
lateral corticospinal                                          anterior corticospinal tract	Carry motor output from cortex to motor neuron of ant. Grey horn which stimulate the skeletal muscles

Blood supply: one ant and two posterior spinal arteries. Other branches: ascending cervical a, pos intercostals a, and the lumbar a

Vein: ant and pos spinal vein.

Development : caudal part of neural tube (neuroectodarm)