
Spinal nerve
Formed by the union of ventral root & dorsal root of the spinal cord within the intervertebral foramen.
Ventral root carry fibers come from anterior horn nuclei(motor in function) and arise from anterolateral sulcus of spinal cord
Dorsal root carry fibers comes from posterior horn nuclei of grey matter (sensory in function) arise from postero-lateral sulcus of spinal cord
31 pairs of Spinal nerve | 33 vertebrae |
8 cervical | 7 cervical vertebrae |
12 thoracic spinal nerve | 12 thoracic vertebrae |
5 lumber nerve | 5 lumbar vertebrae |
5 sacral | 5 sacral vertebra fused as one |
1 coccygeal nerve | 4 coccygeal vertebrae fused as one |
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1st cervical nerve — passes through dorsal part of the superior articular surface of the C1 vertebra
- 5th sacral nerve and 1st coccygeal nerve through sacral hiatus
Difference between ventral root and dorsal root of spinal nerve
Ventral Root | Dorsal Root |
No ganglion in the ventral root
|
Dorsal root ganglia (contain pseudounipolar neuron).
1st order neurons of all ascending tracts arise from this
|
Ventral root motor in function | Dorsal root sensory in function |
Ganglia are the collection of the nerve cell body in PNS (spinal nerve and spinal cord)
Branches of spinal nerve
Dorsal Ramus — supplies dorsal body wall (not to limbs)
Ventral Ramus — supplies ventral body wall and also upper limb and lower limb.
Functional components of spinal nerve
Main theme: Spinal nerve is a mixed nerve
- Sensory from body wall & viscera
- Motor to muscle & viscera
General somatic afferent(GSA) sensory from the body wall to dorsal root ganglia
General visceral afferent(GVA) sensory from viscera to dorsal root ganglia
General somatic efferent(GSE) motor to skeletal muscle
General visceral efferent(GVE) motor to viscera(smooth and cardiac muscle)
Content of vertebral canal (formed by combined vertebral foramen)
- Spinal cord with its meninges and blood vessels ie.one anterior and two posterior spinal arteries
- Epidural space between spinal dura mater & periosteum of the vertebral canal
- Subdural space (below dura mater)
- Sub Arachnoid space (below arachnoid, between the pia and arachnoid mater) contain CSF and blood vessels
Length: 45cm
Superiorly continues as medulla oblongata and inferiorly terminates as conus medullaris.
- Lower tapering end of the spinal cord is called conus medullaris.
- The extension of pia mater below the level of conus medullaris is called film terminalis.
- Dorsal and ventral nerve roots of L2-L5, S1-S5 & Co1 collectively known as cauda equina.
I) Dura mater and arachnoid mater extend up to lower border S2 vertebra.
- Below the lower border of L1, the spinal cord is absent. And up to S2 CSF present. That’s why lumbar puncture can be done between below L2to S2
- Actually done between L3-L4vertebra or L4-L5
- Lumbar puncture is a procedure to withdraw CSF( colorless fluid) for various examinations.
Transverse section of Different spinal segment
Cervical segment
- Cervical enlargement to supply upper limb (origin of brachial plexus ie.root value C5- T1)
- No lateral horn
- Anterior horn (motor in function) broader than the posterior horn as motor supply to the upper limb.
Thoracic segment
- No enlargement
- Anterior horn and posterior horn narrow; no supply to the limb
- Lateral horn present.
Sympathetic fibers from the lateral horn — the ventral root of spinal nerve — Trunk of spinal nerve — Ventral ramus — sympathetic ganglion (collectively form sympathetic chain)
Lateral horn also present in Sacral S2-S4, form pelvic splanchnic nerves for visceral supply ie.hindgut, urinary bladder, genital organs, sexual function (erection= complex vascular and parasympathetic process)
Lumbar segment
- Lumbar enlargement due to origin of lumbar plexus( for lower limb supply)
- Lateral horn only present in L1& L2
- Anterior & posterior horn broad.
- No enlargement
- Lateral horn present (S2-S4) for pelvic splanchnic nerves
Features of spinal cord
Anterior median fissure lodge for anterior spinal artery, formed by the fusion of branches of 4th part of (Rt. & Lf.)vertebral arteries
- Outer white matter
- Inner grey matter
- Center of grey matter have central canal containing CSF
But in cerebrum & cerebellum, Outer grey matter & inner white matter.
In brain stem(mid-brain, pons, medulla) —outer white matter with dispersed nuclei(as grey matter ) within white matter.
Division
- Each half is divided into anterior, lateral & posterior region by anterolateral & posterolateral sulcui.
- Ventral motor root arises from anterolateral sulcus.
- Dorsal sensory root arises from posterolateral sulcus
Grey matter
- Anterior horn- consists of motor nuclei
Axon of these nuclei give lies to the ventral root of spinal nerve - Posterior horn- consists of sensory nuclei
Axon of these sensory nuclei give rise to the dorsal root of spinal nerve - Lateral horn present only in T1-L2 which give rise to sympathetic fibers for visceral supply which also passes through the ventral root of spinal nerve
And lateral horn in S2-S4 gives arise to parasympathetic fibers with also passes through the ventral root
Division of white matter
- Anterior white column (Anterior funiculus)
- Lateral White column (Posterior funiculus)
- Posterior white column(Lateral funiculus)
Note: Tract(collection of nerve fibers) travel through these white columns
- Descending tract(motor) travel through the white column and only synapse with nuclei of anterior horn nuclei of grey matter for supply.
- Similarly ascending tracts (sensory) after synapse with posterior horn nuclei of grey matter, ascend and travel through these white columns.
- Nerve fibers, blood vessels & neuroglia
- Nerve cell body,
- Blood vessels and neuroglia (supporting cell)
Commissure means the connection between two hemispheres
- Connection Between white matter of two hemispheres — White commissure
- Connection Between grey matter of two hemispheres— Grey commissure
Nuclei present in posterior horn of grey matter of the spinal cord
- Posteromarginal nucleus
- Substantial gelatinosa—For pain pathway
- Nucleus proprius
- Nucleus dorsalis
Blood supply of spinal cord
Artery supply
- One Anterior spinal artery (lodge in anteromedian fissure)
- Two posterior spinal arteries (lodge in posterolateral sulci)
Venous drainage
To six longitudinal channels
- One anteromedian vein
- One posteromedian vein
- Two Anterolateral vein
- Two posterolateral vein
These all drain to intervertebral venous plexus
Histology of spinal cord
Embryology/ development of spinal cord
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CNS (Brain & spinal cord)
- PNS ( 12 pairs of cranial nerve & 31 pairs of spinal nerve)
Develop from neural tube (neuroectoderm)
All ganglia
- Cranial nerve ganglia
- Parasympathetic ganglia (3,7,9,10)
- Dorsal root ganglia of spinal nerve
- Sympathetic chain/ganglia of T1-L2 segment of spinal nerve
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