Spinal Cord

The spinal cord is a part of the central nervous system. It is a long pipe-like structure arising from the medulla oblongata, part of the brain consisting of a collection of nerve fibres, running through the vertebral column of the backbone. It is segmented with a pair of roots (dorsal and ventral roots) consisting of nerve fibres joining to form the spinal nerves.

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Spinal Cord Anatomy

In adults, the spinal cord is usually 40cm long and 2cm wide. It forms a vital link between the brain and the body.

The spinal cord is divided into five different parts.

  • Sacral cord

  • Lumbar cord

  • Thoracic cord

  • Cervical cord

  • Coccygeal

Several spinal nerves emerge out of each segment of the spinal cord. There are 8 pairs of cervical, 5 lumbar, 12 thoracics, 5 sacral and 1 coccygeal pair of spinal nerves

It performs the primary processing of information as it carries sensory signals from all parts of the body to the Central Nervous System through afferent fibres.

Nerve tissue consists of the grey and white matter spread across uniformly.

The smooth muscles and the skeletal system carrying nerve fibres liaise different reflexes when ventral horn projects axons which carry motor neurons.

It also helps intercede autonomic control for visceral functions which consist of neurons with descending axons. It is a sensitive site, which is severely affected in case of a traumatic injury.

Understanding the physiology of the spinal cord helps in detecting and determining the various methods to deal with diseases and damage related to the spinal cord.

Also Read: Peripheral Nervous System

Spinal Cord Diagram

Spinal Cord Diagram

Additional Note: The above diagram also showcases the backbone. It contains a total of 24 stacked bones in an adult human. However, at birth, humans have a total of 33 bones in the backbone which eventually fuses to 24 bones.

Structure Of Spinal Cord

The Spinal cord runs through a hollow case from the skull enclosed within the vertebral column. Spinal nerves arise from different regions of the vertebral column and are named accordingly, the regions are – Neck, chest, pelvic and abdominal.

Cross-section of spinal cord displays grey matter shaped like a butterfly surrounded by a white matter.

Grey matter consists of the central canal at the centre and is filled with a fluid called CSF (Cerebrospinal fluid). It consists of horns (four projections) and forms the core mainly containing neurons and cells of the CNS. There are two dorsal and two ventral horns.

The white matter consists of a collection of axons permitting communication between different layers of CNS. A tract is a collection of axons and carries specialized information. Ascending tracts and descending tracts send and transmit signals from the brain respectively to various nerve cells across the body.

Spinal nerves act as mediators, communicating information to and from the rest of the body and the spinal cord. We have 31 pairs of spinal nerves.

Three layers of meninges surround the spinal cord and spinal nerve roots.

  • Dura mater

  • Arachnoid mater

  • Pia mater

Dura mater consists of two layers- periosteal and meningeal. Epidural space is present between the two layers.

Subarachnoid space lies between the arachnoid mater and pia mater. It is filled with cerebrospinal fluid.

Spinal Cord Injuries

Damage to any part of the spinal cord or spinal nerves results in permanent and life-long damage to the spinal cord affecting the normal functioning of the spinal cord without any replacements.

It often causes long-term changes in the strength, body posture and reflexing of the body. Voluntary control of limbs post an injury depends on the severity and location of the injury.

One has a complete injury when he loses the ability to move or sense below the injury. The incomplete injury allows the injured to perform some sensory and motor functions.

Spinal cord injury not only has an impact on the spinal nerves and the vertebral column but affects other muscles and vital organs as well.

Paralysis from an injury can be of two types:

  • Tetraplegic

  • Paraplegic

Tetraplegia is a paralysis that results in total or partial loss of use of all four limbs and torso.

Paraplegia, on the other hand, is similar to tetraplegia, except it doesn’t affect the arms.

These injuries result in the inability to voluntarily move limbs, lose sensation, delayed or exaggerated reflexes, changes in sexual functions, intense shooting pain due to damaged nerve fibres. It also causes shortness of breath, cough and muscle spasms.

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Spinal Cord Nerves

The spinal nerves consist of a group of 31 nerves. These nerves are attached to the spinal cord by two roots- dorsal sensory root and ventral motor root.

The sensory root fibres carry sensory impulses to the spinal cord. The motor roots, on the contrary, carry impulses from the spinal cord.

The spinal nerves carry messages to and from the skin of specific regions of the body called dermatomes.

The spinal cord nerves can be grouped as:

  • Cervical

  • Thoracic

  • Sacral

  • Lumbar

  • Coccygeal

Cervical Nerves

Cervical means of the neck. There are 8 cervical nerves that emerge from the cervical spine (C1-C8).

Thoracic Nerves

Thoracic means of the chest. There are 12 thoracic nerves that emerge from the thoracic spine (T1-T12).

Lumbar Nerves

Lumbar means from the lower back region. There are 5 lumbar nerves that emerge from the lumbar spine (L1-L5).

Sacral Nerves

Sacral means of the sacrum. The sacrum is a bony plate at the base of the vertebral column.

There are 5 sacral nerves that emerge from the sacral bone (S1-S5).

Coccygeal Nerves

Coccygeal means of the tailbone. There is 1 nerve that emerges from the coccygeal bone.

Function Of Spinal Cord

Important functions of Spinal Cord are mentioned below:

  • Forms a connecting link between the brain and the PNS

  • Provides structural support and builds a body posture

  • Facilitates flexible movements

  • Myelin present in the white matter acts as an electrical insulation

  • Communicates messages from the brain to different parts of the body

  • Coordinates reflexes

  • Receives sensory information from receptors and approaches towards the brain for processing.

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Related links:

Human Nervous System
Human Brain

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