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Spinal Cord: Structure, Anatomy, Functions, Injuries, Common Disorders, Practice Problems and FAQs

Spinal Cord: Structure, Anatomy, Functions, Injuries, Common Disorders, Practice Problems and FAQs

Sensitivity in the teeth is a common problem among many people. Nowadays we can see many advertisements that promote the products that help to cure teeth sensitivity. You might have noticed most of the advertisements start by asking about the pain or discomfort while having an ice cream or any cold or hot products. Right? Have you ever felt the same? If yes, how do we feel the pain immediately when we have the cold food items? The reason for this is the presence of nerves that connect the brain and the teeth. They carry the impulses from the teeth to the brain.

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          Fig: Path of teeth sensitivity while having ice cream

The reason is the same for every pain in all parts of the body. But there is a bystander in between the nerves in the body and the brain. It is the spinal cord that lies inside the spinal column, which is made up of 33 bones called vertebrae. So the spinal cord collects all the information from different parts of the body and carries it to the brain and vice versa. Spinal cord helps in both voluntary and involuntary functions of our body. Just think about a situation, where the spinal cord got some injuries. Some serious injuries to the spinal cord can even lead to total body paralysis. Now we are going to discuss more about the structure, anatomy, functions and common disorders of the spinal cord in this article.

Table of contents

  • Central nervous system
  • Spinal cord
  • Structure of spinal cord
  • Anatomy of spinal cord
  • Functions of spinal cord
  • Spinal cord injury
  • Common disorders of the spinal cord
  • Practice Problems
  • FAQs

Central nervous system

The hollow structure that lies along the mid dorsal axis of the body is called the central nervous system or CNS. It is the major site for the processing of information and controlling the body activities. The two main parts of CNS are as follows:

  • Brain
  • Spinal cord


                                   Fig: Central nervous system

Spinal cord

The cylindrical structure that runs through the centre of the spine or mid dorsally from the brainstem to the lower back within the vertebral column is called the spinal cord or myelon. The vertebral column is the bone that protects the spinal cord. This delicate structure has nerve bundles and cells that carry messages from the brain to the rest of the body and vice versa. So it is a major part of the human nervous system.


                         Fig: Spinal cord and vertebral column

Structure of spinal cord

The spinal cord extends from the base of the brain and continues to the level of the first or second lumbar vertebrae. The length of the spinal cord is 42 (female) to 45 (male) cm long in an adult human being. The diameter of the spinal cord varies at different levels. Spinal cord is 0.64 to 0.83 cm in the thoracic region to 1.27 to 1.33 cm in the cervical and lumbar regions. It is larger in the lower cervical and mid lumbar region compared to the thoracic region. The smallest part of the spinal cord is at the inferior tip.


                                       Fig: Spinal cord

Parts of spinal cord

Spinal cord has five main parts as follows:

  • Cervical (neck)
  • Thoracic (chest)
  • Lumbar (lower back)
  • Sacrum
  • Coccygeal


                             Fig: Parts of spinal cord

Anatomy of spinal cord

The human spinal cord is composed of the following parts:

  • Meninges
  • Grey matter
  • White matter
  • Posterior root
  • Anterior root
  • Spinal nerve


                                           Fig: Anatomy of spinal cord

Meninges

The tissue or membrane that protects the spinal cord is called meninges. It is formed of three layers as follows:

  • Dura mater
  • Arachnoid mater
  • Pia mater


                                                     Fig: Meninges

Dura mater

The outermost tough protective coating of the spinal cord is called dura mater.


                                       Fig: Dura mater

Epidural space

The space present between the dura and the surrounding bone of vertebrae is called epidural space. This space is filled with adipose tissue and also contains a network of blood vessels. Doctors insert the anaesthetic in the epidural space to reduce the pain during childbirth and other surgical processes. It is called epidural anaesthesia.


                                                     Fig: Epidural anaesthesia

Arachnoid mater

The middle protective covering of the spinal cord with a web-like appearance is called arachnoid mater.


                              Fig: Arachnoid mater

Subarachnoid space

The space between arachnoid mater and pia mater is called the subarachnoid space. Cerebrospinal fluid or CSF is present in the subarachnoid space. Anaesthetic is injected in this space for surgical procedures like caesarean delivery or knee replacement. It is called spinal anaesthesia.


                                         Fig: Spinal anaesthesia

Lumbar puncture

The procedure of inserting a needle inside the subarachnoid space to collect the CSF is called lumbar puncture or spinal tap.


                                                         Fig: Lumbar puncture

Pia mater

The innermost protective covering of the spinal cord is called pia mater. It directly covers the spinal cord.


                                         Fig: Pia mater

Grey matter

The H or butterfly shaped central region of the spinal cord is called the grey matter. It is composed of nerve cell bodies, dendrites and synapses. The nerve cells are not coated heavily with myelin here. Grey matter covers the central canal of the spinal cord. Central canal is an extension of the fourth ventricle and it contains CSF.


                                  Fig: Grey matter

White matter

The region that surrounds the grey matter is called the white matter. It is composed of bundles of myelinated nerve fibres which helps in the quick transmission of nerve impulses. It has sensory and motor axons.


                                 Fig: white matter

Posterior root

The part of the nerve that branches off the back of the spinal column is called the posterior root or dorsal root. It is the afferent sensory root that carries sensory information to the brain.


                                              Fig: Posterior root

Anterior root

The part of the nerve that branches off the front of the spinal column is called anterior root or ventral root. It is the efferent motor root that carries motor information from the brain.


                                              Fig: Anterior root

Spinal nerve

Spinal nerves are formed by the combination of posterior and anterior roots. Hence it is composed of both sensory and motor fibres. Spinal nerves branch from the second lumbar vertebra of the spinal cord and supply to the rest of the body. These spinal nerves at the end of the spinal cord are collectively called cauda equina, as it resembles the tail of a horse.

Spinal nerves are a part of the peripheral nervous system. There are 31 pairs of spinal nerves. They control the sensation and movement in the body.

Types of spinal nerves

The different types of spinal nerves are as follows:

Cervical nerves

The nerves starting at the neck and running mostly in the head and face are the cervical nerves. There are eight pairs of cervical nerves (C1 - C8).

Thoracic nerves

The nerves in the upper body that extend to the chest region, upper back and abdomen are the thoracic nerves. There are twelve pairs of thoracic nerves (T1 - T12).

Lumbar nerves

The nerves in the lower back of the body that run to the legs and feet are the lumbar nerves. There are five pairs of lumbar nerves (L1 - L5).

Sacral nerves

The nerves in the lower back extending to the pelvis are the sacral nerves. There are five pairs of sacral nerves (S1 - S5).

Coccygeal nerves

The last and smallest spinal nerves are the coccygeal nerves that are located in the distal part of the vertebral column. It is also called tailbone nerves. There is only one pair of coccygeal nerves.


                                     Fig: Spinal nerves

Functions of spinal cord

The major purpose of the spinal cord is to carry the signals throughout the body. The key functions of a spinal cord can be described as follows:

  • Control body movements and functions
  • Reporting senses to the brain
  • Manage the reflexes

Control body movements and functions

The signals from the brain are received by the spinal cord to control the movements and autonomic (involuntary) functions like the heartbeats, breathing rates and functioning of bladder.

GIF: Heartbeat GIF: Breathing rate Fig: Functioning of bladder

Reporting senses to the brain

The signals for sensations like touch, pressure, pain etc., are transmitted through the spinal cord from different parts of the body to the brain.


                                               Fig: Reporting senses to the brain

Manage the reflexes

Spinal cord can act independently of the brain by conducting motor reflexes or involuntary movements. An example is the patellar reflex. It is the involuntary movement of the leg that occurs when tapped (ipsilateral stimulation) in the patellar tendon.


                                 Fig: Patellar reflex

Spinal cord injury

Any high grade injuries on the spinal cord can cause paralysis in most parts of the body, because it is a delicate part. Injuries can be caused due to vehicle accidents, sports activities etc.

Types of spinal cord injury

A spinal cord injury can be complete or incomplete.

Complete spinal cord injury

In a complete spinal cord injury, there will be a complete loss of sensation and motor functions of the body.

Incomplete spinal cord injury

In an incomplete spinal cord injury, the person will still be able to move one side of the body or will show some sensations.

Common disorders of the spinal cord

The common disorders that affect the spinal cord are as follows:

  • Acute transverse myelitis
  • Herniated disks
  • Spinal muscular atrophy
  • Spinal stenosis
  • Spinal tumours

Acute transverse myelitis

The inflammation of both sides in one section (like lumbar, thoracic, sacral or cervical) of the spinal cord is called acute transverse myelitis. This condition damages the myelin, which is the insulating layer of the nerve cells.


                    Fig: Acute transverse myelitis

The patients with transverse myelitis could not receive the messages sent by the spinal cord nerves to the body. As a result there will be acute pain, muscle weakness, paralysis and other sensory problems. It can also cause bladder or bowel dysfunctions.

Treatment of acute transverse myelitis

Medication and rehabilitative therapy can cure this condition. But this is not effective in severe attacks.

Herniated disks

The rubbery disks present between the vertebrae in the spinal column consist of a soft centre called nucleus surrounded by annulus, a tough exterior. When the portion of the nucleus pushes through the crack in the annulus is called the herniated disk. This causes more pressure on the nearby nerves. This condition is also called slipped disk or a ruptured disk.

This can occur in any part of the spine. Depending on the part of the spine, this causes pain, numbness, weakness in arms, legs etc. It is difficult to find out a symptom for herniated disk. Many people won't show any symptoms. Those people with symptoms improve over time. Hence surgery is usually not necessary to relieve the problem.


                                                    Fig: Herniated disc

Spinal muscular atrophy

A genetic neuromuscular condition where the patient loses motor nerve cells in the spinal cord is called spinal muscular atrophy. It occurs due to the deficiency of a motor neuron protein called SMN or survival motor neuron. This results in muscle weakness and wastage, because motor neurons control the muscle movement. Some people with this condition never walk, sit or stand. This usually affects infants and children but can also develop in adults.


                                                          Fig: Spinal muscular atrophy

Diagnosis of spinal muscular atrophy

Spinal muscular atrophy in infants can be diagnosed in pregnancy itself through amniocentesis and chorionic villus sampling (CVS).

Amniocentesis

In this test a sample of amniotic fluid with foetal cells and chemicals produced by the baby, is used for analysing the abnormalities.

GIF: Amniocentesis

Chorionic villus sampling (CVS)

In this test a sample of chorionic villi from the placenta is used for analysing the abnormalities.

Treatment for spinal muscular atrophy

Physical and occupational therapy and assistive devices like orthopaedic braces, crutches, walkers and wheelchairs are used by the patients. Disease modifying therapy and gene replacement therapy are the two common treatment methods used for this condition.

Spinal stenosis

The condition of narrowing of the space of the spinal column is called spinal stenosis. This results in the formation of more pressure on the spinal cord and nerves that travel through the spine. It occurs in the lower back and neck regions. This results in the pinched nerves and spinal cord irritation. Hence causes pain, numbness, tingling and muscle weakness. Through surgery more space can be created inside the spine.


                                                         Fig: Spinal stenosis

Spinal tumours

The growth of tumour (cancerous or benign) within the spinal canal or within the spinal bones is called spinal tumours. The tumour that begins in the spinal cord or its covering (dura) is called intradural tumour. The tumour in the spinal bones or vertebrae is called vertebral tumour. Tumours from other parts of the body can also reach the vertebrae and cause the vertebral tumour.

Spinal tumours result in pain, neurological problems and paralysis. Treatment for a spinal tumour include radiation therapy, surgery, chemotherapy or other medications.


                                    Fig: Spinal tumours

Practice Problems

1. Find the incorrect statement about the spinal cord from the following:

a. Spinal cord is the cylindrical structure that runs mid dorsally from the brainstem to the lower back within the vertebral column
b. Spinal cord is a delicate structure with nerve bundles and cells that only carries messages from the brain to the rest of the body
c. The major five parts of a spinal cord are cervical, thoracic, lumbar, sacrum and coccygeal.
d. The length of the spinal cord is 42 to 45 cm long in an adult human being

Solution: The cylindrical structure that runs through the centre of the spine or mid dorsally from the brainstem to the lower back within the vertebral column is called the spinal cord or myelon. The vertebral column is the bone that protects the spinal cord. This delicate structure has nerve bundles and cells that carry messages from the brain to the rest of the body and vice versa. So it is a major part of the human nervous system. The spinal cord extends from the base of the brain and continues to the level of the first or second lumbar vertebrae. The length of the spinal cord is 42 (female) to 45 (male) cm long in an adult human being. The major five parts of a spinal cord are cervical (neck), thoracic (chest), lumbar (lower back), sacrum and coccygeal. Hence the correct option is b.


                              Fig: Parts of spinal cord

2. In which part of the spinal cord do the doctors insert the needle for spinal tap?

a. Dura mater
b. Epidural space
c. Arachnoid mater
d. Subarachnoid space

Solution: The space between the dura mater and the surrounding bone of vertebrae is called epidural space. This space is filled with adipose tissue and also contains a network of blood vessels. The middle protective covering of the spinal cord with a web-like appearance is called arachnoid mater. The space between arachnoid mater and pia mater is called the subarachnoid space. Cerebrospinal fluid or CSF is present in the subarachnoid space. Anaesthetic is injected in this space for surgical procedures like caesarean delivery or knee replacement. It is called spinal anaesthesia.The procedure of inserting a needle inside the subarachnoid space to collect the CSF is called lumbar puncture or spinal tap. Hence the correct option is d.


                                                    Fig: Lumbar puncture

3. Which of the following can happen if the spinal cord is injured?

a. Could not receive the messages sent by the spinal cord nerves to the body
b. It causes dysfunction of bladder or bowel
c. Causes paralysis or a condition that makes people unable to walk, sit or stand
d. All the above

Solution: Any higher grade injuries on the spinal cord can cause paralysis of most parts of the body, because it is a delicate part. Injuries can be caused by vehicle accidents, sports activities etc. The inflammation of both sides in one section (like lumbar, thoracic, sacral or cervical) of the spinal cord is called acute transverse myelitis. This condition damages the myelin, which is the insulating layer of the nerve cells. The patients with transverse myelitis could not receive the messages sent by the spinal cord nerves to the body. Hence the statement ‘a’ is correct. As a result there will be acute pain, muscle weakness, paralysis and other sensory problems. It can also cause the dysfunction of the bladder or bowel. Hence the statement ‘b’ is correct. A genetic neuromuscular condition where the patient loses motor nerve cells in the spinal cord is called spinal muscular atrophy. It occurs due to the deficiency of a motor neuron protein called SMN or survival motor neuron. This results in muscle weakness and wastage, because motor neurons control the muscle movement. Some people with this condition never walk, sit or stand. Hence the statement ‘c’ is correct. This usually affects infants and children but can also develop in adults. Hence the correct option is d.


                                        Fig: Common spinal cord disorders

4. Find out the incorrect combination from the following:

a. Cervical nerves – Eight pairs
b. Thoracic nerves – Twelve pairs
c. Lumbar nerves – Five pairs
d. Sacral nerves – One pair

Solution: Spinal nerves are formed by the combination of posterior and anterior roots. Hence it is composed of both sensory and motor fibres. Spinal nerves branch from the second lumbar vertebra of the spinal cord and supply to the rest of the body. These spinal nerves at the end of the spinal cord are collectively called cauda equina, as it resembles the horse tail. Spinal nerves are a part of the peripheral nervous system. There are 31 pairs of spinal nerves. They control the sensations and movements in the body. The different types of spinal nerves are cervical nerves (eight pairs), thoracic nerves (twelve pairs), lumbar nerves (five pairs), sacral nerves (five pairs), and coccygeal nerves (one pair). Hence the correct option is d.


                                 Fig: Spinal nerves

FAQs

1. What is cervical enlargement?
Answer:
Spinal cord is flattened from the fifth cervical (C5) to the first thoracic vertebrae (T1). It is called cervical enlargement. It is the region where the nerves arise that supply the arms.


                   Fig: Cervical enlargement

2. Which vitamin is considered good for the spinal cord?
Answer:
The vitamin which is considered good for the spinal cord is vitamin B9. It comes in two forms as folate and folic acid. Folate can be found in vegetables like spinach, broccoli and asparagus. The synthetic form of B9 is the folic acid which is available as pills.


                                    Fig: Vegetables good for the spinal cord

3. Can spinal cord injury cause memory loss?
Answer:
No. Spinal cord injury does not cause memory loss. It will only affect the motor and sensory functions. Memory is a cognitive function that is regulated by the brain.

4. What is myelomere?
Answer:
The segment of the spinal cord where the dorsal and ventral roots are attached is called the myelomere.


                                             Fig: Myelomere

YOUTUBE LINK: https://www.youtube.com/watch?v=Hblw7_SkHvA

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