Spinal Cord – Structure, Functions & Spinal Nerves

Spinal Cord: The nervous system is a highly organised complex system that coordinates the activities of all body organs. The human nervous system has two contrasting functional subsystems, the central nervous system and the peripheral nervous system. We all know that the brain is the master organ of our body that gives the command for the functioning of different body organs and hence regulates their activities. How do these signals from the brain reach the receptor organs is a question of great importance. 

The central nervous system consists of the brain that is continuous with the dorsal tubular spinal cord. Serving as central control, these organs integrate incoming information and determine appropriate responses. The spinal cord acts as the link between the brain and the nerves that stretch throughout the body. To know more about the anatomical structure and functions of the spinal cord, let’s read the article.

Location of the Spinal Cord

Location: Spinal cord forms the posterior part of the central nervous system. It extends from the medulla oblongata and runs mid-dorsally almost the entire length of the vertebral column. It is about 42-45 cm long and has a diameter of about 5 millimetres in an adult. However, the diameter varies with the different stages of development.

Protective Covering of Spinal Cord

Meninges: A protective layer: The spinal cord is protected by the three membranes, altogether called meninges. The different layers of the meninges can be discussed as follows:

1. The outer tough layer is called the dura mater. 
2. The middle layer is called an arachnoid mater. The outermost and the middle layers remain separated by an epidural space. It is the site of injecting anaesthesia during surgery to reduce the sensation of pain.
3. The inner thin layer is the pia mater. The pia mater remains separated from the middle layer through subarachnoid space.
4. A clear, colourless fluid called cerebrospinal fluid is found in the subarachnoid space and circulates in the central canal of the spinal cord.

Study About Sense Organs Here

Fig: The Location of Spinal Cord

Longitudinal Organisation of the Spinal Cord

The spinal cord is divided into the following distinct regions:

1. Cervical spinal cord: There are 8 pairs of nerve roots that arise from the cervical spinal cord and reach to and from the upper limbs to the brain.
2. Thoracic spinal cord: There are 12 pairs of nerve roots that arise from the thoracic spinal cord. These mainly control motor and sensory signals reaching to and coming from the upper back, chest, and abdomen.
3. Lumbar spinal cord: There are five pairs of lumbar spinal nerves. The nerves of the lumbar spinal cord control the communication between the brain and the lower limbs.
4. Sacral spinal cord: Below the lumbar vertebrae, five vertebrae are fused to form a triangular sacrum. The sacrum protects 5 pairs of the sacral spinal nerve roots that connect the brain to receptors of the middle legs and the pelvic organs.
5. Coccygeal spinal cord: A pair of coccygeal nerves provide sensory and motor intervention to the respective dermatomes (area of skin innervated by motor fibres) and myotomes (area of skin innervated by sensory fibres).

Fig: Longitudinal Organisation of the Spinal Cord

Anatomy of Spinal Cord: Cross-Section of Spinal Cord

The cross-section of the spinal cord can be discussed as follows:

1. The spinal cord consists of white and gray matter. The white matter surrounds the Gray matter. The Gray matter penetrates into the white matter and forms an H-shaped or butterfly-shaped central core of the spinal cord.
2. The Gray matter consists of cell bodies of motor neurons and dendrites.
3. The white matter contains axons running longitudinally to and from the brain.
4. There is a small central canal in the centre that runs the entire length and is continuous with the cavities of the brain.
5. The Gray matter on each side of the spinal cord is subdivided into the regions called horns. Those closer to the front of the cord are called anterior (ventral) Gray horns, while those closer to the back are posterior (dorsal) Gray horns. Between the anterior and posterior horns are lateral Gray horns.
6. The motor nerves arise from the anterior horns that carry the signals from the brain to the receptor’s muscles. On the contrary, the sensory nerves that arise from the posterior horns transfer the signals from the sense organs to the brain.
7. The lateral horn and the intermediate column comprise autonomic nerves that intervene in the visceral organs.

Fig: The Cross-Section of the Spinal Cord

Spinal Nerves

There are 31 pairs of spinal nerves. These nerves are grouped into 8 cervical, 12 thoracics, 5 lumbar, 5 sacral, and 1 coccygeal according to the region of the vertebral column from which they arise. Each spinal nerve consists of the following features:

1. Each spinal nerve joins the spinal cord at two points called roots and contains both receptor neurons and effector neurons.
2. The dorsal or posterior root contains sensory afferent fibres that transmit impulses from receptors in the periphery into the spinal cord.
3. At the middle of each dorsal root, there is a swelling called dorsal root ganglion that contains the cyton of the sensory neurons.
4. The other point of attachment of a spinal nerve to the spinal cord is the ventral or anterior root. It contains the motor neurons and transmits the impulses from the spinal cord to the effectors. There is no ventral root ganglion.
5. Immediately after the roots leave the spinal cord, they merge to form a mixed spinal nerve on each side.

Functions of the Spinal Cord

There are the following functions of the spinal cord:

1. The spinal cord conducts impulses to and from the brain and controls most of the reflex activities. For example, knee jerk when tapped in a certain spot is called patellar reflex.
2. It regulates voluntary muscle movements during reflex activities.
3. Several involuntary activities such as peristalsis of the stomach and oesophagus, contraction of the urinary bladder muscle, dilation and contraction of heart muscles are synchronised through the spinal nerves.
4. The Myelin sheath of white matter regulates the speed of conduction of nerve impulses to and from the brain and acts as electrical insulation.

Spinal Cord Injuries

The spinal cord is the delicate part of the body. Damage to any part of the spinal cord and the spinal nerves may cause severe irreparable injuries that affect a person’s physical, social, and mental health. Based on the severity, the spinal cord injuries can be classified as follows:

1. Complete injury: It is the complete loss of sensory and motor function below the spinal cord injury. In case of complete injury, the entire body is unable to feel and control the internal as well as external changes or activities that affect the body’s functioning.
2. Incomplete injury: An incomplete spinal cord injury occurs when the person is still able to perform some sensory and motor functions at or below the point of the injury. The degree of incomplete injury may vary from the least to the maximum.

Paralysis: An spinal cord injury may lead to paralysis that is of two types:

1. Tetraplegia: It is also known as quadriplegia. It is a type of paralysis that causes a partial or total loss of sensory and motor functions of all body parts after spinal cord injury.
2. Paraplegia: It is a type of paralysis that affects all body parts’ sensory and motor functions except the forelimbs.

Fig: Spinal Cord Injuries

Symptoms of spinal cord injury: There are the following symptoms of the spinal cord injury:

1. Extreme back pain.
2. Loss of movement.
3. Loss of sensation through sensory organs.
4. Weakness and paralysis in any part of the body.
5. Exaggerated reflex actions.

Complications due to spinal cord injury:

1. The person is unable to control the bladder and bowel movement that may cause urinary tract infections, kidney stones, etc.
2. A spinal cord injury may cause circulatory problems such as low blood pressure, thrombosis, etc.
3. The abdominal and the thoracic muscles affected due to the spinal cord injury may cause breathing problems.
4. After the spinal cord injury, men may have the problem of erection and ejaculation, and the females may have the problem in lubrication that affects their sexual health.
5. Joint pain, muscle pain, and nerve pain occur due to spinal cord injury.

Causes of spinal cord injury: There may be the following causes of spinal cord injury:

1. Damage to any of the vertebrae of the vertebral column, dislocation of the vertebrae may cause traumatic spinal injury.
2. Arthritis, inflammation, osteoporosis, softening of bones, and disk degeneration may cause non-traumatic spinal injury.
3. Athletic activities, diving in shallow water may cause spinal cord injuries.

Summary

The spinal cord is the part of the central nervous system that carries the nerve impulses between the brain and the body organs. It continues behind the medulla oblongata almost till the entire length of the vertebral column. The cross-section of the spinal cord consists of an internal H-shaped Gray matter. The white matter surrounds the Gray matter. There are 31 pairs of spinal nerves. Each pair consists of a sensory nerve and a motor nerve to transmit the signals to and away from the brain. The spinal cord carries out our body’s reflex activities and controls the involuntary actions of internal body organs. Therefore it is necessary to escape from spinal cord injuries as severe spinal cord injuries result in paralysis and damage to the sensory and motor functions of the different parts of the body.

Frequently Asked Questions (FAQs) on Spinal Cord

Q.1. What is the main function of the spinal cord?
Ans: Spinal cord transfers the signals from the brain to the receptor organs and from the receptors to the brain.

Q.2. What are the main parts of the spinal cord?
Ans: The main parts of the spinal cord are cervical, thoracic, lumbar, sacral, and coccygeal.

Q.3. What happens if the spinal cord is damaged?
Ans: The damage of the spinal cord interrupts the signals from the brain to the receptors and therefore causes the loss of sensation.

Q.4. What is the most common spinal injury?
Ans: The two most common types of spinal injuries are tetraplegia and paraplegia.

Q.5. What are the three layers of protection for the spinal cord?
Ans: The three layers for the protection of the spinal cord are the dura mater, arachnoid mater, and pia mater.

Study About Human Body Here

We hope this detailed article on Spinal Cord will be helpful to you in your preparation. If you have any doubts please reach out to us through the comments section, and we will get back to you as soon as possible.