What is Spinal Cord? Diagram, Anatomy and its Functions

Spinal Cord is an important part of the central nervous system. It is a cylindrical bundle of nerves and support cells present within the vertebral column and is surrounded by the Meninges and Cerebrospinal fluid. It connects the brain to the lower back. The spinal cord is divided into cervical, thoracic, lumbar, and sacral segments. There are 31 pairs of nerves and nerve roots in the spinal cord. The spinal cord carries nerve signals from the brain to the body and vice versa. Injuries or diseases affecting the spinal cord can lead to paralysis, sensory deficits, and impaired organ function.

Spinal Cord Anatomy

Spinal Cord lies in the vertebral canal which is surrounded by meninges and Cerebrospinal fluid. It present above Medulla oblongata and extends from the upper border of the Atlas to the lower border of the first lumbar vertebra in adults. It is 45 cm in an adult maleand 42cm in an adult female. It is surrounded by three meninges namely Dura mater(outer most), Arachnoid mater(middle) Pia mater(inner most). It is divided into five different parts.

• Sacral cord
• Lumbar cord
• Thoracic cord
• Cervical cord
• Coccygeal

There are 31 pairs of spinal nerves including 8 cervical, 5 lumbar, 12 thoracic, 5 sacral, and 1 coccygeal pair of spinal nerves. The Spinal Cord has inner grey matter and outer white matter(no fibers). The spinal cord carries nerve signals, and controls involuntary movements.

Also Read: Anatomy of Brain

Diagram of Spinal Cord

Below is the diagram of the spinal cord showing its different parts:

👁 Spinal-Cord

Structure of the Spinal Cord

The spinal cord is a cylindrical, long structure that runs along the vertebral column and extends from the base of the brain to the lower back. It is composed of nerve tissue, including neurons and glial cells. The spinal cord is divided into segments: cervical, thoracic, lumbar, and sacral. The spinal cord consists of two main types of tissue: grey matter and white matter.

• Grey Matter: Grey matter is located in the centre of the spinal cord and has a butterfly or "H"-shaped appearance in cross-section. It contains cell bodies of neurons, dendrites, unmyelinated axons, and glial cells. It processes and integrates sensory information, as well as initiate motor commands. It serves as the site for synapses between neurons.
• White Matter: It forms the outer part of the spinal cord. The white matter of the spinal cord is arranged in three columns or tracts. anterior, posterior, and lateral. These tracts are formed by sensory nerve fibers ascending to the brain, Motor nerve fibers descending from the brain, and fibers of connector neurons. It help in the transmitting signals to and from the brain.

Sensory Nerve Tracts

These are afferent or ascending tracts in the spinal cord. There are two main sources of sensation transmitted to the brain via the spinal cord, they are 

• The skin(cutaneous receptors):  stimulated by pain, heat, cold, touch, and pressure
• The tendons, muscles, and joints (proprioceptors): are stimulated by stretching.

The ascending tracts consist of the following parts. Lateral Spino thalamic tract, Anterior Spino thalamic, Fasciculus Gracilis tract, fasciculus cuneatus tract, Dorsal Spinocerebellar tract, Ventral Spinocerebellar Tract, Spino-Olivary tract, Spino-Tectal tract.

Motor Nerve Tracts

Motor nerve tracts are efferent descending tracts in the spinal cord. Neurons that transmit nerve impulses away from the brain are called Motor Neurons. Motor neurons stimulation results in 

• Contraction of skeletal ( striated, voluntary )muscle, 
• Contraction of smooth ( involuntary) muscle, Cardiac muscle. 

The descending tracts are of two types.

1. Pyramidal or cortical spinal tracts:  These tracts originate mainly from the pyramidal neurons of the motor and pre-motor cortex. It consists of two parts: Lateral Corticospinal tract and Anterior corticospinal tract 
2. Extra pyramidal: The extra pyramidal system represents older motor path ways that are multi-synaptic with inhibitory influence over pyramidal tracts. It consists of 8 parts: Rubro spinal, lateral vestibulo spinal, medial vestibulo spinal, lateral reticulo spinal, medial reticulo spinal, tecto spinal, olivo spinal, interstitio spinal tracts.

Blood Supply to the Spinal Cord

The arterial supply of the spinal cord is by the following arteries. 1. Anterior spinal arteries 2. Two posterior spinal arteries 3. The radicular arteries. 

Spinal Nerves

Spinal nerves arise in pairs. There are 31 pairs of spinal nerves 8 cervical, 12 thoracics, 5 Lumbar, 5 Sacral, and 1 Coccygeal. Each spinal nerve arises by a series of Six to Eight dorsal and ventral nerve rootlets. These rootlets unite in or near the intervertebral foramen to form the spinal nerve. The spinal cord nerves can be grouped as:

• Cervical: There are 8 cervical nerve. These nerves emerges from the cervical spine (C1-C8) and supply the neck region.
• Thoracic: There are 12 thoracic nerves. These nerves emerges from the thoracic spine (T1-T12) and supply the chest region.
• Sacral: There are 5 sacral nerves. These nerves emerges from the lumbar spine (L1-L5) and supply the lower back region.
• Lumbar: There are 5 lumbar nerve. These nerves emerges from the sacral bone (S1-S5) and supply the sacrum region that is a bony plate at the base of the vertebral column.
• Coccygeal: There are 1 coccygeal nerve. These nerves emerges from the coccygeal bone and supply the tailbone.

Also Read: Cranial Nerve

Difference Between Spinal Cord and Vertebral Column

The Differences Between Spinal cord and vertebral column are as follows:

Feature	Spinal Cord	Vertebral Column
Location	Inside the vertebral column, extending from the brainstem to the lower back.	Surrounds and protects the spinal cord; it is the bony structure made up of vertebrae.
Composition	Nervous tissue, including grey and white matter, neurons, and glial cells.	Bony segments (vertebrae) connected by ligaments and joints.
Function	Facilitates communication between the brain and the peripheral nervous system; processes and transmits sensory and motor signals.	Provides structural support, protection, and flexibility to the spinal cord; surrounds and encases the spinal cord.
Segments	Divided into cervical, thoracic, lumbar, and sacral regions, each associated with specific functions.	Comprises individual vertebrae, including cervical, thoracic, lumbar, sacral, and coccygeal regions.
Flexibility	Flexible and capable of slight movement within the vertebral canal.	Provides flexibility and allows for movements such as bending and twisting.
Anatomical Features	Grey matter (cell bodies) and white matter (nerve fibers) are internal components.	Consists of individual vertebrae, each with a vertebral body, spinous process, and neural arch.
Protection	Surrounded by meninges (protective membranes) and cerebrospinal fluid.	Surrounds and protects the spinal cord from external trauma.
Termination Point	Typically terminates as the Conus Medullaris, around the first lumbar vertebra in adults.	Does not have a specific termination point; extends throughout the vertebral column.

Function of the Spinal Cord 

Spinal Cord has the following functions:

• The spinal cord transmites sensory information from the peripheral nervous system to the brain.
• It coordinates motor responses by transmitting signals from the brain to muscles and organs.
• Spinal cord controls some reflexes (involuntary movements) without involving the brain.
• It allow flexible movements.
• White matter in the spinal cord allow faster transmission of nerve impulses due to the myelination of axons.
• It coordinate various reflexes.
• Coordinating voluntary and involuntary muscle movements and contributes to motor function and control.

Spinal Cord Injuries

Damage or injury to the spinal cord results in the permanent damage to the spinal cord. It affects the regular functioning of the spinal cord and there is no replacement for it. Injury to the spinal cord can damage the spinal nerves and the vertebral column but also affects other muscles and vital organs. Paralysis from an injury can be of two types: Tetraplegic and Paraplegic.

Some of the conditions that affect the spinal cord are:

1. Multiple Sclerosis (MS): This is a demyelinating condition that may affect the brain and spine. This disorder in the spine causes weakness, loss of the senses, tingling, and pain.
2. Spinal cord compression: When the spinal cord is exposed to adverse conditions such as physical pressure, weakness, and loss of sense spinal cord compression can occur.
3. Meningitis: Infection or inflammation of the meninges is called meningitis, also called as spinal meningitis. This disease can cause symptoms like headache, stiff neck, fever, and vomiting.
4. Polio: Polio is the most contagious viral infection which affects the spinal cord. It can be usually prevented by using a vaccine. This causes muscle paralysis of the areas that are controlled by affected spinal cord regions.
5. Cancer: Although spinal cord cancer is not a common disease the tumors can develop in any part of the cord. Meningeal carcinomatosis is the spread of cancer cells throughout the meninges and CSF.

Also Read: Difference Between Brain and Spinal Cord