Anatomy and Function of the Spinal Cord

What Is the Function of the Spinal Cord?

The primary role of the spinal cord in the nervous system is to relay sensory, motor, and autonomic messages between the brain and the rest of the body. Myelinated nerves along the pathways of the spinal cord send electrical signals to each other to facilitate these actions.

• Motor: The motor messages sent through the corticospinal tract eventually reach the corresponding muscle as the spinal nerve branches into smaller peripheral motor nerves that extend to the target muscle. As a result of this nerve stimulation, you can voluntarily move your arms, legs, neck, back, and abdominal muscles.
• Sensory: Your spinal cord sends messages from your peripheral sensory nerves to your brain, allowing you to detect sensations that include light touch, vibration, pain, temperature, and the position of your body.
• Autonomic: The spinal cord sends messages to regulate the internal organs of the body. This includes control of smooth muscles, such as the muscles that move your lungs, stomach, intestines, bladder, and uterus. This part of the nervous system is known as the autonomic nervous system.

Anatomy and Location

The spinal cord is adjacent to and below the medulla, which is the lowest part of the brain. The top region of the spinal cord extends down from the medulla all the way to the lower back.

• Nerves: Throughout the spinal cord, there is a consistent arrangement of spinal nerves. The sensory nerve pathways are located toward the posterior (back) of the spinal cord, while the motor nerve pathways run along the lateral (sides) and anterior (front) regions of the spinal cord.
• Cerebrospinal Fluid: Cerebrospinal fluid (CSF), with nutrients and immune cells, flows around the spinal cord. Meninges, which are layers of protective connective tissue, surround the spinal cord and CSF.
• Meninges: Meninges are composed of three thin layers—the innermost pia mater, the middle arachnoid mater, and the outermost dura mater. All of these structures—the spinal cord, CSF, and meninges—are enclosed in the backbone, which is also referred to as the spine and the vertebral column.

Spinal Cord vs. Vertebral Column
The spinal cord is a band of nerves and cells, while the vertebral column is the term used to describe the bones of your spine, which cover and protect the spinal cord.

What Are the Regions of the Spinal Cord?

From top to bottom, the regions of the spinal cord include

• Cervical
• Thoracic
• Lumbar
• Sacral

Each of these levels corresponds to spinal nerves that emerge from the spinal cord toward structures of the body, such as the arms, legs, and trunk.

How long is the spinal cord?
In most adults, the spinal cord is about 18 inches long.

Gray Matter and White Matter

The deep, central area of the spinal cord is referred to as gray matter, and the portion that is located nearer to the outer edge of the spinal cord is referred to as white matter.

A coating called myelin (a type of fat) insulates all nerves. The white matter tends to have more myelination than the grey matter, giving it a whiter appearance when viewed with a microscope.

The grey matter of the spinal cord is shaped somewhat like an open-winged butterfly lying across the center of the spinal cord. This butterfly-shaped gray matter contains nerve roots. The white matter is composed of several tracts (pathways) that travel up and down the spinal cord.

Sections of the spinal cord include the following.

Anterior Horn

This section is the frontal portion of the gray matter of the spinal cord, and it is composed of nerves that send motor signals to the spinal nerves.

Lateral and Anterior Tracts

These white matter pathways carry motor signals down the spinal cord in the corticospinal tract. This tract travels all the way down the spinal cord at the front and sides of the white matter regions.

Motor control of the voluntary muscles (muscles you choose to move) travels through the spinal cord in the corticospinal tract. Motor signals are initiated in the motor strip, a region of the cerebral cortex of the brain.

Dorsal Horn

These motor signals travel down the internal capsule, and then cross over to the other side of the body in the brain stem. From there, these messages are sent to the anterior horn and the lateral and anterior tracts of the spinal cord. The motor message exits the spinal cord through the ventral root (the front portion) of the spinal nerves.

This area is the posterior region of the grey matter. The spinal nerves deliver sensory messages such as light touch, position sense, and vibration to the dorsal horns.

Posterior Tracts

Also described as the spinothalamic tract, this is a long, white matter pathway that extends all the way up the spine to the brain. The spinal cord mediates sensation coming from the skin, bones, and internal organs.

Your skin detects these sensations and sends messages from peripheral sensory nerves (embedded in the skin) to the spinal nerves, then to the dorsal horn and up through the spinothalamic tracts, crossing over to the other side of the spinal cord before reaching the brain.

Eventually, these messages reach the brain stem, then the thalamus, and then the sensory strip, which is directly behind the motor strip in the cerebral cortex of the brain.

Lateral Horn

The lateral horns of the spinal cord are located at the two sides of the gray matter. This area is composed of nerves that mediate autonomic functions of the body. The autonomic nervous system regulates involuntary functions (actions you don’t purposely control), such as digestion and breathing.

Associated Conditions

There are a number of medical problems that can affect the spinal cord. Disease of the spinal cord is often described as myelopathy. These conditions cause impairment of motor, sensory, and/or autonomic function.

Myelopathy also often causes spasticity, which is stiffness of the affected arm and/or leg. The symptoms of any spinal cord problem typically correspond to the section of the spinal cord that is impaired. Sometimes, spinal cord injuries also affect functions that are controlled by areas below the level of spinal cord damage due to disruption of the spinal cord tracts.

Diagnosis of a spinal cord condition can include tests such as a physical examination, spinal imaging, nerve conduction studies (NCV), and/or electromyography (EMG).

Conditions that affect the spine include:

Multiple Sclerosis (MS)

This is a demyelinating condition that may affect the brain and/or spine. Multiple sclerosis lesions in the spine can cause weakness, sensory loss, tingling, and pain, and they may affect bowel and bladder function.

Spinal Cord Compression

When the spinal cord is placed under physical pressure, weakness, sensory loss, and autonomic deficits can occur. Severe degenerative disease of the bone or cartilage of the spine can cause these structures to fall out of place—potentially resulting in physical impingement on the spinal cord. Metastatic (spreading throughout the body) cancer can cause spinal cord compression as well.

Trauma

An injury can cause the spine to move out of place and can even cause a spine fracture (break), which can injure the spinal cord. Injuries may also cause spinal cord compression due to bleeding, and an injury can directly damage the spinal cord.

Click here to continue reading

Original article published on verywellhealth.com