The spinal cord partners up with the brain to send information around the body as electrical signals.
It tells the body what the brain wants and the brain what the body is feeling. This lesson explains how its structure helps accomplish this.
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What Is the Spinal Cord?
The spinal cord, along with the brain, makes up the central nervous system. It resembles a thick, cream-colored rope and is made up of nerves that relay messages between the brain and the rest of the body. It stretches from the medulla oblongata, at the base of the brain, to the lower back, and is housed in a tunnel made by the vertebrae, or bones of the spinal column. All vertebrate animals have spinal cords, from simple jawless fish to complex birds and mammals.
Functions
The spinal cord works a bit like a telephone switchboard operator, helping the brain communicate with different parts of the body, and vice versa. Its three major roles are:
- To relay messages from the brain to different parts of the body (usually a muscle) in order to perform an action
- To pass along messages from sensory receptors (found all over the body) to the brain
- To coordinate reflexes (quick responses to outside stimuli) that don’t go through the brain and are managed by the spinal cord alone
General Characteristics
In an adult human, the spinal cord measures about 44 cm, or 17-1/4 inches, in length and is as wide as a thumb at the top and as thin as a drinking straw at the bottom. The thick bundle of nerves are protected by three layers of membrane called meninges, like those surrounding the brain. The bundle resembles a rough jute rope with a thick hot dog casing around it. Between the nerve bundle core and the meninges, there is also cerebrospinal fluid for added cushioning. The spinal cord ends in a cascade of nerves resembling a horse’s tail, which is why this part is called the cauda equina.
Anatomy
The cord is organized into five major regions consisting of a total of 33 segments (two of these segments are fused, so it is usually described as having 31 segments).
Each segment contains nerves connected to different parts of the body.
- The cervical region is connected to the head, neck, upper body, arms, and hands
- The thoracic region is connected to the hands, fingers, chest, and abdominal muscles
- The lumbar region is connected to the hips, knee, ankles, and toe muscles
- The sacral region is connected to the legs, toes, bladder, and anal muscles
- The coccygeal region is connected to the skin around the coccyx
The cross section of the spinal cord looks like a taffy candy with a butterfly in the middle. The central core contains gray matter , the bodies and dendrites of the neurons in the bundle, and is surrounded by white matter, the neuron axons. Each segment has a pair of spinal nerves coming out of it, and each of these nerves has two roots. The dorsal root, in the back of the spinal cord, carries sensory messages from the body to the brain so you can detect things like touch, smells, pain, or temperature.
The ventral root, in the front of the spinal cord, carries motor messages from the brain to the body, thus controlling the different muscles of the body.
Examples of the Spinal Cord at Work
Here are two examples of how the spinal cord uses different spinal nerves and roots to transmit messages to and from the brain. In order to flex your biceps, the brain sends an electrical signal down the spinal cord to the 5th cervical segment, where the message gets passed along to the motor neurons connected to the bicep muscles.
This causes them to contract. When you step on something pointy, on the other hand, the sensory receptors on the sole of your foot send an electrical signal, via sensory neurons, to the 4th lumbar segment. From there, the message travels up the spinal cord to the brain.
Lesson Summary
The spinal cord, along with the brain, makes up the central nervous system.
It resembles a thick, cream-colored rope and is made up of nerves that relay messages between the brain and the rest of the body. It is housed in a tunnel made by the vertebrae, or bones of the spinal column. Its three major roles are to relay messages from the brain to different parts of the body, to perform an action, to pass along messages from sensory receptors to the brain, and to coordinate reflexes that are managed by the spinal cord alone.The cord is organized into 5 major regions: the cervical, thoracic, lumbar, sacral and coccygeal. Each segment has a pair of spinal nerves coming out of it, and each of these nerves has two roots. The dorsal root carries sensory messages from the body to the brain so you can detect things like touch, smells, pain, or temperature.
The ventral root carries motor messages from the brain to the body, thus controlling the different muscles of the body.
Vocabulary & Definitions
 |
| Terms | Definitions |
|---|---|
| Spinal Cord | thick cord made up of nerves that relays messages between the brain and the rest of the body |
| Vertebrae | bones of the spinal column |
| Meninges | three layers of membrane |
| Cauda Equina | horsetail-like bundle of nerves at the end of the spinal cord |
| Cervical Region | head, neck, upper body, arms, and hands |
| Thoracic Region | hands, fingers, chest, and abdominal muscles |
| Lumbar Region | hips, knee, ankles, and toe muscles |
| Sacral Region | legs, toes, bladder, and anal muscles |
| Coccygeal Region | skin around the coccyx |
| Gray Matter | bodies and dendrites of the neurons in the bundle |
| White Matter | the neuron axons |
| Dorsal Root | carries sensory messages |
| Ventral Root | carries motor messages |
Learning Outcomes
Complete this lesson and increase your capacity to:
- Remember what the spinal cord looks like
- Note the functions and makeup of the cord itself
- Identify the locations of various regions of the spinal cord
