Peripheral Nervous System

The Nervous System

What Is the Nervous System?

The Central and Peripheral Nervous Systems are the component parts of the body’s nervous system. These interconnect, and work together. The Central Nervous System is comprised of the brain and spinal cord. The Peripheral Nervous System is the system of nerves that exist outside of the brain and spinal cord.

We all have 12 pair of cranial nerves and 31 pairs of spinal nerves together with their corresponding branches, roots, and neuromuscular junctions. The cranial and spinal nerves come in pairs because humans exhibit a symmetrical body, called bilateral symmetry.

These nerves are responsible for the motor and sensory functions of the neck and head. As for the 31 pairs of spinal nerves, these correspond to the vertebral column.

There are 8 pairs of spinal nerves in the cervical region of the spine, 12 pairs in the thoracic region, and 5 pairs for the lumbar region, another 5 pairs in the sacral part, and just 1 pair located in the coccygeal portion of the vertebral column.

How does the Peripheral Nervous System Work?

The Peripheral Nervous System is a complex system of nerves that supports the communication between the body and the brain. It also enables the body to automatically care for itself through involuntary bodily functions, like breathing and heartbeat. It also supports the motor and sensory functions of the body.

Through this system, the brain tells the body what to do, and the body tells the brain what to feel.  To fully understand how this portion of the nervous system works, we need to understand the two divisions of the Peripheral Nervous System. These are the Somatic Nervous System and the Autonomic Nervous System.

What Is The Somatic Nervous System?

The Somatic Nervous System is that part of the system that serves as the messenger between the brain and the body. It has two components: the motor component and a sensory component.

The sensory component of the Somatic Nervous System has afferent neurons. These are responsible for taking information gathered by the body from external stimuli towards the brain. For example, when your hand touches something hot, afferent neurons will send signals to the brain that you felt pain.

The motor component of the Somatic Nervous System has efferent neurons. These carry information directly from the brain and the spinal cord towards the muscle fibers to generate the movement of our body parts.

Neurons from the brain carry signals and messages and travel via the spinal cord. These motor neurons from the Motor Component of the Peripheral Nervous System have nerve endings that are situated extremely near muscle fibre. The area where these meet is called the neuromuscular junction.

So basically, muscles produce movement because they are innervated by motor nerves. These nerves have the capability of releasing chemicals that are received by muscle fibres. These chemicals cause muscle fibres to contract and as a result, the muscle moves.

This system is also known as the Primary Motor Complex System. It occupies a large section of the precentral gyrus of the brain. It allows us to translate the brain’s perceptions into action. For example, your brain will send signals to your hand by this system to remove your hand from the hot object that you touched.

What Is The Autonomic Nervous System?

The Autonomic Nervous System is the division of the Somatic Nervous System that takes care of the body’s involuntary movements. In other words, this part of the Somatic Nervous System controls the body’s actions that we rarely think of, such as:

• Blood flow;
• Digestion;
• Pupillary response;
• Breathing;
• Heart rate; and
• Other functions.

This system can be further divided into two: the Parasympathetic System and the Sympathetic System.

What Is The Sympathetic System?

The Sympathetic System prepares the body for an expected threat that will need a sudden surge of energy as a response to the external stimuli that may harm the body.

When this occurs, a part of the brain called the amygdala sends an alert or a distress signal to another part of the brain called the hypothalamus. With this, the hypothalamus activates the Sympathetic System by releasing the hormone adrenaline and creating that well known feeling of the adrenaline rush.

The rush of adrenaline activates the body’s response called fight or flight. Here are some of the effects of adrenaline rush to the human body:

• Faster heartbeat;
• Increased blood flow to the muscles;
• Dilation of pupils;
• Faster respiration rate (breathing); and
• Release of  adrenaline (adrenaline rush).

What Is The Parasympathetic System?

The Parasympathetic System controls the body’s normal functions. It also conserves the physical resources of the body. For example, if a threat has passed, this system allows the body to return into its normal resting state.

Common functions of the Parasympathetic System:

• Slowing down of the heart rate;
• Reduction of the blood flow to the muscles;
• Slower respiration rate (breathing); and
• Constriction of pupils.

How Can You Test the Peripheral Nervous System?

It is quite common for a patient to make complaints of numbness or tingling in an extremity following an accident. There may also be complaints of weakness in an extremity. There are important tests that your doctor can order to determine whether these complaints are related to an injury to your peripheral nervous system.

Your doctor can order an MRI of your neck or back to determine whether you have a herniated disc, or injury to the spine that has resulted in a nerve root compression. Your doctor may also order elctrodiagnostic studies, like an EMG or NCV study to assess the health of your peripheral nervous system.