Nerves in the Human Nervous System

The nervous system is one of the vital and highly complex domains of the human body. From sending electrical messages to coordinating with movements around, the nerves in the human body are critical to healthy living. Hence, we will be learning about the nerve cell structure, functions, types and other general features of the human nervous system in detail. 

But before all, let us understand what nerve is all about.

What is Nerve?

A nerve consists of a bundle of fibres within the body that helps in impulse transmission as message sensations to the brain, spinal cord, muscles and other interlinked organs. The main part of the nervous system is that of nerves, useful to manage, coordinate and control every part of the human physique. Hence nerves are more like organs to the peripheral nervous system (PNS).

In particular, the spinal and cranial nerves play an important role. The thickest and largest known nerve of the human body is the Sciatic nerve, present in the spinal cord. This runs down towards the thigh’s back and up to the back of the knee. The Sciatic then divides into the Tibial nerve that serves for the lower leg and foot.

One factor that helps in the regular functioning of the nerves is the continuous blood supply. Human nerves require a proper flow of blood and if this supply of oxygen is disturbed or stops, the nerve will immediately lose its function. 

Structure of a Nerve

The complete structure of a neve can be explained with 6 major parts namely Axons, Glycocalyx, Endoneurial Fluid, Endoneurium, Perineurium and Epineurium. 

• Axons are nerve fibres that are present in multiple counts. 

• The bundle of axons together are called Fascicles. 

• Fascicles will hold every other neuron and blood vessel.

• Connective tissues of each fascicle are wrapped in a layer-like form called the perineurium. (holds many fascicles together) 

• With a concentrical lamination, the perineurium is constituted with elements such as basement membranes, collagen fibres and other flattened cells.

• The glycocalyx is a mesh of collagen present as the inner material with the endoneurium. This is a loose and connective tissue, covering the outside of the nervous system. 

• The surrounding fluid of endoneurium is known to be the endoneurial fluid or commonly called the cerebrospinal fluid of the central nervous system (CNS). 

The nerve cell function differs even with its similarity in the structure. There are majorly 3 types of nerves in the human body as in the following context.

Types of Nerves

The 2 key forms of nerves in the human body include the Sensory and Motor nerves. Sensory nerves are known as ‘Afferent’ that carry impulses from sensory receptors to the brain. Motor nerves are ‘Efferent’ ones, carrying electrical impulses away from the brain to the glands and muscles of the body. 

The 3rd type of nerve called the Mixed is a combination of both afferent and efferent nerves.

Sensory Nerves

Sensory nerves primarily send messages from the sense organs to the brain or spinal cord. Information is transmitted from the PNS to the CNS. Humans primarily have touch, smell, taste, sight and hearing sensations, controlled by the sensory nerves. 

The skin is the receptor for touch and temperature. Various concentrations of touch receptors are found in different parts of the body. A few touch receptors are found at the foot with temperature receptors at the elbow. 

Taste sensory nerve is located on the tongue at the taste buds, also termed the facial nerve. Different receptors for tastes such as sour, bitter, salt and sweet are present in various regions of the tongue. The taste sensory fibre is a combination of temperature, smell and texture. 

The optic nerve is the sensory organ for the vision, which transmits information from the eyes to the brain. ‘Conjunctiva’ is the layer for eye-protection against infections and inflammations. 

Motor Nerves

The motor or different nerves are located in the Central Nervous System (CNS). Vice-versa tp sensory nerves, motor ones send signals from the spinal cord or brain to the muscles and other glands of the body. That is, information is sent from the PNS to the CNS.

Motor nerves can also be classified as Alpha, Beta and Gamma, based on their motor neuron subtype. 

• Alpha motor neurons are responsible for movement and other contraction of bones in the Extrafusal skeletal system.

• Beta motor neurons take charge of slow-twitch muscle fibres in the Intrafusal skeletal system.

• Gamma motor neurons are the ones that keep muscles and other spindle fibres in taut. 

As an additional pointer, the cranial nerves III, IV, VI, XI, and XII are called a pure motor. Whereas, the Cranial nerves V, VII, IX, and X are both motor and mixed sensory nerves. 

Mixed Nerves

Mixed or mixed cranial nerves, as the name says, are both motor and sensory nerves in combination (afferent + efferent). Trigeminal nerve (CN V), Facial nerve (CN VII) Glossopharyngeal nerve (CN IX) and the Vagus nerve (CN X) are the 4 major mixed nerves in the human body. The functions of a mixed nerve are to conduct both incoming electrical information as well as outgoing muscle commands in 1 single bundle.

Function of Nerves

Apart from conveying a piece of information and sending electrically transmitted messages, a nerve also performs other activities that are vital for normal human functioning. 

1. Responsible for involuntary responses called the reflex arc

2. Acoustic hearing and balance possibility 

3. Ease of spinal accessory to move the shoulders and head

4. Importance of autonomic nervous system during a ‘fight or flight response’  

Nerve Disorders

With the help of clinical tests and assessments, diagnosing a nerve disorder or disease is much easier today. Proprioception, muscle weakness, poor walking reflex, handwriting tests, directed movements are some of the common ways that neurologists identify a nerve disorder. 

Medical problems relating to the nervous system can be anything from Sleeping problems, Pain, Vertigo, Changes in sensation and perception, Muscle Malfunction, Dysarthria and most commonly a Mental disability. Diabetic neuropathy is an extreme condition caused due to diabetes in affected patients and may range anywhere from Sensory neuropathy, Motor neuropathy or Autonomic neuropathy. 

Using suggested pain killers, electrical treatments, clinical rehabilitation, antidepressants, complementary medications, lifestyle changes, green dieting are all methods and coping mechanisms to prevent and cure certain disorders of the nervous system.