Nervous System: Function, Divisions and Diagram

Organ functioning, perceptions, thoughts, emotions, and almost everything within an individual are under the direct or indirect influence of the nervous system. It manages the quickest communications in our body so that appropriate responses to the stimuli can be made at once. The nervous system obtains information about changes, both external and internal, analyses them, and interprets them to produce the right result. 

Nervous System Function 

The complex command system of the body affects every aspect of an individual’s health, including

• Thoughts, feelings, memory, and learning.
• Balance and coordination.
• Perception of senses: sight, taste, touch, smell, hear, and feel.
• Sleep
• Healing and aging
• Heartbeat 
• Breathing pattern
• Response to situations
• Digestion
• Body processes such as puberty

A neuron or a nerve cell is the structural and functional unit of the nervous system. The following nervous system diagram shows the controls of the nervous system in the human body.

Nervous system diagram depicting the control of the system over the body

Divisions of the Nervous System

In mammals, the divisions of the nervous system are as follows: 

• Central Nervous System
• Peripheral Nervous System
• Autonomic Nervous System

Did you know: Medulla oblongata, pons varoli, midbrain, and hypothalamus are collectively called the brain stem. It is so-called because it is the bottom part of the brain that looks like a stalk. It connects the rest of the brain to the spinal cord.

Central Nervous System (CNS)

The brain and spinal cord constitute the central nervous system. The brain is the upper part of the CNS that lies within the cranium. It continues downward as the spinal cord is placed within the vertebral column. 

The entire nervous system is further protected by three successive layers of meninges. The cerebrospinal fluid is present between two successive layers of meninges. The three layers of this fibrous covering are as follows:

• Pia mater
• Arachnoid mater
• Dura mater

The Brain

In an average adult, the brain weighs about 1350g, i.e., approximately 98% of the entire CNS. Lying within the skull/cranium that protects it from injuries, the brain can be distinguished into the following three regions:

Forebrain  (Telencephalon)
Cerebrum	There are two cerebral hemispheres joined by the corpus callosum (a band of nerve fibres). The cerebrum has an outer layer called the cerebral cortex, which is formed of grey matter. The grey matter surrounds the white matter.     The cerebrum has various convolutions called gyri. The fissures divide the cerebral hemisphere into the following four lobes: Frontal Parietal Temporal Occipital The cerebrum has contralateral control in the body.  Functions of the cerebrum: Centre for motor activities and sensory functions like pain, touch, and temperature.  The motor area in the frontal lobe controls voluntary movements of the muscles.  The premotor area in the frontal lobe controls involuntary movements. The visual area in the occipital lobe is the centre of visual sensation.  The auditory area in the occipital lobe is for hearing sensations. The prefrontal area in the frontal lobe is for intellectual activities.
Hypothalamus	Along with the thalamus forms the diencephalon.  The pituitary gland hangs from the hypothalamus by a stalk/infundibulum.  Functions: It is the highest centre of the autonomic nervous system. It governs emotional reactions. Concerned with the sleep mechanism. Controls the endocrine system. Secretes neurohormones that control the anterior pituitary. Produces ADH and oxytocin. Works as a thermostat and controls the body temperature.
Midbrain (Mesencephalon)
Superior and inferior colliculi on each side of the dorsal surface (The two on one side are called corpora  bigemina, and all four are collectively called corpora quadrigemina)		They serve as centres for visual and auditory reflexes.
Two cerebral peduncles on the ventral side		They connect the cerebral cortex with other parts of the brain and spinal cord.  They serve as coordination centres between the hindbrain and the forebrain.
Nerve cells scattered in the white matter		These nerve cells control muscle tone and motor activities.
Hindbrain (Rhombencephalon)
Cerebellum (Also called the small brain)	It is ⅛ the size of the cerebrum. It is connected to the brain stem by three pairs of peduncles.  Functions of the cerebellum: Controls and balances body posture It has ipsilateral control over the body. Modulates voluntary movements initiated by the cerebral cortex
Medulla oblongata	Functions of medulla oblongata: Several medullary centres control the functions of important organs, such as Cardiac centre for the heart Vasomotor centre for blood vessels Respiratory centre for lungs Reflex centres for vomiting, sneezing, coughing, and swallowing.
Pons varoli	Function: It carries impulses from one hemisphere of the cerebellum to another and coordinates muscle movements on the two sides of the muscle body.

Spinal Cord

The long tube-like structure extending from the brain is called the spinal cord. The spinal cord is composed of a series of 31 segments. Several spinal nerves emerge from the spinal segments in pairs. It has both motor and sensory nerves. 

The spinal cord presents as an extension of the brain stem. The spinal cord begins at the first cervical vertebra level and ends at the first lumbar vertebra in adults. The spinal cord has an inner grey matter surrounded by an outer white matter. The grey matter is a collection of cytons of the neuron, while the white matter is the collection of the fibres.  

Major functions of the spinal cord:

• Transmits impulses to and from the brain
• Acts as a reflex centre

Peripheral Nervous System (PNS) 

It comprises the nerves that arise from the CNS (i.e., the brain and the spinal cord) and connect different parts of the body. 

It consists of the following

• Cranial Nerves
• Spinal Nerves

Cranial nerves: 12 pairs that emerge from the brain. They are in the following order:

1. Olfactory nerve: smell
2. Optic nerve: sight
3. Oculomotor nerve: Eyeball movements such as blinking
4. Trochlear nerve: Eyeball rotation 
5. Trigeminal nerve: Sensations of face and jaw movements.
6. Abducens nerve: Eyeball rotation 
7. Facial nerve: Facial expressions, taste, saliva secretion
8. Auditory/vestibular nerve: Hearing and balancing
9. Glossopharyngeal nerve: Taste and swallowing
10. Vagus nerve: Digestion and heart rate
11. Accessory nerve: Also called spinal accessory nerve. Neck and Shoulder muscle movement
12. Hypoglossal nerve: Tongue movement 

Spinal nerves: The point of emergence is the spinal cord. There are 31 pairs of spinal nerves emerging from the spinal cords into ventral and dorsal roots. 

Peripheral Nervous System Functions

• It connects the brain and the spinal cord to the rest of the body.  
• It regulates internal homeostasis.
• It can control the strength of muscle contractility.
• It handles the release of endocrine gland secretions.  

Autonomic Nervous System

It relays impulses from the central nervous system to the smooth muscles and involuntary organs of the body. It consists of the following two parts: 

• Sympathetic Nervous System: It comprises nerves arising from the spinal cord between the neck and waist region. Its primary function is to prepare the body for violent actions in abnormal conditions. It is mostly stimulated by adrenaline.
• Parasympathetic Nervous System: Located anterior in the head and neck and posterior in the sacral region. Its main function is its involvement in the re-establishment of normal conditions when an abnormal violent action is over.

Sympathetic	Parasympathetic
Prepares the body for any potential danger	Brings the body to a state of calm after an unusual situation
It has a faster response time as the neuron pathways are shorter.	It has a comparatively slower response time as the neuron pathways are longer.
Increases heartbeat	Reduces heartbeat
Dilates the pupil	Contracts the pupil
Saliva secretion is inhibited.	Saliva secretion increases

Autonomic Nervous System Functions

Homeostasis is the primary function of the autonomic nervous system. The autonomic nervous system is also involved in controlling the following life processes:

• Digestion
• Defecation
• Metabolism
• Urination
• Blood pressure
• Sexual response
• Breathing rate
• Body temperature
• Heartbeat
• Fluid balance

Conclusion

The nervous system is your body’s command centre. The main is the major unit of the nervous system that integrates all the functions. A neuron is the structural and functional unit of the nervous system. This system influences all the vital processes, including digestion, breathing and sexual development. It is vital to take good care of your nervous system in order to keep yourself healthy.

Frequently Asked Questions

1. What are the most common nervous system disorders?

A. The commonly occurring nervous system disorders are as follows:

• Alzheimer’s disease: Affects brain function, memory and behaviour. 
• Bell’s palsy: Weakness or paralysis of facial muscles.
• Epilepsy involves seizures or periods of unusual behaviour.
• Parkinson’s disease: Nerve cells of the brain are damaged. 

2. What conditions can affect your nervous system?

A. The following conditions can adversely affect your nervous system:

• Diseases such as cancers, autoimmune disorders, diabetes, rheumatoid arthritis, multiple sclerosis, and more. 
• Strokes wherein the brain’s blood vessel/vessels suddenly burst or get blocked. 
• Accidental injury
• High blood pressure
• Toxic substances such as chemotherapy medicines, alcohol, and drugs.
• Aging process 

3. How do I keep the nervous system healthy?

A. The best practices for a healthy nervous are as follows:

• Positive thinking
• Exercise on a daily basis
• Walks, yoga, and meditation
• Adequate sleep
• Balanced diet 
• Appropriate treatment of any disease affecting the body