Nervous system of Humans- CNS and PNS

The nervous system and the endocrine system jointly and co-ordinates and regulates the metabolic activities of the body (organs).

Where the endocrine system is responsible to control the body by the means of the chemicals, those effects are very general.

Ex – The Growth hormone shows growth in the complete body.

But to target the specific parts nervous system comes into the action, it gives the point-to-point interaction and used for the fast response.

Ex- If you wish to move your index finger, then only your index finger will move. While if the endocrine system was under action then the whole hand or at least the palm will move instead of a finger.

Nervous System

The nervous system of the animals is made of highly specialized cells called neurons.

Neurons have the power to detect, receive, and transmit all kinds of stimuli.

The nervous system varies from organism to organism, it can be made of a network of few neurons (in hydra) to the most complex structures like the human brain.

Human Nervous System

In humans, it is divided into 2 parts-

1. The central nervous system (CNS).
2. The peripheral nervous system (PNS).

Central Nervous System (CNS).

The CNS includes the Brain and the spinal cord.

CNS is the main site for the control and processing of the information.

Brain

All the functions you name it is controlled by the brain whether it is memory, intelligence, speak, movement, breath, write, listen, hear, taste, sight, fear, anger, desire (even sexual), motivation, vomit, etc…

The brain contains the infoldings called Gyri and Sulci, which increases the surface area of the brain, for efficient use of it.

Brain consist of mainly 3 parts-

1. Forebrain
2. Midbrain
3. Hindbrain

This is also divided into different parts to do the specific function and the proper functioning of the brain.

1. Forebrain– into the
   • cerebrum
   • thalamus
   • hypothalamus
   • olfactory lobe
2. Midbrain– into the
   • corpora quadrigemina and crura cerebri.
3. Hindbrain– into the
   • Pons
   • Cerebellum
   • medulla oblongata

Spinal cord

It is the elongation of the medulla oblongata.

The spinal cord is protected by the vertebral column. It comes out from the Foramen of Magnum (a space in the occipital bone or you can say a hole).

The spinal cord is extended from the base of the skull to the L1 vertebra (1st lumbar vertebra). After that, it is converted into the thread-like Filum terminale.

It is made of the 31 segments from each segment one pair of sensory and motor nerve roots (from this many neurons comes out) arise.

The main function of the spinal cord is to provide the root and manage the messages from the brain to organs and organs to the brain.

Rather than that, it is also involved in Reflex actions. It also protects the peripheral nerves and helps in proper dispersal of them.

Peripheral Nervous System(PNS)

The nerves associated with the brain and spinal cord comprise the peripheral nervous system.

That means all the neurons that are not the part of the brain and spinal cord are the part of PNS i.e. Cranial nerve (12 pairs) and Spinal nerve (31 pairs).

PNS is divided into 2 divisions-

A.) Somatic Nervous System (SNS)

The SNS conduct the impulses from the brain to the skeletal muscles.

B.) Autonomic Nervous System (ANS)

The ANS conducts the impulses from the brain to the involuntary organs and the smooth muscles of the body.

ANS is further classified into 2 parts-

1. The sympathetic nervous system (SNS)

Functions during emergency conditions.

SNS prepares the body for either FIGHT or FLIGHT.

Effects–

• Increased blood flow to the skeletal muscle.
• Increased heart rate and BP.
• Increased Glycolysis (to form more glucose).
• Increased Breath rate.
• Decreased blood flow to the skin.
• Decreased Salivation.
• Digestion stops until the situation is over.
• Micturition is stopped.

All the unnecessary functions are stopped or reduced.

Note- Reduced blood to the skin is because it is not essential in emergency and also if there is any injury then the blood loss should be minimal.

2. The parasympathetic nervous system (PSNS)

It deals with the function that is not urgent (that doesn’t they are not necessary) like the digestion, micturition, respiration, and even sex.

Where the SNS is catabolic, PSNS on the other hand conserves the energy.

Nervous Tissue

Like all other tissues, the nervous tissue is the group of the cells (neural cells or neurons and other brain cells).

Nervous tissue is ectodermal in origin.

Nervous tissue is comprised of the –

1 Neuron-

It is the elongated excitable cell. Comprises of the cell body (cyton) and the nerve processes (dendron and axon).

Know more about the neuron structure and the function.

2 Neuroglia

They are the supporting cells of the neurons, that are present all around the neurons.

They are of various types-

Astrocytes	Oligodendrocytes	Microgliocytes
1. Morphology– Large cell Numerous process.	Smaller Few process.	Smallest With branching.
2. Functions- It forms the Blood-Brain-Barrier.	Formation and preservation of the Mylein sheath in CNS.	Scavenger cells of the CNS and phagocytic in nature.

Important points-

Blood-Brain-Barrier (BBB)-

it is the barrier formed by the Astrocyte cells which are coupled by the tight junctions. 

This barrier prevents the entry of the Neurotoxins inside the brain.

Neurotoxins- The compound harmful for the neurons.