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Neural Tissue: Neuron - its Parts and Functions, Neuroglial Cells, Practice Problems and FAQs

Neural Tissue: Neuron - its Parts and Functions, Neuroglial Cells, Practice Problems and FAQs

We read books, learn new things in our daily life and expand our knowledge. We are constantly improving in our life as we learn from past experiences. How is this possible? Which tissue is responsible to memorise and analyse all these things in our life?

Yes, you know the answer is neurons or nerve cells. These neurons form a group of cells called neural tissue. In a complex organism, there is one major organ system that controls and regulates the activities of all other systems.


                                      GIF: Magic of brain

In humans, this is the nervous system that regulates the entire body activities. The nerve cell or neuron is the basic functional unit of the nervous system. It is responsible for the conduction of signals and coordination of activities. Let’s understand more about the neurons and their supporting cells in this article.

Table of contents:

  • Neural tissue
  • Neuron
  • Neuroglial cells
  • Functions of nervous system
  • Practice Problems
  • Frequently Asked Questions

Neural tissue

Neural system is the most complex network that controls the body's responses. Neural tissue consists of excitable and specialised cells called neurons. The rest of the neural system is made up of neuroglial cells.


                                                             Fig: Neural tissue

Neuron

Neuron is the structural and functional unit of neural tissue. It detects and receives information from different sense organs in the form of stimuli and transmits these stimuli to the CNS or central nervous system.

Properties of neuron

It shows the following properties:

  • Excitability
  • Conductivity

Excitability

It is the ability of a neuron to generate electrical impulses in response to the stimuli. Neurons respond to stimulations by the rapid changes in the membrane potential. This excitation occurs in response to various stimuli like light, pressure, temperature or chemicals.

Conductivity

It is the ability of neurons or nerve cells to rapidly transmit the electrical impulse as a wave from one neuron to other neurons, muscles or glands. That means from the site of origin to the site of response along their length in a particular direction.


                                                             Fig: Nervous tissue

Parts of the neuron

Neuron possesses two parts mainly as follows:

  • Cyton
  • Cytoplasmic processes

The cytoplasmic processes include dendrites and axon.


                                                               Fig: Parts of neuron

Cyton

The cell body of a neuron is known as cyton or perikaryon or soma. It is rounded, oval, star shaped or pyramidal. The cytoplasm of a neuron is known as neuroplasm. It possesses a central nucleus, Nissl’s granules, neurofibrils, mitochondria, golgi bodies, Endoplasmic reticulum, and lysosomes.


                                                             Fig: Cyton of a neuron

Nissl’s granules

Nissl’s granules or tigroid bodies are present in the cytoplasm of a neuron and occur as a deeply stained particle. These are categorised as irregular masses of rough endoplasmic reticulum and ribosomes. It is named after Franz Nissl who discovered them. Basic dyes can be used to stain them. It plays a role in the transmission of impulses.


                                                                      Fig: Nissl’s granules

Cytoplasmic processes

Cytoplasmic processes help in the conduction of nerve impulses. They are of two types as follows:

  • Dendrite
  • Axon
Dendrite

Characteristics

They are short and branched with tapering ends.

Function

Dendrites receive nerve impulse from adjacent neurons and transfer it to the cyton of next neurons.

GIF: Transmission of nerve impulse

Image

Fig: Dendrite

Axon

Characteristics

It is a single, long projection arising from the part of the cyton called axon hillock. It is the most sensitive part of the neuron. Axon ends in a number of branches known as axonites. The end of each branch swells at the tip to form a synaptic knob or end plate. It possesses synaptic vesicles with neurotransmitters, mitochondria and vesicles. The cytoplasm present here is called axoplasm and the plasma membrane is called axolemma.

Function

Axon conducts impulse from cyton to the dendrites of adjacent neurons.

GIF: Conduction of impulse by axon

Image

Fig: Axon

Differences between axon and dendrite

Axon

Dendrite

It arises from the cell body and branched at the distal end

It arises from the cell body and branched all along their length

It is very long

They are very short

Branches terminates in synaptic knobs

Branches do not terminate in synaptic knobs

Vesicles with neurotransmitters present in the synaptic knob

Vesicles with neurotransmitters are absent

Neuroplasm lack Nissl’s granules

Neuroplasm possess neurofibrils and Nissl’s granules

It conduct impulses away from the cell body

It conduct impulses towards the cell body

Neuroglial cells

These are supporting cells. They provide support to the brain, spinal cord and ganglions. Here Glia means glue. They are of different types. They have different shapes. They separate and insulate the adjacent neurons. It allows the passage of impulses from one neuron to the next only over the synapse. Glial cells are of four types as follows:

  • Astrocytes
  • Schwann cells
  • Oligodendrocytes
  • Microglia

Astrocytes

These cells possess a characteristic star shape. They form the blood-brain barrier. They help in defence and repair of neural tissues. They provide mechanical support to the neurons. They are of two types as follows:

Fibrous astrocytes

They possess thin and asymmetrical processes. They are normally present in the white matter of the central nervous system.

Protoplasmic astrocytes

They possess thick and symmetrical processes. They are present in the grey matter of the central nervous system.


                                                              Fig: Astrocytes

Schwann cells

They help to form an insulating layer around the neurons, called myelin sheath. The myelin sheath is rich in lipids. It covers the nerve cells.


                                                    Fig: Schwann cell

Oligodendrocytes

They have rounded a nucleus with cytoplasm. The cytoplasm is rich in mitochondria, glycogen and microtubules. They have fewer and shorter cell processes. Oligodendrocytes have numerous projections that extend to many neurons. These cells also help in the formation of myelin sheath around the axons that lie in the brain and spinal cord.


                                                            Fig: Oligodendrocyte

\Microglia

These are considered as the smallest neuroglial cells. They are formed from the mesoderm of the embryo. They are thought to be derived from the monocytes that invade the brain during the foetal life. They are more numerous in grey matter normally. They have short and fine processes. They engulf and destroy microbes, that means they help in phagocytosis. They are considered as scavengers as they remove cellular debris.


                                              Fig: Microglia

Functions of neurons

  • Helps in maintaining homeostasis.
  • It generates reflex actions.
  • It helps in memory and learning.
  • It helps in control and coordination of all activities.
  • It helps in control of movements.

Practice problems

  1. Recognise the figure and identify the correct labelling:

Answer: In the given figure, ‘a’ represents dendrites, ‘b’ represents cyton or cell body and ‘c’ represents axon.

  1. In the human body, the longest cell is _____________.
  1. nerve cell
  2. skeletal muscle cell
  3. bone cell
  4. cell of alimentary canal

Solution: Nerve cell or neuron is the longest cell in the human body. It is considered the longest cell because of the presence of a long axon. Hence, the correct option is a.

3. What does the given GIF represent?

Answer: The given GIF represents the impulse conduction via axon. The impulse is transferred from the cyton to the dendrites of the next neuron through the axon.

4. Identify the cell which is star-shaped?

  1. Astrocytes
  2. Schwann cells
  3. Oligodendrocytes
  4. Microglia

Solution: Astrocytes have a distinctive star form. They are responsible for forming the blood-brain barrier. They aid in brain tissue defence and repair. They also give mechanical support to the neurons. Hence, the correct option is a.

5. The end of the axon forms a __________.

Answer: The end of the axon forms a synaptic knob. It has synaptic vesicles with neurotransmitters like acetylcholine.

6. What is the function of Schwann cells?

Answer: Schwann cells contribute to the formation of the myelin sheath, an insulating coating that surrounds neurons. The myelin sheath has abundant lipid content.

FAQs

  1. Why can't neurons regenerate?

Answer: Neurons have a special architecture that is post-mitotic. A post mitotic cell does not have the ability to divide anymore after its differentiation. There are a few restricted areas in the brain and CNS where new nerve cells are born in an adult brain.

  1. How big will a neuron be?

Answer: There are different types of neurons. They can vary in size. It normally ranges from 4 microns to 100 microns in diameter.

  1. Neurons are said to be fast in conducting impulses. How fast are they?

Answer: Neurons transmit electrochemical signals in the form of the action potentials. These signals travel through the axon to dendrites of other nerve cells. Neurons can send signals at about 50 metres per second, which is more than 100 miles an hour.

  1. How many neurons are present in the brain?

Answer: An average of 86 billion neurons present in the brain. It possesses 85 billion nonneuronal cells also.

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Related Topics:

Human neural system: Overview (CNS and PNS), Practice Problems and FAQs

Synapse and Transmission of impulses, Practice Problems and FAQs

Reflex action and reflex arc, Practice Problems and FAQs

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