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Nervous System

1. Nervous System 2. Structure of Neuron 3. Central Nervous System 4. Peripheral Nervous System 5. Disorders

Biology is defined as the study of living organisms, their origins, anatomy, morphology, physiology, behaviour and distribution. It’s the study of living things and their vital processes. The field deals with all the physicochemical aspects of life. This book contains an idea about the nervous system of our human body. The nervous system is a complex collection of nerves and specialized cells known as neurons that transmit signals between different parts of the body. It is essentially the body's electrical wiring. Structurally, the nervous system has two components: the central nervous system and the peripheral nervous system. The nervous system helps all the parts of the body to communicate with each other. It also reacts to changes both outside and inside the body. Most of the content are written in an easy dialogue style and attach appropriate pictures and diagrams for your study easy. We expect the text book to be helpful for you in learning biology Sumayya Jafar Natural Science KUCTE ANCHAL 18120975010

Nervous system, organized group of cells specialized for the conduction of electrochemical stimuli from sensory receptors through a network to the site at which a response occurs. Nervous System consists of two parts, namely the central nervous system and peripheral nervous system.

The CNS is the processing centre of the body and consists of the brain and the spinal cord.

The PNS consists of the nerves and ganglia

❖ Our nervous system is our body's command center. ❖ Originating from our brain, it controls our movements, thoughts and automatic responses to the world around us. ❖ It also controls other body systems and processes, such as digestion, breathing and sexual development (puberty). ❖ Control of body’s internal environment to maintain ‘homeostasis’. ❖ Memory and learning. ❖ Programming of spinal cord reflexes. ❖ It controls every function inside the human body as well. For your heart to beat, your lungs to breath, and your feet to walk, your nervous system must be functioning properly.

1. On the basis of indicators make a note

❖ What is mean by human nervous system? ❖ Write any two significances of nervous system?

2. Match the following

Central Nervous System

Perpheral Nervous System







3. Fill in the blanks.

a. CNS consists of ……………….. and ………………….. b. Ganglia is a part of ………………… c. Autonomic nervous system consists of ……………….. and parasympathetic nervous system

4. Construct a flow chart about peripheral nervous system?

Neurons (also called neurones or nerve cells) are the fundamental units of the brain and nervous system, the cells responsible for receiving sensory input from the external world, for sending motor commands to our muscles, and for transforming and relaying the electrical signals at every step in between.

Main Parts

Cell body ( Cyton )


It is the main part of neuron. It contains a nucleus and cytoplasm.


It carries impulses from the dendron to axon.

It carries Dendron

Short Filament from the cell

impulses from


dendrites to the cell body.

Receives Dendrite

Branches of dendron

impulses from the adjacent neuron.


Longest filament from the cell body

Carries impulses from the cell body to outside.

Carries impulses Axonite

Terminal branches of axon.

to the synaptic knob

Synaptic knob

Tip of axonite

Secretes neurotransmitter

Axons of most of the neurons are repeatedly encircled by myelin, a membrane containing lipid. This is called myelin sheath. Myelin sheath in the nerves is formed of Schwann cells. Myelin sheath in the brain and the spinal cord is. formed of specialized cells called oligodendrocytes. The myelin sheath has a shiny white colour. The part of the brain and the spinal cord where myelinated nerve cells are present in abundance is called white matter and the part where nonmyelinated nerve cells are present is called grey matter.

The major functions of the myelin sheath are to provide nutrients and oxygen to the axon, accelerate impulses, act as an electric insulator and protect the axon from external shocks.




The outer surface of the plasma membrane of the neuron is positively charged and the inner surface is negatively charged. This is due to the difference in the distribution of certain ions. Impulses are messages conducted through nerves. These impulses transmit in the form of electric charges. Impulses are generated when stimuli evoke changes in polarity in the plasma membrane of receptors, the modified neurons.

The difference in the distribution of ions helps to maintain positive charge on the outer surface and negative charge inside the plasma membrane of the neuron. When stimulated, the ionic equilibrium in the particular part changes. As a result, polarity changes and the outer surface becomes negatively charged while the inner surface becomes positively charged. This change does not persist for long. It regains its original state. But the momentary charge difference in the axon membrane stimulates its adjacent parts and similar changes occur there too.

Synapse, also called neuronal junction, the site of transmission of electric nerve impulses between two nerve cells (neurons) or between a neuron and a gland or muscle cell (effector). A synaptic connection between a neuron and a muscle cell is called a neuromuscular junction.

Synapse helps to regulate the speed and direction of impulses.

When electric impulses from the axon reach the synaptic knob, certain chemical substances are secreted from there to the synaptic cleft. These chemical substances are called neurotransmitters. They stimulate the adjacent dendrite or cell and new electric impulses are generated.

❖ Sensory neuron - These are the nerve cells that are activated by sensory input from the environment. ❖ Interneuron - These are neurons that are found exclusively in the central nervous system. ie, Found in the brain and spinal cord and not in the peripheral segments. ❖ Motor neuron - Motor neurons are a specialized type of brain cell called neurons located within the spinal cord and the brain.

❖ Unipolar neuron - A unipolar neuron is a neuron in which only one process, called a neurite, extends from the cell body.

❖ Bipolar neuron - A bipolar neuron, or bipolar cell, is a type of neuron that has two extensions (one axon and one dendrite).

❖ Pseudounipolar neuron - A pseudounipolar neuron is a type of neuron which has one extension from its cell body. This type of neuron contains an axon that has split into two branches; one branch travels to the peripheral nervous system and the other to the central nervous system.

❖ Multipolar neuron - Each multipolar neuron contains one axon and multiple dendrites.

Nerves and their


peculiarities Sensory nerve ( formed of

Carries impulses from various

sensory fibres)

parts of the body to the brain and the spinal cord

Motor nerve ( formed of

Carries impulses from brain

motor nerve fibres )

and spinal cord to various parts of the body

Mixed nerve ( formed of

Carries impulses to and from

sensory nerve fibres and

the brain and spinal cord

motor nerve fibres )

1. Complete the box given below





Schwann cell

Encircle the axon




Secretes neurotransmitter

2. a) Identify the structure given below

b) Write down its peculiarities?

3. Choose the correct answer

a) Synapse encircle the axon b) Axon is the longest filament from the cell body c) No polarity change during the transmission of impulses d) Sensory nerve formed of motor nerve fibres

4. Draw the structure of neuron and label its parts.

The nervous system consists of two parts, namely the central nervous system and the peripheral nervous system. The central nervous system consists of brain and the spinal cord.

The brain is protected inside the skull. It is covered by the meninges, a three-layered membrane. The cerebrospinal fluid is filled within the inner membranes of meninges and the ventricles of the brain. The cerebrospinal fluid is filled within the inner membranes of meninges and the ventricles of the brain. The cerebrospinal fluid is formed from the blood and is reabsorbed into the blood. The functions of the cerebrospinal fluid are to provide nutrients and oxygen to the tissues of the brain, regulate the pressure inside the brain and to protect the brain from injuries.

Cerebrum: Cerebrum is the largest part of the brain and it has numerous fissures and folds. In cerebrum grey matter is seen in the external cortex and white matter is seen in the internal medulla. Cerebrum is the centre of thought, intelligence, memory and imagination. Cerebrum also evokes sensations and controls voluntary movements.

Cerebellum: Cerebellum is the second largest part of the brain. It is seen behind the cerebrum as two flaps and has fissures, and grooves. Cerebellum coordinates muscular activities and maintains the equilibrium of the body.

Medulla oblongata: The rod shaped medulla oblongata is seen below the cerebrum, located near to cerebellum. Medulla oblongata controls involuntary actions like heart beat, breathing, etc.

Thalamus: Thalamus is situated below the cerebrum. It acts as relay station of impulses to and from the cerebrum. Thalamus analyses impulses from the various parts of the body and sends the important ones to the cerebrum.

Hypothalamus: Hypothalamus is situated just below the thalamus and plays a major role in the maintenance of homeostasis.

The spinal cord is protected inside the vertebral column. Like the brain, the spinal cord is also covered by meninges.

A dorsal root and a ventral root join to form a spinal nerve. Sensory impulses reach the spinal cord through the dorsal root. Motor impulses go out of the spinal cord through the ventral root.

Impulses from different parts of the body are transmitted to and from the brain through the spinal cord. It also coordinates the repeated movements during walking, running, etc.

Reflex Action

The accidental and involuntary responses towards stimuli are called reflex actions.

Reflex Arc Reflex arc is the pathway of impulses in the reflex action.


Receptor Generates impulses

Sensory neuron Carries impulses to spinal cord

Inter neuron The neuron that connects the sensory neuron and motor neuron. Generates quick responses according to the sensory impulse

Motor neuron Carries information from spinal cord to related muscles

Related muscle Withdraws the body part by the action of muscles

1. Complete the diagram






2. Prepare a flowchart about reflex arc ? 3. Write a short note about Spinal Cord ? 4. Write an autobiography of impulse through its travel experiences?

Activities that take place beyond the conscious level are controlled by the autonomous nervous system, a part of the peripheral nervous system. The autonomous nervous system contains the sympathetic system and the parasympathetic system.

The sympathetic nervous system activates the fight or flight response during a threat or perceived danger, and the parasympathetic nervous system restores the body to a state of calm.








The pupil in the eye dilates

The pupil constricts

Production of saliva

Production of saliva





Trachea dilates

Trachea constricts




Heartbeat increases

Heartbeat becomes normal

Gastric activities slow

Gastric activities become



Glycogen is converted to

Glucose is converted to



Intestine Peristalsis slows down


Urinary bladder retains


to normal state

Peristalsis becomes normal

Urinary bladder contracts

1. Fill in the blanks. Sympathetic system

Parasympathetic system

Trachea dilates

Trachea ……………………..

Heartbeat ………………

Heartbeat normal

Production of saliva

Production of saliva



Peristalsis …………………..

Peristalsis …………………..

2. What are the changes takes place in the body during such emergency situations ? 3. Distinguish between sympathetic and parasympathetic system ? 4. Prepare a picture album about autonomous nervous system ?

❖ The nervous system is vulnerable to various disorders. It can be damaged by the following:

➢ Trauma ➢ Infections ➢ Degeneration ➢ Structural defects ➢ Tumors ➢ Blood flow disruption ➢ Autoimmune disorders

❖ Disorders of the nervous system may involve the following:

➢ Vascular disorders - such as stroke, transient ischemic attack (TIA), subarachnoid hemorrhage, subdural hemorrhage and hematoma, and extradural hemorrhage

➢ Infections - such as meningitis, encephalitis, polio, and epidural abscess

➢ Structural disorders - such as brain or spinal cord injury, Bell's palsy, cervical spondylosis, carpal tunnel syndrome, brain or spinal cord tumors, peripheral neuropathy, and Guillain-Barré syndrome

➢ Functional disorders - such as headache, epilepsy, dizziness, and neuralgia

➢ Degeneration - such as Parkinson disease, multiple sclerosis, amyotrophic lateral sclerosis (ALS), Huntington chorea, and Alzheimer disease


Parkinson’s Disease


1. a) Identify the disease given below ?

b) Write down its causes and symptoms ?

2. Watch the video on the youtube channel and write a short note on the topic discussed here ? 3. Prepare a poster on the part of celebrating world Alzheimer’s Day , September 21 ? 4. Find the odd one out ? Alzheimer’s disease

Sickle cell Anaemia

Parkinson’s disease


The nervous system consists of the brain, spinal cord, sensory organs, and all of the nerves that connect these organs with the rest of the body. Together, these organs are responsible for the control of the body and communication among its parts. The brain and spinal cord form the control center known as the central nervous system (CNS), where information is evaluated and decisions made. The sensory nerves and sense organs of the peripheral nervous system (PNS) monitor conditions inside and outside of the body and send this information to the CNS. The nervous system transmits signals between the brain and the rest of the body, including internal organs. In this way, the nervous system's activity controls the ability to move, breathe, see, think, and more. The basic unit of the nervous system is a nerve cell, or neuron. Most of us just take it for granted that our nervous system is working properly. However, if our nervous system is not functioning at peak performance, then we are not at our best.