Human Body
Digital Handwritten Lesson
Unit 1
Human Body
Nervous System
The "Master System" that controls and coordinates everything your body does.
What is the Nervous System?
The nervous system is made up of tiny nerve cells called neurons. Each neuron has three parts: an axon (a long tail-like part), dendrites (short fibrous roots), and a nucleus in the middle surrounded by protoplasm. The axon is longer than the dendrites. 
It controls and coordinates all internal and external activities of the human body and gives commands to all other organ systems. That is why it is called the "Master System" or "Command Centre".
It has three main parts: Central Nervous System (CNS), Peripheral Nervous System (PNS), and Automatic Nervous System (ANS).
A. Central Nervous System (CNS)
The CNS has two parts: the brain and the spinal cord. The brain controls thinking, learning, moving, and feeling. The spinal cord carries messages between the brain and the rest of the body. It is called the "centre" because it collects information from the whole body and coordinates everything.
a. The Brain
The brain sits safely inside the skull. An adult brain weighs about 1.5 kg and is made of soft tissue. It is protected by a thin covering called the meninges. It has 5 main parts: 
Functions: Helps us think, remember, and make decisions. Controls our five senses — sight, sound, smell, taste, and touch. It commands and coordinates all other organs of the body.
Functions: Controls and coordinates muscle movements like walking, running, and eye movement. Helps you keep your balance and posture. It also sends signals it receives to the cerebrum.
Function: Acts as a bridge — passes information from the spinal cord up to the cerebrum, and passes commands from the cerebrum down to the spinal cord.
Function: Acts as another connecting bridge. Information and commands travel through it from the cerebrum down to the medulla oblongata.
Functions: Controls heartbeat and breathing. Also manages reflex actions — automatic responses like pulling your hand from a hot object or blinking when something comes near your eye.
b. Spinal Cord
What is the Spinal Cord?
The spinal cord starts at the bottom of the brain and runs down the back. It is protected by the vertebrae (backbone). It carries nerve signals back and forth between the brain and the body, and also controls reflex actions. 
⚠️ Damage to the spinal cord is called a spinal injury, which can cause disability.
B. Peripheral Nervous System (PNS)
The PNS is a large network of nerves that connects the CNS to all parts of the body. It is made up of 12 pairs of cranial nerves (from the brain) and 31 pairs of spinal nerves (from the spinal cord). Think of it as the body's wiring system — it creates a communication network between the CNS and all body parts.
C. Automatic Nervous System (ANS)
Some activities happen in our body automatically — like heartbeat, breathing, and digestion. We do not have to think about them. The ANS controls these activities. It is divided into two opposite systems:
⚡ Sympathetic System
- Speeds up breathing rate
- Increases heartbeat
- Enlarges (widens) the pupils
- Slows down digestion
Active when you are scared or excited — "fight or flight" mode.
🌿 Parasympathetic System
- Lowers heartbeat
- Increases rate of digestion
- Contracts (narrows) the pupils
- Helps the body rest and relax
Active when you are calm and at rest — "rest and digest" mode.
Functions of the Nervous System
⭐ Key Points — Nervous System
- The neuron is the basic unit of the nervous system (axon + dendrites + nucleus).
- CNS = Brain + Spinal Cord. PNS = network of cranial and spinal nerves.
- Cerebrum → thinking, senses, memory. Cerebellum → balance, muscle coordination.
- Medulla oblongata → heartbeat, breathing, reflex actions.
- Spinal cord = 45 cm long, 31 pairs of spinal nerves.
- The nervous system is called the "Master System" because it controls everything.
Endocrine System
Also known as the gland system — it produces hormones that travel through the blood to control many body functions. 
What is the Endocrine System?
The endocrine system is also called the gland system. Different glands in the body produce hormones and enzymes. These travel through the body via ducts and blood to control different body functions.
There are two types of glands: Exocrine glands (with ducts) and Endocrine glands (without ducts).
A. Exocrine Glands
Exocrine glands produce substances like sweat, tears, saliva, and digestive juices. These substances travel to other organs through ducts (tubes).
Examples: Sweat glands, lacrimal glands (tears), salivary glands, mammary glands (milk), and liver (bile).
Functions: Absorb nutrients, control body temperature, and protect the inner lining of the body.
B. Endocrine Glands
Endocrine glands have no ducts. They release hormones directly into the blood, which then carries them to tissues and organs all over the body.
Functions: Commands and controls all other endocrine glands. Controls growth, blood pressure, water retention, stimulates adrenal glands, helps produce sex hormones, and activates mammary glands during pregnancy.
Function: Produces melatonin hormone, which manages our sleep-wake cycle (when we feel sleepy and when we wake up).
Functions: Regulates breathing, heartbeat, digestion rate, and body temperature. Also controls the growth of bones and muscles and helps with mental development.
Functions: Controls calcium levels in the blood. Manages the balance of phosphorus and calcium. Important for the growth and development of bones.
Functions: These hormones affect digestion, heart rate, oxygen in blood, and sexual activity.
Function: Produces white blood cells (lymphocytes). Develops antibodies in our body that help the immune system fight diseases and infections.
Ovary (female) produces estrogen (produces eggs, develops female characteristics) and progesterone (prepares uterus for a fertilized egg, supports fetus growth).
As exocrine: releases digestive juice. As endocrine: produces insulin and glucagon hormones that control blood sugar level.
Functions of the Endocrine System
⭐ Key Points — Endocrine System
- Exocrine glands use ducts. Endocrine glands release hormones directly into the blood.
- Pituitary gland = master gland (controls all other endocrine glands).
- Pineal gland → melatonin → controls sleep cycle.
- Thyroid gland → thyroxine → controls breathing, heartbeat, growth.
- Adrenal gland → sits on kidneys → produces adrenaline.
- Pancreas = mixed gland → insulin + glucagon → controls blood sugar.
- Thymus gland → produces white blood cells → fights infections.
Reproductive System
The system responsible for producing offspring. Includes both the female and male reproductive organs.
What is the Reproductive System?
Living beings produce offspring to ensure the survival of their species. In humans, fertilization occurs when a sperm (from the male) meets an ovum/egg (from the female). They unite to form a fertilized egg (fetus), which is implanted in the uterus and grows into a child. The whole system of fertilization and producing offspring is called the reproductive system.
A. Female Reproductive System
The female reproductive system produces essential sex hormones and ova (eggs). It provides a safe environment for the growth and development of the fetus until the child is born. It has external and internal parts. 
External Female Organs (Vulva)
The group of external reproductive organs is collectively called the vulva.
It includes:
Labia majora (outer skin folds on both sides of the vagina, with pubic hair during puberty)
Labia minora (small delicate skin folds inside the labia majora, surrounding the vagina and urethra)
Clitoris (made of erectile tissue, located above the vestibules, very sensitive)
Hymen (a thin tissue covering the vaginal opening)
Vestibule (the area between the labia minora, containing the urethral and vaginal openings).
Internal Female Organs
Functions: Provides a passageway for blood during menstruation, receives the penis during intercourse, and provides a passageway for the child during delivery. Connects internal and external female reproductive organs.
Function: Nourishes and houses the fetus until it is ready to be delivered. If pelvic floor muscles weaken, the uterus may drop — this is called uterine prolapse. The Government of Nepal treats this problem free of cost.
Functions: Serve as a pathway for the ovum to travel from the ovaries to the uterus. Fertilization normally occurs inside the fallopian tubes. The fertilized egg then travels to the uterus for implantation.
Functions: Produces eggs (ova) and hormones (estrogen and progesterone). Releases one egg each month — this process is called ovulation.
B. Male Reproductive System
The male reproductive system produces sex hormones and sperm. It also produces protective fluid that helps transport the sperm. It has internal and external parts.
Functions: Produce sperm and the hormone testosterone.
Functions: Stores and carries sperm cells created in the testes. Helps sperm mature and pass into the vas deferens.
Function: Transports mature sperm to the urethra for ejaculation. (Note: Vasectomy is done by cutting and tying the vas deferens to prevent sperm from travelling further.)
Functions: Produces semen and provides nutrition to the sperm.
Function: Delivers semen and sperm into the urethra.
Functions: Secretes seminal fluid that protects the sperm and provides mobility to the sperm. Some older men may face prostate problems (frequent urge to urinate, trouble urinating), which can be treated at health institutions.
Function: Expels both urine and sperm out of the body.
Functions: Takes part in sexual intercourse and delivers semen into the vagina. Also allows for the excretion of urine.
⭐ Key Points — Reproductive System
- Fertilization = when sperm meets ovum, usually in the fallopian tubes.
- Female external organs together are called the vulva.
- The uterus (womb) houses and nourishes the fetus during pregnancy.
- Ovulation = the process of releasing one egg from the ovary each month.
- Testes produce sperm and testosterone. Ovaries produce eggs, estrogen, and progesterone.
- The pancreas is a "mixed gland" — it works as both exocrine and endocrine.
- The fallopian tube is where fertilization normally takes place.
Exercise:
1. Match the organs with their functions
| Organ | Function |
|---|---|
| a. Cerebrum | iii. Reasoning |
| b. Medulla oblongata | i. Reflex action |
| c. Pineal gland | iv. Melatonin production |
| d. Pancreas | v. Insulin production |
| e. Testes | ii. Sperm and testosterone production |
2. Tick the correct answer
| Question | Correct Answer |
|---|---|
| a. Which organ coordinates the speed of the muscles in the body? | ii. Cerebellum |
| b. How many pairs of spinal nerves exit from the spinal cord? | iii. 31 |
| c. Which gland is known as the master gland of the human body? | i. Pituitary gland |
| d. Which of the following glands secretes the insulin hormone? | i. Pancreas |
| e. Which of the following organs is a female reproductive organ? | iv. Uterus |
3. Answer these questions
The nervous system is an internal system of the body that collects information, processes it, and sends instructions to various organs. Its functions are:
- To control and coordinate the activities of all body parts.
- To help the body perceive and respond to external stimuli (like heat, sound, or light).
b. Why is the brain known as the centre of the nervous system?
The brain is called the center because it receives all signals from the senses, interprets them, and acts as a decision-making unit that directs every voluntary and involuntary action of the body.
c. What do you understand by the endocrine system? Write a short description of any three glands.
The endocrine system consists of ductless glands that release chemical messengers called hormones directly into the blood to regulate body processes. Three glands are:
- Pituitary Gland: Located at the base of the brain, it regulates growth and controls other endocrine glands.
- Thyroid Gland: Located in the neck, it produces thyroxin which controls the rate of metabolism.
- Adrenal Gland: Located above the kidneys, it produces adrenaline to prepare the body for "fight or flight" during stress.
d. Pancreas is known as a mixed gland. Why? Justify it.
The pancreas is a mixed gland because it has both exocrine and endocrine functions. It acts as an exocrine gland by producing digestive juices (enzymes) and as an endocrine gland by producing hormones like insulin to regulate blood sugar.
e. Draw a picture of the internal female reproductive organs and name them.
The main organs are the Ovaries (produce eggs), Fallopian tubes (pathway for eggs), Uterus (where the baby grows), and Vagina.
f. Describe the male reproductive organs in brief.
The male reproductive system consists of testes (located in the scrotum) which produce sperm and testosterone. Sperm travels through the vas deferens, mixes with fluids from glands (like the prostate), and is delivered through the penis.
g. Write any two differences between the testes and the ovary.
| Testes | Ovary |
|---|---|
| Found in the male body. | Found in the female body. |
| Produces sperm and testosterone. | Produces eggs (ova) and estrogen. |
Course material curated by Mr. Nripendraswar Acharya