Neuron
A neuron is a specialized nerve cell that is the basic building block of the nervous system.
Neurons receive, process, and transmit information throughout the brain, spinal cord, and body using electrical and chemical signals.
There are approximately 86 billion neurons in the human brain, working together to control every thought, movement, sensation, emotion, and memory.
Parts of a Neuron
Cell Body (Soma)
The cell body (soma) is the main part of the neuron.
Functions
- Contains the nucleus.
- Keeps the neuron alive.
- Produces proteins and energy.
- Processes incoming information before sending it to the axon.
Dendrites
Dendrites are branch-like extensions that receive information from other neurons.
Functions
- Receive nerve signals.
- Carry information toward the cell body.
- Form thousands of connections with other neurons.
Axon
The axon is a long, thin fiber that carries electrical impulses away from the cell body.
Functions
- Transmits action potentials.
- Carries information to other neurons, muscles, or glands.
- Can range from less than 1 millimeter to over 1 meter in length in humans.
Myelin Sheath
The myelin sheath is a fatty insulating layer that surrounds many axons.
Functions
- Protects the axon.
- Speeds up nerve impulse transmission.
- Improves communication between neurons.
- Helps coordinate movement, sensation, and thinking.
How a Neuron Sends a Message
- Dendrites receive information.
- The cell body processes the information.
- If the signal reaches the threshold, an action potential is generated.
- The action potential travels along the axon.
- Neurotransmitters are released into the synapse.
- The neurotransmitters bind to receptors on the next neuron.
- The message continues through the nervous system.
Brain
The brain is the body's control center and one of the most complex organs in humans and other animals.
It controls:
- Thinking
- Learning
- Memory
- Emotions
- Behaviour
- Movement
- Sensation
- Language
- Vision
- Hearing
- Balance
- Breathing
- Heart rate
- Many other vital body functions
The brain constantly receives information from the body, processes it, and sends instructions back through the nervous system.
Protection of the Brain
The brain is well protected by several structures.
Skull
The brain is enclosed inside the skull, a strong bony shell that protects it from injury.
Meninges
Three protective membranes surround the brain and spinal cord:
- Dura mater
- Arachnoid mater
- Pia mater
These membranes are called the meninges.
Cerebrospinal Fluid (CSF)
The brain is surrounded by cerebrospinal fluid (CSF).
CSF:
- Cushions the brain.
- Absorbs shocks.
- Protects against injury.
- Delivers nutrients.
- Removes waste products.
Human Brain Weight
The average adult human brain weighs about:
- 1.3–1.4 kilograms
- Approximately 3 pounds
Although the brain makes up only about 2% of body weight, it uses about 20% of the body's oxygen and energy.
Brain Sizes in Different Animals
Brain size varies greatly among animals. Larger animals generally have larger brains, but brain size alone does not determine intelligence. Scientists also consider the brain-to-body size ratio, known as the encephalization quotient (EQ), when comparing cognitive abilities.
| Animal | Average Brain Weight |
|---|---|
| Sperm whale | Up to 8,000 g (17.6 lb) |
| Elephant | About 4,800 g (10.5 lb) |
| Bottlenose dolphin | 1,500–1,700 g (3.3–3.7 lb) |
| Human | 1,300–1,400 g (about 3 lb) |
| Chimpanzee | About 440 g (15.5 oz) |
| Cow | About 423 g (14.9 oz) |
| Sheep | About 175 g (6.1 oz) |
| Grey wolf | About 120 g (4.2 oz) |
| Raven/Crow | About 10 g |
| Cat | 25–30 g (0.9–1.1 oz) |
| Mouse | About 0.4 g (0.01 oz) |
| Ant | About 0.006 mg |
Although the sperm whale has the largest brain by weight, the human brain has one of the highest brain-to-body ratios among mammals, supporting advanced reasoning, language, planning, and problem-solving.
The Brain Controls
The brain is responsible for:
- Thinking
- Learning
- Memory
- Behaviour
- Emotions
- Personality
- Decision-making
- Speech
- Body movement
- Balance
- Sensory processing
- Vision
- Hearing
- Smell
- Taste
- Touch
Every movement and sensation depends on communication between the brain, spinal cord, nerves, and muscles.
The Spinal Cord
The spinal cord is a long bundle of nerve tissue that connects the brain to the rest of the body.
Functions
- Carries sensory information from the body to the brain.
- Carries motor commands from the brain to the muscles.
- Coordinates reflexes.
- Connects with the 31 pairs of spinal nerves.
Nerves
A nerve is a bundle of axons found in the Peripheral Nervous System (PNS).
Nerves carry information:
- From the body to the brain (sensory or afferent nerves).
- From the brain to the muscles and glands (motor or efferent nerves).
Muscles
Muscles receive messages from motor neurons.
When the brain decides to move:
- The brain sends a signal.
- The signal travels through the spinal cord.
- Motor nerves carry the message to the muscle.
- The muscle contracts.
- Movement occurs.
Examples include:
- Walking
- Writing
- Smiling
- Running
- Picking up objects
The Three Main Regions of the Brain
The brain can be divided into three major regions:
1. Forebrain
The forebrain is the largest part of the brain.
It includes the:
- Cerebrum
- Thalamus
- Hypothalamus
Functions
- Thinking
- Learning
- Memory
- Emotions
- Voluntary movement
- Language
- Decision-making
- Sensory processing
2. Midbrain
The midbrain is located between the forebrain and hindbrain.
Functions
- Eye movement
- Hearing reflexes
- Vision reflexes
- Movement coordination
- Alertness
It acts as an important relay station for sensory and motor information.
3. Hindbrain
The hindbrain includes the:
- Cerebellum
- Pons
- Medulla oblongata
Functions
- Balance
- Coordination
- Breathing
- Heart rate
- Blood pressure
- Swallowing
- Sleeping
These functions are essential for survival.
The Cerebrum
The cerebrum is the largest part of the brain.
Functions
- Thinking
- Intelligence
- Memory
- Language
- Learning
- Emotions
- Personality
- Voluntary movement
- Interpreting sensory information
The cerebrum is divided into the left and right hemispheres and contains the frontal, parietal, temporal, and occipital lobes.
The Cerebellum
The cerebellum is located at the back of the brain beneath the cerebrum.
Functions
- Balance
- Coordination
- Fine motor control
- Muscle tone
- Posture
- Smooth, accurate movement
- Motor learning
It helps ensure that movements such as walking, writing, and catching a ball are coordinated and precise.
Summary
- A neuron is the basic communication cell of the nervous system.
- Dendrites receive information, the cell body processes it, the axon carries it away, and the myelin sheath speeds up transmission.
- The brain is the body's control center, responsible for thinking, behaviour, movement, sensation, learning, memory, emotions, and vital body functions.
- The brain is protected by the skull, the meninges, and cerebrospinal fluid (CSF).
- The average human brain weighs about 3 pounds (1.3–1.4 kg), while brain sizes vary greatly among animals.
- The spinal cord connects the brain to the rest of the body and carries sensory and motor information.
- Nerves carry messages throughout the body, and muscles respond to motor nerve signals to produce movement.
- The brain has three major regions: the forebrain, midbrain, and hindbrain. The cerebrum is responsible for higher thinking and voluntary actions, while the cerebellum coordinates balance and movement.
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