The brain is the control center of the human body, weighing about 1.3–1.4kg and containing around 86 billion neurons. Its main divisions are:

Cerebrum

largest part of brain, divided into left and right hemispheres, each with four lobes:

• Frontal lobe: Responsible for thinking, reasoning, planning, voluntary movement, emotions, and speech production.

• Parietal lobe: Processes sensory information and spatial orientation.

• Occipital lobe: Handles vision and visual interpretation.

• Temporal lobe: Involved in auditory processing, memory, and language comprehension.

Cerebellum

• Sits at the base/back of the brain.

• Coordinates voluntary movements, posture, balance, and motor learning.

Brainstem

• Connects the brain with the spinal cord, vital for autonomic functions like heartbeat and breathing.

• Made up of the midbrain, pons, and medulla oblongata.

Limbic System

• Includes the amygdala, hippocampus,thalamus, and hypothalamus.

• Regulates emotion, memory, motivation, and hormone release.

Pituitary Gland

• The endocrine “master gland,” influencing growth ,metabolism, and reproduction.

Key Brain Functions

• Motor Control: Initiates and coordinates movements.

• Sensory Processing: Receives and interprets information from the body and environment.

• Cognition and Emotion: Enables complex thinking, reasoning, emotion, memory, speech, and creativity.

• Autonomic Functions: Maintains heartbeat, breathing, digestion, and reflexes.

Chemical Reactions in the Brain

The brain’s functions depend on complex chemical reactions involving neurotransmitters and their movement between neurons:

Neurotransmitter Communication

1. Synthesis & Storage: Neurotransmitters are made and stored in vesicles at the ends of neurons.

2. Release: An electrical signal (action potential) triggers calcium influx, causing neurotransmitter vesicles to merge with the neuron membrane and release their content into the synaptic cleft.

3. Binding: Neurotransmitters cross the synaptic cleft to bind with receptors on neighboring neurons, either exciting, inhibiting, or modulating their activity.

4. Second Messenger Cascades: In some cases, neurotransmitter binding activates second messengers (like cyclic AMP or calcium ions), leading to amplified cellular signals and more complex responses inside neurons.

Major Neurotransmitters

• Glutamate: Main excitatory neurotransmitter-crucial for learning and memory.

• GABA: Main inhibitory neurotransmitter-reduces overactivity.

• Dopamine, Serotonin, Norepinephrine: Regulate mood, attention, motivation, and reward.

• Acetylcholine: Muscle activation, attention, and memory.

• Nitric Oxide: A unique, gas-based transmitter that diffuses directly across cell membranes.