🧠 Biological Basis of Behavior


The way we think, feel, and act is not random — it's controlled by systems inside our body, mainly the brain, the nervous system, and hormones. This chapter explains how biology influences behavior, and it’s a foundation of modern psychology.



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1. Brain Structure and Function


The brain is the central organ of the nervous system, and it controls all mental activities and physical actions.


🔹 Major Parts of the Brain:


A. Cerebrum


Function: Thinking, memory, reasoning, learning, voluntary movement.


Structure: Divided into two hemispheres (left and right).


Left: logic, language, maths.


Right: creativity, art, imagination.




📌 Example: When you solve a puzzle or write an essay, your cerebrum is active.



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B. Cerebellum


Function: Balance, coordination, and muscle control.


Located below the cerebrum.



📌 Example: When you dance or ride a bicycle smoothly, your cerebellum helps coordinate your movements.



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C. Brainstem (Medulla, Pons, Midbrain)


Function: Controls basic life functions like heartbeat, breathing, digestion.


Connects brain to spinal cord.



📌 Example: You don’t have to think to breathe — your medulla handles it automatically.



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D. Limbic System


Function: Emotions and memory.


Important parts:


Amygdala (fear, anger)


Hippocampus (memory formation)




📌 Example: If a dog barked at you when you were a child and you still fear dogs — that’s your amygdala and hippocampus in action.



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2. Nervous System


The nervous system is like the body’s messaging system. It sends and receives signals to and from the brain to control actions and thoughts.


🔹 Divisions of the Nervous System:


A. Central Nervous System (CNS)


Includes brain and spinal cord.


Controls most functions of the body and mind.



📌 Example: When you touch something hot, your spinal cord helps you pull your hand back instantly.



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B. Peripheral Nervous System (PNS)


All the nerves outside the CNS.


Carries information between the body and brain.



It has two sub-parts:


1. Somatic Nervous System – Voluntary actions

📌 Example: Moving your hands to eat.



2. Autonomic Nervous System – Involuntary actions


Sympathetic System: Activates “fight or flight” in danger

📌 Example: Heartbeat increases when scared.


Parasympathetic System: Calms the body after stress

📌 Example: Heartbeat slows down once you relax.






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3. Hormones and Behavior


Hormones are chemicals released by endocrine glands. They travel in the blood and affect your mood, behavior, growth, and energy.


🔹 Important Hormones and Their Effects:


Gland Hormone Effect on Behavior


Pituitary Growth Hormone Controls body growth

Thyroid Thyroxine Controls metabolism, energy

Adrenal Adrenaline Increases alertness during stress

Pancreas Insulin Controls blood sugar

Ovaries/Testes Estrogen/Testosterone Controls sexual development and mood



📌 Example 1:

Before a big exam, adrenal glands release adrenaline, making your heart race and increasing focus.


📌 Example 2:

During puberty, changes in testosterone and estrogen cause mood swings and emotional sensitivity.



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🔚 Conclusion


This chapter proves that human behavior is deeply linked to biological systems:


The brain processes thoughts and feelings.


The nervous system sends quick messages through the body.


Hormones silently shape emotions, energy, and growth.



So, whether it’s love, fear, stress, memory, or joy — your biology is work

ing behind the scenes!