Nervous System

The nervous system operates through a network of neurons, specialized cells that transmit electrical and chemical signals. Sensory neurons detect stimuli from the environment and body, relay information to the central nervous system (CNS) — the brain and spinal cord — where it is processed and interpreted. Motor neurons then carry instructions to muscles and glands, resulting in action. The autonomic nervous system regulates internal organs automatically, maintaining homeostasis, while the somatic nervous system controls voluntary movements.

• Brain: Control center for thought, memory, emotion, and coordination
• Spinal Cord: Conduit for signals between the brain and peripheral body
• Peripheral Nerves: Connect CNS to limbs and organs; includes sensory and motor nerves
• Autonomic Nervous System (ANS): Controls involuntary functions; divided into:
• Sympathetic: Prepares body for stress (“fight or flight”)
• Parasympathetic: Promotes rest and recovery (“rest and digest”)
• Sensory Organs: Eyes, ears, tongue, nose, and skin provide sensory input
• Glial Cells: Support, protect, and nourish neurons

• Sensory Input: Detection of external and internal stimuli through sensory neurons
• Integration: Processing information in the brain and spinal cord
• Motor Output: Activation of muscles and glands in response to signals
• Homeostasis Regulation: ANS maintains heart rate, blood pressure, digestion, and temperature
• Reflex Actions: Rapid, involuntary responses to protect the body
• Cognition & Learning: Memory, attention, decision-making, and emotional processing

• Muscular System: Controls voluntary movements and coordination
• Cardiovascular System: ANS regulates heart rate and blood vessel constriction
• Respiratory System: Controls breathing rate and depth
• Endocrine System: Brain (hypothalamus) signals hormone release for growth, metabolism, and stress response
• Digestive System: ANS regulates gut motility and secretions
• Immune System: Nervous system communicates with immune cells for coordinated defense

• The nervous system is divided into CNS (brain & spinal cord) and PNS (peripheral nerves)
• Neurons transmit signals at speeds of up to 250 mph, enabling rapid responses
• Glial cells outnumber neurons and play key roles in supporting, protecting, and repairing neural tissue
• Brain plasticity allows adaptation, learning, and recovery from injury
• Balanced activity, sleep, and nutrition are critical for optimal nervous system function

• Neuropathy: Damage to peripheral nerves causing numbness, tingling, or weakness
• Stroke: Interruption of blood supply to the brain, causing functional deficits
• Neurodegenerative Diseases: Parkinson’s, Alzheimer’s, ALS, affecting movement, memory, or cognition
• Epilepsy: Recurrent seizures due to abnormal electrical activity
• Multiple Sclerosis: Autoimmune attack on myelin, impairing nerve signal transmission
• Migraines & Chronic Pain: Dysfunctional nerve signaling or vascular-neural interactions

• Persistent headaches or migraines
• Numbness, tingling, or weakness in limbs
• Poor coordination or balance
• Memory lapses or difficulty concentrating
• Sleep disturbances
• Sensory disturbances (vision, hearing, taste, or smell changes)
• Mood changes, irritability, or anxiety

• The human brain contains approximately 86 billion neurons
• Reflexes can occur without brain input — spinal cord handles rapid responses
• The brain uses about 20% of the body’s total energy despite being only 2% of its weight
• Neurons communicate via electrical impulses and chemical neurotransmitters
• Regular movement and mental stimulation literally reshape neural connections

• Khan Academy: Nervous System: Detailed lessons covering the structure and function of the nervous system.
• Crash Course: Nervous System: An engaging video on the different parts of the nervous system and how they work together.
• InnerBody: Nervous System: Interactive diagrams and explanations of the nervous system's structure.