Human Nervous System: CNS and PNS

• The human nervous system maintains homeostasis
• The nervous system coordinates all activities in the body
• It regulates sensory input, motor output, and information integration
• The nervous system uses electrical impulses and chemical signals for communication

Major Divisions

• Central Nervous System (CNS) - the command center
• Peripheral Nervous System (PNS) - the communication network
• The CNS and PNS work together to regulate bodily functions, respond to stimuli, and ensure survival

Central Nervous System (CNS)

• The CNS is the control center
• The CNS comprises the brain and spinal cord
• Brain controls thoughts, emotions, memory, and voluntary movements
• Spinal cord transmits signals between the brain and body and controls reflexes

CNS Protection

• Cranium (skull) protects the brain
• Vertebrae shield the spinal cord
• Meninges are three protective layers surrounding the CNS
• Dura Mater is the tough outer layer of the meninges
• Arachnoid Mater is the middle web-like layer of the meninges
• Pia Mater is the inner delicate layer of the meninges
• Cerebrospinal Fluid (CSF) cushions, nourishes, and removes waste

CNS Functions

• Processes sensory information
• Sends commands via motor neurons
• Stores memories and enables learning
• Controls involuntary functions like breathing and heart rate

Peripheral Nervous System (PNS)

• The PNS includes all nerves outside the CNS
• PNS transmits information to and from the brain and spinal cord
• The PNS has two divisions, Autonomic and Somatic

Somatic Nervous System (SNS)

• Voluntary control
• Controls skeletal muscles (walking, writing, speaking)
• Sends sensory information (touch, pain, temperature) to the CNS
• Uses motor neurons to send signals from the brain to muscles for movement

Autonomic Nervous System (ANS)

• Involuntary control
• Regulates automatic body functions (heart rate, digestion, breathing)
• Works without conscious control to maintain homeostasis
• Has 2 divisions, sympathetic and parasympathetic

Sympathetic Nervous System

• Fight or flight
• Prepares the body for emergency situations
• Increases heart rate and blood pressure
• Dilates pupils
• Inhibits digestion
• Increases breathing rate for more oxygen

Parasympathetic Nervous System

• Rest and digest
• Restores the body to a calm state after stress
• Slows heart rate and lowers blood pressure
• Stimulates digestion and nutrient absorption
• Constricts pupils to normal size
• Decreases breathing rate

Neurons

• The functional units of the nervous system
• Has sensory, motor, and interneurons
• Sensory Neurons (Afferent Neurons) carry signals from sensory receptors to the CNS
• Motor Neurons (Efferent Neurons) transmit commands from the CNS to muscles and glands
• Interneurons connect sensory and motor neurons inside the CNS, enabling complex processing and reflexes

Neuron Structure

• Dendrites are signal receivers
• Cell Body (Soma) contains the nucleus and organelles and processes incoming signals
• Axon is the signal transmitter, a long tube-like structure that carries the electrical signal away from the cell body
• Myelin Sheath is a fatty layer around the axon that speeds up signal transmission
• Nodes of Ranvier are small gaps in the myelin sheath where signals jump, increasing speed
• Axon Terminals release neurotransmitters

Synapse

• The communication bridge
• Neurons communicate with each other at synapses through chemical messengers called neurotransmitters
• An electrical impulse travels down the axon to the axon terminals
• Neurotransmitters(dopamine, serotonin) are released into the synaptic gap
• Neurotransmitters bind to receptors on the next neuron

Brain

• The control center of the body
• The brain processes information and controls bodily functions
• It weighs about 1.4 kg (3 lbs) and contains billions of neurons

Brain

• Has 3 major parts, the cerebrum, cerebellum, and brainstem
• The Cerebrum is the largest part of the brain and is divided into two hemispheres (left and right)
• The left hemisphere controls logic, language, and analytical thinking
• The right hemisphere is associated with creativity, intuition, and emotions
• The outermost layer is called the cerebral cortex, responsible for higher-order thinking

Four Lobes of the Cerebrum

• Frontal Lobe is involved in decision-making, problem-solving, emotions, voluntary movement, and personality and controls speech production (Broca's area)
• Parietal Lobes process sensory information (touch, temperature, pain, spatial awareness)
• Temporal Lobe is responsible for hearing, language processing, and memory formation (hippocampus is located here)
• Occipital Lobe processes visual information (sight, color, light interpretation)

Cerebellum

• Located at the back of the brain, beneath the cerebrum
• Responsible for coordination of voluntary movements, posture, and balance
• Helps in learning motor skills, such as playing an instrument or riding a bike

Brainstem

• Connects the brain to the spinal cord and controls automatic functions
• Consists of the midbrain, pons, and medulla oblongata
• Midbrain controls eye movement and auditory/visual processing
• Pons bridges signals between the brain and spinal cord and regulates sleep and breathing
• Medulla Oblongata controls heart rate, breathing, blood pressure, digestion, and reflexes

Limbic System

• Limbic System is located deep within the brain, controlling emotions and memory
• Hippocampus is essential for forming and retrieving memories
• Amygdala controls emotions like fear, anger, and pleasure
• Hypothalamus regulates hormones, hunger, thirst, sleep, and body temperature

Spinal Cord and Reflexes

• It extends from the brainstem down the back and protected by the vertebral column (spine)
• It serves as the main communication highway between the brain and body
• Transmits nerve signals between the brain and the rest of the body
• Controls reflex actions that do not require brain involvement
• Coordinates voluntary and involuntary movements

Spinal Cord Structure

• The spinal cord is divided into cervical (neck), thoracic (upper back), lumbar (lower back), and sacral (pelvic) regions, each controlling different body parts
• The spinal cord is made up of gray matter (nerve cell bodies) and white matter (nerve fibers)

Reflex Arc

• A reflex is a quick, automatic response to a stimulus without conscious brain involvement
• Stimulus (tapping the knee) detected by sensory neurons
• The signal travels to the spinal cord
• The spinal cord sends a response via motor neurons
• The leg jerks as the muscles contract

Nervous System Disorders

• Alzheimer's Disease is memory loss due to neuron degeneration
• Parkinson's Disease is dopamine deficiency leads to tremors and slow movements
• Multiple Sclerosis (MS) is an immune system attacks myelin sheath, affecting signal transmission
• Epilepsy is uncontrolled electrical activity causes seizures
• Stroke is interrupted blood flow to the brain, leading to cell death

Healthy Nervous System

• Proper Nutrition: Omega-3, vitamins B6 and B12 for brain health
• Exercise improves blood flow and brain function
• Adequate Sleep: Essential for memory and cognitive processing
• Stress Management reduces the risk of neurological disorders
• Avoid Drugs and Alcohol prevents damage to neurons
• The nervous system is the body's communication network
• The CNS processes and interprets information
• The PNS transmits signals to and from the CNS
• Neurons communicate through electrical impulses and neurotransmitters
• The autonomic nervous system regulates involuntary functions
• Brain regions have specific functions for movement, thought, and emotions
• Common disorders affect the nervous system and can be prevented with a healthy lifestyle