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The Nervous System Part 1: Neurons 3 Major Functions The nervous system is made up of your brain, spinal cord and neurons. Your nervous system has 3 main jobs: To SENSE To INTERPRET To REACT Monitors changes (stimuli) inside or outside the body using receptors Analyzes information from the receptors and decides what to do Activates muscles or glands to produce a suitable response Stimulus Stimulus A stimulus is any change or signal in the environment that makes an organism react. Stimulus Response After your nervous system detects a stimulus, it causes a response. The Senses The nervous system monitors the environment using the 5 senses. Sight Touch Taste Smell Hearing Neurons Neurons are special cells that carry messages around the body. These messages are called impulses. There are over 100 billion neurons in the human body. Each neuron connects with roughly 100,000 others! Neurons Cell body Dendrites Axon Synapse Types of Neurons There are 3 main types of neurons. Sensory Neuron Motor Neuron Interneuron Detects a stimulus and sends an impulse to other neurons. Carries an impulse to a muscle or gland to create a response. Connects neurons together. Found in brain and spinal cord. Types of Neurons Response Motor Interneuron Stimulus Sensory Neuron Stimulus Sensory Neuron 1. Stimulus Detected by a sensory neuron… Cell Body 1. Stimulus Detected by a sensory neuron… 2. Dendrite Impulse starts at the dendrite and moves to the cell body… Axon 1. Stimulus Detected by a sensory neuron… 2. Dendrite Impulse starts at the dendrite and moves to the cell body… 3. Axon Nerve impulse then moves down the axon … Synapse 1. Stimulus Detected by a sensory neuron… 2. Dendrite Nerve impulse begins in the dendrite and moves to the cell body… 4. Synapse 3. Axon The axon ends at Nerve impulse a synapse: a then moves down junction between the axon … two neurons… Synapse There is a gap where 2 neurons meet. This gap is called a synapse. The synapse is where the impulse jumps from one neuron to the next But electricity cannot “jump”! So chemicals called neurotransmitters do the jumping! Step 1 Impulse in the first neuron causes neurotransmitter molecules to move to the synapse… Step 2 1 Neurotransmitter molecules jump across the synapse to the other neuron Step 3 Neurotransmitters reach the other side and start the impulse in the second neuron Any Questions? The Nervous System Part 2: The CNS and PNS The Nervous System The nervous system is made up of 2 divisions. Central Nervous System (CNS) Peripheral Nervous System (PNS) Made up of the brain and spinal cord. A network of nerves connecting the rest of the body. Acts as the control center of the body. Carry impulses to and from the CNS CNS vs. PNS CNS brain spinal cord PNS all other neurons CNS – The Brain The brain makes up the main part of the central nervous system. It controls most functions in the body. Some actions require thinking: conscious actions Other actions are automatic: subconscious actions Cool Brain Facts An adult human brain weighs 3 pounds. It is the most complex thing in the universe. It contains roughly 100 billion neurons. Each neuron connects with 100,000 others. The brain uses 1/3 of the food we eat each day. The fastest supercomputer in the world is nothing compared to the average brain. Parts of the Brain The brain has 4 major parts: Cerebrum Cerebellum Brain Stem Cortex Each part controls different things… Parts of the Brain Cerebrum Interprets input from the senses, controls movement, and carries out complex thought and memory Cerebellum Coordinates your muscles during movement, helps maintain balance Parts of the Brain Brain Stem Controls involuntary actions, like heartbeat, breathing and digestion Cortex Connects the two brain hemispheres together, coordinates brain activity Brain Hemispheres Left Hemisphere Right Hemisphere “Logical” “Creative” Words & Symbols Pictures & Graphs Read & remember Do & remember Orderly Chaotic Likes predictability Likes spontaneity CNS - The Spinal Cord The spinal cord is the main information pathway. It connects the brain to the peripheral nervous system. The spinal cord is a small tube packed with interneurons It is well-protected inside the vertebral column – your spine. The PNS The peripheral nervous system is a huge network of nerves throughout the body. It carries impulses to and from the CNS. There are a total of 43 nerves, in 23 pairs. It is involved in voluntary and involuntary actions. The PNS The PNS is split into 2 divisions: Somatic Nervous System Autonomic Nervous System Nerves that control voluntary actions. Nerves that control involuntary actions. Walking, learning, talking, eating, etc. Breathing, digestion, reflexes, etc. Reflexes A reflex is a rapid, automatic response that happens without conscious control. Reflexes protect the body from harm. Reflexes are complex actions that bypass the brain They involve the spinal cord and other nerves ONLY Reflex Arc Effector Motor Interneuron Stimulus Sensory Neuron Reflex Arc A reflex arc follows several steps: 1. A sensory receptor detects a stimulus. 2. An impulse is sent down a sensory neuron. 3. Interneurons in spinal cord interpret it. 4. An impulse is sent down a motor neuron. 5. A muscle or gland carries out a response. Any Questions?