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Biology
Grade 9-11
The Human Brain & Nervous System Cheat Sheet
A printable reference covering nervous system organization, neuron structure, action potentials, synapses, reflex arcs, and major brain regions for grades 9-11.
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The human brain and nervous system control sensing, movement, thinking, memory, emotion, and body regulation. This cheat sheet helps students organize the main parts of the nervous system and understand how nerve signals travel. It is useful for reviewing brain regions, neuron structure, reflex pathways, and communication between neurons. These ideas are central to biology, anatomy, and health science courses.
Key Facts
- The central nervous system, or CNS, includes the brain and spinal cord, while the peripheral nervous system, or PNS, includes nerves outside the CNS.
- The somatic nervous system controls voluntary skeletal muscle movement, while the autonomic nervous system controls involuntary functions such as heart rate, digestion, and breathing rate.
- A typical neuron pathway is dendrites receive signals, the cell body processes signals, and the axon sends signals to other cells.
- The sodium-potassium pump helps maintain resting potential by moving 3 Na+ out of the neuron and 2 K+ into the neuron.
- A resting neuron has an electrical potential of about -70 mV, meaning the inside is more negative than the outside.
- An action potential begins when depolarization reaches threshold, usually about -55 mV, causing voltage-gated Na+ channels to open.
- A reflex arc follows the basic pathway receptor, sensory neuron, interneuron in the spinal cord, motor neuron, effector.
- At a chemical synapse, neurotransmitters are released from the presynaptic neuron, cross the synaptic cleft, and bind receptors on the postsynaptic cell.
Vocabulary
- Neuron
- A specialized nerve cell that receives, processes, and transmits electrical and chemical signals.
- Central Nervous System
- The division of the nervous system made of the brain and spinal cord.
- Peripheral Nervous System
- The division of the nervous system made of nerves that connect the CNS to the rest of the body.
- Action Potential
- A rapid change in a neuron's membrane potential that carries a nerve signal along the axon.
- Synapse
- The junction where one neuron communicates with another neuron, muscle cell, or gland cell.
- Neurotransmitter
- A chemical messenger released by a neuron to signal another cell across a synapse.
Common Mistakes to Avoid
- Confusing the CNS and PNS is wrong because the CNS is only the brain and spinal cord, while the PNS includes the nerves outside them.
- Thinking all nervous system actions are voluntary is wrong because the autonomic nervous system controls many involuntary processes such as digestion and heart rate.
- Reversing neuron signal direction is wrong because signals usually enter through dendrites, pass through the cell body, and travel away along the axon.
- Saying reflexes must be processed by the brain first is wrong because many reflex arcs are coordinated through the spinal cord for a faster response.
- Forgetting neurotransmitter receptors is wrong because neurotransmitters affect the next cell only if they bind to matching receptors on the postsynaptic membrane.
Practice Questions
- 1 A neuron has a resting potential of -70 mV and reaches threshold at -55 mV. By how many millivolts must the membrane potential increase to reach threshold?
- 2 If a sodium-potassium pump completes 8 cycles, how many Na+ ions are moved out of the neuron and how many K+ ions are moved into the neuron?
- 3 Put these reflex arc steps in the correct order: motor neuron, receptor, sensory neuron, effector, interneuron in the spinal cord.
- 4 Explain why a hand-withdrawal reflex can happen before a person consciously feels pain.