This cheat sheet covers the major parts of the brain and nervous system that explain how people sense, think, feel, and act. Students need these ideas to understand how biological processes connect to behavior in psychology. It is useful for reviewing brain structures, neuron signaling, and the organization of the central and peripheral nervous systems.
The goal is to make key terms and pathways easy to compare at a glance.
The nervous system is divided into the central nervous system, which includes the brain and spinal cord, and the peripheral nervous system, which connects the body to the central nervous system. Neurons communicate through electrical signals called action potentials and chemical messages called neurotransmitters. Major brain areas include the brainstem, cerebellum, limbic system, and cerebral cortex.
Important formulas and rules include resting potential about -70 mV, action potential threshold about -55 mV, and the all-or-none principle.
Key Facts
- The central nervous system, or CNS, consists of the brain and spinal cord.
- The peripheral nervous system, or PNS, includes all nerves outside the brain and spinal cord.
- A typical neuron receives signals through dendrites, sends signals down the axon, and releases neurotransmitters from axon terminals.
- Resting potential is about -70 mV, meaning the inside of a neuron is more negative than the outside when it is not firing.
- An action potential usually begins when the neuron reaches a threshold of about -55 mV.
- The all-or-none principle means a neuron either fires a full action potential or does not fire at all.
- The sympathetic nervous system prepares the body for action, while the parasympathetic nervous system calms the body after stress.
- The frontal lobe supports planning, decision-making, movement, and impulse control.
Vocabulary
- Neuron
- A specialized nerve cell that receives, processes, and sends information through electrical and chemical signals.
- Synapse
- The tiny gap between neurons where neurotransmitters carry messages from one cell to another.
- Neurotransmitter
- A chemical messenger released by a neuron that affects the activity of another neuron, muscle, or gland.
- Action Potential
- A brief electrical impulse that travels down an axon when a neuron reaches threshold.
- Limbic System
- A group of brain structures involved in emotion, memory, motivation, and basic drives.
- Cerebral Cortex
- The wrinkled outer layer of the brain that supports higher mental functions such as thinking, language, perception, and voluntary movement.
Common Mistakes to Avoid
- Confusing the central nervous system with the peripheral nervous system is wrong because the CNS includes only the brain and spinal cord, while the PNS includes nerves outside them.
- Thinking stronger stimuli create bigger action potentials is wrong because action potentials follow the all-or-none principle and do not vary in size.
- Saying neurotransmitters travel down the axon is wrong because the electrical action potential travels down the axon, while neurotransmitters cross the synapse.
- Assuming the left and right brain hemispheres work completely separately is wrong because most tasks use networks across both hemispheres.
- Labeling the sympathetic system as calming is wrong because the sympathetic system increases arousal, while the parasympathetic system supports rest and recovery.
Practice Questions
- 1 A neuron has a resting potential of -70 mV and reaches threshold at -55 mV. How many millivolts must the membrane potential change to reach threshold?
- 2 If a signal travels along a 1.5 meter nerve pathway at 50 meters per second, how long does the signal take to travel the pathway?
- 3 Name the nervous system division most active when heart rate rises, breathing speeds up, and the body prepares for danger.
- 4 Explain why damage to the frontal lobe can affect both movement and decision-making.
Understanding Brain and Nervous System
Neural signals depend on charged particles moving across a cell membrane. Sodium, potassium, and other ions cannot pass freely through the membrane. They move through tiny protein gates called ion channels.
When enough input opens sodium channels, the voltage changes rapidly and the signal travels along the axon. Afterward, other channels help restore the original charge pattern. This recovery period briefly makes firing difficult.
It helps signals move in one direction and limits how rapidly a neuron can send messages. Some axons have myelin, a fatty covering made by support cells. Myelin lets signals jump between uncovered gaps, which greatly increases speed.
The space between two neurons is called a synapse. A signal reaching an axon terminal causes vesicles to release neurotransmitter molecules into this tiny gap. Receptors on the next cell detect the molecules.
Some receptors make that cell more likely to fire. Others make firing less likely. A neuron constantly adds up thousands of these excitatory and inhibitory inputs.
Neurotransmitters do not remain in the synapse for long. They may be taken back up by the sending neuron, broken down by enzymes, or diffuse away.
Many medicines affect these steps, which is why they can change mood, attention, sleep, pain, or movement. Their effects depend on the brain circuits involved, not on a simple one chemical one behavior rule.
Brain functions come from connected networks rather than isolated spots working alone. The sensory areas of the cortex process input from vision, hearing, touch, and other senses. Motor areas help organize voluntary movement.
Association areas combine information with memories, goals, and context. For example, reading uses visual processing, language networks, attention, memory, and fine control of eye movements. The two cerebral hemispheres communicate through a large fiber bundle called the corpus callosum.
The cerebellum fine tunes timing and coordination. The hippocampus helps form many new explicit memories.
The amygdala helps detect emotionally important events, especially possible threats. These regions influence one another continuously.
Students often meet nervous system ideas in everyday experiences. Stress can raise heart rate, widen attention toward possible danger, and reduce digestion for a short time. Once the situation passes, calming body processes gradually return.
Lack of sleep can weaken attention, reaction time, and memory because neural systems need rest to regulate activity. Practice changes the nervous system through plasticity. Repeated use can strengthen useful connections, while unused connections may weaken.
This does not mean the brain is infinitely flexible or that every skill comes from effort alone. Genes, development, injury, environment, and experience all matter.
When studying diagrams, trace the direction of information and separate structure, function, and evidence. A structure may contribute to a behavior without being its only cause.