Overview of Neural Cells
Neurons
Definition:
Neurons are specialized cells responsible for transmitting information throughout the nervous system. They are the fundamental units that process and communicate information via electrical and chemical signals.Key Features:
- Cell Body (Soma): Contains the nucleus and organelles; integrates incoming signals.
- Dendrites: Branch-like structures that receive signals from other neurons.
- Axon: A long, slender projection that transmits electrical impulses away from the cell body.
- Axon Terminals: Endpoints where the neuron communicates with target cells via neurotransmitters.
Glial Cells
Definition:
Glial cells support, protect, and nourish neurons. They are essential for maintaining the environment around neurons and ensuring proper neural function.Functions Include:
- Providing structural support
- Forming myelin sheaths for insulation
- Regulating the extracellular fluid
- Removing waste products
Understanding both neurons and glial cells is crucial because together they form the cellular basis for all behavior and mental processes.
The Central and Peripheral Nervous Systems: The Reflex Arc
Reflex Arc in the Spinal Cord
Overview:
The reflex arc demonstrates the interaction between the central and peripheral nervous systems in producing rapid responses to stimuli. It involves three types of neurons:- Sensory Neurons (Afferent): Detect stimuli and send signals to the CNS.
- Interneurons: Process information within the spinal cord.
- Motor Neurons (Efferent): Carry signals from the CNS to muscles to produce a response.
Example:
Touching a hot object triggers a reflex where sensory neurons transmit pain signals to the spinal cord, interneurons process the response, and motor neurons prompt your hand to withdraw—all before the brain fully registers the pain.
This basic circuit is fundamental for survival and illustrates the rapid, automatic responses governed by neural pathways.
Neural Transmission: The Basics
Resting Potential and Threshold
Resting Potential:
A neuron at rest has a voltage difference across its membrane (typically about –70 mV), maintained by ion channels and pumps.Threshold:
When the sum of incoming signals raises the membrane potential to a critical level, the neuron reaches its threshold, triggering an action potential.
Depolarization and the All-or-Nothing Principle
Depolarization:
Once the threshold is reached, voltage-gated ion channels open, allowing positively charged ions to rush into the cell. This rapid change in electrical charge is called depolarization.All-or-Nothing Principle:
The neuron either fires a complete action potential if the threshold is met or does not fire at all.
Refractory Period and Reuptake
Refractory Period:
After firing, the neuron undergoes a brief period during which it cannot fire again, ensuring that the action potential moves in one direction.Reuptake:
Neurotransmitters released into the synapse are taken back into the presynaptic neuron for reuse or breakdown, which is crucial for regulating the signal.
Disorders Related to Disruptions
Disruptions in neural transmission can lead to disorders such as multiple sclerosis, where the myelin sheath is damaged, or myasthenia gravis, where communication between nerves and muscles is impaired.
Neurotransmitters and Their Functions
Neurotransmitters are chemicals that transmit signals across a synapse from one neuron to another. They can be excitatory (making a neuron more likely to fire) or inhibitory (making a neuron less likely to fire).
Key Neurotransmitters Studied in AP Psychology
- Dopamine:
Involved in reward, motivation, and motor control. - Serotonin:
Regulates mood, appetite, and sleep. - Norepinephrine:
Influences arousal and alertness. - Glutamate:
The primary excitatory neurotransmitter, essential for learning and memory. - GABA (Gamma-Aminobutyric Acid):
The primary inhibitory neurotransmitter, which calms neural activity. - Endorphins:
Act as natural pain relievers and are involved in pleasure. - Substance P:
Involved in transmitting pain signals. - Acetylcholine:
Plays a key role in muscle activation and memory.
Understanding these neurotransmitters helps explain how chemical signaling affects behavior and mental processes.
Hormones with Neurotransmitter-Like Actions
Although hormones are secreted by endocrine glands, some act similarly to neurotransmitters in influencing behavior and mental processes. For the AP exam, focus on these hormones:
- Adrenaline (Epinephrine):
Increases heart rate and energy, contributing to the “fight or flight” response. - Leptin:
Regulates energy balance by inhibiting hunger. - Ghrelin:
Stimulates appetite, often called the “hunger hormone.” - Melatonin:
Regulates sleep-wake cycles. - Oxytocin:
Involved in social bonding and trust.
Psychoactive Drugs and Neural Firing
Psychoactive drugs alter neural transmission by affecting neurotransmitter function in various ways. They can be classified based on their effects on the nervous system.
Mechanisms of Drug Action
- Agonists:
Mimic the action of a neurotransmitter, encouraging neural firing. - Antagonists:
Block or dampen the effects of a neurotransmitter, reducing neural firing. - Reuptake Inhibitors:
Prevent the reabsorption of neurotransmitters, prolonging their effects.
Categories and Their Effects
- Stimulants (e.g., caffeine, cocaine):
Increase neural activity, leading to heightened alertness. - Depressants (e.g., alcohol):
Decrease neural activity, which can impair cognitive and motor functions. - Hallucinogens (e.g., marijuana):
Alter perception and cognition, causing distortions in reality. - Opioids (e.g., heroin):
Act primarily as pain relievers by affecting neural pathways involved in pain.
Tolerance, Addiction, and Withdrawal
With repeated use, the body may develop tolerance (requiring more of the drug for the same effect) and addiction. Withdrawal symptoms can occur when drug use is reduced or stopped, highlighting the powerful impact these substances have on neural circuits.
Sample Exam Question and Model Answer
Exam Question
Question:
Describe the structure and function of a typical neuron, and explain the process of neural transmission. Include in your answer the roles of the central and peripheral nervous systems in the context of the reflex arc, and discuss how neurotransmitters facilitate communication between neurons. (6–8 minutes)
Model Answer
A typical neuron is composed of a cell body (soma), dendrites, and an axon. The cell body contains the nucleus and organelles necessary for the cell’s functioning. Dendrites extend from the cell body to receive signals, while the axon carries these signals away to other neurons or muscles. In contrast, glial cells provide support, insulation, and waste removal, ensuring the efficient functioning of neurons.
Neural transmission begins with the neuron at its resting potential, typically around –70 mV. When a stimulus is strong enough to reach the threshold, the neuron undergoes depolarization. This all-or-nothing process causes voltage-gated ion channels to open, leading to the generation of an action potential. Following this, the neuron enters a refractory period during which it cannot fire another action potential, ensuring directional signal flow.
In the context of the reflex arc—a basic neural circuit found in the spinal cord—sensory neurons detect stimuli and transmit signals to interneurons, which process the information and pass it to motor neurons that trigger a response, such as the rapid withdrawal of a hand from a hot surface.
Neurotransmitters, such as dopamine and serotonin, are released at synapses where they bind to receptors on adjacent neurons, either exciting or inhibiting them. This chemical communication is crucial for the coordination of complex behaviors and mental processes.
Thus, the integrated action of neurons and glial cells, the orderly process of neural transmission, and the precise roles of neurotransmitters all contribute to the nervous system’s ability to control behavior and cognition.
Study Tips and Final Thoughts
Focus on Definitions:
Understand key terms such as depolarization, refractory period, neurotransmitters, and the differences between excitatory and inhibitory signals.Use Diagrams:
Drawing and labeling a neuron, as well as the reflex arc, can help visualize these concepts.Practice with Real-World Examples:
Apply your understanding to everyday scenarios (e.g., reflex actions, effects of drugs) to reinforce the material.Review Sample Questions:
Regularly practice free-response questions to become comfortable with articulating your knowledge within the exam’s time constraints.
By mastering these concepts and practicing clear, concise responses, you will be well-prepared to answer exam questions on the structure and function of neurons, neural transmission, and the effects of neurotransmitters and psychoactive drugs on behavior and mental processes.
Conclusion
Understanding the neuron and neural firing is essential for grasping the biological bases of behavior. The intricate design of neurons, the systematic process of neural transmission, and the role of chemical messengers like neurotransmitters and hormones together provide the foundation for how our nervous system influences behavior and mental processes. Use these study notes and sample exam question to solidify your understanding and prepare effectively for the AP Psychology exam.