Brain & Behavior
Who proposed dualism?
René Descartes
Name the four regions of a neuron.
1. Dendrites: receive information
2. Soma: integrates information and maintains the cell
3. Axon: conducts the action potential
4. Terminal buttons: communicate with the next cell
K+ (Potassium) and A- (negatively charged proteins)
What is the approximate resting membrane potential of a typical neuron?
-70 mV (Inside of the neuron is 70 mV more negative than the outside)
What are the five phases of an action potential, in order?
1. Depolarization (-70 mV → -40 mV; less negative)
2. Threshold (about -40 mV; reaches threshold!)
3. Rising (-40 mV → +40 mV; becomes positive)
4. Falling (+40 mV → -60 mV; becomes negative again)
5. Hyperpolarization/Undershoot (-60 mV → - 70 mV; more negative) AT RMP AGAIN YAY!
What is the difference between dualism & monism?
Dualism: The mind and body are separate.
Monism: The mind is part of the physical world and can be understood through physical processes, including brain activity.
This type of nerve carries sensory information from the body toward the CNS. What is it called?
Afferent.
- Afferent = sensory = toward CNS
- Efferent = motor = away from CNS
Afferent Arrives at the CNS.
What is the difference between diffusion and electrostatic pressure?
Diffusion: Ions move from an area of high concentration → low concentration.
Electrostatic pressure: Charged particles are affected by electrical forces. Opposite charges attract; same charges repel.
What does the sodium-potassium pump do?
It moves 3 Na+ out of the cell and 2 K+ into the cell. This helps maintain the concentration gradients necessary for the neuron to maintain its RMP and generate action potentials.
What is the difference between a graded potential and an action potential?
Graded potential - small & local changes, occur in dendrites/cell body, variable in size, can be depolarizing/hyperpolarizing, diminishes as it spreads, CAN contribute to reaching threshold
Action potential - large/all-or-none changes, occur along the axon, does not diminish as it travels, requires reaching threshold
A researcher gives a drug to an animal & observes how its behavior changes. Which brain-behavior approach is this, and why?
Somatic intervention.
The researcher is manipulating the body/brain by administering a drug and then observing the effect on behavior.
Manipulate body → observe behavior = somatic intervention
A cell in the CNS is engulfing debris after an injury. Which type of glial cell is most likely responsible?
Microglia.
They function as the immune cells of the CNS. They respond to injury, infection, and cellular debris and can engulf/remove damaged material.
At the resting membrane potential, based on diffusion, in which direction would K+ move, and why?
Out of the neuron.
K⁺ is present at a much higher concentration inside the neuron than outside. Diffusion moves particles from high concentration to low concentration.1
High K⁺ inside → low K⁺ outside → diffusion pushes K⁺ OUT.
If the amount of K+ outside the neuron increases, what happens to K+ movement? (trick question)
Less K+ leaves the neuron.
- K+ normally moves OUT because there is more K+ concentrated inside
- Adding K+ outside makes the concentration difference smaller
- Therefore, less K+ moves out
- Since less positive charge leaves, the inside becomes less negative (depolarizes)
COMPARED TO THE NOMRAL CONCENTRATION! (inside is still becoming more negative if K+ is leaving) just LESS negative than if even MORE K+ left the inside.
A neuron reaches threshold at about -40 mV. What happens next, and which ion is primarily responsible for the rising phase?
Voltage-gated Na⁺ channels open, allowing Na⁺ to rapidly enter the neuron.
Step-by-step:
Over time, our understanding of the brain & behavior has evolved. Early thinkers such as Hippocrates & Galen contributed to the idea that the brain plays a central role in sensation, thought, and behavior. What is the major historical shift in our understanding of the brain & behavior?
The understanded shifted from viewing the heart as the center of mental capacities and the brain as relatively unimportant to recognizing the brain as the seat of thoughts and emotions and the controller of behavior, eventually leading to the scientific study of brain-behavior relationships.
A mutation that causes defective axoplasmic transportation from the soma down the axon. What type of transport is affected, and what materials would be expected to accumulate in the soma?
Anterograde transport (soma to terminal buttons); newly synthesized proteins
A neuron is at -70 mV. K+ has an equilibrium potential of -90mV. Is K+ at equilibrium? Explain which force is stronger and what happens to K+.
No, K⁺ is not at equilibrium. K⁺ will have a net outward movement. (diffusion wins)
A drug blocks the sodium-potassium pump. What would happen to the neuron’s RMP over time, and why?
The RMP would gradually become less negative/depolarize.
The Na⁺/K⁺ pump normally maintains the concentration gradients by moving: 3 Na+ Out, 2 K In
A drug blocks voltage-gated K+ channels. Which phase of the action potential would be most affected, and what would happen to the neuron’s membrane potential?
The falling phase would be most directly affected.
A researcher measures brain activity while a person performs a task, without manipulating the brain or behavior. Which brain-behavior approach is being used, and what can this approach tell us?
Correlation.
The researcher is measuring brain activity and behavior rather than manipulating either one. (Therefore, correlation does not establish _______ by itself?)
It can tell us whether there is a relationship/association between brain activity and behavior.
A patient experiences difficulty with movement after damage occurs to the myelin surrounding axons within the brain & spinal cord. Which type of glial cell is most likely responsible for producing the damaged myelin?
Oligodendrocytes.
The brain and spinal cord make up the central nervous system (CNS), and oligodendrocytes produce myelin within it.
A neuron is at -70mV. Na+ has an equilibrium potential of +55 mV. Considering both diffusion and electrostatic pressure, in which direction would Na+ move if a permeable channel opened? Why?
Na⁺ would move INTO the neuron.
Diffusion: Na⁺ is much more concentrated outside the neuron than inside.
- High Na⁺ outside → low Na⁺ inside → diffusion pushes Na⁺ IN.
Electrostatic pressure: The inside of the neuron is negative at −70 mV. Na⁺ is positively charged.
Negative inside → attracts positive Na⁺ → electrostatic pressure pushes Na⁺ IN.
Both forces work together.
A neuron has a normal RMP of -70 mV. A toxin causes the concentration of K+ outside the neuron to increase substantially, but the sodium-potassium pump continues working normally. What would happen to the neuron's RMP?
The neuron would become less negative because the smaller K+ concentration gradient causes less K+ to leave the cell
K+ is normally more concentrated inside the neuron, so it tends to leave the cell. Increasing K⁺ outside makes the concentration difference smaller, so less K⁺ leaves. Because less positive charge leaves the cell, the inside becomes less negative, causing depolarization.
A toxin prevents voltage-gated Na+ channels from opening when a neuron reaches threshold. What would happen to the rising phase of the action potential, and why would the action potential fail to propagate down the axon?
The rising phase would fail to occur normally, and the action potential would not propagate down the axon.
Normal:
Threshold → Na⁺ channels open → Na⁺ IN → rising phase → next axon segment reaches threshold → AP continues
With toxin (abnormal):
Threshold → Na⁺ channels cannot open → no rapid Na⁺ influx → no normal rising phase → no propagation