Summary Flashcards
Define homeostasis and apply homeostatic control mechanisms to physiological systems.
Homeostasis is a fundamental concept in biology and physiology. It refers to the body’s ability to maintain stable internal conditions despite external changes. In simpler terms, it’s like the body’s way of keeping things in balance.
Homeostatic control mechanisms are processes that help regulate various physiological systems to keep them within a narrow range of optimal conditions. These mechanisms involve sensors, effectors, and feedback loops.
Here’s how it works in physiological systems:
Sensor: The body has sensors, such as receptors, that detect changes in internal conditions. For example, in temperature regulation, skin receptors sense changes in temperature.
Set Point: The body has a set point, which is the ideal or target condition it wants to maintain. For temperature, this could be around 98.6°F (37°C).
Comparison: The sensor compares the current condition to the set point. If there’s a deviation, it sends a signal.
Effector: The effector is a part of the body (like muscles or glands) that can take actions to correct the deviation. In the case of temperature, sweat glands might activate to cool the body down when it’s too hot.
Feedback Loop: There are two types of feedback loops:
Negative Feedback: This is the most common type. When the sensor detects a deviation, the effector takes action to counteract it and bring conditions back to the set point. For example, if the body is too hot, it sweats to cool down; if it’s too cold, it shivers to generate heat. The goal is to maintain stability.
Positive Feedback: This amplifies a deviation rather than correcting it. It’s rare in homeostasis and often related to specific processes like childbirth or blood clotting. Once the goal is achieved, the positive feedback loop stops.
Provide an example of homeostasis:
Blood sugar regulation:
- Sensor: Specialized cells in the pancreas detect blood sugar levels.
- Set Point: The body wants to maintain blood sugar levels around 90 mg/dL.
- Comparison: If blood sugar levels rise above 90 mg/dL, the sensors detect it.
- Effector: The pancreas releases insulin, which helps cells take up glucose from the blood, lowering blood sugar levels.
- Feedback Loop: As blood sugar levels decrease, the sensors detect this and stop releasing insulin, preventing blood sugar levels from dropping too low.
Describe the structure of the plasma membrane.
Phospholipid Bilayer: The fundamental structure of the plasma membrane consists of two layers of phospholipid molecules. Each phospholipid molecule has a hydrophilic (water-attracting) “head” and two hydrophobic (water-repelling) “tails.” The hydrophilic heads face outward, interacting with the aqueous environment both inside and outside the cell, while the hydrophobic tails are sandwiched in between.
Proteins: Integral proteins are embedded within the phospholipid bilayer. These proteins serve various functions, including transporting substances across the membrane, receiving and transmitting signals, and providing structural support. Peripheral proteins are attached to the inner or outer surface of the membrane and play roles in cell signaling and maintaining membrane structure.
Cholesterol: Cholesterol molecules are interspersed within the phospholipid bilayer. They help stabilize the membrane’s fluidity, preventing it from becoming too rigid or too permeable.
Carbohydrate Chains: Carbohydrate chains are often found attached to proteins (glycoproteins) or lipids (glycolipids) on the extracellular surface of the membrane. These carbohydrate chains are involved in cell recognition, adhesion, and signaling.
Explain the role of cell junctions.
Cell junctions are specialized structures that connect adjacent cells together, providing structural support, communication, and coordination between cells. They serve various roles:
Tight Junctions: These junctions form a tight seal between adjacent cells, preventing the leakage of fluids and molecules between them. They are essential in tissues like the lining of the digestive tract, where a strong barrier is needed.
Desmosomes: Desmosomes are anchoring junctions that provide mechanical strength and stability to tissues. They consist of proteins that link the cytoskeletons of adjacent cells together, making them more resistant to physical stress. Desmosomes are commonly found in tissues subjected to stretching, like the skin and heart muscle.
Gap Junctions: Gap junctions allow for direct communication between neighboring cells. They are formed by connexin proteins that create channels, permitting the passage of ions and small molecules. Gap junctions are crucial for coordinating the activities of cells in tissues like the heart and nervous system.
Explain the role of membrane transport systems.
Membrane transport systems are responsible for regulating the movement of ions, molecules, and nutrients across the plasma membrane. There are two main types of membrane transport:
Passive Transport: This includes processes like diffusion and facilitated diffusion, where substances move across the membrane without requiring energy (ATP). Passive transport relies on concentration gradients, with molecules moving from areas of higher concentration to areas of lower concentration.
Active Transport: Active transport processes, such as the sodium-potassium pump, require energy (usually ATP) to move molecules against their concentration gradients. This is essential for maintaining specific ion concentrations inside and outside the cell, which is crucial for various cellular functions, including nerve transmission and muscle contraction.
Understand the concept of membrane potential.
Membrane potential refers to the difference in electrical charge across a cell’s plasma membrane, which separates the inside of the cell from the extracellular fluid. It is also commonly referred to as “resting potential” when the cell is at rest.
Here are key points to understand about membrane potential:
Ion Distribution: Membrane potential is primarily determined by the distribution of ions (charged particles) across the plasma membrane. The two most important ions involved are sodium (Na+) and potassium (K+).
Selective Permeability: The plasma membrane is selectively permeable, meaning it allows certain ions to pass through while restricting the movement of others. For example, potassium ions (K+) can pass through more easily than sodium ions (Na+).
Ion Pumps and Channels: Specialized protein channels and ion pumps are responsible for maintaining the concentration gradients of ions. The sodium-potassium pump, for instance, actively pumps sodium out of the cell and potassium into the cell to establish and maintain these gradients.
Electrochemical Gradient: The movement of ions across the membrane is influenced by both their concentration gradient (from areas of high concentration to low) and their electrical gradient (opposite charges attract, like charges repel). Together, these gradients create an electrochemical gradient that drives ion movement.
Resting Membrane Potential: In a resting cell, the membrane potential is typically negative inside the cell relative to the outside. This negative potential is usually around -70 to -90 millivolts (mV) in neurons, depending on the cell type. This negative resting potential is primarily due to the presence of more negative ions (e.g., proteins and organic anions) inside the cell and a higher concentration of potassium ions (K+) inside as well.
Role in Cell Function: Membrane potential is essential for various cellular processes, including nerve impulse transmission, muscle contraction, and the regulation of ion and nutrient transport. It serves as the basis for generating electrical signals in excitable cells, allowing them to communicate and perform their specialized functions.
Changes in Membrane Potential: Membrane potential can change in response to various stimuli. Depolarization refers to a shift toward a less negative or more positive membrane potential, while hyperpolarization is a shift toward a more negative potential. These changes are involved in the initiation and propagation of electrical signals in excitable cells.
describe the ionic basis of the action potential and basic neuronal function to demonstrate an understanding of neuron to neuron communication.
The ionic basis of the action potential is a key concept in understanding how neurons communicate with one another. Neurons are specialized cells that transmit electrical signals, known as action potentials, to convey information within the nervous system. Let’s break down the process and the ionic mechanisms involved:
- Resting Membrane Potential:
Neurons have a resting membrane potential, typically around -70 millivolts (mV). This negative potential is maintained by the selective permeability of the cell membrane to ions, especially sodium (Na+), potassium (K+), and chloride (Cl-).
At rest, the neuron’s plasma membrane is more permeable to potassium ions (K+) due to the presence of leak channels. Some K+ ions leak out of the cell, making the interior negatively charged.
2. Depolarization:
Neurons receive input signals, often in the form of neurotransmitters released by neighboring neurons at synapses. These neurotransmitters can be excitatory or inhibitory.
If the input signal is excitatory and depolarizes the neuron’s membrane potential (makes it less negative), and if the membrane potential reaches a certain threshold (typically around -55 mV), it triggers the opening of voltage-gated sodium channels.
Sodium ions (Na+) rush into the neuron through these channels, causing a rapid and massive influx of positive charge. This sudden influx of positive ions leads to a rapid depolarization phase, resulting in the inside of the neuron becoming positively charged.
3. Action Potential:
When the depolarization reaches the threshold, it triggers an all-or-nothing event called the action potential. The neuron’s membrane potential rapidly rises to about +30 mV.
This depolarization is followed by the opening of voltage-gated potassium channels. Potassium ions (K+) exit the neuron, repolarizing the membrane and restoring its negative charge.
4. Hyperpolarization and Refractory Period:
After repolarization, the membrane potential briefly becomes more negative than the resting potential, a phase called hyperpolarization.
This hyperpolarization is due to delayed closure of some potassium channels, and it makes the neuron temporarily less excitable.
During this time, known as the refractory period, the neuron cannot generate another action potential.
5. Propagation of the Action Potential:
The action potential travels along the length of the neuron’s axon, as it is a self-propagating event. It does not decrease in strength as it travels because adjacent regions of the membrane undergo the same depolarization and repolarization processes.
The action potential travels quickly down the axon to the axon terminals, where it triggers the release of neurotransmitters into synapses.
6. Neuron-to-Neuron Communication:
At the synapse, neurotransmitters are released from the presynaptic neuron’s axon terminals into the synaptic cleft.
These neurotransmitters bind to receptors on the postsynaptic neuron’s membrane, leading to either excitatory or inhibitory effects, depending on the type of neurotransmitter and receptor involved.
If the postsynaptic neuron receives sufficient excitatory input, it may reach its threshold and generate its own action potential, continuing the signal propagation to the next neuron in the circuit.
In summary, the ionic basis of the action potential is crucial for understanding how neurons communicate. It involves changes in membrane potential driven by the selective permeability of ions through voltage-gated channels. Neurons transmit information by generating and propagating action potentials, and this process allows for communication from one neuron to another in complex neural networks.
