BIO 25 Exam 2 Study Questions
Membrane Transport
Main Component of Cell Membranes
The main molecule that constitutes cell membranes is phospholipids.
Molecules that Cannot Cross the Cell Membrane
Type of Molecules: Large polar molecules and ions.
Reason for Inability to Cross: These molecules cannot pass through the hydrophobic lipid bilayer of the cell membrane without assistance due to their polarity and size.
Functions of Membrane Proteins
Transport: Facilitate the movement of substances across the membrane.
Enzymatic Activity: Act as enzymes to catalyze reactions.
Signal Transduction: Serve as receptors for hormones and other signaling molecules.
Cell-Cell Recognition: Help cells recognize each other through glycoproteins.
Transport Mechanisms for Molecules
Transport Mechanisms Include:
Facilitated Diffusion: Movement down a concentration gradient via carrier proteins.
Active Transport: Movement against a concentration gradient using ATP.
Endocytosis: Cellular uptake of materials by engulfing them.
Exocytosis: Expulsion of materials from the cell.
Facilitated Diffusion vs. Active Transport
Facilitated Diffusion:
Movement of molecules across the membrane using a transport protein down their concentration gradient without energy input.
Active Transport:
Movement of molecules against their concentration gradient using energy (typically ATP).
Osmosis
Definition: The passive movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration.
Osmolarity and Relative Osmolarity
If a solution has an osmolarity of 400 mOsm, it is considered hyperosmotic relative to a typical cell (~300 mOsm), meaning it causes water to move out of the cell.
Tonicity of Solutions
A solution that causes a cell to expand is described as hypotonic since it has a lower concentration of solutes than the cell, leading to water influx.
The Integumentary System
Layer of the Epidermis Containing Melanocytes
Melanocytes are predominantly located in the stratum basale, the bottom layer of the epidermis.
Layer of Epidermis Found Only in Thick Skin
The stratum lucidum is present only in thick skin, such as on the soles of the feet and palms of the hands.
Functions of the Integumentary System
Protection: Acts as a barrier to protect against pathogens and injury.
Sensation: Contains sensory receptors for touch, pain, temperature, etc.
Thermoregulation: Regulates body temperature through sweat and blood flow adjustments.
Vitamin D Synthesis: Synthesizes vitamin D in response to UV radiation.
Disadvantage of Melanocyte Death
If all melanocytes in a person’s skin died, the individual would have significantly reduced protection from harmful UV radiation, increasing the risk of skin cancer and sunburn.
Epidermis Layer in Contact with Environment
The stratum corneum is the outermost layer of the epidermis and is composed of dead keratinized cells.
Types of Burns
A burn that damages or destroys both the epidermis and dermis is classified as a third-degree burn (full thickness burn).
Hair Growth Duration
A typical hair grows for approximately 2-6 years before it enters the resting phase.
Sensory Cell Type for Light Touch Detection
The sensory cell type found in the epidermis that detects light touch is the Merkel cell.
Epidermis Layer with Desmosome Integration
Cells in the stratum spinosum begin to link up with desmosomes, contributing to the structural integrity of the skin.
Predominant Cell Type in Dermis
The predominant cell type found in the dermis is the fibroblast, which produces collagen and elastin for structural support.
Other Cell Types in Dermis
Other cell types in the dermis include:
Mast cells: Involved in inflammatory responses.
Macrophages: Play a role in immune defense.
Adipocytes: Store fat.
Commonality of Eccrine, Apocrine, and Sebaceous Glands
All three types of glands serve as exocrine glands, secreting substances through ducts.
Location and Purpose of Eccrine Glands
Eccrine glands are primarily found all over the body, with a high concentration on palms, soles, and forehead. Their main purpose is thermoregulation through sweat production.
Body Odor in Armpits
Body odor in armpits tends to arise over time due to bacterial breakdown of sweat, particularly from apocrine glands that are rich in organic compounds.
Purpose of Sebaceous Glands
Sebaceous glands produce sebum, an oily substance that helps lubricate and waterproof the skin and hair.
Location and Purpose of Pacinian Corpuscles
Pacinian corpuscles are found in the dermis and are responsible for detecting deep pressure and vibration.
Thermoregulation
Body Temperature Effectors at 89.5 °F
At a body temperature of 89.5 °F, effectors such as shivering, vasoconstriction, and increased thyroid hormone production would be activated in response to hypothermia.
Brain Area as Integrator for Thermoregulation
The hypothalamus acts as the integrator for thermoregulation, coordinating responses to maintain body temperature.
Effectors for Hypothermia and Hyperthermia
Three effectors that function oppositely for both conditions include:
Sweating (for cooling) and shivering (for warming).
Vasodilation (for increased heat loss) and vasoconstriction (for decreased heat loss).
Increased heart rate (for heat dissipation) and decreased heart rate (for conserving heat).
Consequence of Tumor on Thyroid Gland
If a tumor causes excessive thyroid hormone secretion, it can lead to hyperthyroidism, which may manifest as increased metabolism, weight loss, heat intolerance, and hyperactivity.
Membrane Potentials / Action Potentials
Cation Channel Opening and Membrane Potential Changes
If a channel for a cation (e.g., Na+) opens, it leads to a depolarization of the cell as positive ions enter.
Electrical Force on Negative Ion in Positive Membrane Potential
With a positive membrane potential, the electrical force acting on a negative ion (e.g., Cl-) would be out of the cell.
Potassium Concentration Force when Doubling ECF Concentration
If K+ concentration outside the cell (in ECF) is doubled, the concentration force acting on potassium would increase, driving more potassium ions into the cell.
Sodium and Potassium Concentration Differences
The concentrations of sodium (Na+) and potassium (K+) are established primarily by the sodium-potassium pump (Na+/K+ ATPase), which actively transports Na+ out of the cell and K+ into the cell, maintaining the gradient.
Ion Equilibrium Definition
An ion is said to be at equilibrium when there is no net movement of the ion across the membrane, meaning the concentration gradient force is balanced by the electrical force acting on it.
Nernst Equation and Ion Equilibrium Potential
The Nernst equation is used to calculate an ion’s equilibrium potential, which represents the electrical potential required to balance the concentration gradient for that ion, predicting its direction of movement across the membrane.
Ion Movement for X2-
For the ion X2- (with a concentration of 40 mM outside and 4 mM inside), if an ion channel opens for X2-, it will move into the cell, because the net concentration gradient drives it in.
Determining Actual Membrane Potential
The actual membrane potential is determined by the relative permeability of the membrane to different ions (i.e., how many channels are open for Na+ and K+), as well as their respective equilibrium potentials.
Location of Chemically Gated Ion Channels
Chemically gated ion channels can be found on dendrites and the cell body of a neuron, where they respond to neurotransmitters from other neurons.
Consequences of Ion Channel Gates Being Stuck
If all voltage-gated Na+ channel activation gates are stuck closed, the neuron cannot depolarize, preventing action potentials.
If all voltage-gated K+ channels are closed, repolarization is inhibited, leading to potential prolonged depolarization.
If voltage-gated Ca2+ channels are stuck closed, neurotransmitter release will be inhibited.
If all chemically gated channel gates are stuck closed, no synaptic input will be able to affect the neuron.
Definition of Action Potential
An action potential is a rapid, temporary change in membrane potential that propagates along the neuron's axon, initiating typically at the axon hillock.
Threshold Potential
The threshold potential is the critical level of depolarization that must be reached for an action potential to occur, usually around -55 mV.
Graded Potential
A graded potential is a change in membrane potential that varies in size, depends on the strength of the stimulus, and can lead to action potentials if it reaches threshold.
Ion Dynamics During Action Potential
During an action potential, while Na+ is rushing into the cell, K+ does not rush out immediately due to the delayed opening of voltage-gated K+ channels following Na+ channel activation.
Absolute Refractory Period
The absolute refractory period is a phase during which a second action potential cannot be initiated, occurring due to the inactivation of Na+ channels after they open.
Relative Refractory Period
The relative refractory period is a phase following the absolute refractory period where a larger-than-normal stimulus is required to elicit an action potential, occurring when K+ channels are still open.
Trigger for Neurotransmitter Exocytosis
The exocytosis of the neurotransmitter from synaptic vesicles is triggered by the influx of Ca2+ ions when voltage-gated Ca2+ channels open due to action potentials.
Inhibitory vs. Excitatory Postsynaptic Potentials
If a chemically gated channel on a postsynaptic neuron allows Cl- to enter, it would create an inhibitory postsynaptic potential (IPSP), making the neuron less likely to fire.
Temporal Summation in Postsynaptic Neurons
The overlap of effects from two different postsynaptic potentials in a postsynaptic neuron is known as temporal summation, where multiple signals can accumulate to affect the likelihood of action potentials.
The Central Nervous System
Shape of Sensory Neurons in Skin
The sensory neurons in the skin are typically classified by shape as unipolar neurons.
Most Common Neuron Type by Function
The most common type of neuron is the interneuron, which shuttles signals between sensory and motor neurons within the central nervous system (CNS).
Most Common Neurotransmitter
The most common neurotransmitter in the body is acetylcholine (ACh), which plays critical roles in muscle activation and synaptic transmission.
Brain Stem Functionality
The brain stem is part of the central nervous system (CNS), serving vital functions such as regulating heart rate, breathing, and the sleep-wake cycle.
Functions of the Cerebellum
The cerebellum is responsible for:
Coordination of Movement: Ensures smooth and balanced muscle activities.
Motor Learning: Involves adapting and refining motor skills through practice.
Posture Maintenance: Helps maintain posture and equilibrium.
Primary Somatosensory Cortex Location and Function
The primary somatosensory cortex is located in the parietal lobe of the brain, responsible for processing sensory information from the skin, muscles, and joints.
Visual Association Area Location and Function
The visual association area is found in the occipital lobe of the brain, involved in interpreting and processing visual information received from the eyes.
Location of Pre-Motor Cortex Relative to Central Sulcus
The pre-motor cortex is located anterior to the central sulcus and is involved in the planning and coordination of movements before they are carried out.
Location and Function of the Thalamus
The thalamus is located above the brainstem and serves as a relay station for transmitting sensory and motor signals to the cerebral cortex.
The Peripheral Nervous System
Difference Between Neuron and Nerve
A neuron is the basic functional unit of the nervous system, whereas a nerve is a bundle of many neurons that transmits signals between different parts of the body.
Number of Thoracic Spinal Nerves
There are 12 thoracic spinal nerves on each side of the body (T1-T12).
Gray Matter vs. White Matter in the Spinal Cord
Gray Matter: Contains neuron cell bodies, dendrites, and unmyelinated axons; involved in processing and integrating information.
White Matter: Composed of myelinated axons; responsible for transmitting signals between different parts of the central nervous system.
Dorsal Root Ganglia Contents
The dorsal root ganglia contain sensory neuron cell bodies, which transmit sensory information to the spinal cord.
Difference Between Reflex and Reaction
A reflex is an involuntary and immediate response to a stimulus that occurs via the spinal cord. A reaction involves voluntary response and typically requires conscious processing and decision-making.
Reasons for Myotatic Stretch Reflex Speed
A myotatic stretch reflex is faster than a withdrawal reflex due to:
Direct Pathway: It involves a single synapse (monosynaptic reflex arc).
Fewer Interneurons: It has fewer processing steps compared to the multi-synaptic withdrawal reflex.
Interneuron Function in Withdrawal Reflex
In a withdrawal reflex, the inhibitory interneuron releases its neurotransmitter onto motoneurons, which then inhibit opposing muscle contraction to allow withdrawal.
Factors Affecting Neuron Conduction Velocity
Two factors that can affect conduction velocity include:
Myelination of Axons: Myelinated axons conduct impulses faster than unmyelinated ones.
Axon Diameter: Larger diameter axons allow for faster conduction of nerve impulses due to reduced resistance.
Definition of Frequency Coding
Frequency coding refers to the mechanism by which the strength of a stimulus is encoded by the frequency of action potentials generated by a neuron, higher frequency indicating a stronger stimulus.