Interactions Between Cells and the Extracellular Environment

Extracellular Environment

Cells must exchange substance with the extracellular environment in order to survive. Cells must be able to communicate to help maintain homeostasis.

Plasma Membrane

Serves as a physical barrier between cell and the interstitial fluid. Regulates movement in and out of the cell. Maintains the electrochem gradient. Functions in cell comm.

Passive membrane transport

The movement of substances across the plasma membrane without the need for energy input. This process includes diffusion, osmosis, and facilitated diffusion.

Diffusion

The process by which molecules spread from an area of high concentration to an area of low concentration, resulting in even distribution.

Steepness of concentration gradient

What the rate of diffusion depends on, it is the measure of difference in concentration between 2 areas. Steeper the gradient faster the rate of diffusion.

Temperature

The sensitivity of molecular movement that affects the rate of diffusion and transport processes across membranes. Higher temperatures generally increase molecular motion, enhancing diffusion rates.

Osmosis

The movement of water molecules across a semipermeable membrane, influenced by solute concentrations, resulting in tonicity that can be isotonic, hypertonic, or hypotonic.

Tonicity

Ability of a solution to change the volume or pressure of a cell by osmosis.

Isotonic solution

A solution that has the same concentration of solutes as another solution, resulting in no net movement of water across the membrane, thereby maintaining cell volume.

Hypotonic solution

A solution that has a lower concentration of solutes compared to another solution, causing water to move into the cell, which can result in cell swelling or bursting.

Hypertonic solution

A solution that has a higher concentration of solutes compared to another solution, leading to water moving out of the cell, which can cause cell shrinkage or crenation.

Ca 2+ pump

A membrane protein that actively transports calcium ions out of the cell, helping to regulate intracellular calcium levels and maintain cellular homeostasis.

Na+/K+ Pump

A membrane protein that uses ATP to transport sodium ions out of the cell and potassium ions into the cell, crucial for maintaining membrane potential and cellular function.

Membrane Junction

Structural connections between adjacent cells that facilitate communication and adhesion, such as tight junctions, gap junctions, and desmosomes.

Tight Junctions

Specialized connections between epithelial cells that prevent leakage of materials between them, ensuring selective permeability of the tissue.

Desmosomes

Structures that provide mechanical stability by anchoring adjacent cells together, often found in tissues subjected to stretching.

Gap Junctions

Communicating connections that allow ions and small molecules to pass between adjacent cells, facilitating intercellular communication.

keratin

A fibrous protein that provides structural support and strength to cells, commonly found in epithelial tissues and the outer layer of skin.

cadherins

Cell adhesion molecules that play a crucial role in cell-cell adhesion, helping to maintain the structure and integrity of tissues.

Connexons

are protein complexes that form channels in gap junctions, enabling communication between adjacent cells.

Claudin and Occludin

Proteins that are essential components of tight junctions, helping to seal the space between adjacent cells and regulate the passage of substances.

Electrical Signals

Changes in the membranes potential of cells that facilitate communication and coordination between them, such as action potentials in neurons.

Chemical Signals

Secreted by cells into ECF. They are responsible for most communication withing the body via ligands.

Paracrine signals

Secreted by one cell and diffuse to adjacent cells, influencing their behavior and function.

Autocrine signals

Act on the same cell that secreted them to regulate its own function and behavior.

Contact-dependent signals

Signals that require direct contact between cells to communicate, often involving membrane-bound molecules.

Neurocrines

Chemical signals released by neurons that act on nearby cells or the cell that released them, affecting nerve function and communication.

Neurotransmitters

Chemicals secreted by neurons that diffuse across a small gap to the target cell.

Neurohormones

Chemical signals released by neurons into the bloodstream, influencing distant target organs and tissues.

Neuromodulators

Chemical signals that modify the activity of neurotransmitters or influence the response of neurons and other cells.

Cytokines

Proteins that are important in cell signaling, affecting the behavior of other cells, especially in immune responses. Synthesized and secreted by all nucleated cells in response to stimuli.

Electrical Current and the Body

There is an electrical potential on either side of the membranes wehn the # of ions is diff across the membrane and the plasma membrane provides a resistance to ion flow.

Passive Ion channels

Specialized membrane proteins that allow ions to flow across the cell membrane without the need for energy, following their concentration gradient. Always open

Ligand-gated channels

are a type of membrane channel that opens in response to the binding of a specific molecule, allowing ions to flow across the membrane. They play a crucial role in cellular communication and signal transduction.

Voltage-gated channels

are membrane proteins that open or close in response to changes in membrane potential, allowing ions to pass through and contributing to action potentials in neurons and muscle cells.

Resting Membrane Potential

is the electrical potential difference across the plasma membrane of a cell at rest, typically around -70 mV. It is primarily established by the distribution of potassium and sodium ions, maintained by ion channels and pumps.

Depolarization

The inside of the membrane becomes more positive (less neg) maybe lead to an action potential.

Repolarization

The membrane returns to its resting membrane potential (70mV).

Hyperpolarization

The inside of the membrane becomes more negative than the resting potential.

Graded potentials

are changes in membrane potential that vary in size and do not always lead to an action potential. They occur in response to stimuli and can be summed up over time or space.

Action potentials

A rapid, temporary change in membrane potential that occurs when a neuron or muscle cell is activated, resulting in a firing event.

Phases of action potential

Resting state, depolarization, repolarization,hyperpolarization.

Resting State

Na+ and K+ channels are closed. Leakage accounts for small movements of Na+ and K+. Each Na+ channel has 2 voltage gates. Activation gates are closed and inactivation gates are open.

Depolarization Phase

Na+ permeability inc. membrane potential reverses. Na+ gates are opened, K+ gates are closed. Threshold is reached, leading to rapid influx of Na+ ions. (-55 to -55mV). At threshold depolarization becomes self generating.

Repolarization Phase

Sodium inactivation gates close. Membrane permabilty to Na dec to resting lvls. As Na gates close, voltage-sensitive K gates open. K exits the cell and internal neg of the resting neuron is restored.

Hyperpolarization Phase

K gates remain open causing an excessive efflux of K+.This results in the membrane potential becoming more negative than the resting potential, often reaching around -80 to -90 mV before returning to the resting state.

Absolute Refractory Period

The time following an action potential during which a neuron cannot fire another action potential, regardless of the strength of the stimulus. This period occurs because Na+ channels are inactivated.

Relative Refractory Period

The period following the absolute refractory period during which a neuron can fire another action potential, but only if the stimulus is significantly stronger than usual. This occurs because some Na+ channels are still inactivated while K+ channels are still open.

Axon diameter

Larger the diameter the faster the impulse

Presence of myelin sheath

myelination dramatically increases impulse speed.

Electrical synapses

are specialized junctions where electrical signals are directly transmitted between neurons through gap junctions, allowing for rapid signal propagation.

Chemical synapses

are junctions where neurotransmitters are released from one neuron and bind to receptors on another, facilitating communication between neurons.

Presynaptic neuron

is the neuron that sends neurotransmitters across a synapse to communicate with a postsynaptic neuron.

Postsynaptic neuron

is the neuron that receives neurotransmitters from the presynaptic neuron at a synapse, allowing for signal transmission.

Synaptic Cleft

Fluid-filled space separating the pre and postsynaptic neurons. Prevents nerve impulses from directly passing from one neuron to the next. Transmission across this is a chemical event and ensures unidirectional comm between neurons.

Termination of Synaptic Transmission

is the process by which neurotransmitters are removed from the synaptic cleft, ceasing the signal transmission between neurons and allowing the presynaptic neuron to prepare for the next signal.

Agonist

is a substance that binds to a receptor and activates it, mimicking the action of a natural ligand. Agonists can enhance or facilitate a biological response.

Antagonist

is a substance that binds to a receptor but does not activate it, blocking or dampening the biological response. Antagonists can inhibit the action of natural ligands.

Partial Agonist

is a substance that binds to a receptor and activates it, but triggers a weaker response compared to a full agonist. Partial agonists can act as both agonists and antagonists depending on the presence of other ligands.

Inverse Agonist

is a substance that binds to a receptor and induces the opposite effect of an agonist, thereby reducing the receptor's activity. Inverse agonists stabilize the inactive form of the receptor, leading to decreased biological responses.

Signall Transduction

is the process by which a cell converts an extracellular signal into a functional response. This involves receptor activation, relay of signals through intracellular pathways, and ultimately leads to changes in cell behavior.

Activating second messengers

First a signaling molecule bind to a receptor wich activates an enzyme that produces cAMP from ATP. cAMP then activated other enzymes, cell activities change in response.

Gs

is a type of G protein that stimulates adenylyl cyclase, increasing the production of cAMP and amplifying the cellular response to various extracellular signals.

Gi

A type of G protein that inhibits adenylate cyclase activity, leading to decreased levels of cAMP in the cell.

Gq

A type of G protein that activates phospholipase C, resulting in the production of inositol trisphosphate (IP3) and diacylglycerol (DAG), which subsequently mobilize intracellular calcium and activate protein kinase C.

Aquaporins

Aquaporins are integral membrane proteins that facilitate the transport of water molecules across cell membranes, playing a crucial role in maintaining cell osmoregulation.