Module 1 Flashcards
define components of a homeostatic control system
collectively maintain a set point
- STIMULUS: the imbalance
- SENSOR: detects environmental variable; send via afferent pathway
- INTEGRATOR: compares variable to it’s set point; sends via efferent pathway
- EFFECTOR: initiates changes to restore the variable to set point
compare & contrast positive & negative feedback loops with an example of each
NEGATIVE FEEDBACK: effector is signalled to initiate a response in the opposite direction to stimulus, returning it to the set point & halting signals
- i.e. blood glucose regulation occurs following a meal to maximize energy-making potential @ 90mg flu/100mL blood; RESPONSE: insulin release by pancreas into the blood; insulin lowers blood glucose levels by increasing the body’s ability to uptake glucose from blood/liver’s ability to convert glucose to glycogen stores
POSITIVE FEEDBACK: the effector causes changes that amplify the initial signal
- i.e. childbirth; (1) brain stimulates pituitary glands to secrete oxytocin; (2) oxytocin is carried to uterus via bloodstream; (3) stimulates uterine contractions which push baby towards cervix; (4) head of baby pushed towards cervix; (5) nerve impulses from cervix are transmitted to the brain
explain how the plasma membrane acts as a semi-permeable barrier
- regulates internal fluid composition by regulating molecule movement, therefore maintaining homeostasis of the cell, allowing only nutrients/chemical signals to enter & wastes to leave
- components include: PHOSPHOLIPIDS forming the lipid bilayer, CHOLESTEROL maintains fluidity, membrane
PROTEINS maintain cell structure, functioning, allow transport across cell & facilitate signalling, CARBOHYDRATE chains form glycoproteins or glycolipids, stabilizing membrane structure etc. - cell to cell adhesion forms tissues:
- ECM is a network of fibrous proteins surrounding all cells in tissues allowing for nutrient diffusion/waste removal (secreted by fibroblasts in interstitial space); COLLAGEN contributes tensile strength; ELASTIN allows tissues to be stretched/recoil; FIBRONECTIN promotes cell adhesion
- cell adhesion molecules (CAM) help cells stick to each other & surroundings
- cell junctions: DESMOSOMES (adherens) anchor adjacent ells & are composed of dense intracellular thickenings (plaques) connected by glycoprotein filaments containing cadherins; TIGHT JUNCTIONS (impermeable) bw cells form a kiss site with junctional proteins in membrane, usually found in epithelial tissues (i.e. epithelial lining of digestive tract prevents enzyme movement to blood); GAP JUNCTIONS (connexon) formed by 6 connexin proteins per half, forming a tunnel connecting intracellular spaces of cells for direct communication
MEMBRANE PERMEABILITY is thus the make up of components plus determined by molecule size & solubility
using examples, describe differences in diffusion & osmosis
DIFFUSION: a net movement of molecules in and out of the cell across the cell membrane along a concentration gradient
- passive: does not require cellular energy; i.e. ion movement
- facilitated: does not require energy, but uses a carrier for transport down the molecule’s concentration gradient; i.e. glucose transport using GLUT1 channel
- active: requires cellular energy to move a substance against it’s concentration gradient, can either be carrier-mediated or vesicular transport; i.e. Na+/K+ ATPase pump
OSMOSIS: water molecules movement passively across the membrane from a region of low solute concentration to high solute concentration
compare & contrast the different membrane transport mechanisms
MEMBRANE PROTEINS: peripheral or integral
- integral incl. carriers, pumps, channels; channels are either leaky or gated; gated are voltage (respond to membrane potential changes), ligand (chemical messenger interaction) or mechanically (i.e. deformations, stretch) controlled
TRANSPORT MECHANISMS:
- passive: osmosis or DIFFUSION (simple or facilitated)
- active: primary or SECONDARY (co-transport or counter-transport)
- bulk: filtration or VESICULAR (when no specific mechanisms are in place to move certain ions/large molecules; requires energy); EXO or ENDOCYTOSIS (receptor mediated, pinocyotis or phagocytosis - i.e. WBC removal of old cells)
define what is meant by an excitable cell
a change in membrane potential of excitable cells causes ion movement, resulting in an electrical current
describe the relationship between concentration & electrical gradients using K+ as an example
the relationship between membrane potential & ionic currents (membrane potential change causing ion movement, creating an electrical current) is described by OHM’S LAW (voltage (V) = ionic current (I) * resistance (R))
- when channels are closed, R is high & therefore ion movement (I) is very low; when R decreases as channels open, I lowers
- K+ electrochemical gradient: extracellular concentration (Ko) = 5mM; Ki = 150 mM, this drives K+ outwards of cell; ionic charge causes the inside of cells to be more negative due to non-permeable anions (A-) creating an inward driving force
ELECTROCHEMICAL GRADIENT: combination of concentration & electrical gradients either working or opposing each other
NERNST EQ’N: allows for a calculation of equilibrium potential (E); the membrane potential at which that ion will be at equilibrium
- K+, Na+ or Cl- all have a valence (z) = 1; therefore RT/zF = 61
- Ek = 61 log(Co/Ci); K+ then… 61 log(5mM/150mM) = (-)90mV
RESTING MEMBRANE POTENTIAL (RMP): electrical potential across the membrane which depends on types of ion channels, concentrations on either side & relative permeability
- K+ channel cell RMP is -70mV, once K+ channels open K+ will flow out of cell until RMP reaches Ek (-90mV)
- in an K+/Na+ channel cell starting at -70mV K+ moves out while Na+ comes in & RMP cannot become either ENa or Ek
GOLDMAN EQ’N: calculation of combined RMP; Vm = 61 log((P[Na]o + P[K]o + P[Cl]i)/(P[Na]i + P[K]i + P[Cl]o))
define depolarization & hyperpolarization
DEPOLARIZATION: if magnitude of polarization decreases, moving towards 0mV
REPOLARIZATION: after either depolarization or a hyperpolarization, once polarizing begins to return to RMP
HYPERPOLARIZATION: if magnitude of polarization increases, moving even more negative than RMP
describe the three main “states” of a voltage-gated ion channel
conformations of a voltage-gated Na+ ion channel has an activation & inactivation gate controlling Na+ movement; voltage-gated K+ channels function similarly but with 4 differing structural components contributing to activation/inactivation
- CLOSED: pore kept closed by activation gate; inactivation gate is inside the cell but does not interact with pore; occurs at cell resting state but pores are capable of opening
- OPEN: occurs upon reaching threshold potential when voltage sensor allows activation gate to become open & ion enters rapidly; rising phase of membrane potential
INACTIVE: shortly after channel is open, intracellular inactivation gate moves to block the inside of the pore & stop ion movement; falling phase of membrane potential
what is the basis of a refractory period?
a brief period of time following an action potential in which another cannot be generated
ABSOLUTE REFRACTORY PERIOD: all Na+ channels are inactive, preventing a second depolarization
- a second depolarization may occur during the relative refractory period
describe how a neuronal action potential is generated & propagated
INPUT ZONE: where incoming signals are received; contains dendrites & cell body
TRIGGER ZONE: where action potentials are initiated; contains axon hillock
CONDUCTING ZONE: where action potentials are conducted to their target locations; contains the axon
- conduction is initiated from action potential generation; causes inside the membrane to become more positive and to influence adjacent areas to reach threshold potential from rest
- refractory periods ensure one-way propagation forcing action potential to move only in direction of available Na+ channels
OUTPUT ZONE: releases chemical messengers; contains axon terminals
describe the factors that affect the rate of axonal transmission
NEURONAL FIRING RATES: how often a neuron produces an action potential and is largely controlled by refractory periods & frequency
CONDUCTION SPEED: determined by whether or not the fibre is myelinated, as well as fibre diameter
- MYELIN: formed by specialized cells (oligodendrocytes/Schwann cells) providing lipid-rich, insulated regions with regions of exposed fibre called Nodes of Ranvier; contributes to saltatory conduction (excitation jumping)
- diameter & conduction velocity are related: increased diameter decreases resistance to local currents, but there is a limit to axon size
what are IPSPs & EPSPs; how do they control neuronal excitability?
upon interaction of neurotransmitters with chemically-gated ion channels, a graded potential is created which will travel to the axon hillock if strong enough
- inhibitory synapses (IPSPs): generally result when a NT interacts with it’s receptor to activate either Cl- or K+ channels; increase of K+ permeability allows more K+ to flow out the cell & increasing Cl- permeability increases inward flow, causing hyperpolarization away from threshold
- excitatory synapses (EPSPs): interaction of NT with receptor opens nonselective cation channels & allows postsynaptic movement of Na+ & K+ causing slight depolarization
SUMMATION: axon hillock’s membrane potential will be the summation of all arriving graded potentials
- temporal summation: summing of several EPSPs occurring close together in time due to repetitive firing of a single presynaptic neuron
- spatial summation: summation of all EPSPs and IPSPs originating from several different presynaptic inputs having simultaneous effects
