Week 1 Flashcards
Describe ECF
where cells reside, take up O2 and nutrients, discharge waste. divided into interstitial fluid, blood plasma and lymph fluid. 20% body weight. Na+ is most abundant cation.
Describe ICF
cell membrane barrier. 40% body weight, K+ most abundant
Fluid compartment percentages for:
- total body weight
- ICF
- ECF
- Interstitial fluid
- PV
- total body weight = 60%
- ICF = 40%
- ECF = 20%
- Interstitial fluid = 15%
- PV = 5%
Improper compartmentalization of fluids
Edema
Homeostasis
balanced internal condition of cells
- maintained = physiology
- not maintained = pathophysiology
ex. maintenance of blood glucose and body temp
Dynamic constancy
always changing but helps maintain constant of our body (equilibrium)
Equilibrium
process of homeostasis; condition where variable is constant but no amount of energy input is required to maintain constancy (no net change)
Components of homeostatic system
- stressor = triggers mechanism
- sensor = detects stress
- control center = signals traveling from controlling gland to take action upon the stressor
- effector = takes action
- effect = result from effectors
Hyperthermia: Negative Feedback Loop
- stressor = hyperthermia / high body temp
- sensor = heat receptors in the skin
- control center = hypothalamus
- effector = increased activity of sweat glands
- effector = increased blood flow to the skin
- effect = perspiration evaporates thus colling the skin
Hyperglycemia : Negative Feedback Loop
- stressor = hyperglycemia/ high blood glucose
- sensor = pancreas beta cells
- control center = pancreas
- effector = insulin released in blood
- effector = liver and muscle cells uptake glucose from blood
- effect = decreased blood glucose
Afferent path
PNS to CNS
Efferent Pathway
CNS to PNS
Example of a Positive Feedback Loop within a Negative System
Coagulation - accelerating of clotting
Childbirth : Positive Feedback Loop
- stressor = pressure of fetus on uterine wall
- sensor = afferent nerve endings within the uterine wall
- control center = hypothalamus
- effector = production and release of oxytocin in the blood
- effector = increase in uterine contractions
- effect = intensification of contractions
Harmful effects of positive feedback system
-fever: continues to rise unless fever reducing medication is given
- chronic HTN: BV narrow causing increased pressure, further damaging BV
- decreased blood flow to brain: decrease in sympathetic nerve activity = decrease in BP = decreased blood flow
- anaphalaxis: overproduction of histamines
Most abundant cation in ICF
K+
Most abundant cation ECF
Na+
Plasma Membrane Functions
acts as “gatekeeper”
-binding sites for enzymes
Plasma Membrane
selective barrier to passage of molecules; impermeable to Na+
-phospholipid bilayer with hydrophilic heads (polar/outside) and hydrophobic tails (nonpolar/inside)
Phospholipid Bilayer
amphipathic:
hydrophilic heads - polar regions (outside)
hydrophobic tails - nonpolar regions (inside)
Hydrophobic molecules
pass easily through the membrane (attracted to middle of bilayer lacking H2O
ex. O2, CO2, H2O
Hydrophilic Molecules
do not pass easily through the membrane since they are attracted to the polar water molecules in the ECF and cytosol
ex. proteins
integral membrane proteins
cannot be extracted without disrupting the bilayer.
- amphipathic
- transmembrane
- loop through the membrane
- form channels to help with transmission of chemical signals
peripheral membrane proteins
bound to polar region of the integral proteins and on the cytosol surface
Membrane components
- rich in unsaturated fatty acids
- steroid cholesterol: temperature buffer in PM wedged between phospholipid molecules
- carbohydrates: facilitate cell to cell recognition by interacting with other surface molecules
Role of Steroid Cholesterol in Plasma Membrane
temperature buffer between phospholipid molecules
- cool temp = maintains fluidity by preventing tight packing
- high temp = restrains movement of phospholipids to reduce fluidity
Functions of membrane proteins
-transport: channels hydrolyzing ATP to pump substances across; can be selective
-enzymatic activity: uses enzyme to facilitate transport
-signal transduction: specific shape for signal to send message (ex. hormone)
-cell to cell recognition: identification tags for specific recognition (glycoproteins and glycolipids)
-intracellular joining: shapes fit and connect (gap junctions)
-attachment of ECF and cytosol: stabilizes location of membrane proteins
Membrane fluidity is influenced by:
temperature & components
Molecules that cannot pass through the membrane easily:
- large polar molecules (glucose)
- charged molecules (H+, Na+, Cl-, Ca2+)
Molecules that can easily pass through the membrane:
- gases (O2 & CO2)
- hydrophobic molecules (benzene)
- small polar molecules (H2O & ethanol)
Carbohydrates and lipids combine to form:
Glycolipids (cell identity markers)
carbohydrates and proteins combine to form:
glycoproteins (cell identity markers)
Diffusion of substance across membrane with no energy investment
Passive Transport
Simple Diffusion
-Passive Transport
-no energy required / down concentration gradient from high conc. to low conc.
- lipid soluble molecules (O2, CO2, H2O)
- ex. sugar dissolving in water
Facilitated Diffusion
-Passive Transport
-uses transport proteins to move hydrophilic molecules down the concentration gradient (high to low)
-channel proteins: formation of channel to move substance across membrane (sometimes specific)
-carrier proteins: specific size or shape that a molecule must fit in order for carrier protein to bind & bring it to the other side of the membrane
Factors affecting permeability of membrane
-lipid solubility
-size (small is easier to pass than large)
-ion charge: hydrophilic (polar - cannot pass easily) + hydrophobic (nonpolar - can pass easily)
-presence of channels and transporters: allows passage of hydrophilic substances
Osmosis
-Passive Transport: down conc. gradient from high to low
-diffusion of water (solution) across semipermeable membrane from hypotonic to hypertonic solution
-solvent diffuses until equal concentration of water inside and outside of the cell
-aquaporins: water channels / protein pores (always open)
Solution
homogeneous mixture of 2 or more components
-contains solvent & solute
Solute
components in smaller quantities within a solution
Solvent
dissolving medium (water)
Osmotic pressure
needed to keep the cell in equilibrium with H2O
-increase concentration of solutes = increase in osmotic pressure
Tonicity
ability of solution to cause a cell to lose or gain water based on the concentration of solutes
Cytolysis
cells swell and burst
Plasmolysis
cells shrink / shrivel
Equal concentration of water inside and outside of the cell
isotonic solution
-no net movement of water
More H2O outside of the cell than inside of the cell
hypertonic solution (shriveled - plasmolysis)
-movement of water outside of the cell (towards Na+)
More H2O inside of the cell than outside of the cell
hypotonic solution (swollen; may burst - cytolysis)
-movement of water into the cell (towards Na+)
Using energy from ATP & membrane pumps to move substances up concentration gradient (from low concentration to high concentration) across the membrane
Active Transport
Sodium Potassium Pump (Na+/K+ pump)
-inside the cell has high K+, low Na+
-moves 3 Na+ out of the cell, 2 K+ into the cell while hydrolyzing ATP
-uses 30% of cell’s energy
*normally sodium would flow into the cell (since it’s the most abundant ECF cation) but the pump forces the opposite
Steps of Na+/K+ Pump Mechanism
- 3 Na+ bind to cytoplasmic side of the protein
- Phosphate is transferred from ATP to protein
- Phosphorylation changes the shape of the protein, moving 3 Na+ out and across the membrane
- K+ binds to the protein, causing phosphate release
- Release of the phosphate changes the shape of the protein, moving 2 K+ across the membrane and into the cytoplasm of the cell
Bulk Transport
allows small particles or groups of molecules to enter or leave the cell without actually passing through the membrane
- exocytosis
- endocytosis
Exocytosis
bulk tranport
-vesicles fuse with plasma membrane and release large groups/particles to ECF
-how hormones are secreted
Endocytosis
bulk transport
-plasma membrane develops small particles of fluid that seal onto itself to create a vesicle and then enters the cell
-phagocytosis + pinocytosis
type of Endocytosis
cell engulfs particle by creating a vacuole (specific particle)
Phagocytosis
Intracellular Communication
between 2 cells; critical for survival and functionality of the cell
- nervous system and endocrine system
- nervous tissue and skeletal muscle tissue
A cell is a battery with opposite charges
positive charge is OUTSIDE
negative charge is INSIDE
Polarization
any state where the membrane potential is other than 0 mV
Depolarization
the membrane becomes less polarized than the resting potential
-influx Na+ (exceeds threshold)
-open by positive feedback → transmit signals to the brain
*voltage gated Na+ channels
Repolarization
the membrane returns to the resting potential after having been polarized
-inactivate Na+ channels, activate K+ channels
*voltage gated K+ channels
Hyperpolarization
the membrane becomes more polarized + positive than the resting potential (overshoot)
(K+ channels are slow to close → hyperpolarization)
Resting Membrane Potential (RMP)
the voltage (charge) difference across the cell membrane when the cell is at rest- often negative voltage
-maintained by Na+/K+ pump
Leakage Channels
constantly open + allow K+ ions to flow freely across the plasma membrane
-without these, there would be an equilibrium that would never change (same charge inside and outside of the cell)
Peak of Action Potential
Na+ decreases
Rising Phase
Na+ channels open membrane potential and shift towards equilibrium potential for Na+
Threshold
membrane potential at which voltage gated channels open
-55mv
No voltage = no action potentials →
unable to create movement of skeletal muscle
-charge across the membrane is 0 mV
3 Factors producing resting membrane potential (RMP)
- presence of fixed non-diffusable anions in the cell (attract positively charged ions from outside into the cell via leakage channels)
- preferential permeability of the plasma membrane
- Na+/K+ pump
Effectors on membrane potential
- fixed ions (negatively charged inside the cell - do not diffuse into the ECF)
- cellular proteins
- phosphate groups
- other organic compounds (attracting positively charged ions from ECF into the cell via leakage channel)
Cells are primarily permeable to
K+
(K+ leakage channels are in more abundance than Na+ leakage channels)
K+ diffuses down conc. gradient out of the cell via leakage channel
increase in K+ intracellularly, decrease in K+ extracellularly
-attracted to negative charge within the inner membrane
Graded Potential
-ALL OR NONE; can lead to an action potential or stops
-small change within the RMP
-must occur in order to depolarize the neuron to threshold before an action potential can begin
-stimulus is NOT strong enough = NO ACTION POTENTIAL
Synaptic Potential
type of graded potential that leads to an action potential
-to change the RMP, you must modify the ionic flow in relation to how much Na+ is outside the cell vs. how much K+ inside the cell - accomplished by FACILITATED DIFFUSION
How to change the Resting Membrane Potential (RMP)
you must modify the ionic flow in relation to how much Na+ is outside the cell vs. how much K+ inside the cell - accomplished by FACILITATED DIFFUSION
Ligand Gated Channels
open via chemical stimulation
- infusion of Na+ to ICF the cell and K+ to ECF
- cholinergic channels require ACh or neurotransmitter to open → binding to neurotransmitter causes DEPOLARIZATION of plasma membrane
- prevalent in dendrites + neuron body
- Na+ going out > K+ moving in
-LIGAND CHANNELS stimulate need for positive charge (Na+ influx) to get ACTION POTENTIAL
Increasing Ach at dendrites opens more ligand gated channels, meaning
greater degree of depolarization
Greater chemical stimulus = greater _____
DEPOLARIZATION
in order to reach threshold, you need a ….
strong stimulus that occurs for a long period of time to trigger an action potential
Decaying Depolarization
if the stimulus is too small and the distance is too short then it will not reach the length of the axon
-no action potential produced
Voltage Gated Channels open at what voltage charge?
-55 mV (threshold potential)
Once threshold is met, voltage gated channels open:
→ influx of Na+
→ stimulus ends, repolarization occurs (K+ moves into the cell)
→ reaches threshold again (hyperpolarized)
Voltage Gated Channels
open once the potential threshold is met (-55 mV)
-starts action potential process
Na+ Voltage Gated Channels
1st to open - DEPOLARIZATION
- creates a positive charge inside the cell
- FAST
K+ Voltage Gated Channels
2nd to open - REPOLARIZATION
- creates a negative charge once threshold is met
- SLOW to open/close → repolarization OVERSHOOTS its normal RMP
Na+ channels are deactivated → _____ stops
Depolarization stops
-then, K+ channels open and the cell returns to a repolarized state (outside of the cell = positive + / inside of the cell = negative -) → HYPERPOLARIZATION
Absolute Refractory Period
cannot generate another action potential
Relative Refractory Period
action potential goes below the RMP (hyperpolarization)
-can generate an action potential but needs a very strong stimulus
Resting Stage of A.P. Generation
polarized, overall negative charge
- nerve cell = -90 mV (quick A.P.)
- pacemaker cell = -60 mV (slow A.P.)
- skeletal cell = -83 mV
*maintained by Na+/K+ pump
Cell body of a Neuron
input zone
houses the nucleus and organelles
Dendrites
input zone
-projections that increase surface area to receive and send signals towards the nucleus
Axon
conduction zone
tubular extension conducting A.P. away from the body
Axon Terminal
output zone
influences other cells by sending signals (hormone or chemical release)
Classification of Neurons by Poles
→ unipolar: one pole (embryonic stage)
→ bipolar: 2 poles; axon and dendrites are on opposite ends
→ multipolar: nucleus has multiple poles
Classification of Neurons by Function
→ motor = efferent (CNS to PNS); long axon with short dendrites
→ sensory = afferent (PNS to CNS); short axon with long dendrites
Classification of Neurons by Length
→ golgi type 1: long axon; body is CNS; axon reaches remote periphery organs
→ golgi type 2: short axon; present in spinal cord and cerebral cortex
Electrical Synapse
transmits signals through ions between cells (electrical charge)
- utilizes gap junctions
- quick and bidirectional
Chemical Synapse
neurotransmitter binds to a receptor at post-synaptic site
-slow and one directional
Steps in Neurotransmission
- Neurotransmitter molecules are synthesized and packed in vesicles
- An action potential arrives at the presynaptic terminal
- Voltage gated Ca2+ channels open and Ca2+ enters the cell
- An increase in Ca2+ triggers fusion of synaptic vesicles with the presynaptic membrane
- Transmitter molecules diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic cell
- Bound receptors activate the postsynaptic cell
- A neurotransmitter breaks down + is taken up by the presynaptic terminal or other cells, or diffuses away from the synapse
Excitatory Post-Synaptic Potential (EPSP)
influx of Na+ = uptake
-trying to produce an A.P.
-quick succession → EPSP wins over IPSP and generates an ACTION POTENTIAL
-depolarization of neurotransmitter
Inhibitory Post-Synaptic Potential (IPSP)
influx Cl- = downtake
-counteracts EPSP
-hyperpolarization of neurotransmitter
Ionotropic Receptors
open ion channels and ligand gated channels
- neurotransmitter binds to receptor that is linked to an ion channel
- ion channels open → movement of ions across membrane (in/out)
*features of the ion channel determine which ions flow through
*post-synaptic membrane is depolarized or hyperpolarized, depending on what ions flow into the cell
- Na+ driven transport of choline occurs
- Acetylcholinesterase breaks down ACh
- Nicotinic ACh receptor channel activation
- Membrane depolarization
- Action potential excitation
- Muscle contraction
Metabotropic Receptors
activates signal transduction pathway
- secondary messengers produce post-synaptic response → increase intracellular Ca2+ via opening of ion channels
- neurotransmitter binds to receptor linked to signal transduction pathway
- determines possible activation or inhibition of downstream enzymatic pathway
- possibility of final cellular response
- increase Ca2+ / open + close of ion channels
- Na+ driven co-transport of choline occurs
- Acetylcholinesterase breaks down ACh
- Muscarinic ACh receptor activation
- Release of alpha GTP / G protein
- Activation of inward K+ channel
- Membrane hyperpolarization
- Decrease in heart rate
Excitatory Neurotransmitters (amino acid derivatives)
G.A.S.
glutamate
aspartate
serotonin
Inhibitory Neurotransmitters (amino acid derivatives)
GABA
glycine
serotonin
Amine Neurotransmitters
dopamine
epinephrine
norepinephrine
acetylcholine (ACh)
histamine
Peptide Neurotransmitters
dynorphin
substance P
Termination of Synaptic Response
- Enzymatic degradation
- Diffusion away from postsynaptic receptors
- Re-uptake into presynaptic nerve terminal
- Desensitization of postsynaptic receptor to ligand
Neuromuscular Junction (NMJ) aka Motor End Plate
nerve ending location
- ending of action potential
- ACh released from nerve terminal acts at nicotinic receptors at NMJ
An action potential that travels DOWN the motor axon ALWAYS elicits ________ in muscle fibers and contraction of muscle fibers
action potentials
Contiguous Conduction
unmyelinated fibers
- A.P. spreads along every portion of the membrane
- travels slowly
Saltatory Conduction
myelinated fibers
- propagates A.P. much faster than contiguous conduction (50x faster)
- A.P. does not need to be regenerated along the whole axon
Multiple Sclerosis (M.S.)
myelin degenerates and cannot conduct A.P. as fast
-resulting nerve damage disrupts communication between the brain and the body
Synapse
junction between 2 neurons
- can also interact with muscle cells or gwinns
- site of neuronal communciation
Primary means in which one neuron directly interacts with another
synapse
Presynaptic Neuron
sends the signal (action potential) towards synapse
-converts electrical signal to chemical signal in order to cross the cleft
Synaptic Knob
contains the synaptic vesicles
Synaptic Vesicles
store the neurotransmitter & fuse with presynaptic membrane to release (exocytosis) neurotransmitter
Synaptic Cleft
space in between the presynaptic and postsynaptic neurons
What converts an electrical signal to a chemical signal?
presynaptic neuron
Postsynaptic Neuron
receives the signal (action potential) and propagates away from synapse
-receives chemical signal and generates electrical signal
What converts a chemical signal to an electrical signal?
Postsynaptic Neuron
Electrical Synapse
A.P. impulses conduct directly between adjacent cells through gap junctions (visceral, muscular, embryonic tissues)
-bidrectional / fast
-direct ionic current from one cell to the next
Chemical Synapse
membranes are close but do not touch with the presence of synaptic cleft
-one directional / indirect transmission / slow (transmission due to connection with synaptic cleft)
→arrival of nerve impulse
→depolarizing phase of nerve impulse opens voltage gated Ca2+ channels → Ca2+ influx in presynaptic terminal
→triggers exocytosis of synaptic vesicles and chemical release of hormone
→ ion channels open in postsynaptic membrane
Types of Chemical Synapses
- axodendritic (axon + dendrite)
- axosomatic (axon + soma)
- axoaxonic (axon + axon)
Spatial Summation
results from build up of neurotransmitter released simultaneously by several presynaptic end bulbs
Temporal Summation
one end bulb continues to release a neurotransmitter in rapid succession
Paracrines
exert effects on neighboring cells (local)
Neurotransmitters
short range
-diffuse across membrane and join to target cell (neuron, muscle or gland)
Hormones
long range
- secreted into the blood by endocrine glands in response to a signal
- exert effects on target cell that is a distance away
Neurohormones
hormones released into the blood by neurosecretary neurons
-blood distributes to the target cell
Myelin Sheath
concentric layers of protein alternating with lipid
- wrap around the axon 100+ times
- myelinated nerve fiber insulated by myelin sheath
- produced by Schwann cells outside of the CNS
- produced by oligodendrocytes inside the CNS
Classification of Nerve Fibers
structure: myelinated vs. unmyelinated
distribution: somatic nerve fibers (muscles) vs. autonomic nerve fibers (visceral)
origin: cranial nerves (brain) vs. spinal nerves
function: sensory nerve fibers (PNS to CNS - afferent) vs. motor nerve fibers (CNS to PNS - efferent)
secretion of neurotransmitter: adrenergic nerve fibers vs. cholinergic nerve fibers
NERNST Equation
used to calculate the value of equilibrium potential in a particular cell for a particular ion
Vm = 61 / z x log base 10 x [C]o / [C]i
*use Na+ or K+ to get as close to equilibrium potential as possible since they are most abundant ions
*significant for hyperkaelemia (high K+ in blood)
NERNST Equation: Vm
Vm = equilibrium potential for any ion
NERNST Equation: Z
Z = valence of ions (electrons in outer shell)
NERNST Equation: [C]o
concentration of ion X outside of the cell (mol)
NERNST Equation: [C]i
concentration of ion X inside of the cell (mol)
Hyperkaelemia
high K+ in blood
-RMP shifted to a less negative value → more K+ outside of the cell
- common in DKA → causes fatal arrythmia due to cell’s ability to reach A.P. threshold much faster (increased excitability)
- K+ follows sugar; rapidly flows through the leaky channels outside of the cell
> 6 K+ value = RISK
Mitochondria
major site of ATP production
Anaerobic Respiration
use 2 ATP + produce 2 lactic acid
Aerobic Respiration
use 2 ATP, produce 34 ATP
K+ channels activated → cell turns to _____ state
Repolarized
How steroid cholesterol affects the plasma membrane
*acts as a temperature buffer in PM
higher temp → cholesterol packs tightly = less fluid membrane
lower temp → more fluid
Solvent
dissolving medium (water)
