UK PGY 206 exam 1
1 molal solution
# moles solute/kg water
1 molar solution
# moles solute/liter of solution
changes in RMP are produced by
- change in the membrane permeability to any of the ions - change in the ion concentrations on the two side of membrane
velocity of AP
- conduction velocity is proportional to diameter of axon (larger the axon, faster AP goes) - conduction velocity increases in a myelinated axon ---- myelin prevents the movement of charge across the membrane ---- AP's occur at the nodes of ranvier (spaces between myelinated regions ---- saltatory conduction
active transport processes
- requires energy (ATP) - requires a carrier molecule (integral proteins) - moving substances AGAINST concentration gradient - transports larger molecules, charged particles, differences in polarity
carrier- mediated transport
- specificity - carrier proteins interact only with specific molecules - competition - two different molecules can be transported by the same carrier, but they compete for the carrier protein - saturation - when all the carrier proteins in a cell are being utilized to move molecules
presynaptic mechanisms for chemical transmission
1. AP reaches presynaptic terminals 2. depolarization activates voltage-gated Ca+ channels resulting in an influx of Ca+ into the presynaptic terminal 3. Ca+ triggers fusion of synaptic vesicles with the axon membrane leading to release of neurotransmitters into the synaptic cleft by the process of exocytosis
Acetylcholine as a neurotransmitter
1. first neurotransmitter identified 2. stored in vesicles; released from presynaptic terminals into synaptic cleft 3. binds to specific receptors on the postsynaptic cell --- nicotinic - nicotine binds here too --- muscarinic - binds muscarin 4. action can be either excitatory or inhibitory - depends on the receptor and second-messanger systems in the specific cell type 5. degrades by extracellular enzyme acetylcholinesterase (breaks down Ach into 2 parts) - allows your muscles to relax
termination of synaptic transmission
1. neurotransmitter dissociated from the postsynaptic receptor and diffuses away from cleft 2. neurotransmitters are taken back into the presynaptic terminals 3. degrading enzymes break down neurotransmitters
postsynaptic mechanisms for chemical transmission
1. neurotransmitters move across the synaptic cleft and bind to receptors on the postsynaptic membrane 2. chemically-gated (ligand-gated) channels open, allowing ions to flow through which then generate an electrical signal (depolarization or hyper polarization) 3. excitatory postsynaptic potentials (EPSP): small depolarizations of the membrane usually due to the influx of Na+ through its chemically-gated channels 4. inhibitory postsynaptic potentials (IPSP): small hyperpolarizations of the membrane due to outflow of K+ and/or inflow of Cl- through chemically-gated channels
chemical synapses
1. the electrical signal is changed into a chemical signal (neurotransmitter) which diffuses across the extracellular space between 2 cells (synaptic cleft) 2. transmission is unidirectional across a synapse - from presynaptic to postsynaptic cell 3. there are special mechanisms for making the neurotransmitter, causing the release of the neurotransmitter, special receptors on the postsynaptic membrane and special mechanisms to change the chemical signal back into an electrical signal
electrical synapses
1. the electrical signal is directly transmitted between cells - ions flow from one cell to another 2. adjacent cells are joined together by gap junctions (connexins) that permit the direct passage of ions from one cell to the next 3. gap junctions conduct signals bidirectionally 4. electrical synapses found primarily in smooth and cardiac muscle
sodium/potassium pump
3 Na+ out for every 2 Ka+ in - maintains concentration gradients for these ions - contributes to generation of a more negative intracellular environment "electrogenic"
total osmolality of ECF and ICF
300mOsm
action potential characteristics
ALL OR NONE - either occur maximally or not at all - if initial stimulus is strong enough to depolarize the membrane to a certain level then an AP will be generated, and each one will always be the SAME AMPLITUDE - stimulus strength is based on frequency - with a greater stimulus, there will be an increase in the frequency of APs
ion distribution between ICF and ECF
K+ higher ICF Na+ higher ECF *balanced by Cl- in ECF and large, negatively charged proteins in ICF
schwann cells
PNS wrap around axons forming a myelin sheath -- nodes of ranvier: spaces between adjacent schwann cells; where action potentials are conducted (signal jumps from node to node)
synapse
a functional connection between a neuron and a second cell (neuron, gland, structure)
EPSP
a single EPSP changes the membrane potential only a few millivolts and can NOT produce an AP - however, EPSPs can summate and if threshold reached, trigger the opening of the voltage-gated channels, leading to an AP
spatial summation
add together signals in different spaces from multiple neurons
rate of diffusion
all increase rate of diffusion - increased concentration differences across membrane - increased temperature of solution - increased permeability of membrane - increased surface area of membrane
permeability of cell membrane
at RMP, K+ is 75 times more permeable than Na+ (losing potassium- cell becomes negative)
electrical potentials
at rest, a neuron has an excess of positive charges on the outside of the membrane and an excess of negative charges on the inside of membrane (-70 mV)
where do APs originate?
axon hillock because thats where the highest concentration of voltage-gated channels are
central nervous system
brain and spinal cord
dendrites
branched processes that extend from cell body- afferent (bring info in to cell body)
motor/efferent neurons
carry information from CNS to effector organs
sensory/afferent neurons
carry information from sensory receptors to CNS
cerebrum
cerebral cortex, voluntary activity, largest part of the brain
simple diffusion (passive)
concentration difference between two regions
saltatory conduction
conduction of an AP from one node of ranvier to the next
tonicity
describes the effects of a solution on the volume of a cell
osmosis
diffusion of water across membrane - must be a difference in solute concentration across the membrane - membrane must be selectively permeable to water but not the solute (water can cross but solute can't)
how do substances cross the cleft? how long does it take?
diffusion- millisecond high concentration at presynaptic----> low concentration at postsynaptic
primary active transport
directly utilizes the energy released by the hydrolysis of ATP
passive transport
does not require energy in form of ATP gradients- concentration, electrical high to low concentration (moving down concentration gradient)
action potentials
electrical signals carried by neurons
axon terminal
end of axon, communication point
neuron cell body
enlarged portion which contains the nucleus and other organelles
1/3 of water (20% of body mass)
extracellular
oligodendrocytes
form myelin sheath around axons in CNS (surround multiple axons)
interneurons/association neurons
found within the CNS; connect afferent and efferent neurons (stepping on glass/simplistic reflexes don't have these neurons)
tract
group of axons in CNS
nerve
group of axons in PNS
nuclei
group of cell bodies within the CNS
ganglia
group of cell bodies within the PNS
astrocytes
help maintain a normal external environment around neurons; helps maintain bbb
phase 5 of AP
hyperpolarization - voltage-gated K+ channels remain open for a brief period of time after the neuron has reached its RMP
secondary active transport
indirectly utilizes the energy released by the hydrolysis of ATP - sodium-potassium pump maintains the sodium concentration gradient across the membrane - as sodium moves back into the cell, other substances are transported by the same carrier proteins
2/3 of water (40% of body mass)
intracellular
cerebellum
involved in getting signals from periphery, learned movements
passive ion channels
ion channels that are always open and allow ions to move down their concentration gradients
ependymal cells
line cavities of brain and spinal cord; make csf
substances that diffuse across plasma membrane
lipid soluble substances very small polar molecules - require a channel or pore
propagation/conduction of the AP
local current flow - stimulus depolarizes membrane to produce an AP - positive charges are conducted to an adjacent region of the membrane - adjacent membrane regions are depolarized to produce another AP; however, the membrane area that just produced an AP is now refractory and can't produce another AP - AP are unidirectional (except for things like bumping your funny bone) - AP conducted without decrement (reduction)
depolarization
membrane potential becomes less negative (moves towards 0) -- inside of cell becomes more positive with respect to RMP
hyperpolarization
membrane potential becomes more negative (polarized) -- inside of cell becomes more negative with respect to RMP (lower than -70)
multipolar
motor neurons
somatic nervous system (efferent)
motor neurons that stimulate contraction of skeletal muscles
autonomic nervous system (efferent)
motor neurons that stimulate contraction of smooth muscle, cardiac muscle, and glandular tissue
efferent division (PNS)
motor- transmits impulses from CNS to the effector organs
primary active transport (1)
movement of calcium across membrane --- low inside, high outside-- against gradient using calcium ATPase
bulk transport (active)
movement of large molecules across the plasma membrane - requires energy
facilitated diffusion (passive)
movement of large, polar substances across plasma membrane by carrier proteins (integral proteins) -- still moving from high to low concentrations
endocytosis
movement of substances from the extracellular fluid into the cell
exocytosis
movement of substances within a vesicle from the cell interior to extracellular space
plasma
noncellular portion of blood - 20% of ECF volume
phospholipid tail
nonpolar, hydrophobic
voltage-gated channels
open or close when they detect a change in the membrane potential
chemically-gated channels (ligand-gated channels)
open when a substance binds to a receptor on the channel to allow ions to move down their concentration gradients
microglia
phagocytes that help get rid of foreign substances in CNS
phospholipid head
polar, hydrophilic
resting membrane potential
potential across a membrane in a resting neuron
osmotic pressure
pressure required to prevent osmosis indirect measure of solute concentration of solution
peripheral nervous system
primarily nerves that project to and from the CNS
phase 3 of AP
rapid rising phase - once threshold is reached, many more voltage-gated Na+ channels open - depolarization - process continues until AP peaks (positive feedback system)
bipolar
rare, eye(retina)
phase 4 of AP
repolarization - voltage-gated Na+ channels close - process of "inactivation" (Na+ begins to diffuse away from membrane and be pumped out of neuron) - voltage-gated K+ channels open - K+ exit leads to repolarization
active transport
requires energy in form of ATP low to high concentration (moving against concentration gradient)
phase 1 of AP
resting state - ions moving through passive channels to maintain RMP - Na+/K+ ATPase maintains concentrations
repolarization
returning to RMP (-70 mV)
isotonic
same osmolality as the inside of the cell
pseudounipolar
sensory neurons
afferent division (PNS)
sensory- transmits impulses from sensory receptors to CNS receptors, includes photoreceptors, chemical receptors, pressure/touch
temporal summation
signals from a single neuron
axon
single process that extends from cell body- efferent (takes info away from cell body)
axon hillock
site of action potential origin
phase 2 of AP
slow rising phase - stimulus depolarizes the membrane by acting on chemically-gated channels resulting in Na+ moving into the neuron - if the threshold value is reached, an AP will be initiated
primary active transport (2)
sodium-potassium pump - carrier protein is an enzyme that hydrolyzes ATP - pumps sodium and potassium in opposite directions - "electrogenic" - pumps 3 Na+ out for every 2 K+ in
hypertonic
solution with higher osmolality than the inside of cell (low inside, high outside) water leaves cell- cell collapses and shrinks (crenation)
hypotonic
solution with lower osmolality than the inside of cell (high inside, low outside) water moves into cell- pressure goes up, cell bursts (lysis)
synaptic cleft
space between the presynaptic cleft and the postsynaptic membrane
neurons
specially designed to transmit information- electrical charges
glia
supporting cells, protection
satellite cells
surround neuron cell bodies within ganglia in PNS
relative refractory period
the period of time during an AP when a second AP can be produced, but only with a much stronger stimulus
absolute refractory period
the period of time during an AP when the membrane will not respond to a second stimulus - inactivation of voltage- gated Na+ channels (another AP can't be generated until the preceding one is finished)
interstitial fluid
tissue fluid between cells - 80% of ECF volume
osmolarity
total solute concentration of a solution
brain stem
vegetative functions, homeostasis, most things run through the brain stem- eating, blood pressure, body temperature