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