Physiology week 1: principles of neuronal and hormonal communications

physiology

study of the functions operating in living organisms

what do all living cells maintain?

membrane potential

excitable cells

• cells that undergo brief reversals in membrane charge

• nerve and muscle cells

what types of cells can neurons contact and signal?

• other neurons

• muscles

• glands

what happens when a neuron receives a signal?

information is relayed

what happens when a muscle cell receives a signal?

it initiates contraction

what happens when a gland receives a signal?

it causes secretory output

what happens when opposite charges are separated?

• tension is created

• tendency for ions to move back toward each other can be harnessed for cell work

membrane potential

separated charges have the potential to perform work

what is resting potential in a cell?

-70 mV

Na+-K+ ATPase membrane pump

• found in plasma membranes

• helps maintain cell volume

• sets up ion gradients used to generate action potentials

what influences the neuron cell to be negatively charged inside?

• Na+-K pumps 3 Na+ out of cell and 2 K+ into cell

• large negatively charged protein molecules exist inside cell and stay there

• K+ leak channels are more active than Na+ leak channels

what do pumps require?

energy because ions are being pumped against concentration gradient

leak channels are always..?

open

purpose of membrane pump

to set up gradient that Na+ and K+ ions can flow down

types of gated channels

• voltage gated

• chemically gated

• mechanically gated

• thermally gated

voltage gated

• change configuration

• open/close in response to changes in membrane potential

chemically gated

open/close in response to binding of messenger molecules to membrane receptors

mechanically gated

respond to stretching or other type of mechanical deformation

thermally gated

respond to local heat or cold

depolarization

• caused by flow of Na+ ions into intracellular fluid

• charge becomes more positive

repolarization

• flow of K+ ions into extracellular fluid

• causes charge to become more negative

hyperpolarization

• flow of K+ ions out of cell from resting state

• occurs when K+ channels stay open for a little too long

types of membrane potentials

• graded potential

• action potential

• resting potential

graded potential

• short distance signals

• decremental spread

• spread in both directions but dieas after short distance

how does strength of the triggering event affect the graded potential?

• stronger triggering event means more ion channels will open

• graded potential will be larger

neuron anatomy

• cell body: dendrites + cell membrane

• axon: hillock, axon, terminals

where on the neuron do graded potentials arise?

at the cell membrane covering the cell body and dendrites

where do action potentials arise on a neuron?

at the hillock

how do action potentials happen?

• occurs when excitable cell membrane is depolarized to -55 mV by a graded potential

• voltage-gated Na+ and K+ channels open

• ions flow through channels causing reversal of membrane potential from -70 mV to 30 mV

upstroke of action potential

when Na+ enters causing membrane potential to become increasingly more positive

downstroke of action potential

when K+ leaves, charge becomes more negative

action potentials

• long distance signals

• fast moving, large changes in membrane potential

• does not diminish in strength or die out after short distance

all or none phenomenon

action potential only generated once threshold is reached and is not dependent on magnitude of stimulus

what are the 3 configurations off the voltage gated Na+ channels?

• closed but capable of opening

• open (activated)

• closed and not capable of opening (inactivated)

what are the 2 configurations of voltage-gated K+ channels?

• open

• closed