Cell Physiology, Nervous system Flashcards
neural communication
- accomplished by nerve cells
- specialized for rapid electrical signaling and for secreting neurotransmitters
- short-distance
- act on nearby target organs
hormonal communication
- accomplished by hormones
- long distance chemical messengers
- secreted by endocrine glands into the blood
polarization
- anytime the membrane has potential other than 0 mV
- positive or negative direction
depolarization
- membrane becomes less polarized
- going closer to 0mV
- big is an action potential
- small is a graded potential
repolarization
-the membrane returns to resting potential after having been depolarized
hyperpolarization
- membrane becomes more polarized
- inside becomes more negative than resting potential
graded potentials
- occurs in active area of the membrane
- magnitude varies directly with the magnitude of the stimulus
- spread decrementally by local current flow
- die over a short distance
- the larger the triggering event the larger the graded potential
triggering event
-triggers a change in membrane potential by alternating membrane permeability
action potential
- excitable cell membrane is depolarized to threshold potential
- at threshold, NA+ and K+ permeability are initiated
- goes from -70mV to +30mV
threshold potential
between -50 and -55 mV
voltage-gated channels
- when Na+ and K+ channels are activated at threshold
- opening a Na+ channel is dependent on positive feedback cycle
- Na+ exist in 3 conformations (closed and capable of opening, open, closed and not capable of opening)
- K+ channels can exist in 2 conformations (open and closed)
Na+ and K+ channels at resting potential
-all voltage gated channels are closed
Na+ and K+ channels at threshold
- Na+ activation gate opens and permeability of Na+ rises
- Na+ enters cell causing a depolarization to +30mV (rising phase of action potential)
Na+ and K+ channels at peak of action potential
- Na+ inactivation gate closes and the permeability of Na+ falls, ending the net movement into the cell
- at the same time K+ activation gate opens and the permeability of K+ rises
Na+ and K+ channels at the falling phase
-K+ leaves the cell causing repolarization to resting potential
Na+ and K+ channels at returning to resting potential
- Na+ activation gate closes and inactivation gate opens
- resetting channel to respond to another depolarizing triggering event
Na+ and K+ channels at hyperpolarization
- K+ still open and flows outward briefly
- K+ gate closes and sets membrane back to resting potential
refectory periods
- absolute and relative
- ensures the one-way propagation of action potentials
- responsible for setting an upper limit on the frequency of action potentials
absolute refectory periods
- period of time when a patch of membrane cannot be re-stimulated no matter how strong the stimulus
- Na+ channels cannot open again until they reach the “closed but capable of opening again” confirmation when resting potential is restored
relative refractory period
- period of time during which a patch of membrane can only be re-stimulated by a stronger than normal stimulus
- fewer voltage gated Na+ channels are in the position to be jolted open (some take longer to be restored at their capable of opening conformation state)
action potential characteristics
- occur either maximally in response to stimulation or not at all
- the all or none law
- variable strengths of stimuli are coded by varying the frequency of action potentials, not their size
two types of action potential propagation
- contiguous conduction
- saltatory conduction
contiguous conduction
- in unmyelinated fibers
- slower
saltatory conduction
- in myelinated fibers
- faster (jump)
- 50 times faster
- form local currents an action potential at one node produces an action potential at the next node
- schwann cell in PNS and oligodendrocytes in the CNS
myelin
- thick layers of lipids that cover axon at regular intervals
- insulator to prevent leakage of current
- nodes of Ranvier: between myelinated regions, bare patch of membrane
- current flows across the nodes
neurotransmitter action
- excitatory post-synaptic potential (EPSP)
- inhibitory post-synaptic potential (IPSP)
excitatory post-synaptic potential
- if binding of the neurotransmitter opens K+ and Na+ channels that result in a small depolarization
- cell gets closer to threshold
inhibitory post-synaptic potential
- if binding of the neurotransmitter opens either K+ or Cl- channels the result is a small hyperpolarization
- less likely to reach threshold
synaptic summation
- temporal
- spatial
- if excitatory is dominate, the cell is brought closer to threshold, inhibitory is taken further from threshold
- the summation of all inputs are called the grand post synaptic potential (GPSP)
temporal summation
-EPSP/IPSP from a single, repetitively firing, presynaptic input that occur so close together in time they add together
spatial summation
- adding EPSP/IPSP simultaneously from different presynaptic inputs
- faster
neuropeptides
- large molecule made up of 2-40 amino acids
- function as neuromodulators
- act slowly to produce long term changes at the synapse
cellular communication
- direct: via gap junctions and linkup of complementary surface markers
- indirect: carried out through extracellular chemical messengers
- more common
extracellular chemical messengers
- paracrines: local chemical messengers
- neurotransmitters: short range chemical messengers released by neurons
- hormones: long range chemical messengers, secreted into the blood by endocrine glands
- neurohormones: long range chemical messengers secreted into the blood by neurons
hormonal communication
- hydrophilic: highly water soluble, low lipid solubility
- lipophilic: highly lipid solubility, poorly soluble in water, go into cell easier
convergence
- a given neuron that may have many other neurons synapsing on it
- one cell is influenced by many
divergence
- the branching of axon terminals so that a single cell synapse with and influences many other cells
- one cell influences many others
