Nervous System, Graded Potentials (Pt1) Flashcards
Cell communication
Either through:
-endocrine (hormones, chemical message)
- Nervous system, communication with the cells/tissues/organs/systems they control
Neural communication
Nerves and muscles are excitable tissues
Undergo rapid changes in membrane potentials
-critical to function
two kinds of potential change
- graded potentials
-serve as short distance signals - Action potentials
-long distance signals
- whole length of axon
-electrical impulse
Microscope of Neuron
Neuron is a single nerve cell
Nerve is a bundle of neurons
A neuron contains:
dendritic region (input, increased SA)
cell body
axon hillock (if we send ap)
an axon
axon terminals (where we send next impulse)
different types of neurons
bipolar - two way
pseudo unipolar - one way
multipolar - many ways
Parts of neuron in more depth
Cell body: cell function, houses nucleus and organells
dendrites: increases surface area for receiving signals. Sends signals towards cell body. neuron input zone
axon: nerve “fibre”. conducts action potentials away from cell body. from dendrites to axon terminal
axon hillock: where axon meets cell body. neuron trigger zone
axon terminal: synapses with other neuron’s or effector organs. releases chemical messages
Dyneins and Kinesins
Kinesins: carry nutrients, enzymes, organelles away from cell body to terminal end
Dyneins: picks up and carries recycled vesicles, chemical messengers back toward cell body
mircotubles: “railway”
Membrane potential
Plasma membrane of all living cells has a membrane potential (polarized
electrically)
Separation of opposite charges across plasma membrane
- creates negative charge by losing positive to outside. due to differences in concentration and permeability of key ions
Nerve and muscle cells are excitable and can produce rapid changes in mem potential
Resting mem potential is constant is cells that are not excitable tissues and excitable at rest
Resting membrane potential
1 electrode in cell
1 electrode out
-difference in between two
inside is more negative at rest (-70mv)
at rest, na/k pump working and gates are closed
potential is maintained by 4 mechanisms
-Impermeable membrane
-Na+/K+ ATPase pump
-Increased permeability to K+ (Leaks out)
-Anions inside membrane
Movement of ions
depends on:
-permeability (channels)
-electrical gradient (positive charge is drawn to negative)
- concentration gradient (moves from high to low)
- this creates electrochemical gradient
concentration gradient wins but is not as fast at rest
Na, Cl high outside, K high inside at rest
Nernest equation
Describes equilibrium potential for an ion
E NA = +60mv (130 net)
-if sodium was only allowed to move
this number is what membrane potential would be on inside after equilibrium
electrical and concentration gradients encourage inward movement
Ek = -89mv (19mv net change)
Membrane states
Polarization
* State when membrane potential is other than 0mV
Depolarization
* Membrane becomes less polarized than at rest. Closer to 0
Repolarization
* Membrane returns to resting potential after a depolarization. closer to -70
Hyperpolarization
* Membrane becomes more polarized than at rest. past -70
Graded potentials
Initiated by:
Mechanical stimulus
Chemical stimulus
Electrical stimulus
-Usually initiated in Dendrites (sensory)
Local- die away quickly
Summation: can be added together to become a larger amplitude
-want to move to axon hillock
-come from multiple different areas
amplitude of graded potential depends on stimulus strength (poked harder, more gates open, more likely ap)
vary in size (usually small), excitatory or inhibitory
excitatory - depolarizing
inhibitory - hyper polarizing
no recovery (refractory) period
examples of graded potentials
Postsynaptic potentials
Receptor potentials - beginning of sensory neuron
End-plate potentials
Pacemaker potentials - heart
Slow-wave potentials - smooth muscle
