neurons Flashcards
where are neurons located?
neuropiles
nerves
brain
spinal cord
examples of neurons in interconnected neural networks?
sensory organs, motor pathways etc.
what is the morphological division of neurons?
the CNS (brain and spine) the PNS (everywhere else)
what is cephalisation?
the formation of central ganglia and brains in one end of the animal body
(start of CNS)
which type of cord do vertebrates and invertebrates have?
vertebrates - dorsal
invertebrates - ventral
what are the main components of a neuron?
nucleus - containing dna
mitochondria - powerhouse of the cell
cytoplasm - contains molecules and proteins
cell membrane - polarised so enable neuron to generate electrical currents
(typical animal cells)
difference between anions and cations?
anion - negative ion so more electrons than protons
cation - positive ions so contain more protons than electrons
what are the 4 zones in a neuron?
- Input zone (soma and dendrite to get info from enviro)
- Integration zone (whether input should amount to output, between soma and axon)
- Conduction zone (axon)
- Output zone (axon terminals where signal is passed to next cell)
describe ion channels in the neurons, where located and their purpose?
‘selectivity filter’ to only allow ions of certain charge and size through at certain time
located in the membrane and in specific zones in the neuron
allow neuron to generate bioelectric currents through movement of ions
how do ions move?
3 ways
DIFFUSION - when channels open
areas of high concentration to low concentration areas so down concentration gradient
-when ion channels closed:
can diffuse inside the cell and along membrane but not beyond the membrane and out of the cell
electrostatic forces: like charges repel etc.
what is it called when ion channels are open?
and what happens?
semipermeable state of neuronal membrane
ions move and pushed or pulled back depending on how the electrochemical gradient changes as ions cross the membrane
what happens when ion channels close?
non-permeable state of the neural membrane
distribution differs inside and outside of cell which forms an electrochemial gradient
how do ion pumps function?
carrier protein in cell membrane binds to from one side of the membrane and move to area of their higher conc gradient (active transport)
phosphate group detatches from ATP and produces energy to change shape of carrier protein and enable ion to be released
ions on other side bind to protein and phosphate group drops off which changes shape back to normal
what is the main role of ion pumps?
what are the main 2?
ion pumps help to restore and maintain the difference in ion concetrations inside and outside the neurons
main ones: sodium-potassium and calcium
what is Ohm’s law?
voltage = current x resistance
measured using multimeter
how do microelectrode recordings work?
When a metal electrode is inserted in an aqueous ionic solution (electrolyte), ions can react with the electrode.
The distribution of charges can be compared with that of a reference electrode
when is a neuron inactive?
when it doesn’t generate signals
what is the resting potential?
membrane potential of a nerve cell at rest (neuronal membrane is polarised)
what is a neural signal?
change of resting potential to more negative or positive when ions move across the membrane
graded potential:
what is hyperpolarisation?
a more negative membrane potential than the resting potential
(measured in millivolts)
graded potential:
what is depolarisation?
a more positive membrane potential than the resting potential
(measured in millivolts)
what is action potential?
when is the frequency high?
all or nothing response when the depolarisation increases above a neuron-specific threshold (never occur during hyperpolarisation)
stronger the excitation, higher the frequency (how many peaks in a given time) of action potentials generating in Hz
what did Hodgkin and Huxley find about neuronal signals?
won Nobel Prize in 1963
discovered neuronal electrical signal generation
identified between resting potential and neural signal (change of resting to posiitve or negative due to ionic movement across the membrane)
length of neural signals and which ions contributing most to signals and voltage gated channels
how do action potentials work?
6 phases
Resting potential: voltage gated Na+ and K+ are closed (-70mV)
Rising: depolarisation (more positive) caused by the opening of voltage gated Na+ channels and entering of Na+ into neuron in response to stimulation by pre-synaptic neuron
Overshoot: membrane potential becomes positive as more Na+ flow into the cell as more Na+ channels open towards the axon (positive feedback loop)
Falling: Na+ channels become inactivated and close but K+ channels open leading to reduction of positive charge inside the cell as K+ ions leave (repolarisation at +40mV where intracellular space becomes more negative again)
Undershoot: too much K+ flows out of cell through open K+ channels (hyperpolarisation where more negative than resting potential as too many ions have left)
Recovery: all channels then closed and membrane potential returns to resting value through leaky ion channels and sodium-potassium pump as too negative (refractory period)
what are the main functions of the nervous system?
regulate inner organs release chemical messengers change internal states acquire info from in and out of body control movementand language
what do gated ion channels do?
closed until activated
by electrical signals: (voltage gated) located at axon hillock
by drugs: (ligand gated) located at dendrites or cell body
what are leak channels?
always open but only allow specific ions to freely diffuse
what are the 3 classes of ion channels?
leak channels
gated ion channels
ion pumps
describe the process of maintaining the correct ion concentrations?
diffusion through leak channels lets K+ outside
charge outside + and inside -
K+ pulled back due to electrostatic gradient
Na+ diffuses in
cytoplasm now more +
equal K+ has to flow out to maintain correct charges
where are ion pumps and leak channels located?
cell membrane
where do graded potentials occur?
dendrites
