Neurons Flashcards
neuron types (3)
- sensory neuron
- interneuron
- motor neuron
neuron structure
structural variation:
- can be very long or short
neuron components (3)
- cell body
- dendrites
- axon
neuron cell body
- maintains the normal cell functions of the neuron
neuron dendrites
- receive incoming information
neuron axons
- communicate electrical signals across long distances
where do electrical signals occur in neurons
- dendrites, cell body, axon, and synapse
glial cells (2)
- support and surround neurons to maintain them
- required for proper neuron functioning
neural reflex pathways (2)
- simplest neural pathways
- don’t involve brain or consciousness
sensory neuron
- afferent neurons that send signals toward the CNS
motor neuron
- efferent neurons that send signals away from the CNS
sensory receptors and membrane potential (2)
- incoming stimulus causes change in conformation of receptor protein
- causes a signal within the cell that ultimately changes membrane potential
what determines signal intensity in neurons (2)
- frequency of action potentials; # of action potentials/time
- more pressure to neuron when there is higher intensity
graded potentials (3)
- occurs in dendrites and cell body
- only travel short distances
- vary in magnitude and sign
action potentials (3)
- occur in axons
- all or none (always look the same within the cell)
- can be regenerated and conducted along long distances
synaptic potentials (2)
- action potentials arriving at synapse
- cause the release of neurotransmitters
what causes electrical signals in neurons
- graded, action, and synaptic potentials all result in changes in the membrane potential of the cell
depolarization (2)
- becoming more positive
- smaller difference between inside and outside of cell
hyperpolarization (2)
- becoming more negative
- bigger difference between inside and outside of cell
membrane potential (3)
- voltage differences across the membrane
- always reported as charge inside relative to outside
- in both animals and plants, inside of the cell is more negative than outside at rest
Nernst equation
- allows you to calculate the equilibrium potential of any ion
how do we predict the direction of ion movement
- compare the equilibrium potential of that ion with the membrane potential of the cell
permeability importance (2)
- final membrane potential is a weighted average of the equilibrium potentials of the ions and permeability provides the weighting factor
- increased permeability for an ion will increase its weight/importance
why do we only consider Na+, K+ and Cl- in the Goldman equation
- permeability of the membrane to other ions is extremely low under resting conditions
permeability and equations
- when permeability to one ion is much higher than to other ions, the Nernst and Goldman equations are the same
what is the function of changes in membrane potential (2)
- can act as signals within cells
- occur in many cell types in both animals and plants; animals have nerves and tissues that are specialized for electrical signalling
what causes changes in membrane potential
- change in the membrane permeability (channels opening and closing)
how is permeability regulated
- gated ion channels
how do gated ion channels work
- open and close in response to incoming signals
what causes a graded potential
- binding of neurotransmitter to a receptor
what sets the size of a graded potential
- depends on amount of neurotransmitter
- more neurotransmitter = more channel opening/closing = larger change in permeability = larger change in membrane potential
why can graded potentials only travel short distances
- intracellular resistance and leakage of ions across the membrane cause the signal to degrade with distance; gets weaker as it travels
how are action potentials triggered (3)
- graded potentials in the dendrites and cell body alter membrane potential in the axon hillock (trigger zone)
- membrane potential must exceed the threshold potential
- results in action potentials in the axon
threshold potential
- 55 mV
resting potential
- 70 mv
spatial summation (3)
- graded potentials originating at different locations can influence the net change in membrane potential, allowing the neuron to reach threshold
- many positive close together grade potentials can cause the neuron to reach threshold
- positive and negative graded potentials can cancel each other out
changes in permeability that occur during the action potential
- large increase in Na+ permeability
- followed by increase in K+ permeability
- occurs due to the opening of voltage-gated channels
when do Na+ voltage-gated channels open
- when the membrane is depolarized
positive feedback of Na” voltage-gated channels (3)
- positive feedback causes rapid depolarization
- Na+ channel activated gates open -> Na+ enters the cell -> more depolarization -> more gates open
- feedback loops closes after a certain amount of channels close
how does Na+ channel density affect neuron function (2)
- higher density of voltage-grated Na+ channels creates lower threshold required to trigger an action potential
- increases excitability
how do neurons return to resting MP
- inactivation gate on the VG Na+ channel
- VG K+ channels are not required, but are helpful and are responsible for the hyperpolarization phase of the action potential
absolute refractory period (2)
- inactivation gate closed
- no new action potential is possible
relative refractory period (3)
- inactivation gate open
- new action potential possible, but less likely because neuron is hyperpolarized
- only occurs in neurons with VG-K+ channels
what is the purpose of the refractory periods
- makes it less likely for many action potentials to occur consecutively
action potential propogation (2)
- action potentials spread as a wave of depolarization; an electronic current flow
- this triggers actions potentials to be re-generated in nearby regions of the membrane
if a neuron is depolarized in the middle of the axon, which direction would the resulting action potential travel? (2)
- in both directions because the inactivation gates are open on both sides
- normally, it will travel toward the synapse due to inactivation gates closing behind it
myelin (4)
- formed by Scwhann cells wrapped around axons
- insulates the axon
- allows charge to spread further down the axon without degrading (decreasing below threshold) so that fewer action potentials are needed to send signals
- causes saltatory conduction
saltatory conduction
- apparent “leaping” of action potential from node to node
synapses (2)
- can be chemical or electrical
- neurotransmitters are rapidly removed from the synapse
chemical synapses
- convert electrical signals to chemical signals
- neurotransmitters are released into the synapse when VG Ca+ channels open
