Module 1-4A

neurons communicate via electrical and chemical impulses across ______

synapses

cell body / soma jobs

• sends / receives messages

• makes proteins and molecules

• maintenance of cell and growth

cell body / soma location

most located in the CNS

dendrites job

receive impulses, primarily from axons from other neurons

axon jobs

specialized to carry messages

myelin sheath jobs

speeding message transmission

myelin sheath in the CNS is created by ____

oligodendrocytes

myelin sheath in the PNS is created by ____

Schwan cells

axon terminal / end bouton jobs

end projection of the axon that releases neurotransmitters into the synapse

cell membrane (aka phospholipid bilayer) attributes

• proteins span that layer forming channels or receptors

  • molecules an pass through these channels when they are opened

    • charged particles (ions)

examples of ions

calcium, sodium, etc.

electrical characteristics of neurons

• under “rest” conditions, there is a difference in electrical charge between the inside of the cell body and the extracellular fluid

  • a “voltage difference” across the cell membrane, due to the distribution of charged ions inside vs. outside the cell body

at rest, there are more _______ ions outside the cell body

positive

at rest, there are less _______ ions outside the cell body

negative

the voltage inside the cell body is ____ relative to outside

negative

resting voltage inside the cell body

-70 mV

why is the resting voltage inside the cell body negative?

• moves in two ways:

  • electrostatic gradient

  • concentration gradient

electrostatic gradient (movement inside the cell body)

• ions tend to move down electrostatic gradient

• change wants equilibrium, the positive charges want negative charges and vice versa

concentration gradient (movement inside the cell body)

• ions flow from higher to lower concentration

__ mostly outside the cell

Na+

__ mostly inside the cell

K+

membrane is ___ to K+ than Na+

leakier

more ___ ions leave the cell interior than get in, net result is the interior of the cell body at rest is ____ charged relative to the exterior

positive, negative

how do cells generate an electrical signal

• all living cells are polarized

• cells have a semi-permeable membrane

• unlike other living cells, neurons can alter polarization for brief period of time (aka action potential)

what does it mean to have a polarized cell

• positive or negative charge

neurons are ____ charged at rest

negatively

when charged particles (ions) cross the semi-permeable membrane, ___

it changes the charge of the cell

what is an action potential?

• all or nothing event where the neuron rapidly changes its resting electrical potential from negative to positive, then back to negative again

action potential generation

action potentials are generated when the neuron reaches a threshold voltage, initiating conduction down the length of the axon

Excitatory Post Synaptic Potential (EPSP)

• depolarization within the dendritic zone (in the soma where action potential might happen)

  • travels through this zone to reach the axon

there is a brief interval at the end of the voltage change during which the cell is ____

hyperpolarized (in the refractory period)

what happens when the cell is hyperpolarized (refractory period)

the negative intracellular potential is more negative than it is at rest

action potentials are generated at the ____

nodes of ranvier

nodes of ranvier

“jumps” between unmyelinated axon sections

action potential speeds

narrow diameter = slow

wide diameter = faster

unmyelinated = slow

myelinated = fast

action potential failure: tetrodoxin

• blocking of sodium channels

  • looks like sodium enough to get to channel but can’t fit

  • membrane can’t depolarize

  • causes health concerns

classic tetrodoxin story

sailors ate pufferfish which are poisonous

multiple sclerosis

• failure of the action potential

• scars in nervous tissue

dendrites

end bouton

axon

axon terminal

nucleus

node of ranvier

myelin sheath

cell body

schwann cell

cell membrane (phospholipid bilayer)

closed channel

open channel

cell membrane (phospholipid bilayer)

open ion channel

closed ion channel

depolarization

-70 mV

action potential

repolarization

resting potential

refractory period

potassium channels close

sodium channels close

more sodium channels open

potassium channels open

sodium channels open

Excitatory Post Synaptic Potential (EPSP)

Excitatory Post Synaptic Potentials (EPSP’s)

axon

myelin

node of ranvier

nodes of ranvier

myelin sheath