Problem 2 Neurons and potentials Flashcards
Soma/Cell body
contains the nucleus and much of the machinery for the processes of the cell
Dendrites
recipients of the messages from another neuron (its synapses) – input zone
Axon hillock
junction between axon and cell body
Where action potentials emerge
Axon
carries information (message = action potential) from cell bodies to terminal buttons (one-way street) – conduction zone
Myelin sheath
fatty insulation around many axons that speed up the transmission of electrical impulses thus convey information more rapidly
Oligodendrocytes
(glia cells) with extensions (rich in myelin) that wrap around the axon (CNS)
Schwann cells
which can also guide axonal regeneration (helps to build the myelin covering) is a glia cell (PNS swims in your body)
Nodes of Ranvier
the gaps between sections of myelin
Where ion channels are located (APs)
Terminal Buttons
endings of the axon that release neurotransmitters into the synaptic gap (pre-synapse) – output zone
Multipolar neuron/Motor neuron
Most common in CNS
From the neuron to the action (movement)
Bipolar neuron/inter neuron
o PNS (transmit sensory information to CNS) o Analyses the information
Unipolar neuron/Sensory neuron
o PNS (transmit sensory information to CNS)
o Only one axon leaves the cell body and divides into two or more branches
o Pressure heat senor
o From the body to the brain
Multipolar Interneuron
Integrate neural activity within a single brain structure
Nucleus
contains DNA
Cytoplasm
internal (liquid) substance containing organelles
Endoplasmic reticulum
serves as storage reservoir and channel for transporting chemicals through cytoplasm
ribosomes
translate DNA to real material
Mitochondria
extract energy from nutrients o Aerobic (oxygen-consuming) energy release
Golgi-complex
connected system of membranes that packages molecules in vesicles for delivery to buttons
Microtubules
responsible for rapid transport of material throughout neurons
Membrane structure
Composed of a lipid bilayer (two layers of fat molecules)
Embedded in the lipid bilayer are molecule/proteins
o Channel proteins: certain molecules can pass through them
o Signal proteins: transfer a signal to the inside of the neuron when a certain molecule binds to them on the outside of the membrane
- Hydrophobic is the inside
- Hydrophilic is the outside
Diffusion
passive movement of molecules along a concentration gradient
Osmosis
diffusion through a semipermeable membrane from an area of low concentration to an area of high concentration
Selective permeability
membrane that is selective in terms of which molecules can pass and which can’t
Within the cell
more K+ and A- (organic anion is to big to fit through the membrane) keeps the outside always a bit negative
Outside the cell
mainly Na+ and Cl-
Na+ channels (sodium ion channels)
are closed during resting potential (voltage gated channel: like to open around -55mV)
o Substantial pressure for natrium ions to enter the resting neurons
K+ channels (potassium channels)
o K+ pressure to leave cell due to concentration gradient but also to enter cell due to electrostatic pressure -> STEADY STATE
Sodium-potassium-pump
maintains resting potential!!
o At the same rate that K+ leaks out they are actively transported in (2 in)
o At the same rate that Na+ leaks in they are actively transported out (3 out)
II. Depolarisation/hyperpolarisation
Caused by neurotransmitters binding to postsynaptic receptors
Decrease resting potential (excitatory postsynaptic potential – EPSP positive input)
o Increase likelihood that neuron will fire
Increase resting potential (inhibitory postsynaptic potential – IPSP negative input)
o Decrease likelihood that neuron will fire
Threshold for action potential at -55mV (all-or-none response)
Whether a neuron fires or not depends on the balance btw IPSPs and EPSPs reaching its axon (spatial & temporal summation)
III. Depolarisation – begin of action potential
As soon as threshold of excitation is reached sodium channels in membrane open
Na+ comes in but lots of K+ channels are blocked
Rapid change in membrane potential from -70mV to +40mV
IV. Peak
Sodium channels become refractory (absolute refractory period): become blocked and cannot open again until membrane once more reaches its resting potential
o Responsible that APs only travel one way
V. Repolarisation
K+ continues to leave cell causing membrane potential to return to resting level
More Na+ channels close, more K+ channels open
Hyperpolarisation due to gradual closing of K+ channels
VI. Return to resting potential
Sodium-potassium transporters remove Na+ from cell and retrieve the leaked K+
VII. Resting potential
Relative refractory period: axon is able to fire again but only when applying higher than normal levels of stimulation
o Thus rate of firing is related to the intensity of the stimulation (APs always the same but the rate depends – rate law)
Orthodromic conduction
from cell body to buttons
Antidromic conduction
towards cell body
