Neurons
Neurons, Action Potentials, Synapses
Nervous system-Basic Functions
1. Sensory input- being able to perceive environment around you by receptors. Example is observing a glass of water through visual, which is relayed to central nervous system by sensory neuron, which is the brain in humans in central nervous system.
2. Integration Center- where the sensry information is receive, which interprets signals, figuring out response, and sending response out…
3. Motor Output- motor neurons send output away from nervous system, through muscles or glands, which ae the effector organs
Neuron Structures
- Myelin- Stuctures electricaly insulating the axon, highly populated in lipids and allows axon to make the speed to neurons faster
Neuron Components
- Cell body- majority of the organelles are happening in here, neurotransmitters are synthesized in the cell body and then they go down the terminals to be stored
- Dendrites- The reason why these structures are branched is to increase the surface area and therefore there is more reception of incoming signals, more sensitive
Axon
- Signals are traveling down this structure.
- They vary in size, Central nervous system/spinal cord has microscopic neurons, but some extend from nervous system to our feet, and these structures can be larger
- The axon is the conducting region because it conducting signals
- Normally, larger than 10000 axons
Axon terminals
- Secretory region because it can secrete neurotransmitters
- Post synaptic cell receives signals from neuron
- Neurotransmitters
o Can be Excited like acetylcolen
o Can be inhibitory- when its released passed gap and bind to receptor, it can cause cell to be silenced, no action potential or downstreme
Tophat Question: what part of neuron is associated with the reception of action potentials?
My gues: Dentrites Correct answer: Dentristes
General neurophysiology
What is a neuron doing when its at rest
- Resting membrane potential- looking at composition of ions inside and outside the neuron
- Having a resting membrane potential is not unique to neurons all cells have this.
- What makes them special is they can use changes to potential to generate electric signal for communication, short and long-distance communication
- At rest there is a lot of sodium outside of the cell, and there is lots of potassium on the inside.
- Separted charges- potential energy
- Having different concentration in and outside the membrane requires energy to monitor ions coming in and out of the cell
o The stored energy is called voltage
o The movement of ion flowing is called a current
- Negative voltage- inside of the cell is more negative than the outside of the cell
- What allows this to happen
Why is there a negative potential established
At rest there is more sodium outside than inside? takes three sodium from inside of the cell and releases them to the outside of the cell, this require energy because they are being sent outside of their concentration gradient.
While its open its able to grab 2 potassium from the outside and it changes its shape to release potassium inside the cell,
there is a unequal exchange of ions because its releasing 3 NA but bringing 2 K back inside, therefore losing a positive charge every cycle
There is different permeability’s of Na and K across the membrane,
At some point a leak channel which can fuse positive charges inside against their gradients? But how is this model valid then?
- There is more potassium leak channels *100 than sodium
o Potassium is able to leak out of the cell more than sodium is to leak into the cell, this creates this negative resting membrane potential
o Leak channels are just open, there is just a few but refer to statement above
Membrane channels
- Gated channels- stimulus is required to open a gate, there are lots of these
o Ligand gated channel- Opens when the channel binds to a ligand, think of a AcCo, when it binds to receptor it cause the channel to open
o Voltage gated channel- Opens when a voltage difference interact with protein, channel that facilates action potentials
Tophat Question: the concentration of sodium ions is what outside of a neuron at rest and what inside a neuron at rest? My answer: High, Low
Membrane Potential
- Changing the resting potential allow for electric signals that can be used for communication
- Action potential (AP)- long distance signaling and constant strength, all or nothing, autocmatic switch
- Graded Potentials(GP)- When a neuron receives a signal from another cell, GP are the first signals in input zone that is occurring, there is a small signal created here called the graded potential, not all or nothing and they can fissle out with distance, as they all combine at axon, it will create a all or nothing ion potential
o Short distance, varied strength, small region of membrane
Graded potential
- Image descript- neurotransmitter are diffusing by this gap by binding to channels, open and allow Na to flow into the cell and disperse around the cell. Ions are becoming less concentrated as the flow into cell, the further from input zone the weaker it is.
- Localized because it decreases with distance, but a bund of them combine will trigger a action potential
- Opens by ligand gated channels
- Excitatory or inhibitory
- Trigger zone- first voltage gated channel, all sodium ions converge and make a large voltage difference, if it’s enough to trigger opening, it causes all subsequent voltage gated channels
Action gated potential
- If summation potential is strong enough there is a change in membrane potential, VG channels are open, letting sodium in. and doesn’t weaken with distance
Action potential Diagram
- When a AP is activated it causes an increase in sodium ions let inside, therefore it becomes more positive, after a period of time it stops because sodium channels shut, (inactive gate closes)
o VG potasium channels open, but are more delayed
