A&P 1 Chapter 11 (Lecture) [The Nervous System, Part 2] Flashcards
What is the voltage of resting potential?
-70mV
Difference in electrical charge between inside and the oi=utside of a cell membrane (voltage)
Na+/K+ Exchange Pump
Moves 3 Na+ ions our for every 2 K+ in
Na+ (Direction and Number for Na+/K+ Exchange Pump)
Out
3 Na+ ions
K+ (Direction and Number for Na+/K+ Exchange Pump)
In
2 K+ ions
Why is it a big deal when Na+ moves across a membrane?
It generates electricity
Three Types of Gated (Active) Channels
- Chemically Gated
- Voltage Gated
- Mechanically Gated
Chemically Gated Channels
- Open in response to specific chemicals
- Locations: cell body and dendrites
Voltage Gated Channels
-
Open in response to changes in transmembrane potential
- Have an activation gate and inactivation gate
-
Found in excitable membranes
- Axons
- Skeletal Muscle Cells
- Cardiac Muscle Cells
Mechanically Gated Channels
- Open in response to membrane distortion
- Locations: sensory receptors
- Touch, pressure, vibration
Depolarization
- Gated Na+ channels open
- Na+ enters cell
- Membrane potential becomes more positive (less negative)
- Generates Electricity
Hyperpolarization
- Gated K+ channels open
- K+ exits cell
- Membrane potential becomes more negative (-80mV)
- No electric current is made
Graded Potentials (3 Phases)
- Resting
- Stimulation
- Depolarization
- Both Chemically & Mechanically Gated Channels can be involved
GP: Resting Cell
- Transmembrane potential= -70mV
- Chemically regulated Na+ channels closed
GP: Stimulation
- Membrane exposed to chemical
- Chemically regulated Na+ channels open
- Na+ ions begin to enter cell
GP: Depolarization
-
Movement of Na+ into cell depolarizes membrane (at stimulation site)
- Potential moves from -70 mV toward zero (more positive, less negative)
- Movement of Na+ into cell also produces a local current that depolarizes adjacent membrane segments
Voltage
(Potential)
Distance over which electrons can move from positive to negative ends.
Current
Number of electrons passing through a point. (Measured in Amps.)
At resting, where is there more Sodium?
Outside
At resting, where is there more Potassium?
Inside
At resting, where do the the Na+ and K+ ion “want” to be? Why?
Na+ wants in, K+ wants out because of the their concentration gradients.
What are the membrane proteins responsible for allowing Na+/K+ in and out of the cell?
Gated Channels & The Na+/K+ Pump
Action Potential (Phases)
- Resting
- Threshold
- Depolarization/Activation
- Repolarization/Inactivation
- Returning to Resting
Resting Phase (Action Potential)
- Transmembrane potential is around -70mV
- Voltage-gated Na+ channels are closed
Threshold Phase (Action Potential)
- Graded potential (in axon hillock) depolarizes initial segment of axon to threshold (-60mV)
- Na+ gates begin to open
Depolarization/Activation (Action Potential)
- Voltage-gated Na+ channels open
- Produces local current
- Goes to +30mV
Repolarization/Inactivation (Action Potential)
- When the membrane potential reaches about +30mV
- Voltage-gated Na+ ion channels inactive
- K+ gates open
- Na+ gates closed until it reaches -40mV
Return to Resting (Action Potential)
- At -90mV K+ gates close
- Pump resets the potential back to -70mV
Refractory Period
- Period of time during which another action potential cannot be generated.
- Only applies to action potential
- 2 Types:
- Relative
- Absolute
Absolute Refractory Period
Membrane cannot respond to another stimulus (Na+ channels are already open or inactivated)
Relative Refractory Period
- Membrane potential almost normal
- Na+ channels in ready state
- K+ channels are not yet closed
- Larger than normal stimulus can initiate action potential
- Membrane is still hyperpolarized (-90mV)
What are the differences between graded and action potentials? Are they connected to each other?
-
Graded
- Affect only a small portion of a cell membrane (Allow communication over short distances)
-
Action
- Affect the entire surface of a cell membrane (Allow communication over long distances)
- Yes they are connected (Graded CAN produce Action
Continuous Propagation
- Unmyelinated Axons
- Slower
- Every portion of axon membrane must depolarize
- Goes by segments
Saltatory Propagation
- Myelinated Axons
- Faster
- Only axon membrane at nodes of Ranvier must depolarize
Why do action potentials only propagate away from the cell body?
Because the previous segment hasn’t reset yet.
Steps of a Chemical Synapse
- Action potential arrives and depolarizes synaptic knob.
- Synaptic vesicles are exocytosed and neurotransmitter molecules are released. (Ca+ enters synapse)
- Neurotransmitter crosses synaptic cleft and binds to receptor.
- Ion channels open and graded potential is produced.
- Neurotransmitter removed and resting potential membrane is restored.
What type of gated channel is present in a synapse?
Chemical
What is an electrical synapse? How do they work?
- A direct physical connection between cells
- NS (rare)
- Eye
- Some areas of the brain
- Ciliary ganglia of PNS
- Action potential always produced in postsynaptic cell
What is synaptic fatigue? How does it happen?
- Occurs when neurotransmitter cannot be recycled fast enough to meet demands of intense stimuli
- Inactive until neurotransmitter is replenished
What is synaptic delay? What is the synaptic delay in typical humans.
The time it takes from arrival of action potential to the response of the other membrane.
In Humans: 0.2-0.5 milliseconds
2 Types of Postsynaptic Potentials
-
Excitatory
- Depolarization
- Na+ Gated
- Excitatory Postsynaptic Potential (EPSP)
-
Inhibitory
- Hyperpolarization
- K+ Gated
- Inhibitory Postsynaptic Potential (IPSP)
Of the two types of postsynaptic potentials, which can possibly lead to an action potential?
Exicitatory
2 Types of Summation
- Spatial
- Multiple connections, all send signals at once
- Temporal
- One connection, sends multiple signals
Cellular Information Processing
- Involves summation of EPSPs and IPSPs by postsynaptic membrane
- Influenced by:
- Temperature
- Oxygen/nutrients
- Abnormal chemicals
- If there is enough neurons set off it will send signal on.
Higher Level Information Processing
- Involves regulatory neurons
- Facilitate or inhibit presynaptic neurons
What are regulatory neurons and what can they do?
Make presynaptic more or less likely to fire.
Either facilitate (Na+) or Inhibit (K+)
ACh
Acetylcholine
Used in Cholinergic Synapses
Multipolar Neuron
- 2 or more dendrites
- Single axon
- Most common CNS neuron
- PNS motor neurons
- Transmission
Bipolar Neurons
- One dendritic process
- With extensive distal branching
- One axon
- With several telodendria & synaptic terminals
-
Rare; special senses
- Eyes
- Nose
- Ears
Unipolar Neuron
- 2nd most common
- Dendrite continuous with axon
- Soma off to one side
- Initial segmentt located where dendrites fuse
- PNS sensory neurons
Anaxonic Neuron
- Cannot differentiate between axons and dendrites
- Brain, special sense neurons
- Function not yet understood
Somatic Neurons (Sensory Neurons)
Recieves info from external environment
Visceral Neurons (Sensory Neurons)
Monitors Organs
Sensory Neurons
- Somatic
- Visceral
Motor Neurons
- Somatic
- Visceral
Somatic Neurons (Motor Neurons)
Cover skeletal
Visceral Neurons (Motor Neurons)
Smooth Muscle & Cardiac Muscle
Inter Neurons
Connects sensory neurons to motor neurons
Neuroglia of CNS
- Microlgia
- Astrocytes
- Oligodendrocytes
- Ependymal Cell
Astrocytes
Anchor blood vessels (Maintain Homeostasis)
Oligodendrocytes
Myelin Sheath
Microglia
Security & Janitor
Ependymal Cell
Produce CSF (Ciliated)
Neuroglia of PNS
- Schwann Cells
- Satellite Cells
Schwann Cells
Myelin Sheath
Satellite Cells
Act like Astrocytes (Homeostasis)
