Unit One
What are the three subcategories of neurocrines?
Neurotransmitters, neuromodulators, neurohormones
Which neuroglia are found in the CNS
astrocytes, microglia, ependymal cells, oligodendrocytes
what is the resting membrane potential?
-70mV
What is propagation?
the AP moves from the axon hillock down the entire axon length toward the axon terminal. the movement of signals b/w neurons
What is the new name(s) for graded potentials
EPSP: excitatory postsynaptic channels
IPSP: inhibitory postsynaptic channels
A gap junction forms from the union of membrane-spanning proteins on two adjacent cells.
Which two neuroglia are myelin producing cells
oligodendrocytes and Schwann cells
- stabilizes and maintains resting membrane potential
- maintains concentration gradients for Na+ and K+
- three Na+ are pumped out of cell while two K+ are pumped back in
Rate of AP propagation depends on two factors
1. axon diameter
2. degree of myelination
- continuous conduction
- saltatory conduction
Name the neurotransmitters that are amino acids and if they are excitatory or inhibitory
- glutamate (excitatory)
- glycine (inhibitory)
- GABA, gamma aminobutyric acid (inhibitory)
Which signalling pathway is considered a secondary messenger system and why?
GPCRs because it does not open up gates but instead changes the subunits
Characteristics of neurons (3)
- extreme longevity
- amitotic with limited exceptions
- high metabolic rate
What is the difference between depolarization and hyperpolarization
Depolarization: decrease in membrane potential (moves toward zero and above)
Hyperpolarization: increase in membrane potential (away from zero)
What are the two phases of absolute and relative refractory period.
Absolute refractory period:
- Time from opening of Na+ channels until resetting of the channels
- Enforces one-way transmission of nerve impulses
Relative refractory period:
- Occurs in an area of the axolemma that has just completed the absolute refractory period
Temporal summation
- A theoretical example: one presynaptic neuron firing rapidly
- First impulse produces EPSP, and before it can dissipate another EPSP is triggered, adding more excitation to the first impulse
Spatial summation
- Postsynaptic neuron is stimulated once by large number of axon terminals at approximately the same time
- Many EPSP are produced and then summate
Name and describe the steps for a simple neural reflex pathway/
1. Stimulus – a change in a physical variable
2. Sensor or receptor - Sensory receptors detect change in a physical stimulus
3. Input signal “pathway”
4. Integration Centre (central nervous system)
5. Output signaling
6. Targets
7. Responses
What is BBB and which neuroglia regulates it?
A network of blood vessels and tissue that is made up of closely spaced cells and helps keep harmful substances from reaching the brain. The blood-brain barrier lets some substances, such as water, oxygen, carbon dioxide, and general anesthetics, pass into the brain.
Astrocytes regulates BBB
Why does diffusion at the axon hillock NOT go backwards to its original occurrence (dendrites)?
The plasma membrane difference is ligand gated and voltage gated
No backfire because chemical parts is between cells, and electrical within cells
Differentiate b/w Group A, B, and C
Group A fibers
- Largest diameter
- Myelinated somatic sensory and motor fibers of skin, skeletal muscles, and joints
- Transmit at 150 m/s (~300 mph)
Group B fibers
- Intermediate diameter
- Lightly myelinated fibers
- Transmit at 15 m/s (~30 mph)
Group C fibers
- Smallest diameter
- Unmyelinated
- Transmit at 1 m/s (~2 mph)
Explain what happens during presynaptic inhibition and post-synaptic inhibition.
1. Presynaptic inhibition
- the size of the AP is reduced in the presynaptic cell by an axoaxonic IPSP
- Less neurotransmitter is released leading to fewer EPSPs in post-synaptic cell
2. Post-synaptic inhibition
- Inhibition of the AP occurs due to axosomatic IPSP at the axon hillock of the post-synaptic cell
- No AP occurs
Name all Cannon's Postulates
The nervous system regulates the “fitness” of the internal environment
Some bodily systems are under tonic control
Some bodily systems are under antagonistic control
One chemical signal can have different effects in different tissues
b) define the variables and explain the relation b/w them
a) Current (I) = Voltage (V)/Resistance (R)
b)
- Voltage: a measure of potential energy generated by separated charge measured between two points in volts (V) or millivolts (mV)
- Current: flow of electrical charge (ions) between two points
- Resistance: hindrance to ionic movement
- Current is directly proportional to voltage
The greater the voltage (potential difference), the greater the current
- Current is inversely proportional to resistance
The greater the resistance, the smaller the current
Steps of Action Potential
- An action potential begins when a depolarization increases the membrane voltage so that it crosses a threshold value
- At this threshold, voltage-gated Na+ channels in the membrane open, allowing many sodium ions to rush into the cell. This influx of sodium ions makes the membrane potential increase very rapidly
- After a short time, the sodium channels self-inactivate (close and become unresponsive to voltage), stopping the influx of sodium. A set of voltage-gated potassium channels open, allowing potassium to rush out of the cell down its electrochemical gradient. These events rapidly decrease the membrane potential, bringing it back towards its normal resting state.
- The voltage-gated potassium channels stay open a little longer than needed to bring the membrane back to its resting potential. This results in a phenomenon called “undershoot,” in which the membrane potential briefly dips lower (more negative) than its resting potential.
- Eventually, the voltage-gated potassium channels close and the membrane potential stabilizes at resting potential. The sodium channels return to their normal state (remaining closed, but once more becoming responsive to voltage). The action potential cycle may then begin again.
What are the six stages of a chemical synapse?
1. ap arrives at axon terminal
2. voltage-gated Ca2+ channels to open Ca2+ enters the axon terminal
3. Ca2+ entry cases synaptic vesicles to release neurotransmitter
4. Neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on chemically-gated ion channels
5. binding of neurotransmitter opens chemically-gated ion channels, creating graded potentials
6. Neurotransmitter effects are terminated
1. diverging
2. converging
3. reverberating
4. parallel after-discharge