BIOL 1102 Midterm 3

dendrites

branches that receive messages from other neurons at junctions called synapses

dendritic spines

small protrusions in dendrites which further increase SA 

axon hillock

integrates signals from multiple synapses and serves as a junction between cell body and axon; where stimuli are integrated and summed 

axon

tube-like structure that propagates the integrated signal to axon terminals 

myelin

acts as an insulator to minimize dissipation of electrical signal as it travels down the axon, increasing the speed of conduction 

nodes of ranvier

gaps in the myelin where signal is “recharged” as it travels along the axon 

Steps of Action Potential Detailed

1. Resting potential (-70mVs): Na outside, K inside

2. Depolarization: NTs bind to dendrite receptors, ligand-gated ion channels open (Na enters) → membrane becomes more positive

3. Threshold reached (-55mV) w depolarization: action potential begins; synaptic stimuli summer at axon hillock

4. Repolarization: voltage-gated K channels open; K leaves cell and membrane becomes negative

5. Hyperpolarization: too much K leaves; membrane becomes more negative than -70mV

6. Return to resting potential: ion channels reset; Na/K pump restores original gradient

Action (general)

1. Stimuli received by dendrites and cell body

2. Synaptic stimuli summed at axon hillock → action potential triggered if sum is high enough

3. APs go to axon terminal where they release NTs in vesicles 

4. NTs bind to postsynpatic cell membrane 

Sensory (type of neuron + what it does)

pseudopolar; receive sensory and send to brain

interneuron (type of neuron + what it does)

multipolar; neuron in between types of neurons

motor (type of neuron + what it does)

multipolar; brain to muscles

be able to identify the different types in picture + be able to make sense of their relationship

resting potential across membrane conditions

• -70mVs

• more negative on the inside

• extracellular fluid = 0

What ions have biggest impact in membrane potential?

Na, K, and Cl

What is the significance of the electrochemical gradient across the phospholipid bilayer?

what enables important biological processes to happen. If everything was at equilibrium, it would be impossible. 

Why are squids ideal for studying neurons?

they have huge axons; idea that certain animals are good to study for specific topics in biology

resting potential

reflects the baseline state of the neuron; the entire neuron exists in this state when it is inactive

graded potential

temporary change in membrane polarity that forms when a neuron integrates all the different signals it has received; any real value under threshold

T or F? graded potentials are proportional to the strength of the input signal

true

What direction do graded potentials go?

can go either direction; inhibitory (hyper) OR excitatory (de) → hyper or depolarize depending on type of signal received

action potential

forms from a graded potential that has passed a certain threshold; it is a sudden, large reversal of the membrane potential and it is used to convey signals to other cells

Where does an action potential form?

axon hillock

Sodium Potassium Pump

1. 3 Na ions bind to cytoplasmic side of membrane (inside)

2. ATP hydrolyzed (ADP + P) and phosphate attached to pump → acts as energy

3. Phosphorylation causes pump to change shape and3 Na ions are released outside cell

4. 2 K+ ions bind to pump from extracellular (outside)  side

5. Phosphate group detaches from pump and pump returns to original 

6. 2 K+ ions are released into the cytoplasm (inside)

What are K/Na leak channels and why are they important?

selectively permeable to respective ions; allow system to move toward equilibrium 

What is concentration gradient maintained by?

active and passive transport

Electrical and concentration gradients both maintain resting potential but ___ is more important

concentration

Neurons are preferentially permeable to which ion

potassium

What would happen if a neuron increased the amount of Na+ leak channels in its cell membrane?

The neuron would become depolarized (membrane potential more positive).

Types of Channels (3)

1. ligand-gated ion channels

2. mechanically-gated channels

3. voltage gated channels

ligand gated ion channels

specific molecule actives the ion channel (binds) 

mechanically-gated channels

deformation of cell membrane activates ion channel 

• Pressure, vibrations, etc  

voltage gated channels

change in voltage activates

For each step of action potential, know how the voltage-gated channels are acting: resting, depolarization, repolarization, refractory

1. Resting potential 

• Voltage-gated Na and K both closed

• Leak channels active

2. Depolarization

• Voltage-gated Na open 

• Voltage-gated K closed

3. Repolarization 

• Voltage-gated Na closed

• Voltage-gated K open 

4. Refractory/Hyperpolarization 

• Voltage-gated Na closed (resetting)

• Voltage-gated K open (but slowly closing) 

be able to draw membrane, transmembrane proteins, general process for action potential

!

T or F: Propagation is a positive feedback look

true

What is the idea of propagation?

1. Depolarization begins 

2. Propagation: depolarization spreads down the axon 

• Previous section is repolarizing as section begins to depolarize 

3. Resting state

one section activates the next

APs result from summation of graded potentials. Explain this concept

• neuron receives stimulation at its dendrites (chemical signals from other neurons)

• signal produces a slight depolarization of the cell membrane at the axon hillock, a graded potential, which is alone insufficient to reach the threshold

• summation of depolarizing effects of graded potentials exceeds the threshold = action potential forms and propagates

All-or-none phenomenon

it either is triggered or isn’t

• once triggered, it has a magnitude that is independent of the strength of the triggering stimulus

T or F? The duration and intensity of an action potential is proportional to the duration and intensity of the graded potential that preceded it.

false

When a neuron becomes hyperpolarized, it is __ excitable than a resting neuron

less

Are there more or less glial cells than neurons in the nervous system?

many more; glial cells make up over half the volume of human neural tissue

types of cells (4)

1. ependymal cell

2. astrocytes

3. microglia

4. oligodendrocytes

ependymal cell

produce cerebralspinal fluid that cushions brain and spinal cord; located in the ventricles 

astrocytes

contribute to blood-brain barrier and nourish/repair nervous tissue; help structurally support brain to maintain its shape

microglia

abundant, representing up to 10% of brain cells; type of immune cell that clears out plaques, dead cells, and microbes

• Look for alzheimer’s, plques, keeping you from death in general

oligodendrocytes

myelinate cells of the CNS, insulating and metabolically supporting them 

Myelination of axons speeds up signal transmission —> why?

Nodes of ranvier have gated ion channels so action potential moves rapidly via saltatory conduction