BIO 1140 - Cell Transport Across Plasma Membrane (Pt. 2)

Question 1

How are the Electrical Charges Inside and Out the Cell balanced?

Answer 1

Outside the cell, the charges of Na+ ions are balanced by Cl- ions.

Inside the cell, the charges of K+ ions are balanced by negative charges of organic molecules.

Question 2

What creates a Voltage Difference?

Answer 2

Small excesses of positive or negative charge on the two sides of the plasma membrane create a voltage difference.

Question 3

What is Membrane Potential?

Answer 3

This voltage difference across the membrane is called the membrane potential.

Question 4

What is Resting Membrane Potential?

Answer 4

For a cell at rest, the exchange of anions and cations across the membrane is steady
- Resting membrane potential in animal cells varies between –20 to –200 mV.

Question 5

What is the Role of Ion Channels?

Answer 5

Ion channels create membrane potential
- Ion channels create openings for the passive movement of inorganic ions

Question 6

What Channels are responsible for the Resting Membrane Potential?

Answer 6

K+ leak channels are responsible for the resting membrane potential
- At rest, plasma membrane is mostly permeable to K+ (moving out of the cell)
- K+ is the main positive ion inside the cell

Question 7

What other Channel contributes to the Resting Membrane Potential?

Answer 7

The Na+-K+ pumps also contribute to the resting potential
- establish the K+ gradient
- pumps 3 Na+ ions out of the cell for every 2 K+ ions in

Question 8

What do Ion Channels facilitate?

Answer 8

Ion channels facilitate the passage of select inorganic ions.
- Most channels are narrow and highly selective
- Most channels in the cell are ion channels

Question 9

What are the Two Characteristics of Ion Channels?

Answer 9

Two characteristics distinguish Ion channels from pores :
- Ion selectivity
- Fluctuates between open/closure conformations (not continuously open)

Question 10

What are the different types of Gated Ion Channels?

Answer 10

A specific stimulus triggers gated-ion channels to switch between a closed and an open state by a change in their conformation.

1. Ligand Gated
2. Voltage Gated
3. Mechanically Gated
4. Always open (leak channels)

Question 11

What are Voltage Gated Ion Channels?

Answer 11

Voltage-gated ion channels are controlled by changes in the voltage across the membrane

Question 12

What are Ligand Gated Ion Channels?

Answer 12

Ligand-gated ion channels are controlled by the binding of a molecule
- Stimulus molecule binds to receptor site
- polar substance can diffuse across membrane

Question 13

What are Mechanically Gated ion Channels?

Answer 13

Mechanically-gated ion channels are controlled by a physical stimuli
- physical stimuli include light, sound waves, pressure, stretch, touch and vibration

Question 14

What are ion Channels responsible for?

Answer 14

Ion channels are responsible for electric signal generation and transmission in neurons

Question 15

What are Neurons and Electric Signals?

Answer 15

A neuron (a nerve cell) consists of a cell body, axon and denrites.
- An electric signal consists of changes in the membrane potential across the neuron’s plasma membrane.

Question 16

What are the different Components to a Neuron?

Answer 16

1. Cell body: contains nucleus and cell’s organelles
2. Dendrites: receive information from other neurons or sensory cells
3. Axon: carry information from cell body to target cells via axon terminals
4. Axon Terminals: branching of axon into fine nerve endings

Question 17

How are Activities of Neurons recorded?

Answer 17

Activities of neurons are recorded as changes in membrane potential
- Electrodes are used to record electrical events in a cell
- The resting potential of a neuron is usually between –60to –70 millivolts (mV)
- The minus sign indicates that the inside of the cell is electrically negative compared with the outside

Question 18

What is an Action Potential?

Answer 18

A rapid change in membrane potential is an action potential
- Neuron stimulation shifts the membrane potential to a less negative value (toward zero, depolarization)
- Action potentials are sudden, transient, large changes in membrane potential

Question 19

What does Depolarization cause?

Answer 19

Depolarization causes voltage-gated Na+ channels in the membrane to open transiently.

Question 20

What do Action Potentials result from?

Answer 20

Action potentials result from rapid changes in voltage gated Na+ and K+ channels

Question 21

What is Repolarization?

Answer 21

The depolarized axonal membrane returns to its resting potential by the opening of voltage-gated K+ channels (repolarization).

Question 22

What are the Behaviours of Action Potentials?

Answer 22

• Action potentials travel along axons
• Action potentials jump along myelinated axons
• Action potential propagates in one direction

Question 23

Where do Neurons connect to Target Cells?

Answer 23

Neurons connect to their target cells at synapses
- The signal is transmitted to the target cells at specialized junctions known as synapses
- Presynaptic and the postsynaptic cells are separated from each other by synaptic cleft

Question 24

How many Synapses form between Cell Body and Spinal Cord?

Answer 24

Thousands of synapses form on the cell body and dendrites of a motor neuron in the spinal cord

Question 25

What is an Electrical Signal converted into at Nerve Terminals?

Answer 25

The electrical signal is converted into a chemical signal (neurotransmitter)
- Neurotransmitters receptors are ligand-gated ion channels.

Question 26

What is Chemical Signal converted into?

Answer 26

A chemical signal is converted into an electrical signal at a synapse

Question 27

What type of ion Channels are responsible for Muscle Contraction?

Answer 27

Ligand (neurotransmitter)-gated ion channels are responsible for muscle contraction

• The acetylcholine receptor in the muscle cell membrane opens when acetylcholine binds to it

Question 28

What is Acetylcholine?

Answer 28

Acetylcholine is the ligand responsible for Na+ ion channel activity in neuromuscular junction.
- Acetylcholine is a neurotransmitter

Question 29

What does the Nature of Ligand Gated ion Channels determine?

Answer 29

The nature of the ligand-gated ion channel which binds the neurotransmitter determines the excitatory or inhibitory effect on the postsynaptic cell.
- Neurotransmitters can either excite or inhibit a postsynaptic cell.

Question 30

What do Psychoactive Drugs target?

Answer 30

Psychoactive drugs target ligand (neurotransmitter)-gated ion channels
- Alcohol mimics inhibitory neurotransmitters
- Barbiturate, Valium, Ambien and Restoril are sedative and tranquilizers.
- Agonists mimic the ligand. Alcohol is the agonist of GABA.
- Antagonists compete with the ligand for the ligand binding site
- Heroinblocks excitatory neurotransmitters
- Cocaine blocks dopamine re-uptakefrom the synapse
- Nicotinemimicsexcitatory neurotransmitters

Question 31

What type of ion Channels allow us to hear?

Answer 31

Mechanically-gated ion channels in auditory hair cells allow us to hear