Lecture 1: Excitable Cells

Question 1

Cells in the ear: Hearing

Answer 1

 Single cells in the hearing organ of the ear (the cochlear) that detect and respond to sound waves.
 Sound waves (converted to fluid movements in the ear) cause the voltage of these cochlear hair cells to change.
 In special outer hair cells, the voltage change also causes the cells to move/contract, which allows for an amplification of the sound transduction

Question 2

Cells in the Brain Signalling “Wake-Up”

Answer 2

 A single nerve cell in the thalamus fires action potentials- a slow rhythmic frequency. but when the nerve is stimulated (by “depolarization”) the firing pattern changes to a burst firing mode
 This is similar to what happens when we wake up. So this change in firing pattern signals to our cortex to “Wake Up”.

Question 3

Muscle cells contracting

Answer 3

 Muscle contraction is important for movement (skeletal muscles), for processing food, controlling blood flow or secreting substances from glands (smooth muscle), and for heart beat (cardiac muscle).

Question 4

Airway epithelial cells

Answer 4

 Epithelial cells have hairlike projections called cilia.
 These cilia, along with the secreted mucus, help to move particles along the airways. This enables you to swallow or cough up the many bacteria and pollutants in the air.
 Airway epithelial cells need to secrete mucus and water to enable the phlegm to move along the airways. This is driven by osmotic, chemical and electrical gradients across the epithelial
 If your epithelial cells can’t secrete the water and salts effectively, you can get thick mucus and die from respiratory infections (e.g. cystic fibrosis).

Question 5

Excitable Cells

Answer 5

 Uneven charge distribution across the membrane (polarised), from the intracellular surface of the membrane to the extracellular surface, arises due to a different concentration of ions on each side.
 Exist with a potential difference across their cell membrane.
 Import energy substrates and export wastes across their membrane.
 Require electrical/chemical signalling to move substances across their membranes.

Question 6

Neurons: process and transmit information within the CNS and/or PNS

Answer 6

 Neurons stimulated at dendrites by stimuli such as ligand binding (chemical messengers) and mechanical distortion (pressure), light and sound.
 Sodium ions diffuse rapidly from the extracellular fluid into the cell; makes inside cell more positive; results in a depolarised cell membrane.
 If the influx is great enough; results in action potential (axon initiated).
 Clinical complications: diseases such as epilepsy and anxiety.

Question 7

Muscle (cardiac) cells:

Answer 7

actively pumps sodium ions, producing a net polarisation of charge on the pericardium; heart begins cycle of muscular contraction at the SA node and is accompanied by a wave of depolarisation that flows through the atrial tissue; atria depolarised, AV node is stimulated and Purkinje cells cause depolarisation of the ventricles.

Question 8

Sensory cells:

Answer 8

cochlear hair cells deep inside the ear amplify the sound signal.

Question 9

Phospholipid Bilayer

Answer 9

 Considered fluid as the phospholipid and other molecules are not chemically linked and can move about laterally; serves as a barrier to the movement of large polar molecules.
 Polar headgroups can readily interact with water, spontaneously adopt a bilayer configuration when placed in polar solvents.
 Long hydrocarbon chain has no partial charges and cannot readily dissolve in water.
 Numerous proteins which function as membrane transport proteins, enzymes, receptors to communicate with other cells.

Question 10

Integral Membrane Proteins

Answer 10

Transmembrane protein that extend through the bilayer allowing both ends to be touched, protein adopts into alpha-helical configuration.

Question 11

Lipid Anchored Membrane Proteins

Answer 11

Located on the boundary of the cell membrane, covalently attached to lipids embedded within the cell membrane.

Question 12

Peripheral Membrane Proteins

Answer 12

Attached to the exterior of the lipid bilayer, easily separable from the bilayer
Example: cytochrome c carries electrons that aid in generating energy; without cytochrome c, proteins will not receive electrons necessary for generating energy in mitochondria.

Question 13

Cell Membrane Properties

Answer 13

 Protects cells from surroundings; semi-permeable; allows essential molecules to cross
 Excellent electrical insulator; 100mV
 Watery fluids; intracellular and extracellular
 Behaves as a capacitor which effects the voltage response of cell to stimulation
 membrane lipids; phospholipids

Question 14

Polar:

Answer 14

having electrical polarity; partial electric charge (dipoles: unequal sharing of electrons).

Question 15

Non-polar:

Answer 15

do not dissolve in water as they cannot form hydrogen bonds; hydrophobic + lipophilic.

Question 16

Biological Electricity

Electrical Circuit;

Answer 16

driving force is battery, copper wire attaching poles acts as conductor; current is the movement of charge in the form of electrons travelling along the conductor; switch is a break that only allows current to flow when the circuit is complete; resistance in the form of thickness, length, conductivity.

Question 17

Biological Electricity

Biology;

Answer 17

driving force is the electromagnetic driving force, membrane proteins act as the conductors to the ICF and ECF (act as the poles), flow of current across membrane acts as the circuit, small molecular switches in the channels (allow ions to flow across); resistance in the form of ion channel properties.