Muscles, Excitable Cells and Cell Homeostasis

Question 1

What does it mean if a membrane is impermeable to an ion?

Answer 1

No channels let the ion through

Question 2

What does it mean if a membrane is slightly permeable to an ion?

Answer 2

Large driving force is required

Question 3

What does it mean if a membrane is readily permeable to an ion?

Answer 3

Small driving force required

Question 4

Describe the permeability of cell membranes at rest.

Answer 4

Fairly readily permeable to K+ and Cl-
Poorly permeable to Na+
Impermeable to various large organic anions

Question 5

Do substances generally move up or down the concentration gradient?

Answer 5

Down

Question 6

What is the Nernst equation used for?

Answer 6

Tells us the magnitude of the electrical gradient that would exactly balance a given concentration gradient of a given ion
Gives us the equilibrium potential for that ion

Question 7

What two fundamental properties of cells give rise to the existence of a resting membrane potential?

Answer 7

1. Unequal distribution of ions across membrane (maintained by Na+/ K+)
2. Selective permeability of the cell membrane

Question 8

What determines if an action potential will occur?

Answer 8

Changes in membrane potential
Excitatory neurotransmitters cause small changes in membrane potentials which can sum and cause an action potential to happen (EPSPs)
Inhibitory neurotransmitters cause IPSPs which can prevent action potentials firing

Question 9

What is the threshold and what does it vary between?

Answer 9

Degree of polarisation that triggers action potential

Varies between different neurones and between different parts of the same neurone

Question 10

Do thicker or thinner fibres generally have lower thresholds?

Answer 10

Thicker fibres have lower thresholds because they are easier to stimulate

Question 11

What are the two main nervous systems?

Answer 11

Central nervous system (CNS): brain and spinal chord

Peripheral nervous system

Question 12

What are the two parts of the peripheral nervous system?

Answer 12

Somatic: nerves from CNS to skeletal muscles
Autonomic: nerves from CNS to internal organs e.g. heart

Question 13

Describe the somatic nervous system.

Answer 13

Motor neurones to skeletal muscles

Voluntary control

Question 14

Describe the autonomic nervous system.

Answer 14

Neurones to visceral organs
No voluntary control
Parasympathetic (some dude on the internet referred to it as the feed-and-breed lol)
Sympathetic: fight or flight (always flight, who the fuck is choosing to fight?!)

Question 15

Three types of synapses:

Answer 15

Excitatory synapses
Chemical synapses
Electrical synapses

Question 16

What happens at an excitatory synapse?

Answer 16

Electrical activity in presynaptic neurone increases excitability of postsynaptic neurone

Question 17

What happens at chemical synapses?

Answer 17

Prevent direct electrical propagation of AP from pre to post synaptic neurone

Question 18

How big is a synapse?

Answer 18

20-30 nm

Question 19

How long is a typical synaptic delay?

Answer 19

0.5 ms

Question 20

Draw or describe what a synapse looks like.

Answer 20

You better have drawn or described it you dickhead. I can’t do anything if you didn’t, but just know I’m disappointed.

Question 21

Where is smooth muscle located?

Answer 21

Internal organs
Walls of blood vessels
Around hollow organs (e.g. urinary bladder)
Layers around respiratory, circulatory, digestive and reproductive tracts

Question 22

What are the functions of smooth muscle?

Answer 22

Move food, urine and reproductive tract secretions
Control diameter of respiratory passageways
Regulate diameter of blood vessels

Question 23

Describe the structure of smooth muscle cells.

Answer 23

Spindle-shaped
Length: 100-300 micro m
Width: 2-5 micro m
Single nucleus
Not striated
Often embedded in a matrix of connective tissue
Arranged in series and in parallel with one another

Question 24

Main source of Ca2+ ?

Answer 24

Sarcoplasmic reticulum

Question 25

Compare sarcoplasmic reticulum in smooth muscle to SR in cardiac and skeletal muscle.

Answer 25

SR less well organised in smooth muscle

Question 26

Describe the “latch state” of smooth muscle.

Answer 26

Enables sustained smooth muscle tone with low rate of cross-bridge cycling (uses less ATP)
Occurs when some of the cross-bridges attached to thin filaments become dephosphorylated
Greatly slows rate of cross-bridge detachment
Filaments tend to remain locked together

Question 27

Describe the general structure of cardiac muscle.

Answer 27

10 micro m diameter
100 micro m length
Mechanical junctions: fascia adherens, desmosomes
Electrical connections: gap junctions
Striated (alternating light and dark bands)

Question 28

Describe the function of cardiac muscle.

Answer 28

Highly organised contraction to pump blood around cardiovascular systems
Refilling of heart requires synchronised relaxation

Question 29

Where is the action potential initiated in the heart?

Answer 29

Sinoatrial node

Question 30

What is the absolute refractory period and why is it an important adaptation of cardiac muscle?

Answer 30

Allows heart to relax fully between beats
Inactivation of Na+ channels after approx 1ms
Fibrillation (quivering, irregular heartbeat) can occur if duration of ARP is decreased

Question 31

What does the elastic protein “titin” do?

Answer 31

Prevents overstretching and may also serve signalling role as a stretch sensor
Increase contractile force of the heart

Question 32

What is the Frank-starling law?

Answer 32

Stretching occurs at times of increased venous return
Force of contraction is increased by stretch and by sympathetic stimulation
Helps heart pump whatever volume of blood it receives