Muscles, Excitable Cells and Cell Homeostasis Flashcards
What does it mean if a membrane is impermeable to an ion?
No channels let the ion through
What does it mean if a membrane is slightly permeable to an ion?
Large driving force is required
What does it mean if a membrane is readily permeable to an ion?
Small driving force required
Describe the permeability of cell membranes at rest.
Fairly readily permeable to K+ and Cl-
Poorly permeable to Na+
Impermeable to various large organic anions
Do substances generally move up or down the concentration gradient?
Down
What is the Nernst equation used for?
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
What two fundamental properties of cells give rise to the existence of a resting membrane potential?
- Unequal distribution of ions across membrane (maintained by Na+/ K+)
- Selective permeability of the cell membrane
What determines if an action potential will occur?
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
What is the threshold and what does it vary between?
Degree of polarisation that triggers action potential
Varies between different neurones and between different parts of the same neurone
Do thicker or thinner fibres generally have lower thresholds?
Thicker fibres have lower thresholds because they are easier to stimulate
What are the two main nervous systems?
Central nervous system (CNS): brain and spinal chord
Peripheral nervous system
What are the two parts of the peripheral nervous system?
Somatic: nerves from CNS to skeletal muscles
Autonomic: nerves from CNS to internal organs e.g. heart
Describe the somatic nervous system.
Motor neurones to skeletal muscles
Voluntary control
Describe the autonomic nervous system.
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?!)
Three types of synapses:
Excitatory synapses
Chemical synapses
Electrical synapses
What happens at an excitatory synapse?
Electrical activity in presynaptic neurone increases excitability of postsynaptic neurone
What happens at chemical synapses?
Prevent direct electrical propagation of AP from pre to post synaptic neurone
How big is a synapse?
20-30 nm
How long is a typical synaptic delay?
0.5 ms
Draw or describe what a synapse looks like.
You better have drawn or described it you dickhead. I can’t do anything if you didn’t, but just know I’m disappointed.
Where is smooth muscle located?
Internal organs
Walls of blood vessels
Around hollow organs (e.g. urinary bladder)
Layers around respiratory, circulatory, digestive and reproductive tracts
What are the functions of smooth muscle?
Move food, urine and reproductive tract secretions
Control diameter of respiratory passageways
Regulate diameter of blood vessels
Describe the structure of smooth muscle cells.
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
Main source of Ca2+ ?
Sarcoplasmic reticulum
Compare sarcoplasmic reticulum in smooth muscle to SR in cardiac and skeletal muscle.
SR less well organised in smooth muscle
Describe the “latch state” of smooth muscle.
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
Describe the general structure of cardiac muscle.
10 micro m diameter
100 micro m length
Mechanical junctions: fascia adherens, desmosomes
Electrical connections: gap junctions
Striated (alternating light and dark bands)
Describe the function of cardiac muscle.
Highly organised contraction to pump blood around cardiovascular systems
Refilling of heart requires synchronised relaxation
Where is the action potential initiated in the heart?
Sinoatrial node
What is the absolute refractory period and why is it an important adaptation of cardiac muscle?
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
What does the elastic protein “titin” do?
Prevents overstretching and may also serve signalling role as a stretch sensor
Increase contractile force of the heart
What is the Frank-starling law?
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
