Cell communication (electrical) Flashcards
List three distinguishing features of smooth muscle
- No striation
- Dense bodies
- Single central oval nucleus
List three distinguishing features of skeletal muscle
- Cross striations (sarcomeres)
- Long and tubular
- Multiple peripheral nuclei (small and dense)
Briefly describe what is meant by multiunit smooth muscle
A functionally independent smooth muscle cell, which is enervated by a single nerve terminal
What is an example of a multiunit smooth muscle cell
Cells in the walls of blood vessels
Briefly describe what is meant by visceral smooth muscle
Bundles of smooth muscle cells connected by GAP junctions, which contract spontaneously when stretched
What is an example of a visceral smooth muscle cell
Cells in the walls of intestines
What are some features of Type 1 skeletal muscle fibres?
- Predominantly red muscle cells (highly vascularised)
- High myoglobin and mitochondria concentration
- Low ATPase activity
- Slow and sustained contractions
- Fatigue resistant
- Thinner
What are some features of Type 2 skeletal muscle fibres?
- Predominantly white muscle cells
- Low myoglobin and mitochondria concentration
- High ATPase activity
- Fast contraction
- Fatigue faster
- Thicker
What sarcomere band gets smaller during muscle contraction?
I-Band
Describe some features of the sarcomere A-band
- Length of myosin filament
- Darker (more protein)
- Stays same size during muscle contraction
Briefly describe muscle spindles, in what type of muscle are they found?
Sensory specialisations found embedded in skeletal muscle which detect stretch
What are three distinguishing features of cardiac muscle
- Cross-striations
- One centrally placed nucleus (oval and relatively pale)
- Intercalated discs
What is the function of astrocytes?
Scar forming cells of CNS
What forms the myelin sheath around axons in the CNS?
Oligodendrocytes
What forms the myelin sheath around axis in the PNS?
Shawn cells
What is the function of myelinating neurons?
Provide insulation and support
Where in the body would you find ependymal cells?
Lining the ventricles of the brain and central canal of spinal cord
What is the main function of microglia?
Resident macrophage cells of brain and spinal cord
What are the receptive and output surfaces of neurons?
Receptive = Dendrites Output = Axon
Where does the axon arise from?
The axon Hillock
What creates the negative resting membrane potential (-90mV)?
At rest the membrane is more permeable to potassium ions due to its high potassium concentration (as a result of the Na/K pump). Therefore, potassium moves down its concentration gradient, resulting in a net loss of positive ions
What does depolarisation mean?
Membrane becoming more positive
Where are action potentials generated?
Axon Hillock
What is meant by the term graded potential?
Local changes in resting membrane potential, potentially stimulating action potential generation once they reach the axon hillock (if threshold value is met)
How does the Botulin toxin prevent action potential propagation?
Inhibits release of synaptic vesicles (containing neurotransmitters) into the synaptic cleft, by cleaving snare complex’s
What are synapses?
Areas of connection between neurons
What causes calcium channels to open on the synaptic knob?
Calcium channels are voltage gated, opening when the membrane is depolarised. Depolarisation is caused by sodium entering the cell.
What stimulates synaptic vesicles to migrate to synaptic cleft?
Calcium entering the cell, which then interacts with snare complex’s
When is a cell at electro-chemical equilibrium? (resting membrane potential)
When there is a net balance between diffusion and charge gradients
What happens at the peak of action potentials?
Repolarisation:
- Potassium channels open (potassium leaves)
- Sodium ion channels close
What is the threshold value?
Voltage that must be reached in order for an action potential to be generated
What happens at threshold?
- Voltage gated sodium channels open
2. Voltage gated calcium channels open
Why do action potentials only travel in one direction?
Voltage gated sodium channels become inactive for a short period of time after propagation (refractory period), stopping any further stimulus
Do action potential signals deteriorate in strength?
No, once threshold is reached maximum action potential amplitude does not change
Why is it that large axons propagate action potentials at faster velocities?
Faster flow of ions in larger axons
What effect does myelination have on action potential speed?
Increases speed of action potential propagation because action potentials are able to jump over myelin sheaths
What are Pacinian receptors?
Deep pressure receptors
How does the brain interpret the urgency (intensity) of incoming messages?
Action potential frequency
What are nodes of Ranvier?
Gaps in the myelin sheath, between Shawn cells or Oligodendrocytes
What does neurotransmitters binding to protein receptors on post-synaptic membranes do?
Open specific ion channels on the post-synaptic membrane, producing graded potentials
What terminates acetyl-choline in the synaptic cleft?
Acetyl-cholinesterase
What is the main reason causing the synaptic delay of 0.5 to 1 msec?
Diffusion of neurotransmitters to post-synaptic neuron takes time
Briefly explain a scenario in which acetylcholine facilitates propagation of action potentials across the post-synaptic nerve terminal (EPSP’s)
Acetylcholine binding to ligand gated sodium ion channels, allowing sodium to flood into the post-synaptic neuron, pushing the post-synaptic neuron closer to threshold (depolarising) and increasing likelihood of generating an action potential
After AChE cleaves ACh in the synaptic cleft, what happens to the products?
Choline gets taken up by the pre-synaptic terminal to be re-formed into acetylcholine and stored in synaptic vesicles for future messages
Why are action potentials generated at the axon hillock?
This is the region of the neuron with the highest concentration of ion channels
Do graded potentials deteriorate in strength over time?
Yes
Do graded potentials accumulate?
Yes, more graded potentials at a similar point in time will summate, resulting in greater depolarisation at the axon hillock and an increased likelihood of threshold being reached
Briefly explain a scenario in which acetylcholine inhibits propagation of action potentials across the post-synaptic nerve terminal (IPSP’s)
Acetylcholine binds to ligand gated chlorine channels, allowing negatively charged chlorine to enter the post-synaptic nerve terminal, reploarizing the post-synaptic nerve terminal and pushing it further away from threshold, decreasing the likelihood of action potential generation.
Whats the difference between temporal summation and spatial summation?
Temporal summation is ONE pre-synaptic neuron firing two signals close together so the graded potentials summate at the axon hillock. Spatial summation is TWO or more different neurons firing at the same time so the graded potentials summate at the axon hillock.
Both increase the likelihood of action potential generation.
Are nicotinic receptors EPSP’s or IPSP’s
EPSP’s, they open sodium channels (more sodium enters the cell). Therefore, drive the membrane closer to threshold
Are M1 receptors EPSP’s or IPSP’s
EPSP’s, they close potassium channels (less potassium leaves the cell). Therefore, drive the membrane closer to threshold
Are M2 receptors EPSP’s or IPSP’s
IPSP’s, they open potassium channels (more potassium leaves the cell). Therefore, drive the membrane further away form threshold
How does sarin (nerve gas) inhibit action potential propagation?
Inhibits AChE, similar to organophosphates
What is a sarcoplasmic reticulum?
A big ol’ sac of calcium
How does calcium release facilitate muscle contraction?
Binding to troponin, altering the position of tropomyosin, revealing binding sites on actin for myosin cross-bridges to bind
What are the three things ATP do with regard to muscle contraction and relaxation?
- Provides energy for the power stroke
- Break down myosin cross-bridges from actin binding sites
- Drives calcium ATPase pump to pump calcium back into the SR and out of the cell for cardiac and smooth muscle
What are three components of thin myofilaments?
- Actin protein
- Troponin
- Tropomyosin
Where is calcium released from in skeletal muscle?
Sarcoplasmic reticulum (inside the cell membrane, intracellular calcium!)
What are the components of a motor unit?
A single motor neuron and all of the muscle fibres it innovates
Describe what happens in a power stroke
Cross-bridges pull thin actin filaments, releasing ADP and P from cross-bridges
How do cross-bridges re-set after a power stroke
ATP binds to cross-bridges, releasing the linkage between cross-bridges and actin binding sites. ATP splits, returning myosin cross-bridges to their original position
What happens to muscle length during a concentric contraction?
Shortens
What happens to muscle length during an eccentric contraction?
Lengthens
What happens to muscle length during an isometric contraction?
No change in muscle length
What is muscle tetanus?
Maximal sustained contraction
What causes muscle tetanus?
Rapid and sustained stimulation of muscle fibres, preventing muscle from relaxing
When does twitch summation occur?
If muscle fibres are re-stimulated before it has completely relaxed, the second twitch has a higher relative tension (due to summation)
What are the components of the A band?
Myosin and some actin overlap
What is the source of energy muscle use for immediate contraction?
Creatinine phosphate stores within the muscle (broken down by creatinine kinase) and small amounts of stores ATP
What are the four main sources of energy generation for skeletal muscles?
- ATP phosphate stores
- Creatine phosphate stores
- Anaerobic glycolysis
- Aerobic glycolysis
What are three differences between skeletal and cardiac muscle contraction?
- Cardiac muscle is influenced NOT initiated by neuronal input
- Cardiomyocytes are electrically coupled through GAP junctions
- Cardiac muscle has long action potentials
Where are voltage gated calcium ion channels found in contractile cells of the myocardium?
In the T-tubule membrane (extension of the cell membrane)
In cardiac muscle what is the main source of calcium?
Calcium from the extracellular fluid (this stimulates the release of calcium from the SR)
What are four factors which influence cardiac muscle contractility?
- Calcium concentration
- Hormones (epinephrine)
- Autonomic nervous innervation
- Degree of stretch
How does contraction in smooth muscle transmit its force?
Pulling on the basement membrane (via dense bodies)
Which types of muscle have T-tubules?
- Skeletal muscle
2. Cardiac muscle
Does smooth muscle have troponin?
NO!
What connects actin and myosin filaments to the membrane in smooth muscle?
Dense bodies
Briefly describe some characteristics of multiunit smooth muscle
- Individual cells (not connected to one another)
- Discrete innervation
- Poor response to stretch and hormones
Briefly describe some characteristics of single-unit smooth muscle
Network of cells acting as a single unit, attached by desmosomes or GAP junctions. Strong response to neuronal signals, hormones and mechanical stretch
How does calcium enter the cytosol in smooth muscle?
Receptor/hormone mediated opening of calcium channels and voltage gated calcium channels, allowing extracellular calcium to enter the cytosol. Minimal contribution by SR
What does calcium do to facilitate contraction of smooth muscle? (remember smooth muscle lacks troponin!)
Calcium phosphorylates myosin, changing its shape, allowing myosin to bind to actin
What are the steps involved in calcium phosphorylating myosin in smooth muscle?
Calcium binds to the protein calmodulin. The calcium calmodulin complex must then bind to the light-chain kinase. The light-chain kinase then uses ATP to phosphorylate myosin.
Where are Golgi tendon organs found?
Embedded within collagen fibres in the Tendons
Where are muscle spindles found?
Embedded in skeletal muscle
What do Golgi tendon organs detect?
Muscle tension
What do muscle spindles detect?
Rate of change and degree of stretch
What are the two skeletal muscle proprioceptors?
- Golgi tendon organs
2. Muscle spindles
How do muscle proprioceptors produce a reflex response when you trip?
Local negative feedback loop from the spinal cord
What are the five basic components of a simple reflex response?
- Sensor (receptor)
- Afferent arm (input)
- Integration centre (interneuron)
- Efferent arm (output)
- Response
What are the muscle fibres inside muscle spindle connective tissue capsule referred to as histologically?
Intrafusal muscle fibres
Do intrafusual muscle fibres contribute to muscle contraction?
No, they simply detect stretch
What type of motor neuron innervates extrafusal muscle fibres to contract?
Alpha-motor neurons
What type motor neuron innervates muscle spindle fibres (intrafusial fibres)?
Gamma-motor neurons
What is the only monosynaptic reflex?
Stretch
What happens to the antagonist muscle during reciprocal innervation?
Receives inhibitory neurotransmitters, preventing action potential generation, resulting in muscle relaxation
How many motor units is each muscle fibre innovated by?
One!
