Flashcards in cells to systems 4 Deck (94)
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1
two broad-types of smooth muscle, how contract and example of where present in the body
1) Multiunit - represents functionally independent smooth muscle cells which are often innervated by single nerve terminal and never contract spontaneously
Eg - smooth muscle in the walls of blood vessels
2) Visceral - represents bundles of smooth muscle cells connected by GAP junctions, which contract spontaneously if stretched beyond a certain limit
Eg - smooth muscle in the wall of intestine - peristalsis
2
what bands can you see under microscope in sarcomere and what shade
○ Can only really see A and I bands
○ A is the darker band (darker has A in it)
○ I is the lighter band (lighter has I in it)
3
What does the I, A, H band and Z and M line represent
I band - actin filaments
A band - myosin filaments that overlap with actin filaments
H band - zone of myosin filaments (where no overlap)
Z line - where actin filaments join and define boundary of the sarcomere
M line - band of connections between myosin filaments
4
what is a muscle tendon junction and neuromuscular junction
Muscle tendon junction
- Ends of skeletal muscle fibres are connected at muscle tendon junction
○ Linkage between sarcomeres inside muscle and collagen fibres that make up the tendon
Neuromuscular junction
- Way skeletal muscle fibre and nervous system communicate
- Essential to get skeletal muscle contraction
5
cardiac muscle what are the muscle cells called, what are the 2 types and list 3 special characteristics
cardiomyocytes
Type 1 and Type 2 muscle cells
1) muscle spindles
2) intercalated disc
3) purkinje fibres
6
Describe the two types of cardiac muscle cells
Type 1
- Predominantly red muscle cells - large amounts of oxygen needed
- Comparatively thin (allow diffusion of oxygen) and contain large amounts of myoglobin and mitochondria
- Myosin with low ATPase activity - this is what creates larger amount of time between contractions
- Contractions are slow and sustained
Eg - in the control of posture
Type 11
- Predominately found in white muscle - not dependent on oxygen
- Thicker and contain less myoglobin - rely on glycolysis - anaerobic respiration
- ATPase activity of the myosin in white fibres is high and contraction fast
- Type IIA fibres (red). Type IIB/IIX fibres (white) contain only few mitochondria.
7
Muscle spindles, what contain, what surround and function
- Sensory specialisation of muscular tissue
- Contain small specialised intrafusal (within capsule) muscle fibres surrounded by
A capsule of connective tissue
- Detect stretch and prevent over stretching
8
intercalated disc what are the 3 parts and Purkinje fibres function
1) Fascia adherens - anchor actin to nearest sarcomere
2) Mascula adherens - desmosome, stop separation during contraction
3) Gap junctions - allow action potentials to spread between cells
Purkinje fibres
- Conduct stimuli faster than ordinary cardiac muscle
- Allow contraction to spread around the heart rapidly
9
what are the two major classes of cells in the nervous tissues
1) Neurons
2) Glia - or accessory cells
10
neurons what does cytoplasm contain and size of cell
- Cytoplasm contain aggregates of rough ER (nissl-bodies)
○ Prominent in motor neurons and grey matter in spinal cord
- Size of cell depends on level of activity and length of process with neuron has to support
○ Generally longer axon/distance larger cell
11
List the 4 main glia and their main function
1) astrocytes - star shaped, mechanical and metabolic support as well as scar forming cells
2) olgiodendrocytes - form myelin shealth around axons (may surround several axons)
3) microglia - derived from monocytes and become phagocytic with tissue damage
4) ependymal cells - line ventricles of brain and spinal cord often ciliated
12
what are the two main peripheral nervous systems
Efferent neurons - nerve fibres originate from neurons within CNS and pass out of CNS
Afferent neurons - nerve fibres originate from nerve cells outside the CNS but enter the CNS
13
what are the two main cells in the peripheral nervous system and their functions
1) Schwann cells
- Form a sheath around one axon and surrounds this axon with several double layers of cell membrane
- Insulates the axon and improves its ability to conduct
2) Ganglia
- Ganglia are aggregation of nerve cells outside the CNS
- Individual ganglion cells are surrounded by a layer of flattened satellite cells
14
what is the resting membrane potential and how is it maintained
= -70mV
- More negative within the cell than outside the cell
- Dependent on the K+ concentration maintained by the slightly leaky K+ channel
15
What are the 4 stages in a membrane potential
1) pre-threshold
2) threshold
3) post-threshold
4) repolarisation
16
Describe pre-threshold phase of membrane potential
movement of Na+ into the site causes depolarisation and further movement of Na+ into the cell making the inside more positive until it reaches threshold
ways in which Na+ enters
1) Na+ leaking into the cell, via leaky channels
2) Na+ from an action potential further back that flow forward after entering the cell and depolarise the adjacent membrane further upstream of the AP
3) Mechanical disruption to the neuronal membrane to make it more leaky to Na+ etc
17
describe threshold phase of a membrane potential
- -30mV
- Stimulus must reach threshold in order for AP to occur
- Once reach threshold AP is the same magnitude each time no matter the stimulus
○ Always reach +30mV membrane potential
18
describe the post-threshold and repolarisation phase of a membrane potential
3) Post-threshold
- Once threshold reach causes opening of voltage gated Na+ channels causing a rush of Na+ into the cells and rapid depolarisation
- When reach +30mV gates slowly close creating a small plateau
4) Repolarization
- At +30mV voltage gated ion open so K+ leaves the cell and makes the cell more negative so goes back to the resting membrane potential
19
how does propagation of the action potential occur in only one direction
- Na+ floods in and along the axon and depolarises adjacent part of the axon
○ Na+ is sent only forward as when the channels backward start to close they become less sensitive to a charge - (refractory period)
20
what is the refractory period and name and describe the phases
Refractory period
Minimum time during which the neuron is unresponsive to further stimulation
1st phase - absolute refractory period
- Na+ channels have become inactivated are incapable of been opened
2nd phase - relative refractory period
- Some but not all Na+ channels are responsive to further stimulus and are capable of being opened
21
List 4 characteristics of a action potential
1) Unidirectional electrical flow (one way)
2) Constant stimulus strength (self-perpetuating) - strong AP at start and end of propagation
3) Signals can be passed on to other neurons and effector organs (muscles and glands)
4) Larger axons propagate action potentials at faster velocities - less resistant to flow so Na+ moves along the axon quicker
22
myelinated nerves what feature present, what does it do and how achieve
Node of Ranvier - voltage gated ion channels are located at large concentrations
- Myelination increases the speed of action potential propagation
Unmyelinated axon - takes time for ions such as Na+ and K+ to flow in and out
Myelinated axon - action potential jump across myelin sheath so Na+ flow down to adjacent node of Ranvier
23
List and describe one way that sensory information is converted to language that CNS can understand
Pecinian corpuscle - sensory unit in the skin
receives deep pressure and vibration
Unstimulated Pacinian receptor
The Na+ ion channels are closed
Stimulated Pacinian receptor
Compression stretch the membrane and opens the Na+ ion channels allowing Na+ to move through the membrane depolarising the cell
Signal intensity and AP frequency
More pressure more frequent the AP occur telling the brain that there is more pressure applied
24
describe the 6 steps that occur within a synapse
1) AP propagation in the presynaptic axon and the synaptic knob
2) AP causes the opening of Ca2+ channels allowing Ca2+ to flow into the cell
3) Ca2+ migration causes vesicles full of neurotransmitters which causes them to migrate and merge with the presynaptic membrane where the neurotransmitters are released
4) Neurotransmitters diffuse across the synaptic cleft and bind with receptors such as ligand gated channels and may allow Na+ to enter the postsynaptic neuron bringing it closer to threshold
- Can also cause Cl- to move into the cell which hyperpolarises the neuron as the negative charge pushes the cell further away from threshold
5) Acetylcholinesterase (enzymes) are within the synaptic cleft and degrade acetylcholine into acetic acid and choline.
6) The choline is recycled back into the presynaptic membrane via a channel protein preventing them from remaining in the synapse and continually activating the postsynaptic membrane
25
function of neuropeptides and give some examples
modulate activity of neurotransmitters, can assist or inhibit
substance P, cholecystokinin
26
post-synaptic potentials what occurs what type of potential is it called
- The Na+ concentration decreases as move down the cell body towards the axon hillock - Graded potential
- If by the time it gets to the axon hillock (where all the voltage gates ion channels are) the Na+ concentration is at threshold an AP will occur
27
graded potentials how different from action potentials and how does this affect action potentials
- signal dissipates into the cytoplasm so signal becomes less and less until reach axon hillock
-Usually takes multiple stimulus or different stimuli from different areas to generate an action potential at the action hillock therefore the graded potential is additive unlike an action potential
○ To add the two stimulus they must occur within a short time frame - Temporal summation
- To add two stimulus together from different area/pre-synaptic neurons they need to occur within a short time frame from one another - Spatial summation
28
acetylcholine what are the receptors called, the two types and what they do in terms of threshold
A cholinergic synapse
- Nicotinic
○ increases Na+ permeability, drives membrane closer to threshold
- Muscarinic
○ M1 decreases K+ permeability, drives membrane closer to threshold (e.g. exocrine glands)
○ M2 increases K+ permeability, drives membrane further from threshold (e.g. Heart)
29
what is the mechanism of botulinus toxin
Cuts up snare complex which allows neurotransmitters to be released stopping the propagation of AP across the synaptic cleft
As it is an enzyme it can cut up more than one snare complex and therefore move around the cell until it has cut up all the snare proteins
only way to overcome is to produce more SNARE proteins
30