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Cell Biology > Skeletal Muscle And AP > Flashcards

Skeletal Muscle And AP Flashcards

1
Q

What makes up a motor unit

A

A motor neurone attached to its muscle and all the muscle fibres that it stimulates

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2
Q

What do muscle fibres (cells) have

A

Mitochondria and many nuclei

They are formed by myofibrils

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3
Q

Explain the structure of myofibrils

A

Repeating units called sarcomere which have 2 filaments myosin and actin.

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4
Q

Explain all the zones and bands in a sarcomere

A

A band - all the filaments

M line - middle of the sarcomere filaments

I band - only thin actin

Z line - end of sarcomere

H zone - only thick myosin

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5
Q

What happens to muscle / sarcomere when contracted

A

The z lines become closer together due to muscle shortening

I and H zone shorten due to filaments sliding over

A band stays the same (filaments don’t shorten)

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6
Q

What is the purpose of m line

A

It holds thick myosin filaments together

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7
Q

Name the 3 components of actin

A

Actin tropomyosin and Troponin

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8
Q

What are actin molecules called when G actin forms long coils into helix (2 actin chains)

A

F actin - filamentous actin

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9
Q

Where does myosin bind to on actin

A

On g actin molecules

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10
Q

Explain the 3 subunits of troponin - called a trimer

A

T and I bind to actin and tropomyosin which prevents myosin binding at rest

C is where calcium binds and uncovers myosin binding site = contraction

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11
Q

What is summation in muscle

A

When the muscle has no time to relax after ap so the next ap is stronger = stronger twitch

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12
Q

What is recruitment

A

When additional motor units are fired due to a big stimulus which causes greater muscle contraction

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13
Q

Explain where the ap from the EPP hits first and explain structure around myofibrils / muscle fibres

A

The ap hits at the t tubules in the sarcolemma (cytoplasm)

The t tubules then allow the ap to reach the terminal cisternae (end of tubules) where the sarcoplasmic reticulum is

This causes ca2+ release from leak channels

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14
Q

What causes the release of Ca2+ from the SR in the terminal cisternae

A

A triad released from the t tubules which contacts to terminal cisternae and causes ca to be released

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15
Q

Explain the steps of excitation contraction coupling (sliding theory)

A

At rest the myosin sites are blocked by tropomyosin and actin bound to troponin

When ca2 released from SR reaches muscle it binds to troponin which allows myosin to bind to g actin = CROSS BRIDGE FORMED

Myosin becomes in a high energy state due to atp hydrolysis in its head. This causes heads to rotate and pulls actin = POWERSTROKE

ATP then binds again to the head which allows removal of the actin myosin bond (cross bridge)

The myosin later becomes into high energy state when ATP is hydrolysed and the cycle starts again

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16
Q

What is ATP job in excitation contraction coupling

A

ATP allows to break actin myosin bond
I
ATP hydrolysis needed for powerstroke

Needed to remove ca2+ back to SR via the ca ATPase pump (active transport)

17
Q

What is a cross bridge

A

When myosin binds to g actin molecules

18
Q

What is myosin in when atp is hydrolysed at the head before powerstroke

A

A high energy state

19
Q

Why do muscles contract after death

A

No atp so myosin stays attached to actin

20
Q

Explain the 3 components of the human nervous system (from the point of stimulus)

A

The sensory receptors are stimulated causing sensory input

Into the brain(CNS) inter neurones which decide a response

Then impulse sent to motor neurones and effector is stimulated

21
Q

Explain the structure of interneurones

A

A cell body and axon which many dendrites (dendritic tree)

22
Q

Which 2 neurones are multipolar (only 1 axon and many dendrites)

A

Motor neurone and interneurone

23
Q

Sensory neurones which are somatic eg touch receptors are pseudounipolar. What does this mean

A

The axon is split into 2 branches from the cell body

24
Q

Sensory neurones such as for smell and vision are different to somatic. They are bipolar what does this mean

A

They have 2 extensions from the cell body. 1 axon and 1 dendrite

25
Q

Explain transport within a neurone

A

When peptides are produced in cell body eg by rer the contents then are transported around in vesicles from Golgi body. They can then be exocytosed at the terminal

26
Q

How are Golgi vesicles in neurones transported

A

Through dynein and kinesin (like microtubules)

27
Q

What do all neurones have in common

A

All fire AP
Communicate via synapse
No cell division - longevity
Require a lot of o2 and glucose

28
Q

How do graded potentials differ from action potentials

A

Graded potentials vary in strength and get weaker after a short distance down neurones

29
Q

What do graded potentials do (if threshold reached at axon hillock)

A

They generate action potentials

30
Q

What is a graded potential

A

A postsynaptic electrical impulse (starting from when Na enters the postsynaptic neurone in synaptic transmission)

31
Q

What does the graded potentials size depend on

A

Size of stimulus

If big enough it can reach threshold at the post synaptic axon hillock to shoot an AP

32
Q

What is an excitatory Epsp and the 2 types of epsp (excitatory postsynaptic potential)

A

When Na+ is entering the cell and it depolarises it

A sub threshold epsp is one that doesn’t reach threshold

Suprathreshold epsp reaches threshold at axon due to stronger stimulus

33
Q

Post synaptic potentials can also be hyperpolarising for the neurone. How (Hpsp)- also called inhibitory

A

K leaves the cell through ligand Na channel which causes hyperpolarisation

Or Cl- can also enter cell through same Chanel and would decrease the electrical charge of neurone

This causes less likely ap (inhibitory)

34
Q

How does a neurone receive info on strength or duration of a stimulus if an ap follows the ‘all or nothing rule’?

A

The frequency of the APs are recorded. The bigger stimulus causes higher frequency (but not amplitude/size of ap)

35
Q

Why do stronger stimuli cause more frequent APs

A

More NTs are released causing more depolarisation

36
Q

Why is pre synaptic modulation more precise than post synaptic modulation

A

Pre synaptic mean you can add inhibitor or excitatory neurones to affect a specific target cell

Post synaptic modulation can affect any cell attached to the neurone being affected by summation

Cell Biology (21 decks)

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