Title: Physiology 2130 / Module 5: Muscles

Q: The 3 types of muscle cells are [...], [...] and [...] muscle.
A: skeletal; smooth; cardiac

Smooth muscle is found within the walls of blood vessels, airways, the bladder, digestive tract and uterus.

Q: Skeletal muscle is used for [...] motion.
A: voluntary

Q: The 3 principle functions of muslces are:
1. [...]
2. [...]
3. [...]
A: Movement; Heat Production; Body Support & Posture

Q: Whole muscles are made up of bundles of [...].
A: fasciculi

Q: Fascicles are made up of bundles of elongated [...].
A: muscle cells

Q: Muscle cells are made up of bundles of [...].
A: myofibrils

Q: Myofibrils contain [...] and [...].
A: thin; thick myofilaments

Q: [...], [...] and [...] make up thin myofilaments.
A: Actin; troponin; tropomyosin

Q: Thick myofilaments are made of [...].
A: myosin

Q: The interaciton of [...] and [...] results in muscle contractions.
A: thin; thick myofilaments

Q: Fasciculi are surrounded by a white connective tissue called [...].
A: perimysium
Extra: Each fascicle, in turn, is made up of bundles of muscle cells (aka. Muscle fibers). Within each cell there are cylindrical bundles of myofibrils. These myofibrils are composed of 2 types of myofilaments, which are the actual contractile elements of the cell.

Q: Muscle cells/fibers have more than one [...].
A: nucleus

Q: The muscle cell membrane is the [...].
A: sarcolemma

Q: The sarcolemma is the surface which [...] are transmitted.
A: action potentials

Q: Transverse (T) tubules are small tube-like [...] on the [...] that extend down into the cell.
A: projections; sarcolemma
Extra: These T tubules conduct the AP deep into the cell where the contractile proteins are located.

Q: [...] extend down into the cell and conduct action potentials deep into the cell where the contractile proteins are located.
A: Transverse (T) tubules

Q: The [...] and [...] are contractile proteins.
A: thin; thick myofilaments

Q: Myofibrils are surrounded by the [...].
A: sarcoplasmic reticulum

Q: The sarcoplasmic reticulum is a mesh-like network of [...] that contain [...].
A: tubes; Ca++ ions

Q: The [...] is at either end of the SR.
A: terminal cisternae

Q: The terminal cisternae is a [...] enlargement of the SR next to the [...].
A: membranous; T-tubule

Header: Label the part of the muscle:

Header: Label the part of the muscle fiber:

Q: Actin is a [...] protein that makes up [...] myofilaments.
A: globular; thin

Q: [...] has a special binding site for the other contractile protein, myosin.
A: Actin

Q: The 3 subunits of troponin are troponin [...],[...] and [...].
A: A; T; C

Q: Within the thin myofilament structure, [...] binds to actin.
A: troponin A

Q: Tropomyosin [...] the myosin binding sites when the muslce is at rest.
A: covers

Q: Within the thin myofilament structure, troponin T binds to [...].
A: tropomyosin

Q: Within the thin myofilament structure, [...] binds to Ca++.
A: troponin C

Q: When the muscle is at rest, the troponin complex holds the [...] over the myosin binding site.
A: tropomyosin

Header: Label the part of the thin myofilament:

Q: The thick myofilament is made of [...].
A: myosin

Q: Myosin has 2 [...] that can attach to myosin binding sites, and a long, bendable [...].
A: head groups; tail

Q: Myosin head groups have [...] and [...] binding sites.
A: ATP; actin

Q: Splitting of ATP by the myosin head powers [...]
A: muscle contractions

Q: Thin and thick myofilaments are arranged in an [...] pattern along the length of the [...].
A: alternating; myofibril

Q: Thin myofilaments are anchored to the [...] and extend outward in opposite directions from it.
A: Z-disk

Q: Thick myofilaments extend outward from the [...].
A: M line

Q: A [...] is the region from one Z disk to another.
A: sarcomere

Q: The sarcomere is the smallest functional [...] unit of the muscle cell.
A: contractile

Q: Myofilaments extend [...] to the length of the [...].
A: parallel; myofibril

Q: Areas with only thick filaments are called [...] and appear [...].
A: A bands; dark

Q: Areas with only [...] are called I bands and appear lighter.
A: thin filaments

Q: The striated appearance of the muscle is due to the repeating pattern of [...] and [...].
A: thin; thick myofilaments

Q: [...] Theory describes how muscle contractions occur.
A: Sliding Filament

Q: When the head of a myosin molecule attaches to the binding site on actin a [...] is formed.
A: crossbridge

Q: After the crossbridge is formed, myosin undergoes a [...] change which results in a [...].
A: conformational; powerstroke

Q: A powerstroke is the [...] motion of the [...].
A: swinging; myosin head

The powerstroke slides actin (thin) past the myosin (thick) which causes the sarcomeres to shorten and Z disks move closer together.

Q: [...] is the process which an action potential in the sarcolemma excites the muscle cell to produce a contraction.
A: Excitation-contraction coupling

Describe the Excitation-Contraction Coupling Process of muscle contraction:
1. Action potentials are generated in the NMJ and spread over the sarcolemma then down the T-tubules to the core of the muscle cell.
2. The action potential travels very close to the SR and opens Ca++ channels, which releases Ca++ from the terminal cisternae.
3. The Ca++ binds to troponin C which causes tropomyosin to uncover the myosin binding site.
4. Myosin attaches and a powerstroke occurs.

For muscle relaxation to occur:
1. Action potentials stop, which stop Ca++ from diffusing;
2. Ca++ pumps will pump Ca++ back into the sarcoplasmic reticulum, up its concentration gradient;
3. With Ca++ gone from the cytoplasm, tropomyosin will cover the myosin binding site;
4. Myosin will be unable to bind to actin, and powerstrokes will not occur, resulting in the muscle relaxing.

The Actin-Myosin and ATP cycle:
1. ATP attached to myosin is split, prepares it for activity;
2. Once Ca++ is bound to troponin C, formation of crossbridges can occur since tropomyosin has been moved from the binding site;
3.Powerstroke occurs while the myosin head bends and slides the thin filament over the thick filament. ADP and Pi are released from the myosin head;
4. A new molecule of ATP binds to the myosin head.

Q: Rigor mortis occurs [...] hrs after death. The muscles are very stiff for about [...] hrs.
A: 3-4; 12

Q: When the (muscle) cells are dead they no longer release ATP, but the SR degrades and releases Ca++ leaving myosin and actin stuck bound to each other until degradation of the linkage, this produces something that is known as [...].
A: rigor mortis
Extra: ATP = Energy
SR = Sarcoplasmic Reticulum

Q: Muscles can alter the force of contraction by [...] or through the [...].
A: recruiting motor units; summation of twitch contractions

Q: A motor unit is a [...] and all of the the [...] it causes to contract.
A: motor neuron; muscle/cell fibres

Q: 1 motor neuron contacts [...] muscle cells, but 1 muscle cell can only be contacted by [...] motor neuron.
A: many; 1

Q: A [...] motor unit contacts a large number of muscle cells.
A [...] motor unit contacts a few muscle cells.
A: large; small

Q: [...] is the progressive activation of motor units which results in a more forceful contraction.
A: Motor Unit Recruitment

Q: A [...] is the simplest and smallest muscle contraction.
A: muscle twitch
Extra: This is the result of 1 AP in the motor neuron. This single AP will excite the muscle cell & causes the release of enough Ca++ from the SR in order to cause a very small contraction of the muscle. The duration of the twitch is short but can vary from 10 to 100 milliseconds (ms).

Q: One muscle twitch is a result of a [...].
A: single action potential

Q: The latent period is the time difference between when the muscle [...] and when the [...] occured.
A: contracted; action potential

The latent period is caused by events at the NMJ, the genration of the action potential at the muscle and interaction between thin and thick myofilaments.

Q: Twitches can be added because it is a [...] event that relies on [...] interaction.
A: mechanical; protein

Q: Increasing the number of action potentials per second increases the [...] and therefore increases the [...],
A: frequency; force of muscle contraction

Q: At high frequencies a [...] is produced.
A: maximal tetanic contraction

As voltage increases, muscle contractions get stronger due to motor unit recruitment.
As frequency increases, muscle contractions get stronger due to  twitch summation.