L72- Muscles

Question 1

what are the different types of muscles?

Answer 1

• skeletal muscle
• controlling skeletal muscle
• smooth muscle

Question 2

what are the 5 functions of the skeletal muscle?

Answer 2

• Movement: attach to bones to allow us to move
• Posture: muscle tension holds our skeleton in place eg head
• Soft tissue support: abdominal wall supports internal organs
• Guards entrance/exits: digestive and urinary tract are controlled by voluntary muscles for control
• Maintains body temperature: contractions use energy and produce heat

Question 3

why is the sarcoplasmic reticule important in muscles?

Answer 3

plays a role in storing Ca2+ required for contraction

Question 4

what are transverse tubules?

Answer 4

are continuations of the plasma membrane (the sarcolemma) which dip into the cell and allow effective propagation of an action potential

Question 5

what is a muscle made from?

Answer 5

unit of fibres

Question 6

what is myosin?

Answer 6

Myosin is a protein which makes up thick .Heads make up myosin cross-bridges – sites of attachment to thin actin filaments (actin binding site). Myosin head binds ATP and acts as an ATPase

Question 7

what is actin?

Answer 7

makes up the thin filament, I is globular.

Question 8

what is tropomyosin?

Answer 8

is a thread-like molecule that lies next to actin molecules.

• controls access to the cross-bridge binding sites - held in place by the troponin complex
• movement is regulated by calcium

Question 9

what is troponin?

Answer 9

3 polypeptide units that bind to actin, tropomyosin and calcium

Question 10

what is the neuromuscular junction?

Answer 10

is a specialised synapse between an α-motor neuron and a skeletal muscle fibre at the motor end plate

Question 11

what are the properties of a-motors?

Answer 11

neurons are fast, myelinated neurons

Question 12

what happens during contraption( power stroke)?

Answer 12

• myosin cross bridge attaches to the acts myofilament.
• myosin head pivots and bends as I pulls on he actin filament sliding it toward the M line.
• As new ATP ATTACHES TO THE MYOSIN HEAD THE CROSS BRIDGES DETACHES.
• as ATP is split into ADP and Pi cocking of the myosin head occurs.

Question 13

what is the Z lines?

Answer 13

the 2 ends of the sarcomere.

Question 14

what is the M line?

Answer 14

the centre line

Question 15

what is the H band?

Answer 15

space between the 2 myosin molecules in the middle

Question 16

what is the I band?

Answer 16

the space between the z line and the myosin filament at the ends

Question 17

what is the sliding filament theory of contraction?

Answer 17

• increase in ca+ starts sliding filament
• as sliding happens z lines pull closer, sarcomere shortens
• decrease in ca+turns off sliding

Question 18

how is relaxation of muscles controlled?

Answer 18

by reducing Ca2+, removed from cytoplasm
• Also need to remove ACh from the Neuromuscluar Junction – enzyme-mediated breakdown by acetylcholinesterases
• Once the stimulation is removed there is no action potential

Question 19

how does the whole muscle contraction happen?

Answer 19

• acetylcholine released by axon crosses cleft binds to receptor.
• action potential generated on response moves down T tubules of muscle cell.
• this riggers Ca2+ released from sarcoplamic reticulum
• Ca2+bind to tropomyosin and move it to uncover cross bridge binding sire on actin.
• mysin cross bridge attaches to actin this pulls actin towards centre of sarcomere engird from ATP.
• Ca2+ taken up by sarcoplasmic reticulum when no local action potential
• with no Ca2+bound to troponin, tropomyosin slips back to blocking the binding site, and actin slides back to resting potential.

Question 20

what are the major groups of smooth muscle?

Answer 20

• vascular
• gastrointestinal
• urinary
• respiratory
• reproductive
• ocular

Question 21

where are smooth muscles found ?

Answer 21

in walls of hollow organs and tubes

Question 22

what don’t smooth muscles have that controlling muscles do?

Answer 22

• Smooth muscle is not striated, no myofibrils, no
sarcomeres
• Fewer mitochondria
• Contract and relax slower

Question 23

how does smooth muscles work?

Answer 23

• Increase in [Ca2+]i can be generated via ion channels or receptors or release from sarcoplasmic reticulum
• Ca2+ signals through Ca2+-binding proteins such as calmodulin
• Binds 4 calcium ions and then activates further target proteins – e.g. MLCK

Question 24

what does removal of Ca2+ do to smooth muscles?

Answer 24

inactivates MLCK myosin light chain kinase

Question 25

hows does smooth muscle contraption happen?

Answer 25

• Ca2+ increases and enters cell via t tubes released from SR.
• Ca2+ binds to calmodulin (CaM).
• Ca2+- calmodulin activates myosin light chain kinase
• MLCK phosphorylates light chain in myosin heads and increases myosin ATPase activity.
• active myosin cross bridges slide along actin and create muscle tensions.