Phsiology Of Muscle

Question 1

muscle

Answer 1

• A bundle of fibrous tissue that can contract to producing movement

Striated (skeletal) muscle - locomotion and posture
Smooth muscle - peristalsis
Cardiac muscle - heart

Voluntary or involuntary

Question 2

Terminology

Answer 2

• Contraction
• Elasticity
• Hypertrophy
• Hyperplasia

Question 3

Structure of a skeletal muscle

Answer 3

• Tendon
• Epimysium -muscle
• Perimysium -fascicle
• Endomysium - fiber

Question 4

Structure of a skeletal muscle fiber

Answer 4

Fused cells - multinucleated and filled with myofibrils
• Filled with myofibrils - 3 long proteins• Sarcolemma
• •
plasma membrane • Sarcoplasm
cytoplasm
• Sarcoplasmic reticulum (SR)
• •
smooth endoplasmic reticulum • Transverse tubular system (TT)
Invaginations of sarcolemma • Triad
•
Terminal cisterna of SR and TT in close proximity

Question 5

The Sarcomere

Answer 5

• Unit of contraction of the myofibril
• Z-line
• Either end of the sarcomere • Thin filaments insertion
• M-line
• Origin of thick filaments
• A-band
• Overlap of thick and thin
filaments
• I-band
• Only thin filaments

Question 6

Myosin

Answer 6

Protein
Thick filament
Has two heads
Has a hinge to allow it to move

Thick filament
• Multiple myosin molecules • Head
• Actin binding • Tail
• 2 intertwined heavy chains • 2 regulatory light chains
• ATPase activity
• 2 alkali light chains
• Stabilize myosin head
• Hinge
• Movement of myosin head

Question 7

Actin

Answer 7

Protein
Thin filament

Thin filament
• Actin
• Binding site for actin
• Tropomyosin
• Block myosin receptors
• Troponin
• Controls Tropomyosin position

Question 8

Excitation-contraction coupling

Answer 8

Plasma membrane invaginates into transverse tubules (T tubules)
Along T tubule length is associated 2 cisternae of sarcoplasmic reticulum
Sarcoplasmic reticulum acts as storage organelle for Ca2+
T tubule and 2 cisternae referred to as Triad

Question 9

Initiating contaction

Answer 9

Motor neuron releases acetal choline

Question 10

Calcium release into sarcoplasm

Answer 10

Action potential activates T tubule voltage gated l-type ca++ channel
Couple with ryanodine receptors on sarcoplasmic reticulum
Opens channels to release ca++
…

Question 11

Initiation of cross-bridge cycling

Answer 11

Initiation of cross-bridge cycling
Ca2+ modulates contraction through regulatory proteins rather than direct interaction with actin and myosin
3 troponin molecules
• • •
C: binds Ca2+
I: anchors complex to actin
T: binds to tropomyosin
Tropomyosin blocks myosin binding site
Troponin C
• binding of Ca2+ to the high affinity sites causes conformational change in troponin complex
Troponin I moves away from actin filament
Troponin T pushes tropomyosin away from myosin binding site on actin
Myosin head binds to actin

Question 12

The cross-bridge cycle in skeletal muscle

Answer 12

The cross-bridge cycle in skeletal muscle
• Cross-bridge cycle occurs in 5 stages
• Initially myosin head attached to actin filament after “power stroke” from previous cycle – can remain in this state for an indefinitely long period, as occurs in rigor mortis
• Step 1 – ATP binding
• Step 2 – ATP hydrolysis
• Step 3 – cross-bridge formation
Step 4 – release of Pi from myosin
• Step 5 – ADP release

Question 13

Terminating Contraction

Answer 13

Ca2+ must be removed from the cytoplasm for contraction to cease and relaxation to occur
Minor:
-Na-Ca exchanger (NCX)
-Ca pump at plasma membrane (PMCA)
Major:
-Ca reuptake into SR by SERCA-type Ca pump

Calsequestrin major Ca-binding protein in skeletal muscle
Located predominantly at triad junction

Question 14

Whole muscle force generation

Answer 14

-Muscle force can be determined by number of individual muscle fibres stimulated at a given time
-Multiple-fibre summation (or spatial summation)

Amount of force generated depends on:
• Number of active muscle fibres
• Cross-sectional area of muscle
• Initial resting length of muscle
• Rate at which muscle shortens
• Frequency of stimulation

Question 15

Isometric verses Isotonic contraction

Answer 15

Isometric contraction
• Muscle length fixed, stimulation of muscle will cause increase in tension but no shortening
• Try holding a weight in your hand with your arm outstretched, you will feel that the muscle is working without changing length

Isotonic contraction
• Muscle length not fixed. Stimulation of muscle will cause muscle shortening provided tension generated is greater than opposing load
• Try holding a weight in your hand and lifting and lowering your hand, bending at the elbow.

Question 16

Length-tension relationship

Answer 16

Muscle can be stretched

Tension measured before muscle contraction is referred to as passive tension- elasticity

At any fixed length if muscle is contracted an additional active tension develops due to cross- bridge formation

Length-tension relationship is direct result of the anatomy of the thick and thin filaments within individual sarcomeres

Question 17

Force-Length relationship

Answer 17

• Muscles are elastic due to titin
• Muscles are held at resting length
• Maximal tension produced when thick and thin filaments overlap between 80-120%

Question 18

Force-velocity relationship

Answer 18

• Speed of change in length
• Power = force X velocity
• As velocity increases force decreases
• At maximum power is generated at approximately 1/3 shortening velocity

Question 19

Summation in single muscle fibres

Answer 19

One action potential (AP) will lead to a single skeletal muscle twitch (last from 25 – 200 msec)
As muscle twitch far exceeds duration of AP it is possible to initiate a second AP before 1st contraction has subsided
This is summation

Question 20

Different muscle fibers

Answer 20

Slow and fast
Type 1
Type IIa
Type IIb

SAME AS PE A LEVEL