Physiology of muscles Flashcards
Sarcomere structure
- Z line
- I band
- A band
- H zone
- M line
Sarcomere= the region between 2 Z lines
Z band
- In the middle of I band. Anchors actin filaments and is connected to myosin via titin.
I band (Light band) - Consists of actin filaments only
A band (Dark band) - Consists of actin and myosin filaments
H zone
- Zone in the middle of sarcomere, composed of only myosin
M line
- Middle of H zone
Myofibril
Myocyte. Protein filaments composed of:
- Actin
- Myosin
- Titin
And others
Myofilaments
Components of myofibrils. Primary actin and myosin
Myofilaments repeat in myofibrils to form sarcomeres.
Force generation in sarcomere
Optimal sarcomere length is required for greatest force generation during a power stroke.
When the sarcomere is too short
- Actin filaments collide, low force generated
When the sarcomere is too long
- Actin and myosin cannot bind effectively enough= low force
Cross bridge cyclin
- Myosin releases actin: Occurs when ATP binds to myosin head.
- Myosin head cleaves ATP= ADP+ Pi made. This cocks myosin head.
- Myosin head binds to actin in the presence of Ca2+
- 4Ca2+ binds to Troponin C to move tropomyosin from actin binding site. - Power stroke= Release ADP + Pi.
Creatine phosphate
Energy storage in muscles
- Source of Pi for ATP synthesis
Creatine kinase/ phosphokinase (CK, CPK)
- Mechanism
- Diagnosis
Catalyses the conversion of creatine to creatine phosphate (and vice versa).
Mitochondrial CK= produces Creatine phosphate
Myofibrillar CK= produces ATP (release Pi from creatine phosphate)
Diagnosis
- When elevated= marker for muscle destruction.
Troponin C
Section of troponin where Ca2+ binds to. (4Ca in muscle, 3Ca in heart)
- Causes confirmational change which moves tropomyosin
Movement of tropomyosin reveals binding site for myosin to bind to actin
Markers for muscle breakdown
Total Troponin I (TNI)
Cardiac TNI = MI marker
Ryanodine receptors
Located in the plasma membrane of myocyte’s sarcoplasmic reticulum.
Allows efflux of calcium after stimulation from depolarisation via T tubules.
SERCA channel
Located in the membrane ER in myocytes.
Sequestrates Ca2+ back into ER, using ATP.
Rigor mortis mechanism
3rd stage of death that occurs a couple hours after death.
Due to no more ATP produced:
- Myosin cannot release actin, as it requires ATP.
- SERCA cannot sequester Ca2+ back into ER
= Causes constant contraction of sarcomere, stiffens limbs
Wears off a few days later when muscles starts to degenerate.
Tetany
Summation of contraction,- As a result of continuous stimulation from APs
- Muscle is unable to relax due to insufficient Ca2+ sequestration.
Slow twitch fibres
- Colour
- Oxygen
- Size
- Fibre type
- Other features
Red, oxidative, small fibres (in diameter)
Type 1, slow twitch
Contains high numbers of myoglobin and mitochondria
Fast twitch fibres
- Colour
- Oxygen
- Size
- Fibre type
- Other features
White, non-oxidative, large fibres
- Main source of energy is from glycolysis
Type 2
Lower levels of myoglobin
Use= fast, precise movements (i.e eye and hand muscles.)
Compare slow and fast twitch fibres:
- Respiration
- Calcium reuptake speed
- Tension produced
- Fatigue resistance
Respiration
- Slow= aerobic
- Fast= anaerobic
Calcium reuptake speed
- Fast twitch do it much faster than slow twitch
Tension produced
- Fast= maximum tension, slow= lower tension
Fatigue resistance
- Fast= lower than slow fibres.
Soleus muscle fibres
Mainly slow fibres as it is a postural muscle (walking)
- 80% type 1
- 20% type 2a
Vastus lateralis fibres
Quadriceps muscle:
- Mixture of Type 1, 2a, 2x
Motor unit
A single alpha motor neuron and the muscle fibres it innervates
- All the same type of fibres.
Isometric contraction
Variable change in force generation whilst muscle length is unchanged
- Joint angle remains the same
Generates enough force to overcome resistance before isotonic contraction
Isometric contraction example
Initiate stage of picking up a glass
- Biceps and brachiradialis generate force enough to eventually move the forearm at elbow.
As contraction occurs, more motor units are recruited (recruitment)
- The recruited fibres are progressively larger
Isotonic contraction
Change in muscle length as constant force is generated.
Joint angle is changed
Example
- Bringing the glass of water to mouth. Force generated must be constant unless it would smash you in the face
Concentric contraction
Force during contraction
- i.e taking off in long jump
Eccentric contraction
Force during muscle elongation
- i.e landing in long jump
Stretch reflex
Function: for posture and balance
Sensory organ: Intrafusal spindle fibres, changes length of muscle according to stretch.
Example: Patellar reflex
Patella reflex
A type of stretch reflex
- Monosynaptic
- Ipisilateral
- Spinal
Gamma motor neurone
A lower motor neurone
- Adjusts sensitivity of muscle spindles
- Keeps the spindles taut.
Tendon reflex
Function: Protects from overloading of muscle by decreasing force generated.
Sensory organ: Golgi tendon organ
- In series with muscle fibres, detects tension in muscle.
Example: Golgi tendon reflex
Golgi tendon reflex
Changes the force generated in muscle, when there is overloading.
- Ipisilateral
- Disynaptic
- Spinal
Golgi tendon detects change in tension for muscle= stimulates inhibitory neurone
- Motor neurone is inhibited= less contraction of muscle
Westphal sign
Absent/ Decreased Knee jerk reflex
Causes:
- Receptor damage
- Femoral nerve damage
- Peripheral nerve disease
