Micro Muscle Anatomy And Physiology Flashcards
How motion is generated
Forces(muscle)- acting on levers(bones) - about axes(joints)
Skeletal muscle provides the force for motion (torque to occur)
Muscles must convert chemical energy into mechanical work
Types of Human muscle tissue
Smooth muscle
Cardiac muscle
Skeletal muscle
Smooth muscle
Involuntary
Blood vessels and organs
Slow, uniform motion
Fatigue resistant
Ex. Eye iris and digestive tract muscles
Cardiac muscle
Involuntary
Muscles of th heart
Self generating impulses
Features both smooth and skeletal muscle tissue
Very fatigue resistant
Skeletal muscle
voluntary
Connects to bony segments via tendons
Repeated contractions may lead to fatigue
Striated
Anatomy of skeletal muscle
Connective tissue, compromised mainly of the protein collagen
Surrounds all muscle fibre bundles
It is continuous with, and part of the tendons that join muscle to bone
Sometimes the “tendon” is in the form of broad sheets called fassia
Macro to micro: muscle
Muscle
Fascicle
Muscle cell (muscle fibre)
Myofibril
Myofilaments
What is a Muscle cell/muscle fibre
A single cell is the diameter of a thin human hair
Maximum length is 12 cm
Multi-nucleated cylindrical cell
Myocyte
Sarcolemma
Muscle Cell membrane
Sarcoplasm
Cytoplasm
Sacromere
Functional unit (contractile unit) of a muscle fibre
Myofibrils
Made up of contractile proteins
Actin and myosin
Makes up muscles fibres ( a bunch of them together)
Actin
Thin filaments
Forms the framework and slides over (outside)
Myosin
Thick filaments in the middle
Fibrous protein that makes up contractile filaments of muscle cells
Sacroplasmic reticulum
Net like labryinth of tubules inside fiber
T (transverse) tubules
Connects sarcoplasmic reticulum with outer membrane (Sarcolemma)
Mechanical movement required for contraction (sliding filament theory)
Myosin heads (cross bridges) grabs actin, actin slides across myosin causing contraction of the Sacromere unit and thus muscle contraction
(Person climbing tree)
A muscle contracting (sarcomeres)
Many sarcomeres (actin sliding over the myosin)
What changes length in a muscle
Sarcomere units
Sarcomere unit
Myosin and actin (myofilaments)
Muscle contraction ?
Muscles can shorten, stay the same length or enlarge
Isometric state
When muscle force equals the load, the muscles will not change in length
Eccentric state
When muscle force is less than the load, the muscle will lengthen
Ex. Moving heel away from the buttocks is an example of eccentric contraction of the hamstring
Has the greatest force
Concentric state
Classic muscle function
When muscle force exceeds the load, the muscle will shorten
Ex. Moving heel closer to the buttocks is an example of concentric contraction of the hamstring
What contraction state produces the greatest force
Eccentric- greatest force production
Isometric- 2nd greatest force
Concentric state- least force production
Other factors that influence the force of muscle contractions
- The individuals state of health
- The individuals training status
- Joint angle and (coordination of movement)
- Muscle cross-sectional area
- Speed o movement
- Muscle fibre type
- Age
- Sex (male/female)
Joint angle
the type of contraction and the force required to resist an external load as the joint angle changes
-the contraction type and force required depend on wether the external force exceeds, or is less than, the internal (applied) force
-static (isometric) and dynamic (concentric and eccentric) contractions may all be required
-coordination between agonists and antagonists muscle is required
Joint angle and length relationship
maximal force is produced at a joint angle that corresponds to maximal cross-bridge interaction (where is it hardest to lift) ex. Bicep curl, most difficult at the beginning; length tension as you reach 90 the force increases; once you pass 90 the force goes back down, actin has nowhere left to slide
Joint angle (length tension relationship )
A- too far apart fewer cross-bridges can form =less force produced
B- optimal distance apart, maximal cross-bridge formation = maximal force production
C- too close together, cross-bridges overlap= less force production
-maximal force is produced at a joint angle that corresponds to maximal cross-bridge interaction
*reference photo
Muscle cross-sectional area MSCA
1000s of sarcomeres in a muscle fiber; 1000s of muscle fibres in muscle
-body mass is positively correlated with strength, provided that mass is muscle tissue or lean mass
-the larger the muscle cross sectional area the more force it can generate
- the heaviest weights of all are lifted by athletes in the super-heavyweight category
Speed and force ( force-velocity relationship)
Force-velocity relationship: with classic muscle contractions (concentric), as speed of movement increase, then force a muscle can generate decreases (the higher the force you try to produce, the slower it will be)
Why?
-cross bridges are compromised since they cannot couple and uncouple fast enough (myosin heads attaching to the actin filaments)
Muscle fibre types: type 1
slow twitch: the greater the slow-twitch fibre intent of a muscle
-the lower the force-producing capacity
-the slower the contraction speed
-the greater the endurance characteristics of the muscle (energizer bunny)
(Distance athletes have high type one)
Muscle fibre type: type 2
Type 2- fast twitch : the greater the fast-twitch muscle fibre content of a muscle
-the greater the force outpost
-the greater the overall speed of contraction: the nerve feeding a fast-twice higher fibre is thicker=information travels faster
-the greater the fatiguability will be
*fast-twitch fibres are larger, which means there are more sarcomeres = more force
(Sprinters have high type two)
No sex differences for type 2 and type 1 distribution
How AGE effects muscles
-aging affects muscle force output
-there is a loss of fast-twitch fibres associated with aging
-may occur as a result of apoptosis (cell death)
-may occur as a result of diffuse
-sarcopenia is the medical term that described muscle loss
Sex (male vs. female) effects muscles
-the absolute capacity of a female is often less than that of a male
-however there is not much difference between males and female when force and power data are normalized to selected anatomical variables
-the differences between males and females is mainly due to differences that exist in muscle volume
What initiates muscle contractions
The nervous system
-neural impulse are electrical currents that pass along fibres to the muscle (like a light switch)
-also called action potential
-the brain delivers electricity to the muscle to turn on/contract (excitation)
Nervous system ( muscle contractions)
each “motor” nerve innervates (turns on) many muscle fibres and is called a motor unit (one nerve and many fibres)
Motor nerves = motorneurons
Slow twitch motor neurons
-small in diameter
-110 milliseconds to reach peak
-fatigue resistance
-innervates approx. 100 slow twitch muscle fibres
Fast twitch motor neurons
-large in diameter
-50 milliseconds to reach peak
-fatigue quickly
-innervates approx. 500 fast twitch muscle fibres
-therefore generates greater force than slow twitch
How action potential travels
Impulses cross gaps (synapses) between adjoining nerves
-impulses cross gap (motor end plate) to innervates muscle
-both gaps crossed using neurotransmitter, acetylcholine (Ach)
Impulse arrives at neuro-muscular junction (motor endplate)NMJ
Crosses over the synaptic cleft with the aid of acetylcholine
Impulse travels over Sarcolemma, through the t-tubules; causing calcium to be released from storage in sarcoplasmic reticulum
The release of calcium causes molecular cross bridging of actin and myosin
Absence of neural impulse
In the absence of a neural impulse, the calcium is reabsorbed into sarcoplasmic reticulum thus stopping the contraction
Review: muscle contraction
- Impulse arrives at the NMJ (neuromuscular junction)
- Impulse travels over Sarcolemma
- Calcium is released from the SR (sarcoplasmic reticulum)
- Cross bridges form
- Muscle contracts
Volitional contraction (efferent impulse) travelling via…
Pyramidal tract
Reflexive contraction (afferent impulse) travelling via…
Posterior column
Particularly kinaesthetic feedback (2 types)
Vestibular ( semi circular canals)
Proprioceptors ( muscle/joints)
