Muscles Flashcards
How many muscles and joints are there in the body?
650 muscles
187 joints
Primary tissue is divided into 3 types
Name them-
Cardiac muscle - responsible for circulating blood. Small cells, limited repair ability. Involuntary contractions . Each cell has one nucleus
Skeletal muscle- multinucleated. Larger cells (up to 30cm long) can partially repair themselves. Voluntary contractions
Smooth muscle- found in organ walls eg intestines. One nucleus per cell. Has ability to repair itself if it sustains damage. Involuntary contraction
Functions of muscle tissue -
Produces body movement and stabilises body position
Regulates organ volumes - bands of smooth muscle called sphincters - relax to allow release eg within bowel
Movement of substances within body - blood,lymph,urine,air,food and fluids, sperm
Produces heat - involuntary contractions of skeletal muscle (shivering)
What should patients struggling with substance movement do ? Eg venous return from lower leg -
Eg struggle with venous return from lower leg should be encouraged to get.muscles working to aid this. Plantar and Doris flexion of the ankle - muscles contract, increase pressure and aid venous return.
Feet elevation and compression garments are also effective.
Properties of muscle tissue
Excitability -
Conductivity -
Contractivity -
Excitability - responds to chemicals released from nerve cells
Conductivity - ability to propagate electrical signals over membrane
Contractivity - ability to shorten and generate force
Properties of muscle tissue
Extensibility -
Elasticity -
Extensibility - to be selected without damaging the tissue
Elasticity - ability to return to original shape after being stretched
Properties of skeletal muscle tissue:
And how it appears under microscope:
Attaches to bone/skin/fascia, maybe via tendons/aponeurones
Striated with light and dark bands visible with a microscope
Voluntary contraction and relaxation control
Cells are formed from multiple myoblasts, they fuse together and are therefore multinucleated
Functions of skeletal muscle -
Produce Skeletal movement
Maintain body position
Support soft/hard tissues
Guard body openings
Maintain body temperature
Stores nutrient reserves
Proprioception
Skeletal muscle structures
Layers: 1) epimysium -
Outer layer that surrounds the whole muscle
Dense irregular connective tissue
Exterior collagen layer so is therefore not elastic
Connected to deep fascia
Separates muscle from surrounding tissues
Skeletal muscle structures
Connective tissue layers: 2)perimysium:
Middle layer that surrounds fasciculus (find muscle fibres/cells within this)
More elastic than the outer layer as contains elastin as well as collagen
Contains blood vessels and never supply to fascicles
Skeletal muscle structures
Connective tissue layers: 3) endomysium:
Inner layer that surrounds muscle fibres (individual muscle cells) within fascicles
High proportion of elastic fibres which loosely connects them
Contains capillaries and nerve fibres contacting muscle cells
Contains satellite cells (stem cells) that repair any damage
Skeletal muscle:
Describe how connective tissue muscle attach to structures:
All 3 layers that make up the CT come together at the ends of muscles to form connective tissue attachment to bone matrix
Eg tendon (bundle) - transfers force muscle to bone
Apeneurosis (sheet) - broader attachment
Skeletal muscle structures
Nerves: where are they found, functions etc…
In perimysium and endomysium
Nerves control voluntary contractions. Messages from CNS reach muscle tissue via peripheral nerve
Collection of muscle cells are supplies by a motor neurone
One motor nerve and the muscle fibres it supplies = motor unit!!
Each muscle cell supplied by a terminal branch of a motor neurone
Skeletal muscle structures
Blood vessels: functions and muscle contact with them etc..
Muscles have extensive vascular systems that:
Supply large amounts of o2
Supply nutrients
And carry away waste products eg. Co2 h2o ADP
Each muscle cell is in contact with 1 or 2 capillaries
Nerve fibres and capillaries are found in the endomysium between individual cells
Skeletal muscle structures
Muscle tissue (cells/fibres): structure and shape etc..
Long and cylindrical
Develop through mesodermal cell fusion (myoblasts)
Become very large
Contain hundreds of nuclei that are arranged around periphery of cell
Contain many mitochondria
Organisation of skeletal muscle fibres
- the sarcolemma:
The cell membrane of the cell
Surrounds sarcoplasm
Sarcoplasm filled with tiny threads called myofibrils and myoglobin
Contractions begin when there is a change in transmembrane potential
Organisation of skeletal muscle fibres
-Transverse (T) tubules
T tubules are invaginations of the sarcolemma into he centre of the cell
Filled with extracellular fluid
Carry muscle AP’s down into cell
Allow entire muscle fibre to contract simultaneously
Mitochondria lie in rows throughout the cell - near muscle
Proteins present that use ATP during contraction
Organisation of skeletal muscle fibres
- sarcoplasmic reticulum (SR)
A membrane structure surrounding each myofibril
System of tubular sacs similar to smooth endoplasmic reticulum in non-muscle cells
Helps transmit AP’s to the myofibril
Forms chambers at each end (terminal cisternae) attached to the-tubules
Chambers store calcium, when released, contraction begins
Skeletal muscle structures
What is a triad and its benefit ?
One T-tubule and two terminal cisternae make up a triad
Calcium in high conc via ion pumps and allow this to be maintained
Release calcium into sarcomeres to begin muscle contraction
Skeletal muscle fibre organisation
Myofibrils and myofilaments -
Each muscle fibre can have hundreds/thousands of myofibrils depending on size
Muscle fibres filled with threads called myofibrils separated by SR (sarcoplasmic reticulum)
Myofibrils made up of bundles of protein filaments = myofilaments
Myofilaments are the contractile proteins of a muscle (thick and thin myofilaments)
Actin = thin
Myosin = thick
Myofilaments and the sarcomere
** look over the diagram for sarcomere contraction, have to be able to recognise and identify elements ***
What bands contain what filaments ?
Thick and thin filaments overlap eachother in a pattern that creates striations (alternating light I bands and dark A bands)
I band - contains only thin filaments (actin)
A band- contains thick filaments (myosin)
H zone and M zone only have thick filaments
Filaments arranged in compartments which makes up the sarcomere, and separated by Z discs
Name the proteins of a muscle and their 3 actions:
Contractile proteins (myofilaments) - myosin and actin
Regulatory proteins - turn contractions on and off = trooping and tropomyosin
Structural proteins - provide proper alignment, elasticity and extensibility = titin (important one) myomesin, nebulin and dystrophin
Proteins of a muscle
Myosin -
Thick filaments
Each molecule resembles two golf clubs twisted together
Myosin heads (cross bridges) extend towards the thin filaments
Held in place by M line proteins
Proteins of a muscle
Actin - (and other molecules attached)
Thin filaments - also contain troponin and tropomysoin
Myosin binding site present on each actin molecule is covered by tropomyosin in a relaxed muscle
For a contraction to occur, binding site needs to be uncovered so myosin heads can attach to actin molecules
Thin filaments are held in place by Z lines.
How can we classify what one sarcomere is?
One Z line to the next Z line is a sarcomere
Proteins of a muscle
Titin -
Anchors thick filaments to M line and to Z discs. Portion of molecule between Z discs and end of the thick filament - able to stretch to 4x its resting length and spring back unharmed (og shape)
Role in muscle recovery from being stretched, therefore important in eccentric contractions
Other structural proteins
- myomein =
- nebulin =
- dystrophin =
Myomesin - M line, connets titin to adjacent thick filaments
Nebulin - inelastic protein helps align thin filaments
Dystrophin - links thin filaments to sarcolemma and transmit tension generated to the tendon
What happens to the sliding filament model when contracting (isotonic concentric)?
Z discs move closer together
Sarcomeres shorten
Thick and thin filaments don’t change in length - width of band A stays the same
Thin filaments slide towards M line
Describe the stages of skeletal muscle contraction:
Nerve impulses reach an axon terminal and synaptic vesicles release Ach (acetylcholine)
Ach diffuses to receptors on the sarcolemma - Na channels open
Sodium rushes into the cell
A muscle AP spreads over the sarcolemma and down into the T-tubules
AP reaches a triad
Terminal cisternae release Calcium into sarcoplasm
Calcium binds to troponin and causes troponin-tropomyosin complex to move and reveal myosin binding sites on actin
Excitation - contraction coupling
Contraction cycle begins
Describe stages of the contraction cycle:
Repeating sequence of events that causes things to actin filaments to slide between the thick filaments
Cycle steps - exposure of active sites
ATP hydrolysis into ADPand Pi
Attachment of myosin to actin to form cross bridges
Power stroke - pivoting of the myosin head, pulling in the thin filament
Detachment of myosin from actin
Reactivation of myosin
Cycle will repeat as long as there is ATP available and high calcium level near thin filaments
Describe the stages of muscle relaxation:
Acetylcholine breaks down within synaptic cleft
Muscle action potential ceases
Calcium release Channels close
Calcium detaches from troponin
Active transport pumps calcium back into storage in the terminal cisternae of the sarcoplasmic reticulum
Calcium conc falls
Tropomyosin-troponin complex recovers, binding site on actin molecules are now prevented from myosin binding
Contraction ends
Relaxation occurs, muscle returns passively to resting length
Length of muscle fibres
How do we get the greatest amount of tension?
Optimal overlap of thick and thin filaments produces the greatest number of cross bridges and the greatest amount of tension
Length of muscle fibres
What happens as the muscle stretches past optimal length?
And if muscle is overaly shortened (less than optimal)?
As it stretches, fewer cross bridges exist so therefore less force is produced
When short, fewer cross bridges exist and less force is produced. Thick filaments are crumpled by Z discs
What is normal resting muscle length?
70-130% of the optimum length
This can be demonstrated by a graph - length tension curve
Muscle metabolism - name the sources of ATP production and explain briefly why we need them:
Muscle uses ATP at a great rate when active
Sarcoplasmic ATP only last for a few seconds
3 sources of ATP production within muscle:
Creatine phosphate
Anaerobic cellular respiration
Aerobic cellular respiration
Muscle metabolism
Creatine phosphate -
Excess ATP within resting muscle used to form Creatine phosphate
CP is 3-6 times more plentiful than ATP within muscle
It’s quick breakdown provides energy for creation of ATP
Sustains maximal contraction for 15 seconds
Athletes tried Creatine supplemation - gain body mass but shut down bodies own synthesis
Muscle metabolism
Anaerobic cellular respiration -
ATP produced from glucose broken down into pyruvic acid (x2) during glycolysis - net gain 2x ATP
When no O2 present - pyrvic converted to lactic acid which diffuses into the blood
Glycolysis can continue anaerobically to provide ATP for 30-40 seconds of maximal activity
Eg 200m race
Muscle metabolism
Erotic cellular respiration -
ATP for any activity lasting over 30 seconds
If sufficient O2 available, pyruvic acid enters mitochondria to generate ATP, water,heat
Fatty acids and amino acid can also be used by the mitochondria
Provides 90% of ATP energy if activity lasts more than 10mins
