biol ch. 37
isometric force
musle contracts but cannot shorten, muscle still generates force even though it stays the same length and does not shorten
what is a twich
single action potential
is sarcomere length variable in invertebrates?
yes they can have longer sarcomeres, but vertebrates can just shorten to produce movements more quickly bc the sarcomeres are shorter
Can muscles shorten quickly?
yes, they can produce large forces for their weight -insects super fast, compared to vertebrates, then clams are slower but there muscles can do that without getting tired
what are fibers made up of?
long rodlike structures that contain parallel arrays of the actin and myosin filaments that cause a muscle to contract (this is not a sarcomere but these can be further broken down into sarcomeres)
what do skeletal tissues consist of?
mainly an extracellular matrix: secreted by specialized cells, forming a connective tissue external to the cells -bone, tooth enamel, cartilage
What are individual muscle contractions the result of? (so the bigger picture)
many successive cycles of cb formation and detachment -During which chemical energy released by atp hydrolysis is converted into mechanical work
osteoclasts
removal, that secrete digestive enzymes and acid to dissolve the calcium mineral and collagen
What are skeletal muscle fibers organized into?
repeating contractile units called sarcomeres (they make up myofibrils)
endoskeletons
rigid bones are jointed for motion and can be repaired if damaged -first evolved in cambrian explosion, lies internal to most animal tissues -they can grow extensively and when broken be repaired -provide protection from internal organs like brain, lungs and heart
What kind of muscle fibers do skeletal muscles have?
slow twitch and fast twitch
how do muscles interact with hydroskeleton?
-muscles exert pressure against the fluid to produce movement -circular muscles reduce diameter -longitudinal reduce length
What are myosin made up of?
-2 long polypeptide chains coiled together, each ending with a globular head- but it looks like a double headed golf club, and they are arranged in parallel to form thick filaments with numerous myosin heads extending out from their flexible necks along the myosin filament
how do the different types of muscle fiber affect the speed of predators and prey?
-Inheritance of genetic fiber types -High aerobic animals like dogs and antelope have a lot of slow twitch fibers and specialized fast twitch muscle fibers that also have a high oxidative capacity in addition to using glycolysis for rapid atp production -Cats are more fast twitch -Animals with high body temp. and high metabolic rates have larger numbers of oxidative (fast twitch) fibers compared with animals that have lower body temperatures and lower metabolic rates (Reptiles) -Most fish have red slow twitch
What does it mean that they are multinucleated?
-This means gene expression must be coordinated among all nuclei in the muscle fiber -This is necessary when endurance training increases the cells rate of atp production, so that the entire cell contracts uniformly
what do muscles do?
-generate force, produce movement - some are obvious: running, climbing -some aren't muscles in digestive tract
what are the 2 layers?
-thin outer waxy layer minimizes water loss -thicker inner layer tough, making it hard to break
hinge
1 axis of rotation ex. elbow, ankle - can be controlled by 2 antagonist groups
Cross bridge cycle (the how of muscle contraction)
1. Myosin head binds to atp, allows myosin head to detach from actin 2. Myosin head hydrolyzes atp to adp and inorganic phosphate. This results in conformational change so myosin head is cocked back 3. Myosin head binds actin forming a cross bridge 4. Once bound, the myosin head release adp and pi, result is another conformational change in the myosin head called the power stroke. During this myosin head pivots forward and generates a force, causing myosin and actin filaments to slide relative to each other over a distance of approx. 7nm. Power stroke pulls actin filaments toward sarcomere midline 5. Then step 1 again and the cycle repeats
What are the 2 types of muscles?
1. striated 2. smooth
what happens along the myosin?
2 heads of myosin molecules bind to actin at specific sites to form cross bridges between the myosin and actin filaments -myosin filaments pull the actin filaments toward each other by eans of the cross bridges btwn myosin and actin filaments
ball and socket
3 axis of rotation ex. shoulder
when were fibers first seen?
600 million years ago (these are the actual muscle fibers, not the whole bundles)
when do muscles contract?
Calcium regulates actin-myosin interaction through excitation -contraction coupling
what kind of length generates the most force?
INTERMEDIATE- because most overlap
what affects the muscles and why?
Muscle length affects actin-myosin overlap and generation of force -Amount of overlap determines number of cross bridges that can form- so the more overlap the more force that can be produced- except when lengthened then relaxed it is weaker bc less overlap
sliding filament model
Muscles produce force and change length by the sliding of actin filaments relative to myosin filaments
Do the lengths of myosin and actin change?
NO-they never vary, the change is from the sliding of actin with respect to myosin filaments within individual sarcomeres -So the sum of the fractions by which each sarcomere shortens along the fibers length
So what is in the middle then?
NOT directly touching the Z discs are myosin thick filaments- this forms 2 regions of overlap within the sarcomere
removal is _____ then growth
SLOWER
What does muscles ability to generate force depend on?
a combination of electrically excitable cells and contractile proteins within these cells that can be activated by the nervous system
bone marrow
a fatty tissue found btw trabeculae and also within the bones central cavity, contains important cell populations: stem cells, blood forming cells
striated muscles
appear striped under a light microscope -include skeletal (pulls on bones) and cardiac (contract heart muscles to pump blood)
smooth muscles- what are they and where are they found
appear uniform under the light microscope -Found in the walls of arteries to regulate blood flow, in the respiratory system to control airflow and in the digestive and excretory systems to help transport food and waste products
tendons
attach muscles to bones, made of collagen -they transmit muscle forces, allowing the forces to be redirected and transmitted, store and recover elastic energy
why is bone hard to break?
bone absorbs energy before it fractures so that is why it is hard to break -bone becomes more mineralized and brittle as a normal process of aging -sharks evolved unusual skeletons of calcified cartilage rather than mineralized bone tissue to achieve rigid mechanical support
osteoblasts
bone tissue forming cells synthesize and secrete calcium phosphate as hydroxyapatite mineral crystals in close association with the protein collagen
appendicular
bones of the limbs, shoulder and pelvis - was fins in fish that evolved to mammals
how is muscle force summed?
by an increase in stimulation frequency and the recruitment of motor units
how are skeletal muscles stimulated
by motor nerves which conduct action potentials to the neuromuscular junction
What is the difference when a muscle is contracted vs. relaxed?
c: sarcomeres had more actin myosin overlap r: less overlap
spongy bone
consists of small plates and rods known as trabeculae with space btw them- mainly in ends of limb bones and within the vertebrae
insect cuticle
cover their entire body, composed of chitin, a nitrogen containing polysaccharide -originally soft for insects to grow, then hardens but stays soft at joints
What happens when myosin runs into Z disc?
disrupts cross bridge system- this would occur when contraction is in small lengths
characteristics of the fibers
each muscle fiber is an elongated single cell that can be up to 20cm long -they have several nuclei so they are multinucleated
muscle cells are________. specifically skeletal muscles
electrically exitable -Skeletal muscle fibers activated by impulses transmitted by motor nerves to synaptic junctions -In this case neurotransmitter binds with receptors on the muscle opening of Na+ channels, the influx of na initiates wave of depolarization that passes along the length of the muscle fiber
do all vertebrate animals have these?
even vertebrate animals with rigid endoskeletons have hydrostatic elements for flexibility and cushioning of loads transmitted by the skeleton -intervertebral discs: have walls that surround fluid, enable backbone to twist and bend -cartilage: forms joint surfaces between adjacent bones
skull and ribs
form when precursor cells differentiate into osteoblasts that immediately begin producing bone as a skeletal sheet or membrane
other bones
formed as cartilage first called chondroblasts but cartilage is pliable so it grows with the expansion of the skeleton -then cartilage is invaded by blood vessels→ cartilage into mineralized bone
thin filament
formed by 2 helically arranged actin filaments twisted together
compact bone
forms the walls of the bones shaft, mainly dense mineralized bone tissue containing bone cells called osteocytes and the network of blood vessels supplying them with oxygen and nutrients
red slow twitch fibers
found in muscles that contract slowly and consume less atp ex. posture - get energy through oxidative phosphorylation -Greater resistance to fatigue in response to repetitive stimulation -Because they can get mitochondria to supply atp to muscle fibers by aerobic resp. -Contain an abundance of myoglobin and oxygen binding protein related to hemoglobin that facilitates oxygen delivery to the mitochondria -They are red because of iron in them -Long distance runners, weight lifters (this increases size of already existing muscle fiber by synthesis of myosin and actin)
sarcomere
from 1 Z disc to another- this is the basic contractile muscle of a unit of muscle
How do actin thin filaments extend?
from both sides of the Z disc toward the midline of the sarcomere
white fast twitch fibers
generate force quickly, tail movement, but they consume more atp -Energy through glycolysis -Express a fast form of myosin with a high rate of atp hydrolysis, favoring rapid force development and movement -Fatigue quickly because of the drop in pH caused by the accumulation of lactic acid -Larger then red fibers- so generate more force
growth in length occurs at _________
growth plate, region of cartilage btwn middle region called diaphysis and end called epiphysis -adds cartilage toward diaphysis enabling bone length to continue to increase after birth, at maturity plates fuse -bone is added to ends and removed from middle, expanding marrow cavit
3 types of animal skeletons
hydrostatic, endoskeletons, exoskeletons
where is depolarization initiated?
in the plasma membrane-is conducted to the sr through a specialized transmission system, formed from invaginations of the plasma membrane, known as T tubule system- this is in contact with SR and muscle cells plasma membrane
force summation
increasing stimulation -> muscle force increases - it will reach a plateau and continue as stead as stimulation continues
what are finger joints?
intermediate they allow you to flex and extend your fingers as well as spread them laterally or move them together when making a fist
how are myosin and actin organized?
into thin threads called filaments that interact with each other and cause muscles to shorten (this is what happens when you lift weights etc.) -striated: they are in repeating pattern to produce the striated pattern -smooth: they are in irregular pattern, giving these muscles a smooth appearance when viewed
how do vertebrate bones form
intramembranous and endochondral ossification
what is advantage of doing bone growth this way
it can be repaired if damaged, but women usually lose more after menopause
what are the functions of these interactions?
jet propulsions, allows clams to burry etc.
flexion
joint motion in which bone segments rotate closer together
articular cartilage
located at joint surfaces of a bone forms a gel like matrix that resists fluid being squeezed out when forces press on the cartilage during movement -reinforced by type 2 collagen fibers
difference between mollusks/ clams and insects
mollusks, clams have an outer shell made of calcium reinforced by proteins- so it is less brittle and harder to break then if it had been made of 1 thing -insects have more complex
motor unit
motor neuron and the population of muscle fibers that it innervates, they can be relatively few to a 100 -Number of fibers innervated by a given motor unit determines force and how much control a muscle has -Ex. Finger are very small motor units, legs large
fibers
muscle cells, they produce force within an animals body as well as exert forces on the environment
What are inversely related?
muscle force and shortening velocity -muscles shorten quickest when producing low forces -ex. Your arm moves faster when you throw a light ball instead of a heavy one
lengthen contraction
muscle generates much more force than when it remains isometric or shortens ex. every stride you take while running- a brief phase of streth at the begining of contraction is normal because it allows muscles to generate more force then if they remained isometric -this lengthening also reduced the muscles energy consumption because fewer fibers are recruited to generate a given level of force -injury is usually caused by rapid and repetitive stretching
skeletal muscle fibers
produce movement by shortening, thus pulling on bones of the skeleton
What is on both ends and towards middle of sarcomere?
non overlap regions and these are lighter in color then regions of overlap
What is the next step and result?
power stroke - this results in excitation, contraction coupling, producing force and movement - muscle relaxation follows the end of neural signal- ca goes back into SR
antagonistic muscles
produce reciprocal motions at a joint - this is because muscles can only generate force by pulling NOT pushing, occurs in cnidarians and roundworms as well
What are thin filaments attached to?
protein backbones called Z discs that are regularly spaced along the length of the myofibril
exoskeletons
provide hard external support and protection - first ones came with sponges - protection, support, and place for muscles to attach but they limit growth
what does joint shape determine?
range of motion and skeletal muscle organizaton
what is most mobile joint?
shoulder- but most often dislocated or injured
What do all muscles have?
similar force generating properties b/c actin and myosin are preserved
how do muscles exert forces to produce joint motion?
skeletal lever -so skeleton enables muscles to transmit forces that cause joint rotation -muscles that attach father produce slower but stronger movements
What systems activate each type of muscle?
skeletal: somatic nervous system smooth and cardica: autonomic nervous system
axial
skull and jaws of head, spinal column, ribs -formed first so it is the main component of fish
how do muscles contract?
sliding of myosin and actin filaments
what were they key for?
speciation in insects
hydrostatic
support animals by muscles that act on a fluid filled cavity
sarcoplasmic reticulum
surrounds myofibrils- it is a modified form of endoplasmic reticulum
what is strength of rotational movement determined by?
the product of a muscles force and perpendicular lever -muscles produce longer force by being farther or exerting larger force -chek 37-18 on this
What about at resting?
the binding sites are blocked by tropomyosin -BUT Depolarization causes conformation change in troponin which in turn moves tropomyosin away from these binding sites, allowing cross bridges between actin and myosin to form and the muscle to contract (myosin and actin need to be exposed to form cross bridges)
what does force exerted on the muscle depend on?
the frequency of stimulation by the motor nerve because more frequent stimulation increases the amount of calcium that is released to activate cross bridge formation in the muscle fibers
extension
the motion when bones move apart
tetanus
the muscle contraction of a sustained force, this is normal response but can induce by tetani
when did they evolve?
these evolved early, found in almost all multicellular animals as well as in many vascular plants
What is similar between striated and smooth muscles?
they both use the same sets of muscle proteins: myosin and actin to contract and generate force
What do smooth muscles use?
they do not have troponin- tropomyosin mechanism so instead they use the binding of a protein called calmodulin -calmodulin-CA complex activates enzyme myosin kinase that phosphorylates the smooth muscle myosin heads, causing them to bind actin and begin the cross bridge cycle - a second enzyme dephosphorylates-> relaxation - these muscles usually have longer periods of contraction because calcium is returned more gradually
What is different in insects?
they have higher rates to produce more atp- SO myosin can be an enzyme and a protien
what links the myosin filaments to the z discs at the ends of the sarcomere?
titin- it helps with muscle elasticity
what also applies to the way muscles pull on the skeleton to cause joint movement?
trade off of force versus velocity that we saw earlier -muscles that transmit large forces typically have large leverage for strong joint rotation
what runs in the grooves formed by actin helices in thin filament?
tropomyosin- it is a protein that blocks myosin binding sites when needed (so when muscle isnt contracting)
molting
when arthropods shed their cuticle at intervals
When is muscular contraction initiated?
when depolarization of the t tubules causes the SR to release ca, this diffuses into myofibrils and binds to troponin causing change shape, causes tropomyosin to move exposing the myosin binding site along the actin filament
agonists
when muscles combine to produce similar motions
when are animals vulnerable?
when shell sheds but new one hasn't formed, also hard to repair