-
Chapter objectives
- Describe the functions of skeletal muscle tissue
- Describe the organisation of muscle at the tissue level
- identify the structural components of a sarcomere
- explain the key steps involved in the contraction of a skeletal muscle fiber
- compare the different types of muscle contractions
- describe the mechanism by which muscles obtain and use enerty to power contractions
- relate the type of muscle fibers to muscular performance.distinguish between aerobic and anerobic endurance and explain their implication for muscular performance.
- contrast skeletal, cardiac, and smooth muscles in term of structure and function
- Identify the main axial muscles of the body, along with their action.Identify the appendicular muscles of the body,along with their actions
- describe the effects of aging on muscle tissue
- discuss the functional relatonship between the muscular system and other organ systems
-
-
-
-
-
clavis
claviclel; clavicle
-
-
-
-
fasciculus
a bundle: fascicle
-
gaster
stomach; gastronemius
-
-
-
-
-
-
metron
measure; isometric
-
-
-
-
-
-
tetanus
convulsive tensions; tetanus
-
-
trope
a turning; tropomyosin
-
-trophy
nourishing; atrophy
-
Muscle tissue
consists of elongated muscle cells that are highly specialized for contraction
-
Three types of muscle tissue
-
Skeletal muscles
- are organs composed primarily of skeletal muscle tissue,
- but also contains connective tissues, nerves, and blood vessels
- These muscles are directly or indirectly attached to bones of the skeleton
- 700 skeletal muscles
-
Functions of skeletal muscles
- Produce movement of the skeleton
- Maintain posture and body position
- Support soft tissues
- Gaurd entrances and exits
- Maintain body temperature
-
Three layers of connective tissue
- Epimysium
- Permysium
- Endomysium
-
Epimysium
- Surrounds the entire muscle
- layer of collagen fibers that separates the muscle from surrounding tissues and organs
-
Perimysium
- Connective tissue fibers divide the skeletal muscle into bundles of fingers called fascicles
- in addition to collagen and elastic fibers, it contains blood vessels and nerves that supply the fasicles
-
Endomysium
- withing a fasicle, surrounds each skeltal muscle fiber and ties adjacent muscle fibers together.
- Stem cells scattered help repair damaged muscle tissue
-
At the end of each muscle
collagen fibers of all layers come together to form either a tendon or a aponeirosis
-
Aponeuroses
connect different skeletal muscles together
-
Skeletal muscles only contract
- under stimulation from the CNS.
- Axons (nerve fibers) penetrate the epimysium, branch through the perimysium and enter the endomysium to control indivdual muscle fibers
-
Skeletal muscles are often called
Voluntary muscles
-
Sarcolemma
- "cell membrane" of a muscle fiber surrounds the sacroplasm (cytoplasm)
- openings across the surface of the sarcolemma lead into a networkd of nattow tubules called
- transverse tubules or T tubules
- T tubule plats a major tole in coordination the contration of muscle fibers
-
Muscle contraction occurs through the orderly interaction of
both:electrical and chemical events
-
Myofibrils
- Are encircled by t tubules myofibrils
- Are bundles of thick and thin myofiliments, that are protein filaments that contain actin and myosin
- Actin are found in thin filaments
- mysosin are in thick filaments
- are resonsible for muscle contraction
- mitochondria and grandules of glycogen are scattered among them
-
Sarcoplasmic reticulum
- whcih is a specialized for of smooth endoplasmic reticulum.
- Whenever a T tubule enricles a myofibil, the tubule is tightly bought fo the membranes of the SR
-
On either sides of a t tubule expanded chambers of the SR called
Terminal Cisternae
T Tubules are sandwiched between Terminal Cisternae
they contain high concentraions of calcium ions
-
Sacromeres
- Repeating functional units of myofilaments
- smallest functional unit of muscle fiber
- interactions between the thick and thin filaments are responsible for muscle contraction
-
Z lines
are bounddaries of each sarcomere
-
Thin filaments extend toward the center of the sarcomere and pass among the thick filaments in the
zone of overlap
-
M line
is made up of proteins that connect the central protions of each thick filament to its neighbors.
-
A band
contains thick filaments
-
I band
the light region between two sucessive A bands , inculding the Z line
-
Each actin molecule has
an active site capable of interacting with myosin.
-
Tropomyosin
protein that covers the active sites along the thin filament
-
Tropomyosin strands are held in postion by
molecules of tropoin
-
Calcium
- is the key that unlocks that actives sites and starts a contraciton.
- calcium binds to troponis, the protein changes shape.
-
Sliding Filament theory for Sarcomere contraction
I bands get smaller, the Z lines move closer together, and zone of overlap gets larger but the width of the A bands do not change
-
Neuromuscular Junction
Is the communication link between the nervous system and a skeletal muscle fiber.
-
Motor Neuron
Nerve cell that controls each skeletal muscle fiber
-
A single axon of the neuron branches withing the perimysium to from branches, the ends of these branches are called
Synaptic terminal
-
Cytoplasm of the synaptic terminal comtains
mitochondria and vesicles filled with ACh acetychoine
-
Acetylcholine
- is a neurotransmeitter whcih is a chemical released by a neuron to communicate with other cellls.
- Neurotransmitters change the properties of other cells membranes, in this case permiablilty.
- the change in the sarcikemma triggers contraction of the muscle fibers
-
Synaptic cleft
Seperates the synaptic terminal from the sarcolemma
-
Motor end plate
is the portion of the membrane that contain receptors that bind ACh
-
Both the synaptic cleft and motor end plate contain the enzyme called
- Acetylcholinesterase (AChE)
- Which breaks down molecules of ACh
-
AChE (acetylcholinesterase)
- Also know as cholinesterase
- Is contained in both the synaptic cleft and the motor end plate.
- This enzyme breaks down molecules of ACh
-
Action potential
Electrical impulse in the sarcolemma
-
Neurons control skeletal muscle fibers by...
Stimulating the production of an action potential
-
Function in the neuromuscular junction
1
Arrival of an action potential of the synaptic terminal.
-
Function in the neuromuscular junction
2
- Release of ACh when action potential from the axon reaches the synaptic terminal.
- Vesicles in the synaptic terminal fuse with the neuronal membrane and dump their contents into the synaptic cleft.
-
Function in the neuromuscular junction
3
- ACh binding at the motor end plate
- The diffusion across the synaptic cleft and binding of ACh to the receptors on the sarcolemma, increases the membrane permeability to sodium ions.
- Sodium ions then rush into the cell, this produces an action potential in the sarcolemma.
-
Function in the neuromuscular junction
4
- Appearance of an action potential in the sarcolemma.
- An action potential spreads across the surface of the sarcolemma and down all of the transverse tubes toward the terminal cisterne.
- triggers a sudden,massive release of calcium ions by the terminal cisternae.
- While the contraction process occurs AChE breaksdown ACh.
-
Myasthenia gravis
- Is an autoimmune disease charterized by muscle weakness and fatique
- Anti bodies attack acetycholine receptors and impair function of the ACh receptor at the neuromuscular junction.
- Treated by long acting cholinesterase agents.
-
In a resting sarcomere...
- Each cross-bridge is bound to a molecule of ADP and phosphate group (PO43-),
- which are products of the breakdown of an ATP molecule.
-
The cross-bridge of the resting sarcomere stores...
- the energy released by the breakage of the high energy bond.
- Thus, the resting cross bridge is "primed for contraction"
-
The contraction process steps
1
- Active-site exposure.
- The active site is exposed following the binding the calcium ions (Ca2+) to troponin.
-
The contraction process steps
2
Cross bridge formation
The myosin cross-bridge forms and attaches to the exposed active site on the thin filaments.
-
The contraction process steps
3
- Pivoting of myosin head.
- the attached myosin head pivots toward the center of the sarcomere, and the ADP and a phosphate group are released.
- This steps uses the energy that was stored in the myosin molecule at rest.
-
The contraction process steps
4
- Cross- bridge detachement
- The cross-bridges detach when the myosin head binds another ATP molecule.
-
The contraction process steps
5
- Myosin reactivation
- The detached myosin head is reactivated as it splits the ATP and captures the released energy. The entire cycle can now be repeated, beginning with step 2.
-
Depolarization
In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential.
-
Two ways to block the neuromuscular junction
- Depolarizing agents- that substitute for ACh
- Non-depolarizing agents- that block the reuptake of ACh into the nerve terminal
-
Depolarizing neuromuscular blockers
- They substitute ACh
- Unlike Ach, they act over a prolonged time
- That results in continued muscle depolarizaion and muscle paralysis
- Due to Stimulating affect they produce fasiculations
-
Non depolarizing neuromuscular blockers
- They block the reuptake of ACh in the nerve terminal
- This produces excess ACh, and inhibits the stimulation of the muscle.
- They do depolarize the affected fibers and do not cause fasiculations.
-
Botulism
From the consumption of foods (often canned or smoked) contaminated with the bacteria Clostridium perfringens. that prevents the release of ACh, that leads to potentially fatal muscular paralysis
-
Summary of steps involved in Skeletal muscle contraction
1
At the neuromuscular junction, ACh released by the synaptic terminal binds receptors to the sarcolemma.
-
Summary of steps involved in Skeletal muscle contraction
2
The resulting change in the membrane potential of the muscle fibers leads to the production of an action potential that spreads across the entire surface of the muscle fibers and T tubes.
-
Summary of steps involved in Skeletal muscle contraction
3
The SR releases stored calcium ions which increases the calcium concentration of the sarcoplasm in and around the sarcomeres.
-
Summary of steps involved in Skeletal muscle contraction
4
Calcium ions bind to the triponin, which results in the movement of the active sitres on the thin filaments (actin). Cross bridges form when myosin heads bind to active sites.
-
Summary of steps involved in Skeletal muscle contraction
5
The contraction begins as repeated cycles of cross bridge binding,pivoting, and detachment occur, powered by ATP, these events produce filament sliding and the muscle fiber shortens
-
Summary of steps involved in Skeletal muscle contraction
6
Active potential generation ceases as ACh is broken down by AChE
-
Summary of steps involved in Skeletal muscle contraction
7
The SR reabsorbs calcium ions, and the concentration of calcium ions in the sarcoplasm declines.
-
Summary of steps involved in Skeletal muscle contraction
8
when calcium ion concentration approach normal resting levels, the triponin and trpomyosin molecules return to their normal positions. this change recovers the active sites and prevents further cross bridge interaction.
-
Summary of steps involved in Skeletal muscle contraction
9
Without cross-bridge interactions, further sliding cannot take place and the contraction will end.
-
Summary of steps involved in Skeletal muscle contraction
10
Muscle relaxation occurs, and the muscle returns passively to its resting length
-
When muscle contracts, they pull on collagen fibers, producing an active force called
Tension
-
Tension applied to an object tends to
Pull the object toward the source of tension
-
The passive force that opposes movement
Resistance
-
before movement can occur the applied tension must overcome the objects
Resistance
-
Compression
A push applied to an object- tends fto force the object away from the souce of compression
-
Ammount of tension of a skeletal muscle depends on
- the frequecy of neural stimulation
- the number of muscle fibers activated
-
Twitch
is a single stiulus contraction -relaxation squence in a muscle fiber
-
Summation
If a second stimilus arrivces before the relaxation phase has ended, a second , more powerful contraction occurs.
-
Incomplete tetanus
A muscle that produces almost peak tension during rapid cycles of contraction and relaxation.
-
Complete tetanus
occurs when the rate of stimulation is increed until the relaxation phase is completely eliminated which produces maximum tension.
-
Tetanus
- caused by clostridum tetani
- deep tissue injuries
- when active in the body the toxin supresses the machanism that regulates motor neuron activity
-
A typical skeletal muscle
contains thousands of muscle fibers
-
Motor Unit
All the muscle fibers by a single motor neuron consitiute a motor unit
-
Recruitment
- is the activation of more and more motor units
- result is a smoth,steady, increase in muscle tension.
-
All voluntary movements invole the sustaind contracions of skeletal muscle fibers in imcomplete tetanus. The force exerted can be increaed by increading the requency of the action potentials or the number of stimulated motor units (recruitment)
-
Classifictions of muscle contractions
- Isotonic contraction
- Isometric contraction
-
Isotonic contraction
Tehsion rises and the skeltal muscles length changes. thension in the muscle remains a constant level until relaxation occurs.
-
Isometric contraction
the muscle as a whole does not chage length, and the tension produced never exceeds the resistance
-
Elongation of a muscle
passive
-
An active skeletal muscle fiber may require: how much ATP
600 trillion molecules of ATP a second
-
A resting muscle fiber only contains energy reserves to sustain a contraction untill
- Additional ATP can be generated.
- Muscle fibers will generate ATP at roughly the same rate as it is used.
-
Primary funciton of ATP
- transfer energy from one location to another
- NOT the long term storage of energy
-
At rest, a skeletal muscle fiber produces more ATP then it needs. Under these conditions ATP transfers the energy to
Creatine
-
Creatine Phosphate (CP)
ATP+ creatine ---> ADP + Creatine Phosphate
-
During each contraction, each cross bridge breaks down ATP and produces ADP and a phosphate group
Creatine Phosphate recharges ADP to ATP
ATP+ Creatine Phosphate---> ADP +Creatine
-
Creatine phosphokinase (CPK or CK)
Regulates the rechage of ADP to ATP with Creatine Phosphate
-
ATP is generated by
- Aerobic metabolism in the mitochodria
- and through Glycolysis in the cytoplasm
-
Aerobic metabolism accounts for 95% of ATP needed by a resting cell. In this process,
Mitochondria absorb oxygen, ADP, Phosphate ions and small organic substrate molecules in the cytoplasm.
-
The organic substrates are carbon chains produced by the breakdown of carbohydrates, lipids or proteins
- These substrates enter the TCA (tricaboxylic acid) Cycle AKA
- Citric acid cycle or the KREB cycle
- and then are completely dissassembled bu a series of chemical reactions
-
Krebs Cycle
- Carbon atoms and oxygen atoms are released as (CO2).
- Hydrogen atoms are shuttled to respirtatory enzymes in the inner mitochondrial membrane where their elections are removed
- The protons and electrons thus produced recombine with oxygen to from water(H2O)
- During this process large ammounts of energy are released and used to make ATP.
-
Aerobic metabolism of a common carbohydrate substrate, pyruvic acid, is quite efficient
For each pyruvic acid molecule broken down in the TCA cycle , the cell gains 17 ATP molecules
-
Pyruvic acid is provided through the process of
Glycolysis
-
Glycolysis
- Is the breakdown of glucose to pyruvic acid in the cytoplasm of the cell.
- The ATP yeild of glycosis is much lower then that of aerobic metabolism
- it can proceed in the absence of oxygen
-
In resting skeletal muscle the demanded for ATP is low so:
- more than enough oxygen avaiable for the mitochondria to meet the demand and produce a suplus of atp
- ATP is used to build reserves of CP and glycogen
-
As the rate of mitochondrial ATP production rises, so does oxygen consumption.
As long as sufficient oxygen is avaiable the ammount of ATP provided by glycolysis is minimal
-
In peroids of peak activity when oxygen cannot diffuse into the muscle fiber fast enough to enable mitochondria to produce ATP:
Mitochondrial activity provides about 1/3 of ATP needed and glycolysis become primary source.
-
Glycolysis produces pyruvic acid faster then it can be used so...
pyruvic acid levels rise in the cytoplasm and is converted to Lactic acid
-
muscle fatique
is caused bu the exhaustion of energy reserves or the buildup of lactic acid
-
If muscle contractions at or below the maximum rate of mitochondrial ATP generation, the muscle fiber will function
aerobically
-
Recovery period
conditions within the muscle care treturned to normal pre-exertion levels
-
Lactic acid can be recycled during the
recovery period
-
when oxygen is available latic acid can be converted into
pyruvic acid
-
-
Anaerobic endurance
is the length of time muscle contractios can be supported by glycolysis and existing energy reserves of ATP and CP
-
Aerobic endurance
is the length of time a muscle can continue to contract while being supported by mitochontrial activities
-
Terms that indicate postion, direction, or muscle fiber orientation
Anterior
Front
-
Terms that indicate postion, direction, or muscle fiber orientation
Externus
superficial
-
Terms that indicate postion, direction, or muscle fiber orientation
Extrinsic
Outside
-
Terms that indicate postion, direction, or muscle fiber orientation
inferious
Inferior
-
Terms that indicate postion, direction, or muscle fiber orientation
Internus
(deep,Internal)
-
Terms that indicate postion, direction, or muscle fiber orientation
intrinsic
Inside
-
Terms that indicate postion, direction, or muscle fiber orientation
lateralis
lateral
-
Terms that indicate postion, direction, or muscle fiber orientation
medialis/medius
medial, middle
-
Terms that indicate postion, direction, or muscle fiber orientation
obliques
oblique
-
Terms that indicate postion, direction, or muscle fiber orientation
posterior
back
-
Terms that indicate postion, direction, or muscle fiber orientation
profundus
Deep
-
Terms that indicate postion, direction, or muscle fiber orientation
Rectus
Straight, parallel
-
Terms that indicate postion, direction, or muscle fiber orientation
superficialis
superficial
-
Terms that indicate postion, direction, or muscle fiber orientation
Superioris
Superior
-
Indicate spedific regions
abdominis
abdomin
-
Indicate spedific regions
anconeus
elbow
-
Indicate spedific regions
auriculious
auricle of ear
-
Indicate spedific regions
Capitis
head
-
Indicate spedific regions
carpi
wrist
-
Indicate spedific regions
cervicious
neck
-
Indicate spedific regions
cleido/clavious
clavicle
-
Indicate spedific regions
coccygeus
coccyx
-
Indicate spedific regions
costalis
ribs
-
Indicate spedific regions
cutaneous
skin
-
Indicate spedific regions
femorius
femor
-
Indicate spedific regions
genio-
chin
|
|