The Muscular System Flashcards
what control do we have over skeletal muscle
voluntary control
what skeletal muscles don’t all attach to the skeleton
many facial muscles
what are the functions of skeletal muscle
- movement
- posture
- joint stability
- thermogenesis
describe this muscle function: movement
muscles produce tension to move things by pulling or squeezing
how do cells produce tension
rapidly contracting
what type of muscle are sphincters made of
- smooth muscle
- skeletal muscle
what are example of skeletal sphincter muscles
- sphincter at the anus
- sphincter at the urethra
- orbicularis oris
- orbicularis oculi
describe this muscle function: posture
- baseline tension exerted at all times
- holds the body is a certain position against the force of gravity
when do muscles have posture control
when conscious
describe this muscle function: joint stability
constant tension holds joints together
define diarthrotic joints
freely moveable joints
where are most diarthrotic joints found
in the limbs
examples of diarthrotic joints
- shoulder
- hip
- elbow
- knee
what is the relationship between joint mobility and stability
inverse relationship
what are the 3 factors of joint stability
- ligaments holding the joint together
- snugness of fit of the bones comprising the joint
- contribution from muscles crossing over the joint
what type of joint are both the shoulder and hip joint
ball and socket
describe the joint stability of the shoulder joint in comparison to the hip joint
- shallower fit/less snugness of the humerus in the glenoid cavity
- more mobile
- less stable
describe the joint stability of the hip joint in comparison to the hip joint
- deeper fit/more snugness of the femur in the acetabulum
- less mobile
- more stable
what joints are the easiest to dislocate
- shoulder
- mandible
when is the shoulder joint most vulnerable to dislocation
when extended laterally and posteriorly
what muscles help to stabilize the shoulder joint
rotator cuff muscles
define rotator cuff muscles
- 4 muscles surrounding the shoulder joint
- stabilize the humerus head in the glenoid cavity
- insert onto a cuff-like tendon
what are the 4 rotator cuff muscles
- subscapularis
- supraspinatus
- infraspinatus
- teres minor
describe this muscle function: thermogenesis
skeletal muscles can be stimulated by impulses from the hypothalamus to shiver which warms you up
what is the difference between a muscle cell and a muscle fiber
nothing, they are synonymous
what are the 4 characteristics of muscle cells
- excitable
- contractile
- extensible
- elastic
describe this characteristic of muscle cells: excitable
respond to chemical and mechanical stimuli by generating organized wave-like movement of electrical charge across membranes
define resting membrane potential
- voltage across the cell membrane under normal circumstances
- all cells have resting membrane potential
what is a synonym for voltage
electrical potential
what type of cells can use resting membrane potential as a platform to create action potentials
- excitable cells
- ex: muscle cells
what is a synonym for action voltage
action potential
define muscle potential
action potentials in muscles
define action potential in muscle cells
- muscle potential
- the resting membrane potential can have a wave-like change in voltage to create action
what do muscle cells need to have before they can contract
action potential
contraction is ________ by a previous action potential
predicated
what comes first: contraction or action potential
action potential
describe this characteristic of muscle cells: contractile
muscle cells can shorten to produce force
describe this characteristic of muscle cells: extensible
muscle cells can tolerate stretching
what muscle type has the most extensibility
- smooth muscle
- can tolerate the most stretching
skeletal muscle is considered extensible and elastic when compared to ____________
other organs
describe this characteristic of muscle cells: elastic
muscle cells can snap back into position after they stretch
are ligaments extensible or elastic
no, neither extensible or elastic
how far can ligaments stretch
1-2% of their resting length
what happens if ligaments stretch
- not elastic
- won’t snap back into position
- why one dislocation can cause it to be easier to dislocate that joint in the future
list the order of components of muscles from smallest to largest
- myofilaments
- myofibrils
- muscle fibers
- muscle fascicles
- whole muscle
how long can each muscle fiber be
- over 1cm
- as long as the whole muscle
are muscle fibers thick enough to see
no
what is the longest muscle
sartorius
how wide can each muscle fiber be
up to 0.1millimeters (100 micrometers)
what are the strongest muscles in the body
- hamstrings
- quadriceps
what is the relationship between the cross sectional area of a muscle and the strength of the muscle
directly proportional (more area = more strength)
where are the thickest muscle fibers found
in the thickest muscles
how are muscle fibers formed
fusion of myoblasts in embryo
describe myoblasts
- small cells with a single nucleus
- fuse together to become muscle fibers in utero
- myo=muscle; blast=building
- muscle stem cells in a sense
when do we have all the skeletal muscle fibers that we will ever have
at birth
how to muscle cells grow
hypertrophy (NOT hyperplasia)
what hormones cause muscle cells to hypertrophy
anabolic hormones (growth hormone, testosterone)
women produce __% of the amount of testosterone than men produce
5%
how are damaged muscles repaired by the body
- myoblasts are maintained in each muscle fiber throughout life
- myoblasts will fuse together to create new muscle cells if needed
what do sarco- and myo- mean
muscle
define myofilaments
- protein filaments in muscle
- slide past each other during contraction
what is the term for the cytoplasm in muscle cells
sarcoplasm
what is the term for the cell membrane in muscle cells
sarcolemma
what is the old term used for plasma membrane
plasmolemma
what is the term for the smooth endoplasmic reticulum in muscle cells
sarcoplasmic reticulum
define muscular fascia
- surrounds individual muscles and groups of muscles
- connects muscles to each other
define epimysium
- surrounds each muscle
- connective tissue
- bundles fascicles together
define perimysium
- surrounds each fascicle
- connective tissue
- bundles muscle fibers together
define endomysium
- surrounds each muscle fiber
- connective tissue
can muscle fibers be seen with the naked eye
no
what do the epimysium, perimysium, and endomysium converge to form
components of the tendon
define myofibrils
- organelles in each muscle fiber
- contain myofilaments
- each muscle cell has many myofibrils
- takes up most of the muscle cell volume -
describe what happens to the actin and myosin myofilaments during contraction
- do NOT change length
- actin myofilaments slide past the stationary myosin myofilaments
how many myofibrils are in a single muscle fibers
hundreds to thousands
what takes up most of the muscle cell volume
myofibrils
describe the position of the nuclei in a muscle fiber
- pushed to the outer edge of the cell
- makes the cell membrane (sarcolemma) pucker out
define triad in a muscle fiber
- repeating structure composed of 3 elements
- 2 terminal cisterns and 1 T tubule
what is the opening of the T tubule called
pore
what is the plural of cisterna/cistern
cisternae/cisterns
what is the full name of the T tubule
transverse tubule
describe why T tubules are called transverse tubules
the tubule extends across and into the muscle fiber
describe T tubules
- follows the contours of myofibrils from one side of the muscle fiber to the other
- extension of the sarcolemma that helps to communicate action potentials from the sarcolemma to the myofibrils
describe terminal cisterns
specialized portion of the sarcoplasmic reticulum
where are terminal cisterns located
on either side of the T tubule
what ion do terminal cisterns store in high concentrations
calcium
when do terminal cisterns release calcium
when the action potential travels down the T tubule
how much does calcium concentration spike within the cell once the terminal cisterns begin releasing it
10x increase in calcium
what is the chemical link between electrical action potentials and mechanical sliding of actin/thin filaments
calcium ions
describe the path of an action potential from an axon to a sarcomere
- action potential moves from axon terminal to the sarcolemma
- action potential moves down the sarcolemma
- action potential splits in 2 as it hits a T tubule (moves further down the sarcolemma and down the T tubule towards the sarcomeres)
why is it necessary for capillaries to be attached to muscle fibers
muscle fibers need good blood supply to get nutrients needed to convert ATP during movement
what is the atomic unit of contraction
sarcomere
what is the smallest element that can contract in a skeletal muscle cell
sarcomere
list the contractile elements of muscle from smallest to alrgest
- sarcomere
- myofibrils
- muscle fiber
- muscle fascicles
- muscle
how many axons connect to a single muscle fiber
one axon per muscle fiber
where do axons typically connect to the muscle fiber
near the middle of the muscle fiber
how much can sarcomeres contract
up to 2/3 their resting length
list all the steps of a muscle contraction
- action potential moves down the axon which induces the fusion of vesicles containing acetylcholine
- acetylcholine moves into the synaptic cleft through exocytosis
- acetylcholine binds to protein receptors on the motor end plate
- binding of acetylcholine leads to the opening of sodium protein channels
- sodium begins moving from outside the muscle cell to inside causing depolarization of the sarcolemma which stimulates the action potential
- more sodium channels begin to open up as the action potential moves across the sarcolemma
- action potential moves down the T tubule and calcium is released from the terminal cisterns
- calcium will bind to the troponin on actin filaments allowing for myosin binding and therefore contraction
define acetylcholine
neurotransmitter inducing muscle contraction
define synaptic cleft
area between the axon terminal and sarcolemma
define motor end plate
area of the sarcolemma that is opposite of the axon terminal
where is a sarcomere located
between Z discs
define I band
- lighter area of the sarcomere
- less dense
- only contains thin filaments
- 1/2 I band on either side of the Z disc
- split by the sarcomere
define A band
- darker area of the sarcomere
- denser
- contains both thick and thin filaments
- also contains the H zone and the M line
define H zone
- lighter region within the A band
- still darker than the I band
- contains only thick filaments
define M line
- proteins attach thick filaments together
- darker line than H zone
what is the significance of the M line
proteins attach thick filaments together so they can’t slide
describe the organization of thick and thin filaments in the lateral portion of the A band
- thick filaments have hexagonal relationship with thin filaments
- each thick filament associates with 6 thin filaments
describe the structure of each myosin filament
composed of 8 repeating structures of myosin each containing 2 globular heads
describe the structure of each myosin protein within a myosin filament
- 2 myosin polypeptides coiled around each other
- each polypeptide has 1 globular head
how many myosin proteins make up a thick filament
few hundred
what are thin filaments made of
2 chains of actin polymers wrapped around each other
describe a single actin protein that makes up thin filaments
each actin polypeptide is spherical and has its own active site for myosin heads to bind
what are the 2 proteins attached to thin filaments
- tropomyosin
- troponin
describe the structure of tropomyosin
- composed of 2 thin protein threads wrapped around each other
- each protein strand is not long, but they splice together to form a tropomyosin filament
how many tropomyosin filaments are there per thin filament
2, one for each actin strand
where is tropomyosin located when a muscle is relaxed
covering the active sites on actin so myosin heads can’t bind
describe the structure of troponin
- made of 3 unidentical proteins, each with a different job
- one end protein: spherical, attaches to actin
- middle protein: where calcium binds
- one end protein: oval-shaped, attached to tropomyosin
how often are troponin proteins located on actin
every 90 nm
which protein making up troponin causes troponin to contract
middle protein where calcium binds
describe what happens when calcium binds to troponin
- troponin contracts
- tropomyosin moved towards the end attached to myosin
- myosin heads can bind to actin and pull the thin filaments
what is the “origin” and “insertion” points of troponin when calcium binds
- origin: protein attached to actin, part that doesn’t move
- insertion: protein attached to tropomyosin, part that does move
describe how thick filaments are indirectly attached to Z discs
attached via the protein titin
describe titin
- spring-like protein
- attaches thick filaments to Z discs
- 1 polypeptide made of 30,000 amino acids (very long)
- limits the compression of the sarcomere to 2/3 its resting length
where is titin located in a contracted sarcomere
between the Z disc and the A band
what happen to titin in the sarcomere after contraction
extends back to normal position
what protein makes muscles compressible and extensible compared to other oragns
titin
what happens to Z discs as a sarcomere contracts
move towards each other/towards the middle
what happens to the I band as a sarcomere contracts
- I band collapses
- still some I band left in areas where titin is compressed to full extent
what happens to the H zone as a sarcomere contracts
- goes away completely
- no region left without thin filaments
describe dystrophin proteins
- located under the sarcolemma
- keep the sarcolemma from breaking
the lack of what protein causes muscular dystrophy
dystrophin proteins
when are you no longer able to hold a muscle in a contracted position
once you feel fatigue
define complete tetanus
complete contraction of sarcomeres and therefore the muscle
define incomplete tetanus
any range of muscle contraction between completely relaxed and completely contracted
what happens when someone has the disease tetanus
- all skeletal muscles are in complete uncontrolled tetanus
- you cannot relax your muscles
how do people die from tetanus
breathing muscles cannot relax leading to respiratory failure and asphyxiation
what causes the disease tetanus
the bacteria clostridium tetani
how does clostridium tetani often enter the body
through a puncture wound
how does clostridium tetani cause the disease tetanus
- releases a toxin that migrates up nerve axons to the spinal cord
- toxin stops motor neurons from being able to be inhibited so motor neurons have uncontrolled activity
how long is the delay of symptoms for the disease tetanus
2-3 weeks
what predicates tension developed via filament sliding
an electrical impulse (action potential) that radiates from the neuromuscular junction
what is another term for voltage
potential
what happens to pressure and current as voltage increases
- pressure increases
- current increases
what helps to move a current from one place to another
electrical pressure
describe an electrical current
- electrons flowing across a membrane
- energy conversion across a membrane
do all cell membranes have a resting membrane potential
yes
what cell was used to first determine resting membrane potential
neurons in the loligo squid
why were neurons in the loligo squid used to first determine resting membrane potential
- had a large axon that can be seen with the naked eye
- excitable cell
- similar on the molecular level to human neurons
what instrument was used to measure the resting membrane potential
oscilloscope
where are the microelectrodes placed to determine resting membrane potential
- measurement electrode: inside cell membrane
- reference electrode: outside cell membrane
which electrode on an oscilloscope is set to the baseline of 0
reference electrode placed outside the cell membrane
describe what it means that voltage is relative in terms of the resting membrane potential
the voltage of the inner surface of the cell membrane is measured with respect to the voltage of the outer surface of the cell membrane
what is the resting membrane potential neurons
-70 mv
what is the resting membrane potential for human skeletal muscle
-85 mv
what is the resting membrane potential for red blood cells
-10 mv
what is the sign of resting membrane potentials (+ or -)
always negative
how do excitable cells produce action potentials
using resting membrane potential
define leakage channels
- protein channels in cell membranes that allow a specific substance to move through (selective)
- open all the time, allowing substances to move across the membrane constantly
examples of two leakage channels in cell membranes
- Na+
- K+
which type of leakage channel is more abundant
100x more K+ channels than Na+ channels
what are the only substances than can move through Na+ leakage channels
Na+ ions