Muscular Tissue (week 5) Flashcards
what are the types of muscular tissue?
skeletal, cardiac and smooth muscle
where are is skeletal muscle generally attached by?
tendons
describe the shape of skeletal muscle
large, cigar-shaped and multinucleate
what is skeletal muscle also known as and why?
striated muscle (because of it’s obvious stripes) or
voluntary muscle (because only muscle tissue subject to conscious control)
where are skeletal muscle found in the body?
attached to bones or for some facial muscles, to skin
skeletal muscle cells are bundled by which connective tissue components?
endomysium, perimysium, and epimysium
what is endomysium?
a connective tissue component in skeletal muscle- it enclosed a single muscle fiber
what is perimysium?
a connective tissue component in skeletal muscle- it wraps around a fascicle (bundle) of muscle fibres
what is epimysium?
it is a connective tissue component in skeletal muscle- it covers the entire skeletal muscle
*there is fascia on the outside of the epimysium
what are tendons?
cordlike structures, mostly collagen fibers
*often cross a joint because of their toughness and small size
what are aponeuroses?
sheet like structures, attach muscle indirectly to bones, cartilages or connective tissue coverings
which connective tissue component converts the entire skeletal muscle?
epimysium
which connective tissue component covers a single muscle fiber?
endomysium
does smooth muscle have striations?
no
(T/F) smooth muscle is voluntary
false, it is involuntary (no conscious control)
where is smooth muscle found in the body?
found mainly in the walls of hollow visceral organs (such as stomach, urinate bladder and respiratory passages)
what is smooth muscle composed of?
spindle-shaped fibers that are uninucleate
what connective tissue component is cardiac muscle comprised of?
endomysium- it is attached to the fibrous skeleton of the heart
what is the contraction speed of smooth muscle?
contractions are very slow and sustained
what is the contraction speed of skeletal muscle?
slow to fast
does cardiac muscle have striations?
yes it does
(T/F) cardiac muscle is involuntary
true
what connective tissue component is smooth muscle composed of?
endomysium
where is cardiac muscle found in the body?
found only in the walls of the heart
what kind of cells are cardiac muscle?
uninucleate
what are branching cells in cardiac muscle joined by?
gap junctions called intercalated discs
contraction and shortening of muscles are due to what?
movement of microfilaments
what the muscle functions?
all muscles types produce movement
what are the skeletal muscles 3 other important roles?
- maintain posture and body position
- stabilize joints
- generate heat
what are myofibrils?
organelles made of overlapping myofilaments
*skeletal muscle fibers contain myofibrils
what are myofibrils composed of?
sarcomeres arranged end to end, it is a the structural and functional unit of skeletal muscle
what is the microscopic anatomy of skeletal muscle?
skeletal muscle is composed of sarcolemma and myofibrils
what is sarcolemma?
specialised plasma membrane
what gives myofibrils it’s striated (bonded) appearance?
the light (I) bands and dark (A) bands give the muscle it’s striated appearance
Describe light bands (I band)
contains thing filaments and has 2 discs as a midline interruption
describe dark bands (A band)
contains the entire length of thick filaments
- H zone is a lighter central area - M line is in centre of H zone
what kind of filaments are thick filaments?
myosin filaments
describe myosin filaments
composed mostly of the contractile protein actin (anchored to the Z disc)
- at rest, within the A band there is a zone that lacks actin filaments called the H zone
- during contraction, H zone disappears as actin and myosin filaments overlap
what kind of filaments are thin filaments?
actin filaments
describe actin filaments
composed of protein myosin
- contain actin-binding and ATPase enzymes to split ATP to release energy for muscle contractions
- possess projection known as myosin heads
what are myosin heads?
they are known as cross bridges when they link thick and thin filaments during contraction
what is sarcoplasmic reticulum (SR)?
specialised smooth endoplasmic reticulum
what does the sarcoplasmic reticulum do?
- surrounds the myofibrils
- stores and releases calcium- (calcium provides the final “go” for contraction)
what is the special functional properties of skeletal muscles?
Irritability (also called responsiveness)
—> ability to receive and respond to a stimulus
Contractibility
—> ability to forcibly shorten when an adequate stimulus is received
Extensibility
—> ability of muscle cells to be stretched
Elasticity
—> ability to recoil and resume resting length after stretching
What is the nerve stimulus and action potential?
where skeletal muscles must be stimulated by a motor neuron (nerve cell) to contract
what is a motor unit?
one motor neuron and all the skeletal muscles cells stimulated by that neuron
what is neuromuscular junction?
association site of axon terminal of the motor neuron and sarcolemma of a muscle
what is a neurotransmitter?
Chemical released by nerve upon arrival of nerve impulse in the axon terminal
what is the neurotransmitter that stimulates skeletal muscle?
acetylcholine (Ach)
what is the synaptic cleft?
gap between nerve and muscle filled with interstitial fluid
what are the events at the neuromuscular joints?
- nerve impulse reaches the axon terminal of the motor neuron
- calcium channels open, and calcium ions enter the axon terminal
- calcium ion entry causes some synaptic vesicles to release acetylcholine
- Ach diffuses across the synaptic cleft and attaches to receptor on the sarcolemma of the muscle cell
- if enough ach is released, the sarcolemma becomes temporarily more permeable to sodium ions (Na+)
- depolarisation opens more sodium channels that allow sodium ions to enter the cell
- acetylcholinesterase (AChE) breaks down acetylcholine into acetic acid and choline
what causes depolarisation?
due to the entry of sodium ions, they produce an imbalance in which interior has more positive ions
- more sodium ions enter than potassium ions leave
what ends muscle contraction?
Acetylcholinesterase (AChE)
when do cells return to resting state?
- potassium ions (K+) diffuse out of the cell
2. sodium-potassium pump moves sodium and potassium ions back tot heir original positions
what is the mechanism of muscle contraction also known as?
the sliding filament theory
what is the sliding filament theory?
thick filaments (myosin) slide past thin filaments (actin) in muscle contraction
what causes filaments to slide?
- calcium ions (Ca 2+) bind regulatory proteins on thin filaments and expose myosin-binding sites, allowing the myosin heads on the thick filaments to attach
- each cross bridge pivots, causing the thin filaments to slide toward the centre of the sarcomere
- contraction occurs and the cell shortens
what provides the energy for the sliding process?
ATP, which continues as long as calcium ions are present
what are graded responses?
they are different degrees of skeletal muscle shortening
how can graded responses be produced?
- by changing the frequency of muscle stimulation
2. by changing the number of muscle cells being stimulated at one time
(contraction of skeletal muscle as a whole) what does muscle respond to?
increasingly rapid stimulation
describe a muscle twitch
single, brief jerky contraction (not a normal muscle function)
how do muscle contractions get stronger and smoother?
when stimulations become ore frequent
how is fused (complete) tetanus achieved?
when the muscle is stimulated so rapidly that no evidence of relation is seen
what does muscle force depend on?
depends upon the number of fibres stimulated
how is greater muscle tension achieved?
contractions of more fibres
what provides energy for muscle contraction?
ATP- stored in muscle fibres in small amounts
what are the 3 ways to regenerate ATP
- direct phosphorylation of ADP by creatine phosphate
- aerobic pathway
- anaerobic glycolysis and lactic acid formation
describe direct phosphorylation of ADP by creatine phosphate (CP) in relation to providing energy for muscle contraction
- muscle cells store CP, a high energy molecule
- after ATP is depleted, ADP returns
- CP transfers a phosphate group to ADP to regenerate ATP
- CP supplies are exhausted in less than 15 seconds
- 1 ATP is produced per CP molecule
describe aerobic respiration in relation to providing energy for muscle contraction
- supplies ATP at rest and during light/moderate exercise
- a series of metabolic pathways, called oxidase phosphorylation, use oxygen and occur in the mitochondria
- glucose is broken down to carbon dioxide and water, releasing energy (about 32 ATP)
slower reactions; requires continuous delivery of oxygen and nutrients
describe Anaerobic Glycolysis and lactic acid formation in relation to providing energy for muscle contraction
- reaction that breaks down glucose without oxygen
- glucose is broken to pyrrhic acid to produce about 2 ATP
- pyruvic acid is converted to lactic acid
what are the 5 golden rules of skeletal muscle activity?
- (with a few exceptions) all skeletal muscle cross at least one joint
- typically, the bulk of a skeletal muscle lies proximal to the joint crossed
- all skeletal muscles have at least 2 attachments: the origin and the insertion
- skeletal muscles can only pull; they never push
- during contraction, a skeletal muscle insertion moves towards the origin
what are the 2 types of body movements?
- origin
2. insertion
what is origin in the types of body movements?
attachment to an immovable or less movable bone
what is insertion in the types of body movements?
attachment to a movable bone
(types of body movement) what happens when muscle contracts?
the insertion moves toward the origin
(types of body movement) when does body movement occur?
when muscles contract across joints
list the types of body movements
flexion, extension, rotation, abduction, adduction, circumspection
describe flexion
creases the angle of the joint
- brings 2 bones closer together - typical of bending hinge joints (e.g. knee and elbow) or ball-and-sack joints (e.g. the hip)
describe extension
opposite of flexion
- increases the angle between two bones
- typical of straightening the elbow or knee
- extension beyond 180 degrees is hyper extension
describe rotation
movement of a bone around its longitudinal axis (common in ball-and-socket joints)
e.g. moving the atlas around the dens of axis (i.e., shaking your head “no”)
describe abduction
movement of a limb away from the mid line
describe adduction
opposite of abduction
-> movement of a limb toward the mid line
describe circumduction
- combination of flexion, extension, abduction and adduction
- common in ball-and-socket joints
- proximal end of bone is stationary, and distal end moves in a circle
list the special body movements
dorisflexion, plantar flexion, inversion, eversion, supination, pronation and opposition
describe dorsiflexion
lifting the foot so that the superior surface approaches the skin (toward the dorsum)
describe plantar flexion
pointing the toes from the head
describe inversion
turning sole of food medically
describe eversion
turning sole of foot laterally
describe supination
- forearm rotates laterally so palm faces anteriorly
- radius and ulna are parallel
describe pronation
- forearm rotates medically so palm faces posteriorly
- radius and ulna cross each other like an x
describe opposition
moving the thumb to touch the tips of other fingers on the same hand
(T/F) muscles can only pull as they contract )not push)
true
(interactions of skeletal muscles in the body) what is a prime mover?
muscle with the major responsibility for a certain movement
(interactions of skeletal muscles in the body) what is a antagonist?
muscle that opposes or reverses a prime mover
(interactions of skeletal muscle in the body) what is synergist?
muscle that aids a prime mover in a movement or reduces undesirable movements
(interactions of skeletal muscles in the body) what is a fixator?
specialised synergists that hold a bone still or stabilise the origin of a prime mover
what is a fascicle?
a bundle of muscle fibres
describe circular fascicles
fascicles that are in concentric rings
describe convergent fascicles
fascicles that converge on a single insertion tendon
describe parallel fascicles
length of fascicles run parallel to the long axis of the muscle
describe fusiform fascicles
modified parallel arrangements resulting in a spindle-shaped muscle
describe pennate fascicles
short fascicles that attach obliquely to a central tendon
