Muscles Flashcards
1
Q
Role of Skeletal Muscles
A
- Attach to bones
- Produce skeletal movement (voluntary)
- Maintain posture
- Support soft tissues
- Regulate entrances to the body
- Maintain body temperature
2
Q
Properties of skeletal muscles
A
- electrical excitability
- contractility
- extensibility
- elasticity
3
Q
Electrical excitability
A
- ability to respond to stimuli by producing electrical signals such as action potentials
- two types of stimuli:
- auto-rhythmic electrical signals
- chemical stimuli
4
Q
Contractility
A
- ability to contract when stimulated by an AP
- isometric contraction: tension develops, length doesn’t change
- isotonic contraction: tension develops, muscle shortens
5
Q
Extensibility
A
- ability to stretch without being damaged
- allows contraction even when stretched
6
Q
Elasticity
A
- ability to return to its original length and shape
7
Q
Classification
A
According to arrangement of fibers and fascicles:
Parallel muscles
Convergent muscles
Pennate muscles
Circular muscles
8
Q
Parallel muscles
A
- parallel to long axis of muscle
9
Q
Convergent Muscles
A
- Fibers converge on common attachment site
10
Q
Pennate muscles
A
- One or more tendons run through body of muscle - Unipennate, bipennate, multipennate
11
Q
Circular muscles
A
Circular muscles
- Fibers concentrically arranged
12
Q
Origin and insertions of muscles
A
Origin remains stationary
- Typically proximal to insertion
Insertion moves
13
Q
Muscles are identified by
A
- Origin
- Insertion
- Primary action
14
Q
Muscles classified as
A
- Prime mover
- Synergist
- Antagonist
15
Q
Muscle name e.g
A
– Biceps brachii (two heads, arm)
– Vastus femoris (large, femur)
– Orbicularis oculi (circular, eye)
– Rectus abdominus (erect, abdomen)
16
Q
Axial musculature
A
- Arises from and inserts on the axial skeleton
- Positions the head and spinal column
- Moves the rib cage, assisting in breathing
17
Q
Appendicular musculature
A
– Stabilizes or moves components of the appendicular skeleton
18
Q
Image of anterior muscles of body
A
19
Q
Image of posterior muscles of body
A
20
Q
Fascicles
A
- muscles are really groups of fascicles
- the fascicles are groups of muscle fibers = considered to be an individual muscle cell
21
Q
Myofibrils
A
•the muscle fiber is made up of protein filaments = myofibrils
22
Q
Sarcomeres
A
each myofibril is comprised of repeating units
23
Q
What is muscle wrapped in?
A
in a protective fascia
- fascia = sheet of fibrous connective tissue that supports and surrounds muscle or organs
24
Q
Superficial fascia
A
- separates muscle from the overlying skin
- also known as the subcutaneous layer
- made up of areolar tissue and adipose tissue
- provides support for blood vessel and nerves
- the adipose tissue stores most of the body’s triglycerides and provides insulation
25
Deep fascia
- muscles with similar functions are grouped and held together by layers of deep fascia
- dense irregular connective tissue
- allow free movement of muscles, carries nerves, BVs
26
Three layers of connective tissue that extend from the deep fascial layer
– Epimysium
– Perimysium
– Endomysium
- further strengthen and protect muscle
27
Epimysium
outermost layer
encircles the entire muscle
28
Perimysium
– surrounds groups of 10 to 100 individual muscle fibers
– separates them into bundles = fascicles
– give meat its “grain” because the fascicles are visible
- both epimysium and perimysium are dens eirregular connective tissue
29
Endomysium
- penetrating the fasicles and separating them into individual muscle fibers = endomysium (areolar connective tissue)
30
Tendon
- all three layers of connective tissue layers extend beyond the muscle and attaches to other structures
- a tendon is a cord of regular dense CT that attaches a muscle to the periosteum of bone
31
Aponeurosis
when the CT extends as a broad flat sheet
32
Generally what neurovaculature are muscles supplied with?
- with one artery and two veins
- they accompany the nerve
- nerves that induce muscle contraction = somatic motor neurons (part of the somatic division of the PNS)
- communication between muscle and these neurons:
Neuromuscular junction (NMJ)
33
Microanatomy of skeletal muscle fibers
Sarcolemma - cell membrane
Sarcoplasm - cytoplasm
Internal membrane system - sarcoplasmic reticulum
34
How are muscle cells made?
Embryonic development
- stem cells (satellite cells) differentiate into immature myoblasts which begin to make the proteins of the myofilament
- These myoblasts mature into myocytes
- Multiple myocytes fuse to form the muscle cell (muscle fiber)
- once fused, these muscle cells lose the ability of undergo mitosis
- number of muscle cells predetermined before birth
- But satellite cells can repair damaged/dying muscle cells throughout adulthood
35
Muscle Cell Anatomy
**Transverse tubules**
- Invaginations of sarcolemma
- Carry electrical impulses
**Myofibrils within sarcoplasm**
- “skeleton” of protein filaments (myofilaments) organized as Sarcomeres
**Myofilaments form the myofibrils**
- Thin filaments (actin, troponin, tropomyosin)
- Thick filaments (myosin)
36
Transverse tubules
- thousands of tiny invaginations in the sarcolemma
- tunnel in toward the center
- T tubules are open to the outside of the fiber
- filled with interstitial fluid
- AP generated in the neuron travel along the sarcolemma and the T tubules
- allows for even and quick spread of an AP deep into the cell
37
What is inside a sarcoplasm
- substantial amounts of glycogen - can be broken into glucose
- contains myoglobin - binds oxygen needed for muscle ATP production
38
Contractile element of myofibrils
- 2 microns in diameter
- comprised of primarily actin or myosin
- give the muscle its striated appearance
39
Sarcoplasmic reticulum
- Muscle fibers also have a system of fluid-filled membranes
- encircles each myofibril
- similar to the ER
- have dilated end sacs = terminal cisterns
- stores calcium when at rest - releases it during contraction -release is triggered by an AP
40
The Proteins of Muscle
Myofibrils are built of 3 kinds of protein:
– contractile proteins
– regulatory proteins which turn contraction on & off
– structural proteins which provide proper alignment, elasticity and extensibility
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Name of Contractile proteins
myosin and actin
42
Name of regulatory proteins
troponin and tropomyosin
43
Name of structural proteins
Dystrophin – connects sarcomere to sarcolemma, transmits tension along muscle
Actinin – part of Z-line
Titin – connects myosin to Z-line and M-line, Role in recovery after being stretched
Nebulin – forms core of the actin chain/thin filament
44
Types of muscle fibers
- Fast fibers = glycolytic
- Slow fibers = oxidative
- Fibers of one motor unit all the same type
- Percentage of fast versus slow fibers is genetically determined
- Proportions vary with the usual action of the muscle
- neck, back and leg muscles have a higher proportion of postural, slow oxidative fibers
- shoulder and arm muscles have a higher proportion of fast glycolytic fibers
45
Fast Fibers
- Large in diameter
- Contain densely packed myofibrils
- Large glycogen reserves
Fast oxidative-glycolytic (fast-twitch A)
– red in color (lots of mitochondria, myoglobin & blood vessels)
– split ATP at very fast rate; used for walking and sprinting
Fast glycolytic (fast-twitch B)
– white in color (few mitochondria & BV, low myoglobin)
– anaerobic movements for short duration; used for weight-lifting
46
Slow fibers
Half the diameter of fast fibers
– Three times longer to contract
– Continue to contract for long periods of time • e.g. marathon runners
47
Atrophy
wasting away of muscles
– caused by disuse (disuse atrophy) or severing of the nerve supply (denervation atrophy)
– the transition to connective tissue can not be reversed
48
Hypertrophy
- increase in the diameter of muscle fibers
– resulting from very forceful, repetitive muscular activity and an increase in myofibrils, SR & mitochondria
49
Muscle Metabolism - production of ATP
contraction requires huge amounts of ATP
-muscle fibers produce ATP three ways:
1. Creatine phosphate
2. Aerobic metabolism
3. Anaerobic metabolism
50
Creatine Phosphate
- Muscle fibers at rest produce more ATP then they need for resting metabolism
- Excess ATP within resting muscle used to form creatine phosphate
- By the enzyme creatine kinase
- Creatine phosphate: 3-6 times more plentiful than ATP within muscle
- Its quick breakdown provides energy for creation of ATP
- Sustains maximal contraction for 15 sec (used for 100 meter dash).
- Athletes tried creatine supplementation
51
Sarcomere and its structure
sarcomere = regions of myosin (thick myofilament) and actin (thin myofilament)
- bounded by the Z line (actinin)
- actin filaments project out from Z line
- myosin filaments lie in center of sarcomere - overlap with actin and connect via cross-bridges
- myosin only region = H zone
- myosin filaments are held in place by the M line proteins
- actin only region = I band
- length of myosin filaments = A band
- contraction = “sliding filament theory”
- actin and myosin myofilaments slide over each other and sarcomere shortens
52
The Sliding Filament Theory
Explains how a muscle fiber exerts tension
Four step process
- Active sites on actin
- Cross bridge formation
- Cycle of attach, pivot, detach, return
- Troponin and tropomyosin control contraction
53
Contraction
Actin filament has a myosin binding site
- This site is “covered up” by troponin and tropomyosin in relaxed muscle
- Removal of troponin/tropomyosin is required for contraction
- myosin thick myofilament is a bundle of myosin molecules
- each myosin protein has a globular “head” with a site to bind and breakdown ATP (ATPase site) and to bind actin (actin binding site)
54
Events of muscle contraction
- ACh released from synaptic vesicles
- Binding of ACh to motor end plate
- Generation of electrical impulse in sarcolemma
- Conduction of impulse along T-tubules
- Release of Calcium ions by SR - binds to troponin • Exposure of active sites on actin
- Cross-bridge formation and contraction
55
The Neuromuscular junction
- end of neuron (synaptic terminal or axon bulb) is in very close association with the muscle fiber
- distance between the bulb and the folded sarcolemma = synaptic cleft
- nerve impulse leads to release of neurotransmitter (acetylcholine)
- N.T. binds to receptors on myofibril surface
- binding leads to influx of sodium, potassium ions (via channels)
- eventual release of calcium by sarcoplasmic recticulum = contraction
- Acetylcholinesterase breaks down ACh • Limits duration of contraction
56
Motor Units
- Each skeletal fiber has only ONE NMJ
- MU = Somatic neuron + all the skeletal muscle fibers it innervates
- Number and size indicate precision of muscle control
- Muscle twitch
– Single momentary contraction
– Response to a single stimulus
All-or-none theory
– Either contracts completely or not at all
57
How Motor Units fire
Motor units in a whole muscle fire asynchronously
some fibers are active others are relaxed
delays muscle fatigue so contraction can be sustained
58
Why are muscle fibers of different moter units intermingled
Muscle fibers of different motor units are intermingled so that net distribution of force applied to the tendon remains constant even when individual muscle groups cycle between contraction and relaxation.
59
Axial muscles
organized into four groups:
Muscles of the head and neck
Muscles of the vertebral column
Oblique and rectus muscles
Muscles of the pelvic floor
60
Appendicular muscle
Stabilizing pectoral girdle
Stabilizing pelvic girdle
Moving upper and lower limbs
Four groups of muscles:
Muscles that position the pectoral girdle
Muscles that move the arm
Muscles that move the forearm and hand
Muscles that move the hand and fingers
