Skeletal Muscle Physiology Flashcards
(105 cards)
1
Q
What types of muscle are smooth muscles
A
Skeletal and cardiac
2
Q
What are muscle tissues capable of doing
A
developing tension and producing movement through contraction
3
Q
What types of muscles are striated
A
skeletal and cardiac
4
Q
What causes striation
A
Thin actin filaments and thick myosin filaments
5
Q
What are skeletal muscles innervated by and what are they subject to
A
the somatic nervous system - subject to voluntary control
6
Q
What are cardiac and smooth muscles innervated by and what does this result in
A
Autonomic nervous system - involuntary action
7
Q
What are the 5 physiological functions of skeletal muscles
A
maintenance of POSTURE purposeful MOVEMENT in relation to external environment RESPIRATORY movements HEAT production contribution to WHOLE BODY METABOLISM
8
Q
What are skeletal muscle fibres organised into?
A
motor units
9
Q
what is a motor unit
A
a single alpha motor neuron and all the skeletal muscle fibres it innervates
10
Q
Muscles which serve fine movements (external eye muscles, muscles of facial expression and intrinsic hand muscles) have fewer fibres per motor unit. True or false
A
True
11
Q
When precision is more important than power, how many fibres per motor unit will there be
A
few
12
Q
In what case will there be hundreds to thousands of fibres per motor unit
A
Power more important than precision
13
Q
Gap junctions are present in skeletal muscle or cardiac muscle
A
cardiac muscle
14
Q
What initiates contraction in skeletal muscle
A
neurogenic initiation
15
Q
What initiates contraction of cardiac muscle
A
myogenic initiation
16
Q
Where is there a neuromusclular junction present - skeletal or cardiac
A
Skeletal
17
Q
Where does the Ca++ come from in skeletal muscles
A
sarcoplasmic reticulum
18
Q
Where does the Ca++ come from in cardiac muscles
A
From ECF and sarcoplasmic reticulum
19
Q
What is excitation contraction coupling
A
Process whereby the surface action potential results in activation of the contractile mechanism of the muscle fibre
20
Q
When is Ca2+ released from the lateral sacs of the sarcoplasmic reticulum in Skeletal muscles
A
When the surface action potential spreads down the transverse tubules (T Tubules)
21
Q
What are T tubules
A
Extensions of the surface membrane that dip into the muscle fibre
22
Q
What is the transmitter at the neuromuscular junction
A
Acetylcholine
23
Q
What triggers the release of Ca2+ from lateral sacs of sarcoplasmic reticulum
A
The spread of action potential down the T tubules
24
Q
Transverse tubules are surrounded by what
A
Lateral sacs
25
Skeletal muscle consists of parallel muscle fibres bundled by what
connective tissue
26
Skeletal muscle fibres usually extend where
The entire length of the muscle
27
What usually attaches skeletal muscles to the skeleton
Tendons
28
What form lever systems
Bones, muscles and joints
29
What does each muscle fibre contain
Many myofibrils
30
Myofibrils have alternating segments of what
Thick and thin protein filaments
31
Actin and mysocin are arranged into what and what are these
Sarcomeres - these are the functional units of muscle
32
What is the functional unit of any organ
The smallest component capable of performing all the functions of that organ
33
What is the functional unit of skeletal muscle
Sarcomere
34
Where is a sarcomere found
Between 2 Z lines - connect the thin filaments of 2 adjoining sarcomeres
35
What are the 4 zones of the sarcomere
A band
H zone
M line
I band
36
What is the A band made up of
THick filaments along the portions of thin filaments that overlap in both ends of thick filaments
37
What is the H zone
the lighter area within the middle of the A band where thin filaments dont reach
38
Where does the M line extend
Vertically down middle of A band within the centre of H zone
39
What does the I band consist of
Remaining portion of thin filaments that do not project in A band
40
What produces muscle tension
Sliding of actin and filaments on myocin filaments
41
Force generation depends on what
ATP dependent interaction between thick and thin filaments
42
What is ATP required for
Both contraction and relaxation
43
What is Ca2+ required for
to switch on cross bridge formation
44
How does Ca 2+ switch on cross bridge formation
It binds to troponin. This results in repositioning of troponin - tropomyocin complex to uncover the cross bridge binding sites on actin
45
When a muscle fibre is relaxed, why is there no cross bridge binding
Because the cross bridge binding site on actin is physically covered by the troponin tropomyosin complex
46
When a muscle fibre is excited, what happens in terms of Ca2+
Released Ca2+ binds with troponin, pulling troponin-tropomyosin complex aside to expose cross-bridge binding site. Cross bridge binding then occurs
47
What do motor units allow
simultaneous contraction of a number of muscle fibres
48
How is a stronger contraction achieved?
Stimulation of more motor units - motor unit recruitment
49
What helps prevent muscle fatigue
Synchronous motor units recruitment during submaximal contraction
50
Tension developed by each contracting muscle fibre depends on what 3 things?
1. Frequency of stimulation and summation of contraction
2. Length of muscle fibre at the onset of contraction
3. Thickness of muscle fibre
51
Describe the relationship between action potential and duration of resulting twitch
The duration of the AP is much shorter than that of the resulting twitch
52
How is it possible to summate twitches to bring about a stronger contraction of skeletal muscle
Through Repetitive fast stimulation of skeletal muscle
53
Both cardiac and skeletal muscles can be tetanised. True or False
False - cardiac muscle cannot be tetanised
54
Why can cardiac muscle not be tetanised
The long refractory period prevents generation of tetanic contaction
55
How does tension in skeletal muscles increase?
With increasing frequency of stimulation
56
What is an important mechanism for modulating the force of contraction in skeletal muscle
Increasing the frequency of stimulation
57
When can maximal tetanic contraction be achieved?
When the muscle is at its optimal length before the onset of contraction
58
What explain the skeletal muscle length tension relationship
The sliding filament mechanism
59
Skeletal muscle tension is transmitted to bone via what
The stretching and tightening of muscle connective tissue and tendon
60
What are the 2 types of skeletal muscle contraction
Isotonic conraction and Isometric contraction
61
Isotonic contraction is used for what?
body movements and for moving objects - muscle tension remains constant as the muscle length changes
62
Isometric contraction is used fo what?
Supporting objects in foxed positions and for maintaining body posture
Muscle tension develops at constant muscle lenght
63
How are isotonic and isometric contractions transmitted to bone
Via the elastic components of muscle
64
Describe the relationship between velocity of muscle and load
As the load increases, the velocity of muscle shortening decreases
65
What produces purposeful skeletal muscle activity
Input from a variety of sources influence the activity of motor unit to produce purposeful skeletal muscle activity
66
Input to motor nerves could be excitatory or inhibitory. True or False
True
67
What 4 things can cause impairment of skeletal muscle function
Intrinsic disease of muscle
Disease of NMJ
Disease of lower motor neurons which supply the muscle
Disruption of inputs to motor unit
68
What are 3 types of genetically determined myopathies
Congenital
Degeneration (muscular Dystrophy)
Membraine ion channels (myotonia)
69
What are 3 types of acquired myopatihes
Inflammatory (polymyosytis)
Endocrine (Cushing syndrome, thyroid disease)
Toxic (alcohol, statins)
70
What is a reflex action
A stereotyped response to a specific stimulus
71
Reflex actions are the simplest form of what?
coordinated movement
72
What are important for localising lesions in the motor system
The neural pathaways for reflexes
73
Where are pathways responsible fore reflex action located at?
Various levels of the motor system
74
The stretch reflex is the simplest what?
Monosynaptic spinal reflex
75
What does the stretch reflex serve as
A negative feedback that resists passive change in muscle lenghth to maintain optimal resting length of muscle
76
What is the muscle spindle? and when is it activated?
The sensory receptor and By the muscle stretch
77
By stretching the muscle spindle, what does this do to the afferent neurons
It increases firing in the afferent neurons
78
Where do the afferent neurons synapse
In the spinal cord with the alpha motor neurons
79
The stretch reflex is coordinated by what?
simultaneous relaxation of antagonist muscle
80
How cant he stretch reflex be elicited
By tapping the muscle tendon with a rubber hammer
81
What muscle is stretch in the patella tendon reflex (knee jerk)
Quadriceps fermoris
82
Name 5 examples of reflexes that can be elicited by the rubber hammer
Knee, Ankle, Biceps, Triceps Jerk and the brachioradialis
83
What spinal segment is effected in the biceps jerk and brachioradialis
C5-6
84
What peripheral nerve is affected by the brachioradialis and triceps jerk
Radial nerve
85
what spinal segment is affected by the
a) knee jerk
b) ankle jerk
a) L3,4
| b) S1,2
86
What spinal segment is affected in the triceps jerk
C6-7
87
What peripheral nerve is affected by the knee jerk
Femoral nerve
88
What peripheral nerve is affected in the ankle jerk
Tibial nerve
89
What peripheral nerve is affected in the biceps jerk
Musculocutaneous Nerve
90
What are the sensory receptors for the stretch reflex?
Muscle spindles
91
What are muscle spindles
A collection of specialised muscle fibres
92
What are muscle spindles also known as
intrafusal fibres
93
What are ordinary muscle fibres referred to as?
extrafusal fibres
94
Where are muscle spindles found and where do they run
Within the belly of muscles and they run parallel to ordinary muscle fibres
95
Muscle spindles have sensory nerve endings. What are these known as?
Annulospiral fibres
96
What are the efferent neurons that supply muscle spindles called
gamma motor neurons
97
what do gamma motor neurons do?
adjust the level of tension in the muscle spindles to maintain their sensitivity when the muscle shortens during muscle contraction
98
The contraction of intrafusal fibres contributes to the overal strength of the muscle contraction
False - it does not contribute
99
What does the discharge from the muscle spindles sensory ending do?
increases as the muscle is stretched
100
What are the 3 main differences between different types of skeletal muscle fibres
The enzymatic pathways for ATP synthesis
The resistance to fatigue - muscle fibres with greater capacity to synthesise ATP are more resistant to fatigue
The activity of myosin ATPase - ths determines the speed at which energy is made available for cross bridge cycling ie. the speed of contraction
101
What are 3 metabolic pathways that supply ATP in muscle fibres
Transfer of high energy phosphate from creatine Phosphate to ADP
Oxidative phosphorylation (main source when O2 is present)
Glycolysis (main source when O2 is not present)
102
What are type 1 fibres used for
prolonged relatively low work aerobic activities - maintenance of posture, walking
103
What are type 2a fibres used for
prolonged relatively moderate work activities - jogging
104
What are type 2x fibres used for
short term high intensity activities - jumping
105
What are 3 useful investigations in neuromuscular disease
Electromyography (EMG)
Nerve conduction studies
Muscle enzymes
