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Quick Review
Topic Four: The Neuromuscular Junction
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Topic Four: The Neuromuscular Junction
Investigating The Effects of Temperature on Muscle Function
Materials: Ice/ Pen or pencil
1. Write your signature 3 times under the column labelled “Normal”.
2. Obtain a handful of ice and hold it in your writing hand (over a sink!)
2. Write your signature 3 times under the column labelled “Cold”.
3. Place your hands under warm running water for a few minutes and massage your
hands.
4. Write your signature 3 times under the column labelled “Warm”.
Normal
Cold
Warm
Analysis
1. What effect did the changes in temperature have on your hand muscles?
Answer:
2. How could you explain this effect?
Answer:
3. Why do you think dancers wear leg warmers and baseball pitchers wear jackets before
pitching?
Answer:
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Topic Four: The Neuromuscular Junction
You got Nerve...
The nervous system is divided into two parts: the central nervous system and the
peripheral nervous system. While the brain and the spinal cord constitute the central
nervous system, the so-called cranial and spinal nerves form parts of the peripheral
system. The peripheral nerves connect the central nervous system with the sense organs,
i.e. the organs for vision, hearing, smell, taste and perceptional touch, and other effector
organs like muscles and glands. Together, the CNS and PNS work as an electrochemical
communication system that:
o receives sensory signals from the external environment (sensory neurons)
o organizes and integrates information (interneurons)
o interprets information and initiates an appropriate response (motor neurons)
Your brain is made of approximately 100 billion specialized cells called neurons. Neurons
have the amazing ability to gather and transmit electrochemical signals -- they are
something like the gates and wires in a computer. Neurons share the same characteristics
and have the same organelles as other cells, but the electrochemical aspect lets them
transmit signals over long distances (up to several feet or a few meters) and pass
messages to each other.
The Human Nervous System
Central Nervous System (CNS)
Peripheral Nervous System (PNS)
Brain and Spinal Cord
Sensory and Motor Neurons
Somatic Nervous System
Autonomic Nervous System
motor neurons to skeletal muscle
nerves from internal receptors
sensory neurons from receptor sense organs
nerves to smooth muscle
_______________________________________________________________________________________
Remember the Ice Bucket Challenge….
Neuromuscular disorders affect the nerves that control your voluntary muscles.
Amyotrophic lateral sclerosis (ALS) is a nervous system disease that attacks nerve
cells called neurons in your brain and spinal cord. These neurons transmit messages
from your brain and spinal cord to your voluntary muscles. At first, this causes mild
muscle problems. Eventually, you lose your strength and cannot move. When muscles
in your chest fail, you cannot breathe. A breathing machine can help, but most people
with ALS die from respiratory failure.
There is no cure.
Source ~ National Institute of Health, 2014
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Topic Four: The Neuromuscular Junction
Skeletal muscles are told what to do by the nervous system. They only contract when
told to do so. A single motor unit consists of one motor neuron and all of the muscle
fibers it innervates. The neuromuscular junction is the term for the connection
between the nervous system and the muscle fiber.
How do we control and move our muscular system?
4.1.1
Label a diagram of a motor unit
Figure 1
Label:
dendrite, cell body, nucleus, axon, motor end plate, synapse & muscle.
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Motor unit
Topic Four: The Neuromuscular Junction
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Topic Four: The Neuromuscular Junction
Motor Unit Questions
1. Name the different regions of a
motor unit. See Figure 3.
Figure 3
A- A motor unit. B- A motor neurone
Answer:
2. Figure 4 has been created from a slide of skeletal tissue as seen with a light
microscope at a magnification of 800 times. It shows part of two motor
units.
Use evidence from the drawing:
Figure 4 Two motor units in skeletal tissue
(a) What is a motor unit?
Answer:
(b)
Why all the muscle fibres shown will not necessarily contract at the
same time.
Answer:
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Topic Four: The Neuromuscular Junction
Investigation 1 – The Reflex Arc
Task One
Figure 2 Mechanism of knee jerk reflex
Work in pairs. One of you sit crossed
legged in a relaxed position. Your partner
firmly taps your patella tendon using a
patella hammer or ruler (the patella
tendon is positioned just below the knee
cap). Describe and record the response of
the knee to the tap. How can you tell that
this response was a reflex action?
Task Two
Give an example of a skill you have learned which has become an automatic
response to a stimulus.
Answer:
Task Three
Research- Distinguish between an automatic (reflex response) and fast reactions.
Use examples from sporting situations to illustrate your answer.
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Topic Four: The Neuromuscular Junction
Motor Unit Questions Part B
2(c) Briefly describe the sequence of events at the muscle end plate which
leads to an action potential passing along the muscle fibre.
Answer:
3. Figure 5 shows the pathways of transmission of impulses through the central
nervous system during the knee jerk reflex.
(a)
Give the names of the five
structures lettered P-T.
Figure 5: Knee jerk reflex
Answer:
 P =
 Q=
 R =
 S =
 T =
(b)
With reference to figure 5, briefly describe the sequence of events in a
knee jerk reflex.
Answer:
(c)
Describe briefly the structure and function of a synapse.
Answer:
(d)
Explain why the release of a transmitter substance, such as
acetylcholine, into a neuromuscular junction does not stimulate the
muscle to go into prolonged contraction.
Answer:
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4.1.2
Topic Four: The Neuromuscular Junction
Explain the role of neurotransmitters in stimulating skeletal
muscle contraction.
1. Watch… Events at the Neuromuscular Junction:

http://www.as.wvu.edu/~sraylman/physiology/fig_7_6_WITH_LOADING_SCR.html

http://www.dnatube.com/video/5034/Contraction-of-muscle-function-ofneuromuscular-junction
Explain the following terms:

Action potential -

Vesicle -

Neurotransmitter -

Acetylcholine (Ach) -

Cholinesterase –
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Topic Four: The Neuromuscular Junction
Summarize the events that occur at the neuromuscular junction by sequencing the
following steps:
1. The neuron initiates an action potential down its axon to the axon
terminal/motor end plate.
2. Once the neurotransmitters bind to the specialized receptors, a muscle
contraction is initiated.
3. The action potential opens Ca+2 gates and calcium ions enter and interact with
vesicles in the terminal ends of the neuron.
4. ACh is released from receptors and broken down by specialized enzymes in the
synaptic cleft.
5. Vesicles release neurotransmitters that travel to specialized neurotransmitter
receptors on the muscle cell.
6. A motor neuron receives a stimulus and it gets ‘excited’.
See: https://quizlet.com/16523318/exam-3-anatomy-and-physiology-flash-cards/
Identify the key components from the process that ends in a muscle contraction:
o The electrical trigger for a muscle contraction is called an:
o The binding of ACh triggers the exchange of which two ions?
o Ca+2 triggers the release of this neurotransmitter:
o ACh binds to special receptors on which structure?
o The enzyme that breaks down Ach is called:
o Tiny little sacs that store neurotransmitters are called:
Neatly label the following components in figure 6 below. Neatness counts!
o vesicles, neurotransmitters, muscle, neuron, specialized receptors
Figure 6
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Topic Four: The Neuromuscular Junction
The role of neurotransmitters
1. In your own words review and explain the role of acetylcholine and
cholinesterase in the stimulation of skeletal muscle contraction.
Answer:
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Topic Four: The Neuromuscular Junction
Sarcomeres
Myofibrils are the contractile units of the muscle and are organized into sarcomeres.
It’s the sarcomere that contracts, pulling and shortening the entire muscle fiber.
Sarcomeres are defined at each end by a Z-band or Z-line. This is the boundary line
for each sarcomere; one unit is bound on both sides by a Z-line. The action filaments
are attached. Additional areas or distances along the filament can be identified. These
include the I-band, A-band and a middle H-band. Actin filaments attach to the Zbands. I-bands are regions that contain only actin. A-bands are regions that consist of
overlapping actin and myosin. The H-band is a region that contains only myosin.
The banding patterns arise from the organization within the sarcomere of two major
protein filaments: thick myosin filaments surrounded by thin actin filaments. It is the
interaction of these filaments that results in contraction of the sarcomeres.
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Topic Four: The Neuromuscular Junction
In the images of a sarcomere below, clearly label the following:
o The Z bands, the I band, the A band and the location of actin and myosin
1. When the sarcomere shortens, which band(s) will change length?
Answer:
2. When the sarcomere shortens, which band(s) will not change lengths?
Answer:
3. Which protein filament is attached to the Z line?
Answer:
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Topic Four: The Neuromuscular Junction
Structure of a sarcomere
Match the terms:
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Topic Four: The Neuromuscular Junction
The contraction, or shortening, of a muscle powers movement.
The basic contractile unit of a muscle is the sarcomere.
Figure 7: Diagrammatic detail of muscle sarcomere
1. When the muscle contracts, do the actin and myosin filaments shorten?
Answer:
2. Explain how the sarcomere shortens when the parts that make it up don’t
shorten.
Answer:
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4.1.3
Topic Four: The Neuromuscular Junction
Explain how skeletal muscle contracts by the sliding
filament theory.
Let's take a look at what occurs within a skeletal muscle, from excitation to contraction to
relaxation:

An electrical signal (action potential) travels down a motor neuron, causing it to
release the chemical acetylcholine - ACh (neurotransmitter) into a small gap between
the nerve cell and muscle cell. This gap is called the synapse.

The neurotransmitter crosses the gap, binds to a protein (specialized receptor) on the
muscle-cell membrane and causes an action potential in the muscle cell.

The action potential rapidly spreads along the muscle cell and enters the cell through
tubules.

The action potential opens gates in the muscle's calcium store (sarcoplasmic
reticulum).

Calcium ions flow into the cytoplasm, where the actin and myosin filaments are.

Calcium ions bind to troponin molecules located in the grooves of the actin filaments.

Upon binding, troponin changes shape and slides a molecule, tropomyosin out of its
groove, exposing an actin-myosin binding sites. Normally, the rod-like tropomyosin
molecule covers the sites on actin where myosin can form cross-bridges.

The myosin heads then interact with actin by reaching up and pulling on the actin. The
muscle thereby creates force, and shortens. This is the contraction.

After the action potential has passed, the calcium gates close, and calcium pumps
located on the sarcoplasmic reticulum remove calcium from the cytoplasm.

As the calcium gets pumped back into the sarcoplasmic reticulum, calcium ions are
released from the troponin.

The troponin then returns to its normal shape, allowing the tropomyosin to once again
cover the actin-myosin binding sites on the actin filament.

Because no binding sites are available now, no crossbridges can form, and the muscle
relaxes back to its normal length.
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Topic Four: The Neuromuscular Junction
As you can see, a muscle contraction is regulated by the level of calcium ions in the
cytoplasm. In skeletal muscle, calcium ions work at the level of actin (actin-regulated
contraction). They move the troponin-tropomyosin complex off the binding sites, allowing
actin and myosin to interact.
All of this activity requires energy in the form of ATP. The energy released by breaking the
covalent bond holding the last phosphate group is used to reset the myosin cross-bridge
head and release the actin filament. To generate a supply of ATP, the muscle can
complete the following:
o Break down creatine phosphate, adding the phosphate to ADP to create ATP
o Carry out anaerobic respiration, by which glucose is broken down to lactic acid
and a small amount of ATP is formed
o Carry out aerobic respiration, by which glucose (and sometimes glycogen, fats
and amino acids) is broken down in the presence of oxygen to produce large
quantities of ATP.
Review the following…

http://highered.mcgraw-hill.com/olc/dl/120104/bio_b.swf

https://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__myofilament_contraction.html

https://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__sarcomere_contraction.html

http://www.wellcome.ac.uk/Education-resources/Education-and-learning/Big-Picture/All-issues/Exercise-energy-andmovement/WTDV033020.htm
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Topic Four: The Neuromuscular Junction
Role of the various components involved in a Muscle Contraction
Myosin
Actin
Cross bridge
Troponin
Tropomyosin
Sarcoplasmic
reticulum
Acetylcholine
Calcium
ATP
1. Describe the action between myosin and actin during contraction.
Answer:
Great Websites

http://www.wwnorton.com/college/biology/discoverbio3/full/content/ch27/animations.asp

http://www.getbodysmart.com/ap2/muscletissue/contraction/propagation/tutorial.html

http://faculty.massasoit.mass.edu/whanna/201/201_content/topicdir/muscle/muscle_media/muscle_VD/
page143/page143.html

http://www.wellcome.ac.uk/Education-resources/Education-and-learning/Big-Picture/All-issues/Exerciseenergy-and-movement/WTDV033020.htm
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Topic Four: The Neuromuscular Junction
_______________________________________________________________________
What’s rigor mortis?
After death, calcium levels inside the muscle cells rise and the body's level of ATP
naturally drops. Inside the muscles, myosin binds to actin and the muscles contract.
However, with no ATP to reset the cross-bridges and release the myosin, all of
the muscles remain in contraction and are stiff; this state is called rigor mortis.
____________________________________________________________________
1. In your own words, explain the major events that occur during muscle contraction to
your partner.
With a partner: Check your understanding
. . . . . . . . . . . . . . . . . 1. the single functioning unit for muscle contraction
. . . . . . . . . . . . . . . . . 2. the membrane surrounding a muscle tissue
. . . . . . . . . . . . . . . . . 3. the specialized organelle that stores calcium
. . . . . . . . . . . . . . . . . 4. the neurotransmitter released at a muscular junction
. . . . . . . . . . . . . . . . . 5. the thin protein band found in a sarcomere
. . . . . . . . . . . . . . . . . .6. the thick protein band found in a sarcomere
. . . . . . . . . . . . . . . . . .7. the protein filament that holds troponin
. . . . . . . . . . . . . . . . . .8. the ion that reacts with troponin
. . . . . . . . . . . . . . . . . .9. a protein with ‘heads’ that interacts to form cross bridges
. . . . . . . . . . . . . . ……10. a long strand of repeating sarcomeres found in a muscle fiber
https://www.boundless.com/biology/textbooks/boundless-biology-textbook/themusculoskeletal-system-38/muscle-contraction-and-locomotion-218/skeletal-musclefiber-structure-824-12067/
https://quizlet.com/1688264/ap-structure-of-a-muscle-fiber-flash-cards/
http://www.colorado.edu/Outreach/BSI/pdfs/muscleContraction.pdf
https://www.boundless.com/biology/textbooks/boundless-biology-textbook/themusculoskeletal-system-38/muscle-contraction-and-locomotion-218/regulatoryproteins-827-12070/
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Topic Four: The Neuromuscular Junction
Complete the flow chart below
A nerve impulse is sent from the
brain through ______________________
to stimulate muscle contraction
The nerve impulse travels down
the __________ , generating an action
potential which causes calcium
ions to be released from the
__________________.
Ca+ ions diffuse into the sarcomere
and attach to _____________ Which
changes shape.
As ____________ changes shape it
pulls _____________ away from the
myosin binding sites on the actin –
which are now exposed!
When the nerve impulse stops,
the calcium gates close, Ca+ ions
are removed via the _______________
and ________________ returns to
normal shape
______________ covers the myosin
binding sites and the muscle
relaxes.
Myosin heads use _______ to pull
themselves along the actin
molecule, forming __________ at
each binding site before breaking
and __________ stroking to the next
one.
The sarcomere shortens –
___________ moves closer together –
the muscle is contracting
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Topic Four: The Neuromuscular Junction
What is the structure of our muscles?
4.1.4
Explain how slow and fast twitch fibre types differ in
structure and function

Type I Fibres – Slow Oxidative
These fibres, also called slow twitch or slow oxidative fibres, contain large amounts
of myoglobin, a high number of mitochondria and a well developed capillary system.
Type I fibres appear red (due to the high concentration of myoglobin and blood flow),
split ATP at a relatively slow rate, have a slow contraction velocity, are very resistant
to fatigue and have a high capacity to generate ATP by oxidative (aerobic)
metabolic processes. Relative to fast twitch fibres, they have a smaller muscle
diameter. These types of fibres are found in large numbers in the postural muscles of
the neck due to the necessity for endurance.

Type II B Fibres – Fast Glycolytic
These fibres, also called fast twitch or fast glycolytic fibres, contain a low
concentration of myoglobin, relatively few mitochondria, have a limited blood supply
but large amounts glycogen. Type II B fibres are white, geared to generate ATP by
anaerobic metabolic processes, not able to supply skeletal muscle fibres continuously
with sufficient ATP, fatigue easily, split ATP at a fast rate and have a fast contraction
velocity. Such fibres are found in large numbers in the muscles of the arms.

Type II A Fibres – Fast Oxidative
These fibres, also called fast twitch or fast oxidative fibres, are infrequently found in
humans. They contain high concentrations of myoglobin, mitochondria and a rich
blood supply. Type II A fibres are red, have a very high capacity for generating ATP by
oxidative metabolic processes, split ATP at a very rapid rate, have a fast contraction
velocity and are resistant to fatigue.
adapted from

see also
http://www.brianmac.co.uk/muscle.htm
http://courses.washington.edu/conj/bess/types/fibertypes.html
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Topic Four: The Neuromuscular Junction
Investigation- To consider some of the characteristics of fibre types
Training or genetics?
1. Discuss the role of genetics in determining the proportions of muscle fibre
types and the potential for success in selected activities.
Answer:
Find out…
1. What is myoglobin?
Answer:
2. What is glycogen?
Answer:
3. For each muscle fiber type, list three identifying characteristics:
o Slow Twitch (Type 1)
Answer:
o Fast Twitch (Type 2a)
Answer:
o Fast Twitch (Type 2b)
Answer:

Type IIa and IIb are high in glycogen content depending on training status.
https://www.boundless.com/physiology/textbooks/boundless-anatomy-and-physiologytextbook/muscle-tissue-9/skeletal-muscle-96/types-of-skeletal-muscle-fibers-538-5126/
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Topic Four: The Neuromuscular Junction
4. Outline different types of activities that would rely more heavily on each muscle type:
o Type I (slow twitch oxidative)
Answer:
o Type II (fast twitch)
Answer:
http://www.flashcardmachine.com/exercise-physiology19.html
http://athletics.wikia.com/wiki/Types_of_Muscle_Fiber
Read and review the following:
The rate of fatigue
Fast glycolytic fibers fatigue rapidly, while slow oxidative fibers are highly resistant to
fatigue. Muscles that need to be active continuously, such as weight-supporting
postural muscles, contain a higher percentage of fatigue-resistant slow oxidative
muscle fibers.
Size
Slow oxidative muscle fibers have the smallest diameter, fast oxidative fibers are
intermediate in size, and fast glycolytic fibers are the largest. Consequently, the fast
glycolytic fibers produce the most force, since they contain the most myofibrils. Fast
glycolytic motor units also produce more force because they tend to have more muscle
fibers in each motor unit.
Another effect of size relates to recruitment. Recruitment refers to the process of
increasing activation of motor units to increase the force produced by a whole muscle.
The slow oxidative motor units are innervated by somatic efferent neurons with the
smallest cell bodies.
It turns out that the smallest neurons are the easiest to excite. So slow oxidative
motor units are recruited first, for low-intensity activity such as standing. As activity
intensifies and excitatory drive increases, larger and larger somatic efferent neurons
will be excited and so fast oxidative, and finally fast glycolytic motor units will be
recruited. This orderly recruitment of motor units according to size of somatic efferent
neurons is known as the size principle.
http://courses.washington.edu/conj/bess/types/fibertypes.html
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Topic Four: The Neuromuscular Junction
Summary Comparison of Muscle Fiber Types
Characteristics
Fast Twitch Glycolytic
Slow Twitch Oxidative
Relative speed of
contraction
For strength or
endurance?
Fatigue resistance
(high or low?)
Main type of
respiration used
Relative supply
of blood vessels
Relative concentration
of myoglobin
Relative concentration
of mitochondria
Advantageous for
these types of activity
…
Examples of this type …

Think of the aerobic system as the big diesel bus with a massive fuel tank as
opposed to the V8 car of the ATP-PC system and the V6 car of the anaerobic
glycolytic system.

Anaerobic Glycolysis is the transformation of glucose to lactate when limited
amounts of oxygen (O2) are available.
http://www.ptdirect.com/training-design/anatomy-and-physiology/the-aerobic-system
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Topic Four: The Neuromuscular Junction
Refer to the readings and additional resources for help
Type II muscle fiber is also known as fast twitch muscle fiber. Muscle fiber types can
be broken down into two main types: slow twitch (Type I) muscle fibers and fast
twitch (Type II) muscle fibers. These fast twitch fibers can be further categorized into
Type IIa and Type IIb fibers, which are also known as "fast twitch oxidative" and "fast
twitch glycolytic," respectively.
Type I fibers are characterized by low force/power/speed production and high
endurance, Type IIB fibers are characterized by high force/power/speed production
and low endurance, while Type IIA fall in between the two.
It is possible that a fibre might be transformed from Type IIB to Type IIAB to Type IIA
with exercise training.
There are significant benefits to working to the point of temporary fatigue—and
therefore making sure fast-twitch fibers have been recruited. For instance, if you're
looking to increase muscle mass, and improve strength, using fast-twitch fibers is the
only way to do it.
On the other hand, aerobic exercises, those that mainly use slow-twitch fibers, can
increase stamina and the oxygen capacity of your muscles, allowing the body to burn
energy for longer periods of time. A high proportion of slow-twitch fibers has also been
associated with low blood pressure. Previous research has also shown that women
may have a greater distribution of type I muscle fibers and lower distribution of type II
muscle fibers than men.

http://athletics.wikia.com/wiki/Type_II_Muscle_Fiber

http://www.builtlean.com/2012/09/10/muscle-fiber-types/

http://greatist.com/fitness/what-are-fast-and-slow-twitch-muscles

http://ccahill.hubpages.com/hub/Fast-Twitch-vs-Slow-Twitch-Muscle-Fibres-Endurance-orStrength

http://www.ptdirect.com/training-design/anatomy-and-physiology/the-anaerobic- glycolytic-systemfast-glycolysis
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Topic Four: The Neuromuscular Junction
Investigation 1
Table 1 shows the percentage composition of slow twitch fibres found in the leg
muscles of male athletes specialising at different distances of athletic event.
1. Briefly discuss the relationship between the percentage of slow twitch
fibres and race distance, as suggested by the data in Table 1
Table 1: Percentage composition of slow-twitch fibres in male leg muscles
Event
Marathon runners
800 m runners
100/200 m
sprinters
Mean % slow
twitch fibres
Range of %
slow twitch
fibres
85
55
35
50-95
50-80
20-55
Answer:
2. Which group of athletes is the most specialised in terms of slow twitch
muscle fibre composition? Explain your choice by reference to Table 1.
Answer:
3. Arrange the group of runners in rank order according to how closely their
slow twitch muscle fibre composition matches the 'ideal' for their distance.
Answer:
1. List three features of slow twitch fibres that contribute to their greater
aerobic capacity.
Answer:
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Topic Four: The Neuromuscular Junction
Investigation 2: To consider some of the characteristics of fibre types
1. The effects of specialised training can alter the metabolic functioning of
fast twitch type IIb fibres so that they take on some of the characteristics
of type 1 fibres and become type IIa fibres. Describe the ways in which
metabolic functioning of type IIa fibres will change as a result of specialist
aerobic training.
Answer:
2. In which sporting activities would the adaptation of fast twitch (type IIb)
fibres to type IIa fibres be relevant to a sportsperson?
Answer:
3. What types of training would cause the adaptation of fast twitch fibres to
type IIa fibres?
Answer:
4. Using the information in Figure 8, describe the order in which fibre types
are recruited as the number of motor units increase.
Answer:
Figure 8: Recruitment of fibre types
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Topic Four: The Neuromuscular Junction
Review: To consider some of the characteristics of fibre types
Another interesting study is the relationship between distribution of fibre type and
different sporting activities as illustrated in Table 9. Basically, the more explosive and
intense the demands of a sport, the more likely it is that successful sportspeople will
have a higher proportion of fast twitch muscle fibres in their muscles.
Table 9; Percentages of slow-twitch (type I) and fast-twitch (type II) fibres in males and
females (found in leg muscles) compared to sporting activity (based on references 1922).
Event
Distance runners
Cross-country
skiers
Cyclists
800 m runners
Javelin throwers
Shot putters
Sprinters
Untrained
% Type I
Males
Females
79
64
60
48
50
38
24
45
69
59
52
61
43
50
29
55
% Type II
Males
Females
21
36
40
52
50
62
76
55
31
41
48
39
57
50
71
45
1. Using the information from this table, comment on the distribution of
fibre type (for males and females) with respect to different sporting
activities.
Answer:
2. Compare and account for differences in percentage fibre distribution with
respect to males and females.
Answer:
3. Compare and account for differences in percentage fibre distribution
between trained and untrained performers.
Answer:
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Topic Four: The Neuromuscular Junction
Exam Questions
Q.1
Explain the process of contraction once a muscle fibre has been stimulated by a
neurotransmitter. (8)
Q.2
Explain the role of acetylcholine in muscle contraction. (2)
Q.3
Explain how the function of type I muscle fibres differs from the function of type
IIb. (3)