Transcript Muscles and how they work v.2 File

MUSCLES AND HOW
THEY WORK
Pedro Amarante Andrade, PhD
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BIOSCIENCES
FOR SPEECH AND LANGUAGE THERAPY
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MUSCLES AND
HOW THEY WORK
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MUSCULAR TISSUE
Myology
• Produce body movement & stability
• Move substances through the body
(propel fluids + food)
• Produce heat (Thermogenesis)
• Forms 40-50% of body weight
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MUSCULAR TISSUE
Properties
• Electrical excitability
– Chemical or autorhythmic
• Contractility
• Extensibility
• Elasticity
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MUSCULAR TISSUE
Types
(a)Skeletal muscle
• Striated & Voluntary
(b)Smooth muscle
• Nonstriated & involuntary
(c)Cardiac muscle
• Striated & involuntary
Anatomy & Physiology, Connexions Web site.
http://cnx.org/content/col11496/1.6/, Jun 19, 2013.
Author: OpenStax College
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MUSCULAR TISSUE
AGGREGATES
Fascia
Ligaments
Tendons
Bones
Joints
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MUSCLE
FIBER
Tortora & Derrickson, 2012, pp 304
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MUSCLE FIBER
Tortora & Derrickson, 2012, pp 304
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NERVE CELL VS MUSCLE FIBER
Anatomy
Nerve cell
Muscle cell/fibre
Cell membrane
Sarcolemma
Cytoplasm
Sarcoplasm
1 nucleus
Multiple nuclei
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MUSCLE FIBER
Anatomy
Muscle cell/fibre
Sarcolemma
T-tubules
Sarcoplasm
Multiple nuclei
Tortora & Derrickson, 2012, pp 306
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MUSCLE FIBER
Anatomy
Muscle cell/fibre
Sarcolemma
Sarcoplasm
Glycogen
Wikipedia, Mikael Häggström.
Multiple nuclei
Wikipedia, Ben Mills.
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MUSCLE FIBER
Anatomy
Muscle cell/fibre
Sarcolemma
Sarcoplasm
Glycogen
Myoglobin
Multiple nuclei
Wikipedia, Aza Toth
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MUSCLE FIBER
Anatomy
Muscle cell/fibre
“Each skeletal muscle fiber
arises during embryonic
development from the
fusion of a hundred or
more small mesodermal
cells (myoblasts)”
Sarcolemma
Sarcoplasm
Multiple nuclei
Totora & Derrickson, 2012
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SARCOPLAMS
Tortora & Derrickson, 2012, pp 306
Sarcoplasmic reticulum
Stores and release Ca2+
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SARCOPLAMS
Tortora & Derrickson, 2012, pp 306
Myofibrils
The contractile organelles of skeletal muscles
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MYOFIBRILS
Filaments
2 thin
filaments for
each thick fl.
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MYOFIBRILS
Filaments
2 thin
filaments for
each thick fl.
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MYOFIBRILS
Filaments
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MYOFIBRILS
Sliding filaments mechanism
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MYOFIBRILS
Sliding filaments mechanism
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NEUROMUSCULAR
JUNCTION
Tortora & Derrickson, 2012, pp 316
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NEUROMUSCULAR
JUNCTION
Tortora & Derrickson, 2012, pp 316
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MUSCLE CONTRACTION
Twitch phases
Tortora & Derrickson, 2012, pp 321
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MUSCLE CONTRACTION
Temporal Summation
Ca2+
Tortora & Derrickson, 2012, pp 322
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THE NEUROMUSCULAR JUNCTION
Motor Unit
A MOTOR UNIT consists of a somatic
motor neuron plus all the skeletal muscle
fibres it stimulates
This determines the precision of movement
possible, as well as the force of contraction;
more precise control possible with a low
ratio
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THE NEUROMUSCULAR JUNCTION
Motor Unit
Having a low ratio of nerve fibre: muscle fibres
enables high degree of precision in movement
Contrast this with larger limb muscles, or
muscles to control posture
Larynx 1:6-12 versus Hip 1:2000
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THE NEUROMUSCULAR JUNCTION
Motor Unit
Typically, the muscle fibres of a motor unit are
dispersed throughout a muscle rather than
clustered together
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THE NEUROMUSCULAR JUNCTION
Motor Unit
• i.e. one neuron innervates 6 to 12 muscle
fibres in the larynx; in the eye muscles, this
ratio can be as low as 1:5; for some of the
larger, postural muscles, the ratio is much
higher
• In addition, the type of muscle fibre
determines the speed and sustainability of
muscle contractions
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TYPES OF SKELETAL MUSCLE FIBRE
a. Slow-twitch, fatigue resistant fibres; found in the
postural muscles of neck, back and legs
b. Fast-twitch, fatigue resistant fibres; found in leg
muscles
c. Fast-twitch, B fibres; fatigable. White as opposed to
a & b which are red. Strong, rapid contractions;
muscles of the shoulders and arms
MUSCLES have a mixture of all 3 fibres; proportion
depends on function
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SENSORY SUPPLY TO MUSCLES
• 40% of nerve supply for muscle is sensory in
nature
• Sends information regrading range, rate and
force of contraction, and position of muscle
• a. Proprioception = an awareness of body
position and movements of parts of the body
• b. Kinaesthesia = awareness of body motion
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SENSORY SUPPLY TO MUSCLES
PROPRIOCEPTORS
• Muscle spindles
• Tendon organs (Golgi tendon organs)
• Joint kinaesthetic receptors
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SENSORY SUPPLY TO MUSCLES
PROPRIOCEPTORS
Muscle spindles
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SENSORY SUPPLY TO MUSCLES
PROPRIOCEPTORS
Muscle spindles
http://isaacsondianaphysiology.wikispaces.com/12+Muscle+Physiology
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SENSORY SUPPLY TO MUSCLES
PROPRIOCEPTORS
Tendon Organs
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SENSORY SUPPLY TO MUSCLES
PROPRIOCEPTORS
Tendon Organs vs Muscle Spindle
http://kin450neurophysiology.wikispac
es.com/Postural+Control
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SENSORY SUPPLY TO MUSCLES
PROPRIOCEPTORS
Joint Kinaesthetic Receptors
• Some are in the capsule of a joint and respond to
pressure
• Some are in the connective tissue outside the
capsule and respond to acceleration/deceleration of
joint movement
• Ligaments contain receptors similar to tendon organs
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MUSCLES CONTROL
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ACETYLCHOLINE (ACH)
• A key neurotransmitter in the PNS and also
found in the CNS
• Drugs to treat a number of the conditions
which we are interested in as SLT have their
action on Ach. If they reduce the action of Ach
they are called anticholinergics (PD, CPOD). If
they prevent the breakdown of Ach they are
called cholinesterase inhibitors (MG, AD)
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MUSCLE FIBERS
• Each muscle fibre is innervated by one
neuron
• But one neuron can innervate a large
number of muscle fibres
• The greater the number of motor neurons
that are activated, the greater the number
of muscle fibres that will contract
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MUSCLE FIBERS
• Each muscle fibre contracts in an all-ornothing fashion (just like nerve fibres fire
in an all-or-nothing fashion) to their fullest
extent
• Factors that affect the force of contraction
include the number of muscle fibres
contracting (i.e. the number of motor
units, and the size of these units)
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TYPES OF SKELETAL MUSCLE FIBRE
• Muscle fibres vary in colour depending on
the amount of myoglobin they contain
• Myoglobin= a red-coloured protein, binds
oxygen, found in muscles (like
haemoglobin, found in red blood cells)
a. Slow-twitch, fatigue resistant fibres: found
in the postural muscles of neck, back and legs
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TYPES OF SKELETAL MUSCLE FIBRE
b. Fast-twitch, fatigue resistant fibres: found
in leg muscles
c. Fast-twitch, B fibres: fatigable. White as
opposed to a & b which are red in colour.
Produce strong, rapid contractions; for e.g., in
the muscles of the shoulders and arms
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TYPES OF SKELETAL MUSCLE FIBRE
MUSCLES have a mixture of all 3 fibres;
proportion depends on the particular
function of the muscle, and its use
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MUSCLES AND HOW THEY WORK:
A REVIEW
The more you read/see something explained in a
different way, the more sense it makes. Here are some
more You Tube finds, which explain how muscles work.
• First, an overview:
• http://www.youtube.com/watch?v=hzXVe4RS8-A
• Next, the detail of the sliding filament theory:
• http://www.youtube.com/watch?v=ELyoJZom5N0
• Finally, a good explanation of how muscle spindle
and Golgi tendon organs work. We will refer to these
when we look at REFLEXES next week.
• http://www.youtube.com/watch?v=7T4NI_2qDEM
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WORKSHOP ACTIVITY:
Find out the type (smooth or striated), location
and function of the following muscles:
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Stapedius
External intercostals
Orbicularis oris
Vascular muscle (tunica media)
Cricopharyngeus
Vocalis
Ciliary muscle
Bronchiole muscles
Genioglossus
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EXAM QUESTIONS (sample)
• What is the sarcoplasmic reticulum and what is its
main function in muscle cell contraction?
• What is meant by a motor unit?
• Compare the innervation of the facial muscles with
that of the limbs, with reference to the motor units
involved.
• What is the function of the joint kinaesthetic
receptors?
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SUGGESTED READING
• Chapters 6 and 8 in Atkinson &
McHanwell; Seikel et al, Chap 11;
Richards, Clark & Clarke, chap 1;
Manasco, Chap 2
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DIRECTED STUDY
What is the name of the medication
available to help with the symptoms of
Myasthenia Gravis (MG)?
How does it work?
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NOW TRY AND ANSWER THESE
EXAM-TYPE QUESTIONS
1) True/false:
a) actin is a long, thin molecule
b) The sarcoplasmic reticulum is the repository for
Na+ ions
c) A myofibril contains many muscle fibres
2) What role does ATP play in muscle contraction?
3) Name the disease which is characterised by damage
to the sarcolemma.
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NOW TRY AND ANSWER THESE
EXAM-TYPE QUESTIONS
4) TRUE or FALSE:
a. the actin filament has a binding site for the
myosin filament
b. In the resting state, ATP is bound to a region
on the actin filament
c. when Sodium (Na+) enters the sarcoplasmic
reticulum, this results in the binding site being exposed
on the actin filament.
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NOW TRY AND ANSWER THESE
EXAM-TYPE QUESTIONS
5) Describe what happens during the power stroke
phase of contraction. What happens to cause the
filaments to slide in relation to one another?
6) What is the name of the energy carrying molecule
involved in the process of muscle contraction?
7) How does this release of energy result in the relative
movement of the actin and myosin filaments?
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EXERCISE CAN INDUCE CHANGE IN
MUSCLE FIBRES
• Think of a marathon runner v a
weightlifter
• What type of fibres predominate in
the key muscles in these athletes?
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