Lecture 3 - The Muscular system Flashcards
List four functions of the muscular system
- Movement
- Maintaining posture
- Heat production
- Storage of substances (glycogen and oxygen)
- Movement of substances (heart muscle - blood; Digestive tract - food; Urinary system - urine; Diaphragm - draws air in)
Describe the difference between striated and non-striated muscle
Striated muscle contains cells that are aligned in parallel bundles, their different regions forming stripes that are visible under a microscope. (e.g. skeletal and cardiac muscle)
Non-striated muscle contains cells that are randomly arranged (no stripes visible) e.g. smooth muscle
Define the following properties of muscles:
a. Contractability
b. Excitability
c. Extensibility
d. Elasticity
a. Contractability - ability to contract
b. Excitability - the ability to conduct an electrical current
c. Extensibility - the ability to stretch without damage
d. Elasticity - the ability to return to its original length and shape after contraction/extension
Which types of muscles are voluntary and which are involuntary?
Involuntary: Cardiac (heart); Smooth (blood vessels, walls of the gut, iris)
Voluntary: Skeletal
Name the three types of muscle in the body
Skeletal
Cardiac
Smooth
List two functions of skeletal muscle
motion
posture
speech
breathing
Explain the role of ‘fascia’
Fascia is a dense sheet of connective tissue that:
- organises muscle
- secures it to skin
- provides stability
What are ‘myocytes’?
The long cells that muscles are made up of (muscle fibres) are called myocytes.
How many skeletal muscles are there in the body?
640
Which organelle in the myocyte stores calcium and what is it used for?
The sarcoplasmic reticulum (smooth ER) stores calcium needed for muscle contraction
What is myoglobin?
A red-coloured, iron and oxygen-binding protein contained within muscle cells (fibres/myocytes). It stores oxygen.
What is the cell membrane of a myocyte called?
sarcolemma
Why are the many mitochondria within muscle cells located close to myoglobin?
Mitochondria have great need of oxygen in order to produce ATP, and myoglobin stores oxygen which it can then easily access.
What are transverse tubules?
They are tubes that extend from the cell membrane into the cells and help to ensure that electrical impulses get into the cell.
Why are we born with a set number of skeletal cells?
Muscle fibres are formed from the fusion of cells called myoblasts in the embryo. This is why skeletal muscle cells contain many nuclei.
Once mature muscle cells are formed (becoming ‘myocytes’), they can no longer undergo mitosis.
Since muscle fibres do not undergo mitosis, how is it possible for damaged muscles to regenerate?
Through ‘satellite cells’ there is limited regenerative capacity. These are multipotent stem cells found in skeletal muscle between the sarcolemma and the basement membrane. They are quiescent in most healthy adult muscle tissue and are only activated in response to muscle injury.
Where is a) oxygen and b) calcium stored in a muscle fibre?
a) myoglobin
b) sarcoplasmic reticulum
Define ‘myofibrils’
Myofibrils are cylindrical columns formed of bundles of protein filaments within the muscle fibre. They are contractile threads arranged in a striated pattern. They are basically the cytoskeleton of the muscle cell.
Describe the two myofilaments that make up myofibrils
Actin are the thin filaments and Myosin are thicker filaments that are shaped like golf clubs.
Define the following in connection to connective tissue in muscles:
a. epimysium
b. perimysium
c. endomysium
a. epimysium: the entire muscle is surrounded by this connective tissue layer that attaches it to the fascia and tendons
b. perimysium: a layer of connective tissue that surrounds bundles of between 10-100 muscle fibres (fascicles)
c. endomysium: a thin sheath of connective tissue that surrounds individual muscle fibres
What is meant by the term ‘sarcomere’?
A sarcomere is the basic unit of striated muscle and contains the following areas:
H zone = myosin filaments only
A band = dark area where actin and myosin overlap
I band = light area of only actin filaments
Z discs = filaments of actin that are arranged at 90degree angles at each end of the sarcomere
In impingement syndrome, the ____________ tendons (ie. supraspinatus) and/or ______ can become inflamed or damaged.
rotator cuff
bursa
Define impingement syndrome
It describes a shoulder condition in which movements of the shoulder can be painful and limited
What is a syndrome?
A syndrome is a collection of signs and symptoms.
What is the ‘painful arc’?
Typical degree of lateral arm abduction/adduction between 60 to 120 degrees that results in pain in impingement syndrome.
What can cause impingement syndrome?
- Overuse of rotator cuff muscles and working with arms raised overhead
- Increasing age: Blood supply decreases and the tendons can degenerate
- Bone spurs: reduced space for the bursa and tendons to move under the acromion
Define fibromyalgia
Chronic pain is heavily associated with widespread musculoskeletal pain and fatigue which is also accompanied by multiple unexplained symptoms such as anxiety and depression.
List 4 causes of fibromyalgia
- Poor mitochondrial function - due to free radical damage
- Altered stress response - excess cortisol, adrenal fatigue
- Post-viral and chronic toxic load - heavy metals, chemicals
- Poor gut health - dysbiosis, leaky gut syndrome
- Serotonin and noradrenaline deficiencies - play a role in pain tolerance
- Sleep dysregulation - fatigue, increased pain, lower physical activity
Name two signs and symptoms of fibromyalgia
- Widespread musculoskeletal pain
- Pain that results from gentle pressure
- A feeling of ‘swollen joints’ with no actual swelling
- Debilitating fatigue and severely disturbed sleep
- Headaches (muscular or migraine)
- Anxiety and depression
- IBS symptoms
Name two synaptic substances that increase/amplify the pain in fibromyalgia
High levels of substance P and excess post-synaptic nitric oxide
Which two substances are needed for muscle relaxation?
Magnesium and ATP
Which two substances are needed for muscle contraction?
Calcium and ATP
Where in the body can the ‘neuromuscular junction’ be found?
The NMJ is the meeting point (synapse) where motor neurons meet a muscle fibre. It is at this synaptic end bulb (neuron ending) where vesicles can be found that store the neurotransmitter ‘acetylcholine’.
Which two types of skeletal muscles are there and how do they differ?
White muscle fibres: have a low level of myoglobin, have large diameter fibres, uses anaerobic respiration and is used for fast, strenuous work
Red muscle fibres: large quantity of myoglobin, small diameter fibres, uses aerobic respiration and is designed for sustained activity with no fatigue
What is the Neuromuscular Junction?
The NMJ is the meeting point (synapse) of motor neurons and muscle fibre.
Which neurotransmitter is stored in the motor neuron synaptic bulb ending?
Acetylcholine (ACH)
Define fibromyalgia
Fibromyalgia is a chronic pain disorder, heavily associated with widespread musculoskeletal pain and fatigue.
What influences the strength of muscle contraction?
The number of motor neurons conducting an electrical impulse at one time as well as the frequency of impulses
Name four minerals essential for effective muscle activity
Calcium
Magnesium
Sodium
Potassium
Iron
What is the motor end plate?
The motor end plate describes the location where the motor neurons terminate in tiny pads on the muscle fibre.
List two hormones that promote muscle hypertrophy
Growth hormone
Testosterone
Thyroid hormones
Explain the pathophysiology of muscle fatigue
When muscles are overused in sports or due to poor posture, the associated metabolic reserves get depleted. Cell respiration then becomes anaerobic and the by-products such as lactic acid can cause pain.
What pathology is characterised by:
‘If a muscle is continuously contracted, the actin-myosin filaments remain attached’
Muscle shortening
Name two synaptic substances that increase the pain in fibromyalgia
Substance P
Excess post-synaptic nitric oxide
List four causes of fibromyalgia
- Poor mitochondrial function (damage by free radicals)
- Altered stress response (ie. excess cortisol, adrenal fatigue)
- Poor gut health (dysbiosis, leaky gut)
- Post-viral, chronic toxic load (e.g. heavy metals, chemicals)
- Serotonin and noradrenaline deficiencies (play a role in pain tolerance)
- Sleep dysregulation (higher fatigue, less active, more pain felt)
List two signs/symptoms of fibromyalgia
Widespread musculoskeletal pain
Debilitating fatigue and severely disturbed sleep
Pain that results from gentle pressure
Headaches (muscular / migraine)
Anxiety and depression
A feeling of swollen joints with no actual swelling
Describe the pathophysiology of Myasthenia Gravis
Autoimmune antibodies block acetylcholine receptors on the motor end plate, preventing a nerve impulse from being sent to muscle fibres. The muscle becomes progressively weaker.
List two signs/symptoms of Myasthenia Gravis
1- Weakness of ocular muscles, double vision and ptosis
2- Weakness in facial muscles
3- Difficulty with speech, chewing, swallowing
4- Muscle weakness spreading to proximal limbs
5- Death may result from failure of respiratory muscles
Why is the protein deficiency in Duchenne muscular dystrophy important?
Dystrophin anchors the cytoskeleton to the extracellular matrix. If this protein is missing, when the cell contracts, there is no support and the cell membrane becomes leaky, allowing materials to flood in. This results in muscle degeneration and necrosis.
List two common signs/ symptoms of Duchenne Muscular Dystrophy
- Delayed walking
- Difficulty getting up from sitting or lying
- Clumsiness and frequent falls
- Waddling gait
- Speech delay
- Gower’s sign
What blood test is used in Duchenne diagnosis?
Serum creatine kinase
(10-100 x normal)
Are all muscles affected in Duchenne?
Yes, skeletal, smooth and cardiac
