Flashcards in Muscles Deck (64):
What is the prefix used for muscle cell components? What are the terms used to describe the muscle cell membrane, cytoplasm and smooth ER?
The prefix used for muscle cell components is sarco- this denotes flesh or muscle. It comes form the Greek Sarx (sarkos) meaning flesh.
Sarcolemma: The outer membrane of a muscle
Sarcoplasm: The cytoplasm of a muscle
Sarcoplasmic reticulum: The smooth endoplasmic reticulum of a muscle cell.
What are the three types of muscle? Are they striated or not?
Skeletal muscle (striated)
Cardiac muscle (striated)
Smooth muscle (non-striated muscle)
What is myoglobin?
Myoglobin is a red protein containing haem. It functions as an oxygen carrying molecule which provides oxygen to the working muscles. It is structurally similar to haemoglobin. However, it has a higher affinity for oxygen than myoglobin so, Hb gives up oxygen for myoglobin, especially when pH is lowered.
What types of muscle contains myoglobin?
Skeletal and cardiac muscle but not smooth muscle.
What happens to myoglobin when muscles die?
When muscles die (muscle necrosis)myoglobin is released into the bloodstream. This can cause renal damage (myoglobinurea) because it is the kidneys that remove myoglobin form the blood and into the urine.
What is the gross structure of a muscle?
Muscles are made of muscle fibres (cells)
Each muscle fibre is surrounded by the Endomysium. (Endomysium is present between all fibres)
Around 20 muscle fibres together are surrounded by the Perimysium.
Then, all the muscle fibres of a muscle are surrounded by the thicker Epimysium.
Blood vessels are also present between the bundles of muscle fibres surrounded by perimysium.
What is compartment syndrome?
Limbs are divided into compartments delineated by fascia. Trauma in one compartment could cause internal bleeding with exerts pressure on blood vessels and nerves. This can give rise to compartment syndrome.
What are the symptoms of compartment syndrome?
-Deep, constant and poorly localised pain,
-Aggravated by passive stretch of muscle group,
-Paresthesia (altered sensations eg pins and needles),
-The compartment may feel tense and firm,
-Swollen, shiny skin sometimes with obvious bruising,
-Prolonged capillary refill time.
How can compartment syndrome be treated?
Compartment syndrome can be treated by a fasciotomy followed by a skin graft.
What are extrinsic muscles? And what is their role in the tongue?
Extrinsic muscles all have an inserting of bone or cartilage. They protrude the tongue, retract it and move it from side to side.
What muscle allows us to stick out our tongue?
What does hypoglossal nerve damage lead to?
Hypoglossal nerve damage causes paralysis of the tongue. Usually one side of the tongue is affected so when a person sticks out their tongue, it deviates towards the side that is damaged.
What are intrinsic muscles? And what is their role in the tongue?
Intrinsic muscles in the tongue are not attached to bone. They allow the tongue to change shape but not position.
Why is the tongue so mobile?
Because the connective tissue has a high strength and plasticity. Also, the muscle fibres all go in different directions (are multidirectional)
What are the thin muscle filaments called?
What are the thick muscle filaments called?
What are the:
M: middle of the myosin
H: just myosin
A: all the myosin (dArk band)
Z: middle of actin (Z to Z is one sarcomere)
I: just actin (lIght band)
What is muscle atrophy?
This is when destruction of muscle cells is greater than their replacement. This leads to muscle wastage.
What is muscle hypertrophy?
This is when muscle replacement is larger than muscle destruction. This means there are more contractile proteins shindig increase in fibre diameter. Also, there is increased enzyme activity for glycolysis, increased mitochondria, increased stored Glycogen and increased blood flow. Ultimately, these things lead to an increase in the size of the muscles.
What is disuse atrophy and how does it occur?
Disuse atrophy is caused by bed rest, limb immobilisation or sedentary behaviour.
This behaviour results in loss of protein which causes reduced fibre diameter and therefore loss of power.
How much do muscles deteriorate with age?
Muscle atrophy with age begins at about 30. By the time you are 80 you have lost about 50% of your muscle mass. This results in some problems with temperature regulations because you find it difficult to generate heat.
What is denervation atrophy?
This is a sign of lower motor neurone lesions: weakness, flaccidity, muscle atrophy. Re-innervation needs to occur within 3 months for recovery.
When a muscle fibre contracts what happens to the..
A band: this stays the same length as this is the whole length of myosin which doesn’t shrink itself.
H band: this gets shorter because actin and myosin gets closer together (H is just myosin).
I band: this gets shorter because actin and myosin get closer together (I is just actin).
Skeletal muscles are composed of_________which are composed of multi nucleate ________ which are composed of ______ which are composed of _______ (actin and myosin)
Skeletal muscles are composed of fascicles which are composed of multi nucleate muscle fibres (cells) which are composed of myofibrils which are composed of myofilaments (actin and myosin)
Explain briefly how calcium plays a role in muscle contraction.
Increased amounts of ionic Calcium binds to TnC of troponin (a protein present on actin). This causes a conformational change so tropomyosin moves and exposes the actin myosin binding site so that the actin and myosin can form a cross bridge and the filaments can be pulled closer together. (Sliding filament theory)
Why are troponin assays a useful diagnostic tool?
Troponin (especially the I and T forms) are used as a marker for cardiac ischaemia. This is released from ischaemic cardiac muscle cells within an hour but, you must measure these levels within 20 hours.
The smallest changes in troponin levels in the blood are indicative of cardiac damage but, the quantity of troponin is not necessarily proportional to the degree of damage.
This is used by emergency units as the assay of choice.
What is creative kinase?
Creative kinase (CK) is an important enzyme in metabolically active tissues like muscle. It catalyses the conversion of creative to phosphocreatine (PCr) (using ATP). This serves as an energy reservoir for rapid buffering and regeneration of ATP in situ in tissues that consume ATP rapidly eg muscles.
Clinically, what did Creatine Kinase used to be used to diagnose?
CK used to be used to diagnose MIs (heart attacks) with the enzyme increase being largely proportional to infarct size. But, this has been largely superseded by troponin assays.
What can cause a rise in plasma Creatine Kinase?
CK is released into the blood by damaged skeletal muscle and brain. A rise in plasma CK can result from:
Vigorous physical exercise
A fall (especially in the elderly)
Rhabdomyolysis (severe muscle breakdown)
Acute kidney injury
What is the structure of a myosin molecule?
An individual myosin molecule has a rod like structure from which two heads protrude.
What is the structure of the thick muscle filaments?
Each thick filament consists of many myosin molecules whose heads protrude at opposite ends of the filament. In the centre of the sarcomere, the thick filaments are devoid of myosin heads. Instead, they extend towards the actin filaments in regions of potential overlap.
What is the structure of the thin filament?
The actin filament forms a helix. Tropomyosin molecules coil around the actin helix, therefore reinforcing it. A troponin complex is attached to each tropomyosin molecule.
Explain the sliding filament theory
1. Myosin (in a high energy state) cross bridge attaches to the actin filament
2. Working stroke- the myosin head pivots and bends as it pulls on the actin filament sliding it closer to the M line
3. ATP binds to the myosin head (which is now in a low energy configuration) and the cross bridge detached.
4. As ATP splits into ADP and Pi, cocking (bending) of the myosin head occurs.
5.process is repeated!
What is a neuromuscular junction and how does it work?
A neuromuscular junction is small terminal swelling of an axon which contains vesicles of acetylcholine. A nerve impulse causes the release of acetylcholine which binds receptors on the sarcolemma to initiate an action potential propagated along the muscle.
Describe the events that lead to the contraction of skeletal muscle.
1. Initiation: a nerve impulse along a motor neurone axon arrives at a neuromuscular junction
2. This impulse prompts the release of acetylcholine into the synaptic cleft which causes local depolarisation of the sarcolemma
3. Voltage gated Na+ channels open and Na+ enters the cell
4. General depolarisation spreads over the sarcolemma and into the T tubules
5. Voltage sensor proteins of the T tubule membrane change their conformation
6. Gated Ca2+ release channels of adjacent terminal cisternae (in sarcoplasmic reticulum) are activated
7. Ca2+ is rapidly released from the terminal cisternae and into the sarcoplasm
8. Ca2+ binds to the TnC subunit of troponin
9. The contraction cycle is initiated and Ca2+ is returned to the terminal cisternae of the sarcoplasmic reticulum
What is a motor unit?
This is an alpha motor neurone and the muscle fibre it supplies. The smaller the average number of fibres per motor unit, the finer the control. Eg the inferior rectus muscle which moves the eyeball only has 9 fibres whereas the Gastrocnemius (calf muscle) has 1,934.
Each individual muscle fibre is innervated by one motor neurone but, a single motor neurone can innervate many muscle fibres. The muscles that make a motor unit are all of the same contractile type so each motor unit is fast or slow acting.
What is fibrillation of a muscle?
Fibrillation is the contraction of individual muscle fibres.
What is fasciculation of a muscle?
Fasiculation is is the contraction of whole muscle fascicles, often under the innervation of a single motor neurone.
What are muscle spindles?
These are intrafusal muscle fibres (specialised sensory organs the detect the amount and rate of change in length of a muscle fibre) that facilitate proprioception (the relative sense of ones own body parts).
They are innervated by two sensory and one motor axon.
Gamma motor neurones keep the fibres taught
Type Ia sensory neurones relay the rate of change of the muscle length to the CNS (brain)
Type II sensory neurones provide position sense
Spindle is walled off from the rest of the muscle by a collagen sheath
What is large fibre neuropathy?
Patients with large fibre neuropathy are able to perform accurate movements while watching the affected limb but, in the absence of vision, small movements are grossly inaccurate.
What protein has specific forms for cardiac muscle?
There are cardiac specific forms of troponin I and T (although the underlying principles of contraction are relatively similar).
What is the difference between hypertrophy and hyperplasia?
Both hypertrophy and hyperplasia are ways in which muscles increase in size. Hypertrophy is when individual cells get bigger whereas hyperplasia is the multiplication of the cells.
What are natriuretic peptides?
They are hormones that are synthesised by the heart, brain and other organs. The release of these peptides by the heart is stimulated by atrial and ventricular distension, usually in response to heart failure.
What is the main physiological action of natriuretic peptides?
Their main functions ate to reduce arterial pressure by decreasing blood volume and systemic vascular resistance. Normal hearts secrete small amounts of ANP but elevated levels are found in patients with left ventricular hypertrophy and mitral valve disease.
What is ANP?
Atrial natriuretic peptide (ANP) is a 28 amino acid peptide that is synthesised, stored and released by atrial myocytes in response to atrial distension (among other stimulations).
Therefore, elevated levels are found during hypervolemic states (elevated blood volume) which occur in congestive heart failure.
What is BNP?
Brain-type natriuretic peptide (BNP) is a 32 amino acid peptide that is synthesised by the ventricles as well as the brain, where it was first recognised.
BNP is released by the same mechanisms that release ANP and it has similar physiological functions.
What is BNP made from? What can both BNP and another related protein be used for?
BNP is made by the proteolysis of pro-BNP (108 amino acids). This results in BNP (32 amino acids) and the N-terminal piece of pro-BNP (NT-pro-BNP; 76 amino acids).
Both BNP and NT-pro-BNP are sensitive diagnostic markers for heart failure in patients (eg increased left ventricle filling pressures and dysfunction).
A rapid 15 mins immunoassay is possible to identify these.
For what system do the natriuretic peptides serve as a counter regulatory system?
They serve as a counter regulatory system for the renin-angiotensin-aldosterone system.
What are Purkinje fibres?
Purkinje fibres are modified myocytes that transmit action potentials rapidly to the ventricles from the AV node. They rapid conduction allows the ventricles to contract in a synchronised manner.
They are large cells with:
-Extensive gap junction sites.
What are the cells like in smooth muscle? What happens when cells are together?
The cells are spindle shapes (fusiform) with a central nucleus. Thousands of cells form sheets bundles of layers.
What are smooth muscles not?
Smooth muscle is not striated, it has no sarcomeres and no T tubules.
What is different about the contraction of smooth muscle?
Contraction of smooth muscle still relies on actin myosin interactions but, it is slower, more sustained (may remain contracted for hours or days) and requires less ATP. It is still capable of being stretched.
Where is smooth muscle often located?
Smooth muscle can often form the contractile wall of passageways or cavities to modify the volume. Eg of vascular structure (blood vessels) or in the gut, respiratory tract and the genitourinary system.
Smooth muscle is involuntary. Why is the significant?
The involuntary nature of smooth muscle is significant because it can be of clinical significance in disorders such as:
High Blood Pressure (primary hypertension)
Dysmenorrhea (painful menstruation)
Abnormal gut mobility (IBS)
Detrusor muscle instability (overactive bladder syndrome)
What are myoepithelial cells?
Myoepithelial cells are a modified smooth muscle cells. They are stellate cells forming a basket work around the secretory units of some exocrine glands (eg sweat, salivary and mammary glands). Their contraction assists with the secretion of sweat, saliva of milk into secretory ducts. They are also present in the ocular iris and they contract to dilate the pupil.
What are myofibroblasts?
Myofibroblasts are modified smooth muscles cells. They are present at the site of wound healing. They produce a cool genius matrix but they also contract (have abundant actin and myosin). They are prominent in wound contraction and tooth eruption.
How does involuntary control in smooth muscle fibres occur?
Most smooth muscle cells are innervated by autonomic nervous system fibres that release their neurotransmitters from varicosities into a wide synaptic cleft.
Can skeletal muscle repair itself?
Skeletal muscle cells cannot divide but the tissue can regenerate by mitotic activity of satellite cells so that hyperplasia follows muscle injury. Satellite cells can also fuse with existing muscle cells to increase mass (skeletal muscle hypertrophy).
Can cardiac muscle repair itself?
No! Cardiac muscle is incapable of regeneration. Following damage, fibroblasts invade, divide and lay down scar tissue.
Can smooth muscle repair itself?
Yes! Smooth muscle cells retain their mitotic activity and can form new muscle cells. This ability is particularly evident in the pregnant uterus where the muscle wall becomes thicker by hypertrophy (swelling) and by hyperplasia (mitosis) of individual cells.
What can cause muscle atrophy?
Congestive heart failure, COPD, renal failure
Neurogenic - eg motor neurone disease or a spinal cord injury
What diseases are caused by smooth muscle dysfunction?
Detrusor instability (incontinence)
What are some indicators of muscle injury or necrosis?
Creatine Kinase (all muscle).
Myoglobinuria (skeletal and cardiac muscle) -causes urine to go brown because of the iron in the myoglobin that is secreted into the urea.
Troponin I (cardiac) -used to see if patient has has a heart attack.