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TOb > Muscle > Flashcards

Muscle Flashcards

0
Q

Which bands of a sarcomere contain actin myosin or both

A

Actin - a
Myosin - i,z
Both - a

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1
Q

Classify the 3 types of muscle

A

Smooth - involuntary
Striated - skeletal/voluntary
Striated - cardiac/involuntary

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2
Q

Outline the sliding filament theory

A

Actin, tropomyosin and troponin form filaments
Troponin covers binding sites on myosin
When ca2+ binds to Tnc of troponin, conformstional change exposes binding sites
Myosin heads can bind to actin -> contraction
Myosinhead tightly bound to actin
Atp binds to myosin causing it to uncouple from actin
Hydrolysis of atp causes uncoupled myosin head to bend and move 5mm
Myosin head binds weakly to actin filament causing release of inorganic phosphate and power stroke moving myosin head to original position
Myosin head binds tightly again and cycle repeats

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3
Q

Describe innervation of muscle and exitation contraction coupling

A

1) when ap arrives at presynaptic terminal, VG ca2+ channels open
2) influx of ca2+ causes release of ach from vesicles (exocytosis)
3) ach diffuses across synaptic cleft and binds to nicotanic ach receptors on motor end plate
4) post-synaptic receptors are ligand gated ion channels and ach causes them to open -> influx of na+ and eflux of k+ -> depolarsisation of sarcolemma
5) voltage sensoe proteins of t tubule membrane changes their conformation
6) gated ca2+ release channels of adjacent terminal cisternae activated by proteins change in conformation
7) ca2+ rapidly released from terminal cisternae into sarcoplasm
8) ca2+ binds to TnC subunit of troponin
9) contraction cycle is initiated and ca2+ is returned to terminal sarcoplasmic reticulum

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4
Q

Explain the mechanical continuity of muscle fibres, sheath, tendon and bone

A

Each muscle fibre is grouped with others in a fasicle, wrapped by perimysium. Fasicles wrapped in a connective tissue sheath (epimysium)
Muscle is attached to bone by tendons/aponeuroses
Muscles associated with layers of dense connective tissue - deep fascia which surrounds muscles and binds them to functionsl groups

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5
Q

Explain the heirachal composition of muscle

A 
Myofibril
Sarcoplasm
Sarcolemma
Endomysium
Fasiculus
Perimysium
Epimysium
Muscle
Tendon
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6
Q

Describe repair in skeletal muscle

A

Cant divide but can regenerate by mitotic activity of satelite cells so that hyperplasia follows muscle injury. Satelite cells can also fuse with existing muscle cells to increase mass (hypertrophy)

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7
Q

Describe repair of cardiac muscle

A

Cant regenerate. Following damage fibroblasts invade, divide and lay down scar tissue

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8
Q

Describe repair of smooth muscle

A

Retain mitotic activity and can form new smooth muscle cells e.g. In pregnant uterus muscle wall becomes thicker by hypertrophy (swelling) and hyperplasia (mitosis) of individual cells

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9
Q

Describe the histology of cardiac muscle

A

Striated
1/2 centrally positioned nuclei per cell
Intercalated discs for electrical and mechanical coupling with adjacent cells
No distinct myofibrils, actin and myosin form continous masses
Mitochondira and sarcoplasmic reticulum penetrate cytoplasm through myofilaments

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10
Q

Describe the histology of smooth muscle

A

Spindle shape cells (fusiform) with a central nucleus
Not striated, no sarcomeres, no t tubules
Contraction slower and more sustained
Can be stretched
Responds to nerve, hormonal and drug signals
F - contractile wakks of passageways e.g. Respiratory tract

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11
Q

What are myoepithelial cells?

A

Stellate cells forming basketwork around the secretory units of exocrine glands -> assist secretion of sweat etc.

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12
Q

What are myofibroblasts?

A

At sites of wound healing produce collagenous matrix and contract (wound contraction and tooth erruption)

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13
Q

Outline the structure of the purkinje fibres

A

Large cells with abundant glycogen, sparse myofilaments and extensive gap junction sites
They are found in the inner ventricular walls of the heart

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14
Q

What is the function of the purkinje fibres?

A

Transmit action potentials from SAN -> atrioventricular node -> ventricles
To ensure spontaneous rythmic contraction

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15
Q

How is skeletal muscle remodelled?

A

Continous replacement of contractile proteins

About every two weeks

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16
Q

Describe atrophy (causes, symptoms, consequences)

A

Destruction>replacement
Disuse, aging, denervation
Weakness, flacidity, muscle atrophy
Muscle fibres are replaced with fibrous and fatty tissue, leads to contractures -> debilatating

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17
Q

Describe hypertrophy

A

Replacement>destruction
Increase in muscle mass from work, performed against load
More contractile proteins, increasing fibre diameter
Increase enzyme activity for glycolysis, mitochondria, stored glycogen

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18
Q

Describe myosenthia gravis

A

Autoimmune destruction of end plate Ach receptors
Loss of junctional folds at end plates
Widening of synaptic cleft
Symptoms: fatiguability, sudden falling (due to decreased ach) droopin eyelids (ptosis) double vision
Fluctuates due to general health, fatigue and emotions

19
Q

What is botulism?

A

Toxins block ach release, no contractions

Treated with achesterase inhibitors

20
Q

Describe organophosphate poisoning

A

Irreversibly inhibits ach, so ach remains in receptors -> stays contracted
Treated with atropine an antagonist of ach

21
Q

Outline the patholhysiology of duchenne muscular disease

A

Recessive x linked form
Consequence of protein abnormality - muscle fibres tear apart upon contraction
Causing release of creatine phospho kinase into serum
Causes ca2+ to enter cell causing cell death

Pseudo hypertrophy before fat and connective tissue replace muscle fibres

22
Q

Outline the pathophysiology of malignant hyperthermia

A

Rare autosomal dominant disorder
Causes life threatening reaction to drugs used for general anasthetic
E.g. Succinylcholine which inhibits ach by non-competitive inhibition on nicotinic receptors. It is degraded by butylcholinesterase more slowly than ach by acetylcholinesterase
In affected individuals drugs induce uncontrolled increase of skeletal muscle oxidative metabolism, quickly overwhelming the bodys capacity to supply O2, remove CO2 and regulate metabolism

23
Q

What are the treatments for malignant hyperthermia?

A

Dantrolene a muscle relaxant that prevents release of Ca2+
This corrects hyperthemia, acidosis and organ disfunction
discontinue triggering agents

24
Q

Describe the structure of a peripheral nerve

A

Outside the CNS nerve fibres bound together in bundles by connective tissue to form peripheral nerves

Axon surrounded by endoneurium, many axons in a fasicle surrounded by a perineurium, many fasicles with blood vessels within epineurium

25
Q

What are the differences between myelinated and non-myelinated neurones?

A

Grey matter - myelinated
Faster transmission as schwan cells insulate pns, oligodendrocytes cns
Somatic is all myelinated
Myelin provides track for regrowth of damaged
White - non-myelinated

26
Q

How does demyleination affect conduction speed?

A

Slower as impulse has further to travel as salutatory conduction is inhibited
E.g. Multiple sclerosis is destructively removed, replaced by scar tissuewhich prevents conduction. Oligodendrocytes a d axons are also damaged leading to slow velocity

27
Q

Describe the structure of a nerve cell and nerve cell body (perikaryon)

A

Nucleolus, nucleus, nissil substance(granular substance full of rer), dendrite(projections that amplify nerve signals)

28
Q

Explain the function of schwann cells

A

Wrap around nerve fibres to insulate axon, lipid content so dont conduct

29
Q

Explain function of nodes of ranvier

A

Gap to allow depolaraisation -> salutartory propagation (faster)

30
Q

Explain the role of glial cells

A

Support nuerones, maintain homeostasis, form myelin/insulate

31
Q

What is the function of astrocytes?

A

Blood brain barrier, transfer nutrients and waste

CNS

32
Q

What is the function of oligiodendrocytes?

A

Myelination of cns

33
Q

What is the function of microglia?

A

Immune and inflammatory functions

34
Q

What is the function of satellite cells?

A

Physical support of peripheral nuerones

35
Q

Discuss the features of peripheral nerves in relation to function

A

Outside CNS nerve fibres bound together in peripheral nerves
Towards CNS = afferent/sensory, away = efferent/motor
Variable thickness depending on the number of whorls of schawnn cell plasmolemma

36
Q

Discuss the features of the spinal chord in relation to function

A

Dorsal nerve root carriers sensory fibre impulses to the grey matter
White matter contains myelenated nerves and glial cells
Grey matter has dorsal and ventral horns containing large cell bodies
Ventral cell bodies belong to spinal motor nuerones which innervate muscles
Central canal containing cerebro-spinal fluid disappears at puberty

37
Q

Give an outline of the ANS and its division into sympathetic and para-sympathetic

A

ANS is a series of 2 nuerones - pre and post ganglionic
Ganglion is a collection of cell bodies

Sympathetic = fight or flight
Para sympathetic = rest and digest

38
Q

Describe the different pathways the sympathetic ns distributes its fibres to and from target organs

A

Thoraco-lumbar outflow
Nerve fibres have cell bodies in all 12 thoracic and first 2 lumbar
Short pre ganglionic, long post

39
Q

Describe the different pathways the para-sympathetic ns distributes its fibres to and from target organs

A

Cranio sacral outflow

Long pre, short post ganglionic

40
Q

Describe the function of the sympathetic nervous system

A 
Fight or flight
Divert blood to muscles and heart
Increase heart rate
Increase blood pressure
Reduce blood flow to GI and skin
Hyperventilation
41
Q

Describe the parasympathetic nervous system effects

A

Rest and digest
Reduce HR and force of contraction
Promotes bodily function e.g. Bladder emptying
Promotes sleep

42
Q

Describe the transmittors used at the synapses and end organs of the sympathetic NS

A

Pre ganglionic neurones are cholinergic (ach)
Post ganglionic neurones express nicltinic receptors
Post ganglionic nuerones are noradrenogic (noradrenaline)
Exception: perspiration and ejacutlation

43
Q

Describe the transmittors used at the synapses and end organs of the para-sympathetic NS

A

Pre-ganglionic nuerones are cholinergic
Post-ganglionic nuerones express nicotinic receptors
Post-ganglionic receptors are cholinergic

44
Q

Account for the importance of transmittors in the theraputic domain

A

Atropine blocks muscarinic
Nicotine stimulates nicotinic

Drugs can be designed

TOb (16 decks)

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