Week 2 - Muscle Flashcards
Microscopic appearance of SKELETAL muscle
Long cylindrical fibre
Many peripherally located nuclei
Unbranched
Striated
Microscopic appearance of SMOOTH muscle
Fibre thickest in middle
Tapered at each end
1 centrally positioned nucleus
Not striated
Microscopic appearance of CARDIAC muscle
Branched
Cylindrical fibre
1 centrally located nucleus
Interacalated discs join neighbouring fibres
Striated
Fibre diameter for skeletal muscle
Very large
10-100 micrometers
Fibre diameter for cardiac muscle
Large
10-20 micrometers
Fibre diameter for smooth muscle
Small
3-8 micrometers
Connective tissue components for skeletal muscle
Endomysium
Perimysium
Epimysium
Connective tissue components for cardiac muscle
Endomysium
Perimysium
Connective tissue components for smooth muscle
Endomysium
Which muscle types have contractile proteins organised into sarcomeres?
Skeletal
Cardiac
Sarcoplasmic reticulum for muscle types
Skeletal - Abundant
Cardiac - Some
Smooth - Very little
Which muscle fibre type doesn’t have T tubules?
Smooth muscle
Where is the source of Ca2+ for contraction in skeletal muscle?
Sarcoplasmic reticulum
Where is the source of Ca2+ for contraction in cardiac muscle?
Sarcoplasmic reticulum
+
Interstitial fluid
Where is the source of Ca2+ for contraction in smooth muscle?
Sarcoplasmic reticulum + interstitial fluid
What are the regulator proteins for contraction in each of the muscle types?
Skeletal - Troponin + tropomyosin
Cardiac - Troponin + tropomyosin
Smooth - Calmodulin + myosin light chain kinase.
Contraction regulation for skeletal muscle
Acetylcholine released by somatic motor neurones
Contraction regulation for cardiac + smooth muscle
Acetylcholine + norepinephrine released by autonomic motor neurones
+ several hormones
Define the origin point
Proximal attachment that usually remains stationary during contractions
Define the insertion point
Distal attachment that usually moves towards the other during contraction.
Define myology
Scientific study of muscles
What are the functions of muscular tissue
Producing body movements
Stabilising body positions
Storing + moving substances w/in the body
Generating heat.
FUNCTIONS OF MUSCULAR TISSUE
Explain stabilising body positions
Skeletal muscle contractions stabilise joints + maintain body positions.
Postural muscles contract continuously when you are awake.
FUNCTIONS OF MUSCULAR TISSUE
Explain Storing + moving substances w/in the body
Storage is accomplished by sustained contractions of sphincters.
Temporary storage of food in stomach or urine in urinary bladder is possible due to smooth muscle sphincters closing off the outlets of these organs.
Cardiac muscle contractions of the heart pump blood through the bv of the body.
Contraction + relaxation of smooth muscle in the walls of bv help adjust bv diameter = regulating the rate of blood flow.
FUNCTIONS OF MUSCULAR TISSUE
Explain Generating heat.
As muscular tissue contracts, it prod. Heat = thermogenesis.
Involuntary contractions of skeletal muscles, shivering, can ⬆️ rate of heat prod.
What 4 properties enable muscular tissue to function + contribute to homeostasis
Electrical excitability
Contractility
Extensibility
Elasticity
Define electrical excitability
= Ability to prod APs when responding to certain stimuli.
What are the 2 main types of stimuli that trigger APs?
Autorythmic electrical signals arising in the muscular tissue itself
Chemical stimuli i.e neurotransmitters, hormones or even local changes in pH.
Define contractibility
Ability of muscular tissue to contract forcefully when stimulated by an AP.
Contraction = generates tension while pulling on its attachment points.
If this is great enough to overcome the resistance of the object, the muscle shortens + movement occurs.
Extensibility
Ability of muscular tissue to stretch (w/in limits) w.out being damaged.
Elasticity
Ability of muscular tissue to return to its original length + shape after contraction or extension.
Subcutaneous layer / hypodermis
Separates muscle from skin
Composed of:
- areolar connective tissue
- adipose tissue.
What is the purpose of the Subcutaneous layer / hypodermis
Pathway for nerves, bv + lymphatic vessels to enter + exit muscles.
What does the adipose tissue in the Subcutaneous layer / hypodermis store + do?
Most bodys TG
Serves as an insulating layer
Protects muscles from physical trauma.
Describe the fascia
Dense sheet of irregular connective tissue
What does the fascia allow?
free movement of muscles
What are the 3 layers of connective tissue extending from the fascia to protect + strengthen skeletal muscle
Epimysium
Perimysium
Endomysium
Epimysium
Outer layer, consists of dense irregular connective tissue
Perimysium
Sheath of connective tissue surrounding a bundle of muscle fibres.
Endomysium
Penetrates the interior of each fascicle + separates each muscle fibre from 1 another.
What accompanies each nerve that penetrates a skeletal muscle?
Generally an artery + 1 or 2 veins
Somatic motor neurones
Neurones that stimulate skeletal muscle to contract.
Axon extends from brain or spinal cord to a group of skeletal muscle fibres.
Sarcolemma
Plasma membrane of a muscle cell.
Describe Transverse (T) tubules
Invaginations in the sarcolemma that tunnel in towards the centre of each muscle fibre.
——Muscle AP travels along sarcolemma + through T tubules, quickly spreading throughout the muscle fibre. —
What are T tubules filled with?
Interstitial fluid due to being open to the outside of the fibre.
What is the sarcoplasm?
What does it contain?
Cytoplasm of a muscle fibre.
Glycogen + myoglobin
Myoglobin
Muscle protein that binds to O2.
Releases O2 when needed by the mit. For ATP prod.
Myofibrils
Contractile organelles of skeletal muscle.
About 2 micrometers in diameter
Extend the entire length of a muscle fibre.
Sarcoplasmic reticulum (SR)
Fluid-filled system of membranous sacs that encircle each myofibril.
What are terminal cisterns?
What do they store? When do they release it?
Part of the SR.
Store Ca2+
Release when an AP travels down T tubules.
Thin filaments
8nm in diameter
1-2 micrometers long
Composed of Actin.
Thick filaments
16nm in diameter
1-2 micrometers long
Composed of Myosin.
Z discs
Narrow, plate-shaped regions of dense protein material.
Separate sarcomeres.
A band
Darker middle part of a sarcomere, extends the entire length of the thick filaments.
I band
Thin filaments only
Z-disc passes through the centre of each I band.
H zone
Centre of each A band containing only thick filaments.
M line
Region in the centre of H zone that contains proteins holding thick filaments together at centre of sarcomere.
What are the 3 kinds of proteins in myofibrils?
Contractile
Regulatory
Structural
Regulatory muscle proteins
Help switch the contraction process on + off
What are the 2 types of contractile proteins
Myosin
Actin
What are the 2 binding sites on each myosin head?
Actin-binding site
ATP-binding site. (Also functions as an ATPase).
Motor proteins
Pull various cellular structures to achieve movement by converting chemical energy in ATP —> mechanical energy of motion = prod. force.
Describe relaxed muscle + myosin relation
Tropomyosin covers myosin binding sites on actin so myosin can’t bind to it.
What happens when Ca2+ ions bind to troponin?
Troponin undergoes a conformational change = moves tropomyosin AWAY from myosin-binding sites on actin + contraction begins as myosin binds to actin.
What happens to the width of A band during contraction?
Remains unchanged
What happens to the ind. lengths of thick + thin filaments during contraction?
Remain unchanged.
What happens at the onset of muscle contraction?
SR releases Ca2+ into sarcoplasm.
Ca2+ binds to troponin.
What are the 4 stages of the contraction cycle in the sliding filament theory?
- ATP Hydrolysis
- Attachment of myosin to actin
- Power stroke
- Detachment of myosin from actin
What is excitation-contraction coupling
Seq. of events that links excitation to contraction.
Where does excitation-contraction coupling occur?
At the triads of the skeletal muscle fibre.
Define triad
Consists of a T tubule + 2 opposing terminal cisterns of the SR.
Whats at a triad?
T tubule + terminal cisterns mechanically linked together by 2 groups of integral membrane proteins.
TRIAD
What are the 2 groups of integral membrane proteins?
Voltage gated Ca2+ channels
Ca2+ release channels
Voltage gated Ca2+ channels
Located in the T tubule membrane.
Arranged as tetrads.
Main role - to serves as voltage sensors that trigger the opening of the Ca2+ release channels.
Where are Ca2+ release channels
In terminal cisternal membrane of SR.
What happens to the Ca2+ release channels when a skeletal muscle fibre is at REST
Part extended into sarcoplasm is blocked by a cluster of voltage-gated Ca2+ channels.
= Preventing Ca2+ from leaving the SR.
What happens to the Ca2+ release channels when a skeletal muscle fibre is EXCITED
An AP travels along T tubule, voltage-gates Ca2+ channels detect the change in voltage + undergo conformational change.
= Ca2+ release channels open.
What happens once Ca2+ release channels are open?
Lots of Ca2+ flow from SR —> sarcoplasm around thick + thin filaments.
== Ca2+ conc. in sarcoplasm ⬆️.
Ca2+ combines w/ troponin to undergo conformational change = tropomyosin moves away from the myosin-binding sites on actin.
Once binding sites are free, myosin heads bind to them to form cross-bridges + muscle fibres contract.
Terminal cisternal membranes of the SR also contain Ca2+ + ATPase pumps, what do they do?
Use ATP to constantly transport Ca2+ from sarcoplasm into the SR.
What happens after last AP has propagated through the T tubules?
Ca2+ release channels close
What does the length-tension relationship indicate?
That the forcefulness of muscle contraction depends on the length of the sarcomeres w/in a muscle before contraction begins.
As the sarcomeres of a muscle fibre are stretched to a longer length, the zone of overlap shortens + fewer myosin heads can make contact w. thin filaments.
So, the tension the fibre prod. ⬇️.
What happens when a fibre is stretched to 170% of its optimal length?
No overlap between the thick + thin filaments.
= No contraction as none of the myosin heads can bind to the think filaments so the tension is 0.
What are the types of muscle fibre/fascicle arrangement
Parallel
Fusiform
Circular/orbital
Triangular
Pennate
Parallel muscle fibre arrangement
Fibres run in straight line from origin to insertion.
Typically quite flat in shape.
Fusiform muscle fibre arrangement
Muscle belly has a bulbous shape to it.
Considered as a subcategory to parallel as fibres run from origin to insertion points.
Circular/orbital muscle fibre arrangement
Fibres run in a circular direction.
Triangular muscle fibre arrangement
One end of muscle comes into single focal point but other end is quite broad.
Fibres fan out to create triangular shape.
What are the types of Pennate muscle fibre arrangement
Uni
Bi
Multi
Which muscle type is subject to the greatest amount of stretching?
Smooth muscle
What in the muscle limits the range of extensibility + keeps it w/in the contractile range of muscle cells?
The connective tissue
What does the fascia do?
Supports + surrounds muscles + other organs of the body.
Carries nerves, bv + lymphatic vessels + fills spaces between muscles
What can T tubules ensure?
That an AP excites ALL parts of muscle fibre simultaneously
Uni pennate muscle fibres
Fibres run at angle to midline of muscle + all in 1 direction.
Bi pennate muscle fibres
Has central tendon running through middle of muscle.
Fibres converge from either side onto the middle of the muscle. - 2 direction in which muscle fibres run.
Multi pennate muscle fibres
Fibres converge into centre of muscle from different directions.
