Week 6 Flashcards
What are the three types of muscle?
Skeletal, smooth and cardiac muscle
What type of muscle forms the majority of muscle tissue in the body
Skeletal muscle
How is skeletal muscle organised?
Parallel bundles of long, multinucleated fibers
What is the power/stamina of skeletal muscle like?
Skeletal muscle is capable of powerful contractions but can,however tire quickly
Where is skeletal muscle found?
Attached to the skeleton by either tendons or aponeurosis
What is an aponeurosis?
A thin sheet of connective tissue
What are the functions of skeletal muscle?
Moves bones and other structures
Provides support and gives form to the body
Is skeletal muscle controlled voluntarily or involuntarily?
Voluntarily but not always consciously
Where is the muscle belly found?
Between the origin and insertion
How many origins, insertions and bellies can muscles have?
Muscles can have multiple origins,insertions and bellies
What movements can skeletal muscles carry out?
They can contract, stretch beyond its normal length and revert to its original resting length
What are the constituent parts of skeletal muscle?
Muscle fascicles, Muscle fibers, myofibrils and myofilaments
What is a muscle fascicle?
Bundles of muscle fibers (muscle cells)
What is a muscle fiber?
Bundles of myofibrils
What is a myofibril?
Bundles of myofilaments
What are myofilaments?
The proteins responsible fro muscle contraction
What is the endomysium?
A thin layer of connective tissue that surrounds each muscle fiber
What is the perimysium?
A thick layer of connective tissue that surrounds each muscle fascicle
What is the function of the permysium?
To protect the fascicle from damage. It also contains capillaries and nerve fibers
What is the epimysium?
A sheet of thick connective tissue that surrounds the entirety of a skeletal muscle. It may continue at the end of the muscle belly as a tendon and thus become continuous with the periosteum
What is the function of epimysium?
To separate the muscle from surrounding tissues and organs.
What does each skeletal muscle fiber contain?
A plasma membrane (sarcolemma), cytoplasm (sarcoplasm), nuclei, sarcoplasmic reticulum and is composed of bundles of protein fibers
What is the sarcolemma?
The plasma membrane of a muscle fiber. It has invaginations to from the T tubules
What is the function of the sarcolemma?
To receive electrical stimuli and conduct an action potential to the internal structure of the muscle fiber (via the T tubules)
What is the sarcoplasmic reticulum?
A special type of smooth ER found only in skeletal muscle cells
What is the function of the sarcoplasmic reticulum?
Stores large, concentrated stores of calcium
What is the sarcoplasm?
The cytoplasm of muscle cells
What is the function of the sarcoplasm?
To store large amounts of glycogen and myoglobin.
-Glycogen provides energy during muscle contraction
-Myoglobin contains stored oxygen
What are myofibrils?
Thread-like organelles 1-3 micro meters in diameter that extend the length of the muscle fiber
What are the two general types of skeletal muscle fibers?
Slow-twitch (type 1) and fast - twitch (type 2)
What is the structure of fast - twitch muscles like?
Fast twitch muscles are thicker and quicker to contract than slow twitch muscles.
What is the endurance of slow twitch muscles like?
Slow twitch muscles have generally more endurance than fast twitch muscles
Where is cardiac muscle found?
The walls of the heart
What is special about cardiac muscle?
Cardiac muscle is resistant to fatigue and contracts without any external stimulation
What is the word used to describe the nerves that stimulate cardiac muscle?
Autonomic
What does autonomic mean?
The control is involuntary
Where is smooth muscle found?
The walls of internal organs, such as otrgans of the digestive system, walls of blood vessels and the intrinsic muscles of the eye.
What is the structure of smooth muscle?
Smooth muscle is non-striated. It consists of elongated or spindle-shaped fibres.
What type of contractions are smooth muscles capable of?
slow, sustained contractions
How is smooth muscle controlled?
Smooth muscle is able to contract without external stimulation, and is modified by the autonomic nervous system. It is under involuntary control and doesn’t fatigue
What is the electrical excitability of a muscle?
The ability of a muscle to respond to stimuli
What is the contractility of a muscle?
The ability of a muscle to shorten in response to an action potential
What is the extensibility of a muscle?
the ability of a muscle to stretch
What is the elasticity of a muscle?
the ability of a muscle to recover its original shape after contraction or extension
How does muscle contribute to body movement?
The contraction and relaxation of muscles produce movement around various joints of the body
How does muscle contribute to the stabilisation of joints?
Regulates the degree of movement possible at each joint
How does muscle contribute to the maintenance of body positions?
Continuous or sporadic contraction of skeletal muscles around the body helps us to maintain our posture and position
How does muscle contribute to storage of substances?
Contraction of smooth and skeletal muscle at specific points within the body enables certain substances to be kept within one place
How does muscle contribute to the movement of substances?
Relaxtion of cardiac and smooth muscle at specific points within the body controls the movement of substances from one place to another
How does muscle contribute to thermogenesis?
contracting muscles produce heat as a by-product, and this contributes to the maintenance of normal body temperature
How does muscle contribute to communication?
Movement of muscles permits both verbal and non-verbal expression
What is muscle atrophy?
The weakening and shrinking of a muscle
What is muscle atrophy caused by?
Immobilisation or loss of neural stimulation
What is muscle hypertrophy?
The enlargement of a muscle (cell size).
The muscle will develop more capillaries and more mitochondria
What is muscle hypertrophy caused by?
Strenuous exercise or steroid hormones
How does muscle hypertrophy occur?
When slow twitch muscle fibers become tired, fast twitch fibers take over which is when muscle mass will increase
Why do men in general have more hypertrophied muscles than women?
They produce more steroid hormones
What is muscle hyperplasia?
An increase in muscle cell numbers
What type of muscle does hyperplasia occur in?
Smooth muscle is the only type of muscle capable of cell division
Where does excitation-contraction coupling take place?
The sarcoplasm of a muscle fiber
What is the concentration of calcium ions in the cytosol like in a relaxed muscle fiber?
Relatively low
Where are a large number of calcium ions stored?
The sarcoplasmic reticulum
When are the calcium ions released?
During contraction to mediate the process by binding to troponin
What are the general functions of muscles?
movement
heat production
posture
What are muscle fibres coated with?
endomysium
What are fascicles?
groups of muscle fibres
What are fascicles bound by?
perimysium
What are muscles covered by?
epimysium
Describe skeletal muscles
long cylindrical cells
many nuclei
striated
voluntary
rapid contractions
Describe cardiac muscle
branching cells
1 or 2 nuclei
striated
involuntary
medium speed contractions
Describe smooth muscle
fusiform cells
1 nucleus
non-striated
involuntary
slow, wave-like movement
What are some defining features of skeletal muscle?
plasma membrane = sarcolemma
cytoplasm = sarcoplasm
Smooth ER = sarcoplasmic reticulum
many more mitochondria
several nuclei
transverse (T) tubules - inward extensions of the sarcolemma
myofibrils made up from microfilaments
What is a sarcomere?
from Z line to Z line
What is the A band?
The length of the myosin filament
What is the I band?
The regions with no myosin
What is the H zone?
The central region where there is no actin filaments
What connects myosin to the Z band?
titan
Give a summary of muscle excitation and contraction
Nerve impulses reach neuromuscular junction
Acetylcholine is released from the motor neuron
Acetylcholine binds with receptors of the muscle membrane and allow Na+ entry
Na+ influx will generate an action potential in the sarcolemma
Action potential travels down the T-tubule
Sarcoplasmic reticulum releases Ca2+
Ca2+ binds with troponin and moves the troponin-tropomyosin complex
Binding sites on the actin filament are exposed
Myosin heads attach to binding sites and create a power stroke
ATP detaches myosin heads and energises them for another contraction
When action potentials cease the muscles stop contracting
What is a motor unit?
All the muscle cells that are controlled by one nerve cell
Give examples of some motor unit ratios
back muscles 1:100
finger muscles 1:10
eye muscles 1:1
What is muscle tonus?
tightness of a muscle
some fibres always contracted
What is tetany?
sustained contraction of a muscle
result of rapid succession of nerve impulses
What is the refractory period?
brief period of time in which muscle cells will not respond to stimulus
What is muscle atrophy?
weakening and shrinking of a muscle
may be caused by immobilisation or loss of neural stimulation
What is muscle hypertrophy?
enlargement of a muscle
more capillaries
more mitochondria
caused by strenuous exercise and steroid hormones
What is isometric contraction?
produces no movement
used in sitting, standing, posture
What is isotonic contraction?
produces movement
used in walking, moving any part of the body
Describe electrochemical gradient
the input of energy to transport ions across a membrane has created an electrical gradient
The active transport of positive ions out of a cell has created a chemical gradient
the combination of an electrical and chemical gradient is called an electrochemical gradient
However, the cells remain in osmotic equilibrium
The negative ion will try to move down the electrochemical gradient and follow the positive ion out of the cell, but the membrane inhibits its flow
What is resting membrane potential?
The electrical gradient across the cell membrane
What is the resting membrane potential in nerve and muscle cells?
between -40 to -90mV
Describe how K+ ions contribute to resting membrane potential
The membrane is more permeable to K+ ions
K+ leaks out of the cell down its concentration gradient
Excess negative charge build up inside as Pr- cannot cross the plasma membrane
An electrical gradient is formed
The negative charges attract K+ ions back into the cell down the electrical gradient
net movement of K+ stops at the equilibrium potential (E)
What is equilibrium potential?
the point at which the electrical gradient opposes the chemical gradient
What is the E of K+?
-90mV
How do Na+ ions contribute to resting membrane potential?
membrane permeable to Na+ only
same principles hold as in K+ movement
What is the equilibrium potential of Na+?
+60mV
Describe the resting membrane potential in real cells
most cells are 40 times more permeable to K+ than Na+
The resting potential is closer to -70mV because a small amount of Na+ leaks into the cell
The 3Na+ ions are pumped out and 2K+ ions are pumped in by Na+/K+-ATPase
This is also known as an electrogenic pump because it helps maintain an electrical gradient
What types of collagen are found in tendon?
mainly type I
small amounts of types III and IV
What are tendon fascicles held together by?
endotenon
what surrounds some tendons?
paratenon
What is synovium that surrounds tendons called?
tenosynovium
what surrounds endotenon?
epitenon
what is endotenon continuous with?
the periosteum at the tendon-bone interface where collagen fibres enter the bone as Sharpey fibres
What is the function of paratenon?
an elastic sheath allowing free gliding of the tendon against surrounding tissues
which tendons are vascular?
those surrounded by paratenon
which tendons are avascular?
those surrounded by synovial sheaths
what is the key property of tendons?
high tensile strength
what are the functions of tendons?
either generate joint motion during concentric contractions or resist joint motion during eccentric contractions
What are satellite cells?
myoblasts that remain unfused after embryonic development
why can satellite cells aid in the minor regeneration if damaged muscle?
they can still undergo mitosis
What are the three stages of muscle regeneration?
Inflammatory response
activation, differentiation and fusion of satellite cells
maturation and remodelling of newly formed myocytes
