phase 1 week 6 Flashcards
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
