practical 2 Flashcards
Smooth muscle
*resides in the walls of hollow organs
*involuntary/ not striated
*contracts slowly and rhythmically
Cardiac muscle
*involuntary
*own intrinsic contraction rhythm
Skeletal muscle
*make up 40% of body mass
*voluntary
*can contract rapidly, but tires rapidly
upper motor lesion
loss of muscle function as a consequences of strokes damaging neurons in the brain
Excitability
ability of muscle cells (muscle fibers) to respond to stimuli, such as nerve impulses or electrical signals. When stimulated, muscle cells generate action potentials
Contractility
All muscle cells shorten when stimulated
Extensibility
All muscle cells can be stretched, sometimes even more so than their resting lenght
Elasticity
All muscle cells, after being stretched, can recoil to their resting length
skeletal muscle is not _________. (Meaning the muscle does not contract rhythmically)
autorhythmic
What are some functions of muscles?
*generate movement
*Keeps us stationary to maintain posture and balance
*stabilize joints
*generate a lot of heat
tendons connect _______ to _______
tendons connect muscle to bone
when referring to AOI’s, what does the insertion of a muscle imply
the insertion of a muscle refers to the bone or structure that moves
when referring to AOI’s, what does the origin of a muscle imply
the origin of a muscle refers to the bone or structure that is stationary
what is the difference between a direct attachment and an indirect attachment?
direct: the
periosteum/perichondrium is fused with the muscle’s epimysium
indirect: more common, durable, and small (example: tendon). they can blend into the fascia of other muscles to form an attachment
what is a tendon
aka aponeurosis is an example of an indirect attachment. tendons are mostly collagen and rope-like extensions of a muscle’s connective tissue.
- pass around friction points such as boney projections or joints
two or more muscles often work ___________(against each other)
antagonistically; if one muscle is contracting, the other is extending
true or false: skeletal muscle fibers are very large, and multinucleated
true
the sarcolemma of a muscle is known to be the cell ____________; while the sarcoplasm is the ___________
membrane; cytoplasm
_____________ are repeating units of myofibrils, which are themselves repetitive units of skeletal muscle
sarcomeres
sarcomeres display alternating dark __ bands and light __ bands
A; I
- A bands contain thick filaments
- I bands contain thin filaments
sarcomere
runs from Z line to Z line
what protein bisects the H zone
myomesin
what is the contractile unit of muscle
sarcomere
what is the area around the z disc with only thin filaments
light I band
myofilaments
Are made up of Actin and Myosin (aid in muscle contraction)
what is known as the center of the H zone, and within the A band
M line
what is the filament that is composed of myosin proteins.
thick filaments
Tropomyosin
Forms a polypetide strand that spirals around actin to reinforce it.
-*in relaxed muscle fiber, tropomyosin blocks actin’s myosin-binding sites.
what is the filament that is composed of actin proteins
thin filaments
what defines the boundary of each sarcomere
z-discs
___________ fiber is composed of many myofibrils
muscle
define what a t-tubule is?
conducts electrical signals deep into the cell
what is the name of the cell membrane of the muscle fiber
sarcolemma
Troponin
Composed of three globular polypetides, each of which have different function.
what band contains both thick and thin filaments
A band
what does the sarcoplasmic reticulum store
it stores calcium ions
when you hear the word cross bridge cycle think muscle contraction
the cross bridge cycle is a sequence of molecular events that enables muscle contraction.
The Z line is mostly made up of the protein…?
alpha-actinin
Myofibrils are connected together at Z lines by…?
desmin filaments
What are elastic filaments made up of?
Titan
how many steps are in the cross bridge cycle?
there are 4 steps in the cross bridge cycle
elastic filaments run from___to____
the Z line ; thick filaments
-to hold them in place and provide flexible recoil to the sarcomere
list the name of the four steps of the cross-bridge cycle?
- binding (cross bridge)
- power stroke
- detaching
- cocking
Dystrophin links___ to the____, and when deficiently expressed, leads to the pathology______.
thin filaments; sarcolemma; muscular dystrophy
what is happening in the binding (power stroke) phase?
a myosin head binds to an exposed myosin-binding site on the actin filament
what is happening in the power stroke phase
ADP and inorganic phosphate are released from the myosin head, returning to its low-energy state, resulting in a power stroke
3 thick filaments surround each___
and
6 thin filaments surround each____
thin filaments
thick filaments
what is happening in the detaching phase
ATP binds to the myosin head, causing detachment.
what is happening in the cocking phase
hydrolysis of ATP into ADP and inorganic phosphate repositions the myosin head in its high-energy configuration. the cycle repeats
sarcoplasmic reticulum
specialized type of endoplasmic reticulum found in muscle cells, particularly in skeletal and cardiac muscle fibers
each myofibril is surrounded by interconnecting sarcoplasmic reticulum
when talking about electrical events… all plasma membranes carry a resting charge or polarization where the inside of the cell is more negative relative to the outside
the main point to take away from this card is that we will be focusing on the sarcolemma when talking about muscle action potential.
- the sarcolemma is the plasma membrane of muscle fibers
terminal cisterns
large perpendicular cross channels that form the sarcoplasmic reticulum at the A band I band junction
At the A band and I band junction, elongated tube extensions of the sarcolemma dive deeply into the cell and are termed_____.
Ttubules
what is a triad?
T tubule plus terminal cisterns on either side
When a nerve stimulates a muscle, an electrical signale travels down the___, and since___are just tube extensions of it, the electrical signal can thus be carried deep into the muscle.
the initiation and propagation of a muscle action potential involves three steps. what are they?
- acetylcholine binds to its receptor which triggers the opening of chemical ligand gated ion channels for sodium and potassium
- the voltage gated sodium channels respond to change in charge and open allowing positive sodium to enter down its electrochemical gradient
- once the voltage becomes sufficiently less negative, this change closes the voltage-gated sodium channels and opens the voltage gated-potassium channel
Each individual muscle fiber is innervated by a branch of….?
a motor axon
What is a motor unit?
The motor neuron together with all of the individual muscle fiber that innervates
the____ the motor unit, the____the control of the movement in that muscle
smaller; finer
in this card you will find the 3 steps of initiation and propagation of a muscle action potential
- Depolarization: Acetylcholine triggers the opening of voltage-gated sodium channels. Sodium ions rush into the neuron, causing the internal voltage to become less negative.
- Repolarization: After reaching a peak voltage, sodium channels close and voltage-gated potassium channels open. Potassium ions flow out of the neuron, reversing the depolarization by making the inside more negative again.
- Hyperpolarization: Potassium channels close slowly, causing an overshoot that temporarily makes the neuron even more negative than its resting state before it returns to the resting potential.
One motor unit contains how many motor neurons?
one
T/F, the muscle fibers from a single motor unit are typically clustered together.
FALSE; they are typically spread throughout the entire muscle, thus allowing graded control of the entire muscle and just a small portion of it
important note to remember when thinking about action potentials
while repolarizing, the cell cannot be stimulated again until the membrane is sufficiently negative - this is termed the refractory period
where does the muscle action potential travel
it travels along the sarcolemma and down the t-tubles where the depolarization causes voltage-sensitive tubule proteins to undergo a change in shape which leads to opening of calcium release channels in the termina cisterns
when you see the term actin myosin cross bridge cycling
think tropomyosin physically blocks the myosin binding active sites on actin where intracellular calcium is low
The intrinsic muscles of the hand contain___motor units, each innervating only a few muscle fibers.
small
Large muscles like the quadriceps contain___ motor units, each innervating muscle fibers
large
_____in the synaptic cleft quickly breaks down acetylcholine to acetic acid and choline to…..?
Acetylcholinestarase; terminate the signal thus allowing for fine control of the muscle activation
true/false: during a muscle contraction, the thick and thin filaments do not change length
true; they slide past one another which causes the sarcomere as a whole to decrease in physical length- this is referred to as the sliding filament theory
how does skeletal muscle contract
skeletal muscle contracts when a motor nerve stimulates an electrical action potential that propagates along the sarcolemma leading to brief rises in intracellular calcium resulting in completion of excitation-contraction coupling.
what is the term called that refers to the nervous system controlling the number of twitching muscle fibers
recruitment
in what disease are acetylcholine receptors deficient due to autoimmune destruction of the receptors?
Myasthenia gravis
T/F; muscle contraction always shortens the muscle
FALSE; not always
how is a muscle controlled/moved
a whole muscle is controlled by the firing of up to hundreds of motor axons
Isometric muscle contraction
The muscle contracts, but your joints do not move and muscle fibers maintain a constant length.
*muscle tension increases but the muscle length remains constant
what does the term threshold stimulus refer to?
a threshold stimulus is achieved when the stimulus is just strong enough to generate an observable contraction
Isotonic muscle contraction
A body part is moved, and the muscle fibers shorten or lengthen. muscle tension remains constant but the muscle length changes
what is the term used to describe the process by which the nervous system controls the strength of muscle contraction?
recruitment
Isotonic contractions are concentric if…?
The muscle length decreases
Isotonic contractions are eccentric…?
if the muscle length increases during contraction.
What’s an example of an eccentric contraction?
in calf muscles as you walk uphill to prevent over rotating the ankles and to keep you stable as you move.
What’s an example of concentric contraction?
In the biceps while curling a barbell
Action potentials arriving at the axon terminal trigger the release of____into the____
Acetylcholine ; synaptic cleft of the NMJ
Activity in a whole muscle is called
electromyogram (EMG)
what happens during the “recruitment” process of muscle fibers?
during recruitment, the number of active motor units increases, which enhances the strength of muscle contraction. smaller motor units are recruited first, followed by larger ones as more force is required
explain the size principle in the context of motor unit recruitment.
the size principle states that motor units are recruited in order based on their household and size, starting with smaller motor units and progressing to larger ones as the stimulus intensity increases.
define “ tetanus” in muscle physiology and explain how it is achieved.
tetanus is a sustained muscle contraction that occurs when the frequency of stimulation is so high that the muscle does not have time to relax between stimuli, resulting in a smooth and continuous contraction
what is the difference between unfused and fused tetanus
unfused or incomplete tetanus, occurs when a muscle receives stimuli at a rate where there is a partial relaxation phase between contraction. fused tetanus, or complete tetanus happens when stimuli are given at such a high frequency that no relaxation is observed, resulting in a smooth, sustained contraction
In the EMG, you are observing a….?
compound muscle potential (CMP)
The___of the CMP reflects the number of motor units active
magnitude
What neurotransmitter is released at the NMJ?
Ach (Acetylcholine)
What are the three main mechanisms by which ATP is regenerated during muscle contraction?
ATP is regenerated through creatine phosphate directly phosphorylating ADP, anaerobic glycolysis, and aerobic respiration.
What is the brief increase in calcium ions called in muscle fibers?
Intracellular concentration of calcium ions [Ca^2+] increases.
What are the three parts of a muscle twitch?
The latent period, the period of contraction, and the period of relaxation.
