Lecture 9- Skeletal Muscle Neurophysiology 1 Flashcards
What is skeletal muscle specialized for?
Has a highly order structure in order to generate force through contraction and extension. In this way skeletal muscles act as the motor pulling bones into place and allowing for movement.
Skeletal muscle has what construction?
Parallel, fibers run in the same direction ensuring maximum force is produce through contraction.
Order these words from the biggest to the smallest in terms of the structure of muscle.... Fiber Muscle Fasciculus Myofibril
Muscle
Fasciculus
Fiber
Myofibril
All of these are long tube like structures running in parallel which bundle together to make the structure above in list.
Name three things that skeletal muscle is rich in….
- Nerves= connection between the brain and muscles
- Blood vessels= Skeletal muscle uses a lot of energy and therefore needs oxygen + nutrients shipped to it constantly and waste products from metabolism removed.
- Connective tissue= exists throughout every layer of the muscle to provide structure keeping all the fibers correctly orientated. Having it in-between also acts like cushioning preventing rubbing/ friction.
What is the appearance of muscle like?
Striated
True or false: each muscle fiber is a muscle cell?
True
What are sarcomeres? How they are defined in skeletal muscle?
They are the individual contractile units of skeletal muscle.
1 sarcomere is the distance between two Z lines.
What is the outer membrane of a skeletal muscle fiber called?
Sarcolemma
Describe the filaments that make up a myofibril? What are their roles in sarcomere contraction?
- Thin filament= actin. Gets pulled to the center of the sarcomere. The space between the thin filaments in the middle of the sarcomere gets smaller throughout contraction and bigger when relaxed.
- Thick filament= myosin. Is what does the pulling.
Which filament forms the structure of the skeletal muscle fibers themselves?
Actin (thin)
Where does contraction occur in skeletal muscle?
With contraction every sarcomere shortens its length in unison.
What are the two aspects of the muscle excitation problem?
- Muscle fibers respond but don’t think i.e they don’t have pacemaker cells like the heart does and cannot act independently of the brain
- Muscle fibers need to contract simultaneously along their entire length otherwise will get staggered movement (think wave)
What are the two aspects of the muscle excitation problem?
- Muscle fibers respond but don’t think i.e they don’t have pacemaker cells like the heart does and cannot act independently of the brain
- Muscle fibers need to contract simultaneously along their entire length otherwise will get staggered movement (think wave)
What structure is responsible for solving the muscle-excitation problem?
The neuromuscular junction (NMJ)
Describe the events that occur at the NMJ in transferring signals….
-Action potential moves down the myelin-coated axon and arrives at the
pre-synaptic terminal
-Triggers the movement of vesicles to the active zones, releasing acetylcholine (Ach)
-Ach moves into the synaptic cleft and down into the junctional folds
-Ach then interacts with receptors on the sarcolemma, depolarizing the fibre and propagating an action potential
What are active zones?
This is where vesicles containing acetylcholine can bind and release neurotransmitter into the synaptic clef. Need this mechanism others would bind in places we don’t want release.
What is the function of junctional folds?
They increase the surface area between the synaptic clef and sarcolemma. This is lined with acetylcholine receptors therefore, increasing the action that can occur here.
Finnish the sentence:
Depolarisation of a muscle fiber leads to an….
Action potential
How many APs in the muscle fiber result from 1 AP in the terminal?
1, not like in CNS when multiple inputs or multiple actions potentials from the same input
What does a muscle fiber AP trigger?
Contraction (excitation- relation coupling)
True or false: we have the ability to both synthesize and break down acetylcholine?
True
What enzyme do we need for acetylcholine synthesis?
Choline Acetyltransferase
What enzyme do we need for acetylcholine breakdown?
Acetylcholinesterase
What is the acetylcholine lifecycle?
- Acetylcholine is synthesized is presynaptic terminal from choline and acetyl cholA via ChAT
- It is transported into a vesicle and then released at the synaptic clef where it binds to receptors on the post-synaptic membrane to have an effect
- Acetylcholine is then broken down into choline and acetic acid in order to prevent continuous activation.
- Choline is then transported back into the presynaptic terminal via sodium co-transport (takes advantage of favorable sodium gradient)
- Choline can then be made into more acetylcholine
Why don’t we just make Acetylcholine from scratch every time?
It’s too inefficient energy wise (wastes too many resources)
