5.5.10: Muscle Flashcards
What are muscles composed of?
- Cells arranged to form fibres.
- These fibres can contract to become shorter, which produces a force.
Which two protein filaments help to achieve contraction?
-Actin and myosin protein filaments in the muscle cells.
How are muscle cells arranged and why?
- Muscle cells are arranged in opposing pairs so that one contracts and the other elongates.
- because muscle cannot elongate without an antagonist.
In some cases, the antagonist isn’t another muscle, what could it be?
-In some cases, the antagonist may be elastic recoil or hydrostatic pressure in a chamber.
What are the three types of muscle?
- Involuntary (smooth)
- Cardiac
- Voluntary (skeletal or striated) muscle.
What does involuntary (smooth) muscle consist of?
- Individual cells, tapered at both ends (spindle shaped)
- At rest, each cell is about 500 um long and 5 um wide.
- Each cell contains a nucleus and bundles of actin and myosin.
Describe the contraction of smooth muscle.
- Contracts slowly and regularly.
- Does not tire quickly
What is smooth muscle controlled by?
-The autonomic nervous system
Where is involuntary muscle found and how is it arranged?
- In the walls of tubular structures, such as the digestive system and blood vessels.
- Arranged in longitudinal and circular layers that oppose each other.
What does cardiac muscle form?
The muscular part of the heart.
How does the arrangement of cardiac muscles help to ensure that electrical stimulation spreads evenly over the walls of the chambers of the heart and that the contraction is a squeezing action rather than one dimensional?
-The individual cells of cardiac muscle form long fibres, which branch to form cross-bridges between fibres.
What are cardiac muscles joined by?
-Intercalated discs
What are intercalated disks?
- Specialised cell surface membranes fused to produce gap junctions that allow free diffusion of ions between the cells.
- Action potentials pass easily and quickly along and between the cardiac muscle fibres.
Describe the contractions of cardiac muscles.
- Cardiac muscle contracts and relaxes continuously throughout life.
- It can contract powerfully and does not fatigue easily.
What are some fibres in the heart such as Purkyne fibres modified to do?
- Carry electrical impulses.
- These coordinate the contraction of the chamber walls.
Heart muscle is myogenic. What does this mean?
It can initiate its own contractions.
What is the rate of contraction of the heart controlled by?
The SAN
How do cardiac muscles appear when viewed under the microscope?
Striated
Where are voluntary (skeletal) muscles found and what does their contraction cause?
- At the joints in the skeleton.
- Contraction causes movement of the skeleton by bending or straightening the joint.
How are voluntary muscles arranged?
- In pairs called antagonistic pairs.
- When one contracts, the other one elongated.
Describe how the muscle cells in voluntary muscles are arranged into fibres.
- Muscle cells form fibres of about 100um in diameter.
- Each fibre is multinucleate and is surrounded by a membrane called the sarcolemma.
What is the muscle cell cytoplasm in voluntary muscle called and what does it contain?
- Sarcoplasm
- Specialised to contain many mitochondria and extensive sarcoplasmic reticulum.
What are the contents of the fibres in voluntary muscles arranged into?
- Myofibrils, which are contractile elements.
- These myofibrils are divided into a chain of subunits called sarcomeres which contain the protein filaments actin and myosin.
What gives voluntary muscles their striated appearance?
- Actin and myosin are arranged in a particular banded pattern.
- Dark bands are known as the A bands and lighter bands are the I bands.
What are the contractions of skeletal muscles stimulated by?
-The somatic nervous system.
Describe the contraction of voluntary muscles.
- Voluntary muscle contracts quickly and powerfully.
- It also fatigues quickly.
What us the junction between the nervous system and the muscle called?
A neuromuscular junction.
There are five steps to the stimulation of a contraction.
Step 1:
Action potentials arrive at the end of the axon and open calcium ion channels in the membrane. Calcium ions flood into the end of the axon.
There are five steps to the stimulation of a contraction.
Step 1: Action potentials arrive at the end of the axon and open calcium ion channels in the membrane. Calcium ions flood into the end of the axon.
Step 2:
Vesicles of acetylcholine move towards and fuse with the end membrane.
There are five steps to the stimulation of a contraction.
Step 2: Vesicles of acetylcholine move towards and fuse with the end membrane.
Step 3:
Acetylcholine molecules diffuse across the gap and fuse with receptors in the sarcolemma.
There are five steps to the stimulation of a contraction.
Step 3: Acetylcholine molecules diffuse across the gap and fuse with receptors in the sarcolemma.
Step 4:
This opens sodium ion channels, which allow sodium ions to enter the muscle fibre, causing depolarisation of the sarcolemma.
There are five steps to the stimulation of a contraction.
Step 4: This opens sodium ion channels, which allow sodium ions to enter the muscle fibre, causing depolarisation of the sarcolemma.
Step 5:
A wave of depolarisation spreads along the sarcolemma and down transverse tubules into the muscle fibre.
What is a motor unit?
- Many motor neurones divide and connect to several muscle fibres.
- All these muscle fibres contract together, providing a stronger contraction.
How can the electrical activity of muscles be investigated using an electromyograph?
- When a muscle cell is stimulated, the motor neurone created action potentials in the muscle fibres.
- Electrodes applied to the surface of the skin detect the combined effects of the action potentials.
- The amplitude of the EMG recording reflects the number and size of the motor units involved in the contraction.
What does the amplitude of the EMG recording reflect?
-The number and size of the motor units involved in the contraction.
