Muscular system

Question 1

What is the structure of muscle cells?

Answer 1

• **Actin(short) and myosin (long) **– filament proteins
• Chemical to mechanical energy
• Striated
• personal nerve to stimulate contraction
• artery and vein (nutrient)
• Myofibrils combine to create muscle fibre with nuclei, sacromma and mitochondria which combine to form fascicle to make muscle.

Question 2

Explain the sliding filamet theory

Answer 2

1. Actin is blocked by tropomyosin and troponin
2. ATP and calcium lose grasp (secreted by sarcoplasmic reticulum)
3. Sodium channels in the nervous system sends an electrical impulse (acetylcholine) to open voltage gated sodium channels in muscle cell along membrane (sacromma) – this voltage travels down t-tubule opening calcium channel in sarcoplasmic reticulum activating myosin filament
4. Troponin binds to calcium changing shape dragging tropomyosin as well
5. Myosin head which has hydrolyzed and holds ATP to ADP and Pi and energy extending it binds to actin and myosin releases the stored energy changing myosin shape pulling on actin strand shrinking sarcomere and contracting muscle
6. ADP and Pi unbind due to changed shape allowing a new ATP to bind and myosin releases from actin
7. Myosin hydrolyses ATP and process repeats
8. Meanwhile calcium pumps working to restock calcium in sarcoplasmic reticulum unbinding from troposin back to tightly wound shape stopping myosin head binding to act in any longer

Question 3

What are the two types of myofilaments?

Answer 3

actin - thin
myosin - thick

Question 4

what is the z line?

Answer 4

end to end of sacromere - it reduces in size during contraction

Question 5

types of muscle tissue

Answer 5

1. skeletal muscle
2. cardiac muscle
3. smooth muscle

Question 6

What are the characteristics of skeletal muscle tissue?

Answer 6

• Skeletal muscle is voluntary – meaning it is stimulated by nerve impulses and under our conscious control.
• It is striated (see the dark and light lines in the photomicrograph) and multinucleated (i.e., contains several nuclei).

Question 7

Characteristics of cardiac muscle tissue

Answer 7

• Cardiac muscle is AUTO-RHYTHMIC – meaning that it generates its own rhythmic action potentials and it does this automatically (i.e., not under conscious control).
• It is striated and has a single nucleus.
• Cells are branched to connect to other cells and they have intercalated discs which help impulses pass directly from one cell to the next.

Question 8

What are the characteristics of smooth muscle tissue?

Answer 8

• Smooth muscle is found in the walls of hollow structures, for example blood vessels, the digestive system, & respiratory system.
• Smooth muscle is involuntary / auto-rhythmic (i.e., not under conscious control).
• It is non-striated with spinal-shaped cells containing a central nuclei that are arranged in sheets - this helps impulses to pass from one cell to next. – single nuclei

Question 9

What are the functions of muscles?

Answer 9

• Movement – skeletal muscle, bones and joints
• Posture – holding the body in position
• **Regulating organ volume **– stomach, bladder and the use of smooth sphincter muscles
• **Moving substances in the body **– cardiac muscle (heart), smooth muscle (peristalsis), skeletal muscle (lymph/blood)
• **Heat production **– muscle contraction produces heat

Question 10

What are the main characteristics of muscles?

Answer 10

• Excitability (irritability) – ability to respond to a stimuli
• Contractility – ability to contract when stimulated
• Extensibility – ability to be stretched or extended
• Elasticity – ability to return to the original length after stretching

Question 11

explain muscular attachment during contraction

Answer 11

• One end muscle attached to a structure (usually bone) which remains stationary – known as origin of the muscle
• Opposite end moved by contraction is known as the insertion
• Ligaments attach the bone to bone and tendons muscle to bone

Question 12

What is an antagonistic pair? What are the 4 key words associated with this?

Answer 12

• Agonist – prime mover – contracts and shortens to cause an action (for adduction or abduction)
• Antagonist – stretched and yields and lengthens opposing the action of the agonist
• Synergist – contract to stabilise intermediate joints
• Fixator – stabilise the origin of the agonist
  Synergist and fixator stabilise moving body parts making them more efficient

Question 13

Define - motor unit

Answer 13

• A group of muscle fibers that all get their signals from the same single motor neuron

Question 14

What is a twitch?

Answer 14

any motor unit exertion

Question 15

What are the 3 stages of a twitch?

Answer 15

1. latent period (stimuli, SFT, sodium ions causing calcium channels to open, no forced produced)
2. **period of contraction **(myosin heads binding)
3. relaxation period (calcium moved back to sacromma reticulum)

Question 16

Define - grades muscle response

Answer 16

Affected by both the frequency and strength with which they are stimulated (increase force by increasing frequency motor neurons are firing)

Question 17

Define - temporal summation

Answer 17

Lots of twitches adding to each other – calcium ions keep attaching to myosin as longer period of contraction

Question 18

What is tetanus?

Answer 18

• Twitches blend together to feel like one contraction
• ceiling of maximum tension – as finite supply of ATP making it impossible to maintain vigorous muscle activity indefinitely – leading to muscle fatigue

Question 19

What is recruitment?

Answer 19

AKA multiple motor unit summation
-** increased efficiency of twitch as more action’s potentials to more motor units**
- recruitment of motor units follows the size principle
- different sizes motor units with different sized muscle fibers are enlisted to change the energy exertion needed for different skills (larger fibers are less excitatory so take more to start working)

Question 20

What is an istonic movement?

Answer 20

• if the recruitment of motor units exerts enough energy to overcome the mass of the load causing muscular contractions it allows the action (e.g., Lifting a mug) to occur

Question 21

What is an isometric movement?

Answer 21

• the recruitment of motor units **isn’t large enough to overcome the load **then the force exerted will not change the length of the muscles (e.g., Trying to lift a building as energy is exerted but no muscular contraction is occurring

Question 22

Whats the anatomy of skeletal muscle?

Answer 22

• Muscle made of bundles of muscle fibers called fascicles
• Muscle and fibers held together by **connective tissue **
  1. Epimysium – surrounding whole muscle
  2. Perimysium – surrounding bundles of fibers/ fascicle
  3. Endomysin – surrounds individual muscle fibers

Question 23

What are myofibrils made up of?

Answer 23

• myofibrils contain contractile elements of sarcomere and even smaller actin and myosin
• Made up of contractile proteins **Actin and myosin **– myofilaments
• Mitochondria laying between these layers of myofibrils to help cellular respiration as **oxidative phosphorylation **occurs here

Question 24

what does it mean to be striated?

Answer 24

• Overlapping of thin actin and thick myosin give striated (striped) appearance

Question 25

what are three metabolic pathways creating ATP?

Answer 25

1. Creatine phosphate
2. Anaerobic respiration
3. Aerobic respiration

Question 26

What is creatine phosphate as a metabolic pathway?

Answer 26

• Stored in the muscles – 2-3x more stored than ATP
• Short term energy supply for muscles
• It creates ATP for muscular contraction – metabolic pathway
• Coupled reactions of creatine phosphate and ADP to create creatine and ATP with enzyme creatine kinase

Question 27

What is anaerobic respiration as a metabolic pathway?

Answer 27

• Not requiring Oxygen
• 2 stages
  1. Glycolysis – glucose breakdown in cytosol (2 ATP produced) by product pyruvic acid
  2. **Lactic acid formation **– convert pyruvic acid to lactic acid which is released in blood

Question 28

What is aerobic respiration as a metabolic pathway?

Answer 28

• Required Oxygen
• Most efficient as 32-38 ATP produced per glucose molecule
  1. Glycolysis – glucose breakdown to pyruvic acid
  2. Krebs cycle
  3. Oxidative phosphorylation

Question 29

What are some physiological changes during exercise?

Answer 29

• Increased CO2 and lactic acid so pH more acidic (chemoreceptors)
• Increased muscle movement and respiration (proprioceptors)
• Increased return of blood to the heart (**baroreceptors **blood pressure)

Question 30

What is a proprioceptor?

Answer 30

Receptor registering increased muscular movement and respiration

Question 31

What is a chemoreceptor?

Answer 31

receptor registering an increased CO2 and lactic acid so pH more acidic

Question 32

What are baroreceptors?

Answer 32

A receptor registering an increase in the return of blood to the heart - blood pressure