Muscles

Question 1

Describe the three basic types of muscle tissue

Answer 1

• Smooth
• Cardiac
• Skeletal

Question 2

What are the functions of muscle tissue?

Answer 2

Muscles covert chemical energy into mechanical (kinetic energy)

Question 3

Describe the structure of skeletal muscle

Answer 3

Each of your skeletal muscles is a separate organ composed of muscle fibers.

Tendons are cords of dense irregular CT that attach to the muscle to the periosteum of a bone.

Fascia is a broad band of CT that supports and surrounds muscles - allows free movement, caries nerves and blood and lympatic vessels

Question 4

Describe how muscle fibres are stimulated to contract

Answer 4

1. Motor neuron stimulation of a msucle fibres to produce a muscle action potential. 2. Conversion of the electrical muscle action potential signal to a contraction signal in excitation-contraction coupling. 3. The contraction cycle where myosin pulls on actin and the muscles actually contract

Question 5

Outline the events that occur at the neuromuscular junction

Answer 5

The nerve signs to the muscle contract at the neuromuscular junction → this then signals a release of acetylcholine) from synaptic end bulb → triggers action potential in the msucle at the motor end plate

Question 6

Describe the steps involved in muscle contraction

Answer 6

Myofibrils - parallel threads that are contractole elements of the muscle fibre (filaments)

Question 7

Identify/remember the major muscles of the human body

Answer 7

Agonist muscle: causes desired movement.

Antagonist muscle opposite effect to that of the agonist muscle.

Question 8

Describe smooth muscle

Answer 8

Found in the walls of hollow internal structures. This tissue is non-striated (smooth) The acts of the smooth muscle are usually involuntary.

Question 9

Describe the gross structure of a skeletal muscle

Answer 9

Tendon, Fascia.

Beneath the fasicia there are 3 CT that protect and support the muscle:

Epimysium - surrounds the entire muscle

Perimysium - surrounds groups of 10-100+ muscle fibers (fascicles)

Endomysium - surrounds each individual muscle fiber.

Question 10

How are muscle fibres formed?

Answer 10

During embryonic development muscle fibres are formed by the fusion of 100+ cells called myoblasts, as a result each muscle fibre is a single cell with 100+ nuclei.

→ after fusion muscle fibres loose the ability to divide. Muscle fibres your possess is more or less set before you are born.

Question 11

How do muscles grow?

Answer 11

Not a result of division. Process called hypertrophy:

The sacrolemma - is the plasma membrane of muscle fibres.

Sacroplasm - the cytoplasm of muscle fibre Transverse (T) tubules: finger like projections of the sacrolemma that extend towards the centre of each muscle

Sacroplasmic reticulum - acts as an internal store for calcium = action potential

Question 12

What is the structure of a thick and thin filament?

Answer 12

Thin filaments - 8nm diameter

Thick 16nm they are both arranged in a repeating sequence, they are then arranged into sacromeres (these are the basical functional unit of a muscle)

Question 13

What supplies the skeletal muscle structure?

Answer 13

Supplied by nerves and blood vessels.

Nerves carry motor neuron axons that control muscle fibre contraction.

Blood vessels bring nutrients and remove wastes

Question 14

Define myoglobin

Answer 14

The protein that is found only in muscle fibres. It binds and stores oxygen molecules that make their way into the muscle fibre

Question 15

Define a sacromere

Answer 15

Contractile unit of muscle cell.

Z discs - zigzagging proteins that sperate each sacromere.

The A- band extends the entire length of the thick filaments

The H zone - contains only thick filaments

The zone of overlap - Thick and thin filaments over lapping eachother

The I-band: contains only thin filaments, the Z discs divide this band in the middle

The M-line - a collection of proteins that cold the thick filaments together in the centre of the sacromere

Question 16

Define the chemistry of thin filaments

Answer 16

Action: is a contractile protein that helps to form the thin filaments, twists into a helix with two regulatory proteins - tropomyosin and troponin.

Actin molecules contain myosin-binding site that allows the interface for myosin (found in thick filaments)

Troppmyosin and troponin: help turn contracts on and off

Question 17

Describe the chemistry of thick filaments

Answer 17

Contractile protein is myosin, which functions as the motor protein. Myosin is responsible for the movement that will result in muscle fibre contration. Myosin tail, myosin hrad - the heads project towards the thin filaments that surround each thick filament.

Question 18

What happens during contraction?

Answer 18

Myosin heads of thick filaments pull on actin molecules that forms the thin filaments and this shortens the sacromere producing a contraction. Molecules dont shorten in contraction, they slide across eachother

Question 19

What happens when an action potential occurs in a motor neuron?

Answer 19

Signals coming from motor neurons, the axons of the motor neurons make contact with muscle fibres at specialised synapses called neuromuscular junction

Question 20

What is a motor unit?

Answer 20

A motor unit consists of a single motor neuron and all the muscle fibres that it makes synaptic connections with. Muscles that control small, precise movements consist of small motor units. Muscles that are involved in large powerful movements contain larger motor units

Question 21

What happens when an action potential occurs in a motor neuron?

Answer 21

Depolarisation triggers ana ction potential in the muscle fibres, then action potential propagates across the muscle fibre membrane surface. → The muscle action potential then propogates along the sacrolemma and in the T tubules

Question 22

What are the 2 steps involved in excitation-contraction coupling?

Answer 22

Excitation-contraction cooupling refers to the steps that link muscle fibre action potentioals (excitation) to muscle fibre contractions. 1. Calcium release 2. Thick-thin filament

Question 23

What two change occur that allow muscle fibre relaxation?

Answer 23

1.Motor neuron stops firing action potentials. ↓ ACh, ceasing to release Ca2+ ions. 2. Protein pumps on the sacroplasmic reticulum pump Ca2+ ions back into the sacroplasmic reticulum. - Ca2+ from sacroplasm reducing binding to troponin, tropomyosin covers up the myosin binding site on the actin molecule, without myosin binding to actin contraction cannot occur

Question 24

What are the 2 steps involved in excitation-contraction coupling?

Answer 24

Excitation-contraction cooupling refers to the steps that link muscle fibre action potentioals (excitation) to muscle fibre contractions. 1. Calcium release 2. Thick-thin filament

Question 25

Describe step 1 in excitation-contraction coupling

Answer 25

THe sarcoplasmic reticulum responds to the muscle fibre action potential by releasing Ca2+ ions into the sacroplasm

Question 26

Describe step 2 in excitation-contraction coupling

Answer 26

Ca2+ ions bind to Troponin of the thin filaments. The binding of Ca2+ causes tropomyosin to move away exposing the myosin-binding site on the actin molecule

Question 27

What are the 4 steps involved in the contraction cycle of muscle fibres?

Answer 27

Once the myosin binding site on the actin molecule is exposed the contraction cycle can begin. 1, Myosinhead splits ATP into ADP and phosphate. This causes the myosin head to change its position and become energised. 2. The myosin head attaches to the actin molecule (at myosin binding cite). This binding causes it to release the phosphate molecule 3. The power stroke occurs. Myosin head rotates and ADP is released. The rotation generates force that slides the thin filament past the thick 4. Myosin detaches from actin. At the end of the power stroke myosin remains attached to actin. If another molecule binds in ATM the myosin will detach from actin

Question 28

What is ATP?

Answer 28

Adenosine triphosphate Adenine ( base group) Ribose ( sugar) Phosphate groups x 3

Question 29

How do muscle fibres produce ATP required for contraction cycle?

Answer 29

ATP is the only molecule that can directly transfer chemical energy into kinetiic energy. At rest ATP can contract only for a few seconds.

Question 30

What are the 3 ways ATP are able to make more?

Answer 30

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

Question 31

How is ATP produced using creatine phosphate?

Answer 31

While muscle fibres are at rest excess ATP produced is used to create molecules of creatine-phosphate. → ATP is transferred to creatine = ADP & a molecule of creatine-phosphate. At rest creatine-phosphate is 3-6 times more plentiful than ATP. By reversing the reaction ATP required for contraction Lasts only 15 sec

Question 32

What is anerobic cellular respiration ?

Answer 32

Involves a series of enzymatic reaction that breakdown glucose to produce ATP. Does not require oxygen . → Glycolysis (breakdown) (2 molecules of pyruvic acid and 2 molecules of ATP. 30-40 sec) Pyruvic is also used aerobic cellular respiration to produce more ATP - if there is not enough O2 it turns into lactic acid → diffuses out of the muscle fibre into blood. In the liver, lactic acid can be converted into glucose, producing more glucose and reduce acidity of the blood

Question 33

What is aerobic cellular respiration?

Answer 33

When muscles activity lasts longer than 30-40 sec aerobic cellular respiration is required to generate enough ATP. It takes longer because it yields 36 molecules. Requires more oxygen and produces more ATP. Provifing us with prolonged energy for prolonged exercise. Oxygen in muscle fibres comes from 2 sources: diffusion into muscle fibres from blood stream and release from myoglobin within muscle fibre. Nutrients pyruvic acid (glycolysis), fatty acids (fats) aminoacids (proteins)

Question 34

What is produced during erobic cellular respiration?

Answer 34

heat, h20, co2

Question 35

What is central fatigue?

Answer 35

Involves feeling of tirdness and desire to stop the activity. Originates from CNS playing a protective role.

Question 36

What does oxygen debt refer to?

Answer 36

Refers to the extra oxygen (over above what you normally use at rest) that is taken in by the body after a period of exercise. 1. Convert lactic acid into glycogen stores in the liver, 2. Re-synthesize creatine-phosphate and ATP in the muscle fibres 3. Replace oxygen that was removed from the myoglobin present in muscle fibres