Chapter 11 - Musculoskeletal System: MUSCLES

Question 1

What are Tendons

Answer 1

Muscles which are attached to the bones of the skeleton by fibrous inelastic connective tissue ( Hyaline Cartilage) is called TENDONS.

• they are attached to bones in a way which acts as a bridge to the joints so that when contraction occurs the bones move.

Question 2

What is muscle tone

Answer 2

Muscle tone is the maintaining of partial contraction of skeletal muscles; it holds many body parts in position

• at any one time, some muscle fibres are relaxed while others are contracted to produce movement
• not caused by the constant contraction of same muscle fibres but different fibres taking it in turns
• the muscles fibres relieve one another smoothly that the contraction can be kept up for long periods of time

Eg Head is held up by the partial contraction of neck muscles but when a person falls asleep their head drops forward due to loss of tone in neck muscles

Question 3

What is posture?

Answer 3

Posture is the characteristic way a person hold up their body when sitting or standing
- its the positioning of the body and arranges of the limbs

Eg ballerina = elegant, graceful posture
Solider = rigid

It depends on the muscle tone, partial contraction of muscles that hold body in Position

Question 4

What are the skeletal muscles and their characteristic?

Answer 4

Skeletal muscle are muscles that are attached to bones, under voluntary control; also called voluntary or striated

LONG AND SLENDER SHAPE WITH STRIATED LENTHWISE FIBRES WHICH ARE DARK AND LIGHT IN COLOUR

Allow movement to bones to enable us to walk, run and carry out a range of voluntary physical activities.

• under conscious control
• gives body form and contours and allows body to maintain posture

Question 5

What are smooth muscles and their characteristic?

Answer 5

Muscle that is not under conscious control; found in walls of internal organs.

AKA involuntary, smooth, plain or non striated muscle

In a spindle shape

Internal organs (intestines, stomach) have muscles for movement - known as smooth muscle or involuntary muscles.

Question 6

What is the cardiac muscle and its characteristic?

Answer 6

The strongest muscle - cardiac smooth muscle

The muscle that forms the wall of the heart.
* reduces and increases space in chambers, pushes blood into blood vessels

has intercollated discs and nerve receptors and is in a branching shape

Question 7

What are the three properties of muscles distinguishing them from other tissues and allowing movement.

Answer 7

• contractibility (shorten)
• extensibility (stretch)
• elasticity (remain same after stretched)

These allow muscles to work together to create movement.

• muscles can shorten but never can increases length; however can stretch

Question 8

What is the structure of skeletal muscle?

Answer 8

• muscle cells held together in bundles which gives ‘stringy’ appearance when cut longwise.
• a sheath of connective tissues allow adjacent bundles to slide easily over one another as they contract.
• sheaths of connective tissue around each bundle join together and towards the end of the muscle they taper and blend to form the tendon.
• connective tissue gives red meat it’s toughness
• amount of connective tissue increases with age therefore older animals have less red meat, and contributes to gradual decrease in muscular strength

Question 9

What do you see when muscle bundles are examined under microscope?

Answer 9

• muscle cells lie parallel to each other
• each muscle cell is an elongated cylinder with many nuclei
• around the cell is a thin, transparent plasma membrane called sarcolemma
• inside sarcolemma is cytoplasm called sarcoplasm
• these cylindrical cells are the muscle fibres (between 10-100 micrometers in diameter and vary in few millimetres and cm in length
• within sarcoplasm of each fibre there are thread like Myofibrils, lying parallel to each other and running the length of the fibre -> 100s - several 1000s of theses myofibrils in each fibre

Question 10

Sarcolemma vs Sarcoplasm vs Sarcoplasmic Reticulum

Answer 10

Sarcolemma is a cell/plasma membrane

Sarcoplasm is the Cytoplasm found in muscle cells

Sarcoplasmic Reticulum similar to endoplasmic reticulum but contains, stores and releases Ca+2

Question 11

Explain the structure of Myofibrils

Answer 11

MYOFILAMENTS, which are the actual units involved in contraction of the muscle,
made up of protein

There are two type of filaments

• Myosin; which are thick myofilaments, composed of mainly the protein myosin
• Actin; which are thin myofilaments, composed mainly of actin proteins
• when sufficient energy is supplied and nerve impulses activates the muscle fibres, these protein filaments slide past each other in a manner hat shortens the Myofibril.

Question 12

What is a Sarcomere?

Answer 12

Myofibrils can be divided into units called SARCOMERES

1 unit of skeletal muscle which is made up of A and M filaments and contracts.

Question 13

What gives skeletal muscle tissue its striated effect?

Answer 13

1. Arrangement of thick and thin filaments within myofibrils gives a banded effect to the muscle. Bands also give cardiac and skeletal muscles striated appearance when under microscope.
2. The striated apprentice skeletal muscle is due to variations in the action and myosin content in different parts of the sarcomere.

Question 14

Simple Summary of Muscle Structure

Answer 14

SKELETAL MUSCLE is made up of BUNDLES OF MUSCLE FIBRES each of which contains MYOFIBRILS which contain MYOFILAMENTS of two types; ACTIN and MYOSIN

Question 15

Explain the Myosin Structure

Answer 15

• head, neck, tail (structure acts like a lever)
• Head has ATP binding site and Actin binding site
• 100s of heads stick out of filaments and acts as CROSSBRIDGES
• moving myosin head creates a ‘POWER STROKE’ resulting in muscle contraction

MYOSIN FILAMENTS DO NOT MOVE

MYOSIN MOVEMENT IS DRIVEN BY ATP

Question 16

Explain Actin Structure

Answer 16

Z - proteins chains wrapped around each other

TROPONIN: Small round proteins, and acts as Calcium binding sites; allows Ca+2 to bond to it

TROPOMYOSIN: long thin strand, blocks the brining site of myosin acting as a REGULATOR

Question 17

What regulates muscle movement?

Answer 17

The actin filament and actin binding site proteins REGULATES the accessibility of myosin heads.

Question 18

Explain the sliding filament theory

Answer 18

1. Nerve stimulates muscle fibre
2. ATP breakdown into ADP and a Phosphate group (provides the energy)
3. Myosin has thick double heads which try to grab onto the ACTIN.
   * two things are needed; accessibility and ATP for energy.
4. To get access CALCIUM is needed which is released from an action potential nerve signal coming down to fire the muscle.
5. Ca+ grabs onto the tropomyosin and moves the block out of the way
6. Now the MYOSIN head (can lose phosphate group) and grab onto the Actin and Creep along it.
7. Myosin will slide the actin past it.
8. The Z discs move closer together
9. The muscle contracts by pulling the actin past the myosin.

Question 19

Why are muscles which allow movement to occur always grouped into pairs?

Answer 19

• muscles can only contract so they pull bones together (cannot push apart)

If muscles contract, pulling one bone in one direction, another set of muscles must contract to pull the bone in the opposite direction. Thus muscles that move parts of skeleton are always grouped in pairs

Question 20

Agonists vs antagonists

Answer 20

Coordination of the paired muscles provides body movement, with the one of the pair producing movement to bones in one direction and the other producing movement in the opposite direction.

Such pairs are called ANTAGONISTS because the have opposite actions.
The agonist or PM is the muscle that causes the desired action.

Eg. Biceps is contracting to bend arm while triceps are relaxing. So in this situation the biceps are the agonist as it yields the movement. The triceps are the antagonist because it’s movement has opposite effect.

When the triceps are contracting to straighten the arm the biceps are relaxing, therefore the roles are reversed.

Question 21

Belly vs Origin vs Insertion

Answer 21

The belly is the thick, fleshy part of the middle of the muscle.

The origin is the end of the muscle fixed to a stationery bone.

The insertion is the attachment of the other muscle end to the movable bone.

Question 22

Explain the movement of the arms.

Answer 22

The Triceps and Biceps and skeletal antagonist muscles which produce movement in the arm.

• biceps are on the front part of the upper arm fixed to the scapula (shoulder blade), while the other end is attached to radius
• triceps are the muscle at the back of the arm fixed to the scapula and to the humerus at one end and the ulna to the other.

They produce opposite movements by having the triceps straighten the arm and the biceps bend the arm.

To move the forearm about the elbow joint these two muscles must contract to the bend the arm, the triceps must relax, opposite occurs when arm I straightened.