Chapter 11 - Musculoskeletal System - Muscles Flashcards
What characteristic of a muscle cell distinguishes it from other tissues of the body
Muscle cells are in form of long, thin fibres that have the ability to CONTRACT or shorten.
- they are organised in such way that, when they contract they reduce the distance between the parts they are connected to, or decrease the space they surround
What are skeletal muscles?
Skeletal muscle are muscles that are attached to bones, under voluntary control; also called voluntary or striated
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
LONG AND SLENDER SHAPE WITH STRIATED LENTHWISE FIBRES WHICH ARE DARK AND LIGHT IN COLOUR
What are smooth muscles?
Muscle that is not under conscious control; found in walls of internal organs.
AKA involuntary, smooth, plain or non striated muscle
Internal organs (intestines, stomach) have muscles for movement - known as smooth muscle or involuntary muscles
What is the cardiac muscle?
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
Explain extensibility and elasticity in muscle tissues
Muscle tissues posses the properties of extensibility and elasticity.
- Extensibility is the ability to be stretched
- Elasticity is the ability to return to the original length after being stretched
What are the three properties muscle have in order to allow movement
- 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
Structure of skeletal muscle (red meat)
- 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
What do you see when muscle bundles are examined under microscope?
- 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
What is a sarcolemma?
Sarcolemma is a cell/plasma membrane
What is Sarcoplasm
Cytoplasm found in muscle cells
What is the sarcoplasmic reticulum
It is a T - tubes which contains, stores and releases Ca+2
Explain the structure of MYOFIBRILS
The Myofibrils are composed of many smaller 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.
What is a sarcomere?
Myofibrils can be divided into units called SARCOMERES
1 unit of skeletal muscle which is made up of A and M filaments and contracts.
What gives the muscle tissue a banded effect? And striated appearance?
- 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.
- The striated apprentice skeletal muscle is due to variations in the action and myosin content in different parts of the sarcomere.
Basic summary of muscle structure
SKELETAL MUSCLE is made up of BUNDLES OF MUSCLE FIBRES each of which contains MYOFIBRILS which contain MYOFILAMENTS of two types; ACTIN and MYOSIN
The SARCOMERE divisions, sections and lines
Z - lines; are the boundary of sarcomere, where I joins onto the next. It anchors Actin.
A - band; thick filament regions (Dark Band)
I - band; point between thick filaments of actin (dark band region)
H - zone; distance between THIN filaments in middle where myosin is found.
M - line; mid-line of sarcomere
What is the sliding filament theory?
Sliding filament theory is a scientific model of muscle contraction.
This model is used to represent muscle contraction.
Explain the Myosin Structure
- 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
Explain the actin structure
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
What regulates the muscle movement?
The actin filament and actin binding site proteins REGULATES the accessibility of myosin heads.
Summary of the SLIDING FILAMENT THEORY
- Nerve stimulates muscle fibre
- ATP breakdown into ADP and a Phosphate group (provides the energy)
- Myosin has thick double heads which try to grab onto the ACTIN.
* two things are needed; accessibility and ATP for energy. - To get access CALCIUM is needed which is released from an action potential nerve signal coming down to fire the muscle.
- Ca+2 grabs onto the tropomyosin and moves the block out of the way
- Now the MYOSIN head (can lose phosphate group) and grab onto the Actin and Creep along it.
- Myosin will slide the actin past it.
- The Z discs move closer together
- The muscle contracts by pulling the actin past the myosin.
During contraction in diagram
I bands shorten
H zone shortens
Z lines (anchor points for actin) shorten by becoming closer together.
Sarcomere shortens by 1/3rd of its resting length
A band is same length
What are Tendons
Tendons are muscles partly made up of fibrous, inelasic connective tissue that attach to bones to bridge the joints when contraction occurs, so bones can move.
Why are muscles that allow bone movement grouped in pairs?
- 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
What are antagonists?
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.
Explain skeletal movement in arm
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.
What is the agonist or prime mover?
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.
What is a synergist?
Synergists are muscles that help the prime mover. They produce the same movement as the prime mover or may steady a joint during a particular movement so unwanted movement is prevented and agonist can function effectively.
What is a fixatior?
When a synergist immobilises a joint in this way it is called a fixator .
A fixator muscle acts as a stabiliser of one part of the body during movement of another part.
Eg. Wrist would flex every time the fist also pass across the wrist. Synergist muscle immobilise the wrist stopping it from flexing.
What is the belly? Insertion? Origin?
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.
What is muscle tone?
Muscle tone is maintaining partial contraction of skeletal muscles.
At any one time, some muscle fibres are contracted while others are relaxed. This tightens the muscles but not enough contraction to move muscles.
Eg. Neck being held up straight vs flopping down
What is posture?
A person’s posture is the characteristic way they hold their body when standing or sitting. It is the way a person positions their body or arranges their limbs.
Posture depends on muscle tone, the partial contraction of those muscles that hold the body in position.
Eg ballerina vs soldier
