Muscular system

Question 1

Name the 3 types of muscle

Answer 1

skeletal
cardiac
smooth

Question 2

Define the term fascicle

Answer 2

A bundle of muscle fibers, multiple fascicles make up a whole muscle

Question 3

Define epimysium, perimysium, endomysium

Answer 3

Epimysium- refers to the outer layer of the muscle which surrounds the whole muscle
Perimysium- refers to the middle layer of the muscle which surrounds the bundle of fibres (fascicles)
Endomysium refers to the inner layer of muscles which surrounds individual muscles fibres

Question 4

Define & explain the structure of myofibrils

Answer 4

Myofibrils are individual muscle fibres, they are made of actin (thin) and myosin (thick) filaments which create a myofilament, the overlap of actin & myosin creates a striated appearance. Account for 80% of cellular volume, made of chains of sarcomeres

Question 5

Describe characteristics of skeletal muscle

Answer 5

Skeletal muscle involves voluntary control (concious), it is striated (many cells), multinucleated, has rapid contractions, but tires easily

Question 6

Describe characteristics of Cardiac muscle

Answer 6

Cardiac muscle is autorhythmic, it contracts automatically, it is a striated muscle with single nuclei, it is heavily branched to ensure the heart contracts as one unit to improve the efficiency of being a pump. It does not fatigue

Question 7

Describe characteristics of smooth muscle

Answer 7

Smooth muscle is involuntary, non-striated and single nucleus, lines the walls of hollow organs e.g., stomach, oesphagus etc, It forces liquids through tubes of the body, also forming valves to regulate the passing of substances. It has no striations and consists of elongated cells which are involved in slow and sustained contractions

Question 8

Name the functions of muscle

Answer 8

Muscle holds us upright & it enables movement (skeletal), it regulates organ volume and moving of substances (smooth)
Contraction of muscles also generates heat, e.g., shivering

Question 9

Name and explain the 4 characteristics of muscle

Answer 9

1. contractability: the ability to contract when stimulated
2. excitability: ability to respond to a stimulus
3. extensibility: the ability to stretch/ extend
4. elasticity: ability to revert to normal size after contraction/ extension

Question 10

Define the agonist

Answer 10

Contracts to form the movement

Question 11

Define the antagonist

Answer 11

Stretches and yields to the action of the agonist

Question 12

Define the synergist

Answer 12

Contracts to stabilize intermediate joints

Question 13

Define the fixator

Answer 13

Stabilizes the origin of the agonist

Question 14

Define a sarcomere

Answer 14

The region between myofibrils between 2 Z discs, is the smallest contractile unit of a muscle, and contains an A band with an I band at each end, Sarcomeres align side by side

Question 15

Define a myofilament

Answer 15

there are 2 types of contractile myofilaments, they are made up of actin and myosin

Central thick filaments- contain myosin and extend length of band A, connected in the middle by the M line

Lateral thin filaments-contains actin (thin) extend across I bands and into the A band, the Z disc anchors the thin filaments

Question 16

Explain the structure and function of the sarcoplasmic reticulum

Answer 16

a form of SER, It regulates concentraion of calcium. It stores calcium and releases it during muscle stimulation to allow muscle to contract. The SR has lots of mitochondria as well as glycogen granules to provide energy for muscle contraction

Question 17

Explain the structure and function of T tubules

Answer 17

T tubules are elongated tubes that are formed by merging of sarcolemma with inferior cell, they are a continuation of the sarcolemma. They have a wide lumen which creates a larger SA for muscle fibres. Their main role is communication, enabling myofibrils to receive signals at the same time and therefore contract simultaneously

Question 18

Define the sliding filament model theory

Answer 18

The model states that during contraction, thin filaments (actin) slide over thick filaments (myosin), creating an overlap leading to formation of cross bridges. The length of filaments do not change shape during contraction

Question 19

explain the steps of the sliding filament model

Answer 19

1. The nervous tissue stimulates muscle fibres, AP travels from sarcolemma through T tubules, causing SR to release calcium
2. Calcium binds to troponin, shifting tropomyosin which exposes binding sites on actin filaments
3. The myosin heads on the thick filaments bind to the actin binding sites, generating a sliding movement and cross bridges are formed.
4. cross bridges form and break throughout muscle contraction, propelling movement of filaments into sarcomere
5. This shortens the muscle cell