3. Muscular System

Question 1

Functions of Muscles

Answer 1

1. Movement – a result of muscular contraction. This relies on the integrated functioning of the muscles, bones and joints. 2. Maintaining posture - stabilising joints, posture & balance through continued partial muscle contraction. 3. Heat production – also known as thermogenesis. Helps maintain normal body temperature (36.5-37.5 C). Shivering describes involuntary contractions of skeletal muscles. 4. Storage of substances – glycogen & oxygen. 5. Movement of substances:  The heart muscle pumps blood around the body.  Sphincters prevent out-flow from hollow organs.  Smooth muscle in blood vessel walls helps control blood flow.  Smooth muscle moves food through the digestive tract & urine through the urinary system  The diaphragm draws air into airways/lungs.

Question 2

Muscle Properties

Answer 2

1. Contractility: ability to contract (shorten). 2. Excitability: they can conduct an electrical current. Nerve impulses causes muscles to contract. 3. Extensibility: ability to stretch without being damaged. 4. Elasticity: can return to it’s original length and shape after contraction or extension (spring).

Question 3

Muscle Types

Answer 3

Skeletal muscle Cardiac muscle Smooth muscle

Question 4

Skeletal muscle

Answer 4

Striated -attaches between bones and creates movements at joints. •Voluntary muscle. • There are 640 skeletal muscles in the body, accounting for about 40% of body weight. • All of these muscles are voluntary. • Functions include: Motion & posture, Speech(larynx, lips, tongue) and Breathing. • Skeletal muscle is covered by‘fascia’ –a dense sheet of connective tissue that organises muscle, secures it to skin and provides stability. Collagen is a major component. 9

Question 5

Cardiac Muscle

Answer 5

• Striated - forms the heart muscle.
• Involuntary muscles and generate their own rhythmic contraction (they are ‘autorhythmic’).

Question 6

Smooth Muscle

Answer 6

•Non-striated -found in the walls of blood vessels, walls of the gut& in the iris (coloured part of eye). •Involuntary muscle.

Question 7

Striated Muscle

Answer 7

Striated muscles contain cells that are aligned in parallel bundles, so that their different regions form stripes visible with a microscope

Question 8

Non-striated

Answer 8

Non-striated muscles contain cells that are randomly arranged (no stripes visible).

Question 9

Sarcolemma

Answer 9

The cell membrane of a skeletal muscle fibre

Question 10

Sarcoplasm

Answer 10

The muscle cell cytoplasm

Question 11

Tranverse Tubules

Answer 11

Tubes which extend from the cell membrane into the muscle cell.

Question 12

Sarcoplasmic Reticulum

Answer 12

A membrane-bound structure found within muscle cells that is similar to the endoplasmic reticulum in other cells. The main function of the SR is to store calcium ions (Ca2+).

Question 13

Myoglobin

Answer 13

An iron- and oxygen-binding protein found in the skeletal muscle tissue

Question 14

Myocytes (muscle fibres)

Answer 14

Muscle fibres are formed from the fusion of cells called ‘myoblasts’ in the embryo. This is why skeletal muscle cells contain many nuclei. • Once mature muscle cells are formed (becoming ‘myocytes’), they can no longer undergo mitosis. • However there is limited regenerative capacity –by satellite cells. • This means that the number of skeletal muscle fibres each person has is set at birth.

Question 15

Myofibrils

Answer 15

Cylindrical structures formed of bundles of protein filaments within the muscle fibre. They are contractile threads arranged in a striated pattern: • Each myofibril is surrounded by a network of sarcoplasmic reticulum. • Myofibrils are made up of smaller filaments called myofilaments. There are two types:  Actin(thin filaments).  Myosin(thick filaments) –shaped like golf clubs; the ‘myosin heads’ can bind to actin. • The myofilaments overlap to form‘sarcomeres’.

Question 16

Actin

Answer 16

Thin filaments

Question 17

Myosin

Answer 17

Thick filaments

Question 18

Sarcomere

Answer 18

A sarcomere is the basic unit of striated muscle and contains the following areas:  H zone = myosin only. A band= dark area where actin and Myosin overlap.  I band = light area of only actin filaments.  Z disc = filaments of actin that are arranged at 90 degree angles, where they separate sarcomeres.

Question 19

Hierarchy of Muscle from smallest

Answer 19

Actin and myosin - myofilaments Myofibrils which are surrounded by Endomysium, 10 - 100 make up Fascicles which are surrounded by Perimysium The entire muscle is surrounded by Epimysium

Question 20

Neuromuscular Junction (NMJ)

Answer 20

• The ‘Neuromuscular junction’ is the meeting point (synapse) where motor neurons meet a muscle fibre. • The neuron ending is the ‘synaptic end bulb, which contains vesicles that store the neurotransmitter ‘acetylcholine’. • Acetylcholine diffuses across the gap and causes the nerve impulse to continue along the sarcolemma.

Question 21

Acetylcholine

Answer 21

Neurotransmitter causing the nerve impulse

Question 22

Contraction

Answer 22

1. Nerve impulse arrives at the neuromuscular junction.
2. The action potential spreads along the sarcolemma and transverse tubules into the muscle cell releasing calcium (Ca2+) from storage in the sarcoplasmic reticulum.
3. Calcium & ATP cause myosin heads to bind to the actin filament next to it. As the actin and myosin bind, this movement causes the filaments to slide over each other, thereby shortening the fibre.

In a contracted state the actin adn myosin are bound together

Question 23

Relaxation

Answer 23

1. Nerve stimulation stops (no nerve impulse).
2. Using magnesium & ATP, calcium is actively transported (pumped back) into storage, breaking the actin & myosin bond.
3. Actin & myosin slide back into starting positions, lengthening the fibre again (relaxation).

Magnesium makes muscle fibresless excitable and prevents myosin binding with actin.

Question 24

Muscle Growth

Answer 24

• Muscle growth is called ‘muscle hypertrophy’.
• Calcium, magnesium, sodium, potassium andironare essential ingredients for effective muscle activity and athletic performance.
• The following hormones promote muscle hypertrophy:
• Growth Hormone
• Testosterone
• Thyroid Hormones

• During strength training, individuals experience high levels of muscle tissue breakdown and hence protein is required to support hypertrophy.

Question 25

Creatine Phosphate

Answer 25

Creatine phosphate is a protein unique to muscles and is a storage form of energy. • This is important because muscle cells have very little energy within them that they can use up immediately. • Creatine phosphate provides a small, but ready source of energy during the first 15 seconds of contraction. • There is 3 – 6 times more creatine phosphate in a muscle cell than ATP. • ‘Creatinine; is a by-product from the breakdown of creatine phosphate.

Question 26

Slow Oxidative Muscle Fibres

Answer 26

Colour: Dark red Respiration: Aerobic Myoglobin & Mitochondria: Lots Duration: Longeset Good for: Endurance Diameter: Small Examples: Legs and back

Question 27

Fast Oxidative - Glycolytic (FOG)

Answer 27

Colour: White - pink Respiration: Aerobic & anaerobic Myoglobin & Mitochondria: Less Duration: Resistant to fatigue Good for: Walking & Sprinting Diameter: Intermediate Examples: Legs and back

Question 28

Fast Glycolytic (FG)

Answer 28

Colour: White Respiration: Anaerobic Myoglobin & Mitochondria: Least Duration: Fatigues quickly Good for: Weights Diameter: Large Examples: Shoulders and arms

Question 29

Face and Neck muscles

Answer 29

A - Occipitofrontalis B - Obicularis Oculi C- Obicularis Oris D -Temporalis E - Masseter F- Sterocleidomastoid G - Trapezius

Question 30

Occipitofrontalis

Answer 30

Raises eyebrows

Question 31

Orbicularis oculi

Answer 31

Closes eyes

Question 32

Orbicularis ori

Answer 32

Closes/pouts lips

Question 33

Masseter

Answer 33

Mastication

Question 34

Temporalis

Answer 34

Mastication

Question 35

Sternocleidomastoid

Answer 35

Turns & Tilts head

Question 36

Trapezius

Answer 36

Pulls head backward Elevates and retracts shoulders

Question 37

Back Muscles

Answer 37

A - Latissimus Dorsi B - Supraspinatus C - Erector Spinae D - Quadratus Lumborum E - Psoas

Question 38

Latissimus Dorsi

Answer 38

Extends, adducts adn internally rotates arm

Question 39

Supraspinatus

Answer 39

Initial abduction of shoulder

Question 40

Erector Spinae

Answer 40

Extesnsion of the vertebral column. Keeps spine upright

Question 41

Quadratus Lumborum

Answer 41

Bending backwards or sideways

Question 42

Psoas

Answer 42

Hip flexor

Question 43

Chest and Abdomen Muscles

Answer 43

A - Pectoralis Major B - Internal Abdominal Oblique C - External Abdominal Oblique D - Rectus Abdominis

Question 44

Pectoralis Major

Answer 44

Draws arms forward: shoulder flexion and medial rotation

Question 45

Internal and External Obliques

Answer 45

Rotation and bending sideways

Question 46

Rectus Abdominis

Answer 46

Vertbral flexion: bending forward (crunches)

Question 47

Diaphram

Answer 47

Attaches to the lower 6 ribs, sternum and upper lumbar spine. When contracts, it descends into the abdominal cavity, increasing the space for air to enter the lungs. Vital structures pass through the diaphragm, which further emphasises its importance in the body. These structures include the aorta, inferior vena cava, vagus nerve and oesophagus.

Question 48

Arm Muscles

Answer 48

A - Deltoid B - Biceps Brachii C - Triceps Brachii D- Extensor carpi muscles E- Flexsor carpi muscles

Question 49

Deltoid

Answer 49

Attaches from the scapula, acromion and clavicle to the humerus Flexion, abdction & extension of the shoulder joint

Question 50

Biceps Brachii

Answer 50

Attaches from the scapula to the radius Stabiliseds shoulder joint, flexion and supination of forearm

Question 51

Triceps Brachii

Answer 51

Arm adduction, extends elbow

Question 52

Extensor Carpi muscles

Answer 52

Extend the hand at the wrist joint

Question 53

Flexor carpi muscles

Answer 53

Flexes the hand at the wrist joint

Question 54

Legs and Glutes

Answer 54

Note the piriformis and sciatic nerve The sciatic nerve often runs through the belly of the muscle ‘piriformis’. This makes the sciatic nerve particularly vulnerable to compression in this location.

Question 55

Gluteus Maximus

Answer 55

Attaches from teh ilium to the femur External rotaion , abduction and extension of the hip joint

Question 56

Piriformis

Answer 56

Attached from the sacrum to the femur Externally rotates hip

Question 57

Hamstrings

Answer 57

3 separate muscles in the posterior thigh Bend knee (flex)

Question 58

Rectus Femoris

Answer 58

One of 4 quadricep muscles. Attaches from pelvis to the tibia Flexes hip and extends knee

Question 59

Leg Muscles

Answer 59

A - Thigh Adductors B - Gastrocnemius C - Soleus D - Tibialis Anterior

Question 60

Thigh Adductors

Answer 60

Attaches from the pubic to the femur Squeeze thighs together

Question 61

Gastrocnemius

Answer 61

Attaches rom the femur to the calcaneum (heel) Flexes leg at the knee Plantar flexion of foot

Question 62

Soleus

Answer 62

Attaches from the posterior tibia & fibula to the calcaneum (heel) Plantar flexion of the foot at the ankle

Question 63

Tibialis Anterior

Answer 63

Attaches from teh tibia to the metatarsals Dorsiflexion and inversion of the foot (& supports medial arch of foot.)

Question 64

Antagonistic Pairs

Answer 64

Most skeletal muscles are arranged in antagonistic pairs over a joint e.g. biceps brachii/ triceps brachii. Depending on the movement, one muscle is the prime mover, whilst the other is the antagonist. eg. Biceps (prime mover), Tricep (antagonist)

Question 65

Synergist

Answer 65

A synergist assists the prime mover in it’s action e.g. when flexing the elbow, brachialis helps biceps by pulling the ulna towards the humerus.

Question 66

Fixator

Answer 66

A fixator is a muscle that keeps the origin bone stable while a prime mover contracts. E.g. in the shoulder.

Question 67

Cardiac Muscle

Answer 67

Cardiac muscle is a specialised muscle that is only found in the heart. It forms the **myocardium**. • Cardiac muscle fibres are **striated & involuntary**. • Cardiac muscle cells are joined end-to-end by specialised structures known as **intercalated discs**. These are unique to cardiac muscle and allows contraction to spread from cell to cell like a wave. • Cardiac muscle cells are branching cells, so each cell is in contact with 3-4 other cells. This enables the wave of contraction to spread to more cells. * Cardiac muscle is autorhythmic - it generates its own rhythm of contraction, which is approx. 75 times per minute at rest. * Cardiac muscle stays contracted 10-15 times longer than skeletal muscle. * Cardiac muscle depends highly on aerobic respiration and hence the cells contain lots of mitochondria. Cardiac muscle cells therefore require a constant blood supply and delivery of oxygen and nutrients like glucose. * Can also use lactic acid to produce ATP.

Question 68

Smooth Muscle

Answer 68

Smooth muscle is found in the walls of blood vessels, airways, hollow organs (i.e. stomach, bladder), as well as the iris and arrector pili in the skin. • Used to change diameter, shape or orientation of the tissue. • Under autonomic nervous system control (involuntary). • Also contracts in response to hormones, cell-to-cell signalling, and local chemical agents. * Each fibre is just 30 - 200 micro-metres long with a single elongated, central nucleus. * Smooth muscle fibres are non-striated: giving it a smooth appearance. * Filaments are attached to structures called dense bodies (similar function to Z-discs in skeletal muscle) that are not arranged in lines. * During contraction the dense bodies are pulled closer together by the filaments causing the muscle to shorten & twist like a corkscrew.

Question 69

Smooth Muscle Properties

Answer 69

* Smooth muscle contraction is **slower and longer** –slow calcium movement in/out of cells. * Shorten and stretch more than skeletal muscle. * Produce ‘stress-relaxation response’ –allow organs such as stomach and bladder to expand when filled, causing a contraction in order to carry contents. * Smooth muscle maintains partial contraction (important for blood pressure regulation). * Smooth muscle contracts in response to the autonomic nervous system, hormones, stretch and blood gases.

Question 70

Single Unit Muscle Types

Answer 70

* In an organ, smooth muscle fibres function as one unit (all fibres relax & contract together). * Found in the walls of vessels & hollow viscera. * Fibres connected by gap junctions to allow nerve impulses to spread through the muscle.

Question 71

Multi unit smooth muscle

Answer 71

* Fibres are stimulated individually & operate independently from each other. They contain no gap junctions. * Found in walls of large arteries andairways; iris and in arrector pili muscles in hair follicles.

Question 72

Muscle Regeneration: Skeletal

Answer 72

All muscle types can hypertrophy (increase in size). * Skeletal muscle cells can’t divide. * Limited regeneration by satellite cells –when damage occurs, they divide slowly & fuse with existing fibres.

Question 73

Muscle Regeneration: Smooth

Answer 73

* Can increase in number (hyperplasia)–often seen in the uterus and vascular smooth muscle. * Regeneration can occur from stem cells in blood vessels.

Question 74

Muscle Regeneratiion: Cardiac

Answer 74

* Post heart attack, tissue remodeling by fibroblasts (scarring). * More recent evidence has identified that stem cells in the endothelium can undergo division. * Hypertrophy can be physiological (i.e. athletes) or pathological (i.e. heart disease).