3. Muscular System Flashcards
Functions of Muscles
- 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.
Muscle Properties
- 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).
Muscle Types
Skeletal muscle Cardiac muscle Smooth muscle
Skeletal muscle
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
Cardiac Muscle
- Striated - forms the heart muscle.
- Involuntary muscles and generate their own rhythmic contraction (they are ‘autorhythmic’).
Smooth Muscle
•Non-striated -found in the walls of blood vessels, walls of the gut& in the iris (coloured part of eye). •Involuntary muscle.
Striated Muscle
Striated muscles contain cells that are aligned in parallel bundles, so that their different regions form stripes visible with a microscope
Non-striated
Non-striated muscles contain cells that are randomly arranged (no stripes visible).
Sarcolemma
The cell membrane of a skeletal muscle fibre
Sarcoplasm
The muscle cell cytoplasm
Tranverse Tubules
Tubes which extend from the cell membrane into the muscle cell.
Sarcoplasmic Reticulum
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+).
Myoglobin
An iron- and oxygen-binding protein found in the skeletal muscle tissue
Myocytes (muscle fibres)
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.
Myofibrils
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’.
Actin
Thin filaments
Myosin
Thick filaments
Sarcomere
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.
Hierarchy of Muscle from smallest
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
Neuromuscular Junction (NMJ)
• 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.
Acetylcholine
Neurotransmitter causing the nerve impulse
Contraction
- Nerve impulse arrives at the neuromuscular junction.
- The action potential spreads along the sarcolemma and transverse tubules into the muscle cell releasing calcium (Ca2+) from storage in the sarcoplasmic reticulum.
- 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
Relaxation
- Nerve stimulation stops (no nerve impulse).
- Using magnesium & ATP, calcium is actively transported (pumped back) into storage, breaking the actin & myosin bond.
- Actin & myosin slide back into starting positions, lengthening the fibre again (relaxation).
Magnesium makes muscle fibresless excitable and prevents myosin binding with actin.
Muscle Growth
- 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.
Creatine Phosphate
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.
Slow Oxidative Muscle Fibres
Colour: Dark red
Respiration: Aerobic
Myoglobin & Mitochondria: Lots
Duration: Longeset
Good for: Endurance
Diameter: Small
Examples: Legs and back
Fast Oxidative - Glycolytic (FOG)
Colour: White - pink
Respiration: Aerobic & anaerobic
Myoglobin & Mitochondria: Less
Duration: Resistant to fatigue
Good for: Walking & Sprinting
Diameter: Intermediate
Examples: Legs and back
Fast Glycolytic (FG)
Colour: White
Respiration: Anaerobic
Myoglobin & Mitochondria: Least
Duration: Fatigues quickly
Good for: Weights
Diameter: Large
Examples: Shoulders and arms
Face and Neck muscles
A - Occipitofrontalis
B - Obicularis Oculi
C- Obicularis Oris
D -Temporalis
E - Masseter
F- Sterocleidomastoid
G - Trapezius
Occipitofrontalis
Raises eyebrows
Orbicularis oculi
Closes eyes
Orbicularis ori
Closes/pouts lips
Masseter
Mastication
Temporalis
Mastication
Sternocleidomastoid
Turns & Tilts head
Trapezius
Pulls head backward
Elevates and retracts shoulders
Back Muscles
A - Latissimus Dorsi
B - Supraspinatus
C - Erector Spinae
D - Quadratus Lumborum
E - Psoas
Latissimus Dorsi
Extends, adducts adn internally rotates arm
Supraspinatus
Initial abduction of shoulder
Erector Spinae
Extesnsion of the vertebral column.
Keeps spine upright
Quadratus Lumborum
Bending backwards or sideways
Psoas
Hip flexor
Chest and Abdomen Muscles
A - Pectoralis Major
B - Internal Abdominal Oblique
C - External Abdominal Oblique
D - Rectus Abdominis
Pectoralis Major
Draws arms forward: shoulder flexion and medial rotation
Internal and External Obliques
Rotation and bending sideways
Rectus Abdominis
Vertbral flexion: bending forward (crunches)
Diaphram
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.
Arm Muscles
A - Deltoid
B - Biceps Brachii
C - Triceps Brachii
D- Extensor carpi muscles
E- Flexsor carpi muscles
Deltoid
Attaches from the scapula, acromion and clavicle to the humerus
Flexion, abdction & extension of the shoulder joint
Biceps Brachii
Attaches from the scapula to the radius
Stabiliseds shoulder joint, flexion and supination of forearm
Triceps Brachii
Arm adduction, extends elbow
Extensor Carpi muscles
Extend the hand at the wrist joint
Flexor carpi muscles
Flexes the hand at the wrist joint
Legs and Glutes
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.
Gluteus Maximus
Attaches from teh ilium to the femur
External rotaion , abduction and extension of the hip joint
Piriformis
Attached from the sacrum to the femur
Externally rotates hip
Hamstrings
3 separate muscles in the posterior thigh
Bend knee (flex)
Rectus Femoris
One of 4 quadricep muscles. Attaches from pelvis to the tibia
Flexes hip and extends knee
Leg Muscles
A - Thigh Adductors
B - Gastrocnemius
C - Soleus
D - Tibialis Anterior
Thigh Adductors
Attaches from the pubic to the femur
Squeeze thighs together
Gastrocnemius
Attaches rom the femur to the calcaneum (heel)
Flexes leg at the knee
Plantar flexion of foot
Soleus
Attaches from the posterior tibia & fibula to the calcaneum (heel)
Plantar flexion of the foot at the ankle
Tibialis Anterior
Attaches from teh tibia to the metatarsals
Dorsiflexion and inversion of the foot (& supports medial arch of foot.)
Antagonistic Pairs
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)
Synergist
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.
Fixator
A fixator is a muscle that keeps the origin bone stable while a prime mover contracts. E.g. in the shoulder.
Cardiac Muscle
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.
Smooth Muscle
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.
Smooth Muscle Properties
- 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.
Single Unit Muscle Types
- 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.
Multi unit smooth muscle
- 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.
Muscle Regeneration: Skeletal
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.
Muscle Regeneration: Smooth
- Can increase in number (hyperplasia)–often seen in the uterus and vascular smooth muscle.
- Regeneration can occur from stem cells in blood vessels.
Muscle Regeneratiion: Cardiac
- 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).
