Muscle Structure And Function Flashcards
How many muscles and joints does the human body have?
650 muscles
187 joints
What are the three types of muscle tissues?
Cardiac - in the heart
Smooth - found at walls of organs and around blood vessels
Skeletal - large muscles and muscle cells
Describe cardiac muscle
Responsible for circulating blood
Small cells
Single nucleated
Involuntary
Describe smooth muscle
Single nucleated
Involuntary
Describe skeletal muscle
Multinucleated
Voluntary
What are the 3 layers of connective tissues in a muscle?
Epimysium
Perimysium
Endomysium
Describe the epimysium
A tough connective tissue
Surround the whole muscle.
Surrounds bundles of nerve cells that run in long fibres called fascicles.
Describe perimysium
Surround the individual fascicles
Allowing nerves and blood flow to individual fibres
Describe the endomysium
Surrounds each individual fibre
Acts as a protective layer
What are the functions of muscle tissue?
Produce movement Stabilise Produce heat Movement of substances Regulate organ volumes
What are the properties of muscle tissue?
Excitability - responses to chemicals released from nerve cells
Conductivity - produce and receive electrical signals
Contractibility - ability to shorten and generate force
Extensibility - can be stretched without damage
Elasticity - can return to normal shape after being stretched
What is the most common type of muscle?
Skeletal
Describe skeletal muscle
Attaches to bone, skin or fascia
Striated with light and dark bands
Multi nucleated
Voluntary control of contraction and relaxation
What causes the skeletal muscle to be multi nucleated?
Formed out of myoblast cells fusing together.
Each myoblast contains a nucleus so when they fuse it produces a muscle with lots of nuclei.
What are some functions of skeletal muscle?
Produces movement Maintains posture Supports - soft and hard tissues Maintain body temp Proprioception
What are the structures that skeletal muscle is composed of?
Connective tissue
Muscle tissue
Nerves
Blood vessels
What are the connective tissue structures?
Epimysium
Perimysium
Endomysium
What is the epimysiums role?
The outer layer Irregular fibrous tissue Surrounds whole muscle Exterior collagen layer Connected to deep fascia Separated muscle from surrounding tissue
What is the perimysiums role?
Middle layer Surrounds muscle fibre bundles = fascicles Half collagen Half elastin Contains blood vessels and nerve supply
What is the endomysiums role?
Inner layer
Surround individual muscle cells - muscle fibres and myofibrils
Contain capillaries and nerve fibres
Contain satellite cells that repair damage
What occurs with the 3 connective tissues at the end of the muscle?
The come together to form connective tissue attachments to bone such as tendons or aponeurosis.
Describe the nerves in a skeletal muscle
Collection of muscle cells is supplied by a motor neurone
One motor nerve and the muscle fibre it supplies if known as a motor unit.
Each muscle cell is supplied by a terminal branch of a motor neurone
Found in the endomysium
Describe the blood vessels located in a skeletal muscle
Muscles have extensive vascular systems
Get large amounts of oxygen
Supply nutrients
Carry away waste products
Each muscle cell is in contact with 1 or 2 capillaries
Found in the endomysium
Exeter the muscle at the same point as the nerve.
Describe skeletal muscle tissue
Very long and cylindrical
Become very large
Contain hundreds of nuclei
Contain many mitochondria
What are the main structures located in a skeletal muscle?
Sarcolemma T - tubules Sarcoplasmic reticulum Myofibrils and myofilaments Sarcomeres
Describe the Sarcolemma
Cell membrane of a muscle cell
Surround the Sarcoplasm - cytoplasms of a muscle cell
Filled with tiny threads called Myofibrils and myoglobin
A change in its transmembrane potential can begin depolarisation
Describe the T- tubules
Invaginations of the Sarcolemma into the centre of the cell
Allow the whole muscle to contract at the same time
Fill with extra cellular fluid
Carry action potentials down into the cell
Contain many mitochondria
Describe the Sarcoplasmic reticulum
Membranous structure surrounding each Myofibril
System of tubular sacs similar to smooth endoplasmic reticulum
Help to transmit action potentials to myofibrils
Form chambers at each end = Terminal Cisternae
This is where the primary site of calcium is released
Store calcium
Release it to trigger action potentials
What is a triad?
Formed from one T - tubules and 2 terminal cisternae
An active mechanism, that releases calcium to start a muscle contraction.
Describe myofibrils and myofilaments
These are threads that are separated by the Sarcoplasmic reticulum
Maude up of bundle of protein filaments called microfilaments
These are contractile proteins
Describe the sarcomere
Thick and thin filaments over lap each other, forming a striated pattern
Thick = myosin protein
Thin = actin protein known as Light I bands
In the over lap region it’s known as the A band for both actin and myosin cross over
They’re arranged in compartments known as sarcomeres - separated by Z discs at each end
H zone is an area of only myosin filaments
M line if the middle of the sarcomere
Contractile units of the muscle
What are the 4 main muscle proteins?
Myosin, actin, troponin and tropomyosin
What are 4 other proteins found?
Titin, myomesin, nebulin and dystrophin
Describe myosin
Thick filaments
Composed of a long tail and two head
The heads rotate - at the hinge region- to extend towards the thin action filaments - to form cross bridges
They’re held in place my m- line proteins
Tail binds to other myosin proteins
When contraction occurs, myosin doesn’t change length
Describe actin, tropomyosin and tropnin and how they work together
Thin filaments
At resting - tropomyosin heads cover the actin binding sites
To initiate a muscle contraction they have to move to expose the sites
Calcium ions bind to troponin
Causing both proteins to rotate and move away
Exposing the binding site
Myosin heads can now bind = cross bridge formed
Held in place by the z discs
Describe TITIN
Acts as an anchor to thick filaments Attach the m line and the z disc Can stretch to 4 times its resting length Role in recovery Important in eccentric contractions
Describe myomesin
Forms the M line and connects to TITIN and adjacent thick filaments
Describe Nebulin
Inelastic protein
He,so to align thin filaments
Describe Dystrophin
Links thin filaments to the Sarcolemma
Transmits tension generated to the tendon
What occurs is we lengthen our muscle past optimal range?
Fewer cross bridges formed
Less force and contraction produced
What occurs if the muscle is overly Shortened?
Few cross bridges formed
Less force and contraction produced
Thick filaments crumpled by z discs
What does the length tension curve show?
A graph of force of contraction versus length of the sarcomere.
What is ATP’s role in a muscle contraction?
Supplies energy for the contraction
Supplies the energy for active transport of Ca ions into the SR
Amounts already in the muscle is low
Sufficient to power a few seconds
Has to be regenerated quickly for sustainable contractions
What are the 3 sources of ATP production within a muscle?
Creatine phosphate
Anaerobic Cellular Respiration
Aerobic Cellular Respiration
Describe how creatine phosphate works
Excess ATP in a resting muscle is used to form CP
ADP + P - the P is transferred to combine with creatine to make CP
THe CP can be used quickly to create ATP when needed
CP will transfer back its phosphate to ADP to form ATP and creatine
Quick breakdown
Maximal contraction of 15 seconds
Can be taken as a supplement - but this can have negative impacts
Describe how anaerobic respiration works
ATP is produced from the breakdown of glucose into pyruvic acid
Occurs in a process known as glycolysis
Pyruvic acid converted to lactic acid
Diffuses into the blood - too much will cause muscle fatigue and stop the contraction
This process can continue for around 30-40 seconds
Describe how aerobic respiration works
Pyruvate, fatty acids, oxygen, amino acids - all processed in separate compartments in the mitochondria
Uses water and heat
The ATP created lasts for any activity over 39 seconds and up
Sufficient o2 = pyruvic acid enters mitochondria to generate ATP
Fatty acids and amino acids are also used
Provides 90% of ATP
