Muscle Tissue Flashcards
Why do we need muscle tissue?
➢ Locomotion – movement of the body
➢ Stability – maintenance of posture
➢ Movement of substances internally (e.g. blood, food)
➢ Heat production
What does muscle tissue do to organs?
- Pull on a body structure
e.g. A skeletal muscle organ can pull 2 bones closer together. - Alter its’ internal volume
e.g. Contraction of cardiac muscle forces blood out of the heart
chambers.
What in muscle cells allow contraction?
Muscle cells contain networks of protein filaments (actin &
myosin) that facilitate the contraction process.
What are the 3 types of muscle tissue in the human body and what are their features?
➢ Skeletal- Striated,
long fibres
➢ Cardiac - Striated,
branched fibres, endomysium attached to the fibrous skeleton of the heart, slow and rhythmic contraction
➢ Smooth - Non-striated,
spindle-shaped long
cells, endomysium, very slow contractions. some are rhythmic
What do these root words mean?
- mus
- myo
- sarco
- plasm
- lemma
- mere
- muscle
- muscle
- flesh
- form or mould
- sheath or husk
- segment
Skeletal muscles functions
- Skeletal muscles integrate with bones &
joints to form lever systems that facilitate
movement.
➢ Move from place to place (locomotion)
➢ Manipulate objects
➢ Communicate & breathe
➢ Maintain body posture
What are skeletal muscle fibres surrounded by?
- Bundles (10-100) of skeletal muscle fibres are wrapped by
connective tissue & are called fascicles
Structure of skeletal muscle cells
Skeletal muscle cells (fibres) are;
➢ Long cylinders (up to 30cm long)
➢ Striated (striped)
➢ Multinucleated (100+ nuclei in one fibre)
A skeletal muscle fibre contains these structures;
➢ Sarcolemma - muscle fibre plasma membrane
➢ Sarcoplasm - muscle fibre cytoplasm
➢ Myofibrils – long rod-like structures that contain contractile
proteins (make up ~80% cell volume).
Skeletal muscle tissue structure
Muscle fibres posses many myofibrils which contain contractile
units (sarcomeres) which generate movement.
What are myofibrils?
Myofibrils contain repeating contractile units called
sarcomeres which facilitate muscle movement
What are sarcomeres?
➢ Contain interlocking actin (thin) & myosin (thick) filament
proteins.
➢ Contract when a stimulated by a signal from a neurone
(somatic motor).
Thick Myosin filaments
Made up of 200 to 500 myosin molecules. ➢ Attached to the M line in a sarcomere Each myosin molecule consists of rod-like tail terminating at 2 globular heads. ➢ Heads contain sites that bind to actin
Thin Actin Filaments
Fibrous (F) actin filaments are composed of globular (G) actin
subunits
➢ Stiffened by tropomyosin protein strand
➢ Actin filaments are attached to the Z disc in a sarcomere
Myosin heads bind to G actin subunits
➢ Troponin is a molecule attached to tropomyosin that helps
regulate the myosin – actin binding
Sarcomere Contraction
When a skeletal muscle cell is stimulated, actin
filaments in the sarcomere slide over myosin filaments.
The sarcomeres shorten & the muscle contracts.
What tissues do skeletal muscles contain?
- Connective tissue
Layers of connective tissue wrap & reinforce muscle fibres - Nerve cells (neurones)
Supply signals that stimulate muscle cells to contract - Epithelial tissue
Lines inner surface of blood vessels
What are the connective tissue layers?
epimysium, perimysium
& endomysium.
Features of connective tissue layers
➢ are continuous with one another
➢ provide structural reinforcement for the muscle
➢ provide access for nerves & blood vessels
Explain the 4 connective tissue layers
- Deep Fascia: Lines the body wall & separates muscles into
functional groups. - Epimysium: Surrounds an individual muscle organ & blend
with tendons or deep fascia. - Perimysium: Bundles together 10 - 100 individual muscle
fibres into structures called fascicles. - Endomysium: The connective tissue wrapping of an individual
muscle fibre
Where is the primary motor cortex located?
Posterior aspect of the frontal lobe
Motor neurons cross over in which parts of the body
➢ Medulla, or
➢ Spinal cord.
What is a motor unit?
A neurone and all the muscle fibres it innervates
What are fascicles?
Bundles of 10-100 skeletal muscle fibres wrapped by connective tissues
What are the components of a skeletal muscle fibre model?
- Myofibril
- Sarcomere
- Motor end plate
- Motor Neurone
- Synaptic Knob
- Schwann cell
- Node of Ranvier
- Nucleus
- Sarcoplasmic reticulum
- Sarcolemma
- Endomysium
What is Motor Homunculus?
Different regions of the motor cortex control muscle contraction in specific areas of the body
What is contralateral control?
Motor cortex controls skeletal muscle contraction on the opposite side of the body
How do neurons communicate with muscle fibres?
At neuromuscular junctions
- a small gap separates the 2 cells (synaptic cleft)
How many skeletal muscles are in the body?
600
Major Anatomical features of Skeletal Muscles
Origin: Attachment points of muscle to a location which does not move during muscle contraction
Belly: Thicker, middle region of muscle
Insertion: Attachment points of muscle to a location which will be moved by contraction of muscle
How does skeletal muscles attach to the body?
Via a tendon or tendon sheet (aponeurosis)
Criteria of naming muscles (7)
- Direction of muscle fibres
- Relative size of muscle
- Location
- Number of origins
- Location of origin and insertion
- Shape
- Action
What is a movement initiated by a muscle called and how does it do it?
Action, it is done by the muscles pulling on a bone
Antagonists
Oppose of reverse a particular movement
What is a tendon?
▪ Mostly collagen fibers
▪ Often cross a joint because of their toughness and
small size
What is aponeuroses
Attach muscles indirectly to bones, cartilages, or
connective tissue coverings
Skeletal muscle fibre types
▪ Slow-twitch (type I) fibres
▪ Fast-twitch (type II) fibres
▪ Type IIa fibres
▪ Type IIb fibres
2 components of the smooth muscles
Mucosa, Submucosa
Types of muscle contraction
- Isotonic Contractions
Myofilaments are able to slide past each other during contractions ▪ The muscle shortens, and movement occurs ▪ Example: bending the knee; lifting weights, smiling - Isometric Contraction
▪ Muscle filaments are trying to slide, but the muscle is pitted against an immovable object ▪ Tension increases, but muscles do not shorten ▪ Example: pushing your palms together in front of you
I band
light band ▪ Contains only thin filaments ▪ Z disc is a midline interruption
A band
dark band ▪ Contains the entire length of the thick filaments ▪ H zone is a lighter central area ▪ M line is in center of H zone
What is a neuromuscular junction?
Association site of axon terminal of the motor neuron
and sarcolemma of a muscle
Neurotransmitter
Chemical released by nerve upon arrival of nerve
impulse in the axon terminal
Synaptic cleft
Gap between nerve and muscle filled with interstitial fluid
▪ Although very close, the nerve and muscle do not make contact
Events at the neuromuscular junction
CHECK PIC - 6 steps
What leaves the muscle fibre and what enters the muscle fibre during contraction?
Potassium ions leave the fibre, sodium ions enters through permeable synaptic cleft created by Ach
Why do filaments slide (steps)?
▪ Calcium ions (Ca2+ ) bind regulatory proteins on thin filaments and expose myosin-binding sites, allowing the myosin heads on the thick filaments to attach
▪ Each cross bridge pivots, causing the thin filaments to slide toward the center of the sarcomere
▪ Contraction occurs, and the cell shortens
▪ During a contraction, a cross bridge attaches and detaches several times
▪ ATP provides the energy for the sliding process, which continues as long as calcium ions are present
Cross bridge cycle
- Cross bridge formation. The activated myosin head binds to actin forming a cross bridge. Inorganic phosphate is released. Bond between myosin and actin becomes stronger
- Power stroke. ADP is released and the activated myosin head pivots, sliding the thin myofilament toward the centre of the sarcomere
- Cross bridge detachment: When another ATP binds to the myosin head, the link between myosin head and actin weakens and the myosin head detaches
Functional properties of skeletal muscle cells
▪ Extensibility—ability of muscle cells to be stretched
▪ Elasticity—ability to recoil and resume resting length after stretching
▪ Irritability (also called responsiveness)—ability to receive and respond to a stimulus
▪ Contractility—ability to forcibly shorten when an adequate stimulus is received
Three pathways to regenerate ATP
▪ Three pathways to regenerate ATP
- Direct phosphorylation of ADP by creating phosphate
- Aerobic pathway
- Anaerobic glycolysis and lactic acid formation
What is flexion and extension?
Flexion - Decreases angle in joint, common in hinge and ball and socket joins
Extension - Increases angle between two bones
Greater than 180 degrees is called hyper extension
Rotation
▪ Movement of a bone around its longitudinal axis
▪ Common in ball-and-socket joints
What is Dorsiflexion?
▪ Lifting the foot so that the superior surface approaches the shin (toward the dorsum)
What is Plantar Flexion?
Pointing the toes away from the head
What is inversion and eversion?
Inversion
▪ Turning sole of foot medially
Eversion
▪ Turning sole of foot laterally
What is Supination and Pronation?
Supination
▪ Forearm rotates laterally so palm faces anteriorly
▪ Radius and ulna are parallel
Pronation
▪ Forearm rotates medially so palm faces posteriorly
▪ Radius and ulna cross each other like an X
Opposition
▪ Moving the thumb to touch the tips of other fingers on
the same hand
What are the three things can happen when muscles have tension?
- Shorten
- Stay the same
- Lengthen
Agonist
muscle with the major responsibility for
a certain movement
What is a synergist?
muscle that aids a prime mover in a
movement or reduces undesirable movements
What is a fixator?
specialized synergists that hold a bone
still or stabilize the origin of a prime mover
Fascicle Arrangement (4)
Circular
Convergent
Parallel
Pennate
What is a pennate muscle and types?
one or more tendons extending through body. Large feather like oblique angled arrangements of fascicles. 3 types (Multipenate, bipennate and unipennate)
What is a graded response?
▪ Muscle fiber contraction is “all-or-none,” meaning it will
contract to its fullest when stimulated adequately
▪ Within a whole skeletal muscle, not all fibers may be
stimulated during the same interval
▪ Different combinations of muscle fiber contractions
may give differing responses
▪ Graded responses—different degrees of skeletal
muscle shortening
How can graded response be produced?
By changing the frequency of muscle stimulation
By changing the number of muscle cells being
stimulated at one time
Muscle response to increasingly rapid stimulation
▪ Muscle twitch
▪ Single, brief, jerky contraction
▪ Not a normal muscle function
▪ In most types of muscle activity, nerve impulses are
delivered at a rapid rate
▪ As a result, contractions are “summed” (added)
together, and one contraction is immediately followed
by another
▪ When stimulations become more frequent, muscle
contractions get stronger and smoother
▪ Fused (complete) tetanus is achieved when the
muscle is stimulated so rapidly that no evidence of
relaxation is seen
▪ Contractions are smooth and sustained
Muscle response to strong stimuli
▪ Muscle force depends upon the number of fibers
stimulated
▪ Contraction of more fibers results in greater muscle
tension
▪ When all motor units are active and stimulated, the
muscle contraction is as strong as it can get
