Muscle Tissue Flashcards
What are muscle tissues?
Soft tissue specialised for conversion of chemical energy into mechanical energy (specialised for contraction)
What are the functions of skeletal muscle?
- Voluntary movement of skeleton
- Movement of eye/tongue
- Sub-conscious movement to maintain posture and balance
What is the structure (main features) of skeletal muscle?
- Un-branched cylindrical cells (muscle fibres)
- Multiple peripherally located nuclei
- Striated appearance
What is the striated appearance in skeletal muscle caused by?
The arrangement of contractile proteins (myofibrils)
Where is endomysium located in skeletal muscles?
- Around individual muscle fibres
What are fasciculi in skeletal cells?
Groups of muscle fibres that are grouped together
Where is perimysium located in skeletal muscles?
- Around each fasciculi
Where is epimysium locates in skeletal muscles?
- Around entire muscle cell
What spreads through the connective tissues of skeletal muscle?
- Blood vessels and nerves
What is skeletal muscle cell structure highly specialised for?
Contraction/relaxation
What is each myofibril in skeletal muscle separated from each other by?
Sarcoplasm
What is the specialised plasma membrane called in skeletal muscle?
Sarcolemma
What is a myofibril?
Any of the elongated contractile threads found in striated muscle cells
Why are numerous mitochondria found between myofibrils in skeletal muscle?
- As muscle requires a lot of energy to contract
What is the name for the repeating units myofibrils are composed of?
Myofilaments
What are thick myofilaments composed of in skeletal muscle and what colour are they?
- Composed of myosin
- Appear dark in colour
What are thin myofilaments composed of in skeletal muscle and what colour are they?
- Composed of actin
- Appear light in colour
What are the light bands in skeletal muscle bisected by?
Z lines
- Z lines divide each myofibril into contractile units called sarcomeres (functional contractile units of muscle)
What mechanism do sarcomeres contract by?
Sliding filament mechanism
What is the sliding filament mechanism?
- ATP energy allows myosin to bind to actin
- A conformational change causes the filaments to slide over each other causing the sarcomere to shorten (contract)
What innervates skeletal muscle?
Somatic motor neurones
- Individual motor neurones innervate several muscle fibres
What is a ‘motor unit’?
A single motor neurone together with all the muscle fibres it innervates
How are membranous T tubules formed in skeletal muscle?
Sarcolemma invaginates into sarcoplasm
- Continuous with extracellular space
What is sarcoplasmic reticulum?
- Network of tubules associated with T tubules and wrapped around myofibrils
- Ca2+ concentrated with SR (specialised for storage of calcium)
What are the functions of cardiac muscle?
- Only found in the heart
- Specialised for continuous autonomous contractions
- Pump blood through the CVS
What is the structure of cardiac muscle?
- Elongated, branched cylindrical cells
- 1 or 2 centrally located nuclei
- Similar arrangement of contractile proteins as in skeletal muscles causes striated appearance
What are the 3 layers of the heart wall?
- Pericardium
- Myocardium
- Endocardium
What is the pericardium?
- Outer supporting tissue layer
What is the myocardium?
- Cardiac muscle tissue
What is the endocardium?
- Single layer of endothelial cells
What are the specialised intercellular junctions that anchor adjacent cardiac cells together?
Intercalated disks
What are the 5 similarities between skeletal tissue and cardiac tissue?
- Identical arrangement of sarcomeres
- Contain T tubules and sarcoplasmic reticulum
- Numerous mitochondria
- Glycogen and lipid granules
- Contraction by sliding filament mechanism
What are the 5 differences between skeletal muscle and cardiac muscle?
- Cardiac muscles uses autonomous (involuntary contraction) compared to skeletal which is voluntary
- Cardiac muscles SR slowly leaks Ca2+
- Cardiac muscle has intercalated disks
- Modified cardiac muscle cells are known as the conducting system
- Modulated by external autonomic/hormonal stimuli e.g. in times of stress
Is cardiac muscle under voluntary or involuntary control?
involuntary
What controls the rate of heartbeat in heart?
- Sinoatrial node (pacemaker cells)
What is the process of the conducting system of the heart?
- Initiated by SA node
- L and R atria contact
- AV node
- AV bundle (bundle of His)
- Purkinje fibres
- Cardiac muscle fibres
What do modified cardiac muscles consist of?
- Fewer myofibrils
- No T tubules, no intercalated discs
What is the involuntary contraction of cardiac muscle caused by?
- Intrinsic/spontaneous contractile ability
- Pacemaker cells (SA node)
- Slow release of Ca2+ from SR
What is the rate of inherent rhythm in cardiac muscle modulated by?
- Autonomic nervous stimulation
- Hormonal stimulation
What are the functions of smooth muscle?
- Found lining hollow organs
- Specialised for continuous contractions
- Typically to proper lumen contents - peristalsis
What is the structure of smooth muscle?
- Spindle-shaped cells with tapered ends
- Single centrally located nuclei
- No sarcomeres hence no striations
What is peristalsis?
Movement of food through GI tract
What are the 2 layers of smooth muscle in the GIT?
- Inner circular
- Outer longitudinal
What does the inner circular layer of smooth muscle do?
- Constricts lumen diameter
What does he outer longitudinal layer of smooth muscle do?
- Shortens length
What modulates the intensity of peristalsis?
Parasympathetic NS
Does smooth muscle contain sarcomeres?
No
Does smooth muscle contain actin and myosin filaments?
Yes
In what way are actin and myosin arranged in smooth muscle?
- In a criss-cross lattice
What is actin and myosin anchored to cytoplasm and the cell membrane via in smooth muscle?
Focal densities
Explain the relaxed and contracted state of smooth muscle cells?
- In the relaxed state the cell is elongated
- With contraction actin and myosin interact by filament sliding
- Muscle cell becomes shortened and globular
What is contractility in smooth muscle and what is it initiated and modulated by?
- Intrinsic property of smooth muscle
- Initiated by stretch
- Modulated by autonomic nervous system and/or hormonal stimulation
What are peristalsis pacemaker cells called?
Interstitial cells of Cajal
