1.05 - Muscle Flashcards
What are the three types of muscle?
Skeletal
Smooth
Cardiac
Group the three types of muscles based on voluntary/involuntary action
Involuntary: - Cardiac - Smooth Voluntary: - Skeletal
Group the three muscle types based on presence or absence of striations
Striated: - Skeletal - Cardiac Non-striated: - Smooth
What is the sarcolemma?
The Plasma Membrane of skeletal muscle
What is the Sarcoplasm?
The cytoplasm of skeletal muscle
What is the sarcoplasmic reticulum?
Endoplasmic reticulum of skeletal musce
What is the skeletal muscle belly surrounded by?
Epimysium
What are fascicles and what are they surrounded by?
A fascicle is a bundle of skeletal muscle fibres and is surrounded by perimysium, a type of connective tissue.
What are muscle fibres and what are they surrounded by?
Muscle fibres are the individual muscle cells and are surrounded by endomysium
Each muscle fibre is contractile.
Contains myofibrils which are made up of contractile filaments
What are some distinctive features of skeletal muscle cells?
Extremely elongated
Multinucleated (peripherally located nuclei)
Basic 5 sided structure
What are the two types of Skeletal Muscle?
Type 1: Slow Contraction
Type 2: Fast Contraction
Describe Type 1 Skeletal Muscle
Slow contraction Aerobic, using oxidative phosphorylation Contain many mitochondria Cell contain large amount of myoglobin (O2 storage) - Red in colour Many capillaries
Describe Type 2 Skeletal Muscle
Fast contraction
Anaerobic, using glycolysis
Therefore rich in glycogen
White in colour
Describe the Myofibrils
Muscle fibres contain myofibrils
They are elongated cylindrical structures made up of contractile proteins
Cross striations of striated muscle is due to the ordered arrangement of these proteins
List and describe the bands in the myofibrils
I Band: Light. Made up of thin actin filaments
A Band: Dark. Made up of thick myosin filaments
Z Band = Black. Z-Band to Z-Band outlines the sarcomere, anchor points of the actin filaments, and represents the contractile unit.
Describe the Innervation of Skeletal Muscle
Voluntary Muscles
- Motor innervation
- Sensory innervation: maintain posture, coordinates voluntary movement
- Sympathetic innervation: regulate blood flow via effect on vascular smooth muscle
What is a motor unit?
The combination of a motor neuron and the muscle fibres it supplies.
The nerve and all supplied muscle fibres fire as a unit
Describe the transmission of signals to Skeletal Muscle
Neuron action potential causes release of acetylcholine at the neuromuscular junction. ACh binds to receptor and results in an action potential at the motor end plate –> spread of depolarisation throughout the sarcolemma
Describe the structure of Skeletal muscle as it relates to function
T - Tubules - extensions of the sarcolemma allow depolarisation to enter the cell.
Sarcoplasmic reticulum - modified endoplasmic reticulum releases Ca2+ ions –> this activates contraction of myofibrils
Describe a pathological condition associated with Skeletal Muscle
Duchenne’s Muscular Dystrophy
X-linked recessive
Abnormalities in the gene encoding dystrophin protein. it normally concentrates at the plasma membrane over Z bands where it links to cytoplasmic actin
Describe Smooth Muscle
Not striated Involuntary Autonomic and Hormonal control Visceral structures Enables continual contractions of low force
Describe Smooth Muscle Cells
Spindle shaped
Have a single central oval nucleus
Cells form irregular branching fascicle, which are the functional contractile units
Do not have myofibrils as in skeletal muscle and therefore no striations
But have filaments made of myosin and actin
Instead of Z-Bands what do smooth muscle cells have?
Dense Bodies (focal densities): which act as anchor points in the cytoplasm Attachment junctions: Act as anchor points on the cell membrane
Describe the contraction of Smooth Muscle Cells
During contraction, due to the crisscross arrangement of contractile proteins, the cell shortens and becomes ‘plump’
What are the two types of Smooth Muscle?
Single Unit
Multi-unit
Describe Single Unit Type Smooth Muscle
Smooth muscles cells have extensive communications via gap junctions with adjacent cells so that the cells contract as a single unit
Found in the GIT and uterus
Describe Multiunit Type Smooth Muscle
Each smooth muscle cell acts independently from its neighbour. Thus type of muscle behaves like multiple independent cells or groups of cells. Capable of finer control.
Found in the ciliary muscle of the eye, piloerector muscles of the skin
What is the classification system for Smooth Muscle and what are the subtypes?
By activity pattern:
Phasic
Tonic
Describe Phasic Smooth Muscle
Smooth muscle exhibiting rhythmic or intermittent activity.
Often single unit type
GIT or Urogenital
Describe Tonic Smooth Muscle
Continuously active, maintaining a level of “tone”
Often multiunit type
Blood vessels
Describe a pathological condition that affects smooth muscle
Familial Visceral Myopathy
Common cause of chronic primary intestinal pseudo-obstruction
Segmental dilation of the digestive tract and urinary bladder
Degenerating muscle cells
Smooth muscle fibrosis
Describe the basic features of Cardiac Muscle
Cardiac myocytes have features similar to both skeletal and smooth muscle.
Striated
Involuntary
Strong and continual contractions
Describe the structure of cardiac myocytes
Elongated cells
Central nuclei
Branching fibres with intercalated discs
Contractile proteins arranged similarly to skeletal muscle.
Cross striations
Contractile units: sarcomeres made of myosin and actin but also contain troponin and tropomyosin
T-Tubules and Sarcoplasmic reticulum similar to that of skeletal muscle
What are intercalated discs?
Specialised junctions
Permit rapid spread of contractile stimuli due to areas of low electrical resistance –> fibres contract almost simultaneously
Coincide with Z lines
What are the three types of membrane contact that Intercalated discs are made up of?
Fascia Adherens (site of actin insertion) Desmosomes (anchorage for intermediate filaments) Gap junctions (pores with low electrical resistance, enabling ion and molecule transfer between the cells --> coordinated contraction)
Describe a pathological condition that affects cardiac muscle
Cardiomyopathies Myocardial dysfunction due to disease of myocardial muscle. - Dilated cardiomyopathy - Hyperthrophic cardiomyopathy - Restrictive cardiomyopathy
Compare the location of the three muscle types
Skeletal: skeleton, tongue, eye
Smooth: Vessels, Organs
Cardiac: Heart
Compare the presence of striations in the three muscle types
Skeletal: Yes
Smooth: No
Cardiac: Yes
Compare the features of the nucleus in the three muscle types
Skeletal: Multiple and peripheral
Smooth: Single and central
Cardiac: Single and central
Compare the Cell-To-Cell communication in the three muscle types
Skeletal: None
Smooth: Gap Junctions
Cardiac: Intercalated Discs
Compare the Innervation of the three muscle types
Skeletal: Voluntary
Smooth: Involuntary
Cardiac: Involuntary
