ANAPHY LESSON 1 MIDTERM Flashcards
Muscle tissue is categorized into three primary types:
skeletal, cardiac, and smooth
Contraction of skeletal muscles is responsible for the overall movements of the body, such as walking, running, and manipulating objects with the hands.
Movement of the body
Skeletal muscles constantly maintain tone, which keeps us sitting or standing erect.
Maintenance of posture
Contraction of the skeletal muscles of the thoracic cage, as well as the diaphragm, helps us breathe.
Respiration
When skeletal muscles contract, heat is given off as a by-product. This released heat is critical to the maintenance of body temperature.
Production of body heat
Skeletal muscles are involved in all aspects of communication, including speaking, writing, typing, gesturing, and facial expressions.
Communication
The contraction of smooth muscle within the walls of internal organs and vessels causes those structures to constrict.
This constriction can help propel and mix food and water in the digestive tract, propel secretions from organs, and regulate blood flow through vessels.
Constriction of organs and vessels
The contraction of cardiac muscle causes the heart to beat, propelling blood to all parts of the body
Contraction of the heart
refer to the specialized properties that allow a muscle to perform its specific roles in the body.
These characteristics define how muscles respond, contract, stretch, and return to their original shape, enabling movement, force generation, and other essential functions.
Functional characteristics of muscle tissue
four major functional characteristics:
- Contractility – The ability to shorten forcefully.
- Excitability – The ability to respond to stimuli.
- Extensibility – The ability to stretch beyond resting length.
- Elasticity – The ability to return to original shape after stretching.
attached to bones and is responsible for voluntary movements.
It is striated due to the organized arrangement of actin and myosin filaments in sarcomeres.
Skeletal Muscle
Found only in the heart, cardiac muscle is striated and involuntary.
It contracts rhythmically due to a built-in pacemaker (autorhythmicity), which is regulated by the autonomic nervous system and hormones.
are branched and interconnected by intercalated discs, allowing synchronized contractions to pump blood effectively.
Cardiac Muscle
found in the walls of hollow organs such as blood vessels, the gastrointestinal tract, and airways.
It is non-striated and involuntary, controlled by the autonomic nervous system and hormones.
Smooth Muscle
Found under the skin, made of fat and loose connective tissue.
Keeps muscles warm, stores energy (fat), and protects from injury.
Carries nerves and blood vessels to muscles.
Subcutaneous Layer (Hypodermis)
A strong, flexible covering around muscles
Holds muscles together, lets them move smoothly, and carries blood vessels and nerves.
Fascia
Three layers of connective tissue extend from the fascia:
Epimysium (“epi-“ = upon)
Perimysium (“peri-“ = around)
Endomysium (“endo-“ = within)
– covers the whole muscle. Made of dense irregular connective tissue for strength.
Epimysium (“epi-“ = upon)
surrounds bundles of muscle fibers, called fascicles. Fascicles give meat its grainy texture—when you tear meat, it splits along these bundles.
Perimysium (“peri-“ = around) –
wraps around each individual muscle fiber. Made of reticular fibers, giving extra support.
Endomysium (“endo-“ = within) –
Levels of Organization of Skeletal Muscle:
Myofilaments (actin & myosin) → Myofibrils → Sarcomeres → Muscle Fiber → Fascicle → Skeletal Muscle
This organized structure allows skeletal muscle to generate force efficiently for movement
Levels of Organization of Skeletal Muscle
The smallest structural level in muscle.
Filaments (Myofilaments)
Two main types of Filaments (Myofilaments) [Two contractile proteins]:
Thick Filaments (Myosin) – Responsible for muscle contraction by pulling on thin filaments.
Thin Filaments (Actin, Troponin, and Tropomyosin) – Actin is the main protein that interacts with myosin to cause contraction.
These filaments slide past each other to produce movement.
Myosin and Actin, Troponin, and Tropomyosin
are long, cylindrical structures inside muscle fibers, made of repeating units called sarcomeres.
Myofibrils
are the functional units of contraction, containing thick and thin filaments arranged in a pattern that creates the striated (striped) appearance of skeletal muscle.
Sarcomeres
Made of myosin proteins, which have heads that bind to actin.
Responsible for pulling thin filaments to generate contraction.
Thick Filaments (Myosin)
The main protein that myosin binds to during contraction.
Actin
Blocks myosin-binding sites on actin when muscle is relaxed.
Tropomyosin
A regulatory protein that controls tropomyosin movement
Troponin
Troponin has three subunits
Troponin c (TnC)- binds calcium that moves tropomyosin
Troponin I (TnI)- inhibitory subunit
Tropnin T (TnT)- binds to tropomyosin
the plasma membrane of a muscle fiber
regulates and exit
Sarcolemma
cytoplasm of a muscle fiber
contains glycogen for energy
sarcoplasm
long,cylindrical protein structure
confains sarcomere
myofibrils
basic contractile unit
shortens during contraction
sarcomere
a specialized endoplasmic reticulum
stores and releases calcium
sarcoplasmic reticulum (SR)
extension of sarcolemma
helps spread action potentials
transverse tubules (T-tubules)
found in large numbers
produce ATP for muscle
Mitochondria
multiple nuclei per muscle
controls protein synthesis
Nuclei
one t-tubules and wo terminal cisternae
ensure quick calcium
triad
organizing muscle fibers into functional groups for strength and coordination.
fascicle
Types of Skeletal Muscle Fibers
slow oxidative (SO)
fast oxidative glycolytic (FOG)
Fast glycolitic (FG)
SO → FOG → FG (from least to most powerful)
which binds to receptors on the motor end plate of the muscle fiber.
acetylcholine (ACh),
Step-by-Step Process of Muscle Contraction:
Signal Transmission at the Neuromuscular Junction
Excitation-Contraction Coupling
The Contraction Cycle (Sliding Filament Theory)
Muscle Relaxation
This binding opens ligand-gated sodium (Na⁺) channels, allowing Na⁺ to enter the muscle cell, generating a muscle action potential
The action potential spreads along the sarcolemma and down the T-tubules.
Signal Transmission at the Neuromuscular Junction
is the synapse between a motor neuron and a skeletal muscle fiber.
neuromuscular junction (NMJ)
3 Structure of the NMJ:
Axon Terminal (Presynaptic Neuron)
Synaptic Cleft
Motor End Plate (Postsynaptic Membrane)
- The end of the motor neuron that releases neurotransmitters.
- Contains synaptic vesicles filled with acetylcholine (ACh).
Axon Terminal (Presynaptic Neuron)
- The small gap (space) between the axon terminal and the muscle fiber.
- Neurotransmitters must diffuse across this space to bind to receptors.
Synaptic Cleft
- A specialized region of the muscle fiber’s sarcolemma.
- Contains acetylcholine (ACh) receptors, which are ligand-gated ion channels.
Motor End Plate (Postsynaptic Membrane)
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The action potential triggers voltage-gated calcium (Ca²⁺) channels in the T-tubules.
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These channels open the Ca²⁺ release channels in the sarcoplasmic reticulum (SR).
Ca²⁺ is released into the sarcoplasm, increasing the intracellular Ca²⁺ concentration
This shifts tropomyosin, exposing the myosin-binding sites on actin filaments.
Excitation-Contraction Coupling*
This cycle continues as long as Ca²⁺ levels remain elevated and ATP is available.
The Contraction Cycle (Sliding Filament Theory)
Myosin heads contain ATPase, which hydrolyzes ATP into ADP and Pi
This hydrolysis energizes the myosin head, putting it in a cocked position
Step 1: ATP Hydrolysis
The energized myosin head binds to the exposed myosin-binding site on actin, forming a cross-bridge
Step 2: Cross-Bridge Formation
The myosin head pivots from a 90° angle to a 45° angle.
This pulls the thin filament (actin) toward the M-line, shortening the sarcomere.
Step 3: Power Stroke
A new ATP molecule binds to the myosin head, causing it to release from actin.
Step 4: Detachment of Myosin from Actin
When nerve signals stop, no more ACh is released.
Cross-bridge formation stops, and the muscle relaxes.
Muscle Relaxation
breaks down ACh in the synaptic cleft, stopping action potentials.
Acetylcholinesterase (AChE)
different types of contractions.
Isotonic (Muscle Changes Length)
Isometric (No Length Change) –
A motor neuron + the muscle fibers it controls
Motor Unit
Activating more motor units for stronger contraction
Recruitment:
Single contraction from one nerve impulse
Twitch Contraction
Concentric: Muscle shortens (lifting weights)
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Eccentric: Muscle lengthens (lowering weights)
Concentric: Muscle shortens (lifting weights)
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Eccentric: Muscle lengthens (lowering weights)
is found only in the heart and is responsible for pumping blood throughout the body
Cardiac muscle tissue
It has unique structural and functional characteristics that allow it to contract continuously and rhythmically without fatigue.
Cardiac muscle tissue
Contracts involuntarily through autorhythmic fibers (without nervous system input).
Cardiac muscle tissue
Maintains synchronized contraction to ensure efficient blood flow.
Cardiac muscle tissue
Autorhythmic fibers generate action potentials in the Sinoatrial (SA) Node
Electrical Signal Generation:
The signal spreads through gap junctions in intercalated discs, ensuring synchronized contraction
Signal Transmission
Ca²⁺ enters the sarcoplasm, binding to troponin, exposing myosin-binding sites on actin.
Calcium Release
Myosin heads pull actin filaments, shortening the muscle fibers, creating a heartbeat.
Muscle Contraction
Calcium is reabsorbed, and the cycle repeats for the next heartbeat.
Relaxation & Repeat
is an involuntary, non-striated muscle found in the walls
it contracts slowly and rhythmically
Smooth muscle tissue
2 types of muscle tissue 6y
visceral (single unit)
multi unit
connected by gap junction and produces slow,rhythmic contraction
visceral (single unit)
no gap junctions
multi unit
Calcium enters from extracellular fluid via caveolae or is released from the SR.
Ca²⁺ Entry
Ca²⁺ binds to calmodulin, forming a complex
Calmodulin Activation
The Ca²⁺-calmodulin complex activates myosin light-chain kinase (MLCK).
MLCK Activation:
MLCK phosphorylates myosin light chains, enabling myosin to bind to actin.
Phosphorylation of Myosin:
smooth muscle contracts through the sliding filament mechanism.
Cross-Bridge Cycling: \
When Ca²⁺ levels drop, myosin phosphatase deactivates myosin, leading to relaxation.
Relaxation
Muscle tissue originates from the ____, except for muscles like the iris of the eye and arrector pili muscles
mesoderm
Around day 20 of embryonic development, the mesoderm forms columns on both sides
These columns segment into somites, with 42–44 pairs forming by the fifth week.
The number of somites can estimate embryonic age.
Formation of Somites
In healthy muscle, satellite cells remain quiescent (inactive). After muscle damage (e.g., injury, exercise, disease), satellite cells are activated by signals such as growth factors and cytokines.
Activation (After Muscle Injury)
Activated satellite cells divide and increase in number to support muscle repair. Some of these new cells differentiate into myoblasts (immature muscle cells).
Proliferation
forms skeletal muscle of the head, neck, and limbs
myotome
develops into connective tissue and dermis of the skin
dermatome
gives rise to the vertabrae
sclerotome
Myoblasts fuse with the damaged muscle fibers, repairing and strengthening them. If damage is severe, myoblasts can fuse with each other to form new muscle fibers.
Fusion and Muscle Fiber Repair
Some satellite cells return to a quiescent state, ensuring a reserve pool for future muscle repair.
Self-Renewal
