ANAPHY LESSON 1 MIDTERM Flashcards by Jasmine Tabangcora

=Muscle tissue is categorized into three primary types:

skeletal, cardiac, and smooth

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Skeletal muscles constantly maintain tone, which keeps us sitting or standing erect.

Maintenance of posture

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Contraction of the skeletal muscles of the thoracic cage, as well as the diaphragm, helps us breathe.

Respiration

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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

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Skeletal muscles are involved in all aspects of communication, including speaking, writing, typing, gesturing, and facial expressions.

Communication

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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

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The contraction of cardiac muscle causes the heart to beat, propelling blood to all parts of the body

Contraction of the heart

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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

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four major functional characteristics of muscle tissue:

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.

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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

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Found only in the heart, cardiac muscle is striated and involuntary.

It contracts rhythmically due to a built-in pacemaker (autorhythmicity),.

are branched and interconnected by intercalated discs, allowing synchronized contractions to pump blood effectively.

Cardiac Muscle

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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

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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)

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A strong, flexible covering around muscles

Holds muscles together, lets them move smoothly, and carries blood vessels and nerves.

Fascia

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Three layers of connective tissue extend from the fascia:

Epimysium (“epi-“ = upon)

Perimysium (“peri-“ = around)

Endomysium (“endo-“ = within)

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– covers the whole muscle. Made of dense irregular connective tissue for strength.

Epimysium (“epi-“ = upon)

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surrounds bundles of muscle fibers,

Perimysium (“peri-“ = around) –

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wraps around each individual muscle fiber. Made of reticular fibers, giving extra support.

Endomysium (“endo-“ = within) –

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Levels of Organization of Skeletal Muscle:

Myofilaments (actin & myosin) → Myofibrils → Sarcomeres → Muscle Fiber → Fascicle → Skeletal Muscle

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This organized structure allows skeletal muscle to generate force efficiently for movement

Levels of Organization of Skeletal Muscle

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The smallest structural level in muscle.

Filaments (Myofilaments)

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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.

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These filaments slide past each other to produce movement.

Myosin and Actin, Troponin, and Tropomyosin

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are long, cylindrical structures inside muscle fibers, made of repeating units called sarcomeres.

Myofibrils

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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)

1. The end of the motor neuron that releases neurotransmitters. 2. Contains synaptic vesicles filled with acetylcholine (ACh).

Axon Terminal (Presynaptic Neuron)

1. The small gap (space) between the axon terminal and the muscle fiber. 2. Neurotransmitters must diffuse across this space to bind to receptors.

Synaptic Cleft

1. A specialized region of the muscle fiber's sarcolemma. 2. Contains acetylcholine (ACh) receptors, which are ligand-gated ion channels.

Motor End Plate (Postsynaptic Membrane)

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

_____ Muscle shortens (lifting weights) _____ Muscle lengthens (lowering weights)

Concentric: Muscle shortens (lifting weights) 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

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

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

which is regulated by the autonomic nervous system and hormones

autorhythmicity