Anatomy of the Muscular System Chapter 2

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Questions and Answers

What is the characteristic shape of fusiform muscles?

Spindle-shaped with an expanded belly (correct)

Long and narrow

Short and thick

Straplike

Which type of muscle arrangement has fascicles inserting into only one side of a central tendon?

Bipennate

Multipennate

Unipennate (correct)

Circular

Which muscle is primarily responsible for closing the mouth and protruding the lips?

Zygomaticus

Frontalis

Masseter

Orbicularis oris (correct)

What action is facilitated by the temporalis muscle?

Closing the jaw Signup and view all the answers

Which muscle is referred to as the 'smiling' muscle?

Zygomaticus Signup and view all the answers

What is a common feature of pennate muscles?

Fascicles attach obliquely to a central tendon Signup and view all the answers

Which of the following facial muscles allows the movement of the eyebrows?

Frontalis Signup and view all the answers

Which facial muscle is often linked with the ability to squint and blink?

Orbicularis oculi Signup and view all the answers

What is the primary purpose of the heat generated by muscle activity?

To maintain normal body temperature Signup and view all the answers

What are myofibrils primarily composed of?

Chains of sarcomeres Signup and view all the answers

Which protein forms the thick filaments in muscle cells?

Myosin Signup and view all the answers

What is the function of the sarcoplasmic reticulum in muscle fibers?

To store and release calcium Signup and view all the answers

What are the thin filaments primarily composed of?

Actin and regulatory proteins Signup and view all the answers

What structure in muscle cells is analogous to a sleeve surrounding an arm?

Sarcoplasmic reticulum Signup and view all the answers

What do cross bridges link together during muscle contraction?

Thin and thick filaments Signup and view all the answers

Which of the following describes the appearance of muscle cells due to the organization of myofibrils?

Striped or striated appearance Signup and view all the answers

What function do the fibularis muscles primarily perform?

Plantar flexion and eversion of the foot Signup and view all the answers

Which muscle is known as a prime mover for plantar flexion of the foot?

Gastrocnemius Signup and view all the answers

What occurs when acetylcholine is released at the neuromuscular junction?

The sarcolemma becomes more permeable to sodium ions Signup and view all the answers

How is the action potential described in the context of muscle contraction?

An unstoppable electrical current that triggers contraction Signup and view all the answers

What is the role of enzymes in muscle contraction?

They break down acetylcholine to terminate contraction Signup and view all the answers

What initiates the contraction of skeletal muscle cells?

Nerve impulse stimulation Signup and view all the answers

What is a key structural feature of the soleus muscle?

It originates from the tibia and fibula Signup and view all the answers

What occurs to the muscle cell after a contraction is initiated?

It relaxes after the enzyme breaks down acetylcholine Signup and view all the answers

What is the primary role of the prime mover in muscle action?

To cause a particular movement Signup and view all the answers

Which muscle type serves to oppose or reverse a movement?

Antagonists Signup and view all the answers

The term 'rectus' in a muscle's name indicates what about its fiber arrangement?

Fibers run parallel to an imaginary line Signup and view all the answers

What do fixators do in the context of muscle action?

Stabilize the origin of a prime mover Signup and view all the answers

What underlying principle defines the arrangement of circular muscles?

Fascicles are arranged in circular patterns Signup and view all the answers

When a muscle's name contains 'biceps,' what can be inferred about its structure?

It has two origins Signup and view all the answers

Which of the following describes the features of convergent muscles?

They converge towards a single insertion tendon Signup and view all the answers

Which term is used to describe muscles that help prime movers by reducing undesirable movements?

Synergists Signup and view all the answers

What is the primary function of the gluteus maximus muscle?

Hip extension Signup and view all the answers

Which muscle is involved in stabilizing the pelvis during walking?

Gluteus medius Signup and view all the answers

Which group of muscles is known for adducting the thighs?

Adductor muscles Signup and view all the answers

What is the main action of the iliopsoas muscle?

Hip flexion Signup and view all the answers

Which muscles are part of the hamstring group?

Biceps femoris, semimembranosus, semitendinosus Signup and view all the answers

Which muscle is primarily responsible for extending the knee?

Quadriceps group Signup and view all the answers

What is the action of the tibialis anterior muscle?

Dorsiflexion of the foot Signup and view all the answers

Which muscle is a prime mover for toe extension?

Extensor digitorum longus Signup and view all the answers

Study Notes

Muscle Functions and Heat Generation

Muscle activity generates body heat as a by-product of ATP usage, with nearly three-quarters of energy escaping as heat, crucial for maintaining normal body temperature.

Microscopic Anatomy of Skeletal Muscle

Skeletal muscle cells are multinucleate, with oval nuclei located just beneath the sarcolemma (plasma membrane).
Myofibrils are long, ribbon-like organelles nearly filling the cytoplasm, giving muscle cells a striated appearance due to alternating light and dark bands.
Myofibrils are composed of sarcomeres, the tiny contractile units aligned end to end.
Two types of myofilaments exist: thick (myosin) and thin (actin), enabling muscle contraction through the interaction of their components.
Thick filaments contain ATPase enzymes for ATP splitting, facilitating muscle contraction via cross bridges that link thick and thin filaments.
Thin filaments consist of actin and regulatory proteins, anchored to the Z disc, allowing for muscle contraction regulation.
The sarcoplasmic reticulum is a specialized organelle storing and releasing calcium, essential for muscle contraction.

Muscle Movements and Types

Muscles exhibit a variety of movements categorized by roles:
- Prime movers initiate a movement.
- Antagonists oppose the movement, remaining relaxed when prime movers contract.
- Synergists assist prime movers, enhancing or stabilizing movements.
- Fixators stabilize bones or origins for efficient movement execution.

Naming Skeletal Muscles

Muscle names detail aspects such as:
- Direction of fibers (rectus = straight, oblique = slanted).
- Relative size (maximus = largest, minimus = smallest, longus = long).
- Location (temporal and frontal muscles named after nearby bones).
- Number of origins (biceps, triceps, quadriceps indicating two, three, four origins, respectively).
- Shape and action of the muscle contribute to naming conventions.

Fascicle Arrangement in Skeletal Muscles

Fascicle arrangements influence muscle structure and function:
- Circular: arranged in concentric rings; common in muscles surrounding openings.
- Convergent: fascicles converge toward a single tendon; typically triangular or fan-shaped.
- Parallel: fascicles run parallel to muscle's long axis; fusiform muscles are a subtype.
- Pennate: short fascicles attach obliquely to a central tendon; categorized as unipennate, bipennate, or multipennate based on attachment.

Head and Neck Muscles

Facial muscles are grouped as either facial or chewing muscles:
- Five primary facial muscles include frontalis, orbicularis oculi, orbicularis oris, buccinator, and zygomaticus, each with distinct functions ranging from raising eyebrows to facilitating smiling.

Chewing Muscles

The masseter and temporalis are significant chewing muscles responsible for jaw movement; the masseter closes the jaw, while the temporalis aids in jaw elevation.

Muscles at the Hip Joint

Gluteus maximus serves as a powerful hip extensor; gluteus medius stabilizes the pelvis; iliopsoas is the primary hip flexor; adductor muscles facilitate thigh adduction.

Movement at the Knee Joint

The hamstring group (biceps femoris, semimembranosus, semitendinosus) flexes the knee, while the quadriceps group (rectus femoris, vastus muscles) is crucial for knee extension.

Movement at the Ankle and Foot

Key muscles for ankle and foot movement include:
- Tibialis anterior: dorsiflexion and extension of toes.
- Extensor digitorum longus: toe extension and foot dorsiflexion.
- Fibularis muscles: plantar flexion and foot eversion.
- Gastrocnemius: prime mover for plantar flexion; soleus lies beneath, aiding in foot movement without affecting the knee.

Nerve Stimulus and Action Potential

Skeletal muscle contraction is initiated by nerve impulses, releasing acetylcholine (ACh) at axon terminals.
Increased permeability of the sarcolemma to sodium ions generates an action potential, leading to muscle contraction.
Acetylcholine is broken down post-contraction, preventing continuous stimulation of the muscle fiber.

Mechanism of Muscle Contraction

Myosin heads attach to thin filament binding sites upon nervous system activation, initiating the sliding mechanism for muscle contraction.

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Description

This quiz explores Chapter 2 of the Anatomy of the Muscular System, focusing on the functions of muscles, including their role in heat generation and body temperature regulation. It also delves into the microscopic anatomy of skeletal muscle from Chapter 3, examining cellular structures like sarcolemma and nuclei.