Muscular System: Types, Structure, and Function Review

What are the three types of muscle tissue?

Skeletal muscle, smooth muscle, and cardiac muscle.

Where is skeletal muscle located?

Attached to bones.

What is the primary function of cardiac muscle?

To pump blood through the heart.

What is the appearance of skeletal muscle?

Striated (has stripes).

What is the function of intercalated disks in cardiac muscle?

They facilitate communication between cardiac muscle cells.

What is the sarcoplasmic reticulum?

A specialized form of smooth endoplasmic reticulum in muscle cells that stores calcium.

What is the role of calcium in muscle contraction?

Calcium binds to troponin, exposing active sites on actin myofilaments.

What is a sarcomere?

The basic contractile unit of muscle tissue.

What are the components of a sarcomere?

Z disk, M line, H zone, A band, and I band.

What triggers the power stroke in muscle contraction?

The binding of myosin heads to active sites on actin.

What is the neuromuscular junction?

The synapse between a motor neuron and a muscle fiber.

What neurotransmitter is released at the neuromuscular junction?

Acetylcholine (ACh).

What is the resting membrane potential?

The voltage difference across a cell membrane when the cell is not actively sending signals.

What is the all-or-none principle in action potentials?

An action potential either occurs fully or not at all, similar to a camera flash.

What is the function of the sodium-potassium pump?

To maintain the resting membrane potential by moving sodium out and potassium into the cell.

What happens when an action potential reaches the presynaptic terminal?

Voltage-gated Ca2+ channels open, allowing calcium ions to enter.

What occurs after acetylcholine binds to receptors on the postsynaptic membrane?

Ligand-gated Na+ channels open, allowing sodium to enter and depolarize the membrane.

What is the role of the Na+/K+ pump in action potential?

It restores the resting membrane potential after an action potential has occurred.

What is the significance of the threshold in action potentials?

It is the level of depolarization needed to trigger an action potential.

What is the difference between voltage-gated and ligand-gated ion channels?

Voltage-gated channels open in response to voltage changes, while ligand-gated channels open when a specific molecule binds to them.

What happens to acetylcholine after it binds to its receptor?

It unbinds, causing ligand-gated Na+ channels to close.

What enzyme removes acetylcholine from the synaptic cleft?

Acetylcholinesterase

What does acetylcholinesterase break acetylcholine down into?

Acetic acid and choline

How is choline recycled in the presynaptic terminal?

Choline is symported with Na+ into the presynaptic terminal.

What is the role of synaptic vesicles?

They contain neurotransmitters that are released from the presynaptic membrane.

What is acetylcholine's primary function in muscles?

To transmit messages that result in muscular contraction.

What happens during action potential propagation?

An action potential in one area causes another action potential to be produced in the adjacent plasma membrane.

What is a motor unit?

A single motor neuron and all muscle fibers innervated by it.

What are the two types of muscle contractions?

Isometric (no change in length) and isotonic (change in length).

What characterizes slow-twitch muscle fibers?

They contract slowly, are smaller in diameter, have better blood supply, more mitochondria, and are more fatigue-resistant.

What are fast-twitch muscle fibers known for?

They respond rapidly to stimulation, have less blood supply and fewer mitochondria, and are less fatigue-resistant.

What is hypertrophy in muscle fibers?

An increase in muscle size due to an increase in myofibrils and nuclei.

What occurs during muscle atrophy?

A decrease in muscle size, reversing the effects of hypertrophy.

What are the three major ATP-dependent enzymes in skeletal muscle fibers?

The myosin head, the Na+-K+ pump, and the Ca2+ reuptake pump in the sarcoplasmic reticulum.

How long can stored ATP sustain muscle contraction?

For 5-6 seconds.

What is the primary energy source for muscle contraction?

ATP, produced through anaerobic and aerobic processes.

What is the difference between anaerobic and aerobic ATP production?

Anaerobic produces 2 ATP per glucose, while aerobic produces 36 ATP per glucose.

What is the role of the diaphragm in respiration?

It flattens during contraction to increase the volume of the thoracic cavity, resulting in inspiration.

Which muscles elevate the ribs during expiration?

Internal intercostals and transversus thoracis.

What is the function of the external intercostals?

To elevate the ribs during inspiration.

What is the effect of exercise on muscle fibers?

It causes hypertrophy, increasing muscle size and strength.

What is the role of the scalene muscles in respiration?

To elevate the first two ribs during inspiration.

What is the primary action of the serratus anterior muscle?

Elevates the scapula.

Which vertebrae are associated with the muscles of respiration?

Third cervical vertebra and first thoracic vertebra.

What are the main muscles involved in respiration?

External intercostals, internal intercostals, transversus thoracis, and diaphragm.

What is the origin and insertion of the rectus abdominus?

Origin: Pubic bone; Insertion: Lower ribs and xiphoid process of sternum.

What is the action of the rectus abdominus?

Flexes the trunk.

Which nerve innervates the rectus abdominus?

Intercostal nerve.

What muscles stabilize and move the scapula?

Levator scapulae, trapezius, rhomboideus major & minor, serratus anterior, and pectoralis minor.

What are the key upper arm muscles that attach the arm to the thorax?

Pectoralis major and latissimus dorsi.

What are the functions of the deltoid muscle?

Flexes, extends, abducts, and medially/laterally rotates the shoulder.

What are the four rotator cuff muscles?

Supraspinatus, infraspinatus, teres minor, and subscapularis.

What is the primary action of the iliopsoas muscle?

Flexes the hip.

What is the innervation of the iliopsoas muscle?

Femoral nerve.

What are the compartments of thigh muscles and their functions?

Anterior compartment: flex hip/extend knee; medial compartment: adduct thigh; posterior compartment: extend hip/flex knee.

What is the action of the quadriceps femoris?

Extension of the leg at the knee and flexion of the hip (rectus femoris).

What is the innervation of the quadriceps group?

Femoral nerve.

What is the action of the hamstrings?

Flexion and rotation of the knee.

What are the muscles included in the hamstrings?

Biceps femoris, semimembranosus, and semitendinosus.

What is the origin and action of the gastrocnemius?

Origin: Medial and lateral femoral condyles; Action: Plantar flexion.

What is the innervation of the gastrocnemius?

Tibial nerve.

What is the action of the tibialis anterior?

Dorsiflexion of the foot.

What is the innervation of the tibialis anterior?

Fibular nerve.

What is the Achilles tendon also known as?

Calcaneal tendon.

What are the actions of the muscles on the anterior surface of the forearm?

Flexion of the wrist and abduction/adduction of the wrist.

What are the actions of the muscles on the posterior surface of the forearm?

Extension and abduction of the wrist.

What are retinacula in the context of forearm muscles?

Bands of deep fascia that hold tendons, blood vessels, and nerves close to the wrist.