Muscular System Notes

Clinical Terms

• Review chapter 9 and 10 clinical terms, memorize for the quiz.

Physiology of Muscular Tissue

• Three types: Skeletal, cardiac, and smooth.

Skeletal Muscle Tissue

• Packed into skeletal muscles attached to and covering the skeleton.
• Longest muscle cells, have obvious stripes called striations.
• Activated by reflexes, considered voluntary muscle (subject to conscious control).
• Keywords: skeletal, striated, and voluntary.
• Primary function: Overall body mobility.
• Can contract rapidly but tires easily; needs rest after short activity.
• Can exert tremendous power and is adaptable.
• Example: Forearm muscles exerting small or large forces as needed.

Cardiac Muscle Tissue

• Occurs only in the heart; constitutes bulk of heart walls.
• Striated like skeletal muscle.
• Involuntary; contracts without nervous system stimulation.
• Most people have no conscious control over heart rate.
• Keywords: cardiac/heart, striated, and involuntary.
• Contracts at a fairly steady rate set by the heart's pacemaker; neural controls allow speeding up.

Smooth Muscle Tissue

• Found in walls of hollow visceral organs (e.g., stomach, urinary bladder, respiratory passages).
• Forces fluids and substances through internal body channels.
• Forms valves, regulates passage through internal body openings, dilates/constricts pupils, forms erector pili muscles.
• Consists of elongated cells without striations.
• Not subject to voluntary control; contractions are slow and sustained.
• Keywords: visceral organs, non-striated, and involuntary.

Muscle Tissue Comparison

• All muscle tissues have the ability to contract.
• Skeletal and cardiac muscles are striated.
• Cardiac and smooth muscles are involuntary.

Histology Slides

Skeletal Muscles

• Long, cylindrical, multinucleated cells with striations (lines running).

Cardiac Muscles

• Striations present but only one or two nuclei per muscle fiber.

Smooth Muscles

• No striations.
• One nucleus per cell.
• Heart and smooth muscle are typically stimulated by the neural system, hormones, which is an autonomic function or ANS.

Characteristics and Functions of Muscle Tissue

Four Special Characteristics

1. Excitability (Responsiveness)

• Ability of a cell to receive and respond to a stimulus by changing its membrane potential.
• Stimulus is usually a chemical (e.g., neurotransmitter from a nerve cell).
• Ability to receive and respond to a stimulus.

2. Contractability

• Ability to shorten forcibly when adequately stimulated.
• Sets muscle apart from other tissue types.

3. Extensibility

• Ability to extend or stretch.
• Muscle cells shorten when contracting, but can be stretched beyond resting length when relaxed.

4. Elasticity

• Ability of a muscle cell to recoil and resume its resting length after stretching.
• Each skeletal muscle has a limit of elasticity.
• Exceeding this limit leads to strains where muscles can no longer recoil.
• Analogy: Over-stretched hair tie or rubber band losing tightness.
• There are a number of studies focusing on the exact amount of extensibility and elasticity that the fibers have before they can no longer recoil back

Four Important Functions of Muscles

1. Produce Movement

• Skeletal muscles responsible for locomotion and manipulation.
• Enable quick responses (e.g., jumping out of the way of a car).
• Direct eye movements, smiles, frowns.
• Locomotion is moving from point A to point B; can include assisted devices like a wheelchair.

2. Maintain Posture and Body Position

• Muscles function continuously to make adjustments against gravity.
• Important for posture while reading or listening to lectures.

3. Stabilize Joints

• Muscles strengthen and stabilize joints as they pull on bones.
• Example: Low back pain and herniated discs can result from lack of muscular infrastructure that stabilize the spine.
• Muscular imbalances can cause knee pain or patellar tracking issues.

4. Generate Heat

• Muscle contraction generates heat, helping maintain normal body temperature.