Muscle Functions, Types & Structure

• There are three primary functions of muscles; provide motion, maintain posture, and generate heat.
• Motion is facilitated through muscle contraction.
• Muscles help maintain body position and stability against gravity for posture.
• Heat is produced as a byproduct of muscle contractions, which helps to maintain body temperature.

Types of Muscle Tissue

• There are three different types of muscle tissue: skeletal, cardiac, and smooth.
• Skeletal muscle is voluntary and moves bones, controlled by the conscious mind and found attached to the skeleton.
• Cardiac muscle is involuntary, only found in the heart, and responsible for pumping blood.
• Smooth muscle is involuntary, found in walls of hollow organs (e.g., intestines, blood vessels), and responsible for internal movements.

Muscle Structure and Connective Tissue

• Epimysium is the outermost layer of connective tissue surrounding the entire muscle, providing structural support.
• Endomysium is a thin layer of connective tissue surrounding each individual muscle fiber, allowing for electrical and nutrient exchange.

Muscle Attachments and Actions

• Tendons are connective tissue bands that attach muscles to bones.
• Aponeuroses are broad sheets of fibrous tissue that attach muscles to bones or other muscles.
• The origin is the stable attachment point of a muscle that does not move during contraction.
• The insertion is the movable attachment point that undergoes the most movement during contraction.

Muscle Contraction Mechanics

• Agonists are muscles that are the primary movers in a specific action.
• Antagonists are muscles that oppose the action of agonists, providing balance and control.
• Synergists are muscles that assist the agonist in performing a movement.
• Fixators are muscles that stabilize joints to allow for other movements.

Circulatory Pathways

• Pulmonary circulation is the pathway of blood from the heart to the lungs and back and is responsible for oxygenating blood.
• Systemic Circulation is the pathway of blood from the heart to the rest of the body, delivering oxygen and nutrients to tissues.

Anatomy of the Heart

• The apex is the pointed, caudal end of the heart.
• The base is the rounded, cranial end of the heart.
• The mediastinum includes the heart, trachea, bronchi, esophagus, lymph nodes, and major blood vessels.

Heart Valves and Auscultation

• The best auscultation for pulmonary, aortic, and mitral valves is on the left side, assessed cranially to caudally.
• The best auscultation for the tricuspid valve is on the right side.

Pericardium and Heart Layers

• Fibrous pericardium connects to the diaphragm, providing structural support.
• Serous pericardium contains parietal and visceral layers, with the visceral layer also known as the epicardium.
• The epicardium is the outer layer in contact with the pericardium.
• The myocardium is the thick muscular layer responsible for contraction.
• The endocardium is the inner layer lining the heart chambers and valves, in direct contact with blood.

Nervous System Influence on Heart Function

• The parasympathetic nervous system typically causes contraction of smooth muscles, while the sympathetic nervous system generally causes relaxation; can vary based on the specific muscle type and location.
• In the digestive tract, the sympathetic nervous system promotes relaxation, allowing for digestion.
• The sympathetic nervous system can cause contraction in arteries to redirect blood flow to vital organs and the brain during stress.

Heart Structure and Components

• The heart has four chambers: right atrium, right ventricle, left atrium, and left ventricle; each plays a specific role in blood circulation.
• The apex of the heart is the pointed, caudal end, while the base is the rounded, cranial end, providing orientation for anatomical studies.
• Auricles, which are blind pouches attached to the atria, increase their capacity and play a role in blood storage.

Heart Valves and Their Functions

• The heart contains four main valves: mitral (left atrioventricular), tricuspid (right atrioventricular), aortic, and pulmonary (both semilunar valves).
• The mitral valve is located between the left atrium and left ventricle, while the tricuspid valve is between the right atrium and right ventricle.
• Proper functioning of the valves maintains unidirectional blood flow and prevents backflow.

Blood Flow Dynamics

• Blood flows in the following route: right ventricle → pulmonary arteries → lung capillaries → pulmonary veins → left atrium → aorta → systemic arteries → systemic capillaries → systemic veins → vena cava → right atrium.
• This cycle ensures that deoxygenated blood is sent to the lungs for oxygenation and that oxygen-rich blood is delivered to the body.

Blood Pressure and Cardiac Output

• Blood pressure is influenced by heart rate, stroke volume, arterial diameter, and total blood volume; normal MAP is around 93 mm Hg for healthy mammals.
• Systolic blood pressure is the peak pressure during ventricular contraction, while diastolic blood pressure is the lowest pressure during relaxation.
• Cardiac output (CO) can be modified by changes in heart rate and stroke volume.

Diagnostic Techniques and Clinical Relevance

• An ECG measures the electrical activity of the heart to reflect heart rhythm and function, with key components including P wave, QRS complex, and T wave.
• The P wave indicates atrial depolarization, the QRS complex represents ventricular depolarization, and the T wave shows ventricular repolarization.
• An echocardiogram uses ultrasound to visualize heart structure and function, assessing size, shape, and movement.

Common Venipuncture Sites

• Venipuncture sites vary by species; for example, the jugular vein is commonly used in canines and equines, while the cephalic vein is also popular in felines.
• Less common sites include the coccygeal vein in ruminants and rodents.

Explore the primary functions of muscles: motion, posture, and heat generation. Learn about the three types of muscle tissue—skeletal, cardiac, and smooth—and their roles. Understand muscle structure and the function of connective tissues.