Muscle Systems Animal Science I Anatomy, Physiology, and Absorption of Nutrients

Objective Name, locate and describe the functions of the parts of the muscle systems of animals.

Types of Muscles Skeletal Smooth Cardiac Differentiated based on their structure, location and method of control Fig 5-4

Skeletal (striated voluntary) Most of the flesh referred to as meat Called striated because of the dark bands that cross each muscle fiber Subdivided into two types based on color – Red: muscle that is involved in sustained work – Pale/White: muscle that is activated on a more intermittent basis

Skeletal Muscle

Skeletal Muscle Structure Exist in bundles enclosed in connective tissue that contain many muscle fibers of varying length Cylindrical in shape Muscle fibers are enclosed in a sheath of connective tissue Myofibrils are the component parts of muscle fiber Two types of myofilaments (myosin- thick, actin-thin) are found in the myofibril Muscle contraction occurs when the thin myofilaments slide past the thick Fig 5-5

Skeletal Muscle Attachment Usually tendons One end to an unmovable part known as the origin and the other to a more moveable part known as the insertion

Control Controlled by the voluntary nervous system Nerve endings are located on every muscle fibril – Muscles contract when stimulated by an impulse and relax in the absence of stimulation – Degree of contraction is related to the frequency of stimuli – Stimulus over a long period of time leads to fatigue, due to a build up of lactic acid in the muscle and a reduction in stored energy

Adenosine Triphosphate (ATP) Supplies the energy for muscle contraction

Skeletal Muscles At Work Work in pairs or groups Muscles that begin movement are called agonists Muscles that work in opposition of the agonists are called antagonists Even when no work is being done, muscles are in a state to tension This is called muscle tone and allows rapid muscular response as needed

Smooth (unstriated involuntary) Muscles that surround the hollow internal organs of the body Two types: visceral and multiunit Most in the vertebrate body are visceral Multiunit smooth muscle is found where better muscular control is needed

Smooth Muscle Characteristics Activated by the autonomic nervous system Generally act more slowly than the skeletal muscles Do not have myofibrils or dark striations Color is generally white No origin or insertion points ; no attachment to the skeleton Stretchable Cells are smaller than skeletal and cardiac muscle cells Appear spindle shaped Contraction can be stimulated by: myosin-actin mechanism, chemicals, hormones

Cardiac (striated involuntary) Only found in the muscular wall of the heart Striated like a skeletal muscle Rectangular in shape with a central nucleus

Cardiac (striated involuntary) Contain two components not found in other types of muscle: intercalated discs and Purkinje fibers – Intercalated discs are dark thickenings that cross the muscle fibers and separate the cardiac cells – Purkinje fibers are specialized muscle fibers that are found in the lateral ventricles of the heart – They are part of the contractile system, carrying the contraction impulses to the ventricle muscles Autonomic nervous system can speed up or slow down the rate of heart muscle contraction but it does not start the contractions

Cardiac Muscle Contractions Begins in the sinoatrial node that is located in the upper right atrium Nerve stimulation is not required for this contraction to occur When contraction begins it rapidly spreads to the entire muscle Contraction is followed by a period of relaxation— during which it can’t be stimulated to contract again These properties result in the rhythmic beating of the heart that is essential to the circulation of blood through the body

Summary* 3 types of muscles-skeletal, smooth, cardiac Skeletal muscles make up most of the flesh referred to as meat Skeletal muscle cells are cylindrical in shape and occur in bundles Adenosine Triphosphate (ATP) supplies the energy for muscle contraction Smooth muscles surround the hollow internal organs of the body Smooth muscles are spindle shaped Smooth muscles are able to expand Cardiac muscles are only found in the muscular wall of the heart Cardiac muscle cells are rectangular in shape with a central nucleus

Assignment Discussion Questions 6-9 p. 128 due—