Lesson 7 Objectives

Briefly explain the events involved in muscle contraction.

1. A nerve impulse causes ACh (acetylcholine) release at a neuromuscular junction. ACh binds receptors on the motor end plate, initiating a muscle impulse 2. The muscle impulse spreads quickly along the sarcolemma and into the muscle fiber along T-tubule membranes, causing calcium ions to be released into the sarcoplasm 3. Calcium ions bind to troponin, causing tropomyosin to move and expose active sites on actin. Myosin heads attaché to the actin and form crossbridges 4. Myosin heads go through cyclic "attach, pivot, detach, return" events as the thin filaments are pulled past the thick filaments. ATP is required to detach the myosin heads and complete the sequence of cyclic events. The sarcomere shortens, and the muscle contracts. The cyclic events continue as long as calcium ions remain bound to the troponin 5. Calcium ions are moved back into the sarcoplasmic reticulum by ATP-driven ion pumps to reduce calcium concentration in the sarcoplasm, leading to relaxation. Termination of the muscle impulse results in the passive sliding of myofilaments back to the original state.

mitochondria

300 mitochondria per muscle fiber create energy for cell

Know organization of muscle tissue

A muscle is a group of fascicles. A fascicle is a group of myofibers. Myofibers are a group of myofibrils. and myofibrils are a group of myofilaments.

sarcomeres

A sarcomere is the functional contractile unit of a skeletal muscle fiber. The number of sarcomeres will vary with the length of the myofibril within the muscle fiber. Each sarcomere is composed of overlapping thick filaments and thin filaments. each sarcomere is delineated at both ends by Z discs. Z discs (also called Z lines) are composed of specialized proteins that are positioned perpendicular to the myofilaments and serve as anchors for the thin filaments. Although the Z disc appears as a flat disc when the myofibril is viewed from its "end," only the edge of the disc is visible in a side view, and it sometimes looks like a zigzagged line.

What is the structure of a muscle?

A skeletal muscle is composed of numerous skeletal muscle fibers, blood vessels and nerves, and connective tissue sheets that surround the muscle fibers and connect the muscle to bone. Although an individual muscle fiber runs the length of a muscle, it takes groupings of many muscle fibers to form the width of a muscle.

Function of synergist and fixator

A synergist is a muscle that assists the agonist in performing its action. The contraction of a synergist usually either contributes to tension exerted close to the more mobile attachment of the muscle or stabilizes the less mobile attachment of the muscle. Usually, synergists are most useful at the start of a movement when the agonist is lengthened and cannot exert much power. Examples of synergistic muscles are the biceps brachii and the brachialis muscles of the arm. Both muscles work synergistically (together) to flex the elbow joint. Synergists may also assist an agonist by preventing movement at a joint and thereby stabilizing the origin of the agonist. In this case, these synergistic muscles are called fixators.

abduction/adduction

Abduction and Adduction Abduction is moving a body part away from the midline. (Ex. If you stand straight up and move your arm out and away from your body it is considered Abduction). Adduction is the total opposite and it means to move toward the midline. (Bring your arm back down to your side is adduction).

Describe the function of agonists (prime movers)

An agonist also called a prime mover, is a muscle that contracts to produce a particular movement, such as extending the forearm. The triceps brachii of the posterior arm is an agonist that causes forearm extension.

Function of antagonists

An antagonist is a muscle whose actions oppose those of the agonist. If the agonist produces extension, the antagonist produces flexion. The contraction of the agonist stretches the antagonist, and vice versa. As this movement occurs, the stretched muscle usually does not relax completely. Instead, the tension within the muscle being stretched is adjusted to control the speed of the movement and ensure that it is smooth. For example, when the triceps brachii acts as an agonist to extend the forearm, the biceps brachii on the anterior side of the humerus acts as an antagonist to stabilize the movement and produce the opposing action, which is flexion of the forearm.

What is the difference between a tendon and an aponeurosis?

At the ends of a muscle, the connective tissue layers merge to form a fibrous tendon, which attaches the muscle to bone, skin, or another muscle. Tendons usually have a thick, cordlike structure. Sometimes, the tendon forms a thin, flattened sheet, termed an aponeurosis. The difference between tendon and aponeurosis. is that tendon is (anatomy) a tough band of inelastic fibrous tissue that connects a muscle with its bony attachment while aponeurosis is (anatomy) a flattened fibrous membrane, similar to a tendon, that binds muscles together or connects them to other body parts like skin or bone.

What are the functions of muscle tissue?

Bodily movement Maintenance of posture protection and support regulating elimination of materials heat production

Botulism

Botulism is a rare and potentially fatal illness caused by a toxin produced by the bacterium Clostridium botulinum. The disease begins with weakness, blurred vision, feeling tired, and trouble speaking. This may then be followed by weakness of the arms, chest muscles, and legs.

circumduction

Circumduction is sometimes described as simply a circular movement. because circumduction movements of (e.g. the arm and hand) result in the outer edge of the limb (e.g. the finger tips) tracing circles in space.

sarcoplasm

Cytoplasm of a muscle fiber Site of metabolic processes for normal muscle fiber activities

dorsiflexion/plantar flexion

Dorsiflexion refers to the backward or, if you will, 'upward' motion of a part of the body. Think of it as bending something back. It's commonly used with respect to the movement of the hand or foot. Plantar flexion refers to the flexion or extension of the foot at the ankle. It is the movement that decreases the angle between the back of the leg and the sole of the foot. An example of plantar flexion is a ballerina extending her foot in line with her leg.

terminal cisternae

Expanded ends of the sarcoplasmic reticulum that are in contact with the transverse tubules Site of calcium ion release to promote muscle contraction

extension/hyperextension/flexion

Extension is the opposite of flexion, describing a straightening movement that increases the angle between body parts. When a joint can move forward and backward, such as the neck and trunk, extension refers to movement in the posterior direction.

inversion/eversion

Inversion and eversion refer to movements that tilt the sole of the foot away from (eversion) or towards (inversion) the midline of the body. Eversion is the movement of the sole of the foot away from the median plane. Inversion is the movement of the sole towards the median plane.

Explain what is meant by the terms origin and insertion when discussing skeletal muscle attachments.

Most skeletal muscles extend between bones and cross at least one mobile joint. Upon contraction, one of the bones moves while the other bone usually remains fixed. Often the less mobile attachment is called the origin and the more mobile attachment is called the insertion.

Explain how muscle names incorporate action, body region, attachments, orientation, shape/size, and number of heads.

Muscle action: flexor, extensor, pronator body regions: interior, anterior, posterior... attachments: 1st part of name inferior attachment, 2nd part of name, superior attachment orientation: "rectus" means straight, "oblique" refers to the angle shape/size: deltoid- triangle, orbicularus- circle... number of heads: biceps-2, triceps- 3

myofilaments

Muscle fibers, in turn, contain cylindrical structures called myofibrils, which are composed of myofilaments. They are short contractile proteins of two types: thick (composed of myosin) and thin (composed of actin, tropomyosin, and troponin)

Discuss the causes and dysfunction of muscular dystrophy.

Muscular dystrophy is a collective term for several hereditary diseases in which the skeletal muscles degenerate, lose strength, and are gradually replaced by adipose and fibrous connective tissue. In a vicious cycle, the new connective tissues impede blood circulation, which further accelerates muscle degeneration.

Myoblasts

Myoblasts: an embryonic cell that becomes a cell of muscle fiber.

Myotomes

Myotomes: Part of the somite that develops into skeletal muscle.

T-tubercles

Narrow, tubular extensions of the sarcolemma into the sarcoplasm, contacting the terminal cisternae; wrapped around myofibrils Quickly transports a muscle impulse from the sarcolemma throughout the entire muscle fiber

opposition

Opposition brings the thumb and little finger together.

myofibrils

Organized bundles of myofilaments; cylindrical structures as long as the muscle fiber itself. Contain myofilaments that are responsible for muscle contraction About 80% of the volume of a skeletal muscle fiber is composed of long, cylindrical structures termed myofibrils. A skeletal muscle fiber contains hundreds to thousands of myofibrils. During contraction, the myofibrils shorten as their component proteins change position. Because myofibrils are attached to the ends of the muscle fiber, the shortening of the myofibrils during a contraction causes the fiber to shorten. Myofibrils consist of bundles of myofilaments. Whereas a single myofibril runs the length of the muscle fiber, it takes many successive groupings of myofilaments to run the entire length of a myofibril.

pronation/supination

Pronation refers to the inward roll of the foot during normal motion and occurs as the outer edge of the heel strikes the ground and the foot rolls inward and flattens out. Supination (or under-pronation) is the opposite of pronation and refers to the outward roll of the foot during normal motion.

protraction/retraction

Protraction is movement of a body part in the anterior direction, i.e. being drawn forwards. The movement of protraction is the opposite of the movement of retraction.

Rigor mortis

Rigor mortis is one of the recognizable signs of death, caused by chemical changes in the muscles after death, causing the limbs of the corpse to stiffen. Rigor mortis can occur as soon as thirty minutes after death.

lateral rotation/medial rotation

Rotation of body parts is referred to as internal or external, referring to rotation towards or away from the center of the body. Internal rotation (or medial rotation) refers to rotation towards the axis of the body. External rotation (or lateral rotation) refers to rotation away from the center of the body.

thick and thin filaments.

Short contractile proteins of two types: thick (composed of myosin) and thin (composed of actin, tropomyosin, and troponin)

sarcoplasmic reticulum

Smooth endoplasmic reticulum in a muscle fiber Stores calcium ions needed for muscle contraction

Tetanus

Tetanus is a serious bacterial disease that affects your nervous system, leading to painful muscle contractions, particularly of your jaw and neck muscles.

Briefly discuss how skeletal muscle develops in an embryo.

The distribution of embryonic myotomes is at about 6 weeks. Axial muscles form from adjacent segmental myotomes. Upper limb musculature forms from cervical and thoracic myotomes that migrate into the upper limb beginning in the fifth week of development. The myotomes split into two separate groups that later form the flexors and the extensors of the upper limb. Lower limb musculature forms from lumbar and sacral myotomes that migrate into the lower limb beginning in the fifth week of development. The myotomes split into two separate groups that will form the flexors and extensors of the lower limb.

elevation/depression

The terms elevation and depression refer to movement above and below the horizontal. Elevation refers to movement in a superior direction. For example, shrugging is an example of elevation of the scapula. Depression refers to movement in an inferior direction, the opposite of elevation.

Describe the different ways fascicles are organized in skeletal muscles.

There are four different types of fascicle arrangements: 1) Circular Fibers arranged concentrically around an opening Functions as a sphincter to close a passageway or opening (e.g., orbits, mouth, anus) 2)Parallel Fascicles are parallel to the long axis of the muscle Body of muscle increases in diameter with contraction High endurance, not very strong 3) Convergent Triangular muscle with common attachment site Direction of pull of muscle can be changed Does not pull as hard as equal-sized parallel muscle 4)Pennate Muscle body has one or more tendons Fascicles at oblique angle to tendon Pulls harder than a parallel muscle of equal size

nuclei

at center of myoblast

What 4 tissues make up a muscle?

epithelial, connective, muscle, and nervous tissue

cardiac muscle, smooth muscle, and skeletal muscle

go to this link, they did a super good job. https://quizlet.com/5576533/skeletal-cardiac-and-smooth-muscle-flash-cards/

sarcolemma

plasma membrane of a muscle fiber. Surrounds muscle fiber and regulates entry and exit of materials

Briefly explain how skeletal muscle cells develop from myoblasts.

skeletal muscle fibers are multi-nucleated. This increase in the number of nuclei occurs during development when groups of embryonic cells, termed myoblasts, fuse to form single skeletal muscle fibers. During this fusion process, each myoblast nucleus contributes to the eventual total number of nuclei.

Somites

somites: One of the paired segments consisting of cell masses formed in the early embryonic mesoderm on the sides of the neural tube.