What are the

major

functions of

muscle tissue

There are four characteristics associated with muscle tissue:

• Tissue can receive and respond to stimulation

Excitability

• Tissue can shorten and thicken

Contractility

• Tissue can lengthen

Extensibility

• Tissue can return to its resting state

Elasticity

The characteristics of muscle tissue enable it to perform some important functions, including:

Movement (both voluntarily and involuntarily)

Maintaining posture

Supporting soft tissues within body cavities

Guarding entrance and exits of the body

Maintaining body temperature

What are

the 3 types

of muscle

tissue

Fibers are multinucleated with peripheral nuclei

Actin and myosin filaments form distinct cross- striation patterns

Muscle is surrounded by connective tissue epimysium

Muscle fascicles surrounded by connective tissue perimysium

Each muscle fiber surrounded by connective tissue endomysium

Voluntary muscle under conscious control

Skeletal Muscle Tissue features and characteristics:

Sensitive stretch receptors called neuromuscular spindles are present within nearly all skeletal muscles

These spindles consist of a connective tissue capsule, in which are found modified muscle fibers called intrafusal fibers and numerous nerve endings

Neuromuscular spindles monitor the changes in the muscle lengths and activate complex reflexes to regulate muscle activity

Functions of Skeletal Muscle Tissue

Skeletal muscles function in pairs to bring about the coordinated movements of the limbs, trunk, jaws, eyeballs, etc.

Skeletal muscles are directly involved in the breathing process.

Found in hollow organs and blood vessels

Fibers are fusiform in shape and contain single nuclei

Each cell is filled with a specialized cytoplasm, the sarcoplasm and is surrounded by a thin cell membrane, the sarcolemma.

Contain contractile actin and myosin filaments; however, they are not arranged in the regular, cross-striated patterns that are visible in both the skeletal and cardiac muscle fibers

As a result, these muscle appear smooth or nonstriated

Smooth muscle fibers are also involuntary muscles and are, therefore, under autonomic nervous system and hormonal control

Smooth Muscle Tissue features and characteristics:

Smooth muscle controls slow, involuntary movements such as the contraction of the smooth muscle tissue in the walls of the stomach and intestines.

The muscle of the arteries contracts and relaxes to regulate the blood pressure and the flow of blood.

Functions of Smooth Muscle Tissue

Cardiac Muscle Tissue features and characteristics:

Primarily located in the walls and septa of the heart and in the walls of the large vessels attached to the heart(aorta and pulmonary trunk)

Similar to skeletal muscle, cardiac muscle fibers exhibit distinct cross-striations as a result of the arrangement of actin and myosin filaments.

Transmission electron microscopy reveals similar A bands, I bands, Z lines, and repeating sacromere units

Exhibits only one or two central nuclei, are shorter, and are branched

The terminal ends of adjacent cardiac muscle fibers show characteristic and dense-staining, end-to-end junctional complexes called intercalated disks.

Located in the intercalated disks are the gap junctions that enable ionic communication and continuity between adjacent cardiac muscle fibers.

Exhibit autorhythmicity and spontaneously generate stimuli

Cardiac muscle tissue plays the most important role in the contraction of the atria and ventricles of the heart.

It causes the rhythmical beating of the heart, circulating the blood and its contents throughout the body as a consequence.

Functions of Cardiac Muscle Tissue

CONDUCTION

SYSTEM

The heart is influenced by the autonomic nervous system which can increase or decrease the heart rate in line with the requirements of the body. However, due to an intrinsic regulating system, called the conduction system it is possible for the heart to go on beating without any direct stimulus from the nervous system.

This system is composed of specialized muscle tissue that generates and distributes the conduction that causes contraction of the cardiac muscle. These tissues are found in the sinus (or sinoatrial) node, atrioventricular node, bundle of His, bundle branches, and conduction myofibers.

When stimulated by electrical activity, muscle fibers contract and produce motion. In the heart, this electrical activity is referred to as depolarization.

The contraction causes the blood to be pumped around the body. Contracted chambers within the heart are termed systolic.

Relaxation of the heart muscle is caused by electrical repolarisation. Relaxed chambers within the heart are termed diastolic.

Heartbeat Origination in the Sinus Node

Atrial Depolarization

Atrioventricular Nodal Depolarization

Septal Depolarization

Early Ventricular Depolarization

Late Ventricular Depolarization

Ventricular Systole

Ventricular Repolarization

Atrial and Ventricular Relaxation

MUSCLE

CONTRACTION

• Skeletal muscles require stimulation from the nervous

system in order to contract

• Motor neurons are the cells that cause muscle fibers to

contract

(motor neuron)

cell body

dendrites

axon

Synaptic terminals

(synaptic end bulbs)telodendria

axon hillock

Table 7-1

•Once an action potential (AP) is generated

at the motor end plate it will spread like an

electrical current along the sarcolemma of

the muscle fiber

• The AP will also spread into the T-tubules,

exciting the terminal cisternae of the

sarcoplasmic reticula

•This will cause Calcium (Ca+2 ) gates in the

SR to open, allowing Ca+2 to diffuse into the

sarcoplasm

•Calcium will bind to troponin (on the thin

myofilament), causing it to change its

shape. This then pulls tropomyosin away

from the active sites of actin molecules.

•The exposure of the active sites allow the

sliding of the filaments

• If there are no longer APs generated on

the motor neuron, no more Ach will be

released

• AchE will remove Ach from the motor end

plate, and AP transmission on the muscle

fiber will end

• Ca+2 gates in the SR will close & Ca+2 will

be actively transported back into the SR

• With Ca+2 removed from the sarcoplasm

(& from troponin), tropomyosin will re-cover

the active sites of actin

• No more cross-bridge interactions can

form

• Thin myofilaments slide back to their

resting state

Table 7-1

Skeletal muscle fibers shorten as thick filaments interact with thin filaments (“cross bridge”) and sliding occurs (“power stroke”).

The trigger for contraction is the calcium ions released by the SR when the muscle fiber is stimulated by its motor neuron

Contraction is an active process; relaxation and the return to resting length is entirely passive.

Calcium ions regulate contraction in smooth muscle, but they do it in a slightly different way than in skeletal muscle:

Calcium ions come from outside of the cell.

Calcium ions bind to an enzyme complex on myosin, called calmodulin-myosin light chain kinase.

The enzyme complex breaks up ATP into ADP and transfers the Pi directly to myosin.

This Pi transfer activates myosin.

Myosin forms crossbridges with actin (as occurs in skeletal muscle)

When calcium is pumped out of the cell, the Pi gets removed from myosin by another enzyme.

The myosin becomes inactive, and the muscle relaxes.

This process is called myosin-regulated contraction.

Cardiac-muscle contraction is actin-regulated, meaning that the calcium ions come both from the sarcoplasmic reticulum (as in skeletal muscle) and from outside the cell (as in smooth muscle).

Otherwise, the chain of events that occurs in cardiac-muscle contraction is similar to that of skeletal muscle.

GROUP 4DMD1E

ASID, DEVIMNUCUM, JOSHUABANGALISAN, KLYDDENE DE SAGUN, CRISTINE ANNEHORTIZUELA, JOYCE ANNETAGLE, JHAIRA