Question

Due to contraction of which muscle an organ goes away from the main axis of the body?

Answer 1

Answer:

=>Muscle contraction ends when calcium ions are pumped back into the sarcoplasmic reticulum, allowing the muscle cell to relax. During stimulation of the muscle cell, the motor neuron releases the neurotransmitter acetylcholine, which then binds to a post-synaptic nicotinic acetylcholine receptor.

Explanation:

==>THE MUSCULAR SYSTEM

The muscular tissue of the body constitutes from one-third to one-half of the body mass of the average vertebrate.

Muscular tissue functions in:

� movement and locomotion, through its direct connection with the skeletal system

� more subtle movements associated with maintaining posture/vertical position

� help to generate heat due to catabolic reactions that are associated with muscular activity (such that animals shiver or increase overall movement when body temperature drops)

� can be modified into other structures, such as electric organs in some fish

The general structure of a muscle fiber include (Fig. 10.2, p. 347) myofibrils (chains of repeating subunits) composed of two kinds of filaments:

� thin filaments (composed of myosin) and thick filaments (composed of actin, tropomyosin and troponin) that interact by binding to produce a sliding movement between the filaments, and that creates tension in the muscle fiber leading to muscle contraction.

There are three generally recognized muscle tissue types: smooth, cardiac and skeletal, each tissue type with a distinct location in the body, cellular organization (histology), and general action of the muscle fibers (physiology)

Because of the multiple functions of muscles, criteria for classifying muscles include:

1. Color

� red - highly vascularized and rich in myoglobin; resist fatigue

� white - low vascularization and lower in myoglobin; quicker to fatigue

2. Location

� somatic - move bone or cartilage

� visceral - control activities of organs, vessels, or ducts

3. Nervous system control

� voluntary - under immediate conscious control

� involuntary - are not

4. Embryonic origin

5. General microscopic appearance

� skeletal - Fig. 10.2, p. 347

� cardiac - Fig. 10.3, p. 348

� smooth - Fig. 10.4, p. 348

Smooth muscle

� found lining the walls of blood vessels, visceral organs (such as the digestive tract and uterus) and are also found attached to hairs in the integument.

� two general types:

- unitary smooth muscle has self-initiated or myogenic contraction to aid in sustaining the rhythmic movement of the organ with which it is associated

- multiunit smooth muscle has neurogenic contraction, which requires action potentials sent by neurons to regulate its action.

Cardiac muscle

� are found solely in the musculature of the heart wall

� in cardiac muscle the branching of the cells increase its overall connectivity and the cells are firmly united with each other through the intercalated disks

� cardiac muscle does not fatigue readily, which is a desirable trait in the muscles that maintain circulation of blood

� action of the cardiac muscle fibers shows mixed control, such that the myogenic rhythm of the heart is maintained by neurogenic control and the entire unit of the cardiac muscle acts as a syncytium, or single functional unit

Skeletal muscle

� skeletal muscles are closely associated with the skeleton and are used in locomotion

� each skeletal muscle fiber is also a syncytium due to the close connection between cellular units

� fibers are closely associated with connective tissues and are under voluntary control by the nervous system.

Histology

Striated?

Shape

Branched?

Nucleus location

Disks?

Physiology

Neurological control

Speed of action

Smooth

Not striated

Spindle-shaped

Not branched

Nucleus central

No disks

Involuntary

Slow

Cardiac

Striated

Cylindrical

Branched

Nucleus central

Intercalated disks

Involuntary

Fast

Skeletal

Striated

Cylindrical

Not branched

Nucleus peripheral

No disks

Voluntary

Fast

General Muscle terminology

As you are familiar with from lab, many unique terms are associated with the muscular system, ranging from describing how a muscle works to the general shape of the muscle itself.

The term "muscle" has at least two meanings:

� muscle cell or fiber - the active contractile component: muscle cells and their endomysium

� muscle organ - the whole organ: muscle cells plus associated connective tissues, nerves, blood supply

Action

� takes place by contraction, which creates tension in the muscle so that it shortens and thus moves what it is attached to (whether it is a bone, hair or the epithelium of an organ)

� for skeletal muscles, each muscular unit may be described based on a number of factors, such as where the main body of the muscle (belly) is located, such as shoulder muscles, pectoral muscles, gluteal muscles, etc.

Muscle is not attached directly to bone by the contractile muscle fibers - various wrappings of connective tissues extend beyond the ends of the muscle fibers to connect with the periosteum of the bone:

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Answer 2

Answer:

Muscle contraction ends when calcium ions are pumped back into the sarcoplasmic reticulum, allowing the muscle cell to relax. During stimulation of the muscle cell, the motor neuron releases the neurotransmitter acetylcholine, which then binds to a post-synaptic nicotinic acetylcholine receptor.

Explanation: