Muscular System Functions

• Body movement

• Maintenance of posture

• Production of body heat

• Communication

• Constriction of organs and vessels

• Heart beat

Muscle Tissue Types Skeletal

Attached to bones Striated, Voluntary and involuntary (reflexes)

Smooth Walls of hollow organs, blood vessels, eye,

glands, skin Not striated, involuntary

Cardiac Heart Striations, involuntary, intercalated disks

Smooth Muscle

Smooth muscle is found in the walls of blood vessels, tubular organs such as the stomach and uterus. It has the ability to stretch and maintain tension for long periods of time. It is not under voluntary control and each cell exists as a discreet independent unit that is innervated by a single nerve ending. The myofilaments are loosely organized and attached to dense bodies.

Cardiac Muscle

Skeletal Muscles

BicepsTriceps

Biceps-Triceps Muscles Represent an Antagonistic Pair.One contracts while it’s antagonist relaxes.

Organization III:

Structure of Skeletal Muscle:Connective Tissue Covering Epimysium (upon, outside)

Surrounds entire muscle Perimysium (around)

Surrounds bundles of muscle fibers Fascicles (bundle)

Endomysium (within) Surrounds individual muscle fibers

Connective Tissue, Nerve, Blood Vessels

Muscle cell (myofiber) Structure

Sarcolemma Muscle cell membrane

Myofibrils – contractile protein

strands– Striations due to

presence of sarcomeres

Contraction

Sarcomere – the functional unit of myofibrils

Sarcoplasmic reticulum – storage for calcium ions that are used for muscle

contractions

CONTRACTILE PROTEINS1. THIN FILAMENT- Has 3 parts;

i) ACTIN PROTEIN (i.e. the main molecule of this filament). FUNCTION: Binds to myosin head of thick filament.

ii) TROPONIN FUNCTION: Regulatory function by binding to Ca 2+

iii) TROPOMYOSIN FUNCTION: Has a regulatory function by blocking/unblockingthe binding site of actin to the myosin head

CONTRACTILE PROTEINS

1. THICK FILAMENT– made of myosin protein- has 2 main parts i) MYOSIN HEAD - forms cross-bridge with actin.ii) MYOSIN TAIL – forms the shaft of thick bands.

Calcium ?

• Click for video

Sliding Filament Model I:

• Actin myofilaments sliding over myosin to shorten sarcomeres Actin and myosin do not change length Shortening sarcomeres responsible for

skeletal muscle contraction

• During relaxation, sarcomeres lengthen

Mechanism of muscle contraction

SLIDING FILAMENT THEORY

MOTOR UNIT

Motor Unit Single motor neuron & muscle fibers it

innervates Eye muscles – 1:1 muscle/nerve ratio Hamstrings – 300:1 muscle/nerve ratio

The Neuromuscular Junction Site where motor neuron meets the muscle

fibre Separated by gap called the neuromuscular cleft

Motor end plate Pocket formed around motor neuron by

sarcolemma Acetylcholine is released from the motor

neuron Causes an end-plate potential (EPP)

Depolarisation of muscle fibre

Neuromuscular Junction

• Click for a Video

Rigor Mortis• Rigor mortis is one of the recognizable signs of death (Latin mors, mortis) that is caused by a chemical

change in the muscles after death, causing the limbs of the corpse to become stiff (Latin rigor) and difficult to move or manipulate.[1]

• After death, respiration in organisms ceases to occur, depleting the corpse of oxygen used in the making of ATP. ATP is no longer provided to operate the SERCA pumps in the membrane of the sarcoplasmic reticulum, which pump calcium ions into the terminal cisternae.[1] This causes calcium ions to diffuse from the area of higher concentration (in the terminal cisternae and extracellular fluid) to an area of lower concentration (in the sarcomere), binding with troponin and allowing for crossbridging to occur between myosin and actin proteins. [2]

• Unlike normal muscle contractions, the body is unable to complete the cycle and release the coupling between the myosin and actin, creating a perpetual state of muscular contraction, until the breakdown of muscle tissue by digestive enzymes during decomposition.

Rigor Mortis

• Respiration ceases and Oxygen used in making ATP is depleted.

• ATP is no longer provided to operate the pumps in the membrane of the sarcoplasmic reticulum, which pump calcium ions.

• Unlike normal muscle contractions, the body is unable to complete the cycle and release the crossbridges between the myosin and actin, creating a perpetual state of contraction until the breakdown of muscle during decomposition.

Muscle Function All or none law – fibre contracts

completely or not at all Muscle strength gradation

Multiple motor unit summation – more motor units per unit of time

Wave summation – vary frequency of contraction of individual motor units

Animation Links!!• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/

animation__action_potentials_and_muscle_contraction.html

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__sarcomere_contraction.html

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__breakdown_of_atp_and_cross-bridge_movement_during_muscle_contraction.html

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__function_of_the_neuromuscular_junction__quiz_1_.html