Muscular system

MUSCULARMUSCULAR SYSTEM SYSTEM

INTRODUCTIONINTRODUCTION

What are the three muscle types?

• Skeletal Muscle

• Smooth Muscle

• Cardiac Muscle

Skeletal muscle is an organ of the muscular system and consist of skeletal muscle tissue, nervous tissue, blood, and connective tissue.

Structure of a Skeletal MuscleStructure of a Skeletal Muscle

Fascia - a connective tissue that separates adjacent muscles and attaches the muscle to the bone.

Epimysium – a layer of connective tissue that closely surrounds a skeletal muscle.

Perimysium – separates muscle cells into fascicles. Fascicles – bundles of skeletal muscle fibers. Endomysium – separates each individual muscle

fiber.

What do all of these have in common?

Skeletal Muscle FibersSkeletal Muscle Fibers A skeletal muscle fiber is a

single cell that contracts and relaxes

What causes the cell to contract and relax?

Nerve stimulation

Sarcolemma- muscle cell membrane.

Sarcoplasm- cell’s cytoplasm

Skeletal Muscle FibersSkeletal Muscle FibersMyofibrols

– Play a fundamental roll in muscle contraction.

– They contain two kinds of proteins filaments MYOSIN & ACTIN

Myosin & Actin are responsible for the light and dark STRIATIONS or bands of skeletal muscle.

Myofibril

Filaments

Muscle fiber

Skeletal Muscle FibersSkeletal Muscle Fibers

1. I Bands ( light bands ) are composed of thin ACTIN filaments attached to Z lines.

2. A Bands ( dark bands ) are composed of overlapping thick & thin bands.

The Striation part of skeletal pattern consist of two main parts

Skeletal Muscle FibersSkeletal Muscle Fibers

Sarcomere – the segment of a myofibril that extends from one “z” line to another.

sarcomere

Z Lines

Sarcoplasmic reticulum– network of membranous channels… similar to endoplasmic reticulum of other cells.

• Responsible for releasing calcium ions.

Transverse tubules ( T-tubules ) – extent inward and contain extracellular fluid.

Skeletal Muscle FibersSkeletal Muscle Fibers

Skeletal Muscle FibersSkeletal Muscle Fibers

Skeletal Muscle FibersSkeletal Muscle Fibers Describe how connective tissue is part of

a skeletal muscle. Describe the general structure of a skeletal

muscle fiber. Explain why skeletal muscle fibers appear

striated. Explain the relationship between the

sarcoplasmic reticulum and the transverse tubules.

Neuromuscular JunctionNeuromuscular Junction What is the stimulant that moves

a muscle? Nerve impulse

Motor neuron – A nerve fiber that extends outward from the brain or spinal cord and connected to a skeletal muscle fiber.

The connection between the two is called a neuromuscular junction and motor end plate.

Neurotransmitters – chemicals that are stored in tiny vesicles (synaptic vesicles) that stimulates muscle fiber to contract.

Neuromuscular JunctionNeuromuscular Junction

A neuromuscular junction showing motor end plate.

A motor unit. A muscle fiber usually has a single motor end plate. However a motor neuron may connect to several muscle fibers.

Skeletal Muscle ContractionSkeletal Muscle ContractionThe role of myosin and actinThe role of myosin and actin

Myosin – contain protein strands that look like

“Golf Clubs” called Cross Bridges.

Actin molecule contains protein binding sites.

Myosin Crossbridge

Thick Filament

Tropomyosin

Actin

Skeletal Muscle ContractionSkeletal Muscle Contraction

Sliding Filament Theory The head of the myosin cross-

bridge attaches to the actin binding site & pulls the actin filament along.

ATP is used to set the cross-bridge.

As the cross-bridges pull, the actin filament moves toward the center of the sarcomere and they shorten.

Z line

relaxed

contracted

ActinMyosin

Skeletal Muscle ContractionSkeletal Muscle Contraction

Skeletal Muscle ContractionSkeletal Muscle Contraction Describe a neuromuscular junction. Define motor unit. Explain how the filaments of a myofibril

interact during muscle contraction. Explain how a motor nerve impulse can

trigger a muscle contraction.

Support & MovementSupport & Movement

Oxygen DeptOxygen DeptWhen muscles are used during exercise oxygen is used up quickly. The body reverts to anaerobic respiration to produce oxygen, with the help of pyruvic acid. In low oxygen levels pyruvic acid reacts to produce lactic acid which accumulate in the muscles.

As lactic acid accumulate a

person develops Oxygen Dept.Oxygen Dept.

Support & MovementSupport & Movement

Muscle FatigueMuscle FatigueMuscles lose the ability to Muscles lose the ability to contract.contract.– Lactic acidLactic acid– Lack of acetylcholineLack of acetylcholine– Interruption of blood supplyInterruption of blood supply

CrampsCrampsA sustained involuntary contractionA sustained involuntary contractionRigor Mortis, myosin and actin Rigor Mortis, myosin and actin filaments remained linked until filaments remained linked until muscles begin to decompose. ( 72 muscles begin to decompose. ( 72 hrs )hrs )

Muscle ResponsesMuscle ResponsesThreshold StimulusThreshold Stimulus

The minimal strength required to cause a contraction.

All-or-None ResponseAll-or-None Response– A muscle fiber when excited does not contract

partially, if it contracts at all, it contracts completely

TwitchTwitch A single contration that lasts only a fraction of a

second

Muscle ResponsesMuscle Responses

Latent PeriodLatent Period The time the stimulus is applied and the contraction

occurs (0.01s)

Muscle ToneMuscle Tone Even when a muscle appears to be at rest, a certain

amount of sustained contraction occurs in its fibers. Muscle tone is a response to nerve impulses that

originate repeatedly. Is particularly important in maintaining posture.

Support and MovementSupport and MovementQuestions (p189)Questions (p189)

Define threshold stimulus.

What is a none-or-all response?

Distinguish between a twitch and a sustained contraction.

How is muscle tone maintained?