BIOH111 SN11 Muscular System · PDF fileoIntegumentary system oSkeletal system ... Cardiac...

© Endeavour College of Natural Health endeavour.edu.au 1

BIOH111

oCell Module

oTissue Module

o Integumentary system

oSkeletal system

oMuscle system

oNervous system

oEndocrine system


TEXTBOOK AND

REQUIRED/RECOMMENDED READINGS

o Principles of anatomy and physiology. Tortora et al; 14th

edition: Chapter 10


BIOH111 – MUSCLE SYSTEM MODULE

o Session 11 (Lectures 17 and 18) – Muscle

physiology: Building of muscle organ – cells,

tissue, organ and muscle contraction process and

regulation

o Session 12 (Lectures 19 and 20) - Skeletal muscle

metabolism

o Session 13 (Lectures 21 and 22) – Major muscle

groups

BIOH111

Lectures 17 and 18

Muscle physiology: Building of muscle organ

and muscle contraction process and regulation

Department of Bioscience

endeavour.edu.au


PREPARATION FOR THIS SESSION

o Review:

• plasma membrane and endoplasmic reticulum

structure and function

• difference between channels and receptors – think

about this: can they be both in one protein?

• regulated exocytosis

• tissue types


OBJECTIVESLecture 17:

Muscle cells and tissue

Name and describe muscle cells and their function in building and function of

skeletal muscle tissue

Describe structure of connective tissue, nervous tissue and blood supply within

the structure and function of skeletal muscle tissue

Regulation of muscle contraction

Describe process of muscle contraction at the neuromuscular junction

Lecture 18:

Muscle contraction process

Describe the sliding filament theory of muscle contraction from both an

anatomical and physiological viewpoint

Discuss the contraction mechanism and the structures required for this occur


FUNCTIONS OF MUSCULAR SYSTEM

1. Producing body movements - occurs at the cellular level

where chemical energy is changed into mechanical energy

2. Stabilizing body positions – skeletal muscle contractions

stabilize joints and maintain body positions (e.g.

siting/standing)

3. Regulating organ volumes - bands of smooth muscle

called sphincters

4. Movement of substances within the body - blood, lymph,

urine, air, food and fluids, sperm

5. Producing heat - involuntary contractions of skeletal

muscle (shivering)


PROPERTIES OF MUSCLE TISSUE

1. Excitability

• respond to chemicals released from nerve cells

2. Conductivity

• ability to propagate electrical signals over membrane

3. Contractility

• ability to shorten and generate force

4. Extensibility

• ability to be stretched without damaging the tissue

5. Elasticity

• ability to return to original shape after being stretched


MUSCLE TISSUEConsists of elongated cells called musle fibres or myocytes

that are modified for contraction using ATP as energy.

Muscle tissue provides motion, maintenance of posture and

heat.

o Classified into 3 types based on function and location:

1. Skeletal muscle tissue – striated, voluntary control

2. Cardiac muscle tissue - striated, involuntary control

3. Smooth (visceral) muscle tissue – non-striated,

involuntary control


Skeletal Cardiac Smooth

Multi-nucleated cellsBranched,

mononucleated cellsMononucleated cells

Motion, posture,

heat protection and

production

Contraction Motion

Attached to bones

by tendonsHeart

Walls of hollow

internal structures

(e.g. blood vessels,

airways)


SKELETAL MUSCLE TISSUE

o Skeletal muscle is made up of several tissues:

muscle cells (fibers), adipose tissue, connective tissue and

nervous tissue

o 1 skeletal muscle = 1 organ

Building a muscle: cells → tissue → organ


MUSCLE FIBER OR MYOFIBER

o Long, cylindrical &

multinucleated

o Sarcolemma: muscle cell

membrane; form T tubules

o Sarcoplasm: muscle cell

cytoplasm; filled with

sarcoplasmic reticulum,

mitochondria and myofibrils;

contains large amount of

glycogen for energy

production and myoglobin for

oxygen storage

cells → tissue → organ


TRANSVERSE (T) TUBULES

Structure: invaginations of the sarcolemma into the center

of the cell; filled with extracellular fluid

Function: to carry and quickly spread the muscle action

potential to all parts of the muscle fiber.


SARCOPLASMIC RETICULUM

AND MITOCHONDRIAo Sarcoplasmic reticulum:

• Structure: system of tubular sacs

similar to smooth ER in

nonmuscle cells

• Function: storage of Ca+2 in

relaxed muscle (release triggers

contraction)

o Mitochondria:

• Structure: same structure as in

non-muscle cells; lie in rows

throughout the myofibre

• Function: provides ATP needed

for contraction


MYOFIBRILS & SARCOMERE

o Myofibrils: separated by sarcoplasmic reticulum within a sarcolemma; contain the functional units of muscle – sarcomere

o Sarcomere contains myofilaments (thick & thin filaments) - contractile proteins of muscle


CONNECTIVE TISSUEo Superficial fascia : loose connective tissue

& fat underlying the skin

o Deep fascia : dense irregular connective

tissue around muscle

o Connective tissue components of the

muscle include

• epimysium = surrounds the whole

muscle

• perimysium = surrounds bundles

(fascicles) of 10-100 muscle cells

• endomysium = separates individual

muscle cells

• Tendons and aponeurosis



CONNECTIVE TISSUE

o Tendons and aponeuroses are

extensions of connective tissue

beyond muscle cells that attach

muscle to bone or other muscle.

• tendon - cord of dense connective

tissue that attaches a muscle to

the periosteum of a bone

• aponeurosis - tendon that extends

as a broad, flat layer and connects

muscle to whatever it is moving


NERVE AND BLOOD SUPPLY

o Each skeletal muscle is supplied by a nerve, artery and two veins.

o Each motor neuron supplies multiple muscle cells (neuromuscular

junction) – motor unit

o Each muscle cell is supplied by one motor neuron terminal branch

and with one or two capillaries (found in the endomysium between

individual cells)



MOTOR UNITo Motor unit = 1 somatic motor

neuron + all the skeletal muscle cells

(fibers) it stimulates (10 cells to

2,000 cells)

• muscle fibers normally scattered

throughout belly of muscle

• one nerve cell supplies on average 150

muscle cells that all contract in unison.

o Total strength of a contraction

depends on how many motor units

are activated & how large the motor

units are


Anterior horn cell

Motor nerve

fibre


REVISION

Next..


NEUROMUSCULAR JUNCTION (NMJ)

NMJ is a region between the end of axon and the surface of a muscle fiber that

is separated by synaptic cleft or gap. Components of NMJ:

1. Synaptic end or bulb - swellings of axon terminals

2. Synaptic vesicles – contained within the synaptic bulbs; filled with

acetylcholine (ACh)

3. ACh receptors – at the sarcolemma of the motor fiber (motor end plate);

~30 million/synaptic bulb


MUSCLE CONTRACTION - REGULATION

1. Nerve impulse (action potential) → release of ACh from synaptic vesicles

(exocytosis) is calcium-dependent

2. ACh binds to receptors → Na+ influx; K+ efflux

3. Inside of muscle cell more positive → muscle action potential travels over the

cell and down the T tubules

4. Ca+2 released from the SR → muscle cell contraction (details next lecture)

5. Acetyl cholinesterase breaks down the ACh → muscle action potential stops

and muscle relaxes

Is Na+ inside a cell a good

thing? If not, how does the cell

fix that?


OBJECTIVESLecture 17:

Muscle cells and tissue

Name and describe muscle cells and their function in building and function of

skeletal muscle tissue

Describe structure of connective tissue, nervous tissue and blood supply within

the structure and function of skeletal muscle tissue

Regulation of muscle contraction

Describe process of muscle contraction at the neuromuscular junction

Lecture 18:

Muscle contraction process

Describe the sliding filament theory of muscle contraction from both an

anatomical and physiological viewpoint

Discuss the contraction mechanism and the structures required for this occur


SARCOMERE STRUCTURE

o Sarcomere: basic functional unit

of myofibril; contains:

• Z disc – marks boundary of each

sarcomere

• I band – wide light band; contains

only thin filaments; Z disc passes

through the middle of the I band

• A band – wide dark band in the

middle of the sarcomere; contains M

line and H zone

• M line – holds thick filaments

together in the middle of the

sarcomere

• H zone – only thick filaments;

extends on either side of M line


SARCOMERE STRUCTURE


THE PROTEINS OF MUSCLE

o Sarcomere contains 3 groups of functionally distinct proteins:

1. contractile proteins: myosin and actin

2. regulatory proteins: turn contraction on & off; troponin and

tropomyosin

3. structural proteins: provide proper alignment, elasticity and

extensibility, link myofibres to sarcolemma and ECM ; titin,

myomesin, nebulin and dystrophin


THICK FILAMENTS

o Thick filaments are composed of myosin

• each molecule resembles two golf clubs twisted together

• myosin heads (cross bridges) extend toward the thin filaments

o Held in place by the M line proteins.


o Thin filaments are made of actin, troponin, & tropomyosin

o The myosin-binding site on each actin molecule is covered by

tropomyosin in relaxed muscle

o The thin filaments are held in place by Z lines.

THIN FILAMENTS


o Titan anchors thick filament to the M line and the Z disc and maintains

position of thick filament in the middle of the sarcomere

o The portion of the molecule between the Z disc and the end of the thick

filament can stretch to 4 times its resting length and spring back

unharmed.

o Function: role in recovery of the muscle after contracting or stretching

STRUCTURAL PROTEINS: TITIN


STRUCTURAL PROTEINS:

MYOMESIN AND NEBULIN

o Myomesin: structural protein of the M line; function: connects

to titin and adjacent thick filaments

o Nebulin, inelastic protein; function: assists in the alignment of

the thin filaments


o Dystrophin links thin filaments

to sarcolemma and transmits

the tension generated to the

tendon.

STRUCTURAL PROTEINS:

DYSTROPHIN


o Sarcomere shortens

during contraction: Z discs

move toward each other

and thin filaments slide

inward

o Overall action: sarcomeres

shorten → muscle fiber

shortens → muscle

shortens

SLIDING FILAMENT THEORY

Contraction cycle


CONTRACTION CYCLE

https://www.youtube.com/watch?v=Ct8AbZn_A8A

https://www.youtube.com/watch?v=Ct8AbZn_A8A


RELAXATION CYCLE

Contraction cycle has several “break”

points:

1. Degradation of ACh:

Acetylcholinesterase (AChE) breaks

down ACh within the synaptic cleft

→muscle action potential ceases and

Ca+2 release channels close

2. Sequestration of Ca+2:

Ca+2 active transport pumps pump Ca+2

ion back into storage (SR); calcium-

binding protein (calsequestrin) helps

hold Ca+2 in SR

End result: Tropomyosin-Troponin complex

covers myosin-binding site on the actin


MUSCLE CONTRACTION OVERVIEW

Basic steps:

1. Release of ACh in response

to AP

2. Initiation of muscle AP results

in release of Ca+2 from SR

3. Ca+2 interacts with troponin

on thin filament. If thick

filament is activated the

sarcomere contraction is

initiated – sliding theory

4. Ca is sequestered back into

SR and sarcomere relaxes –

tropomyosin and titin


2 molecules are critical for contraction:

Ca+2 and ATP.

We know where Ca+2 comes from, but

where does the ATP used in contraction

cycle come from? Next session!!


WHY IS IT HARDER TO LIFT SOMETHING

WITH AN EXTENDED ARM?

o Length-Tension relationship

o Optimal overlap at the 100%

o Cell too stretched – myosin heads

are not close to actin so no binding

can occur → little force is produced

o Cell is too short: myosin heads

overlap with actin, thick filaments

crumpled by Z discs so little binding

can occur →little force is producedGraph of Force of contraction (Tension)

vs Length of sarcomere


WHY STRETCHING AFTER SITTING

FEELS GOOD?

o Muscle tone

• constant, slightly contracted state of all

muscles, which does not produce active

movement

• resistance to stretch in resting muscle

• normal muscle tone is provided by titin and

weak myosin-actin bonds (when myosin

head is bound to ADP)

Stretching leads to breaking those weak interactions

and overstretching is prevented by titin


Recap of Session 11

Muscle tissue is classified into 3 types: skeletal, smooth and cardiac

(we only cover skeletal in BIOH111)

Skeletal muscle cells (myofibers) contain a specialised component

called myofibril which contain a unit responsible for muscle contraction

– sarcomere

Sarcomere contraction is regulated by nervous system at the NMJ and

the outcome of the regulation is release of calcium from SER

Sarcomere is composed of 3 functional groups of protein: regulatory,

structural and contractile. All work together to enable sarcomere,

myofibril and myofiber to contract


PREPARATION FOR NEXT SESSION

o Complete any missing concepts and linking words from

Session 11

o Review:

• mitochondria structure and function

• contraction cycle

BIOH111 SN11 Muscular System · PDF fileoIntegumentary system oSkeletal system ... Cardiac...

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