Voluntary and involuntary muscles Sliding filament model 13.9-13.10

5.1.5 Plant and animal responses (l) (i) the structure of mammalian muscle and the mechanism of muscular contraction (ii) the examination of stained sections or photomicrographs of skeletal muscle. To include the structural and functional differences between skeletal, involuntary and cardiac muscle AND the action of neuromuscular junctions the sliding filament model of muscular contraction and the role of ATP, and how the supply of ATP is maintained in muscles by creatine phosphate. Practical: An opportunity to monitor muscle contraction and fatigue using sensors to record electrical activity.

Muscle structure: LO: The structural and functional differences between skeletal, involuntary and cardiac muscle There are 3 types of muscle Smooth / Involuntary muscle Cardiac muscle Voluntary / skeletal / striated muscle

Smooth Muscle/involuntary Involuntary control Found in many parts of body: walls of stomach/bladder/blood vessels/digestive tract to control diameter/peristalsis/pupil size/uterine contractions Innervated by neurones of the autonomic nervous system Non-striated muscle Spindle shaped cells which are long and thin cells, lying parallel to each other. No regular arrangement of cells. Cells can contract in different directions. Individual cells each with own nucleus (uninucleated) Contain small bundles of actin and myosin Contract more slowly and steadily, so can stay contracted for a relatively long time

Cardiac Muscle Found only in the heart: 3 types: atrial, ventricular and specialised excitatory/ conductive tissue Function: to pump blood! Involuntary Myogenic: contract without the need of a nervous stimulus. Specialised Striated (fainter than skeletal muscles) Muscle fibres are made of many cells connected in rows Cells branch and form connections so there is simultaneous contraction Contraction intermediate, length of contraction intermediate Intercalated discs separate cells / fibres from each other Gap junctions More mitochondria Uninucleated

Voluntary/striated/skeletal muscle! Make up the bulk of body muscle tissue Their function is to move bones/joints/limbs Cylindrical cells Regularly arranged so muscle contracts in one direction Striated (bands of actin/myosin) Conscious/voluntary control Contraction is rapid, but short lasting Multinucleated

The structure of skeletal muscle Mini plenary: Exam question..9 marks Then the detailed structure of voluntary muscle

Longitudinal Microscope picture of skeletal/voluntary muscle

Structure of Voluntary/striated/skeletal muscle Muscles are made up of bundles of muscle fibres Each fibre is a single muscle cell and can be several cms in length. (0.1mm in diameter) Bound together by connective tissue continuous with tendons. With a cell surface membrane: called sarcolemma Each cell is multinucleate: a single nucleus could not effectively control metabolism of such a long cell! Would take too long to move proteins. Striped: ability to contract

Muscle.... The muscle fibre contains sarcoplasm (cytoplasm) with numerous mitochondria (ATP) (energy for muscle contraction) The sarcoplasm folds inwards: transverse or T tubules to help spread the electrical impulse throughout the sarcoplasm Have the sarcoplasmic reticulum which extends through muscle to provide calcium ions for muscle contraction Protein molecule: myoglobin Each muscle fibre is a bundle of smaller myofibrils arranged lengthways/parallel Each myofibril is made up of 2 kinds of protein myofilaments: actin (thin) and myosin (thick) These make up the contractile units called sarcomeres

Task Put the words given to you in order to explain the structure of a voluntary muscle What other words would you include to describe the structure of skeletal muscle?

Muscle, made up of… Bundle of muscle fibres Muscle fibre is the cell Each muscle fibre is surrounded by the Sarcolemma Each muscle fibre is a bundle of Myofibrils (organelles) Myofibrils are made up of Myofilaments Actin Myosin Sarcomere Missing terms?? The sarcomere is the smallest contractile unit of a muscle……………

Muscle contraction: The contractile unit : the sarcomere is made up of 2 types of protein molecule: Actin: thin Myosin: Thick Contraction is bought about by the coordinated sliding of these proteins filaments within the sarcomere The proteins overlap=striated appearance. Actin only=light (I bands) Actin+myosin=dark (A bands) Myosin only =medium (H zone)

Actin Actin molecules are 2 strands made mainly of the protein actin (F actin) which are coiled around each other (twisted beads!) Associated with 2 other protein molecules: Tropomyosin: rod shaped protein that coils around the F actin, reinforcing it Troponin: these complexes made of 3 polypeptides are attached to each tropomyosin molecule ,one polypeptide binds to tropomyosin, one to the actin and one to calcium ions Actin filaments have binding sites for myosin heads, but these are blocked by tropomyosin when muscle is in a relaxed state.

Myosin: Myosin are the thick protein filaments Each myosin molecule consists of a tail and 2 protruding heads Myosin molecule heads protrude from the fibre Each head has a binding site for the actin and for ATP When a muscle contracts it is the orientation of these that brings about the movement of actin Myosin heads attach to actin, dip forward and slide the actin over the myosin This is the sliding filament theory.

Myosin and actin: Myosin and actin make up the contractile unit: the sarcomere See tips page 371 on how to draw!

The sarcomeres span from one Z line to the next. The Z lines are drawn closer in contraction as I band and H zone are reduced. A band does not change Actin only=light (I bands) Actin connects to Z line Actin+myosin=dark (A bands) Myosin only =medium (H zone)

(a) Diagram showing a section of myofibril to reveal sarcomere layout; (b) diagram showing the bands and zones present. (a) (b)

The banded pattern shown in micrographs is due to the overlapping regions of the two types of fibre 20

Showing transverse section through a myofibril

WHITEBOARDS: DRAW THE BANDING PATTERN! Actin and myosin filaments in one sarcomere relaxed Z line The banding pattern of above The arrangement of the sarcomere when contracted WHITEBOARDS: DRAW THE BANDING PATTERN!

The central band of myosin alone has disappeared Either just actin or actin+myosin

In 1mm fibre=400 sarcomeres! Human thigh muscle=40 000 sarcomeres!

How the Sarcomere Shortens First watch this animation http://highered.mcgraw- hill.com/sites/0072495855/student_view0/chapter 10/animation__sarcomere_contraction.html Bullet point your understanding http://media.pearsoncmg.com/intl/snab_2009/topi c_7/interactives/7_2/topic_7_2.html

A nerve impulse arrives at the neuromuscular junction (where a motor neurone and muscle meet, many to ensure muscle fibres contract simultaneously) causing calcium ion protein channels to open, calcium ions diffuse into synaptic knob. Calcium ions cause vesicles holding neurotransmitter to fuse with the presynaptic membrane. Neurotransmitter diffuses across the synaptic cleft. Neurotransmitter binds to specific receptors on the muscle fibre membrane (sarcolemma) called the motor end plate, causing it to depolarise MUSCLE CONTRACTION: The depolarisation of sarcolemma travels deep into muscle fibre by spreading through T tubules, this causes Calcium ions are released from the sarcoplasm reticulum (specialised ER) Diffuse through the sarcoplasm Bind to troponin molecule Initiates the moving of the myofilaments: actin and myosin.

Myosin heads cannot bind to actin filaments troponin tropomyosin actin filament ADP myosin complex Pi myosin filament At rest, the actin-myosin binding site is blocked by tropomyosin, held in place by troponin Myosin heads cannot bind to actin filaments

Ca2+ (SR) binds to troponin, changing its shape Tropomyosin is pulled out of the binding site: shifts position and exposes myosin binding site Myosin head can bind, the ADP molecules mean they are ready – bond is an actin-myosin cross bridge

When myosin binds to actin stimulates ATPase, breaking down ATP to ADP + Pi Energy provided changes myosin head to nod forward, pulling actin filament along in a ratchet motion over myosin This is the power stroke, ATP is used (Energy is used!)

Free ATP binds to myosin head Actin-myosin cross bridge breaks: myosin head detaches (Energy is used!) ATP is hydrolysed, and myosin head returns to original upright shape (Energy is used!)

With continued stimulation the cycle is repeated The collective bending of many myosin heads combines to move the actin filaments relative to the myosin= muscle contraction

If stimulation ceases, Ca2+ is actively pumped back into sarcoplasmic reticulum (needs ATP) (Energy is used!) Troponin and tropomyosin return to original positions Muscle fibre is relaxed

The role of ATP: Thinking/Linking learning!! List the stages where ATP is involved in muscle contraction In the power stroke: when the myosin head attaches to actin binding site and bends energy is required Energy is required to break the cross bridge and for the myosin head to go back to its original position When contraction finishes to pump calcium ions back into sarcoplasmic reticulum

Maintenance of the ATP supply There is only ATP to provide 1-2 seconds worth of contraction So ATP must be regenerated as quickly as it is used There are 3 mechanisms for this: Aerobic respiration Anaerobic respiration Creatine phosphate

Creatine phosphate Three energy systems summary: Muscle contraction requires energy in form of ATP (LOTS!) Cells cannot store much ATP Aerobic respiration: ATP from oxidative phosphorylation Anaerobic: At start of exercise immediate recharge of ATP is made using creatine phosphate Stored in muscles and can be hydrolysed to release energy Energy is used to regenerate ATP from ADP and Pi. Creatine phosphate provides the Pi Creatine phosphate creatine + Pi ADP + Pi ATP Creatine phosphate + ADP creatine + ATP No oxygen needed Provide energy for 6-10 seconds as store of phosphate is used up. Known as the ATP/PC system

Muscle contraction ATP: provides energy to detach myosin from actin, for the power stroke to move the myosin head, to detach the myosin head and the recovery stroke: myosin back to original position; used in active transport of calcium ions Phosphocreatine : Reserve supply of phosphate Energy is used to regenerate ATP from ADP and Pi. Creatine phosphate provides the Pi. No oxygen needed. Provides energy for 6-10 seconds. Known as the ATP/CP system

Tasks Exam questions The diagram below 8 marks Fig 2 is an electron micrograph..17 marks Total 25 mark test