F Muscles By Ms Cullen

Muscle Structure Constructed of muscle cells that are elongated to form fibres which are able to contract and relax Contain filaments made of the proteins actin and myosin There are 3 types of muscles – can you name them?

3 Types of Muscle Week 29

Involuntary (smooth) muscle Where have we encountered this type of muscle before? What controls the contraction of this type of muscle?

Involuntary (smooth) muscle

Cardiac Muscle Only found in the heart There are 3 types; atrial muscle, ventricular muscle and specialised excitatory and conductive muscle fibres Atrial & ventricular muscle contract in a similar way to skeletal muscle Some cardiac muscle fibres are myogenic, meaning they can contract without a nerve impulse However the autonomic nervous system regulates the rate of contraction by impulses. Sympathetic stimulation increases heart rate and parasympathetic decreases it The SAN in the right atrium contains the most specialised excitatory and conductive muscle fibres Contraction and relaxation continues throughout life. This type of muscle contracts powerfully and does not fatigue

Cardiac Muscle

Voluntary (skeletal or striated) Muscle Voluntary muscle brings about movement at joints This type of muscle contracts quickly but fatigues easily When viewed under the microscope, muscle tissue looks banded

Voluntary (skeletal or striated) Muscle

Activity: View different types of muscle under the microscopes

Myofibrils These are the main component of each muscle fibre, the myofibrils within a fibre is what gives muscle it’s striated appearance Myofibrils consist of 2 types of filament; Myofibrils run the whole length of long muscle cells and are divided into many repeating units known as sacromeres

Structure of Myofibrils Z lines – Sacromere – Myosin filaments are found in the central part of the sacromere M lines – I band – A band – H zone –

Structure of Myofibrils Each myosin filament is associated with 6 actin filaments which surround it…. ….and each actin filament is linked with more than 1 myosin filament Each myosin forms cross bridges with the 6 actin, this produces a more coordinated, smoother and stronger contraction Exam%20Reviews/Exam%203%20Review/CH%2009%20Sarcomere%20Appearance.ht m

Actin and Myosin Structures

Contraction - The sliding filament model

During contraction Actin filaments are pulled between the myosin filaments towards the centre of the sacromere Z lines – I bands and H zones – A bands – The sacromere shortens but this is because the filaments slide BETWEEN each other. Individual filaments stay the same length regardless of whether they are contracting or relaxing

During contraction

The Role of Ca 2+ ions Unblock the binding sites on the actin filaments by moving the tropomyosin This allows the actomyosin cross-bridge to form, initiating muscle contraction When an action potential arrives at a neuromuscular junction, Ca 2+ ions are released from the sacroplasmic reticulum in the sacromeres

The Role of ATP

Maintenance of ATP supply ATP must be generated as quickly as it is used up! There are 3 ways this is done:

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Complete Activity 30 Observing the effect of ATP on muscle contraction

Neuromuscular junction Very similar to a synapse between neurones, but is between a motor neurone and a muscle. The neurotransmitter is acetylcholine Impulses arriving at the junction initiate muscle contraction

Neuromuscular junction

What are the similarities and differences between neuromuscular junctions and other synapses?

How is the strength of muscle contraction controlled?

Strength of Muscle Contractions The brain controls the strength of the muscle contraction Many motor neurones will stimulate a single muscle A cluster of muscle cells are known as a motor unit The more motor units stimulated, the greater the force of contraction This is called the graduation of response

Week 29 The response of isolated whole muscles to electrical stimulation

The ‘Fight or Flight’ Response This involves muscles, nerves and hormones and allows animals to respond to their environment. Using OCR A2 Biology textbooks P Explain how, in mammals, the ‘fight or flight’ response is coordinated by the nervous and endocrine systems.