Skeletal Muscles, Control of Heart Rate and Homeostasis

What is the SAN an its function

Distinct group of cells in the wall on the right atrium that have spontaneous rhythmic electrical activity (action potential)

Referred to as the pacemaker because it initiates the heart heart

What is the AVN and its function

Distinct set of cells between the atria

Responsible for conveying electrical activity down to the ventricles

What is the bundle of His and its function

Specialised conducting tissues through the septum

Divides into smaller branches called purkyne tissues which spread into the ventricles

How does the heart beat

• SAN is myogenic so initiates the heart beat

• SAN causes a wave of electrical activity to spread across both atria causing them to contract

• A layer of non-conductive tissues prevents electrical activity spreading to the ventricles

• The wave of electrical activity enters the AVN and causes a short delay which allows atria to empty before ventricles contract

• The AVN conveys a wave of electrical activity along the bundle of his to the bas of the ventricle

• Purkyne tissues conduct electrical activity into the ventricles, causing them to contract from the base upwards

How does the nervous system react when blood pressure is higher than normal

• If blood pressure is higher than normal, pressure receptors in the aorta and wall of carotid artery sends more impulses via sensory neurones to the cardiac centre

• Cardiac centre sends more impulses via parasympathetic neurones to the SAN and acetylcholine is released

• Heart Rate decreases

• Blood Pressure decreases

How does the nervous system react when blood pressure is lower than normal

• If blood pressure is lower than normal, pressure receptors in the aorta and wall of carotid artery sends more impulses via sensory neurones to the cardiac centre

• Cardiac centre sends more impulses via sympathetic neurones to the SAN and nor-adrenaline is released

• Heart Rate increases

• Blood Pressure increases

How does the nervous system react when blood pH is lower than normal/ high CO2 concentration

• Chemoreceptors in wall of carotid artery sends more impulses to the cardiac centre Cardiac

• Cardiac centre sends more impulses via sympathetic nervous system to the SAN and noradrenaline is released

• Heart rate increase

• Increased blood flow removes CO2 faster via lungs, CO2 levels hence blood pH returns to normal

How does the nervous system react when blood pH is higher than normal/ low CO2 concentration

• Chemoreceptors in wall of carotid artery sends more impulses to the cardiac centre Cardiac

• Cardiac centre sends more impulses via parasympathetic nervous system to the SAN and acetylcholine is released

• Heart rate decreased

• Decreased blood flow removes CO2 slower via lungs, CO2 levels hence blood pH returns to normal

Structure of a muscle

• A muscle contains ___________ that are arranged parallel along the length of the muscle

• Each muscle fibre is a single muscle cell

• Inside muscle cells/muscle fibres are many _________

• Myofibrils are ________________ that cause contraction

• These split up into sections striped called ____________

• Sarcomeres contain thin filament (____) and thick filament (____)

• A muscle contains bundles of muscle fibres that are arranged parallel along the length of the muscle

• Each muscle fibre is a single muscle cell

• Inside muscle cells/muscle fibres are many myofibrils

• Myofibrils are bundles of protein filaments that cause contraction

• These split up into sections striped called sarcomeres

• Sarcomeres contain thin filament (actin) and thick filament (myosin)