Muscle types

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1) Involuntary muscle

Involuntary muscle 

  • It is controlled by the autonomic nervous system so is non conscious movement 
  • It does not appear striated whereas voluntary and cardiac do (long strands)
  • The of the muscle cells are known as 'spindle shaped' 
  • They contain small bundles of actin and myosin 
  • Each cell has one nucleus 
  • Contraction is slow and steady but tires very slowly

Examples include:

1) Walls of the intestine which have circular and longitudinal (length ways) bundles of muscle cells that work to move food along the intestine

2) Iris of the eye which has circular and radial bundles of muscle cells that control the intensity of the light entering the eye - contraction causes the radial muscles to dilate, contraction of the circular muscle constricts the pupil

3) The walls of the arteries and around the arterioles contain circular bundles that can contraction to reduce blood flow or relax to increase blood flow, this is important in exercise and temperature regulation

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2) Cardiac muscle

Cardiac muscle 

Cardiac muscle is found in three forms: 1) artial muscle 2) ventricular muscle 3) specialised excitatory and conductive muscle fibres

  • Excitatory and conductive muscle fibres make up the sinoatrial node which conducts the electrical activity generated (sent by the accelerator or vegas nerves from the medulla oblongata) to the artial walls (made up of artial muscle). Non-conducting fibres seperate the atria and the ventricle so the atrioventricular node conducts the activity over the ventricles via the Purkyne fibres
  • Some of the cardiac muscle is myogenic which is contracts without stimulation 
  • Cardiac muscle fibres are made of many individual cells connected in rows and have intercalated discs which are the cell membranes. The cells fuse at the ends to make gap junctions which allows the movement of ions to occur rapidly and therefore means action potentials are passed along very quickly. 
  • They appear striated like voluntary muscle but unlike smooth muscle
  • This contraction/relaxation is continuous through life, powerfully, without fatigue 
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3) Voluntary muscle

Voluntary muscle 

  • The movement of the skelton is caused by voluntary muscle contracting at the joints 
  • The muscle appease striated 
  • It contains several nuclei 
  • It has many cells that make up a fibre that is surrounded by a sarcolemma (plasma mambrane) and within the sarcolemma is the sarcoplasm (the cytoplasm). 
  • There are key features within the sarcoplasm: many mitochondria, an extensive specialised sarcoplasmic reticulum (endoplasmic reticulum) and many myofibrils which are contractile elements that are made up of smaller contractile elements called sarcomeres
  • They contract powerfully but tire quickly 
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