Types of muscles Cardiac muscle found only in the heartSmooth muscle or involuntary muscle found in the walls of the digestive system, the bladder, the lungs and blood vessels Skeletal (or voluntary) muscle found in body muscles
Movement Muscles have three properties that allow them to work – 1.Contractibility = ability to contract or shorten 2.Extensibility = ability to be stretched 3.Elasticity = ability to return to the original length after stretching Movement occurs due to muscles pulling on bones either side of a joint. When a muscle works, it slides its filaments together (contraction), thus becoming shorter and thicker, and pulling the ends of the bones together, and bending (or straightening) a joint. Muscles can not push bones, so in order for the bones to move in the opposite direction, another set of muscles must contract, while the first set relaxes. Because muscles are elastic, they can stretch when relaxed, and shorten when contracted. These pairs of muscles are called agonist-antagonist pairs. The agonist is the muscle that is contracting or doing the work, while the antagonist is the muscle that is relaxing. Synergists are muscles that help by steadying a joint Fixators are synergists that fixate a joint (stop it moving)
Muscles and tendons Muscles are attached to bones by tendons. The tendon(s) closest to the body, (attached to the fixed bone), is/are called the tendon(s) of origin, while the tendon(s) furthest from the body, (attached to the moveable bone), is/are called the tendon(s) of insertion.
The sarcolemma is a thin transparent membrane surrounding each muscle cell Muscle fibres are cylindrical muscle cells They are made up of many thread-like myofibrils These are made up of many smaller protein filaments called myofilaments
Microscopic structure of muscles There are two types of myofilaments – thick and thin Actin makes up the thinner myofilaments Myosin makes up the thicker myofilaments A sarcomere is a unit containing overlapping bands of actin and myosin
The sarcomere The arrangement of the actin and myosin fibres give the muscles its striated or banded appearance. These are given different names: The I band is where only actin fibres are visible The A band are where actine and myosin overlap to form a darker appearance The Z line is where actin molecules are linked together A similar fainter line can be seen linking the myosin filaments – this is called the M line The H zone is where only myosin filaments are visible M line
Sliding filament model When the muscle contracts, the actin and myosin filaments slide over each other, pulling the z-lines closer and shortening the muscle This requires the use of energy in the form of Adenosine triphosphate When the muscle relaxes the actin and myosin filaments are pulled past each other and return to their previous locations, so the muscle returns to its previous length Actin and myosin don’t change in length – they just slide closer or further apart. Myofibrils comprised of actin and myosin myofilaments
Control of muscle movement Voluntary muscle contraction is initiated by nerve impulses, starting in the brain or spinal cord and travelling through the somatic division of the efferent tract of the peripheral nervous system. One motor neuron will control several muscle fibres. A motor unit is the motor neuron and all the fibres it controls
The neuromuscular junction The neuromuscular junction is the point where the message is passed from neuron to muscle The synaptic knob is the enlarged area at the end of the axon The motor end plate is depression in the surface of the muscle fibre The neurotransmitter used is acetylcholine
Roles of cerebrum and cerebellum The primary motor cortex initiates voluntary muscle contraction and at the same time sends messages to the cerebellum The cerebellum sends messages to co-ordinate different muscles so movement is smooth Balance receptors send messages to the cerebellum so it can track the position and movement occurring in the head Stretch receptors detect muscle and joint activity and send messages to the cerebellum so it can track movements of extremities Upper motor neurons have cell bodies in the cerebrum (and some in spinal cord) Lower motor neurons have cell bodies in the spinal cord
Roles of cerebrum and cerebellum The diagram shows the nerve pathways from the cerebral cortex Show the pathways from sensory receptors to and from cerebellum
Cerebellum involvement Taken from Newton and Joyce p218
Sample questions The neuron illustrated above would be classified correctly as (a) a sensory neuron. (b) a motor neuron. (c) a connector neuron. (d) there is not enough information to say.
Sample exam questions 1. Which of the following is NOT true of structure A? (a) It is surrounded by three layers of meninges. (b) Information from the body terminates in structure A's white matter. (c) Its surface is convoluted to provide greater surface area. (d) It is connected to, and able to influence, the cerebellum. 2. This question refers to the list of features below. (i) regulation of osmotic balance (ii) regulation of the heart rate (iii) coordination of posture and movement- (iv) temperature control Which of the above features are roles played by structure B? (a) (i), (ii) and (iii) only (b) (i), (ii) and (iv) only (c) (i), (ii), (iii) and (iv) only (d) (ii) and (iv) only 3. Which of the following statements is true of the fluid contained in structure C? (a) It is produced by the meninges. (b) It has an important role in protecting the brain from infection. (c) It assists with nourishment of the cerebral cortex. (d) It assists with temperature regulation in the brain.
Sample questions Using a diagram, explain the structures that comprise a synovial joint and their functions.
Synovial joints Synovial capsule surrounds the joint and helps stabilise it and hold it all together Synovial membrane is thin and smooth, to reduce friction, and secretes synovial fluid Synovial fluid is thick and sticky, and acts as a lubricant for the joint Articular cartilage provides a smooth surface to reduce friction as the bones move across each other Articular disc are cartilaginous discs which act as shock absorbers Bursae are fluid filled sacs which act as shock absorbers Accessory ligaments join the bones and keep them together
Sample questions Using diagrams, explain the main differences between compact bone, spongy bone and hyaline cartilage. Relate these differences to the functions of these tissues.
Comparing bone and cartilage Bone has a few cells but also lots of mineral matrix to make it strong, and a good blood supply, which makes capable of repair Compact bone is highly organised into osteons to make columnar Haversian systems – this gives it strength. Spongy bone is less organised, with more spaces – this makes it lighter. The spaces are filled with red bone marrow which make blood cells Cartilage has relatively few cells and lots of matrix. The matrix has more protein than minerals so it is strong and slightly elastic. It has less of a blood supply, so is slower to heal. Compact boneSpongy bone Cartilage