4Types of muscles Cardiac muscle found only in the heart Smooth muscle or involuntary muscle found in the walls of the digestive system, the bladder, the lungs and blood vesselsSkeletal (or voluntary) muscle found in body muscles
5Movement Muscles have three properties that allow them to work – Contractibility = ability to contract or shortenExtensibility = ability to be stretchedElasticity = ability to return to the original length after stretchingMovement 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 jointFixators are synergists that fixate a joint (stop it moving)
6Muscles 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.
8Muscle structureThe sarcolemma is a thin transparent membrane surrounding each muscle cellMuscle fibres are cylindrical muscle cellsThey are made up of many thread-like myofibrilsThese are made up of many smaller protein filaments called myofilaments
9Microscopic structure of muscles There are two types of myofilaments – thick and thinActin makes up the thinner myofilamentsMyosin makes up the thicker myofilamentsA sarcomere is a unit containing overlapping bands of actin and myosin
10The sarcomereThe 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 visibleThe A band are where actine and myosin overlap to form a darker appearanceThe Z line is where actin molecules are linked togetherA similar fainter line can be seen linking the myosin filaments – this is called the M lineThe H zone is where only myosin filaments are visibleM line
11Sliding filament model Myofibrils comprised of actin and myosin myofilamentsWhen the muscle contracts, the actin and myosin filaments slide over each other, pulling the z-lines closer and shortening the muscleThis requires the use of energy in the form of Adenosine triphosphateWhen 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 lengthActin and myosin don’t change in length – they just slide closer or further apart.
12Control 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
13The neuromuscular junction The neuromuscular junction is the point where the message is passed from neuron to muscleThe synaptic knob is the enlarged area at the end of the axonThe motor end plate is depression in the surface of the muscle fibreThe neurotransmitter used is acetylcholine
14Roles of cerebrum and cerebellum The primary motor cortex initiates voluntary muscle contraction and at the same time sends messages to the cerebellumThe cerebellum sends messages to co-ordinate different muscles so movement is smoothBalance receptors send messages to the cerebellum so it can track the position and movement occurring in the headStretch receptors detect muscle and joint activity and send messages to the cerebellum so it can track movements of extremitiesUpper motor neurons have cell bodies in the cerebrum (and some in spinal cord)Lower motor neurons have cell bodies in the spinal cord
15Roles of cerebrum and cerebellum The diagram shows the nerve pathways from the cerebral cortexShow the pathwaysfrom sensory receptorsto and from cerebellum
16Cerebellum involvement Taken from Newton and Joyce p218
17Sample questionsThe 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.
18Sample exam questions1. 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 controlWhich 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) only3. 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.
19Sample questionsUsing a diagram, explain the structures that comprise a synovial joint and their functions.
20Synovial jointsSynovial capsule surrounds the joint and helps stabilise it and hold it all togetherSynovial membrane is thin and smooth, to reduce friction, and secretes synovial fluidSynovial fluid is thick and sticky, and acts as a lubricant for the jointArticular cartilage provides a smooth surface to reduce friction as the bones move across each otherArticular disc are cartilaginous discs which act as shock absorbersBursae are fluid filled sacs which act as shock absorbersAccessory ligaments join the bones and keep them together
21Sample questionsUsing diagrams, explain the main differences between compact bone, spongy bone and hyaline cartilage.Relate these differences to the functions of these tissues.
22Comparing bone and cartilage Compact boneSpongy boneBone has a few cells but also lots of mineral matrix to make it strong, and a good blood supply, which makes capable of repairCompact 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 cellsCartilage 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.