Muscles

HBS3B

The knee jointLabel the diagrams

The knee joint

1 – tendon2 – patella3 – bursa4 – synovial membrane5 – bursa6 – menisci (articular discs) 7 – cruciate ligaments 8 – articular cartilage 9 - synovial capsule10 – fibula 11 – femur 12 – ligament 13 – tibia

Types of musclesCardiac 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 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 shorten2. Extensibility = ability to be stretched3. 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 jointFixators 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.

Muscle structure

Muscle structure

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 musclesThere 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 visibleThe 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 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 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 movementVoluntary 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 axonThe motor end plate is depression in the surface of the muscle fibreThe 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 cerebellumThe diagram shows the nerve pathways from the cerebral cortexShow 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 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 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 questionsUsing 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 questionsUsing 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 bone Spongy boneCartilage