Muscles and how they work LCSC06 Emily Burtenshaw

A type of synapse: the neuromuscular junction cles/notes_muscles.html cles/notes_muscles.html In order to activate a muscle fibre, a nerve must make contact with it. A MOTOR neuron, its terminal axon, and a muscle fibre = a MOTOR UNIT The junction where the axon meets muscle is called the MOTOR END PLATE

Motor Unit Is comprised of a single nerve fibre, neuromuscular junction(s) and nerve fibre(s) In other words, a motor unit = the number of fibres in the muscle innervated by a single neuron This determines the precision of movement possible, as well as the force of contraction; more precise control possible with a low ratio

Facial muscles, tongue, muscles of mastication and larynx Have a low ratio of nerve fibre: muscle fibres Enables high degree of precision in movement Contrast this with larger limb muscles, or muscles to control posture Larynx 1:6-12 v Hip 1:2000

Mp-T0 Mp-T0 Directed study: What is the name of the medication available to help with the symptoms of MG? how does it work?

Muscles and how they contract: Directed study: read page in Atkinson & McHanwell or find relevant pages in other texts. Watch the videos below (it is recommended you do so in the order given): First, an overview of the musculoskeletal system OPE OPE

More animations of muscle contraction – the first is an overview, the rest should be viewed in the sequence given:

Now try and answer these exam-type questions 1) True/false: a)actin is a long, thin molecule b)The sarcoplasmic reticulum is the repository for Na + ions c)A myofibril contains many muscle fibres 2) What role does ATP play in muscle contraction? 3) Name the disease which is characterised by damage to the sarcolemma.

4) TRUE or FALSE: a. the actin filament has a binding site for the myosin filament b. In the resting state, ATP is bound to a region on the actin filament c. when Sodium (Na+) enters the sarcoplasmic reticulum, this results in the binding site being exposed on the actin filament.

5) Describe what happens during the power stroke phase of contraction. What happens to cause the filaments to slide in relation to one another? 6) What is the name of the energy carrying molecule involved in the process of muscle contraction? 7) How does this release of energy result in the relative movement of the actin and myosin filaments?

Sensory supply to muscles 40% of nerve supply for muscle is sensory in nature Sends information re range, rate and force of contraction, and position of muscle a. Proprioception = an awareness of body position and movements of parts of the body b. Kinaesthesia = awareness of body motion

a. Proprioceptors Muscle spindles Tendon organs (Golgi tendon organs) Joint kinaesthetic receptors

a. Muscle spindles

b. Tendon organs

b. Joint kinaesthetic receptors Some are in the capsule of a joint and respond to pressure Some are in the connective tissue outside the capsule and respond to acceleration/deceleration of joint movement Ligaments contain receptors similar to tendon organs 31Q 31Q

Muscle fibres vary in colour… Depending on the amount of myoglobin they contain Myoglobin = a red-coloured protein, binds oxygen, found in striated muscle Haemoglobin = oxygen binding protein found in the blood

Types of skeletal muscle fibre a. Slow-twitch, fatigue resistant fibres; found in the postural muscles of neck, back and legs b. Fast-twitch, fatigue resistant fibres; found in leg muscles c. Fast-twitch, B fibres; fatigable. White as opposed to a & b which are red. Strong, rapid contractions; muscles of the shoulders and arms MUSCLES have a mixture of all 3 fibres; proportion depends on function

Exercise can induce change in muscle fibres Think of a marathon runner v a weightlifter What type of fibres predominate in the key muscles in these athletes?

Workshop activity: Find out the type (smooth or striated), location and function of the following muscles: Stapedius External intercostals Orbicularis oris Vascular muscle (tunica media) Cricopharyngeus Vocalis Ciliary muscle Bronchiole muscles genioglossus

More sample exam questions: What is the sarcoplasmic reticulum and what is its main function in muscle cell contraction? What is meant by a motor unit? Compare the innervation of the facial muscles with that of the limbs, with reference to the motor units involved. What is the function of the joint kinaesthetic receptors?

What to do next: Ensure you have answered the directed study questions posed in this lecture Do some reading in preparation for next week (see timetable week 7): the Big Picture (the organisation of the nervous system) Chapters 6 and 8 in Atkinson & McHanwell; Seikel et al, Chap 11; Richards, Clark & Clarke, chap 1; Manasco, Chap 2