Muscular System (1) PDF

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Summary

Muscular System lecture 1, week 6. ...

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Key points: 1) Fascicle arrangement correlates with muscle power and range of motion 2) Names of muscles provide clues to their function, location, structural characteristics or origin and insertion 3) Recognise the major functional groups of muscles of the axial & appendicular and their actions

SKELETAL MUSCLE TISSUE ✓ Moves by the body pulling on bones to which it inserts ✓ Contraction is an active process while relaxation is a passive process There are 640 muscles in the human body!

Muscle attachments to bone are direct or indirect. • At ends of muscles collagen fibres of fascicles merge; tendons or aponeuroses •

Tendons o Attach muscles to specific points on bones • Aponeuroses o Broad sheet providing attachment over a large area e.g skull, abdomen o May involve more than one bone Some muscles attach directly to bone e.g brachialis, temporalis – epimysium fuses to periosteum

MUSCLE ARCHITECTURE FASCICLES

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Muscle fibres in a single fascicle are parallel

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Organisation of fascicles in relation to the muscle tendon varies Fascicular arrangement is correlated with the amount of power of a muscle can produce and the range of motion a muscle can produce

Muscle types based on fascicular organisation

4 major arrangements: 1. Parallel •

Have parallel fibres

• Two types: strap and fusiform (spindle) 2. Pennate • Feather-like arrangement • 3 sub-divisions 3. Convergent • Triangular 4. Circular •

Sphincter

PARALLEL • • • •

Fascicles run parallel to long axis Most body muscles Strap nor cylindrical Diameter increases on contradiction

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Tension in muscle depends on number of fibres Large range of motion

PENNATE • Fibres run at an oblique angle to tendon insertion • Have more muscle fibres than parallel muscles • Stronger contraction than parallel muscles of same size 3 types: unipennate, bipennate, multipennate CONVERGENT • Fascicles extends over a broad area •

Converge on a common attachment site

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Triangular shape

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Versatile because contractions of different parts of a muscle may change pull direction

CIRCULAR • Orifices and sphincters • •

Concentrically arranged fibres around an opening or recess Contraction decreases lumen diameter

MUSCLE CONTRACTIONS AND LEVERS •

Muscles (apply force) to pull bones (levers) to move body parts via joints (fulcrums).

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Skeletal muscles do not work in isolation Nature & site of attachment determine force, speed and direction of contraction o All interrelated o force x distance = resistance x distance

LEVERS

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Levers change: - direction of an applied force - Distance and speed of movement caused by force - Effective strength of an applied force Produces mechanical advantage or disadvantage Depends on location of fulcrum, load and effort. When fulcrum is located far away from applied force, lever works at a mechanical advantage >> allows a small force to move a large load over a short distance When fulcrum is located close to applied force and load is further away, lever works at a mechanical disadvantage >> reduces the load it can move, however, load can be moved faster over a greater distance 3 classes of levers Note, not all muscles act as part of the lever system

1ST CLASS LEVERS ▪ See-saw type ▪ Fulcrum is between load and applied force ▪ Load moves in opposite direction to applied force ▪ Can produce mechanical advantage or disadvantage ▪ Only a few examples in the body - Flexion/extension of neck at atlanto-occipital joint - Chewing and the temporomandibular joint (incisors vs molars) 2ND CLASS LEVERS ▪ Wheel-barrow like ▪ Force further away from fulcrum than load\load moves in same direction as applied force - Small force can move large load but slower than in 1 st class syst,e

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- Force is increased at expense of speed and distance - Produce mechanical advantage Very few examples in body Are ‘power levers’

3RD CLASS LEVERS ▪ Most common in body ▪ Force is close to fulcrum and away from load ▪ Load moves in same direction as force ▪ Works at mechanical disadvantage to move small loads long distances at fast speeds ▪ Is the ‘speed lever’

Muscle attachments - All muscles cross at least one joint - Usually, the bulk of a muscle lies proximal to the joint being crossed - All muscles have at least 2 attachments o Origins (proximal) often fixed position o Insertion (distal) o Distal attachment moves the muscle towards its origin o In limbs, origin is always proximal, and insertion is distal o Other parts of the body do not always follow this rule Muscle actions - Do not act alone - Prime movies: agonist. Is responsible for movement - Antagonist: muscle whose action opposes that of the agonist. Functional opposite - Synergist: helps prime mover and reduces unwanted movement - Fixations: help prime mover. Stabilises proximal end of joint or limb during movement E.g. elbow flextion

Muscle nomenclature is based on: 1. Location e.g biceps brachii, orbicularis oculi 2. Direction e.g external oblique (lat lower back), inferior oblique (eye) 3. # Origins e.g biceps femoris (thigh), triceps brachii

4. Action e.g pronator teres (arm) 5. Shape e.g trapezius, deltoid 6. Origin-insertion e.g sternocleidomastoid (head/neck) 7. Size e.g gluteus maximus, pectoralis major

MUSCLE GROUPS AND FUNCTION -

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Like bones can be separated into Axial (60%) and Appendicular (40%) Axial muscles originate on the axial skeleton Position head and spinal column Move ribs No role in support or movement of limb girdles Appendicular muscles stabilise or move parts of limbs

TIPS TO IDENTIFY MUSCLES • • •

Body region: axial; appendicular Compartment: anterior or posterior What joints are crossed?

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If muscle contracts what action does it have on a joint?

AXIAL MUSCLE GROUPS

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Head and neck muscles that are not associated with the vertebral column Vertebral column muscles Abdominal muscles Pelvic floor muscles

AXIAL MUSCLES OF THE HEAD Head: - Facial expression - Mastication - Eye movement - Tongue movement - Scalp Neck: - Sternocleidomastoid & anterior triangle - Pharynx/larynx AXIAL MUSCLES OF THE VERTEBRAL COLUMN - Anterior muscles = flexors -for neck (scalene) and lower back - Posterior muscles = extensors Erector spinae

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Deep spinal muscles connect and stabilise vertebral column Postural support

AXIAL MUSCLES OF LOWER TRUNK 4major muscles that as a group flex the vertebral column 1. Reclusive Abdominis (abs) - Flex trunk, compress abdominal cavity - Inserts into lines alba - Separated by tendinous intersections (“6 pack”) 2. Internal oblique - Rotation and lat flexion 3. Transverse abdominus - Deep to IO - Core; to compress abdominal cavity 4. External oblique - Rotation and lat flexion Protects viscera, provides forces for urination, defecation, vomiting & child birth AXIAL MUSCLES OF PELVIS - Support pelvic cavity organs - Flex sacrum and coccyx - Control defecation and urinary movements via sphincter - Perineum is muscular sheet forming floor Anal & urogenital triangles Role in sexual arousal APPENDICULAR MUSCLES - Stabilise pectoral and pelvic girdles. – shock absorbers; weight support - Move limbs Major groups: Shoulder, upper limb, hip, lower limb MUSCLES THAT MOVE THE PECTORAL GIRDLE 1. Trapezius Shoulder shrug and scapula stabilisation 2. Deltoid Prime shoulder abductor. Assists in flexion & extension 3. Latissmus dorsi Prime shoulder extensor. Synergy started adductor of humerus 4. Pectoralis major -rimes shoulder flexor. Also Addict arm/medial rotation due to clavicle and sternum attachments

MUSCLES THAT POSITION THE SCAPULA 1. Serratus anterior Originates on ribs and inserts into anteromedial surface Contraction abducts/protracts scapula and moves shoulder anteriorly 2. Pectoralis minor Helps depress and protract scapula at clavicular end 3. Coracobrachialis Adductor arm. Only shoulder flexor...