Muscular System

Question 1

Structure + Function

Answer 1

• Contraction: thin actin, thick myosin filaments> light and dark alternating bands due to overlap> separated into sarcomeres> actin and myosin slide over each other, cross bridges form at heads of each, shortens sarcomere> requires ATP, CA2+ required> single nerve + muscle fibres= motor unit> neuromuscular junction (between nerve fibre + muscle) = ACh responsible for transmitting impulse across gap
• Tone: slight state of tension= isometric contraction tension, no movement (tone increases) isotonic contraction movement generated> more muscle used, larger it becomes (hypertrophied)> less muscle used, shrinks (atrophied)
• Anatomy: aponeurosis= tendon is a flat sheet of connective tissue> sphincter= circle ring, control entrance + exit> bursa= connective tissue sac lined with synovial membrane + filled with synovial fluid (reduces friction)> bursa: can wrap all the way around the tendon (synovial sheath)

Question 2

Muscles

Answer 2

• Intrinsic: within one region of the body (acts on joints in that part only)
• Extrinsic: one region to another, alter whole part’s position in relation to another
• Types: Smooth (involuntary)= not under control of animal, contains autonomic NS, responds to hormones (oxytocin), spindle shaped, central nucleus, no striations. > Cardiac= heart, elongated, branched, Purkinje fibres (inc. transmission speed). > Skeletal (striated)= bones and cartilage by tendons, voluntary, bundles of parallel fibres, 3 layers of connective tissue surrounding (endomysium, perimysium, epimysium)

Question 3

Muscles of the Head

Answer 3

• Facial expression: intrinsic muscles (move lips, cheeks, nostrils, eyelids + external ears)= innervated by the facial nerve (cranial nerve VII)
• Mastication: O=origin, I=inserts > temporalis= closes the jaw, largest + strongest head muscle, covers most of dorsal and lateral skull surface, covers the temporal fossa + coronoid process of mandible > Digastricus= opens jaw (gravity aids), caudoventral surface mandible O is jugular process (occipital bone), I is ventral surface (mandile) > Masseter= closes jaw, lateral to mandible, O is zygomatic arch, I is masseteric fossa.
• Eye: extrinsic muscles (extraocular muscles) move the eye in its bony socket > rectus= insert on sclera of eyeball near “equator” > oblique= rotate the eye about its visual axis > retractor bulbi= muscular cone around the optic nerve + pulls eye deeper into its socket
• Tongue: intrinsic + extrinsic (delicate movements)
• Pharynx, Larynx, Soft Palate: carry out specific functions (swallowing, sound making)
• Head to Neck: extrinsic muscles attach the two and moves in relation to the neck

Question 4

Muscles of the Trunk

Answer 4

• Vertebral Column: epaxial dorsal to transverse processes of vertebrae, numerous, arranged in 3 longitudinal groups, span whole of column, supports spine, extends vertebral column + allows lateral flexion. hypaxial ventral to transverse processes of vertebrae, regions associated with back + neck, flex neck + tail, contribute to VC flexion
• Thoracic: external intercostals* most superficial, O=caudal border of one rib, I=cranial border of rib behind, assist in inspiration. internal intercostals lie below external intercostals within the intercostal space, O=cranial surface of one rib, I=caudal border of rib in front, assist in expiration (largely passive). diaphragm sheet of muscle separating the thoracic + abdominal cavities, central tendon + muscular periphery, main inspiration muscle
• Abdominal: composed of 4 muscles (broad, flat sheets), fibres in all directions gives abdominal wall strength, protect organs + abdominal structures
• external abdominal oblique* most superficial, O=lateral surface of ribs + lumbar fascia, T=wide aponeurosis(linea alba)
• internal abdominal oblique* intermediate muscle, T: aponeurosis (linea alba)
• transversus abdominus* deepest, T=aponeurosis (linea alba)
• rectus abdominis* O=1st rib + sternum, I=pubis
• area of inguinal ring* slit-like opening in aponeurosis of EAO in groin region, blood vessels from abdomen>external genitalia + mammary glands (spermatic cord to scrotum)
• linea alba* combined aponeuroses of 3 lateral abdominal muscles (Xiphoid process> pubic symphysis)

Question 5

Muscles of Forelimb

Answer 5

• Extrinsic Group: attach forelimb to trunk (synsarcosis) by muscles + not joints brachiocephalicus flexes neck, bends neck laterally (limb is grounded), draws foreleg forward, protracts the limb (limb is taking weight). trapezius draws leg forward, protracts limb. latissimus dorsi retracts the forelimb. pectoral holds foreleg against body wall, adducts (brings it back to central line) limb.
• Intrinsic Group: originate + insert on the forelimb supraspinatus supraspinous fossa of scapula, inserts on greater tubercle of humerus, extends the shoulder, stabilises shoulder joint. infraspinatus infraspinous fossa of scapula, inserts on greater tubercle of humerus, stabilises + flexes shoulder joint
• Elbow Joint: triceps brachii 4 heads, separate origins (3 humerus, 1 scapula), I=olecranon (ulnar), extends elbow joint. biceps brachii supraglenoid tubercle (scapula), I=radius + ulnar, flexes elbow joint. brachialis head of humerus, I=radius + ulnar, flexes elbow joint
• Carpus + Digits: 2 Carpal Extensors O=Humerus, I=Carpals. 2 Digital Extensors O=Humerus, I=3rd Phalanx. 2 Carpal Flexors Run behind carpus + foot. 2 Digital Flexors Superficial inserts=2nd Phalanx, Deep inserts: 3rd Phalanx

Question 6

Muscles of Hind Limb

Answer 6

• Thigh: O=pelvic girdle, I=femur. gluteals 3 muscles (superficial, middle, deep) + tensor fascia latae from rump curve, extends hip joint, abducts (moves thigh away) thigh
• quadriceps femoris= cranial aspect of thigh, 4 parts, extends stifle joint, all 4 parts insert at same site on tibial tuberosity/crest* semimembranous= most medial, pelvis (femur to tibia) semitendinous= pelvis, I=tibia + calcaneus biceps femoris= most lateral, O=pelvis (femur to tibia), I=calcaneus (hock) gracilis= caudal half of medial surface of thigh, adducts limb Sartorius (caudal)= adducts limbs, I=cranial border of tibia pectineus= pubis to distal femur, adducts limb
• Gastrocnemius: O=caudal aspect of femur, I=calcaneus (hock), 2 sesamoid bones (fabellae) that articulate with caudal aspect (stifle joint), extends hock + stifle joint flexes
• Achilles Tendon: runs down back of leg to hock, includes tendons of insertion (gastrocnemius, biceps femoris, semitendinosus), I=calcaneus (bursa here), superficial digital flexor, over point of hock, I=digits
• Hock + Digits: anterior tibialis (proximal end of tibia to tarsus), flexes hock, rotates paw medially, 3 digital extensors (front of hock and foot), 2 digital flexors (behind foot, SDF from femur to phalanges - component of Achilles tendon)