(A) Segment of a Muscle Fiber (Cell) Sarcolemma Myofibril Dark (A) Band Light (I) Band Nucleus

Home , Epimysium, Myofibril, Myofilament, Perimysium, Sarcolemma, Sarcomere

2/7/20

Muscle ﬁber Blood vessel (cell)

Perimysium

Epimysium (wraps entire muscle) Fascicle (wrapped by perimysium)

Endomysium (between ﬁbers) Tendon

Bone

Sarcolemma Z disc H zone Z disc

Thin (actin) myofilament Myofibril Thick (myosin) myofilament

(b) Myofibril or fibril I band A band I band M line (complex organelle composed of bundles Dark Light Nucleus of myofilaments) (A) band (I) band (a) Segment of a muscle fiber (cell)

Axon terminals at neuromuscular junctions Spinal cord

Motor Motor unit 1 unit 2 Sarcomere

M line Z disc Z disc Nerve Thin (actin) myofilament Axon of Motor motor neuron Thick (myosin) neuron myofilament cell bodies

Muscle Muscle fibers (c) Sarcomere (segment of a myofibril)

Slide 1 Myosin Actin Myelinated axon Nerve of motor neuron impulse Axon terminal of Nucleus neuromuscular junction Sarcolemma of the muscle fiber

Synaptic vesicle containing ACh 1 Nerve impulse reaches axon terminal of motor neuron. Axon terminal of motor neuron Mitochondrion Z Z 2+ H 2 Calcium (Ca2+) channels Ca2+ Ca open, and Ca2+ enters the Synaptic axon terminal. cleft Sarcolemma I A I Fusing synaptic vesicle Sarcoplasm 3 Ca2+ entry causes some ACh of muscle fiber (a) Relaxed sarcomere synaptic vesicles to release their ACh Folds of contents (the neurotransmitter sarcolemma acetylcholine) by exocytosis. receptor 4 Acetylcholine diffuses across the synaptic cleft and binds to receptors in the sarcolemma. Ion channel in Na+ K+ 5 ACh binds and opens channels sarcolemma opens; that allow simultaneous passage ions pass. of Na+ into the muscle fiber and K+ out of the muscle fiber. More Na+ ions enter than K+ ions leave, producing a local change in the electrical conditions of the membrane (depolarization). This eventually leads to an action ACh Degraded ACh Ion channel closes; potential. + Z Z Na ions cannot pass. 6 The enzyme acetylcholinesterase I A I breaks down ACh in the synaptic cleft, ending the process. Acetylcholinesterase K+ (b) Fully contracted sarcomere © 2018 Pearson Education, Inc. 9 © 2018 Pearson Education, Inc. 10

Regulatory proteins In a relaxed muscle fiber, the regulatory proteins Myosin-binding site The flood of calcium acts as the final trigger for Ca2+ forming part of the actin myofilaments prevent contraction, because as calcium binds to the myosin binding (see a). When an action potential regulatory proteins on the actin filaments, the (AP) sweeps along its sarcolemma and a muscle proteins undergo a change in both their shape and 2+ fiber is excited, calcium ions (Ca ) are released their position on the thin filaments. This action from intracellular storage areas (the sacs of the exposes myosin-binding sites on the actin, to which sarcoplasmic reticulum). the myosin heads can attach (see b), and the myosin heads immediately begin seeking out binding sites. Myosin myofilament Actin myofilament Upper part of thick filament only (b) (a)

Muscle contracting

The free myosin heads are “cocked,” much like an oar ready to be pulled on for rowing. Myosin attachment to actin causes the myosin heads to snap Origin (pivot) toward the center of the sarcomere in a rowing motion. When this happens, the thin filaments are (c) slightly pulled toward the center of the sarcomere Brachialis (see c). ATP provides the energy needed to release and recock each myosin head so that it is ready to attach to a binding site farther along the thin filament.

Tendon Insertion

Hyperextension Extension

Flexion Hyperextension

Flexion Extension

Flexion

Extension

(a) Flexion, extension, and hyperextension of the shoulder and knee

Rotation

Abduction

Lateral rotation Adduction Circumduction Medial rotation

Dorsiﬂexion

Abduction

Adduction Circumduction Plantar flexion

(e) Dorsiﬂexion and plantar ﬂexion

Pronation Supination (radius rotates (radius and ulna over ulna) are parallel)

Inversion Eversion P s

(f) Inversion and eversion

Cranial Frontalis aponeurosis

Temporalis Opposition Orbicularis oculi Occipitalis

Zygomaticus Buccinator Masseter

Orbicularis oris Sternocleidomastoid

Trapezius (h) Opposition Platysma

Clavicle Pectoralis major

Deltoid

Sternum Rectus abdominis Pectoralis major Transversus abdominis Biceps Internal brachii oblique

Brachialis External oblique Brachio- radialis Aponeurosis

12th 12th rib thoracic vertebra

Iliac crest Psoas major Iliopsoas Gastrocnemius Iliacus 5th lumbar vertebra Anterior superior iliac spine

Sartorius Adductor group Rectus femoris Soleus Vastus lateralis Quadriceps* Vastus medialis Calcaneal (Achilles) tendon

Patella Medial malleolus Lateral Patellar malleolus ligament

Facial • Frontalis Facial • Orbicularis oculi Neck • Temporalis • Zygomaticus • Occipitalis • Masseter • Orbicularis oris • Sternocleidomastoid Neck • Trapezius Shoulder • Platysma • Trapezius • Sternocleidomastoid Thorax Shoulder/Back • Deltoid • Pectoralis minor • Deltoid • Pectoralis major Arm Arm • Serratus anterior • Triceps brachii • Triceps brachii • Brachialis • Biceps brachii • Latissimus dorsi • Intercostals Forearm • Brachialis Abdomen • Brachioradialis • Rectus abdominis • Extensor carpi radialis Forearm • External oblique longus • Brachioradialis • Internal oblique • Flexor carpi ulnaris • Flexor carpi radialis Hip • Transversus abdominis • Extensor carpi ulnaris • Gluteus medius Pelvis/thigh • Extensor digitorum • Iliopsoas • Gluteus maximus

Thigh • Sartorius • Adductor muscles Thigh (Quadriceps) Thigh Iliotibial tract • Rectus femoris • Adductor muscle • Vastus lateralis • Hamstrings: • Vastus medialis Biceps femoris • Vastus intermedius (not shown, deep to rectus femoris) Semitendinosus Semimembranosus Leg • Fibularis longus Leg • Extensor digitorum longus Leg • Gastrocnemius • Gastrocnemius • Tibialis anterior • Soleus • Soleus

• Fibularis longus Calcaneal (Achilles) tendon