Anatomy: The Muscular System

Anatomy of the Muscular System

• Skeletal muscle functions include producing movement, maintaining posture, stabilizing joints, and generating heat through shivering.
• Additional functions of skeletal muscles involve protecting organs, forming valves, controlling pupils, supporting soft tissues, guarding entrances/exits, and storing nutritional reserves.

Characteristics of Muscle Tissue

• Excitability allows muscles to receive and respond to stimuli, typically a chemical stimulus (neurotransmitter, hormone, pH), resulting in action potentials along the sarcolemma and muscle contraction.
• Contractility is the ability to shorten when stimulated.
• Extensibility is the capacity to be stretched or extended.
• Elasticity enables muscles to recoil and resume their resting length after stretching.

Connective Tissue Sheaths

• Muscle fibers are single muscle cells.
• Muscles possess multiple connective tissue layers.
• The endomysium is a fine layer of areolar connective tissue that surrounds each muscle fiber (cell).
• The perimysium is a dense irregular connective tissue sheet around fascicles (groups of muscle fibers).
• The epimysium is a dense irregular fibrous connective tissue that surrounds the entire muscle.

Deep Fascia

• Deep fascia consists of a coarser layer of dense connective tissue, binding muscles into functional groups, such as hamstrings separated from quadriceps.

Muscle Attachment

• Muscles span joints and attach to bones, connecting to bone in at least two places: the origin (immovable or less movable bone) and the insertion (movable bone).

Types of Attachments

• Direct attachments involve the epimysium fusing to the periosteum of bone or perichondrium of cartilage.
• Indirect attachments involve tendons or aponeuroses.

Muscle Action

• Muscles can only pull; never push.
• Muscles operate cooperatively or in opposition.

Functional Groups of Muscles

• Prime movers (agonists) provide the major force for a particular movement, such as the brachialis in elbow flexion.
• Antagonists oppose or reverse a movement, providing resistance to prevent overshoot or control movement rate; a single muscle can be a prime mover for one action and an antagonist for another, like the triceps brachii in elbow flexion.
• Synergists muscles assist the prime mover, promoting the same movement or reducing undesirable/unnecessary movements, and some act as fixators to immobilize bone, aiding in posture.

Muscle Actions by Joint Position

• Muscles crossing on the anterior side of a joint produce flexion.
• Muscles crossing on the posterior side of a joint produce extension.
• Muscles crossing on the lateral side of a joint produce abduction.
• Muscles crossing on the medial side of a joint produce adduction.

Arrangement of Fascicles

• Fascicles facilitate movement parallel to the long axis like a strap-like muscle which may be strap-like (sartorius) or fusiform (biceps brachii).
• Short fascicles attach obliquely to a central tendon running down the muscle's length in pennate muscles.

Forms of Pennate Muscles

• Unipennate muscles insert fascicles into one side of the tendon, like the extensor digitorum longus.
• Bipennate muscles insert fascicles into the tendon from opposite sides, resembling a feather, such as the rectus femoris.
• Multipennate muscles have many feathers side by side, with all quills inserted into one large tendon, like the deltoid.

Circular Muscles

• Concentric rings surround external openings, contracting to close them, such as the orbicularis oculi (mouth) and sphincters. Convergent muscles have fascicles that converge toward a single tendon insertion, forming a triangular or fan shape, like the pectoralis major.
• Muscles with parallel fascicle arrangements shorten the most but are not typically very powerful.
• Muscles with greater numbers of fibers have greater power.
• Stocky bipennate and multipennate muscles, which pack the most fibers, shorten very little but tend to be powerful.

Naming Skeletal Muscles

• Naming is based on location, shape, size, direction of fascicles, number of origins, attachment locations, and action.
• Muscle location refers to the bone or body region the muscle is associated with (e.g., intercostals).
• Muscle shape include deltoid muscle (deltoid = triangle).
• Muscle size uses terms like maximus (largest), minimus (smallest), and longus (long).
• Direction of fascicles can be rectus (straight), transversus (right angles), or oblique (at angles).
• Number of origins refers to biceps (2) or triceps (3).
• Location of attachments are named according to the points of origin and insertion, with the origin named first.
• Muscle action refers to the action produced (e.g., flexor or extensor).
• Several criteria can combine, such as in the name extensor carpi radialis longus.

Muscles of Head and Facial Expression

• These muscles insert into skin or other muscles rather than bones.
• All are innervated by the facial nerve (CN VII).
• The epicranius is the main muscle of the scalp; bipartite muscle
  • Frontal belly (frontalis) covers the forehead and dome of the skull, raising eyebrows and wrinkling the forehead.
  • Occipital belly (occipitalis) is fixed to the aponeurosis and pulls the scalp posteriorly.
• The platysma, from the fascia of the chest to the mandible, helps depress the mandible and tense the skin of the neck.
• The orbicularis oculi is a sphincter muscle surrounding the rim of the orbit. It closes the eye, protects it from light and injury, blinks, squints, and draws eyebrows inferiorly. The orbicularis oris is a multi-layered muscle of the lips. It closes, purses, and protrudes the lips.
• The mentalis, from the mandible to the chin, forms a V-shaped muscle mass of the chin, protrudes the lower lip (pout), and wrinkles the chin.
• The zygomaticus, from the zygomatic bone to the corner of the mouth, raises the lateral corners of the mouth (smiling muscle).
• The buccinator, from the mandible to the orbicularis oris, is deep to the masseter, whistling, sucking, holding food in place when chewing, and especially active in nursing infants.
• The genioglossus, from the mandible to the inferior tongue and hyoid bone, is the prime mover of tongue protrusion. The styloglossus, from the styloid process of the temporal bone to the inferolateral tongue, retracts and elevates the tongue.
• The hyoglossus, from the hyoid bone to the inferolateral tongue.

Muscles of Movement: head, Mastication & Eyeball

• Four pairs of muscles are involved in mastication and are innervated by the mandibular divisions of cranial nerve V.
  • Masseter
    • Originates from the zygomatic arch and bone
    • Inserts into the angle and ramus of the mandible
    • It is the prime mover of jaw closure.
• Temporalis
  • Originates from the temporal fossa
  • Inserts into the coronoid process of the mandible
    • Elevates and retracts the mandible
    • Maintains a closed jaw at rest.
• Medial and Lateral Pterygoid
  • Originates from the pterygoid process of the sphenoid
  • Inserts into the mandible Provide additional jaw movements, grinding movements.

Action and Nerve Control of Extrinsic Eye Muscles

• Lateral rectus moves the eye laterally and is controlled by the abducens nerve (VI).
• Medial rectus moves the eye medially and is controlled by the oculomotor nerve (III).
• Superior rectus elevates the eye and turns it medially, controlled by the oculomotor nerve (III).
• Inferior rectus depresses the eye and turns it medially, controlled by the oculomotor nerve (III).
• Inferior oblique elevates the eye and turns it laterally, controlled by the oculomotor nerve (III).
• Superior oblique depresses the eye and turns it laterally, controlled by the trochlear nerve (IV).

Muscles of the Neck and Vertebral Column

• The sternocleidomastoid moves the head originating from axial skeleton, two-headed muscle deep to the platysma. Fleshy parts on either side of the neck. -Prime mover of head flexion (lift head when lying on back). Flexes and laterally rotates the head. Muscle action on one side for head rotation to opposite side, head tilts to same side.
• Scalenes: cervical vertebrae to first 2 ribs. More laterally and deep to platysma and SCM. Elevates first 2 ribs/ flexes rotates neck which aids in inspiration.
• Splenius : superficial/bandage muscle; head extension or rotation/tilts to same side; hyperextends head.
• Erector spinae consist of iliocostalis, longissimus, spinalis: providing resistance to bending and returning to erect position
• Semispinalis deeper composite muscle extends vertebral column and head, rotation of head, synergistic with sternocleidomastoid muscles
• Quadratus lumborum: individually flexes vertebral column laterally; jointly extends lumbar spine and fix 12th rib maintains upright posture
• External intercostals elevate rib cage during inspiration, internal intercostals depress rib cage during expiration Diaphragm : floor of thoracic cavity dome-shape when relaxed. Prime mover of inspiration, flattens on inspiration increasing thoracic volume

Muscles of Abdominal wall

– 4 paired muscles- lateral/anterior abdominal wall- facia and aponeurosis

• internal obliques
• external obliques
• transversus abdominis
• rectus abdominis
• Trunks movements: support viscera anterior flexion and rotation of trunk
• Actions; urination/defecation

Pelvic Floor and Perineum

• Funnel shaped muscles: levator ani coccygeus: seal inferior openings, support organs, superiorly release feces
• Perineum: region inferior pelvic diaphragm: genitalia and anus

Anterior and Posterior Thorax

• Join shoulder girdle to axial skeleton used for are Movement/scapula fixation
• Subclavious-Stabilizes and depresses pectoral girdle
• Pectoralis minor draws scapula forward/down Serratus anterior: ribs 1-8Holds scapula to chest wall levator scapulae elevates/adducts scapula Rhomboids: aid in scapula movement

Muscles that Cross Shoulder Joint

• 9 muscles Insert on/ move humerus 3 main movers arm1.pectoralis major 2. latissimus doorsi3. Deltoids

Rotator Cuff Muscles for Arm Movement

• Four muscles : supraspinatus, infraspinatus, teres minor, subscapularis are rotator cuff muscles reinforce capsule support synergist fixer act
• Deltoid: abducts prime

Latissimus dorsi and Synergists

• Latissimus dorsi broad flat back muscle move arm extensor that adduct medially rotates
• Swimming rower
• Synergists supraspinatus, infraspinatus, teres, minor subscapsularis and theres major coracobrachialis

Elbow Joint

• Anterior flexor muscles move Biceps brachii two points to flex elbow joint & supinates forearm brachialis ulna immideatly forearm flexion strong

Posterior Extensor Muscles

• Triceps bracii: scapula/humerous to ulna
• Only only muscle of posterior compartment of arm
• Forearm powerful extensor stabilize shoulder may help

Forearm Movement

• Actions: moves wrist; finger/thumb, pronation/supination
• Pronator teres quadratus pronate; supinator: synergist /flexion/supination

Anterior Muscles

• Anterior (all ) flexors via reticulum Posterior (all) via extensor reticulum

Posterior Muscles in the Hand

• Small weak in hand, move metacarpals/fingers like threading a needle Prime move in the hand include Extensor digitorum/ wrist and can abduct fingers using 5thmetacarpal Additional hand movement include wrist Extensor carpi raddials longus/brevis like the Extensor pollicis/ brevis/ longus

Actions of the Lower Limb

• Cross hip in and knee joints which move in the thigh/leg classified as anterior
• Most muscles flex femur/hip
• Most extend leg posterior
• Most extend thigh medial muscles- adduct thigh Actions flexion/ extension

Anterior Thigh Muscles

• Move thigh/flex
• Extend the leg and knee like iliopsoas prime move flexes thigh
• Tensor fascia late steers leg helps abduct thigh

Medial Muscles of the Thigh

• The move: Pectinous/ adduct flex /rotates thigh / Adductors: (longus/ Magnus/ Brevis: also flex/add thigh

Hamsrtings

Are muscles: thigh extension/knee flexion quadriceps antagonist; located:Bicecs femoris semitendinousus, semimembranousus

Extensors In the leg

Largest buttoock muscle Prime movers of the leg during running like Gluteus Maximus/ meduims

Ankle and Toe Dorsiflexion Leg Muscles

Muscles include Tibialis/Extnsr(fibula: shaf/greathloe);Extn digitorum longus

Central Nervous System

• Composed Brain/cord
• Integrates central control

Peripheral Nervous Sytems

• Brain/Spinal Nerves communications outside

Histology of the Nervous Tissue

• Highly cellular; little extracellular space. Has two Main classes of cells
• Neuroglia with Supporting/ wrapping cells for neurons - Astrocytes CNS -Microglial CNS - Ependymal cells CNS -Oligodendrocytes, CNS -Satelite PNS Schwann PNS

Neurons

• Excitable cells transmit electricals
• Neurons: main structural unit which transmit neurons Neurons Characteristics structure: -Specialized Impulse
• Long Lifetime to never divide
• High Metabolism; glucose /oxygen
• Structural Classification: by processes from unit

Classification of Neurons

Multipolar /Bipolar and Unipolar

• • Functions classify sensory direct/motor. interneurons / Brain has complexity due folding not weight Adults brain: cerebrum, Diencephalon brain stem and Cerebellum.

General Spinal Tract Arrangement

Grey/white matter for distribution

• White matters-myelinated Patterns: central (spinal cord) brain also for
• Features from simple Spinal expansion - Brain nuclei scattered/ CEREBRUM: cortex in gray outside. CEREBELLUM

Ventricles

Continuous with fill Spinal fluid

Surface Markings on the Brain

• Gyi raised markers, Sulchows shallow marks Longitude-hemispsheres TRANSVERSE/ cerebelum

  • Several: frontal parietal temporal insula- sulchi -Hemispheres:cerebral cortex and whiter matters

General Overview Cerebral Cortex

• Site brain aware. Sensory mind and behaviors Consists cellulars ( body & UN-) only two mm thick fold to triple

Functions

• Links more organization to process with another Areas include: -Motor _Sensory Associators hemisphere, touch motor sensation/ functions /contro motor

Brain damage effects

• Premotor cortex for touch Brocos affect Speech
• Sensory is conscious area

Body Map

Maps touch are visual spatial to create personality