Muscular System – Part 2: Muscle Locations, IM Injections, Plantar Fasciitis, and Urinary Stress Incontinence

Muscular System – Part 2

Overview of Muscle Locations within the Human Body

This section provides an anatomical overview of major skeletal muscles, organized by body region. Understanding muscle locations is essential for clinical practice, movement analysis, and the administration of intramuscular injections.

• Head Region: Includes muscles of facial expression and mastication such as occipitofrontalis, orbicularis oris, masseter, and temporalis.

• Neck Region: Key muscles include sternocleidomastoid, digastric (anterior belly), sternohyoid, and omohyoid.

• Ventral Thorax & Abdominal Region: Major muscles are pectoralis major, rectus abdominis, external oblique, internal oblique, and transversus abdominis.

• Thorax Region: Includes the diaphragm, external intercostal, internal intercostal, and quadratus lumborum.

• Dorsal Thorax Region: Features the trapezius, latissimus dorsi, deltoid, supraspinatus, and infraspinatus.

• Forearm: Includes biceps brachii, brachialis, brachioradialis, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris.

• Gluteal Region: Gluteus maximus and gluteus medius are the primary muscles.

• Ventral Leg Region: Includes tensor fasciae latae, quadriceps femoris group (rectus femoris, vastus lateralis, vastus medialis), sartorius, and gracilis.

• Dorsal Leg Region: Biceps femoris is a key muscle.

• Lower Leg Region: Includes tibialis anterior, extensor digitorum longus, fibularis longus, soleus, gastrocnemius, and the calcaneal (Achilles) tendon.

Example: The deltoid muscle is a common site for intramuscular injections due to its accessibility and muscle mass.

Eyeball: Extrinsic Muscles

Extrinsic eye muscles control the movement of the eyeball but do not participate in vision accommodation. They are divided into straight (rectus) and oblique muscles.

• 4 Straight Fiber Muscles: Superior rectus, inferior rectus, lateral rectus, medial rectus

• 2 Oblique Fiber Muscles: Superior oblique, inferior oblique

Example: The lateral rectus abducts the eye, moving it away from the midline.

Intramuscular (IM) Injections

Intramuscular injections deliver medications deep into muscle tissue, allowing for rapid absorption due to the rich vascular supply. They are commonly used for vaccines, hormones, and emergency medications.

• Penetration Level: IM injections penetrate through the skin and subcutaneous tissue into the muscle.

• Benefits: Faster absorption than oral or subcutaneous routes; suitable for larger volumes of medication.

• Common Sites:

  • Deltoid muscle (upper arm)

  • Vastus lateralis (lateral thigh)

  • Gluteus medius (upper outer quadrant of the buttock)

• Examples of Medications: Antibiotics, contraceptive hormones (e.g., Depo-Provera), epinephrine (for severe allergic reactions), antipsychotics.

Example: The deltoid is often used for adult vaccinations, while the vastus lateralis is preferred for infants.

Injection Type	Penetration Depth	Absorption Speed	Common Sites
Intramuscular (IM)	Muscle tissue	Fast	Deltoid, Vastus lateralis, Gluteus medius
Subcutaneous (SC)	Subcutaneous fat	Moderate	Upper arm, thigh, abdomen
Intravenous (IV)	Vein	Immediate	Forearm, hand

Plantar Fasciitis

Plantar fasciitis is the inflammation of the plantar fascia, a thick band of fibrous tissue connecting the heel bone to the toes. It is a common cause of heel pain, especially in runners and individuals with prolonged standing or improper footwear.

• Causes: Repetitive injury, running, walking, inadequate shoes, jumping, or landing on feet.

• Symptoms: Heel pain, especially with first steps in the morning or after periods of rest.

• Treatments: Ice, heat, stretching exercises, shoe inserts, and in severe cases, surgery.

Example: Stretching the plantar fascia and calf muscles can help relieve symptoms and prevent recurrence.

Urinary Stress Incontinence

Urinary stress incontinence is the unintentional loss of urine during activities that increase intra-abdominal pressure, such as coughing, sneezing, or exercise. It is more common in women, especially after childbirth.

• Causes: Weakness or damage to the pelvic floor muscles (e.g., levator ani), sphincter dysfunction, or tissue damage from childbirth or surgery.

• Symptoms: Leakage of urine during physical activity or exertion.

• Treatment: Kegel exercises (to strengthen pelvic floor muscles), physical therapy, lifestyle modifications, and in some cases, surgery.

Example: Kegel exercises involve the repeated contraction and relaxation of pelvic floor muscles to improve continence.

Type of Incontinence	Cause	Typical Treatment
Stress Incontinence	Pelvic floor weakness, childbirth, surgery	Kegel exercises, surgery
Urge Incontinence	Overactive bladder muscles	Bladder training, medications
Overflow Incontinence	Bladder outlet obstruction	Catheterization, surgery

Additional info: Strengthening the pelvic floor is also important for men after prostate surgery to prevent incontinence.