Musculoskeletal & Nervous System Practical Review

Joint Classification

Fibrous Joints

• Definition: Bones joined by dense connective tissue; essentially immovable (synarthrotic).
• Sub-types mentioned
  • Sy synchondrosis? (speaker’s slip – should be "synostosis" or "syndesmosis")
  • Gomphosis – peg-in-socket joints (e.g.
    teeth); immobile.

Cartilaginous Joints

• Also generally synarthrotic in examples given.
• Classic example tagged in lab questions: Pubic symphysis (cartilaginous, slightly movable but functionally treated here as synarthrosis).

Synovial (Diarthrotic) Joints

• Fully movable; examples: elbow, knee, shoulder, hip.
• Taggable structures
  • Articular (hyaline) cartilage – caps bone ends.
  • Joint (articular) capsule – fibrous sleeve enclosing the cavity.
  • Inner synovial membrane – produces synovial fluid.
  • Bursa – membrane-bound, fluid-filled “pillow” that reduces friction (especially around knee, shoulder).
  • Meniscus – crescent/circular fibro-cartilage in knee that deepens tibial surface.

Movements Vocabulary

• Lateral flexion – trunk/neck bends sideways.
• Rotation – head or limb around longitudinal axis (NOT flexion).
• Shoulder rotation distinguished from pronation/supination of forearm.
• Supination (“hold the soup” palms up) vs pronation (dump soup).
• Opposition – thumb to fingertip.
• Inversion (sole inward; common ankle sprain) vs eversion (sole outward).
• Elevation (jaw closes) vs depression (jaw opens).

Intervertebral Disc Anatomy & Pathology

• Nucleus pulposus – gelatinous center.
• Annulus fibrosus – concentric collagen rings.
• Bulging disc – annulus weakens/outpouches but nucleus remains contained; less severe.
• Herniated disc – annulus tears, nucleus pulposus extrudes; acidic material irritates nerve roots or cord.
• Conservative care (chiropractic) may temporarily lessen symptoms but doesn’t “fix” fibers; surgical options include discectomy or artificial filler.

Bone Health

• Osteoporosis = "bone full of holes"; loss of mineral density → fragility fractures, spontaneous collapse on falls.

Muscle Tissue Types

• Skeletal
  • Long, cylindrical, multinucleate, heavily striated.
  • Location: voluntary muscles attached to skeleton.
• Cardiac
  • Striated but branched; contains thick intercalated discs.
  • Exclusive to myocardium.
• Smooth
  • No striations, spindle-shaped; lines walls of viscera & blood vessels.

Skeletal Muscle Microanatomy

• Sarcolemma – muscle-cell plasma membrane.
• Sarcomere = region from Z-line to Z-line; functional contractile unit.
• Thin filament: actin backbone + tropomyosin “ribbon” + troponin complexes (Ca^{2+} binding sites).
• Thick filament: myosin with heads for cross-bridge cycling.

Motor Neuron

• Efferent neuron that conducts impulse from CNS to muscle fiber.

Naming Muscles – Key Principles & Examples

• Action: extensor, flexor (e.g.
  wrist flexors/extensors).
• Shape: deltoid (triangle).
• Orientation: rectus (straight).
• Heads: biceps (two), triceps (three).
• Circular arrangement: sphincter.

Functional Groups During Movement

• Agonist (prime mover) – main muscle producing action (Superman analogy).
• Antagonist – opposes or brakes the motion (villain).
• Synergist – helper(s) that enhance efficiency (Super-friends); concept also used in pharmacology (drug synergy).

Key Named Muscles & Regions Likely to be Tagged

Facial & Mastication

• Zygomaticus – “smile” pulls mouth corners up.
• Buccinator – cheek muscle; pushes food onto teeth.
• Temporalis – synergist in jaw elevation.
• Masseter – agonist in chewing (jaw elevation).

Thorax

• Pectoralis major (superficial) vs pectoralis minor (deep, smaller).

Arm & Forearm

• Biceps brachii – anterior arm, elbow flexor.
• Brachioradialis – forearm flexor assisting biceps.
• Triceps brachii – posterior arm, elbow extensor.
• Wrist flexors (anterior forearm) vs wrist extensors (posterior; “motorcycle throttle”).

Abdominal Wall (4)

• Rectus abdominis – “six-pack,” trunk flexion.
• External oblique – superficial diagonal fibers.
• Internal oblique – deeper diagonal opposite direction.
• Transversus abdominis – horizontal fibers, core stabilization.

Hip & Thigh

• Adductor group – pulls legs together.
• Quadriceps femoris (knee extension; \approx2–3× stronger than hamstrings)
  • Vastus medialis (teardrop, medial)
  • Vastus lateralis (lateral)
  • Rectus femoris (superficial, straight down femur)
  • Vastus intermedius (deep to rectus femoris)
• Sartorius – long strap crossing anterior thigh; aids external rotation.
• Tensor fasciae latae (TFL) + iliotibial (IT) band
  • Tightness → "duck-foot" gait; chronic mal-alignment can accelerate hip/knee degeneration.
• Tibialis anterior – dorsiflexes foot; tightness links to IT band issues.

Leg & Foot

• Calcaneal/Achilles tendon – common plantar-flexor tendon.

Hamstrings (posterior thigh – knee flexion, hip extension)

• Biceps femoris (lateral; two heads).
• Semitendinosus (medial, cord-like tendon).
• Semimembranosus (deep to semitendinosus).

Back

• Latissimus dorsi – broad, lateral back; primary pull-up muscle.
• Rhomboids – from spine to medial scapula; retract scapula (rowing motion).

Nervous System Overview

• Central Nervous System (CNS): brain + spinal cord.
• Peripheral Nervous System (PNS): all nerves radiating from CNS.

Neuron Anatomy

• Dendrites – branched input region (information in).
• Soma (cell body) – metabolic center.
• Axon – single long output fiber → axon terminal (synaptic knob).

Synapse Types & Components

• Presynaptic neuron releases neurotransmitter.
• Synaptic cleft – microscopic gap.
• Postsynaptic neuron (dendrite) receives signal.
• Motor neuron + muscle fiber: neuromuscular junction.
• Neuron + gland: neuroglandular synapse.

Neuroglia (Glial Cells)

• Ependymal cells – line ventricles; secrete cerebrospinal fluid (CSF).
• Microglia – CNS phagocytic immune cells.
• Astrocytes – structural “glue”; form blood–brain barrier.
• Oligodendrocytes (CNS) & Schwann cells (PNS) – generate myelin sheath.
  • Myelin = insulating layer analogous to rubber around electrical wire; concentrates current and speeds conduction.
  • Autoimmune demyelination (e.g.
    Multiple Sclerosis) → disrupted signaling, progressive motor deficits; in severe respiratory muscle involvement, can become fatal (ALS also referenced).

Clinical & Practical Connections

• Chronic mal-alignment of lower limb (toes in/out) adds torsional stress → long-term joint degeneration; proactive gait correction can prevent future hip/knee/ankle surgeries.
• Over-powerful quadriceps vs weaker hamstrings predisposes sprinters to hamstring tears.
• Tylenol (acetaminophen) noted as hepatotoxic via enterohepatic filtration (portal system) when overused.
• Chiropractic adjustments may transiently relieve bulging-disc symptoms but do not restore annulus fibers; definitive repair often surgical.

Quick Reference Equations / Values (few explicit in lecture)

• Calcium binding site: \text{Troponin} + \text{Ca}^{2+} \rightarrow \text{Tropomyosin shift} \rightarrow \text{Cross-bridge exposure}