Functional Anatomy and Movement Science

FUNCTIONAL ANATOMY & MOVEMENT SCIENCE

SECTION I — FOUNDATIONAL PRINCIPLES

Anatomical Position

  • Definition: The standard reference position used in anatomy to describe the location and movement of body structures.
  • Characteristics of Anatomical Position:
    • Standing erect
    • Facing forward
    • Arms at sides
    • Palms forward (supinated)
    • Feet slightly apart, toes forward
    • Eyes directed anteriorly
  • Significance: This serves as the zero starting point for describing all planes and motions. All joint movements are defined relative to this position.

Anatomical Directions

  • Superior (cranial): Toward head
  • Inferior (caudal): Toward feet
  • Anterior (ventral): Front
  • Posterior (dorsal): Back
  • Medial: Toward midline
  • Lateral: Away from midline
  • Proximal: Closer to trunk
  • Distal: Farther from trunk
  • Superficial: Toward surface
  • Deep: Away from surface

Diagram Notes

  • Sketch Requirements: Draw a human figure in anatomical position (arms out slightly, palms forward).
  • Planes Illustrated:
    • Sagittal: divides left/right
    • Frontal (coronal): divides anterior/posterior
    • Transverse (horizontal): divides superior/inferior.
  • Directional Terms: Add around the figure for spatial reference.

Planes and Axes of Motion

Basic Motion Terminology

  • Planes and Axes:
    • Sagittal Plane (divides left/right):
    • Axis: Mediolateral axis
    • Example Motions: Flexion / Extension
    • Frontal (Coronal) Plane (divides front/back):
    • Axis: Anteroposterior axis
    • Example Motions: Abduction / Adduction
    • Transverse (Horizontal) Plane (divides upper/lower):
    • Axis: Vertical (longitudinal) axis
    • Example Motions: Rotation (internal/external)

Types of Motion

  • Flexion:
    • Description: Decrease joint angle (e.g., bending elbow)
  • Extension:
    • Description: Increase joint angle (e.g., straightening elbow)
  • Abduction:
    • Description: Movement away from midline (e.g., raising arm laterally)
  • Adduction:
    • Description: Movement toward midline (e.g., lowering arm)
  • Internal (medial) rotation:
    • Description: Anterior surface turns toward midline
  • External (lateral) rotation:
    • Description: Anterior surface turns away from midline
  • Circumduction:
    • Description: Circular movement combining flexion, abduction, extension, adduction
  • Elevation / Depression:
    • Description: Upward / downward scapular motion
  • Protraction / Retraction:
    • Description: Forward / backward scapular glide
  • Supination / Pronation:
    • Description: Forearm rotation (palm up / palm down)
  • Inversion / Eversion:
    • Description: Sole of foot in / out
  • Dorsiflexion / Plantarflexion:
    • Description: Toes up / toes down at ankle

Types of Bones

  • Bone Composition:
    • Compact (cortical): Dense outer shell for strength.
    • Spongy (cancellous): Porous inner structure with red marrow.

Diagram Notes for Bone Structure

  • Sketch Requirements: Sketch a long bone cross-section:
    • Label the epiphysis (ends)
    • Diaphysis (shaft)
    • Periosteum (outer layer)
    • Medullary cavity (yellow marrow)
    • Articular cartilage at ends.

OT Application Box: Bone Health & Loading

  • Therapist Focus: Emphasize weight-bearing tasks (e.g., standing, gripping) to promote bone density and prevent disuse osteoporosis after injury.
  • Encouragement for Clients:
    • Clients with immobilization or paralysis should perform functional reach or transfers to maintain skeletal loading.

Types of Muscles

  • Bone Types:
    • Long Bones: Length > width; act as levers (e.g., Humerus, Femur, Radius)
    • Short Bones: Equal dimensions; provide stability + some motion (e.g., Carpals, Tarsals)
    • Flat Bones: Protect organs, serve as attachment sites for muscles (e.g., Skull, Scapula, Sternum)
    • Irregular Bones: Have complex shapes (e.g., Vertebrae, Facial bones)
    • Sesamoid Bones: Form within tendons to improve leverage (e.g., Patella)

Muscle Types

  • Skeletal Muscle:
    • Control: Voluntary
    • Location: Attached to bones
  • Cardiac Muscle:
    • Control: Involuntary
    • Function: Pumps blood; branched, 1 or 2 nuclei in the middle
  • Smooth Muscle:
    • Control: Involuntary
    • Function: Regulates internal flow in walls of viscera and vessels (e.g., peristalsis); spindle-shaped with 1 nucleus in the middle.

Movement Nerves

  • Types:
    • Sensory (afferent): Carry information to CNS (e.g., Touch receptors from skin)
    • Motor (efferent): Carry commands from CNS to muscles.
    • Mixed nerves: Both motor & sensory; most peripheral nerves

Nerve Classifications

  • Cranial nerves: 12 pairs originating from the brain (e.g., Optic, Facial, Vagus)
  • Spinal nerves: 31 pairs that form plexuses from spinal cord (Cervical → Brachial → Lumbosacral)

Neuromuscular Junction (NMJ)

  • Definition: A specialized synapse between a motor neuron and skeletal muscle fiber that transmits the signal for contraction.
  • Functionality: A special chemical bridge where a motor neuron “talks” to a muscle fiber and tells it to contract. It’s not a physical connection—it’s a synapse using a chemical messenger (acetylcholine, ACh).

Step-by-Step Story of Transmission at NMJ

  1. Electrical Signal: Begins in the motor neuron; an action potential travels down the neuron’s axon to its terminal (imagine an electrical current racing down a wire).
  2. Calcium Entry: Voltage-gated calcium (Ca²⁺) channels open due to the electrical charge; calcium flows into the neuron terminal.
  3. ACh Release: Calcium influx causes synaptic vesicles to fuse with neuronal membrane, releasing ACh into the synaptic cleft (tiny space between neuron and muscle).
  4. ACh Binding: ACh crosses the cleft, binding to receptors on the muscle fiber’s motor end plate (part of the sarcolemma), opening sodium (Na⁺) channels.
  5. Muscle Fiber Depolarization: Sodium rushes into the muscle fiber, making the interior more positive, which spreads along the sarcolemma and down T-tubules.
  6. Calcium from SR: T-tubule voltage sensors signal the sarcoplasmic reticulum (SR) to release calcium into the muscle cell cytoplasm.
  7. Calcium Triggers Contraction: Released Ca²⁺ binds to troponin on thin filaments, moving tropomyosin to expose myosin binding sites on actin, allowing contraction (cross bridges form and filaments slide).
  8. Relaxation: Acetylcholinesterase (AChE) breaks down ACh in the cleft, allowing muscle to relax by pumping Ca²⁺ back inside the SR.

OT Clinical Applications

  • Myasthenia Gravis (MG): Autoimmune disorder where the body produces antibodies that attack ACh receptors at the NMJ, resulting in fewer effective receptors. Relevance: Encourage energy conservation and task pacing. Plan activities with rest breaks and adaptive techniques to manage fatigue.
  • Peripheral Nerve Injury: Damage to the motor neuron leads to loss of ACh release, resulting in muscle atrophy and degeneration of motor end plates. Relevance: Early gentle motions and electrical stimulation can preserve the motor end plate, preventing permanent loss of muscle activation potential.

Mnemonic for NMJ Sequence

  • Phrase: "Nerds Can Always Sing, The Sound Rings Clear Always."
    • Nerve impulse
    • Calcium in
    • ACh released
    • Synapse crossed
    • Triggers sodium entry
    • Spreads (depolarization via T-tubules)
    • Releases Ca²⁺ from SR
    • Contraction happens
    • AChE clears signal

Mechanism of Muscle Contraction — Sliding Filament Theory

Structural Components

  • Sarcomere: Functional unit of contraction (Z-line to Z-line).
  • Myofibrils: Bundles of actin (thin) and myosin (thick) filaments.
  • Regulatory Proteins: Tropomyosin and Troponin are key for controlling actin exposure.

Stepwise Process of Muscle Contraction

  1. Excitation: Neural impulse triggers Ca²⁺ release.
  2. Coupling: Ca²⁺ binds troponin, moving tropomyosin to uncover actin sites.
  3. Contraction: Myosin head forms a cross-bridge with actin and uses ATP for the power stroke.
  4. Detachment: ATP binding breaks the cross-bridge, resetting the myosin.
  5. Relaxation: Ca²⁺ is pumped back into the SR; actin sites are covered; the muscle lengthens.

Key Principle

  • Contraction strength relies on the number of cross-bridges formed.

Diagram Notes

  • Sketch Requirements: Illustrate a sarcomere with overlapping actin & myosin; label Z-lines, A-band, I-band, H-zone; demonstrate shortening during contraction with arrows pointing inwards.

OT Application Box: Energy & Fatigue

  • ATP Demand: Increases during sustained contractions; fatigue occurs when ATP or Ca²⁺ recycling slows. For neuromuscular retraining, maintain balance between repetitions and rest to ensure optimal cross-bridge efficiency.
  • Clinical Relevance: Post-stroke therapy employs short, graded contractions to safely rebuild motor unit recruitment and strength.