Module 2 Study Guide: The Skeletal, Muscular, Nervous Systems, and Special Senses

The Skeletal System

Major Bones of the Human Body

The human skeleton consists of 206 bones, but certain major bones are essential for foundational knowledge in anatomy and physiology.

• Femur: The thigh bone; longest bone in the body.

• Humerus: Upper arm bone.

• Radius and Ulna: Forearm bones.

• Patella: Kneecap.

• Tibia and Fibula: Lower leg bones.

• Phalanges: Finger and toe bones.

Additional info: These bones are commonly referenced in clinical and anatomical contexts.

Classification of Bones

Bones are classified based on their shape and structure.

• Long Bones: Longer than they are wide (e.g., femur).

• Short Bones: Cube-shaped (e.g., carpals).

• Flat Bones: Thin, flattened, and usually curved (e.g., skull, ribs).

• Irregular Bones: Complex shapes (e.g., vertebrae).

Functions of Bones and the Skeletal System

The skeletal system provides structural support and performs several vital functions.

• Support: Framework for the body.

• Protection: Shields vital organs (e.g., skull protects brain).

• Movement: Muscles attach to bones for movement.

• Mineral Storage: Stores calcium and phosphorus.

• Blood Cell Formation: Hematopoiesis occurs in red marrow.

• Fat Storage: Yellow marrow stores fat.

Parts of a Typical Bone

Bones have distinct anatomical features, each with specific functions.

• Periosteum: Protective connective tissue membrane; passage for blood vessels and nerves.

• Sharpey’s (Perforating) Fibers: Secure periosteum to underlying bone.

• Epiphysis: Ends of long bones; contains spongy bone and red marrow.

• Diaphysis: Shaft of long bone; contains yellow marrow.

• Endosteum: Lines internal bone surfaces.

Bone Marrow: Yellow vs Red

Bone marrow exists in two forms, each with distinct functions and locations.

• Red Marrow: Produces blood cells; found in spongy bone of flat bones and epiphyses of long bones.

• Yellow Marrow: Stores fat; found in diaphysis of long bones.

Microscopic Anatomy of Bone

Bone tissue is composed of specialized cells and matrix.

• Osteocytes: Mature bone cells.

• Osteoblasts: Bone-forming cells.

• Osteoclasts: Bone-resorbing cells.

• Osteon (Haversian System): Structural unit of compact bone.

Bone Growth, Remodeling, and Formation

Bones grow and remodel throughout life, starting from a cartilage model.

• Bone Formation (Ossification): Begins with hyaline cartilage, replaced by bone tissue.

• Bone Growth: Increase in length and width during childhood.

• Bone Remodeling: Continuous process of bone resorption and formation.

Bone Fractures and Repair

Bone fractures are classified by their nature, and repair follows a stepwise process.

• Types of Fractures: Simple, compound, comminuted, greenstick, etc.

• Fracture Repair Steps:

  1. Hematoma formation

  2. Fibrocartilaginous callus formation

  3. Bony callus formation

  4. Bone remodeling

Axial vs Appendicular Skeleton

The skeleton is divided into two main regions.

• Axial Skeleton: Skull, vertebral column, rib cage.

• Appendicular Skeleton: Limbs and girdles (shoulder and pelvic).

Vertebral Column Sections

The vertebral column is composed of distinct regions.

• Cervical: Neck region (7 vertebrae).

• Thoracic: Chest region (12 vertebrae).

• Lumbar: Lower back (5 vertebrae).

• Sacral: Sacrum (5 fused vertebrae).

• Coccyx: Tailbone (4 fused vertebrae).

Atlas vs Axis

The first two cervical vertebrae have unique functions.

• Atlas (C1): Supports the skull; allows nodding.

• Axis (C2): Has the dens; allows rotation.

Types of Joints

Joints are classified by structure and function.

• Fibrous Joints: Immovable (e.g., sutures).

• Cartilaginous Joints: Slightly movable (e.g., intervertebral discs).

• Synovial Joints: Freely movable (e.g., knee, shoulder).

The Muscular System

Definition and Major Muscles

The muscular system refers to all muscles responsible for movement, posture, and heat production.

• Biceps, Triceps: Upper arm muscles.

• Gastrocnemius, Soleus: Calf muscles.

• Deltoid: Shoulder muscle.

• Latissimus Dorsi: Back muscle.

• Gluteus Medius and Maximus: Hip muscles.

• Trapezius: Upper back muscle.

Types of Muscle Tissue

Muscle tissue is classified into three types, each with unique features.

• Skeletal Muscle: Voluntary, striated, attached to bones.

• Cardiac Muscle: Involuntary, striated, found in heart.

• Smooth Muscle: Involuntary, non-striated, found in walls of organs.

Microscopic Anatomy of Muscle Fiber

Muscle fibers are specialized cells with unique structures.

• Sarcolemma: Muscle cell membrane.

• Sarcoplasm: Cytoplasm of muscle cell.

• Myofibrils: Contain contractile proteins.

• Connective Tissue Wrappings: Endomysium, perimysium, epimysium.

Functions of Muscle

• Movement: Locomotion and manipulation.

• Posture: Maintains body position.

• Heat Production: Maintains body temperature.

Sliding Filament Model of Contraction

Muscle contraction occurs via the sliding of actin and myosin filaments.

• Sarcomere: Functional unit of muscle fiber.

• Actin: Thin filament.

• Myosin: Thick filament.

• Contraction: Myosin heads bind to actin, pulling filaments together.

Equation:

$\text{Force} = \text{Number of cross-bridges} \times \text{Force per cross-bridge}$

Muscle Stimulation and Role of Calcium

Muscle contraction is initiated by nerve impulses and regulated by calcium ions.

• Acetylcholine: Neurotransmitter at neuromuscular junction.

• Acetylcholinesterase: Enzyme that breaks down acetylcholine.

• Calcium: Released from sarcoplasmic reticulum; triggers contraction.

Neuromuscular Junction

The neuromuscular junction is where motor neurons stimulate muscle fibers.

• Step-by-step events:

  1. Action potential arrives at axon terminal.

  2. Acetylcholine released into synaptic cleft.

  3. Acetylcholine binds to receptors on sarcolemma.

  4. Depolarization of muscle fiber.

  5. Calcium released, contraction initiated.

Graded Response and Types of Contraction

Muscle fibers respond to stimulation with varying force.

• Twitch: Single, brief contraction.

• Summation: Increased force with repeated stimulation.

• Unfused Tetanus: Partial relaxation between stimuli.

• Fused Tetanus: No relaxation; maximal force.

• Isotonic Contraction: Muscle changes length.

• Isometric Contraction: Muscle length remains constant.

• Muscle Tone: Continuous, partial contraction.

ATP Generation in Muscle Cells

Muscle cells generate ATP via aerobic and anaerobic pathways.

• Aerobic Respiration: Uses oxygen; produces more ATP.

• Anaerobic Respiration: No oxygen; produces lactic acid.

Equation:

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + 36\text{ATP}$

Body Movements

Muscles produce various types of movements.

• Flexion: Decreases angle (e.g., bending elbow).

• Extension: Increases angle (e.g., straightening knee).

• Rotation: Movement around axis (e.g., turning head).

• Abduction: Moves limb away from midline.

• Adduction: Moves limb toward midline.

• Circumduction: Circular movement (e.g., arm circles).

• Dorsiflexion: Lifting foot upward.

• Plantar Flexion: Pointing toes downward.

• Inversion: Turning sole inward.

• Eversion: Turning sole outward.

• Supination: Turning palm upward.

• Pronation: Turning palm downward.

• Opposition: Thumb touches fingers.

Muscle Interactions

Muscles work together in various ways.

• Synergy: Muscles cooperate for movement (e.g., biceps and brachialis).

• Antagonism: Muscles oppose each other (e.g., biceps vs triceps).

Muscle Naming

Muscles are named based on characteristics.

• Location: (e.g., temporalis)

• Shape: (e.g., deltoid)

• Size: (e.g., gluteus maximus)

• Direction of fibers: (e.g., rectus abdominis)

• Number of origins: (e.g., biceps)

• Action: (e.g., flexor carpi)

The Nervous System

Organization of the Nervous System

The nervous system is organized into central and peripheral divisions.

• Central Nervous System (CNS): Brain and spinal cord.

• Peripheral Nervous System (PNS): Nerves outside CNS.

Irritability: Ability to respond to stimuli. Conductivity: Ability to transmit impulses.

Glial Cells and Their Functions

Glial cells support and protect neurons.

• Astrocytes: Support, regulate environment.

• Microglia: Immune defense.

• Ependymal Cells: Produce cerebrospinal fluid.

• Oligodendrocytes: Form myelin in CNS.

• Schwann Cells: Form myelin in PNS.

• Satellite Cells: Support PNS neurons.

Neuron Microscopic Anatomy

Neurons are specialized for impulse transmission.

• Cell Body: Contains nucleus.

• Dendrites: Receive signals.

• Axon: Transmits signals.

• Myelin Sheath: Insulates axon; speeds transmission.

Myelin Sheath Formation

Myelin is formed differently in CNS and PNS.

• CNS: Oligodendrocytes form myelin.

• PNS: Schwann cells form myelin.

White Matter vs Gray Matter

• White Matter: Myelinated axons.

• Gray Matter: Cell bodies and unmyelinated fibers.

Afferent vs Efferent

• Afferent (Sensory): Carries impulses to CNS.

• Efferent (Motor): Carries impulses from CNS to effectors.

Functional Classifications of Neurons

• Sensory Neurons: Transmit sensory information.

• Motor Neurons: Transmit commands to muscles/glands.

• Interneurons: Connect sensory and motor neurons.

Action Potential Initiation and Generation

Action potentials are electrical impulses generated by neurons.

• Resting Potential: Maintained by sodium-potassium pump.

• Depolarization: Sodium enters cell.

• Repolarization: Potassium exits cell.

• Propagation: Impulse travels along axon.

Equation:

$\text{Na}^+ \text{influx} \rightarrow \text{Depolarization}$ $\text{K}^+ \text{efflux} \rightarrow \text{Repolarization}$

Reflex Arc

A reflex arc is the pathway for reflex actions.

• Receptor → Sensory Neuron → Interneuron → Motor Neuron → Effector

Gyri, Sulci, and Homunculus

• Gyri: Ridges on brain surface.

• Sulci: Grooves between gyri.

• Homunculus: Map of sensory/motor areas; shows body part representation.

Major Brain Regions and Functions

Refer to Table 7.1 for detailed functions. Additional info: Major regions include cerebrum, cerebellum, brainstem, diencephalon.

Physical Protection of CNS

• Meninges: Dura mater, arachnoid mater, pia mater.

• Cerebrospinal Fluid (CSF): Cushions, nourishes CNS; produced by choroid plexus, recycled via arachnoid villi.

• Blood-Brain Barrier: Protects brain from harmful substances; can hinder drug delivery.

Spinal Cord Structure

The spinal cord differs from the brain in structure.

• Central Canal: Contains CSF.

• Dorsal, Lateral, Ventral Columns: White matter tracts.

• Gray Matter: Butterfly-shaped core.

General Structure of a Nerve

• Bundle of axons surrounded by connective tissue.

Cranial Nerves

Cranial nerves are peripheral nerves arising from the brain.

Parasympathetic vs Sympathetic Nervous System

• Sympathetic: "Fight or flight"; active during stress.

• Parasympathetic: "Rest and digest"; active during relaxation.

Somatic vs Autonomic Nervous System

• Somatic: Controls voluntary movements.

• Autonomic: Controls involuntary functions.

Special Senses

Definition of Special Senses

Special senses include vision, hearing, equilibrium, taste, and smell.

Anatomy of the Eye

The eye consists of internal and external structures.

• Cornea: Transparent front layer.

• Iris: Colored part; controls pupil size.

• Lens: Focuses light.

• Retina: Contains photoreceptors.

Pathway of Light and Visual Transduction

Light passes through cornea → aqueous humor → pupil → lens → vitreous humor → retina. Photoreceptors convert light to electrical impulses, which travel via optic nerve to the brain.

Role of Tears

• Lubrication

• Protection

• Removal of debris

Rods vs Cones

• Rods: Detect dim light; located in peripheral retina.

• Cones: Detect color; concentrated in fovea.

Accommodation Reflex and Vision Defects

The accommodation reflex adjusts lens shape for near/far vision. Common defects include myopia, hyperopia, astigmatism; corrected with lenses.

Anatomy of the Ear and Hearing

Sound waves travel through external ear → tympanic membrane → ossicles → cochlea. Hair cells transduce sound to electrical impulses sent to the brain.

Static vs Dynamic Equilibrium

• Static Equilibrium: Maintains balance when stationary; involves otoliths in vestibule.

• Dynamic Equilibrium: Maintains balance during movement; involves semicircular canals.

Otoliths and Equilibrium

Otoliths are calcium carbonate crystals that detect head position changes.

Smell and Taste Relationship

Both senses require substances to be dissolved in liquid for detection; olfactory receptors are neurons in the olfactory epithelium.

Taste Buds and Perceptions

• Taste Buds: Sensory organs for taste; types include fungiform, foliate, circumvallate.

• Taste Perceptions: Sweet (sugar), salty (NaCl), sour (acids), bitter (alkaloids), umami (glutamate).

Bone Type	Example
Long	Femur
Short	Carpals
Flat	Skull
Irregular	Vertebrae

Muscle Tissue	Location	Control
Skeletal	Bones	Voluntary
Cardiac	Heart	Involuntary
Smooth	Organs	Involuntary

Neuron Type	Function
Sensory	Transmit sensory info
Motor	Transmit motor commands
Interneuron	Connect neurons