BIOL 109 Exam II Study Guide: Skeletal, Muscular, Nervous, Senses, and Endocrine Systems

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Chapter 6: The Skeletal System

Functions of the Skeletal System

The skeletal system provides structural support, protection, and enables movement. It also plays a crucial role in mineral storage and blood cell production.

Support: Acts as the framework for the body, allowing attachment of soft tissues and organs.
Mineral Storage: Stores calcium and phosphate within the bone matrix.
Blood Cell Production: Hematopoiesis occurs in red bone marrow, producing blood cells.
Protection: Bones such as the skull, thorax, and pelvis protect vital organs.
Movement: Bones serve as levers for muscles to pull, enabling movement.

Structure of a Typical Long Bone

Long bones have specialized regions and coverings that support their function and growth.

Diaphysis: The shaft; surrounds the medullary cavity.
Medullary (Marrow) Cavity: Contains bone marrow.
Epiphyses: Enlarged ends of the bone.
Articular Cartilage: Covers the epiphyses, reducing friction at joints.
Periosteum: Outer fibrous covering.
Endosteum: Inner lining of the marrow cavity and spongy bone.
Compact Bone: Dense, strong outer layer.
Spongy Bone: Porous inner bone, supports marrow.

Bone Cells & Calcium Homeostasis

Bone tissue is maintained and remodeled by specialized cells, regulated by hormones to maintain calcium balance.

Osteocytes: Mature bone cells in lacunae; maintain bone matrix.
Osteoblasts: Build bone; produce proteins and promote mineral deposition; become osteocytes when trapped.
Osteoclasts: Break down bone (osteolysis); large, multinucleated, immune-derived cells.
Calcitonin: Hormone that promotes calcium deposition in bone.
Parathyroid Hormone (PTH): Promotes calcium resorption from bone and absorption in intestines.

Bone Growth & Development

Bones grow and develop through two main processes, allowing for both length and diameter increases.

Intramembranous Ossification: Formation of flat bones from fibrous connective tissue (e.g., skull, mandible, clavicle, patella).
Endochondral Ossification: Formation of bones from hyaline cartilage; primary ossification center in diaphysis, secondary in epiphyses.
Epiphyseal Cartilage: Enables longitudinal growth; becomes epiphyseal line after growth ceases.
Appositional Growth: Increase in bone diameter; new bone added externally, resorption internally.

Bone Disorders

Several disorders affect bone growth, density, and function.

Osteoporosis: Reduced bone density, increased fracture risk.
Gigantism: Excess growth hormone (GH) before puberty.
Acromegaly: Excess GH after puberty.
Pituitary Growth Failure: Reduced cartilage activity.
Marfan Syndrome: Excess cartilage growth, cardiovascular issues.
Achondroplasia: Early fusion of epiphyseal plates.
Fibrodysplasia Ossificans Progressiva: Soft tissue ossification.

Chapter 7: The Muscular System

Muscle Organization

Muscles are organized into layers of connective tissue, which support and connect muscle fibers.

Endomysium: Surrounds individual muscle fibers.
Perimysium: Surrounds bundles (fascicles) of fibers.
Epimysium: Surrounds the entire muscle.
Tendon: Cord-like connective tissue attaching muscle to bone.
Aponeurosis: Sheet-like connective tissue attachment.

Muscle Tissue Types

There are three main types of muscle tissue, each with distinct structure and function.

Skeletal Muscle: Long, multinucleated, striated fibers; voluntary control; functions in movement, posture, support, and temperature regulation.
Cardiac Muscle: Found in the heart; short, branched, striated cells; involuntary; intercalated discs allow coordinated contraction.
Smooth Muscle: Walls of hollow organs; spindle-shaped, nonstriated; involuntary; controls movement through tubes.

Muscle Fiber & Neuromuscular Junction

Muscle fibers contain specialized structures for contraction, and are activated by neurons at the neuromuscular junction.

Sarcolemma: Muscle cell membrane.
Sarcoplasm: Muscle cell cytoplasm.
Sarcoplasmic Reticulum (SR): Stores calcium ions (Ca2+).
Myofibrils: Contain contractile units called sarcomeres.
T-tubules: Carry action potential to SR.
Filaments: Thin (actin, tropomyosin, troponin); Thick (myosin).
Neuromuscular Junction: Connection between neuron and muscle fiber.

Excitation–Contraction Coupling

Muscle contraction is initiated by a series of steps involving electrical and chemical signals.

Neuron releases acetylcholine (ACh).
ACh binds to sarcolemma receptors.
Na+ influx causes depolarization.
Action potential travels through T-tubules.
SR releases Ca2+.
Ca2+ binds troponin.
Tropomyosin shifts.
Cross-bridges form.
Power stroke occurs.
ATP allows detachment and reset.

Sliding Filament Theory

Muscle contraction occurs as sarcomeres shorten, with specific changes in band structure.

Sarcomeres: Shorten during contraction.
I band and H zone: Shrink.
A band: Remains unchanged.

Motor Units & Tension

Muscle tension and control depend on the number and size of motor units activated.

Motor Unit: One neuron and its associated muscle fibers.
Small units: Provide precise control.
Recruitment: Activating more motor units increases tension.
Muscle Tone: Resting tension in muscles.

Chapter 8: The Nervous System

Divisions of the Nervous System

The nervous system is divided into central and peripheral components, with further subdivisions based on function.

CNS (Central Nervous System): Brain and spinal cord.
PNS (Peripheral Nervous System): Sensory (afferent) and motor (efferent) divisions.
Somatic NS: Voluntary control of skeletal muscles.
Autonomic NS: Involuntary control; includes sympathetic (fight or flight) and parasympathetic (rest and digest) divisions.

Neurons

Neurons are the functional units of the nervous system, specialized for transmitting electrical signals.

Cell body: Contains nucleus and organelles.
Dendrites: Receive signals.
Axon: Transmits signals away from cell body.
Axon hillock: Initiates action potential.
Axon terminal: Releases neurotransmitters.

Neuron Types: Unipolar, bipolar, multipolar (classified by number of processes).

Synapse: Junction between presynaptic and postsynaptic neurons.

Neuroglia

Neuroglia are supporting cells in the nervous system, with distinct types in CNS and PNS.

CNS:
- Astrocytes: Form blood-brain barrier, provide support.
- Microglia: Immune defense.
- Ependymal cells: Produce cerebrospinal fluid (CSF).
- Oligodendrocytes: Form myelin sheath.
PNS:
- Satellite cells: Surround neuron cell bodies.
- Schwann cells: Form myelin sheath and neurilemma.

Brain & Spinal Cord

The brain and spinal cord are central to processing and relaying information.

Cerebrum: Responsible for thought, memory, movement.
Cerebellum: Coordination and balance.
Diencephalon:
- Thalamus: Sensory relay center.
- Hypothalamus: Controls autonomic functions and hormones.
Brain Stem: Includes midbrain, pons, medulla.
Spinal Cord: Features cervical and lumbar enlargements, conus medullaris, cauda equina.

Reflexes

Reflexes are rapid, automatic responses to stimuli, involving specific neural pathways.

Reflex arc: Receptor → sensory neuron → CNS → motor neuron → effector.
Monosynaptic: Simple stretch reflex.
Polysynaptic: More complex withdrawal reflex.

ANS Comparison

The autonomic nervous system has two divisions with distinct anatomical and functional characteristics.

Feature	Sympathetic	Parasympathetic
Origin	Thoracolumbar	Craniosacral
Preganglionic Fiber	Short	Long
Postganglionic Fiber	Long	Short
Neurotransmitter at Effector	NE (Norepinephrine)	ACh (Acetylcholine)
Response	Widespread	Localized

Chapter 9: The General & Special Senses

General Senses

General senses detect stimuli such as pain, temperature, touch, and chemical changes throughout the body.

Pain: Detected by nociceptors.
Temperature: Detected by thermoreceptors.
Touch, Pressure, Vibration: Mechanoreceptors.
Proprioception: Sense of body position.
Chemoreceptors: Detect chemical changes.

Special Senses

Special senses are localized to specific organs and include olfaction, gustation, vision, hearing, and equilibrium.

Olfaction: Smell.
Gustation: Taste.
Vision: Sight.
Hearing: Auditory perception.
Equilibrium: Balance.

Key Organs

Each special sense is associated with specific organs and pathways.

Olfaction: Odorants bind to receptors; signals travel via CN I to olfactory bulb and cortex.
Taste: Taste buds in papillae; signals via CN VII, IX, X.
Vision: Rods (low light) vs cones (color); retina layers; optic disc (blind spot); accommodation and depth perception.
Hearing & Balance: Outer, middle, inner ear; ossicles; cochlea, vestibule, semicircular canals.

Chapter 10: The Endocrine System

Hormones

The endocrine system regulates body functions through hormones released by glands.

ADH (Antidiuretic Hormone), Oxytocin
TSH (Thyroid Stimulating Hormone), ACTH (Adrenocorticotropic Hormone), GH (Growth Hormone), PRL (Prolactin)
FSH (Follicle Stimulating Hormone), LH (Luteinizing Hormone): Gonadotropins
T3 & T4: Thyroid hormones
Insulin & Glucagon: Pancreatic hormones
Melatonin: Pineal hormone
Sex hormones: Estrogen, testosterone
Adrenal hormones: Cortisol, aldosterone, epinephrine

Hormone Mechanisms

Hormones act through different mechanisms depending on their chemical nature.

Nonsteroid Hormones: Bind to cell surface receptors; activate second messengers (e.g., cAMP); fast, short-lived effects.
Steroid Hormones: Penetrate cell and nucleus; activate gene transcription; slow, long-lasting effects.

Example equation:

Endocrine Disorders

Disorders arise from abnormal hormone secretion or action.

Hypersecretion: Excess hormone production.
Hyposecretion: Insufficient hormone production.
Primary vs Secondary Hyposecretion: Primary: gland dysfunction; Secondary: regulatory failure.

Nervous vs Endocrine Control

The nervous and endocrine systems both use chemical messengers to maintain homeostasis, but differ in speed and duration.

Nervous System: Fast, short-lived responses.
Endocrine System: Slow, long-lasting responses.
Both: Maintain homeostasis.