Anatomy And Physiology 1 Exam 2

Let's delve into the intricate world of Anatomy and Physiology (A&P), specifically focusing on the topics frequently covered in the second exam of an introductory course. This examination often builds upon foundational knowledge, exploring more complex systems and their interrelationships within the human body. Mastering this material requires not only memorization but also a deep understanding of how structures enable function.

Core Concepts of A&P 1 Exam 2

The second exam in A&P 1 typically covers a range of topics, including:

• The Skeletal System: Bones, cartilage, ligaments, bone formation, bone remodeling, and joint classification.
• The Muscular System: Muscle tissue types, muscle contraction, muscle fatigue, types of muscle movements, and major skeletal muscles.
• The Nervous System (Part 1): Basic structure and function of neurons, neuroglia, action potentials, synaptic transmission, and the organization of the nervous system.
• The Endocrine System (Introduction): Glands, hormones, mechanisms of hormone action, and major endocrine glands.

This article will comprehensively explore each of these topics, providing detailed explanations, relevant examples, and study tips to help you excel in your A&P 1 Exam 2.

The Skeletal System: A Framework for Life

The skeletal system provides the body with a rigid framework, protects vital organs, facilitates movement, stores minerals, and produces blood cells. It's a dynamic system constantly being remodeled and adapted to the stresses placed upon it.

Bones: The Building Blocks

Bones are complex organs composed of bone tissue, cartilage, dense connective tissue, epithelium, adipose tissue, and nervous tissue. They are classified based on their shape:

• Long bones: Longer than they are wide (e.g., femur, humerus).
• Short bones: Cube-shaped (e.g., carpals, tarsals).
• Flat bones: Thin, flattened, and usually curved (e.g., skull bones, ribs).
• Irregular bones: Complex shapes (e.g., vertebrae, facial bones).
• Sesamoid bones: Embedded in tendons (e.g., patella).

Bone Structure: A long bone has several key features:

• Diaphysis: The long shaft of the bone.
• Epiphyses: The ends of the bone.
• Metaphyses: Regions between the diaphysis and epiphyses; contain the epiphyseal (growth) plate in growing bones.
• Articular cartilage: Covers the epiphyses where they articulate with other bones.
• Periosteum: A tough, outer fibrous layer covering the bone (except where there is articular cartilage).
• Medullary cavity: A hollow space within the diaphysis containing bone marrow.
• Endosteum: A thin membrane lining the medullary cavity.

Bone Tissue: Two types of bone tissue exist:

• Compact bone: Dense, solid outer layer of bone.
• Spongy bone: Honeycomb-like inner layer of bone containing trabeculae (bony struts).

Histology of Bone Tissue:

• Osteocytes: Mature bone cells that maintain bone matrix.
• Osteoblasts: Bone-forming cells.
• Osteoclasts: Bone-resorbing cells.
• Bone matrix: Consists of inorganic salts (calcium phosphate and calcium hydroxide, which form hydroxyapatite) and organic collagen fibers.

Bone Formation (Ossification):

• Intramembranous ossification: Bone develops directly from mesenchyme (e.g., skull bones).
• Endochondral ossification: Bone develops from hyaline cartilage (e.g., long bones).

Bone Remodeling: A continuous process of bone resorption (by osteoclasts) and bone deposition (by osteoblasts). This process is essential for bone growth, repair, and calcium homeostasis.

Cartilage and Ligaments: Supporting Structures

• Cartilage: A connective tissue that provides support and flexibility. Types include:
  • Hyaline cartilage: Most abundant; found in articular cartilage, costal cartilage, and respiratory structures.
  • Elastic cartilage: Contains elastic fibers; found in the ear and epiglottis.
  • Fibrocartilage: Contains collagen fibers; found in intervertebral discs and menisci.
• Ligaments: Connect bone to bone, providing stability to joints.

Joints: Where Bones Meet

Joints (articulations) are classified structurally and functionally.

Structural Classification:

• Fibrous joints: Bones joined by fibrous connective tissue; lack a joint cavity. (e.g., sutures, syndesmoses, gomphoses)
• Cartilaginous joints: Bones joined by cartilage; lack a joint cavity. (e.g., synchondroses, symphyses)
• Synovial joints: Bones separated by a joint cavity containing synovial fluid; allows for considerable movement. (e.g., shoulder, hip, knee)

Functional Classification:

• Synarthroses: Immovable joints.
• Amphiarthroses: Slightly movable joints.
• Diarthroses: Freely movable joints.

Synovial Joint Features:

• Articular cartilage: Covers the articulating surfaces of bones.
• Joint (synovial) cavity: Contains synovial fluid.
• Articular capsule: Surrounds the joint; has an outer fibrous layer and an inner synovial membrane.
• Synovial fluid: Lubricates the joint, reduces friction, and provides nutrients to articular cartilage.
• Reinforcing ligaments: Strengthen the joint.

Types of Synovial Joints:

• Plane joint: Flat articular surfaces; allows gliding movements (e.g., intercarpal joints).
• Hinge joint: Cylindrical end of one bone fits into a trough-shaped surface on another bone; allows flexion and extension (e.g., elbow joint).
• Pivot joint: Rounded end of one bone fits into a sleeve or ring of another bone; allows rotation (e.g., radioulnar joint).
• Condylar joint: Oval articular surface of one bone fits into a complementary depression in another bone; allows flexion, extension, abduction, adduction, and circumduction (e.g., metacarpophalangeal joints).
• Saddle joint: Each articular surface has both concave and convex areas; allows flexion, extension, abduction, adduction, and circumduction (e.g., carpometacarpal joint of the thumb).
• Ball-and-socket joint: Spherical head of one bone articulates with a cup-like socket of another bone; allows flexion, extension, abduction, adduction, circumduction, and rotation (e.g., shoulder and hip joints).

The Muscular System: Movement and More

The muscular system is responsible for body movement, maintaining posture, stabilizing joints, and generating heat. It comprises skeletal muscle, smooth muscle, and cardiac muscle. The A&P 1 exam typically focuses on skeletal muscle.

Muscle Tissue Types

• Skeletal muscle: Striated, voluntary, attached to bones.
• Smooth muscle: Non-striated, involuntary, found in the walls of internal organs.
• Cardiac muscle: Striated, involuntary, found in the heart.

Skeletal Muscle Structure

• Muscle fibers (muscle cells): Long, cylindrical cells containing multiple nuclei.
• Sarcolemma: Plasma membrane of a muscle fiber.
• Sarcoplasmic reticulum: Endoplasmic reticulum of a muscle fiber; stores calcium ions.
• Myofibrils: Contractile units within muscle fibers; composed of sarcomeres.
• Sarcomere: The functional unit of a muscle fiber; extends from one Z disc to another.

Myofilaments:

• Actin: Thin filaments; contain binding sites for myosin.
• Myosin: Thick filaments; possess heads that bind to actin.
• Troponin and tropomyosin: Regulatory proteins that control the interaction of actin and myosin.

Muscle Contraction: The Sliding Filament Mechanism

Muscle contraction occurs according to the sliding filament mechanism:

1. Nerve impulse: A motor neuron transmits an action potential to the neuromuscular junction.
2. Acetylcholine release: Acetylcholine (ACh) is released into the synaptic cleft.
3. Muscle fiber depolarization: ACh binds to receptors on the sarcolemma, causing depolarization.
4. Calcium release: Depolarization triggers the sarcoplasmic reticulum to release calcium ions.
5. Actin-myosin binding: Calcium ions bind to troponin, causing tropomyosin to move away from the binding sites on actin. Myosin heads bind to actin, forming cross-bridges.
6. Power stroke: Myosin heads pivot, pulling the actin filaments toward the center of the sarcomere.
7. ATP binding: ATP binds to myosin heads, causing them to detach from actin.
8. ATP hydrolysis: ATP is hydrolyzed to ADP and phosphate, providing energy to re-cock the myosin heads.
9. Cycle repeats: The cycle repeats as long as calcium ions are present.
10. Muscle relaxation: When the nerve impulse ceases, calcium ions are pumped back into the sarcoplasmic reticulum, tropomyosin blocks the binding sites on actin, and the muscle fiber relaxes.

Muscle Fatigue

Muscle fatigue is the decline in muscle force generation during prolonged activity. Factors contributing to muscle fatigue include:

• Depletion of energy reserves: ATP, creatine phosphate, and glycogen.
• Accumulation of metabolic byproducts: Lactic acid, inorganic phosphate.
• Failure of excitation-contraction coupling: Impaired release of calcium ions from the sarcoplasmic reticulum.
• Central fatigue: Psychological factors affecting the central nervous system.

Types of Muscle Movements

• Flexion: Decreases the angle of a joint.
• Extension: Increases the angle of a joint.
• Abduction: Movement away from the midline.
• Adduction: Movement toward the midline.
• Rotation: Movement around a longitudinal axis.
• Circumduction: Circular movement.
• Pronation: Palm facing posteriorly.
• Supination: Palm facing anteriorly.
• Dorsiflexion: Toes pointing upward.
• Plantar flexion: Toes pointing downward.
• Inversion: Sole of the foot turns medially.
• Eversion: Sole of the foot turns laterally.

Major Skeletal Muscles

Understanding the origin, insertion, and action of major skeletal muscles is crucial. Some key muscles include:

• Muscles of the Head and Neck:
  • Frontalis: Raises eyebrows.
  • Orbicularis oculi: Closes eyes.
  • Zygomaticus major: Elevates corner of mouth (smiling).
  • Masseter: Elevates mandible (chewing).
  • Temporalis: Elevates and retracts mandible.
  • Sternocleidomastoid: Flexes and rotates head.
• Muscles of the Trunk:
  • Rectus abdominis: Flexes vertebral column.
  • External oblique: Compresses abdomen, rotates trunk.
  • Internal oblique: Compresses abdomen, rotates trunk.
  • Transversus abdominis: Compresses abdomen.
  • Erector spinae: Extends vertebral column.
  • Diaphragm: Prime mover of inspiration.
• Muscles of the Upper Limb:
  • Deltoid: Abducts arm.
  • Biceps brachii: Flexes elbow, supinates forearm.
  • Triceps brachii: Extends elbow.
  • Brachialis: Flexes elbow.
  • Flexor carpi ulnaris: Flexes and adducts wrist.
  • Extensor carpi radialis longus: Extends and abducts wrist.
• Muscles of the Lower Limb:
  • Gluteus maximus: Extends hip.
  • Gluteus medius: Abducts hip.
  • Hamstrings (biceps femoris, semitendinosus, semimembranosus): Flexes knee, extends hip.
  • Quadriceps femoris (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius): Extends knee.
  • Gastrocnemius: Plantar flexes foot.
  • Soleus: Plantar flexes foot.
  • Tibialis anterior: Dorsiflexes foot.

The Nervous System (Part 1): Communication Network

The nervous system is the body's primary control and communication network. It consists of the brain, spinal cord, nerves, and sensory receptors. It's divided into the central nervous system (CNS) and the peripheral nervous system (PNS).

Neurons: The Functional Units

Neurons are specialized cells that transmit electrical signals called action potentials.

Neuron Structure:

• Cell body (soma): Contains the nucleus and other organelles.
• Dendrites: Branch-like extensions that receive signals from other neurons.
• Axon: A long, slender projection that transmits signals to other neurons or effector cells.
• Axon hillock: The region where the axon originates from the cell body.
• Axon terminals (terminal boutons): Branches at the end of the axon that form synapses with other cells.
• Myelin sheath: A fatty insulation that surrounds the axons of some neurons, increasing the speed of signal transmission.
• Nodes of Ranvier: Gaps in the myelin sheath where the axon is exposed.

Types of Neurons:

• Sensory (afferent) neurons: Transmit signals from sensory receptors to the CNS.
• Motor (efferent) neurons: Transmit signals from the CNS to effector cells (muscles or glands).
• Interneurons (association neurons): Located within the CNS; integrate sensory information and coordinate motor responses.

Neuroglia: Supporting Cells

Neuroglia (glial cells) are supporting cells in the nervous system that provide structural support, insulation, and protection for neurons.

Types of Neuroglia:

• Astrocytes: Provide structural support, regulate the chemical environment, and form the blood-brain barrier in the CNS.
• Oligodendrocytes: Form the myelin sheath in the CNS.
• Microglia: Phagocytic cells that remove debris and pathogens in the CNS.
• Ependymal cells: Line the ventricles of the brain and the central canal of the spinal cord; produce cerebrospinal fluid.
• Schwann cells: Form the myelin sheath in the PNS.
• Satellite cells: Surround neuron cell bodies in ganglia in the PNS.

Action Potentials: Electrical Signals

Action potentials are rapid changes in the membrane potential of a neuron that transmit signals over long distances.

Resting Membrane Potential:

• The membrane potential of a neuron at rest is typically around -70 mV. This is maintained by:
  • Unequal distribution of ions across the membrane (more Na+ outside, more K+ inside).
  • Leak channels that allow a small amount of Na+ to leak into the cell and K+ to leak out.
  • The sodium-potassium pump, which actively transports Na+ out of the cell and K+ into the cell.

Steps of an Action Potential:

1. Depolarization: A stimulus causes the membrane potential to become more positive. If the depolarization reaches the threshold (-55 mV), an action potential is triggered.
2. Rapid depolarization: Voltage-gated Na+ channels open, allowing Na+ to rush into the cell, causing a rapid increase in membrane potential to +30 mV.
3. Repolarization: Voltage-gated Na+ channels close, and voltage-gated K+ channels open, allowing K+ to rush out of the cell, causing the membrane potential to return to negative values.
4. Hyperpolarization: The membrane potential becomes more negative than the resting potential due to the slow closing of K+ channels.
5. Restoration of resting membrane potential: The sodium-potassium pump restores the ion concentrations to their resting levels.

Propagation of Action Potentials:

• Action potentials propagate along the axon.
• In myelinated axons, action potentials jump from one node of Ranvier to the next, a process called saltatory conduction. This greatly increases the speed of signal transmission.

Synaptic Transmission: Communication Between Neurons

Synaptic transmission is the process by which neurons communicate with each other at synapses.

Synapse Structure:

• Presynaptic neuron: The neuron that transmits the signal.
• Postsynaptic neuron: The neuron that receives the signal.
• Synaptic cleft: The gap between the presynaptic and postsynaptic neurons.

Steps of Synaptic Transmission:

1. Action potential arrives: An action potential arrives at the axon terminal of the presynaptic neuron.
2. Calcium influx: Voltage-gated Ca2+ channels open, allowing Ca2+ to enter the axon terminal.
3. Neurotransmitter release: Ca2+ triggers the release of neurotransmitters from synaptic vesicles into the synaptic cleft.
4. Neurotransmitter binding: Neurotransmitters bind to receptors on the postsynaptic neuron.
5. Postsynaptic potential: Neurotransmitter binding causes a change in the membrane potential of the postsynaptic neuron.
   • Excitatory postsynaptic potential (EPSP): Depolarizes the postsynaptic neuron, making it more likely to fire an action potential.
   • Inhibitory postsynaptic potential (IPSP): Hyperpolarizes the postsynaptic neuron, making it less likely to fire an action potential.
6. Neurotransmitter removal: Neurotransmitters are removed from the synaptic cleft by:
   • Reuptake: Transported back into the presynaptic neuron.
   • Enzymatic degradation: Broken down by enzymes.
   • Diffusion: Diffuse away from the synapse.

Organization of the Nervous System

• Central Nervous System (CNS): Brain and spinal cord; integrates and processes information.
• Peripheral Nervous System (PNS): Nerves and ganglia outside the CNS; carries information to and from the CNS.

Divisions of the PNS:

• Sensory (afferent) division: Carries sensory information from receptors to the CNS.
• Motor (efferent) division: Carries motor commands from the CNS to effectors (muscles and glands).
  • Somatic nervous system: Controls voluntary movements of skeletal muscles.
  • Autonomic nervous system: Controls involuntary functions (e.g., heart rate, digestion).
    • Sympathetic division: "Fight or flight" response.
    • Parasympathetic division: "Rest and digest" response.

The Endocrine System (Introduction): Chemical Messengers

The endocrine system is a collection of glands that secrete hormones into the bloodstream to regulate various bodily functions.

Glands: Hormone Producers

Endocrine glands are ductless glands that secrete hormones directly into the bloodstream. Major endocrine glands include:

• Pituitary gland: Located in the brain; controls the secretion of many other hormones.
• Thyroid gland: Located in the neck; regulates metabolism.
• Parathyroid glands: Located on the posterior surface of the thyroid gland; regulate calcium levels.
• Adrenal glands: Located on top of the kidneys; regulate stress response, blood pressure, and electrolyte balance.
• Pancreas: Located in the abdomen; regulates blood sugar levels.
• Ovaries (in females): Located in the pelvic cavity; produce estrogen and progesterone.
• Testes (in males): Located in the scrotum; produce testosterone.
• Pineal gland: Located in the brain; secretes melatonin, which regulates sleep-wake cycles.

Hormones: Chemical Messengers

Hormones are chemical messengers that travel through the bloodstream to target cells, where they bind to receptors and elicit a response.

Types of Hormones:

• Amino acid-based hormones: Derived from amino acids (e.g., proteins, peptides, amines).
• Steroid hormones: Derived from cholesterol (e.g., testosterone, estrogen, cortisol).

Mechanisms of Hormone Action

Hormones exert their effects by binding to receptors on target cells.

• Water-soluble hormones (amino acid-based): Bind to receptors on the cell membrane, triggering a signaling cascade within the cell.
• Lipid-soluble hormones (steroid hormones): Diffuse across the cell membrane and bind to receptors in the cytoplasm or nucleus, directly influencing gene expression.

Major Endocrine Glands and Their Hormones

• Pituitary gland:
  • Growth hormone (GH): Promotes growth and development.
  • Prolactin (PRL): Stimulates milk production.
  • Thyroid-stimulating hormone (TSH): Stimulates thyroid hormone secretion.
  • Adrenocorticotropic hormone (ACTH): Stimulates adrenal hormone secretion.
  • Follicle-stimulating hormone (FSH): Regulates reproduction.
  • Luteinizing hormone (LH): Regulates reproduction.
  • Antidiuretic hormone (ADH): Regulates water balance.
  • Oxytocin: Stimulates uterine contractions and milk ejection.
• Thyroid gland:
  • Thyroxine (T4) and triiodothyronine (T3): Regulate metabolism.
  • Calcitonin: Lowers blood calcium levels.
• Parathyroid glands:
  • Parathyroid hormone (PTH): Raises blood calcium levels.
• Adrenal glands:
  • Cortisol: Regulates stress response and metabolism.
  • Aldosterone: Regulates electrolyte balance.
  • Epinephrine and norepinephrine: Mediate the "fight or flight" response.
• Pancreas:
  • Insulin: Lowers blood glucose levels.
  • Glucagon: Raises blood glucose levels.
• Ovaries:
  • Estrogen: Promotes female sexual characteristics.
  • Progesterone: Regulates the menstrual cycle and pregnancy.
• Testes:
  • Testosterone: Promotes male sexual characteristics.
• Pineal gland:
  • Melatonin: Regulates sleep-wake cycles.

Conclusion

This comprehensive review covers the essential topics for your Anatomy and Physiology 1 Exam 2. Remember to focus not only on memorizing facts but also on understanding the underlying principles and relationships between different systems. Good luck with your exam!