Muscle Tissue

Types and Characteristics of Muscle Tissue

• Skeletal Muscle: Voluntary, striated, multinucleated. Responsible for body movement.

• Cardiac Muscle: Involuntary, striated, single nucleus, found only in the heart. Contains intercalated discs for synchronized contraction.

• Smooth Muscle: Involuntary, non-striated, single nucleus, found in walls of hollow organs (e.g., intestines, blood vessels).

• Striations: Skeletal and cardiac muscle are striated due to the regular arrangement of actin and myosin filaments in sarcomeres. Smooth muscle lacks this organization, so it is not striated.

Muscle Microanatomy

• Sarcolemma: The plasma membrane of a muscle fiber.

• Sarcoplasmic Reticulum (SR): Specialized endoplasmic reticulum that stores and releases calcium ions.

• Terminal Cisternae: Enlarged areas of the SR adjacent to T-tubules; release calcium during muscle contraction.

• A Band: Dark band; contains thick (myosin) filaments and overlapping thin (actin) filaments.

• I Band: Light band; contains only thin (actin) filaments.

• Z Disc: Defines the boundary of a sarcomere; anchors thin filaments.

• Myofilaments: Protein filaments (thick = myosin, thin = actin) responsible for contraction.

• Myofibril: Bundles of myofilaments within a muscle fiber.

• Sarcomere: The functional contractile unit of muscle, from Z disc to Z disc.

• Transverse (T) Tubule: Invaginations of the sarcolemma that transmit action potentials into the muscle fiber.

• Actin: Protein forming thin filaments; contains binding sites for myosin.

• Troponin: Regulatory protein that binds calcium and moves tropomyosin.

• Tropomyosin: Regulatory protein that blocks myosin-binding sites on actin at rest.

• Myosin: Protein forming thick filaments; has heads that bind to actin and hydrolyze ATP.

Muscle Growth and Atrophy

• Atrophy: Decrease in muscle size due to lack of use or disease.

• Hypertrophy: Increase in muscle size due to increased use or resistance training.

Neuromuscular Junction

• Axon Terminal: The end of a motor neuron that releases neurotransmitters.

• Motor Endplate: Specialized region of the muscle fiber's sarcolemma with receptors for neurotransmitters.

• Acetylcholine (ACh): The neurotransmitter released by motor neurons to stimulate muscle contraction.

Steps of Muscle Contraction

1. Action potential arrives at the axon terminal of the motor neuron.

2. Acetylcholine is released into the synaptic cleft.

3. ACh binds to receptors on the motor endplate, depolarizing the sarcolemma and generating an action potential.

4. The action potential travels down T-tubules to the sarcoplasmic reticulum.

5. Terminal cisternae of the SR release calcium ions.

6. Calcium binds to troponin, causing tropomyosin to move and expose binding sites on actin.

7. Myosin heads bind to actin, forming cross-bridges, and pull actin filaments toward the M line (power stroke).

Muscle Energy Metabolism

• Aerobic Metabolism: Uses oxygen to produce ATP from glucose, fatty acids, or amino acids; efficient and supports prolonged activity.

• Anaerobic Metabolism: Produces ATP without oxygen, primarily through glycolysis; less efficient, produces lactic acid.

• Glycolysis: The breakdown of glucose to pyruvate, yielding ATP.

• ATP: The primary energy currency of the cell.

Nervous System

CNS vs. PNS

Central Nervous System (CNS): Consists of the brain and spinal cord.

• Peripheral Nervous System (PNS): All neural tissue outside the CNS, including nerves and ganglia.

Functions of the Nervous System

• Sensory Input: Detects internal and external stimuli.

• Integration: Processes and interprets sensory input.

• Motor Output: Activates effector organs (muscles and glands) to respond.

Functional and Structural Classifications

• Afferent (Sensory) Neurons: Carry information to the CNS.

• Efferent (Motor) Neurons: Carry commands from the CNS to effectors.

• Somatic Nervous System: Controls voluntary movements (skeletal muscle).

• Visceral (Autonomic) Nervous System: Controls involuntary functions (smooth muscle, cardiac muscle, glands).

• Sympathetic Division: Prepares the body for 'fight or flight' responses.

• Parasympathetic Division: Promotes 'rest and digest' activities.

Neuron Classifications and Locations

• Structural: Multipolar, bipolar, unipolar neurons.

• Functional: Sensory, motor, interneurons.

• Locations: Sensory neurons in dorsal root ganglia, motor neurons in CNS, interneurons in CNS.

Neural Structures

• Nucleus: Cluster of neuron cell bodies in the CNS.

• Ganglion: Cluster of neuron cell bodies in the PNS.

• Tract: Bundle of axons in the CNS.

• Nerve: Bundle of axons in the PNS.

Neuroglial Cells

• Oligodendrocytes: Form myelin sheaths in the CNS.

• Astrocytes: Support neurons, maintain blood-brain barrier.

• Ependymal Cells: Line ventricles, produce cerebrospinal fluid.

• Schwann Cells: Form myelin sheaths in the PNS.

• Myelin Sheath: Insulating layer that increases the speed of nerve impulse conduction.

Special Senses and Sensory Receptors

• Gustation: Sense of taste; receptors in taste buds.

• Olfaction: Sense of smell; receptors in nasal epithelium.

• Vision: Sense of sight; photoreceptors in the retina.

• Hearing: Sense of sound; mechanoreceptors in the cochlea.

• Other Receptors:

  • Nociceptors: Detect pain.

  • Proprioceptors: Detect body position and movement.

  • Chemoreceptors: Detect chemical changes.

  • Mechanoreceptors: Detect mechanical pressure or distortion.

  • Thermoreceptors: Detect temperature changes.

  • Baroreceptors: Detect pressure changes in blood vessels.

Eye and Ear Anatomy

• Eye: Structures include cornea, lens, retina, optic nerve, rods and cones (photoreceptors).

• Ear: Structures include outer ear (pinna), middle ear (ossicles), inner ear (cochlea, semicircular canals).

Vision Terms

• Myopia: Nearsightedness; image focuses in front of the retina.

• Hyperopia: Farsightedness; image focuses behind the retina.

• Accommodation: The process by which the lens changes shape to focus on near or distant objects.

Endocrine System

Function of the Endocrine System

• Regulates long-term processes such as growth, development, metabolism, and reproduction through hormones.

Nervous System vs. Endocrine System

• Nervous System: Fast, short-term responses via electrical impulses.

• Endocrine System: Slower, long-term regulation via hormones in the bloodstream.

Hormone Types and Mechanisms

• Hydrophobic (Lipid-Soluble) Hormones: Pass through cell membranes, bind to intracellular receptors, alter gene expression (e.g., steroid hormones).

• Hydrophilic (Water-Soluble) Hormones: Bind to cell surface receptors, activate second messenger systems (e.g., peptide hormones).

Hormone-Producing Organs and Target Tissues

• Major organs: pituitary, thyroid, parathyroid, adrenal glands, pancreas, gonads, hypothalamus.

• Target tissues: cells with specific receptors for a given hormone.

Major Hormones and Their Functions

• TSH (Thyroid-Stimulating Hormone): Stimulates thyroid hormone release.

• ACTH (Adrenocorticotropic Hormone): Stimulates adrenal cortex to release glucocorticoids.

• FSH (Follicle-Stimulating Hormone): Stimulates gamete production.

• LH (Luteinizing Hormone): Stimulates sex hormone production.

• GH (Growth Hormone): Stimulates growth and metabolism.

• ADH (Antidiuretic Hormone): Promotes water reabsorption in kidneys.

• Aldosterone: Increases sodium reabsorption in kidneys.

• Parathyroid Hormone: Increases blood calcium levels.

• Calcitonin: Lowers blood calcium levels.

• Glucagon: Raises blood glucose levels.

• Insulin: Lowers blood glucose levels.

• Leptin: Regulates appetite and metabolism.

• Epinephrine/Norepinephrine: Mediate fight-or-flight responses.

• Estrogen, Progesterone, Testosterone: Regulate reproductive functions.

Classes of Adrenal Cortex Hormones

• Mineralocorticoids: Regulate electrolyte balance (e.g., aldosterone).

• Glucocorticoids: Regulate metabolism and stress response (e.g., cortisol).

• Androgens: Sex hormones, mainly produced in testes but also in adrenal cortex.

Blood

Components of Whole Blood

• Plasma: Liquid matrix containing water, proteins, nutrients, hormones, and waste products.

• Formed Elements: Red blood cells (erythrocytes), white blood cells (leukocytes), platelets (thrombocytes).

Hemoglobin

• Protein in red blood cells that binds and transports oxygen and carbon dioxide.

• Each hemoglobin molecule can carry up to four oxygen molecules.

• Equation for oxygen binding:

Anemia and Sickle Cell Anemia

• Anemia: Condition characterized by a deficiency of red blood cells or hemoglobin, leading to reduced oxygen transport.

• Sickle Cell Anemia: Genetic disorder causing abnormal hemoglobin, resulting in sickle-shaped red blood cells that can block blood flow.

Blood Typing

• Determined by the presence or absence of specific antigens (A, B, Rh) on red blood cells.

• Important for safe blood transfusions.

• Table: Blood Types and Antigens

  Blood Type	Antigens Present	Antibodies Present
  A	A	Anti-B
  B	B	Anti-A
  AB	A, B	None
  O	None	Anti-A, Anti-B

Hemostasis

• The process of stopping bleeding, involving three main steps:

  1. Vascular spasm (vasoconstriction)

  2. Platelet plug formation

  3. Coagulation (blood clotting)

• Equation for clotting cascade (simplified):