Study Notes on Tissues and Skeletal/Nervous System
Tissues Classification
Understanding Tissue Classifications
Tissues are groups of similar cells that work together to perform specific functions in the body.
Emphasis on knowing all tissue classifications discussed.
Muscle Tissue Types
Differentiate between types of muscle tissues.
Types include:
Skeletal Muscle
Responsible for voluntary movement, characterized by striations, and attached to bones.
Cardiac Muscle
Found only in the heart, responsible for involuntary pumping of blood, also striated but contains intercalated discs.
Smooth Muscle
Found in the walls of internal organs (e.g., digestive tract, blood vessels), responsible for involuntary movements, lacks striations.
Key focus on the structural and functional differences among these types.
Epithelial Tissue Classifications & Functions
Classifications include:
Simple Epithelia: (single layer of cells)
Simple Squamous
Single layer of flat, scale-like cells; specialized for diffusion and filtration (e.g., lung air sacs, capillary walls).
Simple Cuboidal
Single layer of cube-shaped cells; involved in secretion and absorption (e.g., kidney tubules, gland ducts).
Simple Columnar
Single layer of tall, column-shaped cells; specialized for absorption and secretion, often found with microvilli or cilia (e.g., lining of digestive tract).
Stratified Epithelia: (multiple layers of cells)
Stratified Squamous
Multiple layers of flat cells, with deeper layers being cuboidal or columnar; provides protection against abrasion (e.g., skin surface, lining of mouth).
Stratified Cuboidal
Two or more layers of cube-shaped cells; relatively rare, involved in protection and secretion (e.g., ducts of sweat glands).
Stratified Columnar
Multiple layers of column-shaped cells, with only the superficial layer being columnar; also rare, found in some large ducts and parts of the male urethra.
Transitional Epithelium
Multiple layers of cells that can change shape (distend and retract); found in organs that stretch, such as the urinary bladder.
Importance of structure:
Example: Simple squamous epithelium facilitates diffusion due to thin, flat cells.
Roles in secretion, absorption, and protection.
Connective Tissue Classifications & Functions
Classifications include:
Loose Connective Tissue
A general term for connective tissue that is not densely packed with fibers, providing support and binding tissues while allowing flexibility (e.g., areolar, adipose, reticular).
Dense Connective Tissue
Characterized by a high proportion of collagen fibers, providing strong support and resistance to tension (e.g., tendons, ligaments).
Specialized Connective Tissues (Cartilage, Bone, Blood)
Tissues with specialized functions and structures, such as cartilage for support, bone for structural integrity, and blood for transport.
Structure leads to function:
Example: The loose arrangement in loose connective tissue allows for flexibility.
Skeletal System
Connective Tissue Proper Fiber Types
Types of fibers include:
Collagen Fibers
Strongest and most abundant fibers, providing high tensile strength.
Elastic Fibers
Long, thin fibers that allow for stretch and recoil (e.g., in skin, lungs, blood vessels).
Reticular Fibers
Short, fine, highly branched collagenous fibers that form delicate networks (e.g., in lymphoid organs).
Different functions related to strength and elasticity.
Cartilage Types
Types include:
Hyaline Cartilage (smooth, covers joints)
The most abundant type of cartilage, providing firm but flexible support, found in articular surfaces, tracheal rings, and the nose.
Elastic Cartilage (flexible, ear)
Contains more elastic fibers than hyaline cartilage, providing great flexibility and ability to return to original shape (e.g., external ear, epiglottis).
Fibrocartilage (shock-absorbing, intervertebral discs)
Contains thick collagen fibers, making it highly compressible with great tensile strength, found where strong support and shock absorption are needed (e.g., menisci of knee, intervertebral discs).
Locations and functions:
Example: Hyaline cartilage provides smooth surfaces for joints.
Cartilage Growth
Two primary types of growth:
Appositional Growth
Growth from the outside, adding new layers of cartilage by chondroblasts in the perichondrium secreting matrix onto existing cartilage surface.
Interstitial Growth
Growth from within the cartilage, increasing its overall size as chondrocytes within the lacunae divide and secrete new matrix.
Long Bone Structure
Key components:
Epiphysis
The ends of a long bone, covered with articular cartilage, primarily composed of spongy bone.
Diaphysis
The shaft or central part of a long bone, composed of compact bone with a medullary cavity.
Metaphysis
The narrow portion of a long bone between the epiphysis and diaphysis; contains the growth plate in growing bones.
Periosteum
A dense fibrous membrane covering the surface of bones (except at articulations), providing attachment for muscles and containing bone-forming cells.
Endosteum
A thin vascular membrane lining the inner surface of the bony tissue that forms the medullary cavity of long bones, containing osteoblasts and osteoclasts.
Functions of each component in the overall structure of long bones.
Bone Cells
Types of bone cells include:
Osteoclasts (break down bone)
Large, multinucleated cells that resorb (break down) bone tissue, involved in bone remodeling.
Osteoblasts (build bone)
Bone-forming cells that secrete the bone matrix (osteoid) and mineralize it, leading to new bone formation.
Osteoprogenitor Cells (stem cells for new bone)
Mesenchymal stem cells that can differentiate into osteoblasts, found in the periosteum and endosteum.
Osteon/Compact Bone Structure
Detailed structure includes:
Central Canal
Also known as the Haversian canal, it runs longitudinally through the center of an osteon, containing blood vessels and nerves.
Concentric Lamellae
Rings of calcified matrix that surround the central canal within an osteon.
Lacunae (containing osteocytes)
Small cavities or spaces within the bone matrix, each containing an osteocyte.
Canaliculi (small channels for nutrient exchange)
Tiny channels that connect lacunae to each other and to the central canal, allowing nutrient and waste exchange for osteocytes.
Interstitial Lamellae
Incomplete lamellae located between osteons, often remnants of old osteons that have been partially resorbed.
Circumferential Lamellae
Layers of lamellae located just deep to the periosteum (outer circumferential) and lining the endosteum (inner circumferential), encircling the entire diaphysis.
Types of Ossification
Two types:
Appositional Ossification (growth in width)
Bone growth in thickness or diameter, occurring when osteoblasts in the periosteum secrete new bone matrix on the external bone surface.
Interstitial Ossification (growth in length)
Describes the increase in length of long bones, primarily at the epiphyseal plate via cartilage production and replacement by bone.
Fracture Healing
A complex process involving hematoma formation, fibrocartilaginous callus formation, bony callus formation, and bone remodeling to repair a broken bone.
Fracture Types
Various types noted:
Greenstick Fracture (incomplete fracture, often seen in children)
An incomplete fracture where the bone bends and cracks instead of breaking completely, common in children whose bones are more flexible.
Transverse fracture
A fracture straight across the bone.
Oblique fracture
A fracture at an angle to the bone's axis.
Spiral fracture
A fracture where the break spirals around the bone, often caused by twisting force.
Comminuted fracture
A fracture where the bone shatters into three or more pieces.
Compound (open) fracture
A fracture where the bone breaks through the skin.
Simple (closed) fracture
A fracture where the bone does not break through the skin.
Zones of the Epiphyseal Plate
Key zones to know include:
Zone of Resting Cartilage
Contains small, scattered chondrocytes that anchor the epiphyseal plate to the epiphysis.
Zone of Proliferation
Chondrocytes divide rapidly and arrange into columns, producing new cartilage.
Zone of Hypertrophy
Chondrocytes enlarge significantly, maturing and preparing for calcification.
Zone of Calcification
Cartilage matrix calcifies and chondrocytes die, leaving behind hardened matrix.
Zone of Ossification
Osteoclasts resorb calcified cartilage, and osteoblasts lay down new bone tissue, extending the diaphysis.
Understanding what occurs at each zone during bone development.
Nervous System
Nervous System Cells
Different types include:
Neurons
The primary functional units of the nervous system, specialized for transmitting electrical signals (nerve impulses or action potentials).
Glial Cells
Support cells of the nervous system that provide nutrients, regulate the extracellular environment, and insulate neurons, but do not transmit electrical signals themselves.
Neuron Anatomy
Key components include:
Dendrites
Receiver parts of the neuron that typically pick up signals from other neurons and transmit them towards the cell body.
Cell Body
Also called the soma, it contains the nucleus and most organelles, integrating incoming signals.
Axon
A long, slender projection that transmits electrical impulses away from the cell body to other neurons, muscles, or glands.
Axon Terminals
Distal ends of the axon where neurotransmitters are released to communicate with target cells.
Neuron Potentials
Types of potentials include:
Resting Membrane Potential (typically around -70 mV)
The electrical potential difference across the cell membrane of a neuron at rest, maintained by ion concentration differences and the Na^+/K^+ pump.
Graded Potential
Small, localized changes in membrane potential that vary in strength depending on the stimulus; can be depolarizing or hyperpolarizing.
Inhibitory Postsynaptic Potential (IPSP)
A type of graded potential that hyperpolarizes the postsynaptic membrane, making it less likely to fire an action potential.
Excitatory Postsynaptic Potential (EPSP)
A type of graded potential that depolarizes the postsynaptic membrane, making it more likely to fire an action potential.
Action Potential
A rapid, transient, all-or-none electrical signal actively propagated along the axon, essential for long-distance communication.
Ion movement associated with each potential type:
Example: During action potential, Na^+ ions rush into the neuron.
Neuron Channels
Types include:
Chemically Gated Channels
Ion channels that open or close in response to the binding of a specific chemical neurotransmitter, typically found on dendrites and cell bodies.
Voltage-Gated Channels
Ion channels that open or close in response to changes in membrane potential, crucial for the generation and propagation of action potentials, found abundantly on axons.
Know their locations and the potential changes they induce.
Continuous vs. Saltatory Conduction
Continuous conduction occurs in unmyelinated neurons, whereas saltatory conduction occurs in myelinated neurons, allowing for faster transmission of action potentials.
Continuous conduction is slower as the action potential propagates along the entire unmyelinated axon, while saltatory conduction is faster due to the action potential jumping between nodes of Ranvier in myelinated axons.
Voltage Changes Across a Neuron
Discusses ion movement, particularly the influx of Na^+ and efflux of K^+ during action potentials.
Depolarization occurs due to Na^+ influx, leading to the rising phase of an action potential. Repolarization and hyperpolarization (undershoot) occur due to K^+ efflux, restoring the resting membrane potential.
Ion Movement in Membrane Potential CreationThe shifting concentrations of sodium and potassium ions across the neuronal membrane are crucial in generating the membrane potential, whereby a more positive interior is established during depolarization, and the membrane's polarized state is re-established through the subsequent potassium efflux.
Importance of Na^+/K^+ pump in maintaining resting potential:
Pump moves 3 Na^+ ions out and 2 K^+ ions in.
This active transport pump uses ATP to maintain concentration gradients of Na^+ and K^+ across the membrane, which is critical for establishing and maintaining the negative resting membrane potential.
Refractory Periods
Definition and implications of refractory periods in action potentials.
Discusses how voltage-gated channels function to create these periods, segregating phases of excitation and recovery.
The refractory period is a brief time after an action potential during which the neuron cannot generate another action potential (absolute refractory period) or requires a much stronger stimulus (relative refractory period), ensuring unidirectional signal propagation and limiting firing frequency.