Bio172 - FINAL UH Manoa Spring 2025

Embryonic Development

Animal development involves stages like Sperm, Egg, Zygote, Blastula, Gastrula, Tail-bud, Larval stages, Metamorphosis, and the Adult frog stage.

Fertilization

The fusion of egg and sperm.

Polyspermy

The entry of multiple sperm nuclei into the egg.

Acrosomal Reaction

Triggered when the sperm meets the egg in sea urchins.

Acrosome

The part of the sperm that releases hydrolytic enzymes to digest material surrounding the egg.

Fast Block to Polyspermy

Set up by depolarization of the egg cell membrane upon gamete contact and/or fusion.

Cortical Reaction

Vesicles beneath the egg plasma membrane release contents to form a fertilization envelope that acts as a slow block to polyspermy.

Capacitation

The alteration of sperm motility and structure in the mammalian female reproductive tract before fertilization.

Cleavage

A period of rapid cell division without growth following fertilization.

Blastomeres

Smaller cells formed from the partitioning of the cytoplasm of one large cell during cleavage.

Blastula

A ball of cells with a fluid-filled cavity called a blastocoel.

Yolk Distribution

Influences the pattern of cleavage, with the vegetal pole having more yolk and the animal pole having less yolk.

Holoblastic Cleavage

Complete division of the egg occurring in species with little or moderate amounts of yolk, such as sea urchins and frogs.

Meroblastic Cleavage

Incomplete division of the egg occurring in species with yolk-rich eggs, such as reptiles (including birds).

Morphogenesis

The process by which cells occupy their appropriate locations, involving Gastrulation and Organogenesis.

Gastrulation

The movement of cells from the blastula surface to the interior of the embryo.

Organogenesis

The formation of organs.

Germ Layers

The three layers produced by gastrulation: ectoderm, endoderm, and mesoderm.

Ectoderm

The outer layer of the embryo that contributes to the epidermis of skin, epithelial lining of respiratory, excretory, and reproductive tracts, germ cells, jaws and teeth, pituitary gland, adrenal medulla, and nervous and sensory systems.

Mesoderm

The middle layer of the embryo that contributes to the skeletal and muscular systems, circulatory and lymphatic systems, excretory and reproductive systems (except germ cells), dermis of skin, and adrenal cortex.

Endoderm

The inner layer of the embryo that contributes to the epithelial lining of the digestive tract and associated organs (liver, pancreas), and germ cells.

ENDODERM

inner layer of embryo that contributes to the epithelial lining of the digestive tract and associated organs (liver, pancreas), and germ cells.

Human eggs

have very little yolk.

Blastocyst

the human equivalent of the blastula.

Trophoblast

the outer epithelial layer of the blastocyst that does not contribute to the embryo but initiates implantation.

Extraembryonic membranes

start to form 10-11 days after fertilization, and gastrulation begins 13 days after fertilization.

Gastrulation

in humans produces a three-layered embryo with four extraembryonic membranes: the amnion, chorion, yolk sac, and allantois.

Organogenesis

the process during which various regions of the germ layers develop into rudimentary organs.

Notochord

forms from mesoderm early in vertebrate organogenesis.

Neural plate

forms from ectoderm early in vertebrate organogenesis.

Somites

blocks formed from mesoderm lateral to the notochord.

Coelom

the body cavity formed when the mesoderm lateral to the somites splits.

Apoptosis

programmed cell death.

Determination

the process by which a cell or group of cells becomes committed to a particular fate.

Differentiation

the resulting specialization in structure and function of cells.

Fate maps

descriptions of cell differentiation showing what structures arise from each region.

Axis Formation

the establishment of embryonic axes, involving gravity and pH differences.

Inductive signals

play a major role in pattern formation and development of spatial organization in vertebrate limb formation.

Positional information

molecular cues that control pattern formation, telling a cell where it is within the body.

Limb buds

bumps of tissue from which vertebrate limbs begin.

Sonic hedgehog

a signal released by the ZPA (zone of polarizing activity) that provides positional information to cells along the limb.

Ciliary function

essential for proper specification of cell fate in the human embryo.

Monocilia

nonmotile cilia that act as antennae for chemical signals and play roles in normal kidney development.

Motile cilia

cilia that move signals and play roles in left-right specification.

Kartagener's Syndrome

associated with situs inversus, a condition where the location of internal organs is reversed.

Nerve Cells

Nerve cells (neurons) receive signals at their dendrites and pass these along the axon for rapid communication.

Afferent Nerves

Afferent (sensory) nerves carry signals to the brain or central nervous system.

Efferent Nerves

Efferent (motor) nerves carry signals out from the central nervous system.

Resting Membrane Potential

At rest, a nerve has a negative charge inside and a positive charge outside, called a resting membrane potential (-70 mV).

Action Potential

An action potential is an electrical signal that moves along the axon, characterized by a wave of positive charge rushing in at successive positions.

Depolarization

A stimulus at the dendrite end of the cell opens sodium (Na+) channels, potentially causing depolarization, which flips the membrane potential.

Repolarization

Depolarization triggers K+ flow out of the neuron (repolarization) and undershoot.

All or Nothing Response

An action potential is an 'all or nothing' response; all action potentials are identical and, once triggered, go to completion.

Synapse

Action potentials are transmitted between nerve cells across gaps called synapses.

Neurotransmitters

Transmission across synapses can be electrical or chemical via molecules called neurotransmitters.

Neurotransmitter Function

Neurotransmitter released by one nerve triggers the opening of ion channels on the next nerve; if enough channels open, the nerve will depolarize and pass along its own action potential.

Psychiatric Medicines

Many psychiatric medicines work by altering how long neurotransmitters remain in the synapse.

Clostridium botulinum

Clostridium botulinum causes botulism by releasing a neurotoxin that blocks the release of acetylcholine, a neurotransmitter in muscles.

Clostridium tetani

Clostridium tetani causes tetanus by releasing a neurotoxin that blocks the release of inhibitory neurotransmitters, leading to spastic paralysis.

Signal Speed

Greater axon diameters and myelin sheaths consisting of glial cells (oligodendrocytes and Schwann cells) increase the speed of nerve signal transmission.

Saltatory Conduction

Action potentials jump between gaps between myelin called nodes of Ranvier in a process called saltatory conduction.

Mycobacterium leprae

Mycobacterium leprae causes leprosy by first infecting Schwann cells.

Central Nervous System (CNS)

Bilateral animals have a central nervous system (CNS) (Brain, Spinal cord) that communicates with a peripheral nervous system (PNS).

Peripheral Nervous System (PNS)

The PNS is divided into the Motor system and the Autonomic nervous system.

Motor System

The motor system controls skeletal muscles.

Autonomic Nervous System

The autonomic nervous system governs involuntary body functions and is divided into the Sympathetic division and the Parasympathetic division.

Sympathetic Division

The sympathetic division of the autonomic nervous system is associated with the 'Fight or flight' response.

Parasympathetic Division

The parasympathetic division of the autonomic nervous system is associated with 'Rest and digest' functions.

Sensory Pathways

Sensory pathways have four functions in common: 1. Reception, 2. Transduction.

Sensory pathways

Have four functions in common: 1. Reception, 2. Transduction, 3. Transmission, and 4. Perception.

Reception

Sensory receptors interact directly with stimuli, both inside (Interoceptors) and outside (Exteroceptors) the body.

Interoceptors

Respond to internal conditions like blood O2, CO2, pH, blood pressure, limb position (proprioception), and body temperature.

Transduction

The conversion of stimulus energy into a change in the membrane potential of a sensory receptor.

Receptor potential

The change in membrane potential that occurs during sensory transduction; it is a graded potential.

Transmission

After energy has been transduced, some sensory cells generate the transmission of action potentials to the CNS.

Action potentials

All equal signals; the frequency of the action potentials encodes information about the strength of the sensory stimulation.

Perception

The representations of stimuli constructed in the brain, distinguishing stimuli based on the area where action potentials arrive.

Amplification

The increase in the strength of stimuli from receptors.

Adaptation

The decrease in sensitivity to a constant stimulus over time.

Mechanoreceptors

Respond to sound, touch, and motion.

Electromagnetic receptors

Respond to light and electricity.

Thermoreceptors

Respond to heat and cold.

Pain receptors

Respond to noxious chemicals and temperatures.

Chemoreceptors

Respond to solutes, tastes, and smells.

Neuronal receptors

Receptors that are afferent neurons.

Non-neuronal receptors

Receptors that regulate an afferent neuron; a stimulus leads to neurotransmitter release.

Free nerve endings

Transmit pain signals in response to thermal and mechanical stimuli or molecules released by injured cells.

Hair cells

Receptors with mechanically-gated ion channels that open in response to displacement.

Tympanic membrane

Transmits vibrations from sound to the inner ear.

Volume detection

Detected by the number of hair cells stimulated.

Pitch detection

Detected by the position of the stimulated cells along the basilar membrane.

Statolith-containing organs

Detect movement and position relative to gravity in invertebrates.

Lateral Line

The system of aquatic vertebrates used to detect vibrations and currents in water.

Chemoreception

Detection of specific molecules, important in identifying food, mates/predators, noxious chemicals, CO2, and H2O.

Olfactory cells

Chemoreceptors providing a sense of smell, detecting signals that are distant from their source.

Pheromones

Chemicals used for communication among members of a species.

Vomeronasal organ

An organ in some vertebrates for chemoreception, primarily in response to pheromones.

Flehmen response

Increases its effectiveness by drawing molecules towards the organ.

Gustation

The sense of taste.

Gustatory cells

The receptors of taste that detect signals from contact with chemicals, are food-related, water-soluble, and high concentration.