Kaplan — Biology Flashcards
Neuron
Specialized cell capable of transmitting electrical impulses and then translating those electrical impulses into chemical signals
Soma
Cell body of a neutron where the nucleus, ER, and ribosomes are located
Dendrites
Part of neuron which receive incoming messages from other cells
Axon hillock
Part of neuron that integrates the incoming signals and initiates the action potential if it reaches threshold
Axon
Long appendage that terminates inc lose proximity to a target structure
Myelin
Fatty membrane that prevents signal loss or crossing of signals
Increases the speed of the signal
Oligodendrocytes
Glial cells that produce myelin in the central nervous system
Schwann cells
Glial cells that produce myelin in the peripheral nervous system
Nodes of Ranvier
Exposed areas of the axon membrane where the signal will jump
Nerve terminal or synaptic bouton
Enlarged and flattened structure to maximize transmission of the signal to the next neuron
Neurotransmitter
Chemical that transmit information between neurons
Synaptic cleft
Space between the pre-synaptic and post-synaptic neurons in a synapse
Synapse
Nerve terminal, synaptic cleft, and pre-synaptic membrane
Nerve
Bundle of axons in peripheral nervous system
Tract
Bundle of axons in central nervous system
Ganglia
Cell bodies in peripheral nervous system
Nuclei
Cell bodies in central nervous system
Astrocyte
Nourishes neurons and forms the blood-brain barrier which controls the transmission of solutes from the bloodstream in nervous tissue
Ependymal cells
Line ventricles of brain and produce CSF
Cerebrospinal fluid
Physically supports the brain and acts as a shock absorber
Microglia
Phagocytic cells that ingest and break down waste products and pathogens in the central nervous system
Action potentials
All or nothing electrical impulses that travel down the axon to the synaptic bouton
Resting membrane potential
Net electric potential difference that exists across the cell membrane created by movement of charged molecules across that membrane
Potassium leak channels
Channels that allow the slow leak of potassium out of the cell
Equilibrium potential of potassium
-90 mV; point at which there is no more net movement of potassium
Equilibrium potential of sodium
60 mV
Na+/K+ ATPase
Continually pumps sodium and potassium back to where they started
More ATP is spent doing this than for any other purpose
Hyperpolarization
Lowering the membrane potential from its resting potential & making the neuron less likely to fire
Depolarization
Raising membrane potential from its resting potential & making the neuron more likely to fire
Summation
Additive effect of multiple signals
Temporal summation
Multiple signals are integrated during a relatively short period of time
Spatial summation
Additive effects based on the number and location of the incoming signals
Action potential sequence
(1) Na+ influx to reach threshold
(2) Rapid Na+ influx through voltage gated sodium channels to cause depolarization up to 35 mV
(3) Inactivation of sodium channels and delayed opening of potassium channels causes depolarization
(4) Delayed closing causes hyperpolarization
(5) Sodium-potassium pump returns to resting membrane potential
Three forms for voltage-gated sodium channels
- Closed: before reaching threshold and after reversal of inactivation
- Open: from threshold to approximately 35 mV
- Inactive: from 35 mV to resting potential
Repolarization
Restoration of the membrane potential to the resting membrane potential
Absolute refractory period
No amount of stimulation can cause another action potential to occur
Relative refractory period
Greater than normal stimulation to cause an action potential because the membrane potential is lower than its resting membrane potential
Impulse propagation
Cause depolarization in surrounding regions and bring subsequent segments of the axon to threshold
Signal conduction and length
Increased length = slower conduction
Signal conduction and cross-sectional area
Greater cross-sectional area = faster conduction
Saltatory conduction
Signal “hops” from node of Ranvier to node of Ranvier
Synaptic transmission in a chemical synapse
- NTs are stored in membrane bound vesicles in the nerve terminal
- AP reaches the nerve terminal and opens voltage-gated calcium channels, allowing calcium to flow into the cell
- Calcium triggers fusion of membrane-bound vesicles to the cell membrane
- NTs are released into the cleft
- NTs bind either to metabotropic or ionotropic receptors
Ways for removing NTs from synaptic cleft
- NTs can be broken down by enzymatic reactions
- NTs can be brought back into the pre-synaptic neuron using reuptake carriers
- NTs can diffuse out of the synaptic cleft
Sensory neuron
Transmits sensory information from sensory receptors to the spinal cord and brain
Motor neuron
Transmits motor information from brain and spinal cord to muscles and glands
Interneurons
Between other neurons
Central nervous system
Brain and spinal cord
White matter
Axons encased in myelin sheaths
Gray matter
Unmyelinated cell bodies and dendrites
Spinal cord regions
Cervical → thoracic → lumbar → sacral
Vertebral column
Protects spinal cord and transmits nerves at the space between adjacent vertebrae
Dorsal root ganglion
Cell body of sensory neurons
Peripheral nervous system
Made up of nerve tissue and fibers outside brain and spinal cord
31 pairs of spinal nerves + 12 cranial nerves
Somatic nervous system
Consists of sensory and motor neurons distributed throughout the skin, joints, and muscles
Autonomic nervous system
Manages the involuntary muscles associated with many internal organs and glands
Has two antagonistic branches
Parasympathetic nervous system
Branch of ANS that serves to conserve energy
Post-ganglionic NT for parasympathetic nervous system
Acetylcholine
Pre-ganglionic NT for parasympathetic nervous system
Acetylcholine
Structure of parasympathetic nervous system
Long pre-ganglionic neurons and short post-ganglionic neurons
Effects of parasympathetic nervous system
- Constricts pupils
- Stimulates flow of saliva
- Constricts bronchi
- Slows heartbeat
- Stimulates peristalsis and secretion
- Contracts bladder
Sympathetic nervous system
Branch of ANS that is activated by stress
Post-ganglionic NT for sympathetic nervous system
Norepinephrine
Pre-ganglionic NT for sympathetic nervous system
Acetylcholine
Structure of sympathetic nervous system
Short pre-ganglionic neurons and long post-ganglionic neurons
Effects of sympathetic nervous system
- Increases heart rate
- Redistributes blood to muscles of locomotion
- Increases blood glucose concentration
- Dilates the eyes
- Releases epinephrine into bloodstream
Monosynaptic reflex arc
Single synapse between the sensory neurons that receives the stimulus and the motor neuron that responds to it
Knee-jerk reflex
Monosynaptic reflex arc
Patella of knee is hit, causing the stretch of tendon, leading to contraction of quadriceps of muscles
Polysynaptic reflex arc
One interneuron between the sensory and motor neurons
Withdrawal reflex
Polysynaptic reflex arc
Pulls away one leg in response to painful stimulus and extends the other leg to maintain balance
Ampulla
Widest part of the Fallopian tube where fertilization occurs
Acrosomal apparatus
Sperm that first comes into contact with secondary oocyte’s cell membrane forms a tubelike structure that extends to and penetrates the cell membrane
Cortical reaction
Release of calcium ions in response to penetration of the sperm through the cell membrane
Increases the metabolic rate of the zygote and prevents fertilization by multiple sperm cells
Fertilization membrane
Now depolarizer and impenetrable membrane
Dizygotic (fraternal) twins
Fertilization of two different eggs released during one ovulatory cycle by two different sperm
Each zygote will implant in the uterine wall and have its own placenta, chorion, and amnion
Monozygotic (identical) twins
Single zygote splits into two
Can be classified by the structures that they share
Conjoined twins
When zygote division is incomplete, two offspring will be physically attached
Cleavage
Rapid mitosis cell decisions of a zygote
Increase in N:C and surface area:volume ratios
Indeterminate cleavage
Results in cells that can still develop into complete organisms
Determinate cleavage
Results in cells with fates that are already determined
Morula
Solid mass of cells
Blastula
Hollow ball of cells with a fluid-filled inner cavity (blastocoel)
Blastocoel
Fluid-filled inner cavity
Blastulation
Formation of the blastula (hollow ball of cells)
Blastocyst
Mammalian blastula that consists of two noteworthy cell groups (trophoblast and inner cell mass)
Trophoblast cells
Surround the blastocoel and give rise to the chorion and later the placenta
Inner cell mass
Protrudes into the blastocoel and gives rise to the organism itself
Chorion
Extraembryonic membrane that develops into the placenta formed by trophoblasts
Chorionic villi
Microscopic finger-like projection that penetrate the endometrium and originate from trophoblasts
Umbilical cord
Connects the embryo to the placenta and consists of two arteries and one vein encased in a gelatinous structure
Yolk sac
Supports the embryo until the placenta is functional and is the site of early blood cell development
Allantois
Involved in early fluid exchange between the embryo and yolk sac
Remnants of the yolk sac and allantois form the umbilical card
Amnion
Thin, tough membrane filled with amniotic fluid that surrounds the allantois
Serves as a shock absorber
Gastrulation
Generation of three distinct cell layers
Begins with the invagination in the blastula
Archenteron
Membrane invagination into the blastocoel
Blastophore
Opening of the archenteron
Develops into the mouth in protostomes or anus in deuterostomes
Ectoderm
Forms the epidermis, hair, nails, epithelium of nose & mouth, lens of eye, nervous system, inner ear
Mesoderm
Musculoskeletal, circulatory, excretory systems
Endoderm
Epithelial linings of digestive and respiratory tracts
Pancreas, thyroid, bladder, distal urinarytracts
Induction
Ability of one group of cells to influence the fate of nearby cells
Inducers
Diffuse from organizing cells to the responsive cells
Neurulation
Development of the nervous system
Notochord
Rod of mesodermal cells forms along the long axis of the organism like a primitive spine
Induces a group of overlying ectodermal cells to slide inward to form neural folds which surround a neural groove
Neural tube
Gives rise to the central nervous system
Neural folds growth toward one another until they fuse into a neural tube
Neural crest cells
At the tip of each neural fold
Forms the peripheral nervous system
Teratogens
Substances that interfere with development, causing defects or even death of the developing embryo
Specification
Cell is reversibly designated as a specific cell type
Determination
Commitment of a cell to a particular function in the future
Morphogen
Molecules that cause neighboring cells to follow a particular developmental pathway
Differentiation
Process of a cell undertaking changes to develop into the determined cell type
Stem cells
Cells that have not yet differentiated or that give rise to other cells that will differentiate
Potency
Determines the tissues a particular stem cell can differentiate into
Totipotent
Cells with the greatest potency
Pluripotent
Cells that can differentiate into any cell type except for those found in the placental structures
Multipotent
Cells that can differentiate into multiple types of cells within a particular group
Responder
Cell that is induced by surrounding tissues
Competent
Able to respond to the inducing signal
Autocrine
Signals that act on the same cell that secreted the signal in the first place
Paracrine
Signals that act on cells in the local area
Juxtacrine
Cells directly stimulating receptors of an adjacent cell
Encoring
Secreted hormones that travel through the bloodstream to a distant target tissue
Growth factors
Peptides that promote differentiation and mitosis in certain tissues
Reciprocal development
Development of one tissue by a precursor of another tissue will cause the development of the another tissue from its precursor
Apoptosis
Programmed cell death
Apoptotic blebs
Self contained protrusions formed when a cell undergoes apoptosis
Apoptotic bodies
Formed from apoptotic blebs and can be digested by other cells
Prevents the release of potentially harmful substances into the extra cellular environment
Necrosis
Process of cell death where the cell dies as a result of injury
Regenerative capacity
Ability of an organism to regrow certain parts of the body
Complete regeneration
Lost or damaged tissues are replaced with identical tissues
Incomplete regeneration
Newly formed tissue is not identical in structure or function to the tissue that has been injured or lost
Senescence
Biological aging
Can occur at the cellular or organismal level as these changes accumulate
Telomeres
Ends of chromosomes
Shorten with aging
Fetal hemoglobin (HbF)
Greater affinity for oxygen than maternal hemoglobin (HbA)
Also assists with the transfer (and retention) of oxygen into the fetal circulatory system
Umbilical arteries
Carry blood away from the fetus toward the placenta
Umbilical vein
Carries blood toward the fetus from the placenta
Shunt
Redirect blood away from the liver and lungs during development because they are not commonly used
Foramen ovale
One-way valve that connects the right atrium to the left atrium
Allows blood in the pulmonary circulation to be pumped by the systemic circulation directly
Ductus arteriosus
Shunts leftover blood from the pulmonary artery to the aorta
Allows for blood to be pumped in the systemic circulation
Ductus venosus
Bypasses the liver by shunting blood returning from the placenta into the inferior vena cava
First trimester
Within 8 weeks, most organs have formed and embryo becomes known as the fetus
Second trimester
Tremendous amount of growth for fetus
Face takes on a human appearance, move within amniotic fluid, toes and fingers elongate
Third trimester
High transfer of antibodies to allow for protection
Parturition
Vaginal birth caused by rhythmic contractions of uterine smooth muscle coordinated by prostaglandins and oxytocin
Three basic phases: cervix thins out and amniotic sac ruptures (water breaking), strong uterine contractions cause birth of the fetus, placenta and umbilical cord are expelled (afterbirth)
Prostaglandins
Coordinate rhythmic contractions of uterine smooth muscle
Oxytocin
Peptide hormone that coordinates rhythmic contractions of uterine smooth muscle
Afterbirth
Expulsion of placenta and umbilical cord
