Exam 2 terms Flashcards
Ion
Any atom that has an electrical charge, (Na+, K+, Cl-)
Cation
An ion with a positive charge
Anion
An ion with a negative charge
Electrolyte
Same as an ion
Principle of macroscopic electroneutrality
On a macroscopic level, each fluid compartment has the same concentration, expressed in mEq/L,
Neuronal pathways
groups of neurons that influence each others activity by communicating at neuronal synapses
Synapse
Act as switches that direct the flow of electrical signals within the nervous system.
Neuronal synapses
Are found between successive neurons in a neuronal pathway.
Neuromuscular junctions
Are found between somatic alpha-motor neurons and myofibers of skeletal muscles
Neuroeffector junctions
Are found between autonomic motor neurons and autonomic effectors including smooth muscle and glandular cells.
Effector
Cell or tissue that carries out the desired response (e.g. muscle contraction, glandular secretion).
Presynaptic neuron
Neuron that carries impulse into the synapse. This is the neuron whose synaptic knob is part of the synapse.
Postsynaptic neuron
Neuron that carries the impulse away from the synapse. This is the neuron whose dendrite, soma, and rarely axon is part of the synapse.
Chemical synapses
Two cells forming the synapse are separated by a physical space called the synaptic cleft.
Synaptic cleft
Narrow space ( about 20-30nm) that separates the presynaptic neuron from the postsynaptic neuron (or effector).
Neurotransmitters (NT)
Extracellular signal molecules (ESMs) released by neurons that diffuse across the synaptic cleft to stimulate or inhibit activity in a postsynaptic neuron or effector (muscle or gland).
Neurotransmitter receptor
Membrane proteins found on the postsynaptic neurons (or effectors) that bind a specific NT and generate a response in the postsynaptic cell.
Excitatory postsynaptic potential (EPSP)
Depolarizing graded potential that brings a postsynaptic neuron closer to the threshold for creating action potentials (APs).
Inhibitory postsynaptic potential (IPSP)
Hyperpolarizing graded potential that moves a postsynaptic neuron closer to the threshold for creating action potentials (APs).
Summation
The process of integrating the input from multiple synapses.
Spatial summation
Effect produced by the simultaneous release of NT from more than one (usually a large number) synaptic knobs on a single postsynaptic neuron.
Temporal summation
Effect produced by stimulation of NT release from the same presynaptic knob(s) in rapid succession on a postsynaptic neuron.
Facilitation
Occurs when the membrane potential of a postsynaptic neuron is held nearer to the threshold then normal but not yet above threshold.
Divergent pathways
When the signal entering into a neuronal pool excites a greater # of fibers leaving the pool. (“amplification” and “divergence into multiple tracts” are used)
Convergent pathways
Signals from multiple input fibers (or multiple axons terminals from a single input fiber) come together to excite a single output fiber. (spatial summation is used)
Efferent (motor) neurons
In neural reflex pathways, integrating centers respond to sensory inputs by sending output signals to effectors.
Somatic motor neurons
control skeletal contraction
Autonomic motor neurons
control involuntary effectors
Pupillary light reflex
pupil diameter changes due to contraction of smooth muscle within the iris (colored part of eye) to control the amount of light entering the eye.
Mydrasis
dilation of pupil (sympathetic division of ANS)
Miosis
Constriction of pupil (parasympathetic division of ANS)
Conductor
The name of the material when positive and negative ions can freely move through (water, copper wire).
Insulator
If oppositely charged ions are unable to move through the material separating them, this is the material.
Electrochemical potential
Form of PE (mV) created by the difference between the amounts of the electrical charge (in the form of ions) present at two points like the inner surface and outer surface of a membrane.
Diffusion Potentials of Membrane Equilibrium Potentials
The flow of ions down their concentration gradient creates an electrical imbalance. Eventually the chemical concentration gradient and the opposing electrical imbalance reach an equilibrium.
Resting Potential (V_rest)
When the membrane is “resting” (not actively conducting an electrical impulse) V_rest ranges from -60 to -90 mV in normal excitable cells. (meaning that the inside of the cells has more anions)
Graded potentials
Are a change in the membrane potential whose magnitude is proportional to the strength of the stimulus. They spread via electrotonic conduction and is decremental. Uses dendrites and the soma.
Action potentials (AP)
Are rapidly moving wave of electrical charge that moves along the membrane of an active excitable cell. They are uniform magnitude of +30mV and are nondecremental. Found in axons and sarcolemma of myofibrils.
Voltage-gated channels
Channels whose molecular conformation (opened or closed) responds to the changes in the electrical potential across the cell membrane.
Depolarization
Process of making membrane potential less negative.
Threshold stimulus
A stimulus strong enough to initiate an action potential by triggering opening of the activation gate of the voltage-gated Na+ channels. Stimulus must cause a change in the V_m > 10mV(to 30mV) to open the activation gate of the voltage-gated Na+ channel.
Subthreshold stimulus
A stimulus not strong enough to open the activation gate of the voltage gated Na+ channels and initiate an AP.
Repolarization
Process of regaining V_rest after depolarization.
Hyperpolarization
Undershooting of V_rest on repolarization due to excess K+ ions flowing out of the cell when the voltage-gated K+ channels are open. Contributes to the relative refractory period.
Refractory period
Brief space of time in which an excitable membrane is resistant to further stimulation.
Absolute refractory period
The short period during and immediately after depolarization where a neuron or myofiber will not respond to any stimulus, no matter how strong.
Relative refractory period
Period following absolute refractory period where a neuron or myofiber will only respond to a strong stimulus
Propagation
Is the spread of an action potential (impulse) along the membrane of an excitable cell (e.g. axon of a neuron of sarcolemma of a myofiber).
Continuous propagation
Is used in unmyelinated axons and muscle cells.
Saltatory propagation
Is used in myelinated axons
All-or-nothing principle
Once an action potential has been initiated, it will travel over the entire membrane of the cell if conditions are right (ALL), or not be created at all if the conditions are wrong (NOTHING; e.g. stimulus below threshold, refractory periods).
Myelinated neuron
Neuron whose axon is wrapped with myelin sheaths.
Myelin
A lipid that forms a sheath around an axon.
Nodes of Ranvier
The areas between the myelin sheath that the AP jumps on. By skipping the myelinated areas the AP conductance is 5 to 50-fold faster than in unmyelinated axons.
Sympathetic division
Thoracolumbar division or emergency or fight or flight division.
parasympathetic division
Craniosacral division or rest and repair division.
Autonomic ganglia
Clusters of neuron cell bodies found outside of the CNS.
Preganglionic neuron
Cell bodies of the neurons are found in the CNS and their axons terminate in autonomic ganglia where they form synapses with postganglionic neurons.
Postganglionic neuron
Cell bodies of these neurons are found in autonomic ganglia and their axons terminate on the involuntary effectors to form neuroeffector junctions.
Sympathetic chain ganglia (sympathetic trunk)
Found on both sides of the vertebral column. Axons of the postganglionic neurons extend out from ganglia to effectors.
Acetylcholine (ACh)
A compound that occurs throughout the nervous system, in which it functions as a neurotransmitter. Cholinergic receptors are activated by (ACh).
Norepinephrine (NE)
Released by the adrenal Medulla, is 20% of adrenaline
Cholinergic neurons
neurons that secrete ACh
Adrenergic neurons
neurons that secrete norepinephrine
Neuroeffector junctions
Are synapses found between a postganglionic autonomic neuron and its target cells (effectors)
Varicosities
dilation or swelling
Cholinergic receptors
Are activated by ACh
Nicotinic receptors
Type (1 of 2) of cholinergic receptor: Ligand-gated Na+ (cation) channels. Found in synapses between pre and postganglionic neurons. Also found in chromaffin cess and myofibers.
Muscarinic receptors
Type (2 of 2) of cholinergic receptor: Are G-protein coupled receptors that activate production of intracellular messengers that control ion channel permeability or metabolic activity of the cell. Found on postganglionic effectors of parasympathetic division.
Adrenergic receptors
Activated by binding of the catecholamines NE and Epi.
alpha-Adrenergic receptors
Respond most strongly to NE. alpha_1 are found in neuroeffector junctions on most sympathetic effectors. Activation causes smooth muscle contraction (vascular, GI & bladder, sphincters, arrector pilorum, and radial muscle of iris). alpha_2 are found in neuroeffector junctions on the GI tract and pancreas.
beta-Adrenergic receptors
beta_1: equally responsive to NE and Epi; Deal with cardiac effectors; kidneys; assist with metabolic functions.
beta_2: respond strongly to Epi; Only respond to blood-borne Epi released by adrenal medulla during F-or-F response; stimulate smooth muscle relaxation.
beta_3; respond strongly to NE; Found in adipose tissue, activation leads to lipolysis.
Fight-or-Flight response (F-or-F)
In emergency situation the body prepares for maximal skeletal muscle activity.
Adrenal medulla
The inner area of the adrenal gland is a modified sympathetic ganglion.
Chromaffin cells
Are modified neurons with no axons that are stimulated by ACh.
Adrenaline (Epinephrine, Epi)
Are neurohormones produce by chromaffin cells in the adrenal medulla and secreted into the bloodstream.
Hormones
Are extracellular chemical signals secreted by endocrine glands and tissues that regulate metabolic activities.
Trophic (or tropic) hormones
Are hormones that regulate the release of other hormones.
Target cells
Any cell that contains receptors that bind and react to a specific hormone.
Receptors
Proteins on the surface or within a target cell that specifically bind and respond to a hormone.
Intracellular signaling pathways
Binding of the hormone to its receptor on or in the target cell activates one or more intracellular signaling pathways that connect hormone/receptor binding to activation of target proteins.
Target proteins
Are the last molecules in the signal pathway. Activation of the pathway usually initiates synthesis of or modifies the activity of target proteins, which then generate the response.
Endocrine or circulating hormones
Hormones released by endocrine glands that are carried in the blood plasma to act on distant target cells.
Neuroendocrines (or neurohormones)
Hormones released by neurons that are carried in the blood to act on distant target cells.
Local hormones
Hormones that act on target cells close to the site of their release.
Paracrines
Act on neighboring cells.
Autocrines
Act on the same cell that secreted them.
Steroids or sterols
Hormones that are synthesized from cholesterol.
1st messengers
Water soluble hormones are because they can only deliver their message to the surface and require additional messengers to stimulate a response.
2nd messengers
Are required to actually stimulate a response. Receive signals from 1st messengers.
Molecular switches
Are a protein that can be switched from an inactive state (“OFF”) to an active state (“ON”) in response to an appropriate signal.
Protein kinases
Enzymes that catalyze the addition of a phosphate to protein effectors to turn them “ON”.
Proteins phosphatases
Enzymes that catalyze the removal of phosphate from protein effectors to turn them “OFF”
Heterotrimeric G-proteins
Are molecular switches that link plasma membrane receptors with intracellular signaling pathways.
Amplification
The process of a very small amount of a hormone binding to a receptor to activate a powerful response throughout its target cell.
Hypothalamus
Is the region in the brain that acts as the “collecting center” for sensory information about the internal environment of the animal.
Pituitary gland (hypophysis)
Is attached to the hypothalamus by a delicate stalk-like structure. Is divided into two sections. It secretes hormones.
Hypophyseal stalk or infundibulum
Stalk that connects the pituitary gland to the hypothalamus.
Adenohypophysis
(anterior pituitary) glandular portion consisting of secretory epithelial cells.
Neurohypophysis
(posterior pituitary) Nervous portion consisting of axons and axon terminals of neurons that have cell bodies in the hypothalamus.
Somatotrophs
1 of 5 glandular cells of the adenohypophysis; secrete growth hormone somatotropin.
Lactotrophs
2 of 5 glandular cells of the adenohypophysis; secretes prolactin (PRL).
Corticotrophs
3 of 5 glandular cells of the adenohyphysis: secretes primarily adrenocorticotropicjhormone (ACTH).
Thyrotrophs
4 of 5 glandular cells of the adenohyphysis; secretes thyroid-stimulating hormone (TSH).
Gonadotrophs
5 of 5 glandular cells of the adenohyphysis; secretes gonadotropins.
Gonadotropins
follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
Trophic hormones
Include releasing (RH) & inhibiting (IH). Most are peptides.
Hypothalamo-hypophyseal portal system
Direct trafficking system used to assure that trophic hormones reach the adenohypophysis at high enough concentrations to exert their regulatory effects.
Portal system
A system of blood vessels in which blood, after passing through a capillary bed of one organ (e.g. hypothalamus), is conveyed directly through venules or veins to a capillary bed of a second organ (e.g. adenohypophysis).
Growth hormone (GH, somatotropin)
Is a protein that is secreted by the somatotropes of the anterior pituitary gland (adenohypophysis). (BST)
Somatocrinin (growth hormone releasing hormone or GHRH)
One of two GH released from the anterior pituitary gland controlled by trophic hormones released by neurons in the hypothalamus.
Somatostatin (growth hormone inhibiting hormone or GHIH)
One of two GH released from the anterior pituitary gland controlled by trophic hormones released by neurons in the hypothalamus.
Somatomedins (insulin-like growth factor or IGF)
GH stimulates this release from hepatocytes (liver cells) deals with metabolic effects.
Endocrine pathologies
Are diseases caused by hormone imbalances (hypersecretion & hyposecretion).
Hypersecretion
If hormone is produced in excess; can result from benign and cancerous tumors. Leads to gigantism, acromegaly, Grave’s disease, & Cushing’s disease.
Hyposecretion
If hormone is produced in low than normal levels. Leads to dwarfism, Addison’s disease, & Type I diabetes.
Gigantism (or giantism)
High levels of GH during adolescent growth period can result in humans that grow to around 8’.
Acromegaly
High levels of GH after adolescence growth period, result in increased growth and thickening of bones like cranial bones, nose, jaw, and vertebrae.
Dwarfism
Lack of production of GH or IGF (pigmies) leads to decreased lengthening of long bones during adolescent growth period.
Prolactin (PRL or lactogenic hormone)
Is secreted by the lactotropes of the anterior pituitary. Functions to develop mammary glands and stimulate milk secretion.
Prolactin-inhibiting hormone (PIH)
Is an amine hormone called dopamine.
Adrenocorticotropic
Regulates the adrenal cortex.
Thyroid-stimulating hormone (TSH)
Regulates the thyroid gland.
Follicle-stimulating hormone (FSH)
One of two gonadotropins that regulate the gonads (ovaries and testes).
Luteinizing hormone (LH)
One of two gonadotropins that regulate the gonads (ovaries and testes).
Hypothalamo-hypophyseal tract
The area between the hypothalamus and the neurohypophysis that hormones are transported through.
Oxytocin (OT)
Stimulates uterine contractions during parturition and milk letdown (ejection) from alveoli into the ductal system of mammary glands. Controlled by neurohormone reflex pathways.
Thyroid gland
Consists of two lobes of glandular tissue located along the trachea just below the larynx.
Thyroid follicles
Consists of a secretory substance called “colloid” surrounded by follicular cells.
Parafollicular cells (C cells or Clear cells)
Are cells found between the numerous thyroid follicles.
Thyroid hormones
Target cells for these are virtually all cells of the animal’s body. Stimulate increases in the basal metabolic rate (BMR; resting rate of calorie expenditure by the body) of the animal.
Thyroxine (T4)
Thyroid hormone
Triiodothyronine (T3)
Thyroid hormone
Basal metabolic rate (BMR)
Resting rate of calorie expenditure by the body
Cretinism
Congenital hypothyroidism results in severely stunted physical and mental growth.
