A&P 11: Fundamentals of the Nervous System & Nervous Tissue Flashcards
Nervous system
master controlling and communicating system of the body
Sensory input
information gathered by the nervous system
Integration
process of the nervous system processing and interpreting sensory input and deciding what should be done at each moment
Motor output
the nervous system activates effector organs (muscles and glands) to cause a response, called this
Central nervous system
brain and spinal cord; integrating and control center of the nervous system; interprets sensory input and dictates motor output based on reflexes, current conditions, and past experience
Peripheral nervous system
part of the nervous system outside the CNS; consists mainly of nerves that extend from the brain and spinal cord
Sensory (afferent) division
part of the PNS; consists of nerve fibers (axons) that convey impulses TO the CNS from sensory receptors located throughout the body
Motor (efferent) division
part of the PNS; transmits impulses FROM the CNS to effector organs (muscle and glands)
Somatic nervous system
composed of somatic motor nerve fibers that conduct impulses from the CNS to skeletal muscles; often referred to as the voluntary nervous system because it allows us to consciously control our skeletal muscles
Autonomic nervous system (ANS)
consists of visceral motor nerve fibers that regulate the activity of smooth muscles, cardiac muscles, and glands; AKA the involuntary nervous system
Sympathetic division
division of the ANS that prepares the body for activity or to cope with some stressor (danger, excitement, etc.); the fight, fright, and flight subdivision
Parasympathetic division
division of the ANS that oversees digestion, elimination, and glandular function; the resting and digesting subdivision
Neuroglia
nonexcitable cells of neural tissue that support, protect, and insulate the neurons; glial cells
Astrocytes
shaped like delicate branching sea anemones, these are the most versatile glial cells; numerous radiating processes cling to neurons and their synaptic endings, and cover nearby capillaries; support/brace neurons and anchor them to their nutrient supply line
Microglial cells
small and ovoid with relatively long thorny processes, which touch nearby neurons, monitoring their health; phagocytizes microorganisms or neuronal debris
Ependymal cells
range in shape from squamous to columnar, and many are ciliated; line the central cavities of the brain and spinal cord, where they form a fairly permeable barrier between the cerebrospinal fluid that fills those cavities and the tissue fluid bathing the cells of the CNS
Oligodendrocytes
branch, but with fewer processes than astrocytes; line up along the thicker nerve fibers in the CNS and wrap their processes tightly around the fibers, producing an insulating covering (myelin sheath)
Satellite cells
surround neuron cell bodies in the PNS; thought to have the same function as astrocytes
Schwann cells
AKA neurolemmocytes; surround all nerve fibers in the PNS and form myelin sheaths around the thicker nerve fibers; functionally similar to oligodendrocytes; vital to regeneration of damaged peripheral nerve fibers
Neurons
nerve cells; structural units of the nervous system; typically large, specialized cells that conduct messages in the form of nerve impulses from one part of the body to another
Neuron cell body
consists of a spherical nucleus with a conspicuous nucleolus surrounded by cytoplasm
Perikaryon (soma)
another name for the neuron cell body; major biosynthetic center of a neuron; contains the usual organelles
Chromatophilic substance
rough ER of a neuron; AKA Nissl bodies; stains darkly with basic dyes; most active and best developed rough ER in the body
Neurofibrils
bundles of intermediate filaments; important in maintaining cell shape and integrity; form a network throughout the cell body
Nuclei
clusters of cell bodies in the CNS
Ganglia
cell bodies that lie along the nerves in the PNS
Processes
armlike ___ extend from the cell body of all neurons
Tracts
bundles of neuron processes in the CNS
Nerves
bundles of neuron processes in the PNS
Dendrites
short, tapering, diffusely branching extensions; convey incoming messages TOWARD the cell body
Receptive (input) regions
dendrites; provide an enormous surface area for receiving signals from other neurons
Axon
each neuron has a single one of these
Axon hillock
the initial region of the axon arises from a cone-shaped area of the cell body called this; then narrows to form a slender process that is uniform in diameter for the rest of its length
Nerve fiber
any long axon
Axon collaterals
branches of an axon; extend from the axon at right angles
Terminal branches
terminal arborizations; profuse branching at the end of an axon (10,000+)
Axon terminals (terminal boutons)
the knoblike distal endings of the terminal branches of an axon
Conducting region
axon is the ___ ___ of the neuron - it generates nerve impulses and transmits them, typically away from the cell body, along the plasma membrane
Axolemma
plasma membrane of the neuron
Secretory region
axon terminals are the ___ ___ of the neuron
Myelin sheath
many nerve fibers, particularly those that are long or large in diameter, are covered with this whitish, fatty (protein-lipoid), segmented ___ ___
Myelinated fibers
axons bearing a myelin sheath; conduct nerve impulses rapidly
Nonmyelinated fibers
axons without a myelin sheath; conduct impulses slowly; dendrites are always _____
Nodes of Ranvier
myelin sheath gaps; occur at regular intervals (1 mm apart) along a myelinated axon
White matter
regions of the brain and spinal cord containing dense collections of myelinated fibers; primarily fiber tracts
Gray matter
contains mostly nerve cell bodies and nonmyelinated fibers
Multipolar neurons
have 3+ processes - one axon and the rest dendrites; most common neuron type in humans (>99%); major type of neuron in the CNS
Bipolar neurons
neurons with 2 processes (axon and dendrite); extend from opposite sides of the cell body; rare; found in some of the special sense organs (retina, olfactory mucosa)
Unipolar neurons
neurons with a single short process that emerges from the cell body and divides T-like into proximal and distal branches; found chiefly in ganglia in the PNS, where they function as sensory neurons
Peripheral process
the more distal process of a unipolar neuron; often associated with a sensory receptor
Central process
proximal process of a unipolar neuron; enters the CNS
Pseudounipolar neurons
unipolar neurons are more accurately called this, because they originate as bipolar neurons
Sensory (afferent) neurons
transmit impulses from sensory receptors in the skin or internal organs toward or into the CNS
Motor (efferent) neurons
carry impulses away from the CNS to the effector organs (muscles and glands) of the body periphery; multipolar; except for some neurons of the ANS, their cell bodies are located in the CNS
Interneurons (association neurons)
neurons that lie between motor and sensory neurons in neural pathways and shuttle signals through CNS pathways where integration occurs; most are confined within the CNS; make up over 99% of the neurons of the body, including most of those in the CNS
Voltage
measure of potential energy generated by separated charge; measured in volts (V) or millivolts (1 mV)
Potential difference (potential)
voltage is always measured between 2 points and is called the ___ or the __ ___ between the points
Current
flow of electrical charge from one point to another; can be used to do work
Resistance
hindrance to charge flow provided by substances through which the current must pass; if high = insulator; if low = conductor
Ohm’s Law
current (I) = voltage (V)/resistance (R); current is directly proportional to voltage; there is no net current between points that have the same potential; current is inversely related to resistance
Leakage (nongated) channels
channels that are always open
Chemically gated (ligand-gated) channels
channels that open when the appropriate chemical (in this case a neurotransmitter) binds
Voltage-gated channels
channels that open and close in response to changes in the membrane potential
Mechanically-gated channels
channels that open in response to physical deformation of the receptor (as in sensory receptors for touch and pressure)
Electrochemical gradient
together, electrical and concentration gradients constitute this; ions flowing along these underlie all electrical events in neurons
Resting membrane potential
potential difference in a resting neuron
Polarized
state of a plasma membrane of an unstimulated neuron or muscle cell in which the inside of the cell is relatively negative in comparison to the outside; the resting state
Sodium-potassium pump (Na+ - K+ ATPase)
stabilizes the resting membrane potential by maintaining the concentration gradients for sodium and potassium
Depolarization
a decrease in membrane potential; the inside of the membrane becomes less negative (moves closer to zero) than the resting potential; also includes events in which the membrane potential reverses and moves above zero to become positive
Hyperpolarization
an increase in membrane potential; the inside of the membrane becomes more negative (moves further from zero) than the resting potential
Graded potentials
short-lived, localized changes in membrane potential that can be either depolarizations or hyperpolarizations; cause current flows that decrease in magnitude with distance
Action potential (AP)
a brief reversal of membrane potential with a total amplitude (change in voltage) of about 100 mV
Nerve impulse
in a neuron, an action potential; typically generated only in axons
Threshold
when depolarization at the stimulation site reaches this certain critical level (often between -55 & -50 mV), depolarization becomes self-generating
Repolarization
restoration of the internal negativity of the resting neuron; both the abrupt decline in Na+ permeability and the increased permeability to K+ contribute to repolarization
All-or-none phenomenon
an action potential either happens completely or doesn’t happen at all
Propagated
if it is to serve as the neuron’s signaling device, an AP must do this along the entire axon’s length
Absolute refractory period
the period, from the opening of the Na+ channels until the Na+ channels begin to reset to their original resting state; ensure that each AP is a separate, all-or-none event and enforces one-way transmission of the AP
Relative refractory period
interval following the absolute refractory period
Continuous conduction
AP propagation involving nonmyelinated axons
Saltatory conduction
AP’s are triggered only at the myelin sheath gaps; the electrical signal appears to jump from gap to gap along the axon; 30x faster than continuous conduction
Multiple sclerosis
demyelinating disease; autoimmune; gradually destroys myelin sheaths in the CNS, reducing them to nonfunctional hardened lesions called scleroses
Group A fibers
mostly somatic sensory and motor fibers serving the skin, skeletal muscles, and joints; have the largest diameter and thick myelin sheaths; conduct impulses at speeds ranging up to 150 m/s (>300mph)
Group B fibers
lightly myelinated fibers of intermediate diameter; transmit impulses at an average rate of 15m/s (30mph)
Group C fibers
smallest diameter; nonmyelinated; incapable of saltatory conduction and conduct impulses at a leisurely pace (1m/s or 2mph or less)
Synapse
junction that mediates information transfer from 1 neuron to the next or from a neuron to an effector cell
Axodendritic synapses
synapses between the axon endings of 1 neuron and the dendrites of other neurons
Axosomatic synapses
synapses between axon endings of 1 neuron and cell bodies (soma) of other neurons
Presynaptic neuron
the neuron conducting impulses toward the synapse
Postsynaptic neuron
the neuron transmitting the electrical signal away from the synapse
Electrical synapses
less common type of synapse; consist of gap junctions like those found between certain other body cells; contain protein channels (connexons) that intimately connect they cytoplasm of adjacent neurons and allow ions and small molecules to flow directly from 1 neuron to the next
Chemical synapses
synapses specialized to allow the release and reception of chemical neurotransmitters
Synaptic vesicles
tiny, membrane-bounded sacs, each containing thousands of neurotransmitter molecules
Synaptic cleft
presynaptic and postsynaptic membranes are always separated by this fluid-filled space approximately 30-50 nm wide
Synaptic delay
time required for a signal to cross a synapse between 2 neurons; rate-determining step of neural transmission
Excitatory postsynaptic potentials (EPSPs)
local graded depolarization events that occur at excitatory postsynaptic membranes
Inhibitory postsynaptic potentials (IPSPs)
hyperpolarizing changes in potential
Summate
add together
Temporal summation
occurs when 1 or more presynaptic neurons transmit impulses in rapid-fire order and bursts of neurotransmitter are released in quick succession
Spatial summation
occurs when the postsynaptic neuron is stimulated simultaneously by a large number of terminals from one (or more commonly) many presynaptic neurons
Facilitated
partially depolarized neurons are more easily excited by successive depolarization events because they are already near threshold
Synaptic potentiation
repeated or continuous use of a synapse (even for short periods) enhances the presynaptic neuron’s ability to excite the postsynaptic neuron, producing larger-than-expected EPSPs
Presynaptic inhibition
occurs when the release of excitatory neurotransmitter by one neuron is inhibited by the activity of another neuron via an axo-axonal synapse
Acetylcholine (ACh)
1st neurotransmitter identified; best understood neurotransmitter because it is released at neuromuscular junctions (easier to study than synapses buried in the CNS)
Acetylcholinesterase (AChE)
enzyme that releases ACh and degrades it to acetic acid and choline; located in the synaptic cleft and on postsynaptic membranes
Biogenic amines
include the catecholamines (dopamine, norepinephrine, and epinephrine) and indolamines (serotonin, histamine)
Catecholamines
dopamine, norepinephrine (NE), and epinephrine
Indolamines
serotonin and histamine
Amino acids (as neurotransmitters)
glutamate, aspartate, glycine, gamma-aminobutyric acid
Neuropeptides
strings of amino acids; include a broad spectrum of molecules with diverse effects
Substance P
neuropeptide; important mediator of pain signals
Endorphins
include beta ____, dynorphin, and enkephalins; act as natural opiates, reducing our perception of pain under stressful conditions
Gut-brain peptides
neuropeptides produced by nonneural body tissues; widespread in the gastrointestinal tract; examples: somatostatin and cholecystokinin
Adenosine triphosphate (ATP)
cell’s universal form of energy; major neurotransmitter (perhaps the most primitive one) in both the CNS and the PNS
Adenosine
part of ATP; acts outside of cells on adenosine receptors; potent inhibitor in the brain; caffeine’s well-known stimulatory effects result from blocking these receptors
Nitric acid (NO)
activates guanylyl cyclase (enzyme that makes the 2nd messenger cyclic GMP; participates in a variety of processes in the brain, including the formation of new memories by increasing the strength of certain synapses; neurotransmitter binding to the postsynaptic receptors indirectly activates ___ ___ synthase, the enzyme that makes ___ ___; acts as a retrograde messenger that sends a signal to increase synaptic strength
Carbon monoxide (CO)
activates guanylyl cyclase (enzyme that makes the 2nd messenger cyclic GMP; mode of action similar to NO
Hydrogen sulfide (H2S)
most recently discovered gasotransmitter; appears to act directly on ion channels and other proteins to alter their function
Endocannabinoids
natural neurotransmitters made by the brain; act at the same receptors as THC (active ingredient in marijuana); their receptors (cannabinoid receptors) are the most common G protein-linked receptors in the brain
Neuromodulator
term used to describe a chemical messenger released by a neuron that does not directly cause EPSPs or IPSPs but instead affects the strength of synaptic transmission
Channel-linked receptors
ionotropic receptors; ligand-gated ion channels that mediate direct neurotransmitter action; composed of several protein subunits in a rosette around a central pore; as the ligand binds to 1+ receptor subunits, the proteins change shape; this event opens the central channel and allows ions to pass; as a result the membrane potential of the target cell changes; always located precisely opposite sides of neurotransmitter release
G protein-linked receptors
activity mediated by these is indirect, complex, slow, and often prolonged; receptors in this class are transmembrane protein complexes - include muscarinic ACh receptors and those that bind the biogenic amines and neuropeptides
Second messengers
cyclic AMP, cyclic GMP, diaclglycerol, or Ca2; act as go-betweens to regulate (open/close) ion channels or activate kinase enzymes that initiate a cascade of enzymatic reactions in the target cells
Neural integration
neuronal pools and their patterns of communicating with other parts of the nervous system
Neuronal pools
functional groups of neurons that integrate incoming information received from receptors or different __ ___ and then forward the proceeded info to other destinations
Circuits
patterns of synaptic connections in neuronal pools; determine the pool’s functional capabilities
Serial processing
the whole system works in a predictable all-or-nothing manner
Reflexes
rapid, automatic responses to stimuli, in which a particular stimulus always causes the same response
Reflex arcs
reflexes occur over neural pathways called this that have 5 essential components - receptor, sensory neuron, CNS integration center, motor neuron, and effector
Parallel processing
inputs are segregated into many pathways and different parts of the neural circuitry deal simultaneously with the information delivered by each pathway
Neuroblasts
potential neurons
Growth cone
the growing tip of an axon; a prickly fanlike structure that gives the axon the ability to interact with its environment
