Ch 12: Nervous System Flashcards
combines behavioral and life sciences
neurobiology
which two systems maintain internal coordination?
endocrine and nervous system
system: communicates by means of chemical messengers (hormones) secreted into the blood
endocrine system
system: employs electrical and chemical means to send messages from cell to cell
nervous system
3 steps of nervous system
1: sense organs receive information and transmit coded messages to the brain and spinal cord (CNS: central nervous system)
2. CNS processes this information, relates it to past experiences and determines appropriate response
3. CNS issues commands to muscles and gland cells to carry out such a response
what are the two major subdivisions of the nervous system?
central nervous system and peripheral nervous system
what is the central nervous system made up of?
brain and spinal cord
what is the peripheral nervous system composed of?
the entire nervous system except the brain and spinal cord: composed of nerves and ganglia
a bundle of nerve fibers
nerve
a cluster of neuron cell bodies
ganglion
peripheral nervous system contains ________ and _______ divisions each with ____________ and __________subdivisions
sensory, motor, somatic, visceral
division: carries signals from receptors to CNS
sensory
division: carries signals from receptors in the skin, muscles, bones, and joints
somatic sensory division
carries signals from the viscera (heart, lungs, stomach, and urinary bladder)
visceral sensory division
division: carries signals from CNS to effectors
motor (efferent) division
division: carries signals TO skeletal muscles
somatic motor division
division: carries signals to glands, cardiac and smooth muscle
visceral motor division (autonomic nervous system)
what are the two subdivisions of the visceral motor division (autonomic nervous system)
sympathetic division, parasympathetic division
division: tends to arouse body for action, accelerates heart beat and respiration, while inhibiting digestive and urinary systems
sympathetic division
division: tends to have calming effect; slows heart rate and breathing, stimulates digestive and urinary systems
parasympathetic division
universal properties of neurons
excitability, conductivity, secretion
property of neuron: respond to environmental changes called stimuli
excitability (irritability)
property of neuron: respond to stimuli by producing electrical signals that are quickly conducted to other cells at distant locations
conductivity
property of neuron: when an electrical signal reaches the end of nerve fiber, the cell secretes a chemical neurotransmitter than influences the next cell
secretion
kind of neuron that detects stimuli and transmits information towards the CNS
sensory (afferent) neurons
kind of neuron; lies entirely within CNS connecting motor and sensory pathways (about 90% of all neurons); receives signals from many neurons and carries out integrative functions (makes decisions on responses)
interneuron (association neuron)
kind of neuron; send signals out to muscles and gland cells (the effectors)
motor (efferent) neuron
control center of neuron
soma (aka cell body or neurosoma)
what are the two things a neuron does not have?
centrioles; mitosis
tapered off branches that come off soma; primary site for receiving signals from other neurons
dendrites
originates from the soma at the axon hillock; cylindrical, relatively unbranched for most of its length; specialized for rapid conduction of signals away from soma
axon (nerve fiber)
branches of axon
axon collaterals
cytoplasm of neuron
axoplasm
neuron plasma membrane
axolemma
how many axons per neuron
only 1
little swelling that forms a junction with the next cell
synaptic terminal
one axon; multiple dentrites; most common- most neurons in CNS
multipolar neuron
one axon and one dendrite; olfactory cells, retina, inner ear
bipolar neuron
single process leading away from soma; sensory cells from skin and organs to spinal cord
unipolar neuron
many dendrites but no axon; retina, brain, and adrenal gland
anaxonic neuron
two way passage of proteins, organelles, and other material along an axon
axonal transport
movement down the axon away from soma
anterograde transport
movement up the axon towards the soma
retrograde transport
what guides materials along axon
microtubules
motor proteins carry materials on their backs while they crawl along microtubules. what are two motor proteins
kinesin; dynein
motor proteins in anterograde transport
kinesin
motor proteins in retrograde transport
dynein
what mode of axonal transport do organelles, enzymes, synaptic vesicles, and small molecules use?
fast anterograde transport
what mode of transport do recycled materials and pathogens use?
fast retrograde transport
is slow axonal transport retrograde or anterograde
ALWAYS anterograde
what transport moves enzymes, cytoskeletal components, and new axoplasm down the axon during repair and regeneration of damaged axons?
slow axonal transport
about how many neurons in the nervous system
1 trillion neurons
cells: protect neurons and help them function; outnumber neurons 10 to 1; bind neurons together and form framework for nervous tissue; in fetus, guide migrating neurons to their destination
neuroglia or glial cells
what are the 4 types of glia in the CNS?
oligodendrocytes, ependymal cells, microglia, astrocytes
type of glia- form myelin sheaths in CNS that speed signal conduction
oligodendrocytes
type of glia: line internal cavities of the brain; secrete and circulate cerebrospinal fluid (CSF)
ependymal cells
type of glia: wander through CNS looking for debris and damage
microglia
most abundant glial cell in CNS with diverse functions: forms supportive framework, extensions contact capillaries and stimulate them to form blood brain barrier, convert glucose to lactate and supply this to neurons, secrete nerve growth factors, communicate electrically with neurons, regulate chemical composition of tissue fluid by absorbing excess neurotransmitters and ions
astrocytes
when neuron is damaged, astrocytes form hardened scar tissue and fill in space
astrocytosis or sclerosis
what are the only two types of glia in the PNS?
schwann cells and satellite cells
type of glia- envelope nerve fibers in pns to produce a myelin sheath; assist in regeneration of damaged fibers
schwann cells
type of glial cells: surround the neurosomas in ganglia of the PNS, provide electrical insulation and regulate the chemical environment of the neurons
satellite cells
insulation around a nerve fiber; formed by oligodendrocytes in CNS and Schwann cells in PNS; consists of the plasma membrane of glial cells
myelin sheath
production of myelin sheath; begins at week 14 of fetal development, proceeds rapidly during infancy, completed in late adolescence, dietary fat is important to CNS development
myelination
thick outermost coil of myelin sheath, contains nucleus and most of its cytoplasm; external to neurilemma is basal lamina and a thin layer of fibrous connective tissue (endoneurium)
neurilemma
do nerve fibers in CNS have a neurilemma or endoneurium?
no
gap between segments on myelin sheath
nodes of ranvier
myelin covered segments from one gap to the next
internodes
short section of nerve fiber between axon hillock and first glial cell
initial segment
the axon hillock and the initial segment
trigger zone
masses of rapidly dividing cells
tumors
what do brain tumors arise from?
meninges (protective membranes of CNS), metastasis from nonneuronal tumors in other organs, glial cells that are mitotically active throughout life
grow rapidly and are highly malignant; blood brain barrier decreases effectiveness of chemo; treatment is radiation or surgery
gliomas
disease; oligodendrocytes and myelin sheaths in the CNS deteriorate; myelin replaced by hardened scar tissue; nerve conduction disrupted (double vision, tremors, numbness, speech defects ; no cure (onset from 20-40; fatal from 25 to 30) cause may be autoimmune triggered by virus
multiple sclerosis
disease: abnormal accumulation of glycolipid called GM2 in myelin sheath, normally decomposed by lysosomal enzyme that is missing in individuals homozygous for this allele; accumulation of ganglioside disrupts conduction of nerve signals; blindness, loss of coordination and dementia; fatal before age 4
tay-sachs disease
speed at which nerve signal travels along surface of nerve fiber depends on two factors
diameter (larger=faster)and presence of myelin (myelin speeds conduction)
where are slow signals sent?
gastrointestinal tract
where are fast signals sent?
to skeletal muscles where speed improves balance and coordinated body movement
what are the conditions of regenerating a peripheral nerve fiber?
some intact; neurilemma remains
can regeneration of damaged nerve fibers in the CNS occur?
no
protein secreted by a gland, muscle, or glial cells and picked up by the axon terminals of neurons; prevents apoptosis in growing neurons; enables growing neurons to make contact with their targets
nerve growth factor
study of cellular mechanisms for producing electrical potentials and currents (basis for neural communication and muscle contraction)
electrophysiology
a difference in concentration of charged particles between one point and another
electric potential
cells have more ___________ particles on the _________ of membrane than outside
negative, inside
flow of charged particles from one point to another
electrical current
movements of ions
currents
exists because of unequal electrolyte distribution between extracellular fluid and intracellular fluid
resting membrane potential
resting membrane potential results from what 3 factors?
concentration gradient, selective permeability, electrical attraction
which ion has the greatest influence on RMP
potassium (plasma membrane more permeable to potassium than any other ion; leaks out until electrical charge of cytoplasmic anions attracts it back in and equilibrium is reached no more movement of k+)
cannot escape due to size or charge
cytoplasmic anions
membrane is not very permeable to
sodium
changes in membrane potential of a neuron occurring at and nearby the part of the cell where gated channels are stimulated
local potentials
change in membrane potential toward zero mV (entry of positive ion; cell less negative)
depolarization
properties of local potentials
graded (vary in magnitude with stimulus strength), decremental (get weaker the farther they spread from the point of stimulation), reversible (if stimulation ceases, the cell quickly returns to its normal resting potential), either excitatory or inhibitory (neurotransmitters make the membrane potential more negative- hyperpolarize it so it becomes less likely to produce action potential
dramatic change in membrane polarity produced by voltage gated ion channel
action potential
what are the characteristics of action potential?
all or none law (if threshold is reached, neuron fires at its maximum voltage, if threshold is not reach, it does not fire, nondecremental- does not get weaker with distance, irreversible- once started goes to complete and cannot be stopped)
time during an action potential, and for a few milliseconds after when it is difficult or impossible to stimulate that region of a neuron to fire again
refractory period
what are the two phases of the refractory period
absolute refractory period and relative refractory period
no stimulus of any strenth will trigger AP; lasts as long as Na+ channels are open then inactivated until RMP is established
absolute refractory period
only especially strong stimulus will trigger new AP; k+ channels are still open and any effect of incoming Na+ is opposed by outgoing K+; generally lasts until hyperpolarization ends
relative refractory period
have voltage gated channels along entire length
unmyelinated fibers
signals seem to jump from node to node
saltatory conduction
which fibers use saltatory conduction
myelinated
two neurons needed for synapses
presynaptic neuron and postsynaptic neuron
releases neurotransmitter
presynaptic neuron
responds to neurotransmitter
postsynaptic neuron
gap between neurons
synaptic cleft
occur between some neurons, neuroglia, and cardiac and single unit smooth muscles
electrical synapses
ions diffuse through the gap junctions from one cell to the next
gap junctions
molecules that are released when a signal reaches a synaptic terminal that binds to a receptor on another cell and alters that cells physiology
neurotransmitters
4 major chemical categories of neurotransmitters
acetylcholine, amino acid neurotransmitters, monoamines, neuropeptides
neurotransmitter- formed in acetic acid and choline
acetylcholine
neurotransmitter: includes glycine, glutamate, aspartate, and aminobutyric acid (GABA)
amino acid neurotransmitters
neurotransmitter: includes catecholamines: epinephrine, norepinephrine, dopamine
monoamines
neurotransmitter: chains of 2-40 amino acids; includes cholecystokinin
neuropeptides
chemicals secreted by neuron that have long term effects on groups of neurons
neuromodulartor
the ability to process, store and recall info, and use it to make decisions
neural integration
what allows for decision making?
chemical synapses
based on the postynaptic potentials produced by neurotransmitters
neural integration
voltage change from RMP toward threshold
excitatory postynaptic potential
occurs when the cells voltage becomes more negative than it is when its at rest (less likely to fire)
inhibitory postynaptic potential
the process of adding up postsynaptic potentials and responding to their net effect
summation
occurs when a single synapse generates EPSPs so quickly that each is generated before the next one fades
temporal summation
occurs when EPSPs from several different synapses add up to threshold at an axon hillock
spatial summation
process in which one neuron enhances effect of another
facilitation
process in which one presynaptic neuron suprresses another one (opposite of facilitation)
presynaptic inhibition
way the nervous system converts information into a meaningful pattern of action potentials
neuron coding
depends on which nerves fire
qualitative information
information about the intensity of a stimulus
quantitative information
neurons function in large groups, each of which consist of thousands of interneurons concerned with a particular body function
neural pools
one nerve fiber branches and synapses with several postsynaptic cells
diverging circuit
input from many different nerve fibers can be funneled to one neuron or neural pool
converging circuit
neurons stimulate each other in linear sequence but one of more of the later cells restimulates the first cell to start the process all over
reverberating circuits
input neuron diverges to stimulate several chains of neurons
parallel after discharge circuits
physical basis of memory is pathway through brain called
memory trace/engram
the ability of synapses to change
synaptic plasticity
the process of making transmission easier
synaptic potentiation
what are the kinds of memory
immediate, short, and long term
ability to hold something in thoughts for a few seconds; needed for reading
immediate
memory lasts from seconds to a few hours
short term memory
rapid arrival of repetitive signals at a synapse may foster brief memories
tetanic stimulation
appears to be involved in jogging memory from a few hours ago
posttetanic protentiation
memory may last a lifetime and can hold more info that short term memory
long term memory
types of long term memory
declarative and procedural
retention of events you can put into words
declarative
retention of motor skills
procedural
disease: atrophy of gyri folds in cerebral cortex, neurofibrillary tangles and senile plaques; formation of protein from breakdown product of plasma membranes
alzheimers
disease: progressive loss of motor function; degeneration of dopamine releasing neurones of the substantia nigra resulting in inhibition of motor cortex
parkinsons disease
disease: associated with degeneration of caudate and putamen resulting in overactivation of motor cortex (characterized by jerky movements)
huntingtons disease
