Ch. 46 Animal Nervous System Flashcards
neuron
a cell that is specialized for the transmission of nerve impulses
- parts: dendrite, axon, soma
- do not reproduce, you have what you’ve got
(aka) nerve cell
All animals except ______ have neurons and muscles
sponges
basic types of nervous systems
1) nerve net
2) central nervous system (CNS)
nerve net
a nervous system in which neurons are diffuse instead of being clustered into large ganglia or tracts
- found in cnidarians (jellyfish, hydra, anemones) & ctenophores (comb jellies)
central nervous system (CNS)
large numbers of neurons aggregated into clusters called ganglia in bilaterian animals
- integrates info from many sensory neurons
- (vertebrates) consists of large ganglia (brain) & spinal chord
sensory receptor
sensory nerve ending that transmits streams of data about the internal/external environment via the sensory neuron
- found in: skin, eyes, ears & nose
sensory neuron
a nerve cell that carries signals from sensory receptors to the central nervous system
- found in afferent division PNS
- stimulates interneurons
What happens to the signal pathway when it encounters a dead neuron?
signal will find new pathway through different neurons
nerve
a long, tough strand of nervous tissue, typically containing thousands of axons, wrapped in connective tissue
- carries impulses between the CNS & some other part of the body
interneuron
a neuron that passes signals from one neuron to another
- connects sensory neurons
- stimulates motor neurons
motor neuron
a nerve cell that send signals from the CNS to effector (response) cells in glands or muscles
- found in efferent division of PNS
peripheral nervous system (PNS)
all the components of the nervous system that are outside the CNS
- wires CNS to whole body
- includes: somatic nervous system & autonomic nervous system
dendrite
a short extension from a neuron’s cell body that receives electrical signals from axons of adjacent cells/neurons
- extension of the cytoplasm
soma
the part of a neuron that contains the nucleus where incoming signals are integrated and generates an outgoing signal
(aka) cell body
axon
a long projection of a neuron that can propagate an action potential
- sends signal to the dendrites of other neurons
membrane potential
a difference in electric charge across a cell membrane
- a form of potential energy
- measured in millivolts (mV)
(aka) membrane voltage
There are generally ______ (more/less) negative ions on the inside of the plasma membrane than the outside.
more
membrane potentials in neurons
about 70-80 mV
electric current
flow of charge due to ion movement from area of like charge to area of unlike charge
electrochemical gradient
the combined effect of an ion’s concentration gradient & electrical (charge) gradient across a membrane that affects the diffusion of ions across the membrane
resting potential
the membrane potential of a cell at resting, or normal, state
- neuron @ rest, not communicating with other neurons
- represents energy stored as concentration gradients in a series of ions
plasma membrane
membrane that surrounds a cell
- separates it from the external environment
- selectively regulates passage of molecules & ions in/out of cell
(aka) cell membrane
ways ions can cross plasma membrane
- Along their electrochemical gradient through an ion channel
- Carried via a membrane cotransporter protein or antiporter protein
- Pumped against an electrochemical gradient by a membrane proteit hat hydrolyzes ATP
ion channel
a type of channel protein that allows certain ions to diffuse across a plasma membrane down an electrochemical gradient
cotransporter
a transmembrane protein that facilitates diffusion of an ion down its previously established electrochemical gradient
- used the energy of that process to transport some other substance, in the same or opposite direction, against its concentration gradient
(aka) secondary active transporter
antiporter
a carrier protein that allows an ion to diffuse down an electrochemical gradient using the energy of that process to transport a different substance in the opposite direction against its concentration gradient
Maintaining the resting potential is tied to the movement of _____ across the membrane & out of the cell
potassisum (K+)
As K+ moves out of the cell, the inside becomes more ________ (negatively/positively) charged relative to the outside.
negatively
equilibrium potential
the membrane potential at which there is no movement of a particular ion into or out of a cell
- each type of ion has its own equilibrium potential
sodium-potassium pump
a transmembrane protein that uses ATP to move sodium ions OUT of the cell and potassium cells IN
(aka) Na+/K+ - ATPase
action potential
a rapid, temporary charge in electrical potential across a membrane
- from negative to positive, back to negative
- occurs in cells (neurons) & muscle cells that have an excitable membrane
- all-or-none event
depolarization
phase in which the membrane becomes less negative
- moves toward a positive charge
- a normal phase in an action potential
- caused by taking in sodium ions
repolarization
return to a resting potential after a membrane potential has changed
- a normal phase in an action potential
hyperpolarization
a change in membrane potential from its resting negative state to an even negative than it was during the resting potential
- normal phase in an action potential
- caused by removal of potassium ion
threshold potential
the membrane potential that will trigger an action potential in a neuron or other excitable cell
(aka) threshold
phases of action potential
1) depolarization
2) repolarization
3) hyperpolarization
Why does an action potential occur?
because specific ion channels in the plasma membrane opened/closed in response to changes in voltages
steps to action potential propogation
1) Na+ enters a cell @ onset of an action potential, (+) charges in cell are repulsed, (-) charges are attracted; results in charge spreading away from the sodium channels
2) As positive charges are pushed farther from the initial sodium channels, they depolarize adjacent portions of the membrane
3) Nearby voltage-gated Na+ channels pop open in response to depolarization; positive feedback occurs; full-ledged action potential results
How come action potentials do not propagate back up the axon?
Because sodium channels are refractory. Once they have opened/closed, they are less likely to open again for a short period of time
refractory
no longer responding to stimuli that previously elicited a response
- lasts briefly
How come a signal does not diminish?
Because the response is all-or-none
properties of large axons
- fewer sodium channels
- less current leaks
- charge spreads farther down the membrane
- transmits action potentials much faster
- large diameter
*compared to small axons
properties of small axons
- more sodium channels
- more current leaks
- charge does not spread farther down the membrane
- transmits action potentials much slower
- small diameter
*compared to large axons
myelination
interpreted as rapid transmission of electrical signals possible in small-diameter axons
myelin sheath
multiple layers of myelin derived from the cell membranes of certain glial cells
- wrapped around the axon of a neuron
- provides electrical insulation
- speeds up action potential
- prevents ions from leaking out as it spreads down an axon
Schwann cell
a type of glia cell that wraps around axons of some neurons outside the PNS
- formed a myelin sheath that provides electrical insulation
oligodendrocyte
a type of glia cell that wraps around axons of some neurons outside the CNS
- formed a myelin sheath that provides electrical insulation
glia
collective term for several types of cells in nervous tissue that are not neurons & do not conduct electrical signals
- perform otro functions
glia function
support
nourishment
electrical insulation
node of Ranvier
unmyelinated section of axon
- occurs periodically along an axon
- site where an action potential can be regenerated
- contains a dense concentration of voltage-gated Na+ channels
If myelin degenerates, the transmission of electrical signals ______.
slows considerably
multiple sclerosis (MS)
a human autoimmune disease in which the immune system attacks the myelin sheaths that insulate axons of neurons
- damage to myelin sheath
- impaired electrical signaling
- muscles weaken
- less coordination
- causes twitchy motion or tremors
neurotransmitter (nt)
a molecule that transmits signals from 1 neuron to another OR from a neuron to a muscle/gland
- chemical messengers
- may function as ligand
types of neurotransmitters
1) acetylcholine
2) dopamine
3) serotonin
4) norepinephrine
5) glutamate
6) gamm-aminobutyric acid (GABA)
7) endorphrine
neurotransmitter categories
A) acetylcholine
B) monoamines
C) amino acids
D) peptides
synapse
the interface between two neurons OR between a neuron & effector cell
- may be modulatory
synaptic vesicle
a small neurotransmitter containing vesicle @ the end of an axon that releases neurotransmitter into the synaptic cleft by exocytosis
- has membranes
synaptic cleft
the space btwn 2 communicating nerve cells (or btwn a neuron & effector cell) @ a synapse, across which neurotransmitter diffuse
- space btwn dendrite & axon
presynaptic neuron
the sending neuron
- releases nts to another neuron/effector cell @ synapse
postsynaptic neuron
the receiving neuron
- receives nts from presynaptic neuron @ synapse
steps of synaptic transmission
1) action potential arrives @ end of axon
2) action potential triggers entry of calcium ions into the presynaptic cell
3) in response, synaptic vesicles fuse w/ the presynaptic membrane, then release the neurotransmitter
4) neurotransmitters bind to receptors on postsynaptic membrane, initiating an action potential if the threshold potential is reached
5) response ends as the neurotransmitter is broken down & reuptake by the presynaptic cell
ligand
any molecule that binds to a specific site on a receptor molecule
- bind to ligand-gated ion channels
ligand-gated ion channel
an ion channel that open/closes in response to binding by a certain molecule
second messenger
a nonprotein signaling molecule produced or activated inside a cell in response to stimulation @ cell surface
- commonly used to relay the message of a hormone or otro extracellular signaling molecule
what can the second messenger trigger?
changes in:
- gene expression
- enzyme activity
- membrane potential
excitatory postsynaptic potentials (EPSPs)
a change in membrane potential (usually DEPOLARIZATION) @ neuron dendrite
- makes an action potential MORE likely
- not all-or-none
- graded by size
- short-lived
inhibitory postsynaptic potentials (IPSPs)
a change in membrane potential (usually HYPERPOLARIZATION) @ neuron dendrite
- makes an action potential LESS likely
- important b/c without it we would feel everything
- not all-or-none
- graded by size
- short-lived
modulatory
modification of neuron’s repsonse to other ESPSs or IPSPs
What does size of EPSP/IPSP depend on?
the amount of neurotransmitter that is released @ the synapse
Why are EPSP/IPSP signals short lived?
Because neurotransmitters do not bind irreversibly to channels in the postsynaptic cell
What happens when an EPSP & IPSP occur close together in space or time?
The change in membrane potential tend to cancel each other out
What happens when several EPSP & IPSP occur close together in space or time?
They sum & make neuron likely to fire an action potential
↑ impulse, ↑ likelihood to feel impulse/stimuli
summation
the additive effect of different postsynaptic potentials (EPSP/IPSP signals) on a nerve or muscle cell such that several subthreshold stimulations can cause or inhibit an action potential
- determines whether an action potential begins in the postsynaptic cell
axon hillock
the site in a neuron where an axon ions the cell body
- where action potentials are first triggered
- triggered by Na+ channels
main parts of the vertebrate system
1) central nervous system (CNS)
2) peripheral nervous system (PNS)
systems that make up the peripheral nervous system (PNS)
1) afferent division
2) efferent divsion
afferent division
the part of the NS that transmits info about the internal & external environment to the CNS
- consists mainly of sensory neurons
- MONITOR conditions inside/outside the CNS
efferent divsion
the part of the NS that carries commands from the CNS to the body
- consists mainly of motor neurons
- carry signals that allow for a RESPONSE
parts of the efferent divsion
1) somatic nervous system
2) autonomic nervous system
somatic nervous system
(part of the PNS) controls skeletal muscles
- voluntary responses
- conscious control
autonomic nervous system
(part of the PNS) controls smooth/cardiac muscles
- involuntary responses
- unconscious control
- includes: parasympathetic & sympathetic nervous system
autopilot
parasympathetic nervous system
part of autonomic nervous system that promotes relaxation or digestion
- functions to conserve/restore energy
rest & digest
PARAsympathetic calms body like how PARAmedics calms the injured person
sympathetic nervous system
part of autonomic nervous system that prepares organs for stressful situations
- stimulates “fight or flight” response
- tense
- emergency
fight or flight
parasympathetic nervous system symptoms
constrict pupils stimulates salivation slow heartbeat constrict airways stimulate activity of stomach inhibit release of glucose stimulate gallbladder (for digestion) stimulate activity of intestine (digestion) control bladder promote erection of genitals
sympathetic nervous system symptoms
dilate pupils inhibit salivation increase heartbeat (more oxygen) relax airway (breathe better) inhibit activity of stomach stimulate release of glucose inhibit gallbladder (for digestion) inhibit activity of intestine (digestion) relax bladder promote ejaculation & vaginal contraction
spinal cord
part of CNS
- made up of many nerves
- serves as info conduit/highway
brain
a large mass of neurons
- located in the head region of animal
- involved in information processing
(aka) cerebral ganglion
parts of the brain
1) cerebrum
2) cerebellum
3) diencephalon
4) brain stem
cerebrum
the most anterior section of the vertebrate brain
- divided into left/right hemispheres & lobes
- makes up bulk of brain
- involved in conscious thought & memory
parts of the cerebrum
1) frontal lobe
2) parietal lobe
3) occipital lobe
4) temporal lobe
frontal lobe
1 of 4 major areas of the cerebrum
- responsible for complex decision making (in humans)
parietal lobe
1 of 4 major areas of the cerebrum
- responsible for integrating sensory & motor functions
occipital lobe
1 of 4 major areas of the cerebrum
- responsible for receiving/interpreting visual info
temporal lobe
1 of 4 major areas of the cerebrum
- functions in memory, speech (humans) & interpreting auditory info
cerebellum
posterior section of the vertebrate brain
- involved in coordination of complex muscle movement (motor patterns)
(ie) locomotion & maintaining balance
diencephalon
the part of the mammalian brain
- relays sensory info to the cerebellum
- center of brain
- FCN: maintain homeostasis
- instincts
- lust (lymbic system)
brain stem
the most posterior portion of the brain
- connects brain to spinal cord
- the autonomic center for regulating heart, lungs & digestive system
corpus callosum
a thick band of neurons that connects the two hemispheres of the cerebrum in the mammalian brain
Paul Broca
responsible for developing methods for mapping cerebrum
- studies mental abilities of people who have suffered brain damage or lesions
- proved that fcns are localized to specific brain areas
Wilder Penfield
pioneered a different approach to studying brain function
- studied w/ severe epileptics
- mapped brain function by electrically stimulating portions of the cerebrum of conscious patients during brain surgery
serotonin
a neurotransmitter involved in many brain functions
- released after learning takes place
- increase EPSPs
- increases likelihood of motor neuron generating action potential
(ie) sleep, pleasure & mood
synaptic plasticity
long-term changes in the responsiveness or physical structure of a synapse that can occur after particular stimulation patterns
- thought to be the basis of learning & memory
neurogenesis
the formation of new neurons
memory
retention of learned info
learning
an enduring change in an individual’s behavior that results from specific experience(s)
