Chapter 7 - Nervous System Flashcards
the nervous sytem enables organisms to
receive and respond to stimuli from their external and internal environments
neurons
functional units of nervous system
neuron converts stimuli into
electrochemical signals
electrochemical signals are
conducted through nervous system
the nervous system responds ____ to stimuli than the endocrine system
more rapidly
the neuron consists of
elongated cell consisting of several dendirtes, a body, a single axon
dendrites
form & fxn
cytoplasmic extensions that receive information and transmit it towards the cell body
cell body (soma)
contains nucleus and controls metabolic activity of the neuron
axon
long cellular process that transmits impulses away from teh cell body
most mammalian neuron body and axon are
sheathed by insulating substance - myelin
myelin
sheates body and axon of neuron
allows axons to conduct impulses faster
myelin produced by
glial cells
oligodendrocytes
produce myelin in central nervous system
schwann cells
produce myelin in peripheral nervous system
nodes or Ranvier
gaps between segments of myelin
axons end as swellings known as
synaptic terminals
neurotransmitters released from ____ into _____
synaptic terminals;
synapse (synaptic cleft)
synapse (synaptic cleft)
gap between axon terminals of one cell and dendrites of next cell
axons travelling from spine to tip of foot may be
very long
neurons are specialized to
receive signals from sensory receptors or other neurons in body and transfer information along length of axon
action potentials are
impulses that travel the length of the axon and invade the nerve terminal
action potentails cause
release of neurotransmitters into the synapse
resting potential
potential difference between extracellular space and intracellular space when neuron is at rest
even at rest, a neuron is
polarized
potential difference is the result of
unequal distribution of ions between inside and outside of the cell
typical resting membrane potential is
-70 millivolts
typical resting membrane potential of -70 mv means that the inside of the neuron is
more negative than the outside
the potential difference is due to
selective ionic permeability of neuronal cell membrane
the potential difference is maintained by
active transport by Na+/K+ pump
concentration of K+ is higher _____
the concentration of Na+ is higher ____
inside; outside
in addition to K+/Na+ difference; negatively charged proteins are
trapped inside cell
the resting potential is created because the neuron is selectively permeable to
K+
selective permeability of neuron to K+ means that
K+ diffuses down its concentration gradient, leaving net negative charge inside
neurons are impermeable to
Na+
because neurons are impermeable to Na+
cell remains polarized
ionic gradients are restored by
Na+/K+ pumps
the Na+/K+ pump operates using ____ for energy
ATP
the Na+/K+ pump transports _____ out for every ____ transported into the cell
3 Na+
2 K+
nerve cell body receives both ____ and _____ impulses from other cells
excitatory and inhibitory impulses
action potential generated when
cell becomes sufficiently excited
or
depolarized (less negative)
the minimum threshold membrane potential is
-50 mV
the minimum threshold membrane potential is the level at which
action potential is initiated
Na+ wants to go ____ the cell because _____
into;
it is more negative inside hte cell (electrical gradient) and there is less Na+ inside (chemical gradient)
in response to changes in voltage,
ion channels located in nerve cell membrane open
voltage-gated ion channels
ion channels located in nerve cell membrane that open in response to changes in voltage are called
action potential begins when
voltage-gated Na+ channel open in response to depolarization
voltage-gated Na+ channels open in response to
depolarization
the opening of the voltage-gated Na+ channels allows Na+ to
rush down electrochemical gradient into the cell
depolarization leads to opening the voltage-gated Na+ channels, allowing Na+ to rush down its electrochemical gradient into the cell
this causes
rapid further depolarization of that segment of the cell
after the cascade of depolarization, the voltage-gated Na_ channels close and then
the voltage-gated K+ channels open and K+ rushes out down electrochemical gradient
voltage-gated K+ channels opening and allowing K+ ions to rush down the electrochemical gradient allows for
the cell to return to a mor enegative potential
repolarization
the cell returning to a more negative potential after the voltage-gated K+ channels open to allow K+ ions to rush down the electrochemical gradient to balance the depolarization of the Na+ ions
hyperpolarization
neuron may shoot past resting potential and become even more negative inside than normal
refractory period
immediately following action potential, may be very difficult or impossible to initiate another action potential
all-or-none response
action potential all-or none response
when threshold membrane potential is reached, action potential with consistent size and duration is produced
nerve fires maximally or not at all
stimulus intensity is coded by
frequency of action potentials
axons can theoretically propagate action potentials bidirectionally, however, information transfer occurs only
in one direction:
dendrite —> synaptic terminal
backward information transfer through the axon is impossible because
synapses operate only in one direction
and
refractory periods make backward travel of action potentials impossible
speeds of action potentials
different axons can propagate action potentials at different speeds
speed of action potential depends on
the greater the diameter
and
the more heavily it is myelinated
the faster the impulses
myelin increases conduction of velocity down the axon by
insulating segments of hte axon
membrane permeable to ions only at nodes of Ranvier
action potential “jumps” from node to node
synapse
gap between axon terminal of one neuron and dendrites of another neuron
presynaptic neuron
neuron before synapse
postsynaptic neuron
neuron after synapse
neurons may communicate with
neurons
muscles or glands
effector cell
The muscle, gland or organ cell capable of responding to a stimulus at the terminal end of an efferent neuron or motor neuron.
neurotransmitters
chemical messengers stored in membrane-bound vesicles at the nerve terminal
nerve terminal contains thousands of membrane-bound vesciles full of
neurotransmitters
(chemical messengers)
when the action potential arrives at the nerve terminal and depolarizes it
the synaptic vesicles fuse with the presynaptic membrane and release neurotransmitters into the synapse
once the synaptic vesicles fuse with presynaptic membrane and release neurotransmitters into the synapse,
the neurotransmitter…
diffuses across the synapse and acts on receptor proteins embedded in the postsynaptic membrane
neurotransmitters diffuse across the synapse and act on
receptor proteins on the post-synaptic membrane
the neurotransmitter can lead to ____ on the post-synaptic cell and consequent _____
depolarization;
firing an action potential
how is neurotransmitter removed from synapse?
(3)
- taken back up into nerve terminal via uptake carrier (protein)
- degraded by enzymes located in the synapse
- diffuse out of synapse
neurotransmitmter may be taken back into the nerve terminal from synapse via
a protein: uptake carrier
enzymes that may degrade neurotransmitters in the synapse
acetylcholinesterase inactivates neurotransmitter acetylcholine
curare
(drug)
blocks post-synaptic acetylcholine receptors so that acetylcholine is unable to interact with receptor
leads to paralysis by blocking nerve impluses to muscles
botulism toxin
prevents realease of acetylcholine from pre-synaptic membrane
results in paralysis
anti-cholinesterases
used as nerve gases and in insecticide parathion
inhibit activity in acetylcholinesterase enzyme
acetylcholine is not degraded in the synapse and continues to affect post-synaptic membrane
no coordinated muscular contractions can take place
afferent neurons
sensory neurons
efferent neurons
motor neurons
afferent neurons carry sensory information about
external or internal environment to the brain or spinal cord
efferent neurons carry motor commands
from brain or spinal cord **to **various parts of the body (e.g. muscles, glands)
interneurons
only in local circuits
linking sensory and motor neurons in the brain and spinal cord
cell bodies and nerve terminals in same location
nerves are
bundles of axons covered with connective tissue
plexus
network of nerve fibers
ganglia
neuronal cell bodies clustered together in the periphery
nuclei
neuronal cell bodies clustered together in the central nervous system
nervous system divided into two major systems
central nervous system
peripheral nervous system
central nervous system
brain
spinal cord
peripheral nervous system
somatic
autonomic
autonomic nervous system
sympathetic
parasympathetic
central nervous system (CNS) consists of
brain and spinal cord
brain
composition
mass of neurons in the skull
brain
function
interpreting sensory information
forming motor plans
cognitive functions (thinking)
brain
structure
outer portion - gray matter (cell bodies)
inner portion - white matter (myelinated axons)
brain divided into three parts
forebrain
midbrain
hindbrain
forebrain
composition
telencephalon
diencephalon
telencephalon
cerebral cortex
olfactory bulb
cerebral cortex
highly convoluted gray matter that can be seen on teh surface of the brain
processes and integrates sensory input and motor responses
important for memory and creative thought
diencephalon
thalamus
hypothalamus
thalamus
relay and integration center for spinal cord and cerebral cortex
hypothalamus
controls visceral functions
e.g. hunger, thirst, sex drive, water balance, blood pressure, temperature regulation
control endocrine system
midbrain
composition
mesencephalon
midbrain
(mesencephalon)
function
relay center for visual and auditory impulses
motor control
hindbrain
location
posterior part of brain
hindbrain
composition
cerebellum
pons
medulla
cerebellum
modulate motor impulses initiated by cerebral cortex
maintenance of balance, hand-eye coordination, timing of rapid movements
pons
relay center
allows cortex to communicate with cerebellum
medulla oblongata
controls vital fxns
breathing, heart rate, gi activity
brainstem
composition
midbrain, pons, medulla
spinal cord
elongated extension of brain
conduit for sensory information to the brain
motor information from the brain
reflexes
spinal cord can integrate simple motor responses by itself
spinal cord
structure
outer white matter - motor and sensory axons
inner gray matter area - nerve cell bodies
dorsal horn
sensory information enters spinal cord through the dorsal horn
dorsal root ganglia
contain cell bodies of sensory neurons
ventral horn
all motor information exits spinal cord through ventral horn
for simple reflexes
e.g. knee-jerk reflex
sensory fibers (entering through dorsal root ganglion) synapse directly on ventral horn moter fibers
example of other reflexes:
interneurons between sensory and motor fibers
allow for some preocessing in spinal cord
peripheral nervous system (PNS)
consists of
nerves
ganglia
sensory nerves which enter CNS and motor nerves which leave CNS are part of the
PNS
PNS two primary divisions
somatic nervous system
autonomic nervous system
both somatic and autonomic nervous systems have both
sensory and motor components
somatic nervous system
innervates skeletal muscles and is resopnsible for VOLUNTARY movement
autonomic nervous system
aka
involuntary nervous system
ANS regulates
body’s intenral environment without aid of conscious control
autonomic innervation of body includes both
sensory and motor fibers
ANS innervates these two types of muscle
cardiac
smooth muscle
smooth muscle
located in blood vessels, digestive tract, bladder, bronchi
ANS innervates smooth muscle, which is located in the bladder, digestive tract, bronchi, blood vessels
so it is not surprising that the ANS is important in
excretory processes, respiration, gastrointestinal motility and reproductive processes
ANS composed of two subdivisions
sympathetic nervous system
parasympathetic nervous system
parasympathetic nervous system and sympathetic nervous system act ______ to each other
in opposition
sympathetic nervous system
“fight or flight”
increases blood pressure and heart rate
increases blood flow to skeletal muscles
decreases gut motility
dilates bronchioles to increase gas exchange
sympathetic nervous system uses _____ as it’s primary neurotransmitter
norepinephrine
parasympathetic nervous system
acts to conserve energy and restore activity levels following exertion
“rest and digest”
lowers heart rate
increase gut motility
vagus nerve
parasympathetic nerve
innervates thoracic and abdominal vicsera
parasympathetic nervous system uses ____ as it’s primary neurotransmitter
acetylcholine
the eye and ear are examples of
specialized receptors designed to detect stimuli
the eye detects
light energy
after detecting light energy, the eye transmits information about ____ to the _____
intensity, color, shape to the brain
sclera
thick, opaque layer covering the eyeball
“white” of the eye
choroid layer
beneath the sclera
helps supply retina with blood
dark, pigmented area
reduces reflection in the eye
retina
innermost layer of the eye
contains phtoreceptors that sense light
cornea
transparent layer at the front of the eye
bends and focuses light rays
pupil
rays travel through this opening
diameter of pupil is controlled by
pigmented, muscular iris
iris
responds to intensity of light and surroundings (makes pupil constrict)
lens
light continues through lens after going through pupil
suspended behind pupil
focuses the image onto the retina
the shape and focal length of the lens is controlled by
ciliary muscles
photoreceptors
in the retina
transduce light into action potentials
two main types of photoreceptors
cones
rods
cones
type of photoreceptor in retina
respond to high-intensity illumination
sensitive to color
rods
type of photoreceptor in retina
detect low-intensity illumination
important in night vision
cones and rods contain various pigments that
absorb specific wavelengths of light
cones and pigments (absorb wavelengths of light)
contain 3 different pigments
absorb red, green, blue wavelengths
rod and pigments (absorb wavelengths of light)
rod pigment: rhodopsin
absorbs a single wavelength
photoreceptor cells synapse into
bipolar cells
bipolar cells synapse into
ganglion cells
axons of the ganglion cells bundle to form
optic nerves
optic nerves
conduct visual information to the brain
blind spot
point at which the optic nerve exits the eye
photoreceptors not present here
fovea
small area of retina
densely packed with cones
high acuity vision
vitreous humor
jellylike material composing most space between lens and retina
maintains shape and optical properties of eye
aqueous humor
formed by eye
exits through ducts to join venous blood
disorders of the eye
5
myopia
hyperopia
astigmatism
cataracts
glaucoma
myopia
(nearsightedness)
image is focused in front of retina
hyperopia
(farsightedness)
image is focused behind retina
astigmatism
caused by
irregularly shaped cornea
cataracts develop when
lens becomes opaque
light cannot enter the eye and blindness results
glaucoma
increase of pressure in the eye
due to blocking of outflow of aqueous humor
ear
function
transduces pressure waves (sound energy) into impulses perceived by brain as sound
sound waves pass through ___ regions as they enter the ear
regions sound waves pass through when entering ear
- outer ear
- middle ear
- inner era
outer ear
consists of
auricle (external ear)
auditory canal
at the end of the auditory canal is the
tympanic membrane (eardrum)
of the middle ear
tympanic membrane (eardrum)
vibrates at same frequency as incoming sound
middle ear
- tympanic membrane (eardrum)
- ossicles (bones) (3- malleus, incus, stapes)
- oval window
three ossicles (bones) of the ear
malleus
incus
stapes
fxn of ossicles
amplify the stimulus
transmit stimulus through oval window
oval window (last part of middle ear) leads to
inner era
inner ear is filled with
fluid
inner ear consists of
cochlea
vestibular apparatus
vestibular apparatus
maintains equilibrium
vibration of the ossicles exerts pressure on _____
fluid of the cochlea
pressure on the fluid of the cochlea stimulates ____
hair cells in the basilar membrane to transduce pressure into action potentials
pressure —-> action potentials via hair cells in basilar membrane
action potentials transduced by hair cells in the basilar membrane travel via the _____ to the ____ for processing
auditory (cochlear) nerve
brain
basilar membrane
within the cochlea of the inner ear
stiff structural element
separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani
protozoa nervous system
unicellular organisms - no organized nervous system
single celled organisms may respond to stimuli such as
touch
heat
light
chemicals
cindaria nervous system
simple nervous system - nerve net
network of nerve cells
may have limited centralization
jellyfish nervous system
clusters of cells and pathways
coordinate movements required for swimming
annelida nervous system
central nervous system
the central nervous system of annelida (earthworm) consists of
ventral nerve cord
anterior “brain” of fused ganglia
nerve pathways between receptors to effectors
arthropoda nervous system
brains similiar to annelids
more specialized organs
examples of complex organs in arthropoda
(related to nervous system)
compound or simple eyes
tympanum for detecting sound
