Chapter 11: Nervous System Flashcards
what are the 3 divisions of the nervous system?
- central (CNS)
- Peripheral (PNS)
- Enteric (ENS)
what makes up the CNS?
brain and spinal cord
what is the function of the CNS?
information processing (integrate and process, then coordinate motor and sensory commands)
what makes up the PNS?
all nervous tissue outside CNS (excluding ENS)
what makes up the ENS?
nervous tissue in wall of gastrointestinal tract
what is the function of the ENS?
help control digestive function
what are the 2 divisions of the PNS?
- sensory afferent division
2. motor efferent division
what is the function of the sensory division of PNS?
bring info from receptors to CNS
where is the sensory division of PNS most prominent?
sensory organs (Smell, taste, sight, balance, hearing0
what is the function of the motor division of the PNS?
carry motor commands form CNS
what 2 groups is the motor division of PNS divided into?
- somatic (SNS)
2. autonomic (ANS)
what is the autonomic nervous system?
involuntary, automatically regulates
what is the somatic nervous system?
voluntary, conscious control of movement
receptors
detect changes in internl/external environment
____ respond to commands of CNS
effectors
what are the 3 regions of a neuron?
- dendrites
- cell body
- axon
dendrites
receive stimuli from environment/other neurons
cell body
contains nucleus and other organelles
axon
carries information towards other cells
axon hillock
origin of axon form cell body
initial segament of axon hillock
where AP originates
axolemma
axon plasmalemma
axoplasm
axon cytoplasm
what is contained in the axoplasm?
neurofibrils, neurotubules, vessicles, lysosomes, mitochndria, enxymes
synapse
where neuron communicates with another cell
neurotransmittors are packaged in ___ in axon terminals
synaptic vessicles
____ allow a single neuron to communicate with multiple cells
collateral branches
what are the 3 types of synapses?
- between neurons
- neuromuscluar
- neuroglandular
most CNS neurons lack ___ and cannot divide
centrioles
some neural stem cells exist, but most are ___
inactive
neural stem cells are active in which 3 places?
- olfactory epithelium (smell)
- retina of eye (vision)
- hippocampus (memory)
what are the 4 anatomical classes of neurons?
- anaxonic neurons
- bipolar neurons
- unipolar neurons
- multipolar neurons
structure of anaxonic neurons
small, dendrites indistinguishable from axon
location of anaxonic neurons
brain and special sense organs
functions of anaxonic neurons
poorly understood
structure of bipolar neurons
branching dendritic process and axon with cell body in middle (small)
location of bipolar neurons
special sense organs (rare)
structure of unipolar neurons
dendrites and axon continuous (very long, can extend from toes to spine) cell body off to one side
initial segment of unipolar neuron
where dendrites converge (rest is axon)
location of unipolar neurons
most sensory neurons in PNS
structure of multipolar neurons
2/more dendrites and a single axon, can be as long as unipolar neurons
location of multipolar neurons
most common neurons in CNS
all motor neurons to skeletal muscles are
multipolar neurons
what are the 3 functional classes of neurons?
- sensory
- interneurons
- motor neurons
which functional class of neuron is most abundant?
interneurons
function of sensory receptors
detect stimuli
structure of sensory receptors
processes of sensory neurons or cells monitored be sensory neurons
what are the 3 types of sensory receptors?
- interoceptors
- proprioreceptors
- exteroceptors
interoreceptors monitor ____ and detect ___,___, and ___
internal organs; distension (stretch), deep pressure, pain
proprioreceptors monitor __
position/movement of skeletal muscles and joints
exteroreceptors monitor __
external environment (touch, temp, pressure, special senses)
function of afferent fibers
carry info to CNS
ganglion structure
collection of neuron cell bodies in PNS
sensory neurons are mostly ___ neurons with cell bodies in ___
unipolar; sensory ganglia
somatic sensory neurons monitor ___
outside world and body
visceral sensory neurons monitor ___
internal conditions and organs
interneurons are located in the ___, usually between ___ and ___ neurons
CNS; sensory and motor
function of interneurons
receive information from PNS and CNS; higher functions like learning and memory
somatic motor neurons innervate ___ and provide ___ control
skeletal muscles; conscious
the cell body of a somatic motor neuron in in the __ and the axon extends within a ___
CNS: peripheral nerve
what is a nerve?
bundle of axons in the PNS
visceral motor neurons are part of the __ nervous system
autonomic
visceral motor neurons innervate ____, including ___ (4)
all other effectors; smooth, cardiac, glands, adipose tissue
visceral motor neurons are located in the ___ nervous system(s)
CNS/PNS
autonomic ganglia
location of cell bodies for visceral motor neurons going to peripheral receptors
function of efferent fibers
carry info from CNS to effectors
what are somatic effectors?
skeletal muslces
what are visceral effectors?
cardiac/smooth muscle, glands
function of neuroglia
support/protect neurons
____ comprise half of the total volume of nervous system
neuroglia
4 types of CNS glial cells
- ependymal cells
- microglia
- astrocytes
- oligodendrocytes
location of ependymal cells
lining central canal (spine) and ventricles (brain)
function of ependymal cells
produce, circulate, monitor cerebrospinal fluid (CSF)
structure of microglia
mobile phagocytic cells
function of microglia
remove cellular debris, waste, and pathogens
5 functions of astrocytes
- maintain blood-brain barrier
- structural support
- regulate ion, nutrient, and gas concentration around neurons
- absorb/recycle neurotransmitters
- make scar tissue
2 functions of oligodendrocytes
- provide CNS framework by stabalizing axons
2. produce myelin
how do oligodendrocytes produce the myelin sheath?
cell process wraps axon in layers of myelin and PM
function of myelin sheath
speeds up nerve conduction
myelinated axons appear __ because of the __ content of the myelin
white; lipid
parts of axon with myelin are called
internodes
parts of axon without myelin are called
nodes of Ranvier
parts of CNS that are unmyelinated appear _-
grey
2 types of neuroglia in PNS
- schwaan cells
2. satellite cells
location of schwaan cells
cover peripheral axons
function of schwaan cells
participate in axon repair
location of satellite cells
surround peripheral cell bodies
function of satellite cells
regulate environment around neurons
the function of satellite cells in the PNS is similar to ___ in CNS
astrocytes
myelinated axons in the PNS are made by
myelinating outer surface of schwaan cells (neurilemma)
each myelinated schwaan cells represents
1 internode
in unmyelinated axons, schwaan cells surround ___ that lie in __
segments of a group of axons; membrane folds
function of membrane folds in unmyelinated schwaan cells
stabalize axons and protect them from chemicals
in unmyelinated axons, there are no __ between schwaan cells
nodes
axon regeneration in CNS is limited because (3)
- many more axons are involved
- astrocytes making scar tissue, block axon growth
- astrocytes release chemicals that block axon regrowth
membrane potential
potential difference across a membrane due to unequal charge distribution
inside membrane is slightly __ compared to outside
negative
the slightly negative internal charge is due to __-
different permeability of PM to ions and from active transport
resting membrane potential (definition)
membrane potential of undisturbed cell; starting point
graded potential (definition)
temorary, localized change in resting potential
what produces a graded potential?
typical stimulus
the graded potential ___ with distance form stimulus
decreases
action potential (definition)
electrical event that involves one location on the axon membrane, but the spreads along axon towards terminals
action potential is triggered by __
sufficiently large graded potential
presynaptic cell releases __-
neurotransmitters
neurotransmitters bind to __ on ___ cell membrane, which changes ____ and produces ___
receptors; postsynaptic; permeability; graded potential in post. membrane
response of postsynaptic cell depends on ___ and ___
action of stimulated receptors and other stimuli acting at the same time
the simplest form of information processing in the nervous system is __-
synaptic activity
what are 4 contributors to resting membrane potential?
- ECF has high [na, cl]
- cytosol has high [k+, Pr-]
- na and k are main factors influencing mp
- proteins and ions cant freely move across membrane
the resting membrane potential is a form of ___ energy
potential
resting membrane potential in body cells ranges from
-5mV to -100 mV
resting membrane potential of a neuron is near
-70mV
maintaining the resting membrane potential involves ____ forces and ____ process
passive; active
maintance of the resting potential by passive forces is done by __ channels
leak
diffusion of Na/K+ ions through leak channels is driven by
chemical and electrical gradients
what is the active process in maintaining the resting membrane potential?
Na/K pumps
what are leak channels?
passive membrane channels that are always open
__, __, and __ determine which ions can diffuse through leak channels
size, shape, structure
the pump kicks out __(#) __(ion) and brings in __(#) __ (ion)
3 Na; 2K
gated ion channels change the ___ of the plasma membrane in response to stimuli
permeability
what are the 3 types of gated ion channels?
- chemically gated
- voltage gated
- mechanically gated
chemically gated ion channels are also called
ligand gated ion channels
chemically gated ion channels open when
specific chemicals bind to them
where are chemically gated ion channels most abundant in the body?
dendrites and cell body of a neuron, where synaptic communication happens
voltage gated channels open/close in response to _-
changes in membrane potential
voltage gated channels are characteristic of ___ membranes, which generate/spread __
excitable; action potentials
what are the 2 gates in a Na voltage gated channel?
- activation gate
2. inactivation gate
role of activation gate
opens on stimulation to let sodium in
role of inactivation gate
closes to block entry of sodium ions
mechanically gated channels open in response to
physical distortion of membrane srface
location of mechanically gated channels in body
sensory receptors for stretch, pressure, vibration, sense of touch and hearing
where on a neuron are volatge-gates Na/K+ channels found?
along axon
where on a neuron are voltage gated ca2+ channels found?
axon terminals
what are graded potentials?
changes in membrane potential that cannot spread far from site of stimulation
what causes graded potentials?
stimuli that open gated ion channels
what is the first step in a graded potential?
membrane exposed to chemical that opens the chemically gated sodium channels, leading to depolarization
what happens to Na ions once entered the cell in graded potential?
move away from channels, attracted to negative surface of membrane (local current)
degree of depolarization in graded potential ___ with distance from stimuli and __ with size of stimuli
decreases; increases
what is the 2nd step in a graded potential?
Na is moved out of cell and repolarization occurs to bring back normal resting potential
graded potentials, whether depolarizing or hyperpolarizing, share what 4 characteristics?
- effect of stimulus decreases with distance
- effect spreads passively through local currents
- the change in membrane potential reflects whether + charges enter or exit area
- stronger stimulus results in more area affected and greater change in membrane potential
definition of an action potential
propagated changes in the membrane potential that affect the entire excitable membrane
a neuron receives graded potentials at its __
dendrites or cell body
action potentials at axon terminals release __
neurotransmitters
action potentials allow ____ between cell body and axon terminals
long-range communication
resting membrane potential depends on ___ channels
leak
graded potentials depend on ___ channels
chemically gated ion
action potentials depend on __ channels
voltage gated
first step in action potential generation
resting membrane potential: volatge gated NA/K channels closed
second step in action potential generation
depolarization to threshold: initial stimulus, sodium channels open and rapid depolarization occurs
definition of threshold
membrane potential at which channels open
different stimuli that bring membrane to threshold result in ___ action potentials
identical
third step in action potential generation
inactivation of Na channels, activation of K channels: K leaves cell and potential shifts back to resting (repolarization)
Na channels shift from inactivated to __ as membrane potential returns to near threshold
closed, but capable of opening
absolute refractory period
time where membrane cannot respond to more stimulation
relative refractory period
time where membrane can respond, but only to a stimulus thats stronger than normal
action potentials are generated at __ segment of axon
initial
what are the 2 types of propagation?
- continuous propagation
2. saltatory propagation
describe movement of action potential by continuous propagation
action potential appears to move step by step through entire axon
where does continuous propagation occur?
unmylenated axons
describe movement of action potential by saltatory propagation
depolarizes only at nodes, skips internodes
why does the AP skip internodes?
ions cant cross membrane where there is myelin
is continuous or saltatory propagation faster? why?
saltatory; larger diameter has less resistance to ion movement
synapse definition
location where information is transferred from a neuron to another, or to an effector cell
what are the 2 types of synapses?
- chemical
2. electrical
what is the most abundant type of synapse?
chemical
what types of synapses are chemical?
all synapses between neurons and other cell types and most interneuron synapses
chemical synapses depend on release of ___
neurotransmitters
synapses that release ACh are called
cholinergic synapses
1st step at cholinergic synapse
axon terminal depolarized by arriving action potential
2nd step at cholinergic synapse
depolarization opens voltage gated Ca channels, ca triggers ACh release into cleft
3rd step at cholinergic synapse
Ach binds receptors on chemically gated Na channels, which opens channels for Na to rush in and rapid depolarization
4th step at cholinergic synapse
AChe breaks down bound ACh and other Ach diffuse away from binding sites
what causes synaptic fatigue
neurotransmitter not keeping up with demand
what is synaptic delay?
time lag between arrival of AP at axon terminal and effect on postsynaptic membrane
how do electrical synapses work?
changes is membrane potential of one cell produce local currents in adjacent cell, as if sharing common membrane
what are the 2 types of postsynaptic potentials?
- excitatory postsynaptic potential (EPSP)
2. inhibitory postsynaptic potential (IPSP)
EPSP is graded ___
depolarization
EPSP brings membrane potential ___ threshold
closer to
in EPSP, the membrane is ___, meaning less stimulus needed to trigger AP
facilitated
IPSP is graded __
hyperpolarization
IPSP shifts membrane ___ threshold
further from
in IPSP, the mebrane is __, meaning larger than normal stimulus required to trigger action potential
inhibited
