BHSC 1200 FINAL QUESTIONS AND
VERIFIED ANSWERS
organization of nervous system - ANSWER-1) central nervous system = brain and spinal cord
-processes many different kinds of incoming sensory information
-source of thoughts, emotions and memories
-produces signals causing muscles to contracts and glands to secrete
2) peripheral nervous system = consists of all nervous tissue outside the CNS
-further divided into sensory (afferent) division [provides information about somatic senses] and motor
(efferent) division [conveys output from CNS to effectors]
-efferent division is further divided: somatic nervous system (conveys output from CNS to skeletal
muscle) and autonomic nervous system (conveys output from CNS to smooth muscle, cardiac muscle,
and glands)
-autonomic nervous system is further divided: sympathetic nervous system and parasympathetic
nervous system (usually have opposing actions)
functions of nervous system - ANSWER--sensory function: sensory receptors detect internal stimuli;
sensory information is carried to brain and spinal cord
-integrative function: nervous system processes sensory information by analyzing it and making decisions
-motor function: nervous system activates effectors causing muscles to contract and glands to secrete
parts of a neuron - ANSWER--cell body: contains a nucleus surrounded by cytoplasm which includes
organelles
-dendrite: receiving or input portions
-axon: long, thin, cylindrical projection; propagates nerve impulses toward another neuron
-axon hillock: cone shaped elevation; joins axon to cell body
-trigger zone: junction of axon hillock and initial segment; generates nerve impulses which travel along
the axon to their destination
-axon terminal: numerous fine processes originating from the axon
-synaptic bulb: bulb-shaped swellings of the tips of axon terminals; contain synaptic vesicles that store
neurotransmitters
structural classification of neurons - ANSWER--multipolar: have several dendrites and one axon; brain
and spinal cord
-bipolar: one main dendrite and one axon; retina of eye, inner ear, olfactory area of brain
-unipolar: have dendrites and one axon that are fused together to form a continuous process that
emerges from the cell body; function as sensory receptors
functional classification of neurons - ANSWER--sensory: afferent neurons; either contain sensory
receptors at their distal ends or are located just after sensory receptors that are separate cells; forms
action potentials; most are unipolar
-motor: efferent neurons; convey action potentials away from CNS to effectors; most are multipolar
-interneurons: association neurons; mainly located within CNS between sensory and motor neurons;
process incoming sensory information and elicit motor response by activating motor neurons; most are
multipolar
characteristics and function of astrocytes - ANSWER--most abundant, versatile, and highly branched glial
cells
-cling to neurons, synaptic endings, and capillaries
,-functions: support and brace neurons; play role in exchanges between capillaries and neurons through
BBB; guide migration of young neurons; respond to nerve impulses and neurotransmitters; influence
neuronal functioning
characteristics and function of microglia - ANSWER--small, ovoid cells with thorny processes that touch
and monitor neurons
-migrate toward injured neurons
-can transform to phagocytize microorganisms and neuronal debris
characteristics and function of ependymal cells - ANSWER--range in shape from squamous to columnar
-may be ciliated (cilia beat to circulate CSF)
-line the central cavities of the brain and spinal column
characteristics and function of oligodendrocytes - ANSWER--branched cells
-processes wrap CNS nerve fibres, forming insulating myelin sheaths thicker nerve fibres
myelin sheath - ANSWER-lipid protein material that acts as an insulator of nerve cells and speeds up
nerve conduction
structure and function of satellite cells - ANSWER--cover surface of nerve cell bodies
-regulation of extracellular environment of PNS neurons
characteristics and function of Schwann cells - ANSWER--wrap around axon in jelly roll fashion
-one cell forms one segment of myelin sheath
myelination of neurons in CNS vs myelination of neurons in PNS - ANSWER-CNS: an oligodendrocyte puts
forth about 15 broad, flat processes that spiral around CNS axons, forming myelin sheath
PNS: a Schwann cell spirals around an axon many times, forming myelin sheath. The outer nucleated
cytoplasmic layer of the Schwann cell is the neurolemma, found only in PNS
composition of white and gray matter - ANSWER--white matter: regions of the brain and spinal cord with
dense collections of myelinated fibres
-gray matter: mostly neuron cell bodies and nonmyelinated fibers
organization of white and gray matter in brain and spinal cord - ANSWER-brain: white matter = deep;
gray matter = superficial
spinal cord: white matter = superficial; gray matter = deep
resting membrane potential - ANSWER--charge of plasma membrane at rest; potential difference across
membrane of resting cell
-approximately -70mV in neurons (cytoplasmic side of membrane negatively charged relative to outside)
-membrane termed polarized
-generated by: differences in ionic makeup of ICF and ECF; differential permeability of the plasma
membrane
discuss the role of ion channels in establishing the resting membrane potential - ANSWER--leak channels:
gated channels that randomly open and close; found in nearly all cells
-ligand-gated channels: gated channels that open in response to binding of ligand (chemical) stimulus;
found in dendrites of some sensory neurons and dendrites and cell bodies of interneurons and motor
neurons
-mechanically-gated channels: gated channels that open in response to mechanical stimulus (i.e., touch,
pressure, vibration, or tissue stretching); found in dendrites of some sensory neurons
-voltage-gated channels: gated channels that open in response to voltage stimulus (change in membrane
potential); found in axons of all types of neurons
,discuss the role of intracellular proteins in establishing the resting membrane potential - ANSWER--ECF is
rich in Na+ and Cl-; ICF is rich in K+
-plasma membrane has more K+ leak channels than Na+ leak channels so the inside of membrane
becomes increasingly negative as more K+ leave the cell than Na+ enter
-this is why the resting membrane potential is negative
discuss the role of the Na/K pump in establishing the resting membrane potential - ANSWER--stabilizes
resting membrane potential
-maintains concentration gradient for Na+ and K+
-3 Na+ pumped out of cell; 2 K+ pumped in
graded potential vs action potential - ANSWER--graded potential: small deviation from the resting
membrane potential that makes the membrane either more polarized or less polarized; occurs when a
stimulus causes mechanically-gated or ligand-gated channels to open or close in an excitable cell's
plasma membrane
-action potential (aka impulse): a sequence of rapidly occurring events that decrease and reverse the
membrane potential and then eventually restore it to the resting state; occurs in the axon of a neuron
when depolarization reaches a certain level termed the threshold (-55mV)
define threshold, depolarization, repolarization, and hyperpolarization - ANSWER--threshold: -55mV in
most neurons; action potential occurs when this level is reached
-depolarization: negative membrane potential becomes less negative, reaches zero, and then becomes
positive
-repolarization: membrane potential is restored to resting state of -70mV
-hyperpolarization: membrane potential temporarily becomes more negative than the resting level
role of voltage-gated Na+ channels in the depolarization phase - ANSWER-Na+ channels open first,
allowing Na+ to rush into the cell, causing the depolarizing phase
role of voltage-gated K+ channels in the repolarization phase - ANSWER-after depolarization, K+ channels
open, allowing K+ to flow out, causing the repolarizing phase
define absolute and relative refractory periods and explain their significance - ANSWER--absolute
refractory period = when voltage-gated Na+ channels open, neuron cannot respond to another stimulus;
time from opening of Na+ channels to resetting of the channels; ensures that each AP is an all-or-none
event; enforces one-way transmission of nerve impulses
-relative refractory period = period of time during which a second AP can be initiated, but only by a
larger-than-normal stimulus; coincides with the period when the voltage-gated K+ channels are still open
after inactivated Na+ channels have returned to their resting state
significance: act as a protective mechanism so we can't have multiple AP constantly firing
discuss how an action potential is propagated - ANSWER--depends on positive feedback loop
-travel from where they arise at the trigger zone to the axon terminals
-action potential keeps its strength as it spreads along the membrane (propagation)
-sodium flows in, voltage gated ion channels open
-action potential travels along membrane, regenerating over and over at adjacent regions of membrane
from the trigger zone to the axon terminals
-can only propagate in this direction because the regions it has already passed are in their absolute
refractory period
, compare continuous and saltatory conduction - ANSWER--continuous conduction: step-by-step
depolarization of each adjacent segment of the plasma membrane; occurs in unmyelinated axons and in
muscle fibres
-saltatory conduction: impulse jumps from one Ranvier's node to the next; occurs along myelinated
axons due to the uneven distribution of voltage-gated channels
describe the components of the synapse - ANSWER--presynaptic neuron: a nerve cell that carries a nerve
impulse toward a synapse
-postsynaptic neuron: a cell that receives the signal
-synaptic cleft: fluid-filled space separating the presynaptic and postsynaptic neurons
steps involved in neurotransmission - ANSWER-1) nerve impulse arrives at synaptic end bulb of a
presynaptic axon
2) depolarizing phase opens voltage-gated Ca2+ channels, causing Ca2+ to flow inward
3) increase in concentration of Ca2+ inside the presynaptic neuron serves as a signal that triggers
exocytosis of synaptic vesicles. vesicle membranes merge with plasma membrane, releasing
neurotransmitter molecules into the synaptic cleft
4) neurotransmitter molecules diffuse across the synaptic cleft and bind the neurotransmitter receptors
in the postsynaptic neuron's plasma membrane
5) binding of neurotransmitter molecules to their receptors on ligand-gated channels opens the channels
and allows particular ions to flow across the membrane
6) as ions flow through the opened channels, the voltage across the membrane changes (called a
postsynaptic potential). depending on which ions the channels admit, this could be a depolarization or a
hyperpolarization
7) when a depolarizing postsynaptic potential reaches threshold, it triggers an action potential in the
axon of the postsynaptic neuron
discuss how neurotransmitters excite or inhibit postsynaptic structures - ANSWER--excitatory
postsynaptic potential: a neurotransmitter that causes depolarization of the synaptic membrane,
bringing it closer to the threshold
-inhibitory postsynaptic potential: a neurotransmitter that causes hyperpolarization of the synaptic
membrane, causing it to become more negative inside and even farther from the threshold
explain the three ways in which neurotransmitter activity is stopped - ANSWER-1) diffusion: some of the
released neurotransmitter molecules diffuse away from the synaptic cleft. once out of reach of its
receptors, the neurotransmitter can no longer exert an effect
2) enzymatic degredation: certain neurotransmitters are inactivated through enzymatic degradation; ex.
acetylcholinesterase breaks down acetylcholine
3) uptake by cells: many neurotransmitters are actively transported back into the neuron that released
them (reuptake) or into the neighbouring neuroglia (reuptake)
VERIFIED ANSWERS
organization of nervous system - ANSWER-1) central nervous system = brain and spinal cord
-processes many different kinds of incoming sensory information
-source of thoughts, emotions and memories
-produces signals causing muscles to contracts and glands to secrete
2) peripheral nervous system = consists of all nervous tissue outside the CNS
-further divided into sensory (afferent) division [provides information about somatic senses] and motor
(efferent) division [conveys output from CNS to effectors]
-efferent division is further divided: somatic nervous system (conveys output from CNS to skeletal
muscle) and autonomic nervous system (conveys output from CNS to smooth muscle, cardiac muscle,
and glands)
-autonomic nervous system is further divided: sympathetic nervous system and parasympathetic
nervous system (usually have opposing actions)
functions of nervous system - ANSWER--sensory function: sensory receptors detect internal stimuli;
sensory information is carried to brain and spinal cord
-integrative function: nervous system processes sensory information by analyzing it and making decisions
-motor function: nervous system activates effectors causing muscles to contract and glands to secrete
parts of a neuron - ANSWER--cell body: contains a nucleus surrounded by cytoplasm which includes
organelles
-dendrite: receiving or input portions
-axon: long, thin, cylindrical projection; propagates nerve impulses toward another neuron
-axon hillock: cone shaped elevation; joins axon to cell body
-trigger zone: junction of axon hillock and initial segment; generates nerve impulses which travel along
the axon to their destination
-axon terminal: numerous fine processes originating from the axon
-synaptic bulb: bulb-shaped swellings of the tips of axon terminals; contain synaptic vesicles that store
neurotransmitters
structural classification of neurons - ANSWER--multipolar: have several dendrites and one axon; brain
and spinal cord
-bipolar: one main dendrite and one axon; retina of eye, inner ear, olfactory area of brain
-unipolar: have dendrites and one axon that are fused together to form a continuous process that
emerges from the cell body; function as sensory receptors
functional classification of neurons - ANSWER--sensory: afferent neurons; either contain sensory
receptors at their distal ends or are located just after sensory receptors that are separate cells; forms
action potentials; most are unipolar
-motor: efferent neurons; convey action potentials away from CNS to effectors; most are multipolar
-interneurons: association neurons; mainly located within CNS between sensory and motor neurons;
process incoming sensory information and elicit motor response by activating motor neurons; most are
multipolar
characteristics and function of astrocytes - ANSWER--most abundant, versatile, and highly branched glial
cells
-cling to neurons, synaptic endings, and capillaries
,-functions: support and brace neurons; play role in exchanges between capillaries and neurons through
BBB; guide migration of young neurons; respond to nerve impulses and neurotransmitters; influence
neuronal functioning
characteristics and function of microglia - ANSWER--small, ovoid cells with thorny processes that touch
and monitor neurons
-migrate toward injured neurons
-can transform to phagocytize microorganisms and neuronal debris
characteristics and function of ependymal cells - ANSWER--range in shape from squamous to columnar
-may be ciliated (cilia beat to circulate CSF)
-line the central cavities of the brain and spinal column
characteristics and function of oligodendrocytes - ANSWER--branched cells
-processes wrap CNS nerve fibres, forming insulating myelin sheaths thicker nerve fibres
myelin sheath - ANSWER-lipid protein material that acts as an insulator of nerve cells and speeds up
nerve conduction
structure and function of satellite cells - ANSWER--cover surface of nerve cell bodies
-regulation of extracellular environment of PNS neurons
characteristics and function of Schwann cells - ANSWER--wrap around axon in jelly roll fashion
-one cell forms one segment of myelin sheath
myelination of neurons in CNS vs myelination of neurons in PNS - ANSWER-CNS: an oligodendrocyte puts
forth about 15 broad, flat processes that spiral around CNS axons, forming myelin sheath
PNS: a Schwann cell spirals around an axon many times, forming myelin sheath. The outer nucleated
cytoplasmic layer of the Schwann cell is the neurolemma, found only in PNS
composition of white and gray matter - ANSWER--white matter: regions of the brain and spinal cord with
dense collections of myelinated fibres
-gray matter: mostly neuron cell bodies and nonmyelinated fibers
organization of white and gray matter in brain and spinal cord - ANSWER-brain: white matter = deep;
gray matter = superficial
spinal cord: white matter = superficial; gray matter = deep
resting membrane potential - ANSWER--charge of plasma membrane at rest; potential difference across
membrane of resting cell
-approximately -70mV in neurons (cytoplasmic side of membrane negatively charged relative to outside)
-membrane termed polarized
-generated by: differences in ionic makeup of ICF and ECF; differential permeability of the plasma
membrane
discuss the role of ion channels in establishing the resting membrane potential - ANSWER--leak channels:
gated channels that randomly open and close; found in nearly all cells
-ligand-gated channels: gated channels that open in response to binding of ligand (chemical) stimulus;
found in dendrites of some sensory neurons and dendrites and cell bodies of interneurons and motor
neurons
-mechanically-gated channels: gated channels that open in response to mechanical stimulus (i.e., touch,
pressure, vibration, or tissue stretching); found in dendrites of some sensory neurons
-voltage-gated channels: gated channels that open in response to voltage stimulus (change in membrane
potential); found in axons of all types of neurons
,discuss the role of intracellular proteins in establishing the resting membrane potential - ANSWER--ECF is
rich in Na+ and Cl-; ICF is rich in K+
-plasma membrane has more K+ leak channels than Na+ leak channels so the inside of membrane
becomes increasingly negative as more K+ leave the cell than Na+ enter
-this is why the resting membrane potential is negative
discuss the role of the Na/K pump in establishing the resting membrane potential - ANSWER--stabilizes
resting membrane potential
-maintains concentration gradient for Na+ and K+
-3 Na+ pumped out of cell; 2 K+ pumped in
graded potential vs action potential - ANSWER--graded potential: small deviation from the resting
membrane potential that makes the membrane either more polarized or less polarized; occurs when a
stimulus causes mechanically-gated or ligand-gated channels to open or close in an excitable cell's
plasma membrane
-action potential (aka impulse): a sequence of rapidly occurring events that decrease and reverse the
membrane potential and then eventually restore it to the resting state; occurs in the axon of a neuron
when depolarization reaches a certain level termed the threshold (-55mV)
define threshold, depolarization, repolarization, and hyperpolarization - ANSWER--threshold: -55mV in
most neurons; action potential occurs when this level is reached
-depolarization: negative membrane potential becomes less negative, reaches zero, and then becomes
positive
-repolarization: membrane potential is restored to resting state of -70mV
-hyperpolarization: membrane potential temporarily becomes more negative than the resting level
role of voltage-gated Na+ channels in the depolarization phase - ANSWER-Na+ channels open first,
allowing Na+ to rush into the cell, causing the depolarizing phase
role of voltage-gated K+ channels in the repolarization phase - ANSWER-after depolarization, K+ channels
open, allowing K+ to flow out, causing the repolarizing phase
define absolute and relative refractory periods and explain their significance - ANSWER--absolute
refractory period = when voltage-gated Na+ channels open, neuron cannot respond to another stimulus;
time from opening of Na+ channels to resetting of the channels; ensures that each AP is an all-or-none
event; enforces one-way transmission of nerve impulses
-relative refractory period = period of time during which a second AP can be initiated, but only by a
larger-than-normal stimulus; coincides with the period when the voltage-gated K+ channels are still open
after inactivated Na+ channels have returned to their resting state
significance: act as a protective mechanism so we can't have multiple AP constantly firing
discuss how an action potential is propagated - ANSWER--depends on positive feedback loop
-travel from where they arise at the trigger zone to the axon terminals
-action potential keeps its strength as it spreads along the membrane (propagation)
-sodium flows in, voltage gated ion channels open
-action potential travels along membrane, regenerating over and over at adjacent regions of membrane
from the trigger zone to the axon terminals
-can only propagate in this direction because the regions it has already passed are in their absolute
refractory period
, compare continuous and saltatory conduction - ANSWER--continuous conduction: step-by-step
depolarization of each adjacent segment of the plasma membrane; occurs in unmyelinated axons and in
muscle fibres
-saltatory conduction: impulse jumps from one Ranvier's node to the next; occurs along myelinated
axons due to the uneven distribution of voltage-gated channels
describe the components of the synapse - ANSWER--presynaptic neuron: a nerve cell that carries a nerve
impulse toward a synapse
-postsynaptic neuron: a cell that receives the signal
-synaptic cleft: fluid-filled space separating the presynaptic and postsynaptic neurons
steps involved in neurotransmission - ANSWER-1) nerve impulse arrives at synaptic end bulb of a
presynaptic axon
2) depolarizing phase opens voltage-gated Ca2+ channels, causing Ca2+ to flow inward
3) increase in concentration of Ca2+ inside the presynaptic neuron serves as a signal that triggers
exocytosis of synaptic vesicles. vesicle membranes merge with plasma membrane, releasing
neurotransmitter molecules into the synaptic cleft
4) neurotransmitter molecules diffuse across the synaptic cleft and bind the neurotransmitter receptors
in the postsynaptic neuron's plasma membrane
5) binding of neurotransmitter molecules to their receptors on ligand-gated channels opens the channels
and allows particular ions to flow across the membrane
6) as ions flow through the opened channels, the voltage across the membrane changes (called a
postsynaptic potential). depending on which ions the channels admit, this could be a depolarization or a
hyperpolarization
7) when a depolarizing postsynaptic potential reaches threshold, it triggers an action potential in the
axon of the postsynaptic neuron
discuss how neurotransmitters excite or inhibit postsynaptic structures - ANSWER--excitatory
postsynaptic potential: a neurotransmitter that causes depolarization of the synaptic membrane,
bringing it closer to the threshold
-inhibitory postsynaptic potential: a neurotransmitter that causes hyperpolarization of the synaptic
membrane, causing it to become more negative inside and even farther from the threshold
explain the three ways in which neurotransmitter activity is stopped - ANSWER-1) diffusion: some of the
released neurotransmitter molecules diffuse away from the synaptic cleft. once out of reach of its
receptors, the neurotransmitter can no longer exert an effect
2) enzymatic degredation: certain neurotransmitters are inactivated through enzymatic degradation; ex.
acetylcholinesterase breaks down acetylcholine
3) uptake by cells: many neurotransmitters are actively transported back into the neuron that released
them (reuptake) or into the neighbouring neuroglia (reuptake)
