Cells of the Nervous System
Nervous System Neurons
Functions (CRIME) § Also called nerve cells
1. Controlling muscles and glands. § Receive stimuli, conduct action potentials,
2. Receiving sensory input. transmit signals
3. Integrating information.
4. Maintaining homeostasis. Cell body – contains a single nucleus; source of
5. Establishing and maintaining mental activity. information for gene expression n
Divisions of the Nervous System Dendrites – extensions of the cell body; receive
I. Central Nervous System information from other neurons; transmit the info
§ Brain and spinal cord toward the neuron cell body
II. Peripheral Nervous System Axon – single long cell process; conduct action
§ Nerves and ganglia potentials from one part of the brain or spinal cord to
a. Sensory Division – afferent (toward) another part
division; conducts action potentials Ø Axon of sensory neurons – conduct action
from sensory receptors to the CNS potentials towards the CNS
• Sensory neurons – neurons Ø Axon of motor neurons – conduct action
that transmit action potentials potentials away from the CNS
from the periphery to the CNS
Axon hillock – where the axon leaves the neuron cell
i. Somatic Sensory Fibers – carry body
info from stimuli coming from
the skin, skeletal, muscles, Nissl bodies – rough ER found in the cell body of a
joints neuron
ii. Visceral Sensory Fibers – Schwann cells – form a myelin sheath (increases speed
transmits impulses coming from of impulse transmission)
the visceral organs
Collateral axons – branches of axons
b. Motor Division – efferent (away)
division; conducts action potentials Types of Neurons
from the CNS to effector organs 1. Multipolar neurons – many dendrites + a single
• Motor neurons – neurons that axon
transmit action potentials
from the CNS toward the 2. Bipolar neurons – two processes: 1 dendrite + 1
periphery axon
i. Somatic Motor Nervous 3. Pseudo-unipolar neurons – single process that
System / Voluntary – divides into 2 processes: extends to the
transmits action potentials periphery + extends to the CNS
form the CNS to the skeletal
muscles Neuroglia
§ Non-neuronal cells of the CNS + PNS
ii. Autonomic Motor Nervous § More numerous than neurons
System / Involuntary – § Retain the ability to divide
transmits action potentials
from the CNS to cardiac, 1. Astrocytes – major supporting cells in the CNS;
smooth muscles and glands stimulate/inhibit the signaling activity of nearby
1. Sympathetic – figth-or- neurons; help limit damage to neural tissue
flight system v Blood brain barrier – protects neurons from
2. Parasympathetic – toxic substances in the blood; allows
resting and digesting exchange of waster products + nutrients
system
2. Ependymal cells – produce cerebrospinal fluid;
iii. Enteric Nervous System – help move the cerebrospinal fluid through the CNS
unique subdivision; both
sensory and motor neurons 3. Microglia – act as immune cells of the CNS’
contained within the digestive protect the brain by removing bacteria and cell
tract debris
M o r a n o , M . A .
, 4 – 5. Oligodendrocytes (CNS) and Schwann cells Electrical Signals and Neural Pathways
(PNS) – provide an insulating material that Resting Membrane Potential
surrounds axons Polarized cell membrane – uneven distribution of
charge
Neural Signaling
§ Communication among neurons Resting membrane potential – uneven charge
distribution in an unstimulated/resting cell; polarized
1. Reception – stimuli received by visual receptors Ø Higher concentration of K+ inside CM
in the eye Ø Higher concentration of Na+ outside CM
Ø Greater permeability of CM to K+ than to Na+
2. Transmission – sensory neurons transmit info to
CNS Leak channels – always open
3. Integration – info given is interpreted and an Gated channels – closed until opened by specific signals
appropriate response is determined
Chemically gated channels – opened by
4. Transmission – the CNS transmits info to motor neurotransmitters
neurons
Voltage gated channels – opened by a change in
5. Actual response – muscle/glands receive info membrane potential
and instruction from motor neurons
Sodium potassium pump – required to maintain the
Myelin Sheaths greater concentration of Na+ outside the CM and K+
§ Highly specialized insulating layer of cells inside
Unmyelinated axons – action potentials are conducted Action Potentials
slowly bcos in travels along the entire axon Excitable cells – RMP changes in response to stimuli
that activate gated ion channels
Myelinating axons – action potentials are conducted
rapidly by salutatory conduction Local current – Na+ diffuses quickly into cell
Nodes of Ranvier – gaps in the myelin sheath; where Depolarization – a change that causes the inside of the
ion movement can occur CM to become positive
Organization of Nervous Tissue Local potential – result of depolarization
Gray Matter – groups of neuron cell bodies + their
dendrites; very little myelin Threshold value – attainable local potential (critical pt.)
Ø In the CNS;
v Cortex – GM on the surface of the brain Action potential – constitution of depolarization and
v Nuclei – GM located deeper within the repolarization
brain
Ø In the PNS; Hyperpolarization – the charge on the CM briefly
v Ganglion – a cluster of neuron cell becomes more negative than the RMP
bodies
All-or-none fashion – threshold is reached = action
White Matter – bundles of parallel axons + myelin potential occurs; if the threshold is not reached = action
sheaths potential doesn’t occur
Ø In the CNS
v Nerve tracts – conduction pathways; Continuous conduction – the action potential is
propagate action potentials from one conducted along the entire axon CM
area of the CNS to another
Saltatory conduction – action potentials jump from one
Ø In the PNS;
node of Ranbier to the next
v Nerves – bundles of axons + connective
tissue sheaths
The Synapse
Synapse – a junction where the axon of one neuron
interacts with another
Presynaptic terminal – end of the axon
Postsynaptic membrane – membrane of the dendrite or
effector cell
Synaptic cleft – space separating the presynaptic &
postsynaptic membrane
M o r a n o , M . A .
Nervous System Neurons
Functions (CRIME) § Also called nerve cells
1. Controlling muscles and glands. § Receive stimuli, conduct action potentials,
2. Receiving sensory input. transmit signals
3. Integrating information.
4. Maintaining homeostasis. Cell body – contains a single nucleus; source of
5. Establishing and maintaining mental activity. information for gene expression n
Divisions of the Nervous System Dendrites – extensions of the cell body; receive
I. Central Nervous System information from other neurons; transmit the info
§ Brain and spinal cord toward the neuron cell body
II. Peripheral Nervous System Axon – single long cell process; conduct action
§ Nerves and ganglia potentials from one part of the brain or spinal cord to
a. Sensory Division – afferent (toward) another part
division; conducts action potentials Ø Axon of sensory neurons – conduct action
from sensory receptors to the CNS potentials towards the CNS
• Sensory neurons – neurons Ø Axon of motor neurons – conduct action
that transmit action potentials potentials away from the CNS
from the periphery to the CNS
Axon hillock – where the axon leaves the neuron cell
i. Somatic Sensory Fibers – carry body
info from stimuli coming from
the skin, skeletal, muscles, Nissl bodies – rough ER found in the cell body of a
joints neuron
ii. Visceral Sensory Fibers – Schwann cells – form a myelin sheath (increases speed
transmits impulses coming from of impulse transmission)
the visceral organs
Collateral axons – branches of axons
b. Motor Division – efferent (away)
division; conducts action potentials Types of Neurons
from the CNS to effector organs 1. Multipolar neurons – many dendrites + a single
• Motor neurons – neurons that axon
transmit action potentials
from the CNS toward the 2. Bipolar neurons – two processes: 1 dendrite + 1
periphery axon
i. Somatic Motor Nervous 3. Pseudo-unipolar neurons – single process that
System / Voluntary – divides into 2 processes: extends to the
transmits action potentials periphery + extends to the CNS
form the CNS to the skeletal
muscles Neuroglia
§ Non-neuronal cells of the CNS + PNS
ii. Autonomic Motor Nervous § More numerous than neurons
System / Involuntary – § Retain the ability to divide
transmits action potentials
from the CNS to cardiac, 1. Astrocytes – major supporting cells in the CNS;
smooth muscles and glands stimulate/inhibit the signaling activity of nearby
1. Sympathetic – figth-or- neurons; help limit damage to neural tissue
flight system v Blood brain barrier – protects neurons from
2. Parasympathetic – toxic substances in the blood; allows
resting and digesting exchange of waster products + nutrients
system
2. Ependymal cells – produce cerebrospinal fluid;
iii. Enteric Nervous System – help move the cerebrospinal fluid through the CNS
unique subdivision; both
sensory and motor neurons 3. Microglia – act as immune cells of the CNS’
contained within the digestive protect the brain by removing bacteria and cell
tract debris
M o r a n o , M . A .
, 4 – 5. Oligodendrocytes (CNS) and Schwann cells Electrical Signals and Neural Pathways
(PNS) – provide an insulating material that Resting Membrane Potential
surrounds axons Polarized cell membrane – uneven distribution of
charge
Neural Signaling
§ Communication among neurons Resting membrane potential – uneven charge
distribution in an unstimulated/resting cell; polarized
1. Reception – stimuli received by visual receptors Ø Higher concentration of K+ inside CM
in the eye Ø Higher concentration of Na+ outside CM
Ø Greater permeability of CM to K+ than to Na+
2. Transmission – sensory neurons transmit info to
CNS Leak channels – always open
3. Integration – info given is interpreted and an Gated channels – closed until opened by specific signals
appropriate response is determined
Chemically gated channels – opened by
4. Transmission – the CNS transmits info to motor neurotransmitters
neurons
Voltage gated channels – opened by a change in
5. Actual response – muscle/glands receive info membrane potential
and instruction from motor neurons
Sodium potassium pump – required to maintain the
Myelin Sheaths greater concentration of Na+ outside the CM and K+
§ Highly specialized insulating layer of cells inside
Unmyelinated axons – action potentials are conducted Action Potentials
slowly bcos in travels along the entire axon Excitable cells – RMP changes in response to stimuli
that activate gated ion channels
Myelinating axons – action potentials are conducted
rapidly by salutatory conduction Local current – Na+ diffuses quickly into cell
Nodes of Ranvier – gaps in the myelin sheath; where Depolarization – a change that causes the inside of the
ion movement can occur CM to become positive
Organization of Nervous Tissue Local potential – result of depolarization
Gray Matter – groups of neuron cell bodies + their
dendrites; very little myelin Threshold value – attainable local potential (critical pt.)
Ø In the CNS;
v Cortex – GM on the surface of the brain Action potential – constitution of depolarization and
v Nuclei – GM located deeper within the repolarization
brain
Ø In the PNS; Hyperpolarization – the charge on the CM briefly
v Ganglion – a cluster of neuron cell becomes more negative than the RMP
bodies
All-or-none fashion – threshold is reached = action
White Matter – bundles of parallel axons + myelin potential occurs; if the threshold is not reached = action
sheaths potential doesn’t occur
Ø In the CNS
v Nerve tracts – conduction pathways; Continuous conduction – the action potential is
propagate action potentials from one conducted along the entire axon CM
area of the CNS to another
Saltatory conduction – action potentials jump from one
Ø In the PNS;
node of Ranbier to the next
v Nerves – bundles of axons + connective
tissue sheaths
The Synapse
Synapse – a junction where the axon of one neuron
interacts with another
Presynaptic terminal – end of the axon
Postsynaptic membrane – membrane of the dendrite or
effector cell
Synaptic cleft – space separating the presynaptic &
postsynaptic membrane
M o r a n o , M . A .
