Unit #7 Nervous
System:
Neurons
Maintaining homeostasis
• Two systems of
communication
– Nervous system
• Rapid response
• Uses action potentials
– Endocrine system
• Slower response
• Uses hormones
released into blood
stream
• Controlled by the NS
Did You Know?
• Many types of
mental illnesses
are related to
imbalances in
chemicals that
transmit
messages
between neurons
Organization of the nervous system
Central nervous
system: Brain and
spinal cord
Peripheral nervous
system: all nervous
tissue outside the
CNS- nerves going
to organs and
muscles
Divisions of the PNS
Tortora
Fig 9.1 pg 254
• I. Somatic (SNS): sensory neurons send
information into to brain via somatic receptors
• II Autonomic (ANS) sends messages from
internal organs to brain. Sends messages to
smooth and cardiac muscles & glands from the
brain. Under involuntary control
• III. Enteric (ENS) the “brain of the gut”
controls digestion, peristalsis, secretions of GI
tract organs. Involuntary control
Endocrine system
Master glandshypothalamus and
pituitary- located in
brain
– Communicate with
other e. organs by
hormones
Regulates growth,
development,
metabolism, and
homeostasis in the body
Functions of the nervous system
I. Sensory functionDetect and transmit
information to the
brain
•
•
•
•
•
Sight
Hearing
Touch
Taste
Smell
Functions of Nervous System
II. Integrative
• The NS processes
sensory
information
–
–
–
–
Analysis
Storage (memory)
Decisions
Responses
Functions of Nervous System
III. Motor
Once info. is
integrated, a motor
response is generated
by activating effectors
(muscles and glands).
Stimulation causes
muscles to contract and
glands to secrete.
Neurons: cells of the nervous system
3 distinct areas
• Cell body
(soma)
• Dendrites
• Axons
• Messages
travel from
the dendrites
towards the
axon
Neuron
organelles
– Nucleus
– Typical cell
organelles
– No mitotic
spindle.
– Will the cell divide?
.
Dendrites
– Usually short and
thick.
– Usually highly
branched.
– Receives
impulses.
– Conducts
impulses towards
cell body.
Dendrites surrounded by
neuroglial cells.
Axons
Tortora
256
• Axons
– Neurons have a single
axon.
– Usually long and very
thin.
– Can be branched
(collaterals)
– Axon terminals contain
vesicles.
– Vesicles contain
neurotransmitters.
Axon surrounded by
neuroglial cells
3 types of
neurons:
– Multipolar
– Bipolar
– Unipolar
• Multipolar: have
several dendrites, 1
axon- brain, spinal cord
neurons
• Bipolar: 1 main
dendrite, 1 axon- retina
of eye, inner ear,
olfactory area of brain
• Unipolar: dendrites &
axon are fused
together, cell bodies
off to the side (in
ganglia)- sensory
receptors (touch, pain,
thermal)
Functional classification
• Sensory, Motor,
and Connecting
Neurons
– Sensory are
referred to as
afferent.
– Motor are referred
to as efferent.
– Connecting are
referred to as
association
Organization of Nervous System
• Somatic Vs
Autonomic
– Somatic is voluntary
• Sensory nerves and
motor nerves.
– Autonomic is
involuntary
• Mostly motor nerves
leading to smooth
muscle, cardiac
muscle, and glands.
Neurons and neuroglia
• Two different
types of cells
– Neurons conduct
impulses.
– Neuroglial cells
support and
protect neurons.
Neurons found in the
spinal cord.
• Neuroglia cells
– Smaller than
neurons.
– Outnumber
neurons 5 to 50
times.
– Function: support,
protect neurons
make cerebrospinal
fluid, create the myelin
sheath
Glioma: brain tumor
made of glial cells :
malignant
Myelin sheath
• Myelin sheath
– Speeds impulse
along axon.
– Insulates axon .
– Composed of
neuroglial cells.
(PNS)
– Schwann cells
produce myelin
(lipoprotein) in PNS
– Nodes of Ranvier
are gaps in myelin
sheath.
Myelin sheath structure
White and
gray matter
– White matter
is myelinated:
axon is
surrounded by
a myelin
sheath
– Gray matter
is
unmyelinatedaxon (not
wrapped)
Nerve Impulses
• Nerve impulse
– An impulse is a
change in the
electrical charge
(potential) on the
membrane of the
neuron.
– Due to ions moving
into and out of the
neuron.
Nerve Impulses
– Ions move through
very selective
membrane channels.
– Channels are
transmembrane
proteins.
– Voltage gated
channels pass pulse
down the axon to
the terminus
Tortora
Pages 260-262
Nerve Impulses
• Membrane Potentials
– Resting potential - no
impulse.
• Positive outside
• Negative inside.
– Action potential.
• Positive inside.
• Negative outside.
– Potentials are due to
ions.
• Na +
• K+
• Large negative ions
(proteins)
Tortora
Pages 261
Nerve Impulses
Tortora
Pages 210-213
• Resting potential
– No impulse.
– Positive outside
neurolemma
– Negative inside.
– 30x more K+ inside.
– 15x ore Na+ outside.
– Large negative ioins
trapped inside.
– Sodium - Potassium pump
creates these conditions.
– Membrane is “polarized”.
Creating An Impulse
Along An Axon
Continuous and saltatory
conduction
Caffeine & the
Nervous System
Conduction
Across Synapses
• Impulses are sent
to:
– Glands
– Muscles
– Other neurons.
• Impulse must
bridge the synapse
for the message to
be sent
Conduction Across Synapses
• Synapses have
ability to transmit
impulses or inhibit
impulse
transmission.
Conduction
Across Synapses
• Presynaptic neuron
– Synaptic vesicles
– Neurotransmitter
– Role of calcium ions
• Synaptic cleft
• Postsynaptic
neuron.
– receptors
Voltage gated
channels
Na+/K+
Pump
Conduction
Across A Synapse
Synaptic disruptions
• Most brain
disorders involve
disruption of
synaptic
communication.
• Toxins can block
both the
transmission and
reception of
neurotransmitters.
What is a nerve?
• Nerves are groups of
neurons.
– Mixed contain
dendrites and
axons.
– Motor contain
axons only.
(Efferent)
– Sensory contain
dendrites only.
(Afferent)
REGENERATION OF NERVOUS TISSUE
• Neurons have limited
powers of
regeneration.
• Neurons ability to
reproduce is lost at 6
months of age.
• A destroyed neuron is
lost.
• PNS neurons can
repair.
• CNS neurons cannot
repair.
Axon regeneration