Download Nervous System - De Anza College

Overview of Neurons, Synapses
& Nervous System
Ch 48, 49 (8th ed.); Ch 48 (7th ed.)

Neurons: nerve cells that transfer information
within the body

Two types of signals:



long distance – electrical signals
short distance chemical signals
Glial cells: support nerve cells

Neurons transfer different types of
information:

control heart rate, coordinate hand-eye
movement, record memories, generate dreams

Higher order processing is carried out by
groups of neurons: ganglia, brain

Connection by neurons specify the
information transmitted

Sensory neurons transmit
information from sensors
that detect stimuli:


external stimuli – light,
sound, touch, heat small,
taste
internal stimuli – blood
pressure, carbon dioxide
level, muscle tension

Integration centers: analyze
and interpret the sensation
obtained from sensory input


Motor neurons: exit the processing centers and
trigger muscle or gland activity
Information processing


Central nervous
system (CNS):
Brain and
longitudinal
nerve cord
(spinal cord)
Peripheral
nervous system
(PNS): neurons
that carry
information in an
out of the CNS
Central nervous
system (CNS)
Brain
Spinal
cord
Peripheral nervous
system (PNS)
Cranial
nerves
Ganglia
outside
CNS
Spinal
nerves

Dendrites
Stimulus
Nucleus
Cell
body
Axon
hillock
Presynaptic
cell
Axon
Neuron structure:
 Cell body: contains nucleus and
organelles
 Dendrites: branched extensions of
the cell body that receive signals
 Axon: single extension that
transmits signals to other cells
 Axon hillock: cone shaped
extension where it joins the cell
body
Synapse
Synaptic terminals
Postsynaptic cell
Neurotransmitter

Dendrites
Stimulus
Nucleus
Cell
body
Axon
hillock
Presynaptic
cell
Axon
Synapse
Synapse: junction where one
neuron transmits information to
another neuron or effector cell or
organ
 Synaptic terminal: branch of the
axon that forms the specialized
connection
 Neurotransmitters: chemical
messengers that send
information from the transmitting
neuron (presynaptic cell) to the
receiving neuron (postsynaptic
cell)
Synaptic terminals
Postsynaptic cell
Neurotransmitter

Transmission of electrical signal:

changing K+, Na+ and Cl- concentrations inside
and outside the cell

Resting
potential:
membrane
potential of a
resting neuron


negative inside
the membrane
positive
outside the
membrane.
OUTSIDE [K+]
CELL
INSIDE
CELL
[K+]
[Na+]
[Cl–]
[Na+]
[Cl–]

Action potential:


rapid change in membrane potential of an
excitable cell
it is triggered by a stimulus, caused by opening
and closing of voltage sensitive gates in sodium
and potassium ion channels
Axon

Action potential is
generated as Na+
ions flow in at one
location: causes
depolarization
Action
potential
Na+
Plasma
membrane
Cytosol
Axon

Depolarization
triggers action
potential in the
neighboring region
and the previous
region gets
repolarized as K+
flows out
Plasma
membrane
Action
potential
Cytosol
Na+
K+
Action
potential
Na+
K+

Depolarization and
repolarization
continues down the
axon; propagation
of action potential
down the length of
the axon
Axon
Plasma
membrane
Action
potential
Cytosol
Na+
K+
Action
potential
Na+
K+
K+
Action
potential
Na+
K+

Myelin sheath:


Schwann cells wrap around the axon forming
layers of myelin
insulates, gaps are known as nodes of Ranvier
Node of Ranvier
Layers of myelin
Axon
Schwann
cell
Axon
Nodes of
Myelin sheath Ranvier
Schwann
cell
Nucleus of
Schwann cell
0.1 µm

Chemical synapse:
1. action potential depolarizes the plasma membrane of the
synaptic terminal
2. opens voltage-gated calcium channels in the membrane;
influx of Ca++
+
5
Synaptic vesicles
containing
neurotransmitter
Voltage-gated
Ca2+ channel
Postsynaptic
membrane
1 Ca2+
4
2
Synaptic
cleft
Presynaptic
membrane
3
Ligand-gated
ion channels
6
K+
Na


3. elevated Ca++ causes synaptic vesicles to fuse
with presynaptic membrane
4. vesicles release neurotransmitters into synaptic
cleft
5
Synaptic vesicles
containing
neurotransmitter
Voltage-gated
Ca2+ channel
Postsynaptic
membrane
1 Ca2+
4
2
Synaptic
cleft
Presynaptic
membrane
3
Ligand-gated
ion channels
6
K+
Na+


5. neurotransmitters bind to ion channels and open
them
6. neurotransmitters are released and ion channels
close
5
Synaptic vesicles
containing
neurotransmitter
Voltage-gated
Ca2+ channel
Postsynaptic
membrane
1 Ca2+
4
2
Synaptic
cleft
Presynaptic
membrane
3
Ligand-gated
ion channels
6
K+
Na+

Neurotransmitters:




Acetylcholine
biogenic amines (serotonin, dopamine)
amino acids
gases

Nervous system in animals:


sessile and slow-moving – simple sense organs
with no cephalization
active and predatory – sophisticated nervous
system with cephalization and corresponding well
developed sense organs


Cnidarians: diffused nerve net
Sea stars: radial nerves connected to nerve
ring
Radial
nerve
Nerve
ring
Nerve net
(a) Hydra (cnidarian)
(b) Sea star (echinoderm)

Bilaterally symmetrical bodies show
cephalization: arthropods, squids,
salamanders
Brain
Ventral
nerve cord
Brain
Ganglia
Segmental
ganglia
(e) Insect (arthropod)
(g) Squid (mollusc)
Brain
Spinal
cord
(dorsal
nerve
cord)
Sensory
ganglia
(h) Salamander (vertebrate)

Spinal cord transmits
information to and
from the brain and also
has nerve circuits that
produce reflexes
Cell body of
sensory neuron in
dorsal root
ganglion
Gray
matter
White
matter
Quadriceps
muscle
Hamstring
muscle
Spinal cord
(cross section)
Sensory neuron
Motor neuron
Interneuron

Cerebrospinal fluid circulates through



central canal
ventricles in the brain
cushions the brain

Brain and spinal cord had gray and white matter


Gray matter: neuron cell bodies, dendrites and
unmyelinated axon
White matter: myelinated axons

Functional
hierarchy in PNS
PNS
Afferent
(sensory) neurons
Efferent
neurons
Autonomic
nervous system
Motor
system
Locomotion
Sympathetic
division
Parasympathetic
division
Hormone
Gas exchange Circulation action
Hearing
Enteric
division
Digestion
Cerebrum (includes cerebral cortex, white matter,
basal nuclei)
Diencephalon (thalamus, hypothalamus, epithalamus)

Vertebrate
brain
Midbrain (part of brainstem)
Pons (part of brainstem), cerebellum
Medulla oblongata (part of brainstem)
Diencephalon:
Cerebrum
Hypothalamus
Thalamus
Pineal gland
(part of epithalamus)
Brainstem:
Midbrain
Pons
Pituitary
gland
Medulla
oblongata
Spinal cord
Cerebellum
Central canal

Regionalizations in the vertebrate brain
Frontal lobe
Parietal lobe
Speech
Frontal
association
area
Somatosensory
association
area
Taste
Reading
Speech
Hearing
Smell
Auditory
association
area
Visual
association
area
Vision
Temporal lobe
Occipital lobe