The Nervous System
Juliana Paz
Bio 490
Dr. Smith
May 20, 2010
Overview
 Irritability: The capacity of cells and the whole
organism to respond in a characteristic
fashion to stimuli.
 Specific responses for specific stimuli.
 The nervous system is made up of
interconnecting fibers that communicate via nerve
impulses.


Sensory (Afferent) Impulses
Motor (Efferent) Impulses
 Central Nervous System (CNS)
Phylogenetic Development
Cnidara
 Slender Sensory Cells

Afferent apparatus
 Nerve Net
 Ex: Hydra
Ctenophora
 Nerve Net

Localized
differentiation
 Oral ring
 Ex: Jelly Combs
Platyhelminthes
Mollusca
 Evident Organization
 Increased cephalization
 Brain made of nerve
 Ganglia
tissue
 Nerve Cord

Extension of the brain
tissue

Increased number of
knots on the nerve cell
body.
 Ex: Snails and Clam
 Ex: Flatworm
Annelida
 Sensory cells on the
head
 Two ganglia
 Double fused nerve
cord
 Ex: Earthworms
Neuron


A specialized cell
Composed of:





Dendrites
Cell Body
Axon
Myelin Sheath
Glial Cells
 Neuroglia: support cells
of the Central Nervous
System (CNS).
 Schwann Cells: Support
cells of the Peripheral
Nervous System (PNS).
Arthropoda
 Simple sense organ on
head
 Ventral surface
 Motor coordination
 Ex: Insects
Nerve Impulse
 Early Theories:
Axon was the passive portion of the impulse
Nerve impulse decrease voltage
 The location of the electrical conductor


Nerve Impulse
 Resting State



The neuron is at
resting potential
(RP)
RP is maintained by
two factors:
imperablity to Na
and the Na/K pump.
Creates a negative
charge because of
their interactions.
2) Action Potential
 The start of neuron
stimulation.
 The cell membrane
become suddenly
permeable to Na
 Leads to
depolarization
 Action Potential: the
shift in the charge that
creates the neural
impulse.
3) Repolarization
 Occurs when action
potential reaches a
+40mV and the
membrane becomes
impermeable to Na+
 K+ is also pumped out
to balance Na
4) Refractory Period
 Restoration of the
Na+/K+ gradient.
 Incapable of creating
a new impulse until at
-60mV.

The impulse is
recreated on the axon
Sodium/Potassium Pump
 The channels are guarded by voltage sensitive
proteins.
 Potassium has only one channel opening, while
sodium has two channel openings


Activation Gate
Inactivation Gate
All or None Principle
Each neuron has a threshold, where the minimum
strength is needed to initiate depolarization.
Saltatory Conduction
 Aided by the Myelin Sheath and the Nodes of
Ranvier
 The impulse is transmitted as an electrical current
rather than a chemical process.
Synapse
 The point at which the axon and dendrite
associate
 Invertebrate nerve nets have the axons and
dendrites touch each other
 Simpler vertebrates have a discrete neural
pathway.
 Vertebrates have a unique characteristic of
moving in one direction.

Movements across the Synaptic Cleft is a chemical
event mediated by neurotransmitters like
acetylcholine (Ach), norepinephiren, γ-aminobutynic
acid (GABA), and Serotonin.
Action potential
reaches the synaptic
knobs
 Synaptic vesicles
rupture and release
neurotransmitters.

Excitatory
Postsynaptic Potential
(EPSP)



Some
neurotransmitters can
inhibit



Temporal summation
Spatial summation
GABA and the
inhibitory postsynaptic
potential (IPSP)
Excitatory synapse
Reflex Arc
 The functional unit of
the nervous system
and has an
unchanging,
automatic response.
 Simple reflex arc is
the physical pathway
of the impulse as it
moves from the
receptor of the
afferent neuron to the
effectors of the motor
neuron.
Receptors and Effectors
 Receptors: modified dendrite endings of sensory
nerves that
respond to specific kinds
of stimuli.
Muller’s Doctrine of Specific Nerve Energies
Based of the specificity of the receptor, it must have
a low threshold and send only one kind of
message to the CNS.
Exteroceptors
Proprioceptors
 Interoceptors


 Effectors: Specific response
Sensory Organs

Light
 Eyeball, cornea, pupil,
iris, retina (rods and
cones, bipolar cells,
optic neuron), optic
nerve.

Sound
 Ears, pinna, auditory
canal, eardrum, three
contiguous bones,
cochlea (oval window
and round window,
perilymph, organ of
Corti (basilar membrane
and tectorial
membrane)) cochlear
nerve.

Gravity and Motion
 Vestibular apparatus
(saccule, utricle, and
semicircular canals),
macula (otoconia),
ampullae cupula)

Taste and Smell
 Chemorecepetors: taste
buds and nasal
epithelium.

Touch and Pressure
 Meissne’s corpuscles
and free nerve endings,
hair, pacinian
corpuscles.

Heat and Cold
 Ruffini corpuscles and
Krause end bulbs.
Brain and Spinal Cord
 Protected by the bony skull ,three meninges, and
cerebrospinal fluid (CSF).
 The brain has three regions: hindbrain, midbrain,
and forebrain.
 Hindbrain
Medulla oblongata,
pons, celebellum
 Control the
involuntary,
mechanical
processes.

 Midbrain


Connector
Assists in visual and
auditory processes.
 Forebrain
Cerebrum split into
four lobes
 Location of complex
activities.

 Limbic system
Hypothalamus: hormone regulation and body
regulator.
 Thalamus: A series of cerebral nuclei (basal
ganglia).
 Reticular formation: region of nuclei in close
association.
 Mood regulator? The hippocampus, amygdala, and
cingulate are apposed with the olfactory nerve.

 Spinal Cord
a thick, dorsal neural tract extending from the brain
stem to the lower back.
 Protected by bone.
 Consists of ascending tracts that conduct impulses
to the brain and descending tracts that carries the
impulse toward motor neurons within the spinal
cord.

 Gray matter houses the central canal.
 Ventricles hold CSF.
 Process sensory impulses from the
PNS.


Dorsal root ganglia
Ventral horn
Brain Specialization
 The brain hemispheres can specialize in
something.

Left hemisphere controls speech and the right
hemisphere can regulates spatial perceptions.
 Corpus callosum allows communication.
 The neocortex is quick to create new synapses
By means of central circuits and the association
area of the parietal lobe.
 Short term and long term memory

 Learning occurs in two ways:


Engrams
Modification of the neural apparatus.
Autonomic Nervous System

Sympathetic Nervous
System
 Preparation for
emergencies

Parasympathetic
Nervous System
 Lie near the target
organ
 Restoration functions

Both effector impulse
begin at a motor neuron
and meet at the
ganglion.
 SNS-chain along the
spine
 PNS- in the target organ
(Ach).