NERVOUS SYSTEM AND
NERVOUS TISSUE
Anatomy, activity and memory
Nervous System – Ch 11
General scheme, fig
11.1
– Receives information
from receptors–
sensory input.
– Interprets and
develops a plan of
action – integration.
– Sends plan of action to
effector(s) – motor
output.
Organization of the Nervous
System
Central Nervous System (CNS) – spinal
cord and brain; interpretation & integration,
fig 11.2.
Peripheral Nervous System (PNS) – links
the rest of the body to the CNS.
– 12 pair of cranial nerves and 31 pairs of spinal
nerves.
Organization of the Nervous
System
PNS divisions
– Sensory division (afferent) – relays
information from receptors to CNS
– Motor division (efferent) - relays information
from CNS to effectors.
Organization of the Nervous
System
Histology
80% cells; neurons and neuroglia
(supporting cells). 10X as many neuroglia
as neurons.
Neuroglia of the CNS, 4 types (fig 11.3)
– Astrocytes –
– Microglia –
Histology
Neuroglia of the CNS cont’d
– Ependymal –
– Oligodendrocytes –
– **Brain tumors
Neuroglia of the PNS, 2 types
– Satellite cells - ?function
– Schwann cells – form myelin sheaths
Histology
Neurons (fig 11.4)
– Features: very irritable, long lived, amitotic
(except in the hippocampus?), high metabolic
rate.
– Cell body (soma): large single nucleus with a
prominent nucleolus, Nissl bodies (rough ER)
and Golgi apparatus, + other organelles.
Biosynthetic center. Primarily located in CNS
Histology
Neurons cont’d
– Processes
Dendrites – usually branched, input or receptive
regions; carry impulses TOWARD the cell body.
Axons – usually one per cell, arise from axon
hillock, short to very long, terminal branches.
Output regions, carry impulses AWAY from the cell
body.
Nutrients and repair parts (proteins, etc) travel
from cell body to axon and back again.
**Viruses and bacteria.
Histology
Neuron (fig 11.5)
– Myelin sheaths: protein/lipid sheet wrapped
around axons only, outer layer is neurilemma.
Discontinuous - spaces are Nodes of Ranvier.
Functions: electrically insulate axon and speed up
transmission of electrical impulses.
– Gray matter – unmyelinated axons and cell
bodies
– White matter – myelinated axons
Neurophysiology - Review
Membrane Ion
Channels (fig 11.6)
Neurophysiology - Review
RMP (fig 11.7 & 11.8)
– Cell membrane at rest
is polarized, negative
inside vs. outside (-40
to -90 mV).
– Generated by different
concentrations of Na
and K inside the cell
and out.
– Resting membrane
maintained by Na+ K+
ATPase.
Synapses
The nervous system is like telegraph or
“old” telephone lines.
Synapse = connection points among the
lines (neurons).
– Electrical
– Chemical
There may be 100’s or 1000’s of synapses
on a single neuron.
Chemical Synapse Model
Chemical Synapses in Nervous
System
Types of chemical
synapses based on
position:
– Axodendritic
– Axosomatic
– Axoaxonic, etc
**Presynaptic neuron
vs Postsynaptic
neuron
Neurophysiology
Membrane potentials that act as signals,
fig 11.9
– Depolarization: decreases membrane
potential (less negative).
– Hyperpolarization: increases membrane
potential (more negative).
– Graded potentials – local changes in
membrane potential. Short lived, magnitude
varies with stimulus strength.
Neurophysiology
Membrane potentials that act as signals
– Graded potentials cont’d
EPSP –
IPSP –
Function: control of unintentional or unnecessary
impulses to and from your brain.
Neurophysiology
Membrane potentials that act as signals
– Graded potentials
Summation – combination of these graded, local
potentials at the axon hillock can bring about an
action potential or inhibit the generation of the
action potential.
– Spatial: stimulation by many neurons at one time.
– Temporal: increased numbers of impulses per minute.
Summation of Graded Potentials
Neurophysiology
Membrane potentials that act as signals
– Action Potential – rapid and large change in
membrane potential, i.e. from -50 to +30 mV.
Occurs only in axons = nerve impulse.
– Action Potential and ion channels – review???
Memory – Ch 12
Basis: Most neurons are amitotic but new
synapses form continually and existing synapses
can be “trained” to work more efficiently.
– Repeated EPSPs at the synapses of the same
neuronal pathway causes physical changes called
LONG TERM POTENTIATION.
– Receptor proteins are altered to respond more quickly
or more dramatically and generate an AP.
– Studying – reading is input; recall or output = write it,
say it, explain it, draw it, act it out, etc.
Memory - Stages
Short-term (STM) – working memory (RAM on
the computer).
– Limited to 7-8 “chunks” of information.
– May be forgotten immediately.
Long term (LTM) is like information on the hard
disk on the computer).
– Limitless
– Conversion of STM to LTM is affected by emotional
state, rehearsal and association but can be
automatic.
Memory
Categories:
– Declarative (facts)
– Non-declarative: procedural (skills), motor,
emotional memories. Come from practice
and experience.
– Involve different pathways in brain???
Storage in different areas of the brain –
association areas near sensory/motor
areas concerned with that particular cue.
Proposed Memory Circuits
Declarative
Procedural
Figure 12.23
Memory
Mechanisms - what has been observed:
– Increased mRNA synthesis
– Changes in dendrites
– “New” protein at synapses involved in LTM
– Increased number and size of presynaptic
terminals and neurotransmitter released
– “New” neurons in the hippocampus.