Occupational Therapy Functional Organization of the Nervous System

1. Functional Organization
of the Nervous System

5. II. Cells of the nervous system
A.Cell types: Neurons and Neuroglia (nerve glue)
B. Neurons
- Neurons receive stimuli and transmit action
potentials
- Form complex networks.

7. 3. Three main components
a. Cell body (soma)
- Single large nucleus with prominent nucleolus
- Is the primary site of protein synthesis and contains
an extensive endoplasmic reticulum.
- Contains large numbers of intermediate filaments /
microtubules

8. b. Dendrites (lat. tree)
- Generally short, highly branched cytoplasmic
extensions of the cell body
- Contain dendritic spines and are tapered toward
end
- Usually conduct electric signals toward the cell
body.
- Respond to neurotransmitter

9. c. Axons (lat. axel)
- Eminate form axon hillock
- Cytoplasmic extensions of the cell body (axoplasm)
- That transmit action potentials to other cells.
- Uniform diameter / straight

11. C. Types of Neurons
1. Multipolar neurons
a. Several dendrites and a single axon.
b. Association and motor neurons are multipolar.
2. Bipolar neurons
a. A single axon and dendrite
b. Found as components of sensory organs.
3. Unipolar neurons
a. Have a single axon.
b. Most sensory neurons are unipolar.

12. D. Neuroglia
- 1. Neuroglia are nonneural cells that support and
aid the neurons of the CNS and PNS.

13. 2. CNS neuroglia
- a. Astrocytes - provide structural support for
neurons and blood vessels and forms the blood
brain barrier that regulates the movements of
substances between the blood and the CNS.
- b. Microglia -macrophages that phagocytize
microorganisms, foreign substances, or necrotic
tissue.
- c. Ependymal cells - line the ventricles and the
central canal of the spinal cord. Some are
specialized to produce cerebrospinal fluid.
- d. Oligodendrocytes - form myelin sheaths around
the axons of neurons of the CNS.

15. 3. (PNS neuroglia)
- a. Schwann cells, (neurolemmocytes) - form myelin
sheaths around the axons of neurons of the PNS.
- b. Satellite cells support and nourish neuron cell
bodies within ganglia.

16. E. Axon Sheaths
- 1. Unmyelinated axons rest in invaginations of
oligodendrocytes (CNS) or Schwann cells (PNS). They
conduct action potentials slowly.
- 2. Myelinated axons are wrapped by several layers
of cell membrane from oligodendrocytes (CNS) or
Schwann cells (PNS). Spaces between the wrappings
are the nodes of Ranvier, and action potentials are
conducted rapidly be saltatory conduction from one
node of Ranvier to the next.

17. F. Nerve Fibers are classified by size
1. Type A - large diameter
- a. (15-22 m/sec) motor and sensory nerves - rapid
response
2. Type B - medium diameter
- a. (3-15 m/sec) autonomic nervous system - heart
lung
3. Type C- small diameter
- a. (2 m/sec) autonomic NS – digestion

18. III. Organization of Nervous Tissue
A. CNS Structure - Nervous tissue can be grouped into
white an gray matter.
1. White matter is made up of myelinated axons and
functions to propagate actions potentials.
- a. White matter forms nerve tracts in the CNS and
nerves in the PNS
(1) Association fibers
(2) Commissural fibers
(3) Projection fibers

20. 2. Gray matter is collections of neuron cell bodies and
unmyelinated axons.
- a. Gray matter forms cortex and nuclei in the CNS and ganglia
in the PNS.
- b. Within gray matter axons synapse with neuron cell bodies,
- This is functionally the site of integration in the nervous
system.
- In the brain, gray matter is found on the outside of the cortex
and white of the cortex and white matter makes up the nerve
tracts within the brain.
- In the spinal cord, gray matter if found internal
(anterior/posterior horn) and white matter is surrounds the
gray matter on the outside.

22. B. PNS structure
1. Bundles of axons and their sheaths from nerves.
- The endoneurium surrounds individual axons.
- Fascicles are groups of axons that are bound together by the
perineurium.
- The epineurium holds groups of fascicles together to form the
nerve.

23. IV. The Synapse
A. Anatomy of the synapse.
- 1. presynaptic terminals - The enlarged ends of the axon that
contain synaptic vesicles.
- 2. postsynaptic membranes - contain receptors for the
neurotransmitter and are found on other neurons, muscles or
glands.
- 3. synaptic cleft - the space that separates the presynaptic and
postsynaptic membranes.

25. B. Synaptic transmission
- 1. An action potential arriving at the presynaptic terminal
causes Ca++ gates to open
- 2. Ca++ ion diffuse into the synaptic terminal
- 3. Ca++ causes synaptic vesicles containing the
neurotransmitter to bind to the synaptic membrane releasing
the neurotransmitter,
- 4. The neurotransmitter diffuses across the synaptic cleft and
binds to the receptors of the postsynaptic membrane.
- 5. Binding of a ligand to the receptor invokes a response in the
postsynaptic cell.

26. C. Neurotransmitter inactivation (three methods):
1. The neurotransmitter is broken down by an enzyme
- a. Eg. Acetylcholinesterase
2. The neurotransmitter is taken up by the presynaptic terminal.
- a. Epinerpherine is taken up repackaged in vessicles and reused
or inactivated within the presynaptic terminal by monoamine
oxidase (MAO).
3. The neurotransmitter diffuses out of the synaptic cleft.

27. D. Receptor molecules in synapses
1. Receptors for neurotransmitters are specific.
2. A neurotransmitter can bind to several different receptor types
- a. Therefore a neurotransmitter can be stimulatory (depolarize)
in one synapse and inhibitory (hyperpolarize) in another,
depending on the type of receptor present.
3. Some presynaptic terminals have receptors.
- a. Release of norepinepherine (NE) can bind- to presynaptic
receptors which decrease the release of NE. (modifies its own
release).

28. E. Neurotransmitter and Neuromodulators
1. Neurotransmitters are substances released at a synapse that
affect another cell.
2. Once thought that each neuron contained only one
neurotransmitter.
- a. Some neurons can secrete more than one type of
neurotransmitter.
- b. A neuron makes use of the same combination of chemical
messengers at all of its synapses.
- c. Contrary to book, neurons can release one neurotransmitter
in greater abundance compared to another neurotransmitter.
(1) Size of versicle and frequency of action potential

29. 3. Neuromodulators influence the likelihood that an action
potential in a presynaptic terminal will result in an action
potential in a postsynaptic cell.
- a. Can influence the release of other neurotransmitters.
4. Types of Neurotransmitters

30. Substance Location Effect Example
1. Small molecule
transmitters
substances
Acetylcholine Used by motor neurons in
spinal cord and at all
nerve skeletal muscle
junctions. Widespread use
throughout the brain and
in ANS
Excite or inhibit Alzheimer’s disease
decrease in Ach release
Myasthenia gravis -
decrease in ACH receptors.
2. Biogenic Amines
Dopamine
Norepinephrine
Epinephrine
Serotonin
Histamine
Cateholamines (DNE) from
tyrosine. excite exictatory /
inhibitory
exictatory / inhibitory
Inhibitory inhibitory
Parkinson’s - dopamine
schizophrenia/vomiting.
Amphetamines / cocaine
increase epi.
Mood anxiety sleep
arousal from sleep and
thermoregulation
3. Amino Acids
GABA
Glycine
Glutamate and
aspartate
major inhibitory trans.
Inhibitory exitatory
Used to treat epilepsy
blocked by strychnine
drugs prevent seizures.

31. 4.
Neuropeptides
(Over 50 ha
ve been identifed.)
Opioids regulate pain,
reproduction,
thermoregulation and
maternal behaviors
Endorphins /
enkephalins
Tachykinins regulate sex, Substance P,
Gastrins regulate sex and
maternal behaviors
CCK, Galanin
Neurohypophyseal vassopressin, oxytocin,
neurophysins
Secretins glucagon, VIP, Growth
Hormone RH ,
histidine
Insulins regulate blood sugar
levels and growth
insulin, insulin-like
growth factors

32. V. Excitatory and Inhibitory Postsynaptic Potentials
A. A combination of neurotransmitters causes either a
depolarization (excitatory)or hyperpolarization
(inhibitory)of the postsynaptic membrane.
B. Depolarization
1. caused by an excitatory postsynaptic potential (EPSP) an
increase in membrane permeability to Na+ ions
2. Caused by.
3. If depolarization reaches threshold then an action potential is
generated.
4. Novocain decreases permeability to Na+.

39. C. Hyperpolarization
1. Caused by an increase in membrane permeability to chloride
ions or potassium ions is an inhibitory postsynaptic potential
(IPSP).
- a. Cl- moves into cell making inside more negative.
- b. K+ moves out of cell making inside more negative.

40. D. Presynaptic inhibitions and facilitation
1. Axoaxonic synapses on presynaptic terminal can alter the
amount of neurotransmitter released.
- a. Presynaptic inhibition decreases neurotransmitter release.
- b. Presynaptic facilitation increases neurotransmitter release.
2. The greater the amount of neurotransmitter the greater the
IPSP or EPSP

41. E. Spatial and temporal summation
1. Presynaptic action potentials through neurotransmitters
produce local potentials in postsynaptic neurons.
- a. Summation: A series of presynaptic action potentials causes
a series of local potentials in the postsynaptic neurons that act
at the axon hillock to generate an action potential if the local
potentials are strong enough. These local potentials can
summate to produce an action potential at the axon hillock.
- 2. Two type of summation
- a. Spatial summation occurs when two are more presynaptic
terminals simultaneously stimulate a postsynaptic neuron.
- b. Temporal summation occurs when two are more action
potentials arrive in succession at a single presynaptic terminal.

44. E. Spatial and temporal summation
1. Presynaptic action potentials through neurotransmitters
produce local potentials in postsynaptic neurons.
- a. Summation: A series of presynaptic action potentials causes
a series of local potentials in the postsynaptic neurons that act
at the axon hillock to generate an action potential if the local
potentials are strong enough. These local potentials can
summate to produce an action potential at the axon hillock.
- 2. Two type of summation
- a. Spatial summation occurs when two are more presynaptic
terminals simultaneously stimulate a postsynaptic neuron.
- b. Temporal summation occurs when two are more action
potentials arrive in succession at a single presynaptic terminal.

45. 3. Inhibitory and excitatory presynaptic neurons can converge an a
postsynaptic neuron.
The activity of the postsynaptic neuron is determined be the
integration of the EPSPs and IPSPs produced in the postsynaptic
neuron.
The two types of postsynaptic potentials are EPSP and IPSP. EPSP
stands for the Excitatory Postsynaptic Potential and IPSP stands for
the Inhibitory Postsynaptic Potential.
EPSP is a temporary depolarization that is caused by the flow of
positively-charged ions into the postsynaptic cell while IPSP is a
hyperpolarization caused by the flow of negatively-charged ions into
the postsynaptic cell.
The main difference between EPSP and IPSP is that EPSP facilitates
the firing of an action potential on the postsynaptic membrane

46. VI. Reflexes
A. A reflex arc is the functional unit of the nervous system.
- 1. Sensory receptors respond to stimuli and produce action
potentials in afferent neurons.
- 2. Afferent neurons propagate action potentials to the CNS.
- 3. Association neurons in the CNS synapse with afferent neurons
and with efferent neurons.
- 4. Efferent neurons carry action potentials from the CNS to the
effector organ.
- 5. Effector organs such as muscles or glands respond to the action
potential

47. - B. Reflexes do not require conscious thought, and they produce a
consistent and predictable result.
- C. Reflexes are homeostatic. They remove the body from painful
stimuli, keep the body from falling, maintain blood pressure, pH,
CO2 levels, and water intake.
- D. Reflexes are integrated within the brain and spinal cord. Higher
brain centers can suppress or exaggerate reflexes.

50. - VII. Neuronal pathways and Circuits.
A. Organization of the neurons varies from simple to extremely
complex.
- 1. Branching / synaptology can be complex to simple.
- 2. There are three basic patterns of neuronal circuitry: convergent,
divergent and oscilating
B. Convergent pathways have many neurons synapsing (converge)
with only a few neurons.
- 1. Eg. Spinal cord convergence of CNS circuits and sensory neuron
in reflex arc.
C. Divergent pathways have a few neurons synapsing with many
neurons.
- 1. Information in one circuit can be spread to several other circuits.
- 2. Eg. Sensory nerve sends information to 1)an interneuron the
goes out to the motor neurons and another neuron that goes to

52. D. Oscillating circuits have collateral branches of postsynaptic
neurons synapsing with presynaptic neurons or themselves
1. Lets circuits produce action potentials more than once (after
discharge)
- a. Prolongs response (positive feedback circuit)
- b. Stimulation continues until:
(1) fatigue is reached
(2) inhibited by another neuron.
- c. CNS control of respiration (breathing in and out) is controlled by
an oscillating circuit.