Enteric Nervous System

• gutgut

Central Nervous System (CNS)

• brainbrain

• spinal cordspinal cord

Peripheral Nervous System (PNS)

• cranial nerves (12 pr)cranial nerves (12 pr)

• spinal nerves (31 pr)spinal nerves (31 pr)

CNS PNS

sensory receptor

sensory input

integration

motor input

effector

cell body

dendrite

SynapseaxonMyelin sheath

Schwann Cells

Axon

Nodes of Ranvier

bipolareye, ear, & olfactory

unipolar multipolarmost abundant type in CNSDorsal root

ganglion cells

sensory receptors

sensory neuron

interneuron

motor neuron

effector

Presynaptic neuron

Postsynaptic membrane

Ca2+

Synaptic vesicles containing neurotransmitters

• Acetylcholine- slows heart rate; PNS • Glutamate- most prevalent neurotransmitter in the brain• Aspartate- in CNS• GABA- inhibitory neurotransmitter• Glycine- inhibitory neurotransmitter• Norepinephrine- awakening from deep sleep• Epinephrine- increase heart rate• Dopamine- movement of skeletal muscles• Seratonin- sensory perception, temp regulation, mood,

sleep• Nitric oxide- may play a role in memory and learning• Enkephalin- inhibit pain impulses by suppressing release

of substance P• Substance P- enhances perception of pain

tyrosine

Converging circuit• same source• Pacinian corpuscles -- pressure• different sources• control of respiration

Diverging Circuit• permits broad distribution of a specific

input typesA.  amplificationB.  divergence into multiple tracts

Parallel after-charge circuit• several neurons process same

information at one time• each chain has a different number of

synapses, but eventually they all reconverge on a single output

• output neuron may go on firing for some time after input has ceased

• important in withdrawal reflexes• longer-lasting output from small period of

pain 

Reverberating Circuit• axons extend back toward the sources of

an impulse and further stimulate the presynaptic neuron

• helps maintain consciousness, muscular coordination, normal breathing, short term memory... 

synapses

Efferent (motor)

Afferent (sensory)

Inte

grat

ion

cent

er

• Mature neurons are amitotic• If the soma of a damaged nerve is intact, axon

will regenerate• Involves coordinated activity among:

– Macrophages—remove debris– Schwann cells—form regeneration tube and

secrete growth factors– Axons—regenerate damaged part

• CNS oligodendrocytes bear growth-inhibiting proteins that prevent CNS fiber regeneration

Figure 13.4 (1 of 4)

Endoneurium

Dropletsof myelin

Fragmentedaxon

Schwann cells

Site of nerve damage

The axonbecomesfragmented atthe injury site.

1

Figure 13.4 (2 of 4)

Schwann cell Macrophage Macrophagesclean out thedead axon distalto the injury.

2

Figure 13.4 (3 of 4)

Fine axon sproutsor filaments

Aligning Schwann cellsform regeneration tube

3 Axon sprouts,or filaments,grow through aregeneration tubeformed bySchwann cells.

Figure 13.4 (4 of 4)

Schwann cell Site of newmyelin sheathformation

4 The axonregenerates anda new myelinsheath forms.

Single enlargingaxon filament

Multiple Sclerosis• Autoimmune disease• Destruction of myelin sheath• Scar tissue may form

Epilepsy• Rapid synchronous firing of neurons• Seizure

Treatments:• Drugs• Implants• Brain surgery

INQUIRY

1. What voltage is the threshold potential?

2. Describe depolarization, repolarization and hyperpolarization.

3. Which ion causes the neurotransmitters to be released across the synapse?

4. Name 2 instances that you can stimulate a neuron to depolarize.

5. What disease is characterized by myelin sheath degeneration?

6. Can all parts of the CNS regenerate if damaged?