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Nervous System
Some Interesting Facts
• 85 billion (85,000,000,000) neurons in the human brain.
• 3,000 years one cell/second
• 1 neuron cell body = 10 microns wide
85,000,000,000 neurons = 850 km
• If you use a basketball (diameter = ~24 cm) as the cell body, then
your axon would have to be 240,000 cm (2.4 kilometers)
in length!
► A baby's brain is a mystery.
► The mystery begins in the womb -- only four weeks into
gestation the first brain cells, the neurons, are already
forming at an astonishing rate: 250,000 every minute.
► Billions of neurons will form links with billions of other
neurons and eventually there will be trillions and trillions of
connections between cells.
► Every cell is precisely in its place, every link between neurons
carefully organized. Nothing is random, nothing by chance.
CNS Development
Functions of the Nervous System
1. Sensory input
 changes = stimuli
2. Integration
 processing
3. Motor output
 response to stimuli
(The response activates muscles or glands)
Neuron
 Extensions
outside the cell
body
 Dendrites –
toward the cell
body
 Axons –
away from the
cell body
Figure 7.4a
Slide 7.10
Neurons
Glial Cells
Figure 12.2b
Anatomy of the Nervous System
 Central nervous system (CNS)
 Brain
 Spinal cord
 Peripheral nervous system (PNS)
 Nerve outside the brain and spinal cord
Slide 7.2
Central nervous system (CNS)
– Brain
– Spinal cord
CNS is protected by
• Bone
• Meninges
• CSF
Bone
Meninges
CSF
Spinal cord
LP?
CSF ?
Structure of spinal cord
• Roots
dorsal, ventral
• Horns
anterior, posterior, lateral
• Columns
anterior, posterior, lateral
Spinal Cord
Gray
Matter
Dorsal
White
Matter
Central
Canal
Ventral
Gray Matter
Horns
Dorsal
Lateral
Ventral
v
v
• Root
dorsal, ventral
• Nerve
• Ramus/Brunch
anterior, posterior
Spinal Cord White Matter
Dorsal
Ventral
White
Matter
Ascending (Sensory)
touch & conscious proprioception
unconscious proprioception
Figure 16.1
pain & temperature
Descending (motor)
Muscle balance
Muscle movement
Brain