section 1, chapter 10
Nervous System I
Basic Structure and Function
The nervous system is divided into 2 subdivisions
The Central Nervous System (CNS)
consists of the brain and spinal cord.
The Peripheral Nervous System (PNS)
• Consists of 12 pairs of cranial
nerves and 31 pairs of spinal nerves
• Nerves may be motor (efferent),
sensory (afferent), or both (mixed)
Divisions of the PNS
The Somatic Nervous System is under voluntary control
Somatic motor controls skeletal muscles
Somatic sensory relays info regarding touch, pressure, and
pain to the brain
The Autonomic Nervous System is under involuntary control
autonomic motor controls smooth muscles, cardiac muscles,
autonomic sensory relays visceral info regarding pH, blood
gasses, etc. to the brain
Figure 10.2. (a) overview of nervous system. CNS is grey, PNS is yellow. (b) CNS
receives sensory input from PNS, and sends motor output to PNS. Somatic division of
PNS is under voluntary control, while the autonomic division is under involuntary control.
The Autonomic Nervous System (ANS) is further
divided into two branches.
The Sympathetic branch
• prepares the body to respond to a stressful situation.
• “Fight or Flight” Response
The Parasympathetic branch
• Maintains normal body activities at rest
• “Resting and Digesting”
Cells of the Nervous System
• Integrate, regulate, and coordinate body functions
• Receive information - sensory
• Conduct impulses - motor
• Connect neurons - integrative
Neuroglia (glia = “glue”)
• Neuroglia provide neurons with
nutritional, structural, and functional
Neurons vary in shape and size
3 Components of a neuron
1. Dendrites receive impulse
2. Call body (soma)
3. Axon – transmits the impulse away
from the cell body
Dendrites conduct information to the soma.
A cell may have a few dendrites, many
dendrites, or no dendrites.
Dendritic Spines are additional contact
points on some dendrites that increase the
number of synapses possible by a neuron
Cell Body – Soma
Contains organelles such as the nucleus
Mitochondria, Golgi Apparatus, etc.
The rough ER is often called
chromatophilic substance (Nissl Bodies)
Axon Hillock is a specialized part of the soma
that connects to the axon.
The axon hillock is often called the Trigger
Zone because action potentials begin here.
Each neuron has only 1 axon, but it may divide
into several branches, called collaterals
The end of the axon is called the axon
terminal and it enlarges into a synaptic
Microtubules called neurofibrils support long axons
and aid in axonal transport (transport of biochemicals
between the soma and the axon terminal)
Myelination of Axons
The myelin sheath is a thick fatty coating of insulation surrounding the
axon that greatly enhances the speed of impulses.
Myelination of axons occurs differently in the PNS than in the CNS.
Myelination of axons in the PNS.
Schwann Cells form the myelin sheath in the PNS.
They wrap around the axons in a jelly-roll fashion to
form a thick layer of fatty insulation.
The cytoplasm and the nucleus are pushed to the
outermost layer, forming the neurolemma
Schwann cells are separated by gaps, called Nodes
Schwann cells still surround the axons of
unmyelinated neurons, but they do not form the
Unmyelinated axons with a Schwann cell.
A myelinated axon with a Schwann Cell.
Myelination of Axons in CNS
Within the CNS the myelin sheath is formed
1 Oligodendrocyte may form the myelin
sheath of several axons.
Gray and White Matter
A mass of myelinated axons in
the CNS forms the white matter.
A mass of cell bodies (which are
unmyelinated) along with unmyelinated
axons form the gray matter.
end of section 1, chapter 10