The Nervous System
Poudre High School
By:
Ben Kirk
Functions
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Regulation of all body function
Sensory: Information reception
Response: Response transmission
Integrate: Integrate and interpret all body
changes/stimuli
Organization
 Central Nervous System (CNS): Brain
and Spinal Cord
 Control center for the entire nervous system
 Receives, processes, integrates and
produces responses to all stimuli
 Higher Functioning (the brain primarily):
intelligence, memory, thought, emotion and
learning
The Central Nervous System
http://www.sruweb.com/~walsh/cns_pns.jpg
Organization
 Peripheral Nervous System (PNS): All
neural tissue outside the CNS
 Delivery of sensory information from sensory
glands/organs to the CNS
 Transmission of motor information from the
CNS to effectors glands/organs
Organization
 Peripheral Nervous System
 Somatic Nervous System: Voluntary
 Controls voluntary muscle contractions (skeletal
muscle)
 Autonomic Nervous System: Involuntary
 Involuntary movements, processes and reflexes
 Visceral organs, cardiac muscle, smooth muscle
and glands (heart rate, vessel diameter,
digestion, etc…)
Organization
 Autonomic Nervous System
 Sympathetic Nervous System: Expenditure of
energy
 Fight or Flight
 Increased Heart Rate
 Parasympathetic Nervous System: Restoration
and conservation of energy
 Rest and Digest
 Slows Heart Rate
http://www.sirinet.net/~jgjohnso/nervous.html
Histology
 Neuroglia: Glial Cells
 6 Types of glia cells
 Primary Function is to protect and support
neurons
 Smaller and more numerous (5-10X) than
neurons
 Common source of tumors (Gliomas)
 40-45% of all brain tumors
Histology
 Neurons: Conduct impulses from one part of
the body to another
 Cell Body (Soma):
 Large, pronounced nucleus
 No myotic apparatus in cytoplasm
 Neuron reproduction/regeneration is compromised
 Dendrites:
 Highly branched processes extending from cell body
 Each neuron in the CNS has 10,000-100,000 dendrite
branches.
 Each branch has 100,000-1million sensory inputs!!!
Histology
 Neurons:
 Axon: Single thin extension that sends
electrical impulses to other neurons or
tissues
 1mm-1meter in length
 Axon Terminal contains neurotransmitters that
are released to trigger subsequent impulses
 Axon Hillock: Where all electrical impulses
are summated to trigger an impulse, or not.
The Neuron
Histology
 Neuron:
 Myelin (myelin sheath): Multiple layered,
lipid and protein sheath covering neuron
axons (not all axons are myelinated)
 Electrically insulates axon and increases
conduction speed (Ex. Leaky garden hose)
 Multiple Sclerosis: Autoimmune disease that
breaks down the myelin sheath in the CNS.
 Tremors: Unregulated electrical impulses
Histology
 Neurons:
 Myelin:
 Myelin Production
 Schwann cells (PNS): Myelinate a single segment of a single
axon.
 Have limited ability to regenerate PNS neural tissue
 Oligodendrocyte (CNS): A single oligodendrocyte can
myelinate multiple segments of multiple axons
 CNS neuron regeneration is very complex and relatively
nonexistent.
 Myelination = White
 Unmyelinated = Gray
Classification of Neurons
 Structural: Based on the # of processes
extending from the cell body
 Multipolar: many dendrites and one axon
 Most cells of the CNS
 Bipolar: One dendrite and one axon
 Retina of eye, inner ear and nose
 Unipolar: Has one continuous branch with both an
axon and a dendrite (cell body off to side)
 Dorsal root ganglia (sensory cell bodies of spinal nerves)
Classification of Neurons
 Functional: Based on the direction of impulse
propagation
 Sensory (Afferent): Transmit impulses from
receptors in skin, muscles, sensory organs, joints,
and viscera to the CNS
 Motor (Efferent): Transmit impulses from the CNS
to peripheral effectors (muscles and glands)
 Interneuron (Association): Carry impulses from
sensory neurons to motor neurons within the CNS
 Make up the majority of human neurons
Grouping of Neural Tissue
 Nerve Fiber: Any process projecting from a
cell body
 Axon or dendrite
 Nerve: A group of many fibers within the PNS
 Not a neuron
 Usually contain both sensory and motor nerve fibers
 sciatic nerve, ulnar nerve
 Ganglia: Group of cell bodies and synapses
within the PNS.
Grouping of Neural Tissue
 Tract: Bundle of fibers within the CNS
 May run long distances up or down the spinal
column or connecting parts of the brain
 Ascending tracts carry information upward (sensory)
 Descending tracts carry information downward
(motor)
 White Matter: Group of myelinated axons from
many neurons
 Look white due to myelination
Grouping of Neural Tissue
 Gray Matter: Unmyelinated axons,
dendrites, or cell bodies within the CNS
 Found covering the outer surfaces and in the
deeper regions (nuclei) of the brain
 Compose the “horns” of the spinal cord