Nervous System- Chapters 7, 8
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Surgical Papyrus
• Egyptian hieroglyphics.
• 17th Century B.C.
• Oldest known surgical
treatise.
• 48 case histories are
outlined.
2
Organization of the Nervous System
• Consists of two divisions:
– Central Nervous System (CNS).
• Brain and spinal cord.
– Peripheral Nervous
System (PNS).
• All nervous tissue
outside the CNS.
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1) Nervous tissue consists of _________
and ____________.
– A) neurons and ganglia
– B) neurons and meninges
– C) neurons and neuroglia
– D) neurons and nerves
– E) morons and gangly ganglia
4
Nervous System
• Neurology- (neur- gr. nerve) the scientific
study of the nervous system.
• Nervous Tissue
– Neurons (nerve cells)
– Neuroglia
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Neurons
• Neuron- the functional unit of the nervous
system.
• Numbers
– 100 billion in the brain.
– 1 billion in the spinal cord.
• Neurons consist of dendrites, cell bodies,
and axons.
6
Dendrites
Synaptic end bulbs
Nucleus
Axon terminal
Cell Body
Axon Myelin Sheath Nodes of Ranvier
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8
Functional Classification of Neurons
• Based on the direction the neurons transmit
nerve impulses.
– Sensory neurons
• Transmit nerve impulses from receptors in the skin,
sense organs, muscles, joints, and organs toward the
spinal cord and brain.
– Interneurons
• Transmit nerve impulses from one neuron to another.
– Motor neurons
• Transmit nerve impulses away from the spinal cord to
muscles or glands.
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Types of Neurons
Dorsal-Root
Ganglion
Sensory
Receptor
Interneuron
Ventral-Root
Ganglion
Effector
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Nervous System Functions
• Sensory
– Detecting internal and external stimuli.
• Sensory receptors and sensory neurons
• Integrative
– Processing sensory information by analyzing,
storing, and making decisions regarding
appropriate responses.
• Interneurons
• Motor
– Responding to integration decisions.
• Motor neurons
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Neuroglial Cells
•
•
•
•
•
Neuroglia (glia= gr. glue).
Half the volume of the CNS.
Smaller than neurons.
50X more numerous.
Functions
– Support and protect the neurons.
– Maintain homeostasis in the fluid that bathes
neurons.
• 6 types of neuroglia.
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1) Which of the following is not considered
a nervous system structure?
A) spinal cord
B) Jeff’s brain
C) ganglia
D) heart
E) enteric plexus
F) sensory receptors
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Nervous System Structures
• Brain
– 12 pairs of cranial nerves and their
branches.
• Spinal cord
– 31 pairs of spinal nerves and their
branches.
• Ganglia- clusters of cell bodies in
the peripheral nervous system.
• Enteric plexus- a network of nerves
in the GI tract.
• Sensory receptors- parts of
neurons or specialized cells that
monitor changes in the internal or
external environment.
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What is a nerve?
• Nerve- a bundle of long axons outside the
central nervous system.
Axon
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Lining the Brain & Spinal Cord= Meninges
• Meninges- 3 layers of
protective tissue lining
the brain and spinal
cord.
– Dura Mater
– Arachnoid Mater
– Pia Mater
• The spaces between
the meninges are
filled with cerebral
spinal fluid.
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Gray and White Matter
• White matter- aggregations of myelinated processes.
• Gray matter- nerve fibers with little to no myelin.
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The Brain
• One of the largest organs in the body, 3 lbs.
• Average length- 7 inches, width- 5.5, height- 4.
• Center for registering sensations, correlating them
with one another and with stored information.
• Center for intellect, emotions, behavior, and memory.
• Chemistry- 78% H2O, 12% lipids, 8% protein, 2%
other.
• Consists of four principal parts:
–
–
–
–
Cerebrum
Cerebellum
Diencephalon
Brain stem
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4 Principal Parts of the Brain
Thalamus
Hypothalamus
Midbrain
Pons
Medulla
Oblongata
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The Cerebrum
• The cerebrum is the largest
portion of the human brain.
– Communicates with and
coordinates activities of other
parts of the brain.
– Divided into left and right
cerebral hemispheres.
– The outer layer is termed the
cerebral cortex.
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Lobes of Cerebrum
Motor
Sensory
Visual
Auditory
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True or False
1) If you eat right hemispheric sheep brains
biweekly, while watching the movie “The Man
With Two Brains”, you will be more creative
than someone who eats left hemispheric
brains and watches the movie “The Wedding
Crashers.”
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Hemispheric Lateralization
Verbal
Nonverbal
Logical
Intuitive
Analytical Creative
Rational
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Higher Mental Functions
• Memory is the ability to hold a thought in the mind
or to recall events from the past.
– Short-term- prefrontal lobe.
– Long-term- hippocampus.
– Amygdala- adds emotional overtones to memories.
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Limbic System- long-term memory
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Brain Stem
• Functions
– Acts as a relay station between the cerebrum and the
spinal cord and cerebellum.
– Reflex center for visual, auditory, and tactile responses.
Midbrain
Pons
Medulla
Oblongata
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Cerebellum
• Functions
– Acts as an integration center for sensory input from the
eyes, ears, joints, and muscles that relates to body
position.
– Sends motor impulses to skeletal muscles that maintain
posture and balance.
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Diencephalon
• Consists of the hypothalamus and thalamus.
• Functions
– Homeostasis for hunger, sleep, temp, water balance.
– Receiving center for all sensory input, except smell.
– Plays a role in memory and emotions.
Thalamus
Hypothalamus
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Alzheimer’s Disease
• Presence of abnormal
neurons in the brain.
– Amyloid plaque envelopes
axons.
– Tangled axons
(neurofibrillary tangles).
• 5% of adults 65-74 years
in age. 50% of those 85
and over.
• Appears to be partly
genetic, APOE4.
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Parkinson’s Disease
• Characterized by trembling or shaking.
• Due to the degeneration of dopamine-releasing neurons
in the brain.
• The lack of dopamine results in the sending out of
excess signals to effectors (muscles).
• 1% of those over the age of 60.
• Treatment is with L-dopa.
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Cranial and Spinal Nerves
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Spinal Cord
• Anatomy
– Flattened cylinder, 16-18
inches in length and
3/4 inch diameter.
– In adult ends at L2.
• Functions
– Provides communication
between the brain and the
peripheral nerves.
– Spinal cord reflexes.
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Spinal Nerve
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Peripheral Nervous System (PNS)
• Somatic Nervous System (somat-body)
– Neurons that conduct impulses from somatic and special
sense receptors to the CNS.
• Enteric Nervous System (enter-intestines)
– Two plexuses that extend the length of the
gastrointestinal tract.
• Autonomic Nervous System (auto-self, nomic-law)
– Motor neurons that convey impulses from the CNS to
smooth muscle tissue, to cardiac tissue, and to glands.
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Somatic vs. Autonomic
• The ANS pathway is a 2 neuron pathway, while
the SNS is a 1 neuron pathway.
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Divisions of the ANS
Sympathetic
• 2 Major Divisions
– Sympathetic
• Speeds up the
visceral effector.
– Parasympathetic
• Slows down the
visceral effector.
• Most body organs receive
dual innervation.
• Hypothalamus regulates
balance between these two
divisions.
Parasympathetic
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Sympathetic Responses
• The sympathetic system dominates during physical
or emotional stress conditions.
– “E situations”- emergency, embarrassment, excitement, exercise.
• Alarm reaction- flight or fight response.
–
–
–
–
–
–
–
–
Dilation of pupils.
Increase of heart rate and blood flow to muscles.
Decrease in blood flow to nonessential organs.
Increase in blood flow to skeletal and cardiac muscles.
Airways dilate and respiratory rate increases.
Blood glucose level increases.
Decrease in intestinal activity and inhibition of urination.
Causes genital erection.
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Parasympathetic Responses
• Rest-and-digest activities.
• Mechanisms that help conserve and restore
body energy during times of rest.
• SLUDD responses
–
–
–
–
–
Salivation
Lacrimation
Urination
Digestion
Defecation
• 3 “decreases”- decreased
– Heart rate, diameter of airways, and diameter of pupils.
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Development of the Nervous System
• Appears around 3-4
weeks.
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