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Exercise 17
Histology of Nervous Tissue
Introduction
 2 principle cell populations:
 Neuroglia- also called glial cells
 In central nervous system (CNS), they are astrocytes,
oligodendrocytes, microglia, ependymal cells
 In peripheral nervous system (PNS), they are Schwann
cells, satellite cells
 Brace, protect & insulate neurons
 Act as phagocytes
 Myelinate neuronal extensions
 Participate in capillary/neuron exchanges
 Control chemical environment around neurons
 NOT capable of generating or transmitting nerve
impulses
Introduction (continued)
 Neurons
 Basic functional unit of nervous tissue
 Highly specialized to transmit nerve impulses from
one part of the body to another
 Neuron anatomy
 Cell body
 Found in CNS in clusters called nuclei, outside CNS in
clusters called ganglia
 Make up the grey matter of the nervous system
 Large, rounded nucleus surrounded by neuroplasm
(cytoplasm)
Neuron Anatomy (continued)
 2 types of neuron processes:
 Dendrites- receptive regions; they receive
nerve impulses
 Axons- generate & conduct nerve impulses
 Know figures 17.1, 17.2 & 17.3
 Neuron processes running through the
CNS form tracts of white matter
 In the PNS, they form peripheral nerves
Neuron Classification
 Classification by structure
 Unipolar- one short process extends from cell body &
divides into peripheral & central processes; most distal
portions of peripheral process act as dendrites, the rest,
along with central process, act as axons; neurons that
conduct impulses to the CNS
 Bipolar- 2 processes attached to the cell body; found in
receptor apparatus of the eye, ear & olfactory mucosa
 Multipolar- many processes extending from cell body;
single axon, the rest are dendrites; most CNS neurons
& those carrying impulses away from CNS are
multipolar
 Know figure 17.5
Neuron Classification (continued)
 Classification by function
 Sensory (afferent)- carry impulses from sensory
receptors in viscera, skin, skeletal muscles, joints or
special sensory organs; cell bodies typically found in
ganglia outside CNS; typically unipolar
 Motor (efferent)- carry impulses from CNS to viscera,
body muscles & glands; cell bodies usually in CNS;
usually multipolar
 Interneurons (association neurons)- situated between
pathways connecting sensory & motor neurons; outside
CNS; multipolar
 Know figure 17.6
Neuroglia of the CNS
 Most common glial
cell type
 Each forms myelin
sheath around
more than one
axons in CNS
 Analogous to
Schwann cells of
PNS
Structure of a Nerve
 A nerve is a bundle of nerve fibers (processes) wrapped in
connective tissue
 Extend to and/or from the CNS and viscera or structures of the
body periphery
 Nerves carrying both sensory (afferent) & motor (efferent) fibers
are called mixed nerves; all spinal nerves are mixed
 Nerves that only carry sensory impulses to CNS are called
sensory (afferent)
 Nerves that carry only motor fibers are called motor (efferent)
 Each fiber is surrounded by an endoneurium
 Groups of fibers are surrounded by a perineurium, forming
bundles called fascicles
 Groups of fascicles are bound by epineurium forming a nerve
 Blood & lymphatic vessels are also present within the nerve
 Know figure 17.7
Structure of a Multipolar Neuron
Nerve bundle (PNS)
Exercise 19
Gross Anatomy of the Brain and Cranial
Nerves
Introduction
 Divisions:
 Central nervous system (CNS)- brain and spinal cord
 Peripheral nervous system (PNS)- cranial & spinal
nerves, ganglia, and sensory receptors
 Sensory portion- nerve fibers that conduct impulses
toward the CNS
 Motor portion- nerve fibers that conduct impulses away
from the CNS
 Somatic (voluntary) division- controls skeletal muscles
 Autonomic (involuntary) division- controls smooth & cardiac
muscles and glands
 Sympathetic division
 Parasympathetic division
The Human Brain
 During embryonic development, the CNS first appears as a
neural tube
 Neural tube then develops into 3 regions
 Prosencephalon (forebrain)
 Mesencephalon (midbrain)
 Rhombencephalon (hindbrain)
 Remainder of the neural tube becomes the spinal cord
 Those 3 regions become the secondary brain vesicles, which
then develop into various adult brain structures
 Know figure 19.1
The Human Brain (cont.)
 Cerebral hemispheres (continued)
 Hemispheres share some functions
 Each is also specialized in some ways
 Left is usually associated with language (analytical)
 Right is associated with abstract, conceptual, and spatial
processes (artistic & creative)
 Those functions are mainly carried out in the outermost grey
matter, called the cerebral cortex
 Most of the deeper tissue, the white matter, is involved in
carrying impulses to & from the cortex
The Human Brain (cont.)
 Brain stem
 Includes:
 Cerebral peduncles- connect the pons to the cerebrum
 Pons- primarily sensory & motor fiber tracts that
connect the brain to lower CNS centers
 Medulla oblongata- primarily composed of fiber tracts;
houses many vital autonomic centers involved in
control of heart rate, respiratory rhythm, and blood
pressure, as well as involuntary centers controlling
vomiting, swallowing, etc.
The Human Brain (cont.)
 Cerebral hemispheres
 Develop out of the telencephalon of the forebrain
 Most superior portion of the brain
 Entire surface consists of gyri that are separated by shallow
grooves called sulci (singular = sulcus) & deeper grooves
called fissures
 Hemishpheres are divided by the longitudinal fissure
 Frontal & parietal lobes are separated by the central sulcus
 Temporal & parietal lobes are separated by the lateral sulcus
 Occipital & parietal lobes are separated by the parietooccipital sulcus
 Know figures 19.2 (a, b, & c, not d) & 19.3
The Human Brain (cont.)
 Diencephalon
 Sometimes considered the most superior
portion of the brain stem
 Embryologically part of the forebrain
 Includes olfactory bulbs & tracts, optic nerves,
the optic chiasma, optic tracts, the pituitary
gland, and the mammillary bodies
 Know figures 19.4 a & b, 19.5
The Human Brain (cont.)
 Cerebellum
 Projects dorsally from under the occipital lobes
of the cerebrum
 2 major hemispheres
 Outer cortex of grey matter & inner white
matter
 Know figure 19.6
Meninges of the Brain
 3 connective tissue membranes: dura mater (outermost),
arachnoid mater, pia mater (innermost)
 Dural layers are fused together, except in 3 places where the
innermost layer extends inward to secure brain structures (falx
cerebri)
 Meningitis- inflammation of the meninges; caused by infection
 Encephalitis- inflammation of the neural tissue of the brain
 Know figure 19.7
Cerebrospinal Fluid (CSF)
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Formed by the choroid plexuses
Similar to plasma in composition
Cushions the brain
Circulates from the 2 lateral ventricles to the 3rd ventricle via
the interventricular foramina, then through the cerebral
aqueduct into the 4th ventricle
 CSF returns to the blood in the dural sinuses
 Improper drainage leads to a build-up, which puts pressure on
the brain in adults; causes hydrocephalus in infants
 Know figure 19.8
Cranial Nerves
 Actually part of the PNS
 12 pairs
 Primarily serve the head & neck; only the vagus
nerves extend into the thoracic & abdominal
cavities
 Most are mixed; exceptions are the optic,
olfactory & vestibulocochlear
 Table 19.1: know name, number & function
 Know figure 19.9
Human brain
Human brain sagittal
Our brain model
Sheeps brain
Sheep sagittal #1
Sheep sagittal #2
Sheep brain
1. cerebrum
2. lateral ventricles
3. third ventricle
4. cerebral aquaduct
5. fourth ventricle
6. pons
7. cerebellum
8. arbor vitae
9. medulla oblongata
10. genu of corpus callosum
11. body of corpus callosum
12. splenium of corpus callosum
13. fornix
14. massa intermedia
15 & 21. optic chiasma
16. hypophysis
17. infundibulum
18. mammillary body
19. superior colliculus
20. olfactory bulbs
21 & 15. optic chiasma
23. longitudinal cerebral fissure
24. cerebral cortex
25. central white matter
26. choroid plexus
Sheep frontal sections
Sheep brain
1. cerebrum
2. lateral ventricles
3. third ventricle
4. cerebral aquaduct
5. fourth ventricle
6. pons
7. cerebellum
8. arbor vitae
9. medulla oblongata
10. genu of corpus callosum
11. body of corpus callosum
12. splenium of corpus callosum
13. fornix
14. massa intermedia
15 & 21. optic chiasma
16. hypophysis
17. infundibulum
18. mammillary body
19. superior colliculus
20. olfactory bulbs
21 & 15. optic chiasma
23. longitudinal cerebral fissure
24. cerebral cortex
25. central white matter
26. choroid plexus
Exercise 20
Electroencephalography
Brain Wave Patterns and the
Electroencephalogram
 EEG- record of the electrical activity of the brain
 Recorded as waves
 Represents summed synaptic activity of many
neurons
 Frequency of 1-30 Hz (cycles per second)
 Dominant rhythm of 10 Hz
 Average amplitude of 20-100 microvolts
 Vary in frequency in different areas of the brain
Brain Wave Patterns (cont.)
 Waves
 Alpha waves- average frequency of 8-13 Hz;
produced in a relaxed state with eyes closed;
alpha block (suppression) occurs if eyes are
opened or if the person begins to concentrate
on something; as concentration or excitement
increases, frequency increases & amplitude
decreases
 Beta waves- related to alpha waves, but with
higher frequency (14-30 Hz) & lower
amplitude; typical of alert state
Brain Wave Patterns (cont.)
 Waves (cont.)
 Delta waves- very high amplitude; frequency of 4 Hz or
less; seen in deep sleep
 Theta waves- frequency of 4-7 Hz; high amplitude;
abnormally contoured; normal in children; abnormal in
adults
 Brain waves vary with age, sensory stimuli, brain
pathology, and chemical state of body
 Spontaneous brain waves are ALWAYS present
 Lack of brain waves is considered clinical
evidence of death
Brain wave patterns
Exercise 21
Spinal Cord, Spinal Nerves, and the
Autonomic Nervous System
Anatomy of the Spinal Cord
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Continuation of the brain stem
Association & communication center
Enclosed within the vertebral column
Extends from the foramen magnum to the 1st or 2nd lumbar
vertebra, terminating in the conus medullaris
The filum terminale, an extension of the pia mater, extends
into the coccygeal canal
CSF does flow through the spinal canal and can be removed
below L3 (lumar tap)
31 pairs of spinal nerves
Know figures 21.1 & 21.2
Grey Matter
 Looks like an H or a butterfly in the spinal cord
 The dorsal horns contain interneurons & sensory
fibers
 The ventral horns mostly contain cell bodies of
motor neurons of the somatic division of the motor
portion of the PNS
 The lateral horns contain cell bodies of motor
neurons of the sympathetic division of the ANS
(PNS)
White Matter
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Composed of myelinated fibers
White matter on each side of the spinal cord is divided into 3 white
columns:
 Posterior funiculi
 Lateral funiculi
 Anterior funiculi
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Each funiculus contains tracts
 Ascending tracts carry sensory impulses to the brain
 Descending tracts carry motor impulses from the brain
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Severe trauma to the cord can cause a loss of both sensory & motor
functions served by that area of the cord, as well as below
 Paraplegia- permanent flaccid paralysis of both legs
 Quadriplegia- permanent flaccid paralysis of all 4 limbs
The Autonomic Nervous System
(ANS)
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Subdivision of PNS
Also called involuntary nervous system
Regulates body activities not normally under voluntary control
Serves cardiac & smooth muscle & internal glands
Consists of chains of 2 motor neurons:
 Preganglionic neuron- resides in the brain or spinal cord; its
axon leaves the CNS & synapses with the 2nd (ganglionic)
neuron
 Ganglionic neuron- resides in a ganglion outside the CNS; its
axon extends to the organ it serves
 2 divisions: sympathetic & parasympathetic
ANS
 Parasympathetic & sympathetic divisions have antagonistic
effects
 Parasympathetic division
 “Resting & digesting” system
 Maintains internal organs for normal functions & homeostasis
 Sympathetic division
 “Fight or flight” response
 Readies the body to deal with situations that threaten
homeostasis
 Increases heart rate & blood pressure, dilates bronchioles in
the lungs, increases blood sugar levels, etc.
Spinal cord
Spinal cord cross section