Nervous system terminal brain

Ivano-Frankivsk National Medical University
The Department of Human anatomy
Terminal brain. The structure of limbic cortex.
Pathways of spinal cord and brain, their classification.
Associative, comissural and projection ways. Ascending
projection ways. Descending (efferent) pathways.
Prepared by PhDPrepared by PhD
Tetyana Knyazevych - ChornaTetyana Knyazevych - Chorna

 The telencephalon is the
biggest compartment of
the brain, it consists of
right and left cerebral
hemisphere, partially
separated by cerebral
longitudinal fissure.

External feature
 The cerebral transverse
fissure intervenes between
the hemispheres and the
cerebellum
 Each hemisphere has
three surfaces:
superolateral, medial and
inferior

Three principal sulci
 Central sulcus
 Lateral sulcus
 Parietooccipital sulcus
Central sulcus
Lateral sulcus
Parietooccipital sulcus

Five lobes
 Frontal lobe
 Parietal lobe
 Temporal lobe
 Occipital lobe
 Insular lobe
Frontal lobe
Parietal lobe
Occipital lobe
Temporal lobe
Insular lobe

Sulci and gyri of Superolateral
surface
Frontal lobe:
 Precentral sulcus
 Superior frontal sulcus
 Inferior frontal sulcus
 Precentral gyrus
 Superior frontal gyrus
 Middle frontal gyrus
 Inferior frontal gyrus

surface
Precentral sulcus
Precentral gyrus
Superior frontal sulcus
Inferior frontal sulcus
Superior,
middle
and inferioe
frontal
gyri

Parietal lobe:
 Postcentral sulcus
 Postcentral gyrus
 Intraparietal sulcus
 Superior parietal lobule
 Inferior parietal lobule
 Supramarginal gyrus
 Angular gyrus

Sulci and gyri of Superolateral surface
Postcentral sulcus
Postcentral gyrus
Superior parietal lobule
Supramarginal
gyrus
Angular gyrus
Intraparietal sulcus

Temporal lobe:
 Superior temporal sulcus
 Inferior temporal sulcus
 Superior temporal gyrus
 Middle temporal gyrus
 Inferior temporal gyrus
 Transverse temporal gyri

surface
Superior temporal sulcus
Inferior temporal sulcus
Superior temporal gyrus
Middle temporal gyrus
Inferior temporal gyrus

Sulci and gyri of Superolateral surface
Precentral sulcus
Precentral gyrus
Superior frontal sulcus
Inferior frontal sulcus
Superior,
middle
and inferioe
frontal
gyri
Postcentral sulcus
Postcentral gyrus
Superior parietal lobule
Supramarginal
gyrus
Angular gyrus
Superior temporal sulcus
Inferior temporal sulcus
Superior temporal gyrus
Middle temporal gyrus
Inferior temporal gyrus

Sulci and gyri of medial surface
 Corpus callosum
 Callosal sulcus
 Cingulate gyrus
 Cingulate sulcus
 Marginal ramus
 Paracentral lobule
 Calcarine sulcus
 Cuneus
 Lingual gyrus

Sulci and gyri of medial surface
Corpus callosum
Callosal sulcus
cingulate gyrus
Cingulate sulcus
Marginal ramus
Paracentral lobule
Calcarine sulcus
Cuneus
Parietooccipital sulcus
Lingual gyrus

Sulci and gyri of inferior surface
 Olfactory bulb
 Olfactory tract
 Olfactory trigone
 Anterior perforated substance
 Collateral sulcus
 Occipitotemporal sulcus
 Medial occipitotemporal gyrus
 Lateral occipitotemporal gyrus
 Hippocampal sulcus
 Parahippocampal gyrus
 Uncus
 Hippocampus
 Dentate gyrus
Hippocampal formation

Inferior surface
Olfactory bulb
Olfactory tract
Olfactory trigone
Anterior perforated
substance
Collateral sulcus
Occipitotemporal sulcus
Medial and lateral
occipitotemporal
gyri
Parahippocampal
gyrus
Uncus

Hippocampus
Dentate gyrus
Hippocampal
formation

The grey matter of
cerebral hemispheres
 Cerebral cortex (new)
 Basal nuclei (older)
Cerebral cortex
1) the Molecular layer
2) the External granular layer
3) the External Pyramidal layer
4) the Internal Granular layer
5) the Internal Pyramidal layer
6) the Polymorphic or Multiform
layer

Functional location of
cerebral cortex

First somatic motor area
Position: located in precentral gyrus and anterior
portion of paracentral lobule

First somatic motor area
Characteristic
 Representation is inverted, but
head and face are upright
 A body part is represented by a
cortical area proportional to its
use rather than its size
 Receiving fibers from
postcentral gyrus sending out
fibers to form pyramidal tract,
controlling voluntary movements

First somatic sensory area
Position － lies in
postcentral gyrus
and posterior portion
of paracentral lobule

First somatic sensory area
Characteristics
 Sensory
representation, like
motor area, is
crossed and inverted
 Receiving and
interpret sensation
from opposite side of
body

Auditory area
 Located in
transverse temporal
gyri (Heshl’s gyri)
 Receive auditory
information from both
ears

Visual area
 Lie on either side of
calcarine sulcus in
medial surface of
occipital lobe
 Visual cortex of one
hemisphere receives
impression from lateral
part of retina of same
side and medial part of
opposite side
 Lesions of visual cortex
produce contralateral
homonymous visual
field defections

 Vestibular area: located in middle and inferior
temporal gyri
 Olfactory area: located in the uncus
 Taste area: located in the uncus

Language area
It is dominant in left hemisphere in
right-handed person
 Motor speech area (Broca’s
center).
 Located in posterior portion of inferior
frontal gyrus
 Damage: motor aphasia
 Writing area
 Located in posterior portion of middle
frontal gyrus
 Damage: agraphia
 Auditory speech area (Vernike’s
center).
 Located in posterior portion of superior
temporal gyrus
 Lesion: sensory aphasia
 Visual speech area
 Located in angular gyrus
 Lesion: alexia

 I. Motor analyzer of speech
articulation (Broca’s
center).
 II. Motor analyzer of writing
language.
 III. Auditory analyzer of
spoken language (Vernike’s
center).
 IV. Visual analyzer of
written language.
 1. Motor analyzer.
 2. Analyzer of common
rotation of head and eyes
to the opposite side.
 3. Analyzer of complex,
combined manual
movements.
 4. Analyzer of statokinetic.
 5. Interoceptive analyzer.
 6. Analyzer of general sensitivity.
 7. Analyzer of stereognosis.
 8. Auditory analyzer.
 9. Projection of visual analyzer
(sulcus calcarynus).
 10. Projection of olfactory
analyzer.
 11. Projection of gustatory
analyzer.

Lateral ventricle
 Position:
located in cerebral
hemispheres
 Four parts
 Central part: lies in parietal
lobe
 Anterior horn: extends into
frontal lobe
 Posterior horn extend into
occipital lobe
 Inferior horn: extend into
temporal lobe
Internal structures

 Communication
lateral ventricle → interventricular foramen → third
ventricle

Basal nuclei
 Corpus striatum
Lentiform nucleus
Caudate nucleus (head,
body, tail)
 Claustrum
 Amygdaloid body
Basal nuclei assist with
posture, balance, location
of sound
Globus pallidus
putamen
Neostriatum
－ paleostriatum

 the corpus striatum belong to extrapyramidal
system (+subthalamic nucleus, substantia nigra,
and red nucleus, along with their
interconnections with the reticular formation,
cerebellum, and cerebrum) that is a functional,
rather than anatomical, unit comprising the
nuclei and fibers (excluding those of the
pyramidal tract) involved in motor activities; they
control and coordinate especially the postural,
static, supporting, and locomotor mechanisms.
 Injury: motor disorders like tremor in arms, labored
movements (parkinsonism), involuntary forced
movements, tonus disorders.

Commissural
fibers-
－ run between left and
right hemisphere
 Corpus callosum:
rostrum, genu, trunk,
splenium
 Anterior commissure
 Fornix and commissure
of fornix

The internal capsule
Three parts
 Anterior limb of internal capsule
 Lies between caudate nucleus and
lentiform nucleus
 Containing frontopontine tract and
anterior thalamic radiation
(tr.frontothalamicus)
 Genu of internal capsule
 Is angle at which anterior and posterior
limbs meet
 Containing corticonuclear tract
 Posterior limb of internal
capsule
 Lies between thalamus and lentiform
nucleus
 Contain corticospinal tract,
corticorubral tract, central thalamic
radiation, parieto-occipito-temporo-
pontine tract, acoustic radiation and
optic radiation

Anterior thalamic radiation
Frontopontine tract
Lentiform nucleus
Corticorubral tract
Parieto-occipito-
temporo-pontine tract
Acoustic radiation
Optic radiation
Head of caudate nucleus
Corticonuclear tract
Corticospinal tract
Dorsal thalamus
Central thalamic
radiation
Medial geniculate body
Lateral geniculate body

АА. (capsula interna):
а) (tractus frontothalamicus);
б) (tractus frontopontinus);
в) (tractus corticonuclearis);
г) (tractus corticospinalis);
д) (tractus thalamocorticalis);
е) (tractus
occipitoparietotemporopontinus);
ж) (tractus acusticus centralis);
з) (tractus opticus centralis).
1. (caput nucleus caudatus).
2. (thalamus).
3. (globus pallidus medialis et lateralis).
4.(putamen).
5. (claustrum).
6. (capsula externa).
7. (cortex insula).
8. (capsula extrema).

Limbic system
 Hippocampus and associated structures:
Hippocampus: Required for the formation of long-term memories and
implicated in maintenance of cognitive maps for navigation.
Amygdala: Involved in signaling the cortex of motivationally significant
stimuli such as those related to reward and fear in addition to social
functions such as mating.
Fornix:carries signals from the hippocampus to the mammillary bodies
and septal nuclei.
Mammillary body: Important for the formation of memory;
 Septal nuclei: Located anterior to the interventricular septum, the
septal nuclei provide critical interconnections
 Limbic lobe
Parahippocampal gyrus: Plays a role in the formation of spatial memory
Cingulate gyrus: Autonomic functions regulating heart rate,
blood pressure and cognitive and attentional processing
Dentate gyrus: thought to contribute to new memories

 The limbic system operates by influencing
the endocrine system and the autonomic
nervous system. It is highly interconnected with
the nucleus accumbens, the brain's pleasure
center, which plays a role in sexual arousal and
the "high" derived from certain recreational
drugs.
 In 1954, Olds and Milner found that rats with
metal electrodes implanted into their nucleus
accumbens as well as their septal
nuclei repeatedly pressed a lever activating this
region, and did so in preference to eating and
drinking, eventually dying of exhaustion.

 Nucleus basalis of Meynert, and also known
as the nucleus basalis, is inferior to the
globus pallidus and within an area known as the
substantia innominata. It has wide projections to
the neocortex and is rich in acetylcholine
and choline acetyltransferase.
 In Parkinson and Alzheimer diseases the
nucleus undergoes degeneration. A decrease in
acetylcholine production is seen in Alzheimer's
disease, Lewy body dementia and some
Parkinson disease patients showing abnormal
brain function, leading to a general decrease of
mental capacity and learning.

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A neural pathway connects one part of
the nervous system with another and
usually consists of bundles of
elongated, myelin-insulated neurons,
known collectively as white matter. Neural
pathways serve to connect relatively
distant areas of the brain or nervous
system, compared to the local
communication of grey matter.

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Classification
 Association
 Commissural
 Projection pathways
1) Ascending (afferent)
2) Descending (efferent)

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Association fibers connect areas within the same hemisphere.
 Short association fibers connect areas that are located in the
same lobe (arcuate fibers).
 Long association fibers connect areas that are located in different
lobes of the brain:
- Superior longitudinal fasciculus
- Inferior longitudinal fasciculus
- The cingulum
- The uncinate fasciculus

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 Commissural
fibers connect the
hemispheres of the brain.
The corpus callosum,
the anterior
commissure, and
the posterior
commissure are all
composed of
commissural fibers.

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Projection pathways
1) Ascending (afferent):
 Exteroceptive
 Proprioceptive
 Interoceptive
2) Descending (efferent):
 Pyramidal
 Extrapyyramidal

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Exteroceptive pathways
Transmit the impulses from the skin receptors, the
retina, the internal ear and the tongue
- Lateral spinothalamic tract (pain and
temperature)
- Anterior spinothalamic tract (light touch (crude
touch), pressure, tickle, itch)
- The pathways of sense cranial nerves (visual,
auditory, taste)

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Lateral spinothalamic tract (pain
and temperature)
 The first neurons
(pseudounipolar
cells) reside within
the spinal ganglia.
The dendrites run
to the skin, the
axons form the
posterior root.

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 The second neurons
reside in the nucleus
proprius. The axons
decussate and enter the
lateral funiculus to form
the lateral spinothalamic
tract. The tract traverses
the medulla oblongata,
pons, midbrain and ends
in thalamus.

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 The axons of
the third
neurons pass
through the
posterior limb
of internal
capsule, join
the corona
radiata and
terminate in
the poscentral
gyrus.

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Anterior spinothalamic tract (touch,
pressure)
 The first neurons
are the
pseudounipolar cells
of the spinal ganglia.
The dendrites run to
the skin, the axons
form the posterior
root.

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 The second neurons reside in
the gelatinous substance of
the posterior gray column. The
axons decussate and enter the
anterior funiculus to form the
anterior spinothalamic tract.
The tract traverses the
medulla oblongata, pons,
midbrain and ends in
thalamus.
 The axons of the third neurons
terminate in the poscentral
gyrus.

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Proprioceptive pathways
 Transmit the information from the
muscles, fascia, joints.
 Provides spatial sensation of body posture
and muscle tonus.
The proprioceptive pathways divided into:
- The pathways to the cerebral cortex
- The pathways to the cerebellum

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The proprioceptive tract to the
cerebral cortex (tr.bulbothalamicus)
 The body of the first neurons
(pseudounipolar cells) reside
in the spinal and the cranial
ganglia. The dendrites form
the receptors muscles, fascia,
tendons, joints. The axons
form the posterior root of the
spinal cord (or the sensory
root of the cranial nerves).
Then it form the cuneate and
gracile fasciculi.

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tr.bulbothalamicus
 The gracile fasciculus (Goll’s
tract) carries the impulses
from the lower limbs and the
lower portion of the body. The
cuneate fasciculus (Burdach’s
tract) carries the impulses
from the upper limbs, the
upper portion of the body and
the neck.

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tr.bulbothalamicus
 The second neurons give off
the external arcuate fibers
(form the proprioceptive tract
to the cerebellum) and the
internal arcuate fibers, which
decussate, form the medial
lemniscus (runs through the
medulla oblongata, pons,
midbrain and ends in
thalamus).

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 The axons of the
third neurons
(runs through the
posterior limb of
the internal
capsule, corona
radiata)
terminate in the
poscentral gyrus.

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The proprioceptive tract to the
cerebellum
 The anterior (ventral) spinocerebellar tract
(Gowers’ tract)
 The posterior (dorsal) spinocerebellar tract
(Flechsig’ tract)

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The anterior spinocerebellar tract
(Gowers’ tract)
 The first neurons - pseudounipolar cells, reside in the
spinal ganglia. The axons form the posterior roots
and reach the grey matter to synapse with the cells of
the intermediomedial nucleus.
 The axons of the second neurons form decussation
and reach the lateral funiculus. It passes the medulla
oblongata, pons and reaches the superior medullary
velum. Upon entering the velum the fibers decussate
again and turn back to enter the superior cerebellar
peduncle.
 The fibers terminate in the cortex of vermis.

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The posterior spinocerebellar tract
(Flechsig’ tract)
 The first neurons - pseudounipolar cells,
reside in the spinal ganglia. The axons form
the posterior roots and reach the grey matter
to synapse with the cells of the thoracic
nucleus.
 The axons of the second neurons do not
decussate and proceed to the lateral funiculus
on the same side. It passes the medulla
oblongata and enter the cerebellum via
inferior cerebellar peduncle.
 The fibers terminate in the cortex of vermis.

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Interoceptive pathways
 Transmit the impulses from the internal
organs, glands and smooth muscles to the
brain.
 The afferent fibers of vegetative NS, spinal
nerves, some cranial nerves (V,VII,IX,X)
are the conductive part.

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Ascending Pathway LesionsAscending Pathway Lesions
 Unilateral lesion usually causes
contralateral anaesthesia (loss of pain and
temperature). Anaesthesia will normally
begin 1-2 segments below the level of
lesion, affecting all caudal body areas.
This is clinically tested by using pin pricks.

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Ascending Pathway LesionsAscending Pathway Lesions
If lesion is hemisection (halfway across the spinal cord)
(causing hemiplegia)) it is known as Brown-Séquard
syndrome.
Brown-Séquard syndrome may be caused by a
spinal cord tumour, trauma (such as a gunshot
wound or puncture wound to the neck or back),
ischemia (obstruction of a blood vessel), or
infectious or inflammatory diseases such as
tuberculosis, or multiple sclerosis.
Any presentation of spinal injury which is an incomplete lesion can
be called a partial Brown-Séquard or incomplete Brown-Séquard
syndrome, so long as it is characterized by features of a motor
loss on the same side of the spinal injury and loss of sensation
on the opposite side.

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I. funiculus posterior.
II. funiculus lateralis.
III. funiculus anterior.
1. (fasciculus gracilis (Golli).
2. (fasciculus cuneatus (Burdach).
3. (fasciculus proprius posterior).
4. (tractus spinocerebellaris posterior (Flechsig).
5. (tractus spinocerebellaris anterior (Gowers).
6. (tractus olivospinalis).
7. (tractus corticospinalis lateralis).
8. ( tractus rubrospinalis (Monakov).

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 9. (tractus spinothalamicus lateralis).
 10. (tractus spinotectalis).
 11. (fasciculus proprius lateralis).
 12. (fasciculus longitudinalis medialis).
 13. (tractus tectospinalis).
 14. (tractus corticospinalis anterior).
 15. (tractus reticulospinalis).
 16. (tractus spinothalamicus anterior).
 17. (fasciculus proprius anterius).
 18. (tractus vestibulospinalis).

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Descending (efferent) pathways:
 Pyramidal pathways conduct voluntary
motor inpulses from the cerebral cortex
 Extrapyramidal pathways deals with the
basal nuclei, maintain interrelations and
act as a single unit

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Pyramidal pathways
 Corticonuclear fibers
 Corticospinal fibers
The first neurons- gigantic
pyramidal cells (of Betz) of
precentral gyrus and the
paracentral lobule. The axons
form the pyramidal fasciculus
that descends to the
brainstem and spinal cord.

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 Some fibers decussate yet in the
brainstem and terminate on the motor
nuclei of the cranial nerves (III and IV
pairs in midbrain; V-VIII in pons; IX-XII
in medulla) and form the corticonuclear
fibers.
 The motor cells of the nuclei of cranial
nerves are the second neurons. Their
axons quit the brainstem and reach the
areas of the responsibility

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 The larger portion of the
fibers descends to the
pyramids of the medulla as
a corticospinal fibers.
 80% decussate and enter
the lateral funiculus to form
the lateral corticospinal
tract. The rest of fibers
proceed to the anterior
funiculus to form the
anterior corticospinal tract.

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 Injury of the
pyramidal tracts
results in central
paralysis of both
limbs while the
diaphragm and the
muscles of trunk
manifest little
malfunctioning.

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Extrapyramidal pathways
 the extrapyramidal system is a neural
network that causes involuntary reflexes and
movement, and modulation of movement.
Extrapyramidal tracts are chiefly found in
the reticular formation of the pons and medulla,
and target neurons in the spinal cord involved
in reflexes, locomotion, complex movements,
and postural control.

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 These tracts are in turn modulated by various
parts of the central nervous system, including
the nigrostriatal pathway, the basal ganglia,
the cerebellum, the vestibular nuclei, and
different sensory areas of the cerebral cortex.
All of these regulatory components can be
considered part of the extrapyramidal system,
in that they modulate motor activity without
directly innervating motor neurons.

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Extrapyramidal pathways
 The rubrospinal tract
 The tectospinal tract
 The vestibulospinal tract
 The olivospinal tract
 The reticulospinal tract

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 I. funiculus posterior.
 II. funiculus lateralis.
 III. funiculus anterior.
 1. (fasciculus gracilis (Golli).
 2. (fasciculus cuneatus (Burdach).
 3. (fasciculus proprius posterior).
 4. (tractus spinocerebellaris posterior (Flechsig).
 5. (tractus spinocerebellaris anterior (Gowers).
 6. (tractus olivospinalis).
 7. (tractus corticospinalis lateralis).
 8. ( tractus rubrospinalis (Monakov).

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 9. (tractus spinothalamicus lateralis).
 10. (tractus spinotectalis).
 11. (fasciculus proprius lateralis).
 12. (fasciculus longitudinalis medialis).
 13. (tractus tectospinalis).
 14. (tractus corticospinalis anterior).
 15. (tractus reticulospinalis).
 16. (tractus spinothalamicus anterior).
 17. (fasciculus proprius anterius).
 18. (tractus vestibulospinalis).

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Olfaction – Sense of Smell
The olfactory system represents
one of the oldest sensory
modalities in the phylogenetic
history of mammals. As a chemical
sensor, the olfactory system
detects food and influences social
and sexual behavior.

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 The olfactory area related to the superior
nasal concha and adherent portion of nasal
septum. The olfactory part comprise 3 types
of cells: receptor cells, supporting cells,
basal cells.
 The axons of receptor cells pass the
cribriform plate of ethmoid bone as the
olfactory nerve, they reach the olfactory bulb
to synapse with the second neurons.

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 The second neurons form the olfactory
tract, which terminates within the
olfactory trigone, the anterior perforated
substance, septum pellucidum, where the
3-d neuron stay.

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 Axons of 3-d neuron
run to amygdaloid
body, the olfacrory
cortex of
parahippocampal
gyrus, uncus.
 It has the
connections with the
mammilary bodies,
reticular formation,
nuclei of cranial
nerves.

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Gustation – Sense of Taste
 Gustatory receptors are housed in specialized taste buds
on the surface of the tongue.
 4 types of papillae:
 filiform
 fungiform
 vallate
 foliate
The tongue detects five basic taste sensations:
 salty
 sweet
 sour
 bitter
 umami

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 The first neurons are the
pseudounipolar neurons of the
sensory ganglia of facial and
glossopharyngeal nerves.
 Lingual nerve of facial cranial
nerve (from anterior 2/3 of
tongue) and lingual branches
of glossopharyngeal nerve
(from posterior 1/3 of tongue)
terminates the nucleus of
solitary tract, where the bodes
of 2-d neurons stay.
 The axons of 2-nd neurons
decussate and join the medial
lemniscus that ascends to the
thalamus.
 The axons of 3-d neurons of
thalamus reach the uncus of
the parahippocampal gyrus.

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Visual Pathways
 a pathway over which a visual
sensation is transmitted from
the retina to the brain.
 The fibers of an optic nerve traveling through
the optic chiasm to the the thalamus,the lateral
geniculate body and superior coliculi, and
optic radiations terminating in an occipital lobe
(sulcus calcarinus). Each optic nerve contains
fibers from only one retina. The fibers from the
middle parts of the retinas cross to the
opposite side of the brain at the optic chiasm.

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 The fibers from the lateral
part of each eye do not
cross at the optic chiasm,
pass through the lateral
geniculate body on the
same side of the brain,
and continue back to the
occipital lobe. If the right
optic tract were
destroyed, a person
would lose partial vision
in both eyes - the right
medial and the left lateral
fields of vision.

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 Sound waves
funneled by pinna
(auricle) into
external auditory
meatus
 External auditory
meatus channels
sound waves to
tympanic
membrane
Ears & Hearing - Outer Ear
10-47

17-97
 Malleus (hammer) is
attached to tympanic
membrane
 Carries vibrations to
incus (anvil)
 Stapes (stirrup)
receives vibrations
from incus, transmits
to oval window
Ears & Hearing - Middle Ear
10-49

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 Stapedius muscle, attached to stapes,
provides protection from loud noises
Can contract & dampen large vibrations
Prevents nerve damage in cochlea
Ears & Hearing - Middle Ear
10-50

17-99
Ears & Hearing - Cochlea
 Cochlea consists of a tube that looks like snail
shell
10-51

17-100
 Tube is divided
into 3 fluid-filled
chambers
 Scala vestibuli,
cochlear duct,
scala tympani
10-52

17-101
 Oval window attached to scala vestibuli (at base of
cochlea)
 Vibrations at oval window induce pressure waves in
perilymph fluid of scala vestibuli
 Scalas vestibuli & tympani are continuous at apex
 So waves in vestibuli pass to tympani & displace round
window (at base of cochlea)
 Necessary because fluids are incompressible & waves would not be
possible without round window
10-53

17-102
 Low frequencies can travel all way thru vestibuli & back in
tympani
 As frequencies increase they travel less before passing directly
through vestibular & basilar membranes to tympani
Fig 10.20
10-54

17-103
 High
frequencies
produce
maximum
stimulation of
Spiral Organ
closer to base
of cochlea &
lower
frequencies
stimulate closer
to apex
10-55

17-104
Spiral Organ (Organ of Corti)
 Spiral Organ is
where sound is
transduced
 Sensory hair cells
located on the basilar
membrane
 1 row of inner cells
extend length of
basilar membrane
 Multiple rows of
outer hair cells are
embedded in
tectorial membrane
10-56

17-105
Spiral Organ (Organ of Corti)
 Pressure waves moving thru cochlear duct
create shearing forces between basilar &
tectorial membranes, moving & bending
stereocilia
10-57

17-106
Neural Pathway for Hearing
 Info from 8th
nerve goes to
pons, then to
inferior
colliculus, then to
thalamus, & to
auditory cortex
10-58

17-107
Neural Pathways for Hearing
 Neurons in
different regions
of cochlea
stimulate
neurons in
corresponding
areas of auditory
cortex
 Each area of
cortex represents
different part of
cochlea & thus a
different pitch
10-59

17-108
Vestibular Apparatus
 Provides sense of
equilibrium
 =orientation to gravity
 Vestibular apparatus &
cochlea form inner ear
 V. apparatus consists
of otolith organs
(utricle & saccule) &
semicircular canals
10-35

17-109
Semicircular Canals
 Provide information
about rotational
acceleration
 Project in 3
different planes
 Each contains a
semicircular duct
 At base is crista
ampullaris where
sensory hair cells
are located
Fig 10.12
10-42

17-110
 Utricle and saccule provide info about linear
acceleration
 Semicircular canals, oriented in 3 planes, give sense of
angular acceleration
10-37

17-111
 Hair cells are receptors for equilibrium
 Each contains 20-50 hair-like extensions called stereocilia
 1 of these is a kinocilium
10-38

17-112
 When stereocilia are bent toward kinocilium, hair cell
depolarizes & releases NT that stimulates 8th nerve
 When bent away from kinocilium, hair cell hyperpolarizes
 In this way, frequency of APs in hair cells carries information about
movement
10-39

17-113
Utricle & Saccule
 Have a macula containing hair cells
 Hair cells embedded in gelatinous otolithic membrane
 Which contains calcium carbonate crystals (=otoliths) that resist
change in movement
10-40

17-114
Utricle & Saccule
 Utricle sensitive to
horizontal
acceleration
 Hairs pushed
backward during
forward
acceleration
 Saccule sensitive
to vertical
acceleration
 Hairs pushed
upward when
person descends
10-41

17-115
Semicircular Canals
 Provide information
about rotational
acceleration
 Project in 3
different planes
 Each contains a
semicircular duct
 At base is crista
ampullaris where
sensory hair cells
are located
10-42

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