Diencephalon, Brain Stem and
Cranial Nerves
Day 5
Pages: 242-246
Diencephalon
• Located between the cerebral hemispheres and above
midbrain
• Composed largely of gray matter
• Surrounds 3rd ventricle
• Includes:
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Thalamus
Hypothalamus
Optic tracts
Optic chiasma
Infundibulum
Posterior pituitary gland
Mammillary bodies
Pineal gland
Parts to Diencephalon
• Optic tracts/optic chiasma
– Formed by optic nerve fibers crossing over each other
• Infundibulum
– Behind optic chiasma, attachment for pituitary gland
• Posterior pituitary gland
– Hangs from floor of hypothalamus
• Mammillary Bodies
– Two rounded structures behind infundibulum
• Pineal gland
– Cone shaped structure attached to upper portion of
diencephalon
Thalamus
• Bulge into 3rd ventricle
• Central relay station for all sensory impulses except smell (ascending
fibers)
• Channels impulses to appropriate regions of cortex for interpretation
• Can communicate with cerebral cortex by means of descending fibers
Hypothalamus
• Located below thalamus and forms floor of 3rd
ventricle
• Maintains homeostasis and links endocrine to nervous
system
• Regulates:
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Heart rate and arterial BP
Body Temp.
H2O and electrolyte balance
Control of hunger and body weight
Control movements and glandular secretions of stomach
and intestines
– Production of neurosecretory substances and stimulation
of pituitary gland to secrete hormones
– Sleep and wakefulness
Other functions of Diencephalon
• Limbic System
– Comprised of parts of: cerebral cortex, frontal and
temporal lobes, hypothalamus, thalamus basal ganglia
and other deep masses called nuclei
• Controls emotional experiences and expressions
• Can modify the way a person acts
– Fear, anger, pleasure, and sorrow
• Guides persons behavior towards a likely increase
in survival.
Brain Stem
• Bundle of nervous tissue that connects
cerebrum to spinal cord.
• Consists of three parts
– Midbrain
– Pons
– Medulla Oblongata
Midbrain
• Located at the top
between diencephalon
and pons
• Contain corticospinal
tracts which are the main
motor pathways between
cerebrum and lower parts
of nervous system
• Contains several masses
of gray matter that serve
as reflex centers.
Pons
• Rounded bulge on
underside of brain stem
• Dorsal side relays
impulses to and from
M.O and cerebrum.
• Ventral side transmits
impulses to cerebrum
and cerebellum.
• Also relays sensory
impulses from PNS to
higher brain centers
Medulla Oblongata
• End of brain stem
• All ascending and descending nerve fibers pass
through MO
• Controls vital visceral activites
– Cardiac center
• Alters heart rate
– Vasomotor Center
• Constricting and dilating of blood vessels
– Respiratory Center
• Regulate rate, rhythm, and depth of breathing
• Also responsible for coughing, sneezing, swallowing
and vomiting.
Reticular Formation
• Found throughout the brain stem
• Network of nerve fibers
• Responsible for taking sensory impulses and
activating cerebral cortex into a state of
wakefulness
• Decreased activity in reticular formation is known
as sleep.
• Comatose state:
– Point at which the reticular formation is injured and
cannot be aroused even with strong stimulation.
Cerebellum
• Large mass of tissue located
below occipital bone.
• Divided into two
hemispheres
• Surrounded by cerebral
cortex
• Communicates with CNS by
three pairs of nerve tracts
– Cerebellar peduncles
Cellebellar Peduncles
• Inferior
– Brings sensory information concerning position of
limbs, joints, and other body parts
• Middle
– Transmits signals from the cerebral cortex to the
cerebrellum concerning desired positions of these
parts. After interpretation/analysis, sends pulses on to
3rd pair
• Superior
– Incorporated into motor impulses that get sent down
brainstem to move body in desired way.
Cerebellum
• Reflex center for integrating sensory information
concerning position of body parts and
coordination of skeletal muscle movements
• Maintains posture
• Damage/Injury
– Tremors
– Inaccurate movements of voluntary
muscles
– Loss of muscle tone
– Reeling walk
– Loss of equilibrium
Review
• What are the major functions of the thalamus?
The hypothalamus?
• How may the limbic system influence behavior?
• List the structures of the brain stem.
• What vital reflex centers are located in the brain
stem?
• What is the function of the reticular formation?
• Where is the cerebellum located?
• What are the major functions of the cerebellum?