diencephalon, midbrain, and the brainstem

1. ivyanatomy.com
section 4, chapter 11
The Diencephalon,
Brainstem, and Cerebellum

2. Diencephalon
The diencephalon is located between cerebral
hemispheres and superior to the midbrain.
• It surrounds the third ventricle
Structures within the diencephalon:
• Thalamus
• Epithalamus
• Hypothalamus
• Optic tracts & Optic chiasm
• Mammillary bodies
• Pituitary Stalk (infundibulum)
• Pineal gland
Figure 11.21.
A sagittal section showing the diencephalon in
brown and the brainstem in yellow.

3. Thalamus
The thalamus is a sensory
relay center:
• Receives all sensory
impulses (except smell)
• The thalamus relays
impulses to appropriate
areas of the cerebral cortex
for interpretation
Example: Figure 12.42. The lateral
Example: Figure 12.42. The lateral
geniculate nucleus (LGN) within the
geniculate nucleus (LGN) within the
thalamus relays impulses from the retina
thalamus relays impulses from the retina
to the visual cortex for interpretation.
to the visual cortex for interpretation.

4. Hypothalamus
The hypothalamus regulates a variety of visceral activities including:
1. Body temperature
2. Heart rate and blood pressure
3. Hunger and thirst
4. Sex drive
5. Influences moods and emotions
6. regulates endocrine system

5. The Limbic System
The limbic system is a region of the diencephalon and the deeper regions of the
cerebrum important for controlling emotions and memory.
Functions of the Limbic System
1.Memory
2.Reproduction
3.Emotions
(fear, anger, pleasure, sorrow)
4.Hunger and feeding

6. The Limbic System
1.
Cingulate Gyrus – Satisfaction Center
• Feeling satisfied after a meal or after
sexual intercourse
• Damage may result in voracious appetite
or unusually high sex drive
2.
Hippocampus
• Within deep temporal lobe
• Role in memory and spatial cognition
• Alzheimer's results in degeneration of
hippocampus
3.
Amygdala -Assigns emotion to a memory
(pleasant or unpleasant)
• Like or dislike a person you see
• Primal fears (heights, fire, insects,
etc.)

7. Brainstem
The brainstem connects the brain to the spinal cord.
It includes three parts:
1. Midbrain
2. Pons
3. Medulla Oblongata
Figure 11.15a. Sagittal section of the brain. The
Figure 11.15a. Sagittal section of the brain. The
three portions of the brainstem are shown in yellow.
three portions of the brainstem are shown in yellow.

8. Midbrain
The midbrain is located between the diencephalon and the pons.
Fibers of the midbrain join lower parts of brainstem and
spinal cord with higher part of brain
Corpora Quadrigemina “Body of 4 twins”
located on the posterior surface of the midbrain.
• Superior Coliculi – visual reflexes
• Inferior Coliculi – auditory reflexes
Cerebral Peduncles located on the ventral
surface of the midbrain
• Main motor pathway from cerebrum to
lower CNS

9. Midbrain
Substantia nigra
• Involved in coordinating voluntary movements
• Secretes dopamine – inhibitor neurotransmitter
• Communicates with Basal Nuclei within cerebrum
Parkinson’s disease results in degeneration of substantia
nigra and basal nuclei.
Cross section through midbrain. Dark portions
are substantia nigra. Opening in center is the
cerebral aqueduct.

10. Pons
The pons appears as a rounded bulge on the ventral aspect of
the brainstem. It’s located between the midbrain and medulla
oblongata
The Pons is a “Bridge”
The dorsal surface contains
longitudinal fibers connect the medulla
oblongata to the higher brain.
The ventral surface contains transverse
fibers that connect the pons to the
cerebellum.
The Pontine Respiratory Center helps
maintain the basic rhythm of breathing
Figure 11.20a. Ventral
Figure 11.20a. Ventral
view of the brainstem.
view of the brainstem.

11. Medulla Oblongata
The medulla is an enlarged extension of the spinal cord.
Conducts ascending and descending impulses between
brain and spinal cord
Structures:
1.Pyramids
•
Site of motor tract decussation
(crossing over)
2.
•
Olives
Passages for fibers to cerebellum

12. Medulla Oblongata
Nuclei of Medulla:
1.Cardiac center – regulates heart rate
2.Vasomotor center – regulates blood pressure
3.Respiratory center – regulates rhythmic breathing

13. Ventral surface of the brainstem
1 = cerebral peduncles.
2 = pons with transverse fibers
leading towards cerebellum.
3 & 4 = pyramids on the
medulla

14. Cerebellum
The cerebellum “little brain” is inferior to occipital
lobe of the cerebrum, and posterior to the pons.
Functions of the cerebellum include:
1.Integrates sensory information
2.Balance and posture
3.Coordinates motor activity
4.Learning and practicing
Cells within the cerebellum
1.Purkinje cells – larges cells in CNS
Gatekeepers of impulses leaving the cerebellum
2.Dentate Nucleus – balance and proprioception

15. Cerebellum
The cerebellum communicates with the CNS by means of tracts, called
cerebellar peduncles:
1.Inferior peduncles – relays sensory impulses of the actual position of
limbs and joints from the medulla to the cerebellum
2.Middle peduncles – transmits impulses from the cerebral cortex to the
cerebellum of the desired position of these body parts.
3.Superior peduncles – sends correcting impulses from dentate nucleus
of cerebellum to midbrain, adjusting the position of a limb.
Damage to cerebellum may result in loss of balance,
tremors, and inaccurate movements

16. Figure 11.22 the cerebellum communicates with other
parts of the CNS by means of the cerebellar peduncles.

17. End of section 4, chapter 11