section 4, chapter 11
The Diencephalon, Brainstem, and Cerebellum
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Diencephalon
The diencephalon is located between cerebral hemispheres and superior to the midbrain.• It surrounds the third ventricle
• Thalamus• Epithalamus• Hypothalamus• Optic tracts & Optic chiasm• Mammillary bodies• Pituitary Stalk (infundibulum)• Pineal gland
Structures within the diencephalon:
Figure 11.21. A sagittal section showing the diencephalon in brown and the brainstem in yellow.
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 geniculate nucleus (LGN) within the thalamus relays impulses from the retina to the visual cortex for interpretation.
Example: Figure 12.42. The lateral geniculate nucleus (LGN) within the thalamus relays impulses from the retina to the visual cortex for interpretation.
Thalamus
HypothalamusThe hypothalamus regulates a variety of visceral activities including:
1. Body temperature2. Heart rate and blood pressure3. Hunger and thirst4. Sex drive5. Influences moods and emotions6. regulates endocrine system
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 System1.Memory2.Reproduction3.Emotions (fear, anger, pleasure, sorrow)4.Hunger and feeding
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.)
The Limbic System
Brainstem
The brainstem connects the brain to the spinal cord. It includes three parts:1. Midbrain2. Pons3. Medulla Oblongata
Figure 11.15a. Sagittal section of the brain. The three portions of the brainstem are shown in yellow.Figure 11.15a. Sagittal section of the brain. The three portions of the brainstem are shown in yellow.
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 ventralsurface of the midbrain
• Main motor pathway from cerebrum to lower CNS
Midbrain
Substantia nigra• Involved in coordinating voluntary movements• Secretes dopamine – inhibitor neurotransmitter• Communicates with Basal Nuclei within cerebrum
Cross section through midbrain. Dark portions are substantia nigra. Opening in center is the
cerebral aqueduct.
Parkinson’s disease results in degeneration of substantia nigra and basal nuclei.
PonsThe pons appears as a rounded bulge on the ventral aspect of the brainstem. It’s located between the midbrain and medulla oblongata
The dorsal surface contains longitudinal fibers connect the medulla oblongata to the higher brain.
The Pons is a “Bridge”
Figure 11.20a. Ventral view of the brainstem.Figure 11.20a. Ventral view of the brainstem.
The Pontine Respiratory Center helps maintain the basic rhythm of breathing
The ventral surface contains transverse fibers that connect the pons to the cerebellum.
Medulla OblongataThe 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
Nuclei of Medulla:1.Cardiac center – regulates heart rate2.Vasomotor center – regulates blood pressure3.Respiratory center – regulates rhythmic breathing
Medulla Oblongata
1 = cerebral peduncles.
2 = pons with transverse fibers leading towards cerebellum.
3 & 4 = pyramids on the medulla
Ventral surface of the brainstem
CerebellumThe cerebellum “little brain” is inferior to occipital lobe of the cerebrum, and posterior to the pons.
Functions of the cerebellum include:1.Integrates sensory information2.Balance and posture3.Coordinates motor activity4.Learning and practicing
Cells within the cerebellum1.Purkinje cells – larges cells in CNS
Gatekeepers of impulses leaving the cerebellum
2.Dentate Nucleus – balance and proprioception
CerebellumThe 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
Figure 11.22 the cerebellum communicates with other
parts of the CNS by means of the cerebellar peduncles.
End of section 4, chapter 11
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