section 4, chapter 11

The Diencephalon, Brainstem, and Cerebellum

ivyanatomy.com

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