Chapter 11, Section 4

The Diencephalon, Brainstem, and Cerebellum

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

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

Thalamus

• 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.

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

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. Memory1. Memory

2. Reproduction

3. 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

The Limbic System

• 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

• Fear of heights

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

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”

• Superior Coliculi – visual reflexes

• Inferior Coliculi – auditory reflexes

• Cerebral Peduncles

•Ventral surface of 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

cerebral aqueduct.

•Parkinson’s disease results in degeneration of substantia

nigra and basal nuclei.

Pons

• The pons appears as a rounded bulge on the ventral aspect

of the brainstem

• Located between the midbrain and medulla oblongata

• Dorsal aspect – Longitudinal fibers

connect medulla oblongata and cerebrum

The Pons is a “Bridge”

connect medulla oblongata and cerebrum

•Ventral aspect- Transverse fibers

connect cerebellum and cerebrum

Figure 11.20a. Ventral

view of the brainstem.

•Pontine Respiratory Center – functions

with medulla to maintain basic rhythm of

breathing

Medulla Oblongata

• The medulla is an enlarged extension of the spinal cord.

•Conducts ascending and descending impulses between brain and

spinal cord

Structures: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 rate

2. Vasomotor center – regulates blood pressure

3. Respiratory center – regulates rhythmic breathing

Medulla Oblongata

1 = cerebral peduncles.

2 =pons with transverse fibers leading

towards cerebellum.

Ventral surface of brainstem.

towards cerebellum.

3 & 4 = pyramids on the medulla

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 practicing4. 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

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 medulla to 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 Chapter 11, Section 4