Published on February 6, 2014
ivyanatomy.com section 4, chapter 11 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 Figure 11.21. A sagittal section showing the diencephalon in brown and the brainstem in yellow.
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.
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.Memory 2.Reproduction 3.Emotions (fear, anger, pleasure, sorrow) 4.Hunger and feeding
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.)
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.
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
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.
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.
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
Medulla Oblongata Nuclei of Medulla: 1.Cardiac center – regulates heart rate 2.Vasomotor center – regulates blood pressure 3.Respiratory center – regulates rhythmic breathing
Ventral surface of the brainstem 1 = cerebral peduncles. 2 = pons with transverse fibers leading 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 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 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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