2. CENTRAL NERVOUS SYSTEM
Major Parts of the Brain

3. The adult brain consists of four major parts:
Brain Stem,
Cerebellum,
Diencephalon
Cerebrum
The brain stem is continuous with the spinal cord and consists
Medulla Oblongata
Pons
Midbrain
Posterior to the brain stem is the cerebellum (little brain)..

4. Superior to the brain stem is the diencephalon which as noted previously consists
thalamus,
hypothalamus,
epithalamus.
Supported on the diencephalon and brain stem is the cerebrum the largest part of the brain.

7. THE BRAIN STEM AND RETICULAR FORMATION
Medulla Oblongata ( VIII –XII)
The medulla begins at the foramen magnum and extends to the inferior border of the pons, a distance of about 3 cm (1.2 in.).
The cardiovascular center
The medullary rhythmicity area
vomiting, coughing, and sneezing
Inferior Olivary nucleus. Neurons here relay impulses from proprioceptors to the cerebellum

9. 1.Vestibulocochlear (VIII) nerves.
Several cochlear nuclei in the medulla receive sensory input from and provide motor output to the cochlea of the internal ear via the cochlear

10. Glossopharyngeal (IX) nerves.
Nuclei in the medulla relay sensory and motor impulses related to taste, swallowing, and salivation via the glossopharyngeal nerves

11. 3. Vagus (X) nerves.
Nuclei in the medulla receive sensory impulses from and provide motor impulses to the pharynx and larynx and many thoracic and abdominal viscera via the vagus nerves.

12. 4. Accessory (XI) nerves (cranial portion).
These fibers are actually part of the vagus (X) nerves. Nuclei in the medulla are the origin for nerve impulses that control swallowing via the vagus nerves (cranial portion of the accessory nerves).

13. 5. Hypoglossal (XII) nerves.
Hypoglossal nuclei in the medulla are the origin for nerve impulses that control tongue movements during speech and swallowing via the hypoglossal nerves.

14. Pons ( V-VIII)
The pons (_bridge) lies directly superior to the medulla and anterior to the cerebellum and is about 2.5 cm (1 in.)
Together with the medullary rhythmicity area, the pneumotaxic and apneustic areas help control breathing

15. Trigeminal (V) nerves.
Nuclei in the pons receive sensory impulses for somatic sensations from the head and face and provide motor impulses that govern chewing via the trigeminal nerves.

16. 2. Abducens (VI)
. Abducens nuclei in the pons provide motor impulses that control eyeball movement via the abducens nerves.

17. 3. Facial (VII) nerves.
Nuclei in the pons receive sensory impulses for taste and provide motor impulses to regulate secretion of saliva and tears and contraction of muscles of facial expression via the facial nerves.

18. 4. Vestibulocochlear (VIII) nerves
. Vestibular nuclei in the pons receive sensory impulses from and provide motor impulses to the vestibular apparatus via the vestibular branches of the vestibulocochlear nerves. These nerves convey impulses related to balance and equilibrium

19. Midbrain ( III- IV)
The midbrain (mesencephalon) extends from the pons to the diencephalon
The aqueduct of the midbrain (cerebral aqueduct) passes through the midbrain, connecting the third ventricle above with the fourth ventricle
The anterior part of the midbrain contains a pair of tracts called cerebral peduncles.
The posterior part of the midbrain, called the tectum , contains four rounded elevations

21. Midbrain

22. The two superior elevations are known as the superior colliculi (visual activities.)
The two inferior elevations, the inferior colliculi, (auditory pathway)
These two nuclei also are reflex centers for the startle reflex, sudden movements of the head and body that occur when you are surprised by a loud noise such as a gunshot.
The midbrain contains several nuclei, including the left and right substantia nigra which are large, darkly pigmented nuclei

23. Finally, nuclei in the midbrain are associated with two pairs of cranial nerves
1. Oculomotor (III) nerves. Oculomotor nuclei in the midbrain provide motor impulses that control movements of the eyeball,while accessory oculomotor nuclei provide motor control to the smooth muscles that regulate constriction of the pupil and changes in shape of the lens via the oculomotor nerves.
2. Trochlear (IV) nerves. Trochlear nuclei in the midbrain provide motor impulses that control movements of the eyeball via the trochlear nerves.

24. Reticular Formation
The broad region where white matter and gray matter exhibit a net like arrangement is known as the reticular formation
It extends from the superior part of the spinal cord, throughout the brain stem, and into the inferior part of the diencephalon.
The ascending portion of the reticular formation is called the reticular activating system (RAS), which consists of sensory axons that project to the cerebral cortex, both directly and through the thalamus.

25. Reticular Formation
Many sensory stimuli can activate the ascending portion of the RAS.
Visual And Auditory Stimuli;
Mental Activities;
Stimuli From Pain,
Touch, Pressure Receptors;
And Receptors In Our Limbs And Head That Keep Us Aware Of The Position Of Our Body Parts.

26. Reticular Formation

27. The most important function of the RAS
✓ Consciousness, a state of wakefulness in which an individual is fully alert mental activities.
✓ The arousal or awakening from sleep.
✓ Attention and alertness.
✓ prevents sensory overload by filtering out
✓ Inactivation of the RAS produces sleep, a state of partial consciousness from which an individual can be aroused.
Damage to the RAS, on the other hand, results in coma

28. cerebellum
The cerebellum is posterior to the medulla and pons and inferior to the posterior portion of the cerebrum
A deep groove between the cerebrum and cerebellum known as the transverse fissure is occupied by the tentorium cerebelli which supports the posterior part of the cerebrum and separates it from the cerebellum
Three extensions of the dura mater separate parts of the brain.
(1) The falx cerebri separates the two hemispheres (sides) of the cerebrum.
(2) The falx cerebelli separates the two hemispheres of the cerebellum.
(3) The tentorium cerebelli- separates the cerebrum from the cerebellum.
The central constricted area is the vermis (worm), and the lateral “wings” or lobes are the cerebellar hemispheres

29. The flocculonodular lobe on the inferior surface contributes to equilibrium and balance.
Three paired cerebellar peduncles attach the cerebellum to the brain stem
The inferior cerebellar peduncles carry sensory information from the vestibular apparatus of the inner ear and from proprioceptors throughout the body into the cerebellum.
The middle cerebellar peduncles voluntary movements
The superior cerebellar peduncles contain axons that extend from the cerebellum to the red nuclei of the midbrain and to several nuclei of the thalamus.

30. Damage to the cerebellum can result in a loss of ability to coordinate muscular movements, a condition called ataxia
People who consume too much alcohol show signs of ataxia because alcohol inhibits activity of the cerebellum

31. THE DIENCEPHALON
The diencephalon forms a central core of brain tissue just superior to the midbrain.
It is almost completely surrounded by the cerebral hemispheres The diencephalon extends from the brain stem to the cerebrum and surrounds the third ventricle; it includes
Thalamus
Hypothalamus
Epithalamus.
Projecting from the hypothalamus is the hypophysis, or pituitary gland

32. The thalamus which measures about 3 cm (1. 2 in
The thalamus which measures about 3 cm (1.2 in.) in length, makes up 80 percent of the diencephalon.
The thalamus is the major relay station for sensory impulses (except smell) that reach the primary sensory areas of the cerebral cortex from the spinal cord, brain stem, and midbrain.
The thalamus contributes to motor functions by transmitting information from the cerebellum and basal nuclei to the primary motor area of the cerebral cortex
HYPOTHALAMUS
The hypothalamus is a small part of the diencephalon located inferior to the thalamus this tiny area of the brain is much more important than its size suggests.

33. 1. Control of the ANS contraction of smooth and cardiac muscle and the secretions of many glands
Through the ANS, the hypothalamus is a major regulator of visceral activities, including heart rate, movement of food through the gastrointestinal tract, and contraction of the urinary bladder.
2. Production of hormones. First, hypothalamic hormones are released into capillary networks in the median eminence.
The bloodstream carries these hormones directly to the anterior lobe of the pituitary, where they stimulate or inhibit secretion of anterior pituitary hormones. Second, axons extend from the paraventricular and supraoptic nuclei through the infundibulum into the posterior lobe of the pituitary. The cell bodies of these neurons make one of two hormones (oxytocin or antidiuretic hormone). Their axons transport the hormones to the posterior pituitary, where they are released.

34. 4. Regulation of eating and drinking
4. Regulation of eating and drinking. The hypothalamus regulates food intake through the arcuate and paraventricular nuclei.It also contains a thirst center. When certain cells in the
hypothalamus are stimulated by rising osmotic pressure of the extracellular fluid, they cause the sensation of thirst. The intake of water by drinking restores the osmotic pressure to normal,
5. Control of body temperature. If the temperature of blood flowing through the hypothalamus is above normal, the hypothalamus directs the autonomic nervous system to stimulate activities that promote heat loss. When blood temperature is below normal, the hypothalamus generates impulses that promote heat production and retention.
6. Regulation of circadian rhythms and states of consciousness.
The suprachiasmatic nucleus establishes patterns of awakening and sleep that occur on a circadian (daily) rhythmThis nucleus receives input from the eyes(retina) and sends output to other hypothalamic nuclei, the reticular formation, and the pineal gland.
The epithalamus a small region superior and posterior to the thalamus, consists of the pineal gland and habenular nuclei. The pineal gland is about the size of a small pea and protrudes
from the posterior midline of the third ventricle The pineal gland is part of the endocrine system