SG 15

1. The four main regions of the brain are the Cerebrum, Diencephalon, Brainstem, and Cerebellum.

2. Brain tissue can be classified as
   a. Gray matter which is composed of cell bodies (and unmyelinated axons) and dendrites
   b. White matter which is composed of myelinated axons. The color is due to the presence of myelin

3. Gray matter
   a. The outer region of gray matter is called the Cerebral Cortex
   b. The inner clusters of gray matters are called the Cerebral nuclei

4. White matter
   a. The tracts that form the white matter can be classified as
   i. Commissural tracts which connect the two cerebral hemispheres
   ii. Association tracts which connect regions within the same hemisphere
   iii. Projection tracts connect the brain to spinal cord

5. Gyri and sulcus
   a. The brain surface has folds called Gyri that are separated by Sulci

Cerebrum

6. The cerebrum has two cerebral hemispheres which are separated by the Longitudinal fissure

7. Both hemispheres are connected by the Commissural fibers

8. Lobes
   a. Each hemisphere has five lobes which are frontal, parietal, occipital, temporal, and insula.
   b. Frontal Lobe
   i. The frontal lobe is responsible for voluntary motor functions, decision making, planning, personality, and verbal communication.
   ii. The primary motor cortex is located in the precentral gyrus

9. This region is responsible for controlling the opposite body side.

10. The representation of the body on the primary motor cortex is called the Motor homunculus.
    a. In this representation, the size of the brain region that is dedicated to a body part is proportionate to number of neurons responsible for that body part.
    b. The hand has a bigger brain region than the trunk (T)
    iii. The frontal lobe is separated from the parietal lobe by the Central sulcus
    c. Parietal lobe
    i. The primary somatosensory cortex is located in the postcentral gyrus

11. This region is responsible for processing general sensory information (touch, pain, temperature).

12. The map of the body on the primary somatosensory cortex is called the Sensory homunculus.
    a. The size of the brain region is proportionate to number of neurons responsible for that body part.
    b. The thigh has a bigger brain region than the face (F)
    d. Temporal lobe
    i. The temporal lobe is responsible for hearing and olfaction.
    e. Occipital lobe
    i. The occipital lobe is responsible for processing visual information and storing visual memory.
    f. Insula
    i. The insula lobe is responsible for memory and taste interpretation.

13. Functional brain regions
    a. Broca's area is responsible for speaking and is located in the frontal lobe.
    b. Wernicke's area is responsible for understanding words and is located in the temporal and parietal lobes.

The Diencephalon

10. The diencephalon is made up of the epithalamus, thalamus, and hypothalamus.

11. The epithalamus contains the pineal gland which produces a hormone called melatonin.
    a. This hormone helps to set circadian rhythm.

12. The thalamus sorts sensory and motor information.
    a. The medial geniculate is responsible for sorting auditory information.
    b. The lateral geniculate is responsible for sorting visual information.

13. The hypothalamus controls the pituitary gland.
    a. Hypothalamic nuclei
    i. Suprachiasmatic nucleus controls the circadian rhythm.
    ii. Preoptic area (or anterior hypothalamus) controls the body temperature.
    iii. Lateral hypothalamic area stimulates hunger.
    iv. Ventromedial nucleus suppresses your appetite.

The Brainstem

14. The brainstem is made up of the midbrain, pons, and medulla oblongata.

15. Mesencephalon
    a. The mesencephalon is also called the midbrain.
    b. Cerebral peduncles are bundles of motor neurons on their way to the spinal cord.
    c. Periaqueductal gray is involved in the processing of pain.
    d. Substantia nigra makes a neurochemical called dopamine.
    i. Dopamine is a part of circuits that control movement, reward, and addiction.
    ii. Damage to this region leads to Parkinson's disease.
    e. The corpora quadrigemina is composed of the superior colliculi and inferior colliculi.
    i. Superior colliculi is involved in visual reflexes.
    ii. Inferior colliculi is involved in auditory reflexes.

16. Pons
    a. The pons works with the medulla oblongata to control respiration.

17. Medulla Oblongata
    a. The medulla oblongata is connected to the spinal cord inferiorly.
    b. Pyramids (corticospinal tracts) are bundles of motor neurons on their way to the spinal cord.
    i. Decussation of the pyramids is responsible for contralateral motor control.

18. Because of the decussation, the muscles on the right side of the body are controlled by the left side of the brain.
    c. Cardiac center controls the heart rate.
    d. Vasomotor center controls the diameter of the blood vessels.
    e. Respiratory center controls breathing.
    f. Other reflexes controlled by the medulla oblongata include coughing, sneezing, hiccuping, swallowing and vomiting.

19. Reticular Formation
    a. The reticular formation runs through the brainstem.
    b. The reticular formation is critical for filtering sensory input and for the control of sleep.

Cerebellum

19. The cerebellum contains two hemispheres which are connected by the vermis.

20. Each cerebellar hemisphere contains three lobes which are anterior, posterior, and flocculonodular.

21. The cerebellum is connected
    a. to the pons by the middle cerebellar peduncle.
    b. to the mesencephalon by the superior cerebellar peduncle.
    c. to the medulla oblongata by the inferior cerebellar peduncle.

22. The cerebellum is involved in our sense of balance and in equilibrium (also fine-tune movements).

Meninges

23. Meninges are membranes that cover the brain and spinal cord.

24. The deepest meningeal layer is the pia mater.

25. The middle meningeal layer is the arachnoid mater.

26. The most superficial meningeal layer is the dura mater.

27. The dura mater
    a. The dura mater has two layers:
    i. The periosteal layer is next to the skull and the meningeal layer is next to the arachnoid mater.
    b. Dural venous sinuses are formed by the separation of the periosteal and meningeal layers.
    i. Dural venous sinuses transport venous blood and CSF.
    c. Dural septa are formed by the meningeal layer of the dura mater.
    i. The falx cerebri runs in the longitudinal fissure.
    ii. The falx cerebelli runs on top of the vermis.
    iii. The tentorium cerebelli runs in the transverse fissure.
    iv. The diaphragma sellae covers the sella turcica.

28. Arachnoid mater
    a. Subarachnoid space is located between the arachnoid mater and the pia mater.
    i. CSF flows inside this space.

Ventricles and CSF

29. The brain has four ventricles which are
    a. 2 lateral ventricles that are located in the cerebrum.
    b. 1 third ventricle that is located in the diencephalon.
    c. 1 fourth ventricle that is located in the brainstem.

30. The fourth ventricle is continuous with the central canal of the spinal cord.

31. The ventricles contain choroid plexus which produces cerebrospinal fluid.

32. Path of CSF
    a. CSF from lateral ventricles flows through the interventricular foramen (of Monro) to enter the third ventricle.
    b. From the third ventricle, CSF flows through the cerebral aqueduct (of Sylvius) to enter the fourth ventricle.
    c. From the fourth ventricle, CSF flows through median and lateral apertures (foramina of Magendie and Luschka) to enter the subarachnoid space.
    i. Some CSF from the fourth ventricle also enters the central canal of the spinal cord.
    d. CSF leaves the subarachnoid space by flowing through arachnoid villi/granulations to enter the dural venous sinuses.

33. Three functions of CSF are buoyancy, protection, and circulation.

Development of the Nervous System

34. Brain development begins at approximately week 3 of pregnancy from an embryonic structure called the neural tube.

35. The three primary brain vesicles are prosencephalon, mesencephalon, and the rhombencephalon.

36. The secondary vesicles are
    a. Telencephalon and Diencephalon which come from the prosencephalon.
    b. Metencephalon and Myelencephalon which come from the rhombencephalon.
    c. Mesencephalon remains the same.

37. Final Brain Structure
    a. The cerebrum develops from the telencephalon.
    b. Thalamus, hypothalamus, epithalamus and retina develop from the diencephalon.
    c. Midbrain develops from mesencephalon.
    d. Pons and cerebellum develop from metencephalon.
    e. Medulla oblongata develops from myelencephalon.