CNS-Brain-Cerebrum-Fall 2024presentation

## The Cerebrum: Orchestrating Consciousness and Cognition

The cerebrum, the most expansive and intricate structure within the human brain, stands as the pinnacle of neural evolution. It’s the command center for higher-level cognitive functions, the very essence of what makes us human. From the simplest sensory perception to the most complex abstract thought, the cerebrum orchestrates the symphony of our mental lives. This detailed exploration delves into the cerebrum's anatomy, physiology, development, and clinical significance, illuminating its pivotal role in the central nervous system (CNS).

**I. Anatomical Architecture: A Landscape of Complexity**

The cerebrum is anatomically divided into two cerebral hemispheres, the left and the right, separated by the deep longitudinal fissure. These hemispheres, while exhibiting a degree of symmetry, are functionally specialized, a phenomenon known as lateralization. The hemispheres are interconnected by the corpus callosum, a massive bundle of nerve fibers that facilitates interhemispheric communication and coordination.

Each hemisphere is further subdivided into four distinct lobes, each with specialized functions:

* **Frontal Lobe:** Located at the anterior aspect of the cerebrum, the frontal lobe is the executive center, responsible for higher-order cognitive functions such as planning, decision-making, problem-solving, working memory, and voluntary motor control. It also plays a crucial role in personality, social behavior, and emotional regulation. The prefrontal cortex, the most anterior part of the frontal lobe, is particularly important for executive functions.
* **Parietal Lobe:** Situated posterior to the frontal lobe, the parietal lobe is primarily involved in processing sensory information related to touch, temperature, pain, and pressure. It also contributes to spatial awareness, navigation, and mathematical reasoning. The somatosensory cortex, located in the parietal lobe, receives and processes tactile information from the body.
* **Temporal Lobe:** Located on the lateral sides of the cerebrum, the temporal lobe is responsible for auditory processing, memory formation (particularly long-term memory), and the recognition of objects and faces. It also plays a significant role in language comprehension, with Wernicke's area, a key language center, located in the temporal lobe.
* **Occipital Lobe:** Located at the posterior aspect of the cerebrum, the occipital lobe is the primary visual processing center, responsible for interpreting visual information received from the eyes. The visual cortex, located in the occipital lobe, processes visual stimuli and allows us to perceive the world around us.

**II. Microscopic Structure: Gray and White Matter**

The cerebrum is composed of two primary types of tissue:

* **Gray Matter:** The outer layer of the cerebrum, known as the cerebral cortex, is composed of gray matter. It consists primarily of neuronal cell bodies,dendrites and unmyelinated

1. Central Nervous System BRAIN

2. NERVOUS SYSTEM

3. Central nervous system which comprises of brain and spinal cord is responsible for integrating, coordinating the sensory information and ordering appropriate motor actions. It is the seat of learning, memory, intelligence and emotions. Peripheral nervous system includes 12 pairs of cranial nerves and 31 pairs of spinal nerves. These provide afferent impulses to CNS and carries efferent impulses to muscles, glands and blood vessels. Afferent component provides sensory information to CNS. Efferent component carries motor information to muscles, glands, blood vessels and heart via somatic nervous system for the control of skeletal muscles and autonomic nervous system for the control of heart, smooth muscle of the organs, glands and blood vessels.

4. BRAIN The human brain is the central organ of the human nervous system, and with the spinal cord makes up the central nervous system. It controls most of the activities of the body, processing, integrating, and coordinating the information it receives from the sense organs, and making decisions as to the instructions sent to the rest of the body. Weight of the brain is 1500 grams i.e. about 2% of the total body weight. It is 167 mm long, 93 mm high and 140 mm wide (approximately).

5. Brain development forebrain, midbrain and hindbrain

6. Anatomical classification Cerebral hemispheres Diencephalon Thalamus Hypothalamus Brain stem Midbrain Pons Medulla Cerebellum Spinal cord

7. PARTS OF THE BRAIN

8. Brain protection 1 . Meninges 2. Cerebrospinal fluid 3. Blood brain barrier

9. Meninges Dura mater : 2 layers of fibrous connective tissue, fused except for dural sinuses Periosteal layer attached to bone Meningeal layer - proper brain covering Arachnoid mater Pia mater Note superior sagittal sinus

10. Dura mater - dural partitions Subdivide cranial cavity & limit movement of brain Falx cerebri In longitudinal fissure; attaches to crista galli of ethmoid bone Falx cerebelli Runs vertically along vermis of cerebellum Tentorium cerebelli Sheet in transverse fissure between cerebrum & cerebellum

11. Arachnoid mater Between dura and arachnoid : subdural space Dura and arachnoid cover brain loosely Deep to arachnoid is subarachnoid space Filled with CSF Lots of vessels run through (susceptible to tearing) Superiorly, forms arachnoid villi : CSF valves Allow draining into dural blood sinuses Pia mater Delicate, clings to brain following convolutions

12. Cerebrospinal Fluid CSF Made in choroid plexuses (roofs of ventricles) Filtration of plasma from capillaries through ependymal cells (electrolytes, glucose) 500 ml/d; total volume 100-160 ml (1/2 c) Cushions and nourishes brain Assayed in diagnosing meningitis, bleeds, MS Hydrocephalus: excessive accumulation

13. Subarachnoid space Aqua blue in this pic Under thick coverings of brain Filled with CSF Red: choroid plexus ________

14. Ventricles Central cavities expanded Filled with CSF (cerebrospinal fluid) Lined by ependymal cells (these cells lining the choroid plexus make the CSF: see later slides) Continuous with each other and central canal of spinal cord

15. Lateral ventricles Paired, horseshoe shape In cerebral hemispheres Anterior are close, separated only by thin Septum pellucidum

16. Third ventricle In diencephalon Connections Interventricular foramen Cerebral aqueduct

17. Fourth ventricle In the brainstem Dorsal to pons and top of medulla Holes connect it with subarachnoid space

18. CSF circulation: through ventricles, median and lateral apertures, subarachnoid space, arachnoid villi, and into the blood of the superior sagittal sinus CSF: - Made in choroid plexus - Drained through arachnoid villus

19. Blood-Brain Barrier Tight junctions between endothelial cells of brain capillaries, instead of the usual permeability Highly selective transport mechanisms Allows nutrients, O2, CO2 Not a barrier against uncharged and lipid soluble molecules; allows alcohol, nicotine, and some drugs including anesthetics

20. Lobes of the Cerebrum Slide 7.29a Fissures (deep grooves) divide the cerebrum into lobes Surface lobes of the cerebrum Frontal lobe Parietal lobe Occipital lobe Temporal lobe

21. Lobes of the Cerebrum Slide 7.29b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.15a

22. CEREBRUM Cerebrum is made up of two cerebral hemispheres which are incompletely separated from each other by longitudinal fissure. The two hemispheres are connected to each other across the median plane by the corpus callosum. Each hemisphere contains a cavity called the lateral ventricle.

23. LOBES OF CEREBRAL HEMISPHERES

24. LOBES OF CEREBRAL HEMISPHERES

25. SULCI AND GYRI Cerebral cortex is folded into gyri which are separated from each other by sulci. This pattern increases the surface area of the cerebral cortex and allows more neurons to be packed into the cortex which increases the brain's ability to process information.  The total area of the cortex is estimated to be more than 2000 cm 2 , and approximately two-thirds of this area is hidden from the surface within sulci.

26. Lobes of the Cerebrum Slide 7.29b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.15a

27. Cerebral cortex Executive functioning capability Gray matter: of neuron cell bodies, dendrites, short unmyelinated axons 100 billion neurons with average of 10,000 contacts each No fiber tracts (would be white) 2-4 mm thick (about 1/8 inch) Brodmann areas (historical: 52 structurally different areas given #s) Neuroimaging: functional organization (example later)

28. Specialized Areas of the Cerebrum Slide 7.30 Somatic sensory area – receives impulses from the body’s sensory receptors Primary motor area – sends impulses to skeletal muscles Broca’s area – involved in our ability to speak

29. Specialized Area of the Cerebrum Slide 7.32a Cerebral areas involved in special senses Gustatory area (taste) Visual area Auditory area Olfactory area

30. Specialized Area of the Cerebrum Slide 7.32b Interpretation areas of the cerebrum Speech/language region Language comprehension region General interpretation area

31. Specialized Area of the Cerebrum Slide 7.32c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.13c

32. PREFRONTAL CORTEX Large area lying anterior to precentral area. Includes the superior, middle and inferior frontal gyri, medial frontal gyrus, orbital gyri and anterior half of the cingulate gyrus. Includes brodmann’s area 9, 10, 11 and 12. Connected to other areas of cerebral cortex, corpus striatum, thalamus and hypothalamus. Also, connected to the cerebellum through the pontine nucleus. Controls emotions, concentration, attention, initiative and judgement.

33. FUNCTIONAL AREAS OF CEREBRAL CORTEX MOTOR AREA The primary motor area has been identified on the basis of elicitation of motor responses at a low threshold of electric stimulation which give rise to contraction of skeletal musculature. These areas give origin to corticospinal and corticonuclear fibres. SENSORY AREA In these areas, electrical activity can be recorded if appropriate sensory stimulus is applied to a particular part of the body. The ventral posterior nucleus is main source of afferent fibres for the first sensory area. This thalamic nucleus is the site of termination of all the fibres of the medial lemniscus and of most of the spinothalamic and trigeminothalamic tracts.

34. ASSOCIATION AREA In these regions, the direct sensory or motor responses are not elicited. These areas integrate and analyse the responses from various sources. Many such areas are known to have motor or sensory functions. The motor and sensory functions also overlap in the same region of cortex. If the motor function is predominant, it is known as motor-sensory and where sensory function is predominant, it is called sensori -motor.

35. MOTOR AREA PRIMARY MOTOR AREA Located in the precentral gyrus , including the anterior wall of central sulcus, and in the anterior part of paracentral lobule on the medial surface of cerebral hemispheres. Corresponds to area 4 of Brodmann . Electrical stimulation of primary motor area elicits contraction of muscles that are mainly on the opposite side of body. Although cortical control of musculature is mainly contralateral, there is significant ipsilateral control of most of the muscles of the head and axial muscles of the body.

36. Another significant feature in this area is that the size of the cortical area for a particular part of the body is determined by the functional importance of the part and its need for sensitivity and intricacy of the movements of that region. The area for the face, especially the larynx and lips, is therefore disproportionately large and a large area is assigned to the hand particularly the thumb and index finger. Movements of the joints are represented rather than the individual muscles.

37. SENSORY AREAS FIRST SOMESTHETIC AREA SECOND SOMESTHETIC AREA SOMESTHETIC ASSOCIATION CORTEX RECEPTIVE SPEECH AREA OF WERNICKE

38. Sensory and Motor Areas of the Cerebral Cortex Slide 7.31