Central Nervous System (CNS) CNS composed of the brain and spinal cord Cephalization

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1 Central Nervous System (CNS) CNS composed of the brain and spinal cord Cephalization Elaboration of the anterior portion of the CNS Increase in number of neurons in the head Highest level is reached in the human brain

2 The Brain Composed of wrinkled, pinkish gray tissue Surface anatomy includes cerebral hemispheres, cerebellum, and brain stem

3 Embryonic Development During the first 26 days of development: Ectoderm thickens forming the neural plate The neural plate invaginates, forming the neural folds Superior edges fuse forming neural tube which detaches from the ectoderm and sinks deeper Neural tube differentiates into the CNS Brain forms from neural tube (rostrally) as well as spinal cord (posterior/dorsally) Neural crest cells give rise to some neurons destined to reside in ganglia

4 Embryonic Development Figure 12.1

5 Brain Development: Primary Brain Vesicles The anterior end of the neural tube expands and constricts to form the three primary brain vesicles Prosencephalon the forebrain Mesencephalon the midbrain Rhombencephalon hindbrain Remainder of neural tube becomes the spinal cord

6 Neural Tube and Primary Brain Vesicles Figure 12.2a, b

7 Secondary Brain Vesicles In week 5 of embryonic development, secondary brain vesicles form Telencephalon and diencephalon arise from the forebrain Mesencephalon remains undivided Metencephalon and myelencephalon arise from the hindbrain

8 Secondary Brain Vesicles Figure 12.2c

9 Adult Brain Structures Fates of the secondary brain vesicles: Telencephalon cerebrum: cortex, white matter, and basal nuclei Diencephalon thalamus, hypothalamus, and epithalamus Mesencephalon brain stem: midbrain Metencephalon brain stem: pons Myelencephalon brain stem: medulla oblongata

10 Adult Neural Canal Regions Figure 12.2c, d

11 Adult Neural Canal Regions Adult structures derived from the neural canal Telencephalon lateral ventricles Diencephalon third ventricle Mesencephalon cerebral aqueduct Metencephalon and myelencephalon fourth ventricle

12 Adult Neural Canal Regions Figure 12.2c, e

13 Space Restriction and Brain Development Figure 12.3

14 Space Restriction and Brain Development Flexures: midbrain and cervical, which bend the forebrain toward the brain stem Cerebral hemispheres: grow posteriorly and laterally and almost envelop the diencephalon and midbrain Continued growth causes the surface to crease and fold producing convolutions thus increasing the surface area

15 Basic Pattern of the Central Nervous System Spinal Cord Central cavity surrounded by a gray matter core External to which is white matter composed of myelinated fiber tracts Brain Similar to spinal cord but with additional areas of gray matter Cerebellum has gray matter in nuclei Cerebrum has nuclei and additional gray matter in the cortex

16 Basic Pattern of the Central Nervous System Figure 12.4

17 Ventricles of the Brain Continuous with one another and with the central canal of the spinal cord Filled with cerebrospinal fluid and lined with ependymal cells Paired lateral ventricles C-shaped reflects the pattern of cerebral growth Septum pallucidum separates lateral ventricles via the interventricular foreamen Third ventricle connected to the fourth ventricle via the cerebral aquaduct Fourth ventricle is continuous with the central canal of the spinal cord Fourth ventricle is also continuous with the fluid filled space surrounding the brain (subarachnoid) via lateral and medial apertures.

18 Ventricles of the Brain Figure 12.5

19 Cerebral Hemispheres Form the superior part of the brain and make up 83% of its mass Contain ridges (gyri) and shallow grooves (sulci) Contain deep sulci called fissures Are separated by the longitudinal fissure Transverse fissure separates the cerebral hemispheres from the cerebellum Prominent gyri and sulci are the same in all human brains and are anatomical landmarks Have three basic regions: cortex, white matter, and basal nuclei

20 Major Lobes, Gyri, and Sulci of the Cerebral Hemisphere Deep sulci divide the hemispheres into five lobes: Frontal, parietal, temporal, occipital, and insula These are named for the cranial bones under which they lie Central sulcus separates the frontal and parietal lobes. Bordered by the precentral gyrus (anteriorly) and the postcentral gyrus (posteriorly)

21 Brain Lobes Figure 12.6a b

22 Major Lobes, Gyri, and Sulci of the Cerebral Hemisphere Parieto-occipital sulcus separates the parietal and occipital lobes Lateral sulcus outlines the temporal lobe and separates the parietal and temporal lobes Insula: buried within the lateral sulcus and forms part of the floor The precentral and postcentral gyri border the central sulcus

23 Cerebral Cortex: Our conscious mind The cortex superficial gray matter; accounts for 40% of the mass of the brain. Gray matter: neuron cell bodies, dendrites, associated glia, blood vessels It enables sensation, communication, memory, understanding, and voluntary movements Each hemisphere acts contralaterally (controls the opposite side of the body) Cerebral cortex has been extensively mapped

24 Functional Areas of the Cerebral Cortex The three types of functional areas are: Motor areas control voluntary movement Sensory areas conscious awareness of sensation Association areas integrate diverse information All neurons here are interneurons not sensory & motor neurons Each hemisphere is chiefly concerned with the sensory and motor functions of the opposite side of the body Each side has specialization and is not necessarily bilateral

25 Functional Areas of the Cerebral Cortex Figure 12.8a

26 Functional Areas of the Cerebral Cortex Figure 12.8b

27 Cerebral Cortex: Motor Areas (Voluntary Movement) Lie in the posterior part of the frontal lobes: Primary (somatic) motor cortex Premotor cortex Broca s area Frontal eye field

28 Primary Motor Cortex (Brodmman s Area #4) Located in the precentral gyrus of the frontal lobe of each hemisphere Pyramidal cells whose allows conscious control of precise, skilled, voluntary movements. Their long axons project into the spinal cord forming the massive pyramidal tracts (corticospinal tracts) The entire body is represented spatially in the primary motor cortex of each hemisphere (this type of mapping is called somatotopy)

29 Premotor Cortex (Brodmman s Area #6) Located anterior to the precentral gyrus in the frontal lobe Controls learned, repetitious, or patterned motor skills Coordinates movement by sending impulses to the primary motor cortex Involved in the planning of movements Controls voluntary movements that depend on sensory feedback

30 Broca s Area: Brodmann Area #44 & 45 Broca s area Located anterior to the inferior region of the premotor area Present in one hemisphere (usually the left) A motor speech area that directs muscles of the tongue Is active as one planning to speak

31 Frontal Eye Field: Brodmann s Area #8 Frontal eye field Located anterior to the premotor cortex and superior to Broca s area Controls voluntary eye movement

32 Sensory Areas Primary somatosensory cortex Somatosensory association cortex Visual and auditory areas Olfactory, gustatory, and vestibular cortices

33 Sensory Areas Figure 12.8a

34 Primary Somatosensory Cortex: Brodmann s Area #1-3 Located in the postcentral gyrus of parietal lobe Receives info. From sensory receptors in the skin and proprioceptors in the skeletal muscles, joints, tendons Neurons identify the body region being stimulated (spatial discrimination) Body is represented spatially: contralaterally and upside down The amount of sensory cortex devoted to a given body region is related to the degree of sensitivity in that region, and not the body size (e.g. face, lips, fingertips)

35 Somatosensory Association Cortex: Brodmann s Areas 5 &7 Located posterior to the primary somatosensory cortex Integrates sensory information relayed from the primary somatosensory cortex to produce an understanding of the object being felt Determines size, texture, and relationship of parts

36 Visual Areas: Brodmann s Areas Primary visual (striate) cortex Seen on the extreme posterior tip of the occipital lobe Most of it is buried in the calcarine sulcus Receives visual information from the retinas Visual association area Surrounds the primary visual cortex Interprets visual stimuli (e.g., color, form, and movement)

37 Auditory Areas: Brodmann s Areas Primary auditory cortex Located at the superior margin of the temporal lobe Receives information related to pitch, rhythm, and loudness Auditory association area Located posterior to the primary auditory cortex Stores memories of sounds and permits perception of sounds Wernicke s area

38 Olfactory Cortex: Brodmann s Areas: 28 & 34 Located in the medial aspect of the temporal lobe dominated by the uncus Afferent fibers from smell receptors in the superior nasal cavities send impulses along olfactory tracts and relay them to the olfactory cortex The O.C. is part of the primitive rhinencephalon

39 and the other corteces Gustatory cortex (located in the insula) Deep to the temporal lobe Taste Visceral sensory area (also in the insula) Located just posterior to the gustatory cortex Perception of visceral sensations Vestibular (equilibrium) cortex Located in the posterior part of the insula Balance

40 Multimodal Association Areas Information flows from sensory neurons to Primary sensory cortex to Sensory association cortex to Multimodal association cortex Gives meaning to the information Stores it in memory Decision making area Relay decisions to premotor cortex and then the motor cortex