Central Nervous System Brain and Spinal Cord
Learn and Understand • Brain function is both localized and lateralized but information sharing is key to success • Spinal cord also exhibits localization • Nature has physically and chemically protected the brain and spinal cord • Cerebral cortex is the seat of consciousness, most other areas coordinate with the cortex subconsciously • Each sense is mapped to a particular location of the cortex • Superior and anterior portions of the cerebrum represent more “advanced” areas; best developed in the primates and humans, in particular
Comparative Vertebrate Brains Cephalization • Similarities in location, form, and function • Areas associated with rationality, use of hands
Regions and Organization Adult brain regions 1. Cerebral hemispheres – five lobes, basal nuclei, nerve tracts 2. Diencephalon – thalamus, hypothalamus, epithalamus 3. Brain stem – midbrain, pons, and medulla 4. Cerebellum – hemispheres and subdivisions Ventricles span the first three regions
Ventricles of the Brain Lateral ventricle Anterior Posterior horn Septum horn Interventricular pellucidum foramen Inferior Third horn ventricle Inferior horn Cerebral aqueduct Lateral Median aperture aperture Fourth ventricle Lateral aperture Central canal Anterior view Left lateral view • Filled with cerebrospinal fluid (CSF) produced by ependymal cell lining • CSF slowly flows from space to space before being reabsorbed into blood
Protection of the Brain 1. Bone (skull) 2. Protective Membranes (meninges) 3. Watery cushion (cerebrospinal fluid) 4. Selective membrane (Blood brain barrier)
Figure 12.22 Meninges: dura mater, arachnoid mater, and pia mater. Skin of scalp Periosteum Bone of skull Dura mater • Periosteal layer • Meningeal layer Superior sagittal Arachnoid mater sinus Pia mater Subdural Arachnoid villus space Blood vessel Subarachnoid space Falx cerebri (in longitudinal fissure only)
2. Meninges • Cover and protect CNS • Protect blood vessels and enclose venous sinuses • Contain cerebrospinal fluid (CSF) • Form partitions in skull • Three layers – Dura mater • Strongest meninx – Arachnoid mater - Middle layer with weblike extensions • Subarachnoid space contains CSF and largest blood vessels of brain • Arachnoid villi protrude into superior sagittal sinus – Pia mater • Delicate, vascularized connective tissue that clings tightly to brain
3. Cerebrospinal Fluid (CSF) • Composition – Watery solution formed from blood plasma • Less protein and different ion concentrations than plasma – Constant volume maintained through regular production and loss • Normal volume ~ 150 ml; replaced every 8 hours • Functions – Gives buoyancy to CNS structures • Reduces weight by 97% – Protects CNS from blows and other trauma – Nourishes brain and carries chemical signals
Figure 12.24a Formation, location, and circulation of CSF 4 Superior Arachnoid villus sagittal sinus Choroid plexus Subarachnoid space Arachnoid mater Meningeal dura mater Periosteal dura mater 1 Right lateral ventricle Interventricular (deep to cut) foramen Third ventricle 3 Choroid plexus of fourth ventricle Cerebral aqueduct Lateral aperture 1 The choroid plexus of each Fourth ventricle Ventricle produces CSF. 2 Median aperture 2 CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. 3 CSF flows through the Central canal subarachnoid space. of spinal cord 4 CSF is absorbed into the dural (a) CSF circulation venous sinuses via the arachnoid villi. Lateral ventricles -> third ventricle via interventricular foramen -> Third ventricle -> fourth ventricle via cerebral aqueduct-> apertures to subarachnoid
4. Blood Brain Barrier • Helps maintain stable environment for brain • Separates neurons from some bloodborne substances • Selective barrier – nutrients move by facilitated diffusion – Metabolic wastes, proteins, toxins, most drugs, small nonessential amino acids, K + all stopped at barrier – Allows any fat-soluble substances to pass, including alcohol, nicotine, and anesthetics • Composition – Continuous endothelium of capillary walls – Thick basal lamina around capillaries – Feet of astrocytes - Provide signal to endothelium for formation of tight junctions
Cerebral Hemispheres • Surface markings – Ridges ( gyri ), shallow grooves ( sulci ), and deep grooves ( fissures ) – Longitudinal fissure • Separates two hemispheres – Transverse cerebral fissure • Separates cerebrum and cerebellum • Five lobes – divided by sulci – Frontal – Parietal – Temporal – lateral sulcus separates temporal and parietal lobes – Occipital – Insula – deep to temporal lobe
Figure 12.4b Lobes, sulci, and fissures of the cerebral hemispheres. Left cerebral hemisphere Transverse cerebral Brain stem fissure Cerebellum Left lateral view
Figure 12.4c Lobes, sulci, and fissures of the cerebral hemispheres. Central Precentral Postcentral sulcus gyrus gyrus Frontal lobe Parietal lobe Parieto-occipital sulcus (on medial surface of hemisphere) Lateral sulcus Occipital lobe Temporal lobe Transverse cerebral fissure Cerebellum Pons Medulla oblongata Fissure Spinal cord (a deep sulcus) Gyrus Cortex (gray matter) Sulcus White matter Lobes and sulci of the cerebrum
Figure 12.4d Lobes, sulci, and fissures of the cerebral hemispheres. Central Frontal lobe sulcus Gyri of insula Temporal lobe (pulled down) Location of the insula lobe
Figure 12.4a Lobes, sulci, and fissures of the cerebral hemispheres. Anterior Longitudinal Frontal lobe fissure Cerebral veins and arteries Parietal lobe covered by arachnoid mater Left cerebral Right cerebral hemisphere hemisphere Occipital lobe Posterior Superior view
Cerebral Cortex • Thin (2 – 4 mm) superficial layer of gray matter – Billions of neurons and associated neuroglia • 40% mass of brain • Location of conscious mind: – Awareness – Sensory perception – Voluntary motor initiation – Language – Memory storage – Understanding – Motivation and decisionmaking
4 General Considerations of Cerebral Cortex 1. Three types of functional areas – Motor areas — control voluntary movement – Sensory areas — conscious awareness of sensation – Association areas — integrate diverse information 2. Each hemisphere concerned with contralateral side of body 3. Lateralization of cortical function in hemispheres – Sides process info separately while sharing 4. Conscious behavior involves entire cortex in some way – Cortical domains perform specific functions with much input from other areas – Memory and association occur throughout cerebral cortex
Figure 12.6a Functional and structural areas of the cerebral cortex Sensory areas and related Motor areas Central sulcus association areas Primary motor cortex Primary somatosensory Premotor cortex cortex Somatic Somatosensory Frontal sensation association cortex eye field Broca's area Gustatory cortex Taste (outlined by dashes) (in insula) Prefrontal cortex Working memory Wernicke's area for spatial tasks (outlined by dashes) Executive area for task management Primary visual Working memory for cortex object-recall tasks Vision Visual Solving complex, association multitask problems area Auditory association area Hearing Primary auditory cortex Lateral view, left cerebral hemisphere Primary motor Motor association Primary sensory Sensory Multimodal association cortex cortex cortex association cortex cortex
Figure 12.6b Functional and structural areas of the cerebral cortex Cingulate Primary Premotor Central sulcus gyrus motor cortex cortex Corpus Primary somatosensory callosum cortex Frontal eye field Parietal lobe Somatosensory Prefrontal association cortex cortex Parieto-occipital sulcus Occipital Processes emotions lobe related to personal and social interactions Visual association Orbitofrontal area cortex Olfactory bulb Primary visual cortex Olfactory tract Calcarine sulcus Fornix Parahippocampal Uncus Temporal Primary gyrus lobe olfactory cortex Parasagittal view, right cerebral hemisphere Primary motor Motor association Primary sensory Sensory Multimodal association cortex cortex cortex association cortex cortex
Motor Areas of Cerebral Cortex • Plan and control voluntary movement • Located in frontal lobe – Primary (somatic) motor cortex • precentral gyrus – Premotor cortex • anterior to primary MC – Broca's area • usually only in the left hemisphere – Frontal eye field
Primary Motor Cortex • Large pyramidal cells of precentral gyri • Long axons pyramidal (corticospinal) tracts of spinal cord • Allows conscious control of precise, skilled, skeletal muscle movements • Motor homunculi - upside-down caricatures represent contralateral motor innervation of body regions
Figure 12.7 Body maps in the primary motor cortex and somatosensory cortex of the cerebrum . Posterior But cortex and motor unit cannot be precisely mapped Motor Sensory Anterior Motor map in Sen Sensor sory y ma map in in precentral gyrus post stcentral l gyr yrus Trunk Neck Hip Knee Foot Toes Genitals Jaw Primary motor Primary somato- Tongue cortex sensory cortex Intra- Swallowing (precentral gyrus) (postcentral gyrus) abdominal
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