The Central Nervous System Components • Brain • Spinal Cord � 1
Protection of the Brain • The brain is protected from injury by – The skull – enough said! You already know this. � What else protects your Brain? � 2
Protection of the Brain – The Meninges • Cover and protect the CNS • Enclose and protect the vessels that supply the CNS • Contain the cerebrospinal fluid • Consists of three layers – Dura Mater – Arachnoid Layer – Pia Mater � 3
The Meninges � 4
Protection of the Brain – Cerebrospinal Fluid (CSF) • Provides a liquid cushion for the brain and spinal cord • The brain “floats” in CSF • Formed in choroid plexuses in the brain ventricles � 5
Protection of the Brain – CSF • Circulation of CSF � 6
Protection of the Brain ‐ CSF • Reabsorption of CSF � 7
Protection of the Brain – Blood ‐ Brain Barrier • Prevents most blood ‐ borne toxins from entering the brain – Impermeable capillaries, surrounded by astrocyte projections creating a double layer, throw in some tight junctions and it works pretty effectively! • Not an absolute barrier – Nutrients such as oxygen pass through – Allows alcohol, nicotine, and anesthetics through � 8
Brain Ventricles • Ventricles – General Information – Expansions of the brain’s central cavity – Filled with cerebrospinal fluid – Lined with ependymal cells – Continuous (interconnected) with each other • Though flow of CSF is unidirectional – Continuous with the central canal of the spinal cord � 9
Brain Ventricles • The brain’s ventricles and associated structures: – Lateral ventricles – located in cerebral hemispheres • Horseshoe ‐ shaped from bending of the cerebral hemispheres – Third ventricle – lies in diencephalon • Connected with lateral ventricles by interventricular foramen – Cerebral aqueduct – connects 3rd and 4th ventricles – Fourth ventricle – lies in hindbrain • Connects to the central canal of the spinal cord • Contains median and lateral aperatures � 10
Brain Ventricles � 11
Brain Components & Organization • Brain is divided into four general regions: – Cerebral hemispheres – Diencephalon – Brain stem – Cerebellum – All of which contains gray & white matter � 12
Brain Components & Organization • Organization of neural matter (gray vs. white) – Deeply (internally) located gray matter – Intermediately located white matter – Additional layer of gray matter superficial to white matter • Due to groups of neurons migrating externally • Forms the Cortices – outer layers of gray matter – Formed from neuronal cell bodies – Located in cerebrum and cerebellum (the cerebral cortex & cerebellar cortex respectively) � 13
The Cerebral Hemispheres • General Information & Terminology – Account for 83% of brain mass • Superficial thin (1 ‐ 2 mm) cortex & a deep cortex • Deep white matter with localized centers of gray matter (basal ganglia) – Fissures – deep grooves – separate major regions of the brain, generally have dura mater in the fissure • Transverse fissure – separates cerebrum and cerebellum • Longitudinal fissure – separates cerebral hemispheres � 14
The Cerebral Hemispheres – Sulci – shallow grooves on the surface of the cerebral hemispheres, does not contain dura mater in the sulci • Several deep sulci define the lobes (which are named according to the overlying skeletal structures) – Central sulcus » Separates the frontal and parietal lobes – Parieto ‐ occipital sulcus » Separates the occipital from the parietal lobe – Lateral sulcus » Separates temporal lobe from parietal and frontal lobes � 15
The Cerebral Hemispheres – Gyri – twisted ridges between sulci • Important gyri • Prominent gyri and sulci are similar in all people – Insula – deep region within the lateral sulcus • Has it’s own cortex � 16
The Cerebral Hemispheres • Frontal section through forebrain showing organization of gray and white matter – Cerebral cortex – Cerebral white matter – Deep gray matter of the cerebrum (basal nuceli/ ganglia) � 17
The Cerebral Cortex • Composed of gray matter – Neuronal cell bodies, dendrites, and short axons, axon terminals, synapses • Folds in cortex – triples its size – Unfolded gives a surface about that of a pillowcase • Approximately 40% of brain’s mass • Brodmann areas – 52 structurally distinct areas � 18
Functional and Structural Areas of the Cerebral Cortex � 19 Figure 13.11a
Functional and Structural Areas of the Cerebral Cortex � 20 Figure 13.11b
The Cerebral Cortex Motor Areas – Primary Motor Cortex • Controls motor functions • Located in precentral gyrus (Brodmann area 4) • Pyramidal cells – large neurons of primary motor cortex • Corticospinal tracts descend through brainstem and spinal cord – Axons signal motor neurons to control skilled movements – Contralateral – pyramidal axons cross over to opposite side of the brain � 21
The Cerebral Cortex Motor Areas – Primary Motor Cortex • Motor homunculus – body map of the motor cortex – Specific pyramidal cells control specific areas of the body – Face and hand muscles – controlled by many pyramidal cells • Somatotopy – body is represented spatially in many parts of the CNS � 22
The Cerebral Cortex Sensory Areas Primary Somatosensory Cortex • Located at/on/in the postcentral gyrus – Corresponds to Brodmann areas 1 ‐ 3 • Involved with conscious awareness of general somatic senses • Spatial discrimination – precisely locates a stimulus � 23
Cerebral Cortex Sensory Areas – Primary Somatosensory Cortex • Projection is contralateral – In that the cerebral hemispheres receive sensory input from the opposite side of the body • Sensory homunculus – a body map of the sensory cortex � 24
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Cerebral White Matter � 26 Figure 13.13a
Deep Gray Matter of the Cerebrum • Consists of: – Basal forebrain nuclei (Meynert’s nucleus) – Basal nuclei (ganglia) • Caudate nucleus • Lentiform nucleus – Putamen – Globus pallidus • Claustrum – Amygdala • located in cerebrum but is considered part of the of the limbic system � 27
The Diencephalon • Forms the center core of the forebrain • Surrounded by the cerebral hemispheres • Composed of three paired structures: – Thalamus, hypothalamus, and epithalamus • Border the third ventricle • Primarily composed of gray matter � 28
The Diencephalon � 29
The Diencephalon – The Thalamus • Makes up 80% of the diencephalon • Contains approximately a dozen major nuclei • Send axons to regions of the cerebral cortex • Nuclei act as relay stations for incoming sensory messages • Afferent impulses converge on the thalamus – Synapse in at least one of its nuclei • Is the “gateway” to the cerebral cortex • Nuclei organize and amplify or tone down signals � 30
The Thalamus � 31
The Diencephalon – The Hypothalamus • Lies between the optic chiasm and the mammillary bodies • Pituitary gland projects inferiorly • Contains approximately a dozen nuclei • Main visceral (autonomic) control center of the body � 32
The Diencephalon – The Epithalamus • Forms part of the “roof” of the third ventricle • Includes the pineal gland (pineal body) – Secretes the hormone melatonin – Under influence of the hypothalamus Epithalamus highlighted in red � 33
The Brain Stem and Diencephalon � 34 Figure 13.20a, b
The Brain Stem • Includes the – Midbrain – Pons – medulla oblongata • Several general functions – Produces automatic behaviors necessary for survival – Passageway for all fiber tracts running between the cerebrum and spinal cord – Heavily involved with the innervation of the face and head • 10 of the 12 pairs of cranial nerves attach to it � 35
The Brain Stem – The Midbrain • Lies between the diencephalon and the pons • Central cavity – the cerebral aqueduct with gray matter surrounding (periaqueductal gray matter) • Cerebral peduncles located on the ventral surface of the brain – Contain pyramidal (corticospinal) tracts • Superior cerebellar peduncles – Connect midbrain to the cerebellum • Corpora quadrigema –large nuclei – Superior & Inferior colliculi • visual and auditory reflex centers � 36
The Brain Stem – The Pons • Located between the midbrain and medulla oblongata • Contains the nuclei of cranial nerves V, VI, and VII • Contains the pneumotaxic and apneustic centers of respiration � 37
The Brain Stem – The Medulla Oblongata • Most caudal level of the brain stem – Continuous with the spinal cord – Choroid plexus lies in the roof of the fourth ventricle – Pyramids of the medulla – lie on its ventral surface • Decussation of the pyramids – crossing over of motor tracts – Cranial nerves VIII–XII attach to the medulla � 38
The Brain Stem – The Medulla Oblongata • The core of the medulla contains: – Additional nuclei of the reticular formation • Nuclei influence autonomic functions – Cardiac center – Vasomotor center – The medullary respiratory center – Centers for hiccupping, sneezing, swallowing, and coughing � 39
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