Brain

Dr. Ahmed Alsharef FarahDr. Ahmed Alsharef Farah 1 • The brain is a delicate organ that is surrounded and protected by three membranes called the meninges. • The outermost membrane, the (tough mother), is the strongest. • This double-layered membrane is continuous with the periosteum of the cranium.

Dr. Ahmed Alsharef Farah 2 Coronal cross section of meninges. Dr. Ahmed Alsharef Farah 3 Dr. Ahmed Alsharef Farah 4 • Located between the dura mater and the cranium are the meningeal vessels, which supply blood to the cranium and meninges. • There is also a potential space between the dura and the cranium called the epidural (extra-dural) space. • Located between the two layers of dura mater are the dural sinuses, which provide venous drainage from the brain.

Dr. Ahmed Alsharef Farah 5 • Folds of dura mater help to separate the structures of the brain include: The separates the cerebral hemispheres. the tentorium cerebelli, which spreads out like a tent, forms a partition between the cerebrum and cerebellum. The falx cerebelli separates the two cerebellar hemispheres.

Dr. Ahmed Alsharef Farah 6 Axial CT of falx cerebri and tentoriumDr. Ahmed cerebelli. Alsharef Farah 7 Coronal, T1-weighted MRI of falx cerebri and tentorium cerebelli. Dr. Ahmed Alsharef Farah 8 Sagittal, T1-weighted MRI of tentoriumDr. Ahmed cerebelli. Alsharef Farah 9 • The middle membrane, known as the arachnoid membrane (spiderlike), is a delicate, transparent membrane that is separated from the dura mater by a space called the . • The inner layer, or (delicate, tender mother), is a highly vascular layer that adheres closely to the contours of the brain.

Dr. Ahmed Alsharef Farah 10 Coronal cross section of meninges.

Dr. Ahmed Alsharef Farah 11 • The subarachnoid space separates the pia mater from the . • This space contains that circulates around the brain and and provides further protection to the central nervous system (CNS).

Dr. Ahmed Alsharef Farah 12 Coronal cross section of subarachnoid space.

Dr. Ahmed Alsharef Farah 13 Ventricular system Ventricles: • The ventricular system provides a pathway for the circulation of the cerebral spinal fluid (CSF) throughout the CNS. • A major portion of the ventricular system is composed of four fluid-filled cavities (ventricles) located deep within the brain.

Dr. Ahmed Alsharef Farah 14 Lateral view of ventricular system. Dr. Ahmed Alsharef Farah 15 Anterior view of ventricles.Dr. Ahmed Alsharef Farah 16 Superior view of ventricles in relation to surfaceDr. Ahmed Alsharef of brain. Farah 17 • The two most superior cavities are the right and left lateral ventricles. • These ventricles lie within each cerebral hemisphere and are separated at the midline by a thin membrane known as the septum pellucidum.

Dr. Ahmed Alsharef Farah 18 Axial, T1-weighted MRI of lateral and thirdDr. Ahmed ventricles. Alsharef Farah 19 Axial CT of lateral and third ventricles.Dr. Ahmed Alsharef Farah 20 • The lateral ventricles consist of a central portion called the body and three extensions: the frontal (anterior), occipital (posterior), and temporal (inferior) horns. • The junction of the body and the occipital and temporal horns form a triangular area termed the trigone (atria). • The lateral ventricles communicate inferiorly with the third ventricle via the paired interventricular foramen (foramen of Monro).

Dr. Ahmed Alsharef Farah 21 Lateral view of ventricular system. Dr. Ahmed Alsharef Farah 22 Anterior view of ventricles.Dr. Ahmed Alsharef Farah 23 Axial CT of temporal horns of the lateralDr. ventricles. Ahmed Alsharef Farah 24 Coronal, T2-weighted MRI of temporal horns of theDr. Ahmedlateral Alsharef ventricles. Farah 25 • The third ventricle is located midline just inferior to the lateral ventricles. • The anterior wall of the third ventricle is formed by a thin membrane termed the lamina terminalis, and the lateral walls are formed by the thalamus. • The third ventricle communicates with the fourth ventricle via a long, narrow passageway termed the cerebral aqueduct (aqueduct of Sylvius).

Dr. Ahmed Alsharef Farah 26 Lateral view of ventricular system.Dr. Ahmed Alsharef Farah 27 • The fourth ventricle is a diamond-shaped cavity located anterior to the cerebellum and posterior to the pons. • CSF exits the ventricular system through foramina in the fourth ventricle to communicate with the subarachnoid space within the basal cisterns. • The major exit route is the median aperture (foramen of Magendie), located on the posterior wall of the fourth ventricle, which communicates with the .

Dr. Ahmed Alsharef Farah 28 Axial CT of fourth ventricle. Dr. Ahmed Alsharef Farah 29 Coronal, T1-weighted MRI of lateral and fourthDr. Ahmed ventricles. Alsharef Farah 30 Sagittal view of the median aperture (foramenDr. Ahmed of AlsharefMagendie Farah ). 31 • There are two lateral apertures, termed the foramen of Luschka, which communicate with the cerebellopontine angle cistern. • From the fourth ventricle, CSF continues into the spinal cord via the central canal.

Dr. Ahmed Alsharef Farah 32 Anterior view of ventricles.Dr. Ahmed Alsharef Farah 33 • Located within the ventricular system is a network of blood vessels and nerve cells termed the , which produces CSF. • Excess CSF is reabsorbed in the dural sinuses by way of the arachnoid villi which are berrylike projections of arachnoid that penetrate the dura mater.

Dr. Ahmed Alsharef Farah 34 Sagittal view of choroid plexus.Dr. Ahmed Alsharef Farah 35 Axial CT of lateral ventricles with calcified choroidDr. Ahmed plexus.Alsharef Farah 36 Coronal CT reformat of calcified choroid plexus inDr. lateralAhmed Alsharef ventricles. Farah 37 Coronal cross section of Arachnoid villi. Dr. Ahmed Alsharef Farah 38 Cisterns: • The subarachnoid space is a relatively narrow, fluid-filled space surrounding the brain and spinal cord. • There are locations, primarily around the base of the brain, where the subarachnoid space becomes widened. • These widened areas or pools of CSF called the basal (subarachnoid) cisterns.

Dr. Ahmed Alsharef Farah 39 • The basal (subarachnoid) cisterns: Cisterna magna. . Prepontine cistern. Cerebellopontine angle (CPA) cistern. Ambient cistern. Quadrigeminal cistern. Suprasellar (chiasmatic) cistern.

Dr. Ahmed Alsharef Farah 40 Axial view of basal cisterns. Dr. Ahmed Alsharef Farah 41 Axial, T2-weighted MRI of ambient, suprasellar, and interpeduncular

cisterns. Dr. Ahmed Alsharef Farah 42 Axial CT of ambient, suprasellar, and interpeduncularDr. Ahmed Alsharefcisterns. Farah 43 Axial, T2-weighted MRI of cerebellopontine angleDr. Ahmed (CPA) Alsharef cistern. Farah 44 Axial CT of cerebellopontine angle (CPA)Dr. Ahmed cistern. Alsharef Farah 45 Cerebrum • The cerebrum is the largest portion of the brain and is divided into left and right cerebral hemispheres. • Each hemisphere contains neural tissue arranged in numerous folds called gyri.

Dr. Ahmed Alsharef Farah 46 • The gyri are separated by shallow grooves called sulci and by deeper grooves called fissures. • The main sulcus that can be identified on CT and MR images of the brain is the central sulcus, which divides the precentral gyrus of the frontal lobe and postcentral gyrus of the parietal lobe.

Dr. Ahmed Alsharef Farah 47 Lateral view of central sulcus. Dr. Ahmed Alsharef Farah 48 Sagittal, T1-weighted MRI of cerebral lobes andDr. centralAhmed Alsharef sulcus Farah. 49 The two main fissures of the cerebrum are:

• The longitudinal fissure: Is a long, deep groove that divides the left and right cerebral hemispheres. • The lateral (Sylvian fissure): Is a deep groove that separates the frontal and parietal lobes from the temporal lobe.

Dr. Ahmed Alsharef Farah 50 Coronal view of cerebrum.Dr. Ahmed Alsharef Farah 51 Coronal, T1-weighted MRI of cerebrum.Dr. Ahmed Alsharef Farah 52 Gray and White Matter Organization:

• The cerebrum consists of gray matter (neuron cell bodies) and white matter (myelinated axons).

Dr. Ahmed Alsharef Farah 53 • The cerebral cortex, the outermost portion of the cerebrum, is composed of gray matter. • The cortex receives sensory input and also sends instructions to the muscles and glands for control of body movement and activity. • Deep in the cortex is the white matter, which contains fibers that create pathways for the transmission of nerve impulses to and from the cortex.

Dr. Ahmed Alsharef Farah 54 • The largest and densest bundle of white matter fibers within the cerebrum is the corpus callosum which is a midline structure that forms the roof of the lateral ventricles and connects the right and left cerebral hemispheres. • The four parts of the corpus callosum, from anteroinferior to posterior, are the rostrum, genu, body, and splenium.

Dr. Ahmed Alsharef Farah 55 Midsagittal view of cerebral cortex and corpusDr. Ahmed Alsharefcallosum Farah . 56 Axial view of cerebral cortex and corpusDr. callosum Ahmed Alsharef. Farah 57 Midsagittal, T1-weighted MRI of cerebral cortex andDr. Ahmed corpus Alsharef callosum Farah . 58 Axial, T1-weighted MRI of corpus Dr.callosum Ahmed Alsharef. Farah 59 Coronal, T1-weighted MRI of cerebral cortex andDr. corpus Ahmed Alsharef callosum Farah . 60 • Two other important bundles of white matter fibers are: The anterior commissure crosses the midline within the lamina terminalis and connects the anterior portions of each temporal lobe. The posterior commissure crosses the midline posterior to the third ventricle, immediately above the cerebral aqueduct and inferior to the pineal gland.

Dr. Ahmed Alsharef Farah 61 Midsagittal view of anterior and posterior commissures. Dr. Ahmed Alsharef Farah 62 Midsagittal, T1-weighted MRI of anterior and posteriorDr. Ahmed commissures Alsharef Farah . 63 Axial, T2-weighted MRI of anterior and posterior commissures. Dr. Ahmed Alsharef Farah 64 Cerebral Lobes: • The cerebral cortex of each hemisphere can be divided into four individual lobes: Frontal. Parietal. Occipital. Temporal. • These four lobes correspond in location to the cranial bones with the same name.

Dr. Ahmed Alsharef Farah 65 Lateral view of cerebral lobes.Dr. Ahmed Alsharef Farah 66 Dr. Ahmed Alsharef Farah 67 • The frontal lobe is the most anterior lobe of the brain. • The boundaries of the frontal lobe are the central sulcus, which separates it from the parietal lobe, and the lateral fissure, which separates it from the temporal lobe.

Dr. Ahmed Alsharef Farah 68 • The frontal lobe mediates a wide variety of functions, such as reasoning, judgment, emotional response, planning and execution of complex actions, and control of voluntary muscle movement. • The frontal lobe is also involved in speech production and contains the motor speech (language) center, Broca’s area.

Dr. Ahmed Alsharef Farah 69 Lateral view of cerebral lobes.Dr. Ahmed Alsharef Farah 70 Sagittal, T1-weighted MRI of cerebral lobes andDr. AhmedBroca Alsharef’s area. Farah 71 • The parietal lobe is located in the middle portion of each cerebral hemisphere just posterior to the central sulcus. • The horizontal portion of the lateral fissure separates the parietal lobe from the temporal lobe. • The parietal lobe is associated with the perception of temperature, touch, pressure, vibration, pain, and taste and is involved in writing and in some aspects of reading.

Dr. Ahmed Alsharef Farah 72 • The most posterior lobe, the occipital lobe, is separated from the parietal lobe by the parieto- occipital fissure and this lobe is involved in the conscious perception of visual stimuli. • The temporal lobe is anterior to the occipital lobe and is separated from the parietal lobe by the lateral fissure. Conscious perceptions of auditory and olfactory stimuli and dominance for language are functions of the temporal lobe.

Dr. Ahmed Alsharef Farah 73 • Deep in the temporal lobe is another area of cortical gray matter termed the Insula (Island of Reil), often referred to as the fifth lobe. • The insula is separated from the temporal lobe by the lateral fissure and is thought to mediate motor and sensory functions of the viscera.

Dr. Ahmed Alsharef Farah 74 Dr. Ahmed Alsharef Farah 75 Axial view show insula. Dr. Ahmed Alsharef Farah 76 Axial CT of Insula. Dr. Ahmed Alsharef Farah 77 Axial, T1-weighted MRI of Insula.Dr. Ahmed Alsharef Farah 78 Coronal CT reformat of cerebral lobes.Dr. Ahmed Alsharef Farah 79 Coronal, T1-weighted MRI of Insula.Dr. Ahmed Alsharef Farah 80 End of this Lecture

Dr. Ahmed Alsharef Farah 81 Assignment:

ORBIT sectional anatomy.

Dr. Ahmed Alsharef Farah 82