Brain and Associated Structures - Slides (1) PDF

Anatomy of the head and Neck – The Brain Anatomy of the Head & Neck The brain [email protected] ANATOMY 0 Learning outcomes Ø To identify the lobes of the brain and the main fissures Ø To describe the main regions of the brain – forebrain, midbrain and hindbrain – and some of the principal n...

Anatomy of the head and Neck – The Brain Anatomy of the Head & Neck The brain [email protected] ANATOMY 0 Learning outcomes Ø To identify the lobes of the brain and the main fissures Ø To describe the main regions of the brain – forebrain, midbrain and hindbrain – and some of the principal nuclei within each Ø To associate topography with function Ø To describe the meningeal layers and venous sinuses associated with the brain ANATOMY 1 Neurulation – origins Ø Neuroectoderm cells receive inductive signals from the notochord Ø This cell causes cells to thicken, thus forming the neural plate Ø Lateral neural plate margins then fold inwards to form the neural tube Embryonic day 20 Neural plate Neuroectoderm (midline ectoderm) Notochord (within mesoderm) Neural folds Neural groove ANATOMY 2 Neurulation – development Embryonic day 24 Ectoderm Neural crest cells Differentiate into: (1) Neurons and glial cells of the sensory and autonomic nervous systems + ganglia (2) Cells of the adrenal gland (3) Epidermis (4) Skeletal/connective tissue of the head Mantle layer - Becomes brain parenchyma (= functional component) Ependymal layer - Lines ventricles (= spaces) Lumen - Becomes ventricles + central canal ANATOMY 3 Neural tube defects Failure of anterior neuropore to close = Anencephaly (fatal) (1 in 10,000 births) Failure of posterior neural tube to close = Spina bifida (divided by a cleft) (1 in 1,000 pregnancies) - Leads to open vertebral canal ANATOMY Spina bifida occulta (hidden, vertebral arch defect only) Spina bifida cystica (e.g.; meningocele = meninges projects out) 4 Brain – origins Ø The cranial end expands to form three distinct swellings (vesicles) PRIMARY VESICLES The future… Prosencephalon => Forebrain Mesencephalon => Midbrain Rhombencephalon => Hindbrain Coronal view ANATOMY Embryonic day 21-28 5 Brain - development SECONDARY VESICLES Telencephalon = Cerebral hemispheres Prosencephalon (forebrain) Optic vesicles = Eyes Diencephalon = Thalamus/hypothalamus Mesencephalon (midbrain) Rhombencephalon (hindbrain) Metencephalon = Pons/ cerebellum Myelencephalon = Medulla Coronal view ANATOMY Embryonic day 36+ 6 Adult brain FOREBRAIN: BRAINSTEM: Cerebral hemispheres (Telencephalon) MIDBRAIN: Midbrain (Mesencephalon) Thalamus/ hypothalamus (Diencephalon) * HINDBRAIN: Pons (Metencephalon) Medulla (Myelencephalon) (Mid-sagittal view) ANATOMY * Cerebellum (Metencephalon) 7 Gray and white matter Ø The CNS is made up of gray and white matter Ø Gray matter - mainly neuronal cell bodies (e.g. cerebral cortex, brain nuclei) Ø White matter - mainly myelinated axons Cerebral cortex (gray matter) White matter ANATOMY Brain nuclei (gray matter) (Coronal view) 8 Telencephalon, aka Cerebrum Ø The telencephalon encompasses the - cerebral hemispheres/cerebral cortex - hippocampus - basal ganglia Telencephalon Cerebral hemispheres ANATOMY (Mid-sagittal view) 9 Cerebral cortex – gross anatomy Ø Divided topographically into four lobes (see next slide) Ø Its most prominent surface characteristic is the presence of gyri (elevations) and sulci (groves) Ø The pattern of gyri and sulci in unique between individuals Ø Also visible are the cerebral fissures, that border between lobes Central sulcus (separating frontal from parietal lobe) Postcentral gyrus (sensory) Precentral gyrus (motor) Lateral sulcus ANATOMY (divides temporal from parietal lobe) 10 Cerebral cortex – topography Ø Each hemisphere is divided into lobes based on a common role carried by its individual elements: Ø The frontal lobe is associated mostly with motor function Ø The parietal lobe is associated with somatosensory processing Ø The temporal lobe is associated with auditory processing but also speech, vision and memory Parietal lobe Ø The occipital lobe is associated with visual processing Frontal lobe Occipital lobe ANATOMY Temporal lobe 11 Functional areas of cortex Primary motor cortex (Control of movement) Supplementary motor cortex Somatosensory cortex Premotor cortex Visual cortex Motor speech, Motor Broca’s area Sensory Association/ cognition 80% of cortex is involved in association (perception of world) and cognition Prefrontal cortex Auditory cortex Olfactory cortex ANATOMY Gustatory (taste) cortex + Insula 12 White matter – corpus callosum Ø One of the most prominent examples of white matter is the corpus callosum, which links the two cerebral hemispheres Ø This tract carries axons that relay information from one hemisphere to the other Corpus callosum nu Ge ANATOMY (Mid-sagittal view) Body Sp len ium (Coronal view) 13 White matter – the capsules Ø The capsules are another prominent examples of white matter tracts Ø These carry axons that travel vertically or anterior-posterior Ø Associated with information travelling between the cortex and spinal cord/internal nuclei (anterior) Internal capsule Internal to lentiform nucleus External capsule ANATOMY External to lentiform nucleus (Coronal view) 14 (Horizontal view) Deep brain structures Ø The brain contains several nuclei and white matter tracts that are deep within the cerebral hemispheres Ø These are interconnected to form important neural networks, or systems. Two of the most well known examples are: Limbic system, occasionally labelled as the ‘emotional brain’ on account of its recognized role in mediating several processes that lead to an emotional response (e.g. pleasure, pain, anger and associated memories) as well as behaviour, drive and memory Basal ganglia, which is Involved in the control of posture and voluntary movement but also reported to mediate higher cognitive processes such as attention, memory and planning ANATOMY 15 The limbic system – components Ø This network of nuclei extends from the upper portion of the corpus callosum to the floor of the forebrain (diencephalon), that include some of the thalamic subdivisions, mammillary bodies of the hypothalamus, olfactory bulbs, as well as the hippocampus, amygdala and cingulate gyrus (Mid-sagittal view) Cingulate gyrus/cortex Corpus callosum Fornix Hypothalamus ANATOMY (part of diencephalon) Mammillary bodies Amygdala (Within temporal lobe) Hippocampus 16 The fornix Ø The fornix is a semi-circular white matter tract connecting the hippocampus (learning and memory) to the mammillary bodies (recollective memory) Body of fornix Mammillary body Fornix (Coronal view) ANATOMY White matter tract Amygdala Hippocampus (posterior) 17 The hippocampus Ø The hippocampus gets its name from a resemblance to a sea horse Ø This nucleus sits on the floor of the lateral ventricle Body of fornix (anterior) Pes (foot) hippocampus (Lateral) (Medial) Hippocampus LHS ANATOMY (Coronal view) 18 Basal ganglia Ø The name given to the collective group of interconnected nuclei located within the subcortical region at the base of forebrain Ø This group consists of the corpus striatum plus the subthalamic nucleus and substantia nigra Ø The basal ganglia is functionally linked to the motor cortex and thalamus Putamen Lentiform nucleus Corpus striatum Globus pallidus Caudate nucleus ANATOMY 19 Basal ganglia – anatomical features Ø Lentiform nucleus gets its name because it is lens-shaped, located within the internal and external capsules Ø Caudate nucleus is C-shaped and sits in the wall of lateral ventricle Body of caudate nucleus Head of caudate nucleus (anterior) ANATOMY Lentiform nucleus Tail of caudate nucleus 20 Basal ganglia – Cont. Ø The coronal/horizontal view illustrate how the position of the lentiform nucleus relates to caudate nucleus (anterior) Caudate nucleus Lentiform nucleus (Coronal view) ANATOMY Caudate nucleus (Horizontal view) 21 Diencephalon Ø The region of the brain that sits around the third ventricle Ø Its two most prominent constituents are the thalamus and hypothalamus Ø This central location equates to a ‘central’ role within neuronal networks Corpus callosum Fornix Diencephalon Thalamus Hypothalamus ANATOMY (Mid-sagittal view) 22 The thalamus Ø A paired structure, one on each hemisphere Ø Its role is as a relay of sensory information to the cortex Ø Information regarding voluntary movement, personality, consciousness or alertness Thalamus ANATOMY (Coronal view) 23 The hypothalamus Ø As the name suggests, it is located inferiorly to thalamus Ø Its primary role is the maintenance of homeostasis Ø Specifically, it coordinates ANS and endocrine responses, eg thermoregulation, hunger, thirst, sexual and emotional behaviour Ø Receives inputs from the limbic system Thalamus Pineal gland (Produces melatonin) Hypothalamus ANATOMY Pituitary gland (endocrine gland) 24 The hypothalamus – cont. Ø Viewing the brain from below, the hypothalamus sits between the optic chiasm and mammillary bodies Olfactory bulbs (CN1) Optic chiasm (CN2) Frontal lobe Temporal lobe ANATOMY Optic nerves converge/decussate to form optic tracts Hypothalamus Mammillary bodies 25 Brainstem Ø Comprises the Mesencephalon (midbrain) and Rhombencephalon (pons and medulla oblongata) Ø Thus connects the forebrain to the spinal cord Pineal gland Midbrain Pons Continuous with spinal cord Medulla (Anterior view) ANATOMY (Posterolateral view) 26 Brainstem - constituents Ø The brainstem is the locale for: - Cranial nerves nuclei, within all three regions - Vital respiratory and cardiovascular centres - Vomiting centre - Nuclei involved with motor control, or sleep Ø This includes all the relevant white matter tracts that interlink these nuclei to the rest of the CNS Ø Proper details will be provided in a follow-on lecture ANATOMY 27 Cerebellum Ø Located posterior to brainstem its featured are: - Outer gray matter - Underlying white matter - Outer surface reveals two cerebellar hemispheres and three lobes - Inner mass also contains nuclei Ø Main functions are of motor control: - Control of posture - Coordinating and planning limb movements - Control of eye movements ANATOMY 28 The meninges Ø The brain (and spinal cord) are protected not only by bone, i.e. skull or vertebrae – but also by a film of cerebrospinal fluid and a sheet-like structure formed by collagen, the meningeal layers Ø This sheet is 3-layered, from superficial to deep: - dura -arachnoid - pia ANATOMY 29 Meninges – cont. Ø The dura (tough) mater lies immediately below the skull and acts as a mechanically protective covering Ø The arachnoid (web-like) mater is considerably more delicate and made of non-vascular connective tissue Ø The pia (intimate) mater is continuous with the surface of brain/spinal cord. It supports the vessels that supply the brain as well as forming the choroid plexus (CSF production), alongside the ependymal cells ANATOMY 30 Meninges – gross anatomy ANATOMY 31 Meningeal partitions 1 Ø In specific regions within the skull the meningeal layers project from under the surface into the intracranial region Ø These projections serve the purpose of ensuring that the brain moves alongside the skull, since the brain is not otherwise anchored to the bony skull, being essentially surrounded by CSF ANATOMY 32 Meningeal partitions – examples Ø Falx cerebri, is the partition between the two cerebral hemispheres, i.e. in the longitudinal fissure. The term ‘Falx’ (Latin for sickle) is derived from the fact that this partition is narrow at the front where it attaches to the crista galli of the ethmoid and broad behind, where it connects to the upper surface of the tentorium cerebelli - The upper margin of the falx cerebri is attached to the inner surface of the skull, leaving a gap that forms the superior sagittal sinus - The lower margin has a free edge and encloses the inferior sagittal sinus Ø Falx cerebelli, is the partition between the cerebellar hemispheres, whereby a short process of dura mater projects from the internal occipital crest below the tentorium and bifurcates into two, passing on either side of foramen magnum ANATOMY 33 Meningeal partitions – examples cont. Ø Tentorium cerebelli, as the name translates to, sits as the roof of the cerebellum Ø In other words, this partition sits between the occipital lobes and cerebellar hemispheres, with an opening surrounding the brainstem ANATOMY 34 Venous sinuses Ø At specific areas between the skull and dura gaps exist that create channels that allow venous blood to flow Ø This network of channels (or gaps, hence ‘sinus’) receive blood from the brain and ultimately drain into the internal jugular vein Ø The rhs image, below, shows the more prominent examples ANATOMY 35 Cavernous and petrosal sinuses Ø In the petrous region of the sphenoid bone, at the base of the brain, are both the cavernous and petrosal sinuses Ø The cavernous sinus gets blood from the eye region, among others, and drain into the petrosal sinuses (superior and inferior) which in turn drain into the internal jugular Ø Because of a lack of valves along the veins of face and the cavernous sinus infections can easily spread from teeth, eye or nose, leading to cavernous sinus thrombosis. This was often fatal prior to the use of penicillin ANATOMY 36 Venous Sinuses – gross anatomy Sigmoid sinus Sup Sagittal sinus Transverse sinus Left cavernous sinus ANATOMY 37 The ventricular system Ø The ventricles refer to the cavities, or spaces, within the brain that produce and contain cerebral spinal fluid (CSF) Ø This system comprises one midline, two lateral, a 3rd and 4th ventricles Ø The two lateral ventricles open into the 3rd via the interventricular foramen (of Monro). The latter then opens to the 4th via a narrow passageway – the cerebral aqueduct Ø Cerebrospinal fluid is formed in the ventricles from choroid plexus and reabsorbed via arachnoid granulations into systemic veins (e.g. superior sagittal sinus) ANATOMY 38 Clinical relevance: Subdural haemorrhage Ø Rupture to the veins located in the subdural space can lead to a build up of blood between the dura mater and the arachnoid Ø This is referred to as subdural (‘under the dura’) haemorrhage and if it compresses the brain then it can be life- threatening Ø Other symptoms are loss of consciousness or paralysis Ø Also, it can be either acute or chronic ANATOMY 39 Extradural or Epidural haemorrhage Ø Trauma to the skull can in turn lead to an epidural haemorrhage, i.e. between the dura and the skull Ø The bleed is often the result of rupture to the middle meningeal artery ANATOMY 40 Clinical relevance: Subarachnoid haemorrhage Ø Any haemorrhage that occurs in the space between the arachnoid and the pia mater is termed subarachnoid Ø Most likely the result of an aneurysm Ø Likely symptoms are sight problems, pain (face) or headaches. But it can also be fatal ANATOMY 41 CSF Rhinorrhea Ø A fracture of the sinuses or cribriform plate may result in a condition termed CSF rhinorrhea Ø The result of a disruption to the skull, subarachnoid and dura can lead to the the CSF- containing subarachnoid space coming into direct contact with the nasal mucosae ANATOMY 42 Questions? Questions? Email: [email protected] ANATOMY 43