An adult brain weighs between 1.35 and 1.4 kilograms (kg) (around 3 pounds) and has a volume of about 1200 cubic centimeters (cc). Cerebrum is 83% of brain volume; cerebellum contains 50% of the neurons Brain size is not directly correlated with intelligence It is not the physical size of the brain that determines intelligenceit is the number of active synapses. Embryonic development:neural tube
Metencephalon: pons, cerebellum Myelencephalon: medulla oblongata The Brains 4 Major Regions Cerebrum, diencephalon, brainstem, and cerebellum. The cerebrum is divided into two halves, called the left and right cerebral hemispheres. Each hemisphere is subdivided into five functional areas called lobes. Outer surface of an adult brain exhibits folds called gyri (gyrus) and shallow depressions between those folds called sulci (sulcus).
The brain is associated with 12 pairs of cranial nerves. Support and Protection of the Brain The brain is protected and isolated by multiple structures: Bony cranium Meninges: Protective connective tissue membranes
surround and partition portions of the brain. Cerebrospinal fluid (CSF) acts as a cushioning fluid. Blood-brain barrier: prevents entry of harmful materials from the bloodstream.
Brian Cushing Brain Cushing Three dense regular connective tissue layers: Separate the soft tissue of the brain from the bones of the cranium.
Enclose and protect blood vessels that supply the brain. Contain and circulate cerebrospinal fluid(CSF). Parts of the cranial meninges form some of the veins that drain blood from the brain. From superficial to deep, the cranial meninges are the dura mater, the arachnoid, and the pia mater. Cranial Meninges Dura mater
Strongest of the meninges. Dura mater is composed of two layers. periosteal layer, attaches to the periosteum of the cranial bones meningeal layer lies deep to the periosteal layer Arachnoid Lies immediately internal to the dura mater.
Composed of a delicate web of collagen and elastic fibers(arachnoid trabeculae). Between the arachnoid and the overlying dura mater is the subdural space. Immediately deep to the arachnoid is the subarachnoid space. Pia mater The innermost of the cranial meninges.
Thin layer of delicate connective tissue that tightly adheres to the brain Cranial Dural Septa The meningeal layer of the dura mater extends as flat partitions (septa) deep into the cranial cavity;
at four locations called cranial dural septa. Membranous partitions separate specific parts of the brain and provide additional stabilization and support to the entire brain. 1 1. falx cerebri 2. tentorium cerebelli 3. falx cerebelli 4
MRI of the brain, T1-weighted sagittal cut. 1, Occipital lobe. 2, Tentorium cerebelli. 3, Cerebellum. 4, Midbrain. Brain Ventricles
Cavities or expansions within the brain that are derived from the lumen (opening) of the embryonic neural tube. Continuous with one another as well as with the central canal of the spinal cord. Four ventricles in the brain. two lateral ventricles are in the cerebrum, separated by a thin
medial partition called the septum pellucidum within the diencephalon is a smaller ventricle called the third ventricle each lateral ventricle communicates with the third ventricle through an opening called the interventricular foramen The fourth ventricle is located within the pons and cerebellum. (Foramen of Monro)
Frontal(anterior) horn Occipital(Post.) horn Temporal(Inferior) horn (Foramen of Luschka) (Foramen of Magendie) Cistern Magna
A clear, colorless liquid that circulates in the ventricles and subarachnoid space. Is similar to blood plasma. Made in choroid plexuses (roofs of ventricles) Filtration of plasma from capillaries through ependymal cells (electrolytes, glucose) 500 ml/d; total volume 100-160 ml (1/2 c) Performs several important functions.
buoyancy protection environmental stability nourishes brain Assayed in diagnosing meningitis, bleeds, MS Hydrocephalus: excessive accumulation Subarachnoid cisterns Areas within the subarachnoid space where the pia mater and arachnoid membrane are not in close approximation.
Subarachnoid space and CSF gathers to form pools or cisterns. Some major subarachnoid cisterns: 1. cisterna magna (cerebellomedullary cistern): the largest of the subarachnoid cisterns 2. pontine cistern 3. suprasellar cistern 4. interpeduncular cistern 5. quadrigeminal cisterns (superior cistern or cistern of the great cerebral vein) 6. ambient cistern
7. Cerebellopontine angle(CPA) cistern Subarachnoid cisterns Cerebral hemispheres: note lobes Divided by longitudinal fissure into right & left sides Central sulcus divides frontal from parietal lobes Lateral sulcus separates temporal lobe
from parietal lobe Parieto-occipital sulcus divides occipital and parietal lobes (not seen from outside) Transverse cerebral fissure separates cerebral hemispheres from cerebellum Insula deep within the lateral sulcus Organization of Brain Tissue During brain development, an outer, superficial region of gray matter
forms from migrating peripheral neurons. External sheets of gray matter, called the cortex, cover the surface of most of the adult brain (the cerebrum and the cerebellum). Gray matter: outer motor neuron and interneuron cell bodies, dendrites, axon terminals unmyelinated axons. White matter: inner composed primarily of myelinated axons. Within the white matter: discrete innermost clusters of gray matter called cerebral nuclei (or
basal nuclei). are oval, spherical, or sometimes irregularly shaped clusters of neuron cell bodies. Cerebral cortex
Composed of gray matter-- 3 mm thick Neuronal cell bodies, dendrites, and short axons Folds in cortex triples its size 2 types of cells stellate cells have dendrites projecting
in all directions pyramidal cells have an axon that passes out of the area Functional areas of the cortex
Three kinds of functional areas Motor areas Sensory areas Association areas Motor areas
Anterior to central sulcus Primary motor area Precentral gyrus of frontal lobe (4) Conscious or voluntary movement of skeletal muscles Large neurons called pyramidal cells
Their axons: form massive pyramidal or corticospinal tracts Decend through brain stem and spinal cord Cross to contralateral (the other) side in brainstem Therefore: right side of the brain controls the left side of the body, and the left side of the brain controls the right side of the body Motor areas continued Brocas area (44): specialized motor speech area Base of precentral gyrus just above lateral sulcus in only one hemisphere, usually left
Word articulation: the movements necessary for speech Damage: can understand but cant speak; or if can still speak, words are right but difficult to understand Motor areas continued Premotor cortex (6): complex movements associated with highly processed sensory info; also planning of movements Frontal eye fields (inferior 8): voluntary movements of eyes Sensory areas
Posterior to central sulcus Primary somatosensory cortex: postcentral gyrus of parietal lobe (allows conscious awareness of sensation and the ability to localize it: where the sensation is from) Somatosensory association area: behind it (understanding of what is being felt: the
meaning of it) From special sense organs Occipital lobe: visual Primary visual cortex (17) Visual association area (18 & 19) Face recognition is usually on the right side Hearing: temporal lobe Primary auditory area (41)
Auditory association area (22) Smell (olfactory sense): uncus Deep in temporal lobe along medial surface Homunculus little man Body map: human body spatially represented Where on cortex; upside down Refer back to this labeled version as needed
Auditory Association Area The auditory association area contains two special regions. BROCA'S AREA is a region of the brain that allows for speech. WERNICKES AREA is the region of the brain that allows understanding of words. Arcuate Fasciculus - A white matter tract that connects Brocas Area and Wernickes Area through the temporal, parietal and frontal Lobes. Allows for coordinated, comprehensible speech. Damage may result in Conduction Aphasia - Where auditory
comprehension and speech articulation are preserved, but people find it difficult to repeat heard speech. Cerebral White Matter Extensive communication Areas of cortex with each other
Areas of cortex with brain stem and spinal cord Via (mostly) myelinated axon fibers bundled into tracts Commissures Association fibers Projection fibers Cerebral White Matter
Types of tracts or fibers Commissures composed of commissural fibers Allows communication between cerebral hemispheres Corpus callosum the largest commissure Association fibers Connect different parts of the same hemisphere
44 Projection tracts Projection fibers run vertically Cerebral cortex running down (with motor instructions) Or ascend to cerebral cortex from below (sensory info to cortex)
Internal capsule projection fibers form a compact bundle Passes between the thalamus and basal nuclei Corona radiata superior to the internal capsule Fibers run to and from the cerebral cortex Projection fibers
_________________ Corona radiata: fanning out of the fibers Internal capsule: bundled, ___________________ pass down Commisure Corpus callosum: connects right and left hemispheres
Decussation: crossing of pyramidal tracts _____________________ _____________________ White Matter-Fractional Anisotropy map of DTI
White Matter Fiber Tracts Association Projection Callosum Wakana S, Jiang H, Nagae-Poetscher LM, van Zijl PC, Mori S. Fiber tract-based atlas of human white matter anatomy. Radiology. 2004 Jan;230(1):77-87. Epub 2003 Nov 26.
Basal nuclei A group of nuclei deep within the cerebral white matter Caudate nucleus arches over the thalamus(head, body and tail) Lentiform nucleus lens shaped Amygdala sits on tail of the caudate nucleus
Functionally belongs with the limbic system Lentiform nucleus Divided into two parts Globus pallidus Putamen Basal nuclei
Cooperate with the cerebral cortex in controlling movements Receive input from cortical areas, send most of output back to motor cortex through thalamus Involved with stopping/starting & intensity of movements
Dyskinesias-bad movements Parkinsons disease: loss of inhibition from substantia nigra of midbrain everything slows down Huntington disease: overstimulation (choreoathetosis) degeneration of corpus striatum which inhibits; eventual degeneration of cerebral cortex The Diencephalon
Border the third ventricle Surrounded by the cerebral hemispheres Primarily composed of gray matter Forms the center core of the forebrain Composed of three paired structures:
Thalamus, hypothalamus, and epithalamus The Thalamus Two large lobes of gray matter
Laterally enclose the 3rd ventricle Gateway to cerebral cortex: every part of brain that communicates with cerebral cortex relays signals through a nucleus in the thalamus Processing (editing) occurs also in thalamus (Mass intermedia) The Diencephalon The Hypothalamus
Lies between the optic chiasm and the mammillary bodies Pituitary gland projects inferiorly
Contains approximately a dozen nuclei Main visceral control center of the body The Hypothalamus Functions include the following:
Control of the autonomic nervous system Control of emotional responses
Regulation of body temperature Regulation of hunger and thirst sensations Control of behavior Regulation of sleep-wake cycles Control of the endocrine system Formation of memory Mammillary Bodies A pair of small round bodies at the anterior end of the fornix Part of the diencephalon; they form part of the limbic system.
They relay information (recognition memory) from the hippocampus. They also add the element of smell to memories. Damage to the mammillary bodies due to thiamine deficiency (vit B1) or alcohol causes Wernicke-Korsakoff syndrome (anterograde amnesia) The Diencephalon The Epithalamus
Forms part of the roof of the third ventricle Consists of a tiny group of nuclei Includes the pineal gland (pineal body) Secretes the hormone melatonin
Under influence of the hypothalamus Functional Brain Systems The Limbic System
Location Medial aspect of cerebral hemispheres Also within the diencephalon Composed of: Septal nuclei, cingulate gyrus, and hippocampal formation Part of the amygdala The fornix and other tracts link the limbic system together The emotional brain
Cingulate gyrus Allows us to shift between thoughts Interprets pain as unpleasant Hippocampal formation Hippocampus and the parahippocampal gyrus The Brain Stem
Includes the midbrain, pons, and medulla oblongata Several general functions Produces automatic behaviors necessary for survival Passageway for all fiber tracts running between the cerebrum and spinal cord 10 of the 12 pairs of cranial nerves attach to it
The Brain Stem The Midbrain Lies between the diencephalon and the pons Central cavity the cerebral aqueduct Cerebral peduncles located on the ventral surface of
the brain Contain pyramidal (corticospinal) tracts Superior cerebellar peduncles Connect midbrain to the cerebellum The Brain Stem The Midbrain Corpora quadrigemina the largest nuclei Divided into the superior and inferior colliculi
Superior colliculi nuclei that act in visual reflexes Inferior colliculi nuclei that act in reflexive response to sound 70 The Brain Stem The Midbrain
Two pigmented nuclei Substantia nigra neuronal cell bodies contain melanin Functionally linked to the basal nuclei Red nucleus lies deep to the
substantia nigra Largest nucleus of the reticular formation The Brain Stem The Pons
Located between the midbrain and medulla oblongata Contains the nuclei of cranial nerves V, VI, and VII Two general groups of cranial nerve nuclei Motor nuclei Sensory nuclei
73 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 Cranial nerves VIIIXII attach to the medulla 75 76 Functional Brain Systems The Reticular Formation
Runs through the central core of the medulla, pons, and midbrain Forms three columns
Midline raphe nuclei Medial nuclear group Lateral nuclear group Functional Brain Systems The Reticular Formation The Cerebellum
Located dorsal to the pons and medulla Smoothes and coordinates body movements Helps maintain equilibrium Consists of two cerebellar hemispheres Surface folded into ridges called folia
Hemispheres each subdivided into anterior and posterior Thick tracts connecting the cerebellum to the brain stem Superior cerebellar peduncles Middle cerebellar peduncles Inferior cerebellar peduncles 80 The Cerebellum
Composed of three regions Cortex gray matter Internal white matter Deep cerebellar nuclei deeply situated gray matter Cerebellum must receive information On equilibrium On current movements of limbs, neck, and trunk
From the cerebral cortex 82 Outline
The Organization of brain Meninges Ventricular System: Ventricles and Cisterns Cerebrum: Lobes and Basal ganglion Diencephalon: Thalamus, Epithalamus, Hypothalamus
, Pituitary gland Limbic System Brain Stem: Midbrain, Pons and Medulla Oblongata Cerebellum Cerebral Vascular system: Arterial and Venous System Principle Brain Arteries Internal Carotid Artery( ICA) The segments of the internal carotid artery are as follows:
1. Cervical segment or portion, or C1 2. Petrous segment, or C2 3. Lacerum segment, or C3 C2 and C3 compose the commonly termed Petrous portion 4. Cavernous segment, or C4, commonly used Cavernous portion 5. Clinoid segment, or C5, lies between the commonly used Cavernous portion and Cerebral or Supraclinoid portion 6. Ophthalmic, or supraclinoid segment, or C6 7. Communicating, or terminal segment, or C7
The vertebral-basilar arteries supply about 20% of the blood flow to the brain. Derived from subclavian arteries in the thoracic cavity. When they get to the atlas, they exit the spine and migrate backwards toward the atlantooccipital membrane . Shortly after entering the cranial vault the vertebral arteries unite and become the basilar artery. Vetebral-Basilar system include: Posterior inferior cerebellar artery (PICA) Anterior inferior cerebellar artery (AICA)
Pontine artery Superior cerebellar artery(SCA) Posterior circulation -Vertebral arteries Circle of Willis The Circle of Willis is composed of the following arteries: 1. Anterior cerebral artery (ACA) 2. Anterior communicating artery(ACoA)
3. Internal carotid artery (lCA) 4. Posterior cerebral artery (PCA) 5. Posterior communicating artery (PCoA) The basilar artery and middle cerebral arteries, supplying the brain, are not considered part of the circle Circle of Willis 2 1
3 5 4 Lenticulostriate Arteries Supply the Basal Ganglia and Internal Capsule Anatomy and Vascular Territories of the 3 Main Cerebral Arteries:
Middle Cerebral Artery M3 M2 M1 Anterior Cerebral Artery and Posterior Cerebral Artery Superficial and Deep Arterial Supply to the Cerebral Hemispheres
Coronal Plane Superficial and Deep Arterial Supply to the Cerebral Hemisphere Axial Plane
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