Unit 12a: The Nervous System The Brain. MDL231 Principle of Anatomy

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1 Unit 12a: The Nervous System The Brain MDL231 Principle of Anatomy The Brain - Overview Cerebrum T PP H midbrain Cerebellum pons m.o. Brain stem medulla oblongata (M.O.) pons midbrain (mesencephalon) Diencephalon thalamus hypothalamus epithalamus (pineal gland) Cerebrum Cerebellum 1

2 Cranial Meninges Three layers: Dura mater, Arachnoid mater, Pia mater Cranial Meninges Dura mater tough, fibrous outer layer; 2 layers thick around brain (superficial periosteal layer /deeper meningeal layer ) with creation of dural (venous) sinuses between layers, and dural folds into cranial cavity 2

3 Dural folds Folds that create septa to subdivide cranial cavity and stabilize the brain. Includes: falx cerebri between cerebral hemispheres in longitudinal fissure tentorium cerebelli between cerebrum & cerebellum in transverse fissure falx cerebelli between cerebellar hemispheres diaphragma sellae lines sella turcica Dural Sinuses Spaces between dural layers and dural folds functioning as veins for drainage of blood from cerebral veins, and CSF from subarachnoid space (superor sagittal sinus) Enclosed regions of the meninges that collect venous blood and drain it to the infernal jugular veins of the neck 3

4 Cranial Meninges Arachnoid mater spidery web-like middle layer with fine collagen & elastic connections to underlying Pia Mater Pia mater delicate, thin inner layer Cranial Meninges Subarachnoid space between arachnoid & pia mater; contains cerebrospinal fluid (CSF) Arachnoid granulations (villi) projections of arachnoid into dural sinuses for drainage of CSF 4

5 Cerebrospinal Fluid (CSF) clear, colorless fluid formed by filtration of blood plasma by choroid plexuses within ventricles of the brain. functions in protection of CNS, support, nutrient supply, waste removal Cerebrospinal Fluid (CSF): Circulation Lateral ventricles (in cerebral hemispheres) interventricular foramen third ventricle (in diencephalon around and between R/L thalamus) cerebral (mesencephalic) aqueduct of midbrain fourth ventricle (between pons/cerebellum) subarachnoid space & central canal of SC 5

6 Cerebrospinal Fluid (CSF): Circulation Reabsorption of CSF through arachnoid granulations (arachnoid villi) of dural sinuses (superior sagittal sinus) into cerebral veins Blood supply to Brain Brain requires large amounts of O2 and nutrients (glucose) Internal carotid arteries + basilar artery (from vertebral arteries) cerebral arterial circle (of Willis) Venous drainage from dural venous sinuses & cerebral veins into vertebral and internal jugular veins 6

7 Brain Stem Medulla oblongata continuation of the SC above the foramen magnum contains the pyramidal decussation cranial nerve nuclei (XII-VIII (cochlear) cardiac, vasomotor, & respiratory reflex centers Pons bridge linking cerebellum to SC & other parts of brain cranial nerve nuclei (VIII (vestibular) V) respiratory center Midbrain (mesencephalon) cerebral peduncles location of ascending (sensory) & descending (motor) tracts tectum posterior aspect of brainstem; contains corpora quadrigemina superior colliculi visual reflex centers inferior colliculi auditory reflex centers cranial nerve nuclei (IV-III) Brain Stem reticular formation network of interconnected nuclei throughout brainstem responsible for maintaining states of consciousness 7

8 The Diencephalon Thalamus surrounds 3 rd ventricle 2 sides (left & right thalamus) usually connected by intermediate mass (interthalamic adhesion) comprised of nuclei that function primarily as sensory relay stations The Diencephalon Hypothalamus connects to pituitary gland via the infundibulum has many important functions relating to maintaining homeostasis including (but not limited to): -integrating nervous & endocrine systems through control over pituitary gland -integration of ANS from visceral stimuli -hunger/satiety, thirst, body temp. regulation, circadian rhythms -hormone production (ADH, oxytocin) mamillary bodies reflex centers associated with eating, & processing of olfactory sensations 8

9 The Diencephalon Epithalamus - Pineal gland secretes Melatonin which helps regulate day-night cycles (circadian rhythm) The Cerebellum Separated from cerebrum by transverse fissure Tentorium cerebelli encloses straight sinus & transverse sinus Two hemisphereres joined by vermis Hemispheres have 3 lobes anterior, posterior & flocculonodular outer cortex of gray matter folded into folia inner white matter arbor vitae Transverse fissure 9

10 The Cerebellum Links to brainstem by cerebellar peduncles inferior cerebellar peduncle M.O. middle cerebellar peduncle pons superior cerebellar peduncle midbrain Functions include: control of skeletal muscles (unconscious) for balance, coordination & posture stores patterns of movement convolutions gyrus sulcus The Cerebrum Transverse fissure 10

11 Lobes of Cerebral Hemispheres Central sulcus Parietal lobe Frontal lobe Parieto-occipital sulcus Occipital lobe Lateral sulcus (Insula is deep to lateral sulcus) Temporal lobe Lobes of Cerebral Hemispheres insula 11

12 Gray & White matter of cerebrum Gray matter : superficial cortex functional areas includes sensory, motor, & higher order functions deep cerebral nuclei (aka basal nuclei/basal ganglia) White matter: fibers association commissural projection White matter of cerebrum Projection fibers Association fibers Commissural fibers association fibers connect gyri in same hemisphere commissural fibers connect gyri in opposite hemispheres (e.g. corpus callosum) projection fibers connect cerebrum with other parts of brain & spinal cord 12

13 Gray matter of cerebrum Basal (cerebral) Nuclei Paired clusters of gray matter deep within cerebral hemispheres Include: caudate nucleus, claustrum, putamen, globus pallidus, amygdaloid body. Involved primarily in subconscious control of skeletal muscle tone, and coordination of movement patterns once movement is initiated Gray matter of cerebrum Cerebral Cortex - Functional areas Motor and Sensory areas receive sensory info & generate motor (skeletal muscle) responses Association areas interpretation of sensory info & planning and coordination of motor responses Cerebral processing centers - higher order integrative & analytical functions 13

14 Motor & Sensory precentral gyrus is an important motor area located within frontal lobe Motor & Sensory primary sensory cortex (postcentral gyrus) 14

15 Motor & Sensory primary motor cortex (precentral gyrus) primary sensory cortex (postcentral gyrus) gustatory cortex visual cortex auditory cortex olfactory cortex Association areas somatic motor association area (premotor cortex) interpret incoming sensations; coordinate motor responses visual association area 15

16 Cerebral Processing Centers higher-order integrative centers may be unilateral motor speech center (Broca s) - Lt hemisphere usually general interpretive area (Wernike s) Lt hemisphere usually Prefrontal cortex (bilat.) Hemispheric Specialization Higher order centers in brain not bilaterally symmetrical in regards to function: Left hemisphere more involved in linear, mathematical, verbal, analytical functions Right hemisphere more involved in abstract analysis, spatial perception, sensory relationship, music, emotional context of language 16

17 Functionally related areas in cerebrum, thalamus & hypothalamus involved in emotional states, drives & behaviors linking conscious areas of cerebrum with unconscious areas of brainstem long term memory Major areas include: Amygdaloid body Cingulate gyrus Dentate gyrus Parahippocampal gyrus Hippocampus Fornix Mamillary bodies Limbic System Cranial Nerves 12 pairs of nerves that connect to the brain; provide motor, sensory &/or autonomic (parasympathetic) function 17

18 I Olfactory smell II Optic sight III Oculomotor motor to eye muscles; ANS for accommodation of lens & pupil constriction IV Trochlear motor to one eye muscle V Trigeminal motor to muscles of mastication, sensation to face & mouth VI Abducens motor to one eye muscle Cranial Nerves VII Facial motor to muscles of facial expression; taste; ANS to lacrimal & salivary glands VIII Vestibulocochlear equilibrium & hearing IX Glossopharyngeal swallowing, taste, ANS to salivary glands, sensory reception from monitoring of blood pressure in large arteries X Vagus sensation from viscera; ANS visceral muscle movement (respiratory, digestive, cardiovascular systems) XI Accessory motor to muscle of pharynx, SCM & Trapezius XII Hypoglossal motor to tongue muscles 18