LT_Anatomy of the CNS (2) PDF

The Central Nervous System Learning Outcomes By the end of this session the student will be able to:- Describe the structure of the meninges Describe the flow and function of cerebrospinal fluid Describe the location & relations, gross structure & main functions of the principle parts...

The Central Nervous System Learning Outcomes By the end of this session the student will be able to:- Describe the structure of the meninges Describe the flow and function of cerebrospinal fluid Describe the location & relations, gross structure & main functions of the principle parts of the brain Name the lobes and principal sulci of the brain Describe the blood supply to the brain Describe the venous drainage from the brain Identify the above on anatomical models, diagrams and radiographic images Structure of session Overview of the brain Structure and functions of the principle parts of the brain Important structures in/around the brain (meninges, CSF, ventricular system, blood supply, venous drainage) Spinal cord and cranial nerves- covered next week! How amazing is the brain? ‘What other bunch of cells can send people to the moon, can create the Declaration of Human Rights, re- engineer genes, produce a Mozart sonata or a Turner landscape?’ (Diamond et al., 1985) The brain: Constructs our living world Structurally changes in response to training and learning Is truly unique to every individual ‘transplant the brain, transplant the person’ Many parts of it are still unknown- new research enlightening us on functionality all the time! Gross anatomy of the brain Mushroom shaped Contained within the cranium (part of the skull) Weight: 3lbs (1300g) Four principle parts… 1. Cerebrum Largest part (7/8th of total brain weight) Supported on the diencephalon and brain stem Occupies most of the cranium 2. Diencephalon Superior to the brain stem Consists of the thalamus and hypothalamus 3. Brain stem ‘stalk of the mushroom’ Continuous with spinal cord Consists of the medulla oblongata, pons and the midbrain (mesencephalon) 4. Cerebellum Lies posterior to the brain stem Cerebrum  The largest part of the brain )‘great brain’) Rests in the anterior and middle cranial fossae of the The Cerebrum base of the skull Surrounds the midbrain and diencephalon Posterior portion (occipital lobe) is superior to the cerebellum Convex in general outline Upper surface in ovoidal Broader posteriorly Divided in the midline into 2 halves Right and left cerebral hemispheres Divided by the falx cerebri Hemispheres connected internally by the corpus callosum Each cerebral hemisphere has- A convex outer surface (corresponds with the cranial vault) A flattened inner surface (in contact with the opposite hemisphere) An irregular inferior surface (this rests in front of the anterior/middle cranial fossae of the base of the skull and behind on the tentorium cerebelli) Brain tissue Cells of the brain consist of Excitable cells- neurones Connective tissue- neuroglia Astrocytes, oligodendrocytes, ependymal cells, microglia Neurones ‘nerve cell’ Cell bodies form the grey matter Axons form the white matter Microscopic Groups of cell bodies in the CNS- nuclei Groups of cell bodies in the PNS- ganglia Axons found within the brain and periphery of the spinal cord- tracts Axons found outside the brain and spinal cord- nerves Cerebral cortex Each of the cerebral hemispheres consist of two layers Grey matter (outer layer- also known as the cerebral cortex) White matter (inner layer) Cerebral cortex Why do you think the two layers appear different? What is difference between what makes up the grey matter and white matter? The cortex is 2-4mm outer layer containing the functional cell bodies of the neurones. Cerebral cortex Contains ‘bumps’ and ‘dips’ ‘Bumps’ = gyri Dips = sulci Very deep dips/grooves= fissures The surface of the cortex can be mapped out structurally and functionally Three key fissures: 1. Longitudinal fissure Separates left and right hemispheres 2. Lateral fissure (sometimes called lateral sulcus) Separates the temporal lobe from the frontal lobe 3. Central sulcus Separates the frontal and parietal lobe  Lobes of the brain (functional Frontal lobe areas) Concerned with reasoning, planning, , problem-solving, planning, parts of speech (lower part) and movement (motor cortex), emotions Parietal lobe Concerned with perception of stimuli relating to touch, pressure, temperature and pain Temporal lobe Recognition of auditory stimuli and memory Occipital lobe Concerned with many aspects of vision  Functional Areas of the Cortex Specific types of signals are processed in certain areas of the cerebrum: Sensory areas – receive & interprets sensory impulses Motor areas – initiate movements Association Areas – complex integrative functions such as memory, emotions, reasoning, will, judgement, personality, intelligence Two key gyri are the Pre-central gyrus Located in frontal lobe Primary motor cortex Post-central gyrus Located in parietal lobe Primary sensory cortex Which surround the central sulcus The parts of the 1* sensory and motor cortex which process particular parts of the body can be mapped out onto the homunculus  Limbic lobe …considered the 5th lobe of the brain Located medially …at the junction of cerebrum and brain stem Concerned with processing of memories and sexual and emotional aspects of behaviour Cerebral white matter The nerve tracts run in 3 principle directions; Association fibres Fibres which connect and transmit pulses between gyri within the same hemisphere Commissural fibres Fibres which connect and transmit impulses from gyri of one hemisphere to another… Projection fibres Fibres which connect and transmit impulses from the cerebrum to the lower parts of the brain and spinal cord (internal capsule)  Left: Association fibres Fibres which connect and transmit pulses between gyri within the same hemisphere Right: Projection fibres Above: Commissural fibres Fibres which connect Fibres which connect and and transmit impulses transmit impulses from gyri from the cerebrum to of one hemisphere to the lower parts of the another… brain and spinal cord (internal capsule) Images: ‘The Human Brain Colouring Book’ Diamond, Scheibel and Elson Significant commissural fibres Important landmarks (particularly in CT and MRI) Corpus callosum Anterior commissure Posterior commissure  Basal ganglia Located deep within the cerebral hemispheres Act as a ‘relay’ station between the brain stem and the cerebral cortex Involved in initiation of fine movement control and learned activities (e.g. walking) Damage to BG- jerky, clumsy, uncoordinated movements Basal ganglia …are essentially groups of neuronal cell bodies (grey matter= nuclei) Contain Caudate nucleus Lentiform nucleus Putamen Globus pallidus Diencephalon Diencephalon …connects the cerebrum to the midbrain Is composed of the structures that surround the 3rd ventricle: thalamus and hypothalamus Thalamus Paired (L and R) masses of grey and white matter Located on each side of the 3rd ventricle Primarily a relay station for sensory impulses to the cerebral cortex Hypothalamus ‘Small but mighty’ gland Located inferiorly to the thalamus, superior to the pituitary gland Forms the floor of and part of the lateral walls of the 3rd ventricle Plays a significant link between the nervous and endocrine system via the pituitary gland Main functions: homeostasis (body temperature, appetite, water balance), emotions, sexual behaviour, circadian rhythms Endocrine glands …releases hormones that are released directly into the blood Significant endocrine glands of the brain; Pineal gland Secretes melatonin (involved in sleep rhythms) Pituitary gland Roles include growth, blood pressure, lactation Brain stem  One of the most important parts of the brain The brain stem Controls functions vital to life: breathing, heart beat, Throughout the brainstem you have reticular formation, a network of interspersed grey and white matter (which maintains consciousness, awakening from sleep, regulation of muscle tone Three key areas (S-I): Midbrain (mesencephalon) Pons Medulla oblongata  Extends from the lower aspect of The Mid brain the diencephalon to the pons 2.5cm in length Surrounds the cerebral aqueduct Contains fibres and tracts Anterior portion- tegmentum- contains a pair of fibre bundles- cerebral peduncles Posterior portion- tectum- contains superior and inferior colliculi (crucial for hearing and sight) Contains other nuclei including the substantia nigra and red nuclei Pons Lies directly above the medulla, below the midbrain, anterior to the cerebellum and posterior to the clivus 2.5cm in length Located in the anterior portion of the posterior cranial fossa Provides a relay centre (spinal cord-brain; brain-brain) Contains both nuclei and tracts Helps control respiration with the medulla Nuclei for cranial nerves (V-VIII)  Medulla oblongata The most inferior part of the brain stem Is essentially a continuation of the spinal cord Anterior to the cerebellum and slightly superior to the foramen magnum 3cm in length Located in the posterior cranial fossa Superior portion forms floor of 4th ventricle The medulla contains all ascending and descending tracts that communicate between the spinal cord and various parts of the brain… Medulla oblongata On the anterior aspect of the medulla are 2 triangular structures- ‘pyramids’ The pyramids are composed of the largest motor tracts that pass from the outer portion of the cerebrum to the spinal cord It is the point at which many of the nerves from the left side of the body cross to the right side and vice versa (decussation) The medulla contains nuclei that control functions such as breathing, heart rate and blood pressure Contain nuclei cranial nerves 8-12 Cerebellum Cerebellum 1/8 of the brain’s mass Butterfly shaped Occupies the inferior and posterior aspects of the cranial cavity Lies posterior to the brain stem and inferior to the occipital lobes Attaches to the brainstem by 3 paired fibres: Superior cerebellar peduncles- midbrain Middle cerebellar peduncles- pons Inferior cerebellar peduncles- medulla and spinal cord Role is controlling posture, balance, coordination and learned movements Damage to the cerebellum may lead to ataxia (uncoordinated muscles including those for speech and walking) Cerebellum Separated by the cerebrum by the tentorium cerebelli Comprised of a two wing shaped hemispheres joined together by the vermis (worm shaped) The two hemispheres separated by the falx cerebelli Each hemisphere contains 3 lobes: anterior, posterior and flocculonodular The outer cortex (grey matter) is folded into a series of slender, parallel ridges called folio Beneath this lies white matter tracts – arbor vitae- (resemble branches of a tree) Within the white matter are masses of grey matter nuclei which connect the cerebellum to other brain centres and the spinal cord Important structures in and around the brain The meninges The brain and spinal cord are completely surrounded by 3 protective membranes- the meninges Inner- Outer Pia (more inner layer) Arachnoid (middle layer) Dura (outer layer) ‘P.A.D.’  The most outer layer, also the most tough Contains 2 layers (spinal only has one) Dura mater Outer periosteal layer (continuous with inner surface of the skull) Inner meningeal layer, continuous with the dura mater of the spinal cord The inner layer folds around the brain, essentially separating it into compartments The falx cerebri- fold down the interhemispheric fissure and separates the left and the right cerebral hemispheres The falx cerebelli- separates the two hemispheres of the cerebellum The tentorium cerebelli- folds to separate the cerebrum from the cerebellum The folds of dura mater contain the main dural venous sinuses (venous system of brain)  Thin, web-like membrane Arachnoid mater (trabeculae); avascular Lies closely to the dura mater, separated from the pia mater from the subarachnoid space (CSF flows around this) In some areas, finger-like extensions – arachnoid villi- extend into the dural space, filtering CSF back to the venous sinuses Pia mater Pia mater (inner membrane) –very delicate membrane; highly vascular –Continuous with the outer surface of the brain cortex –Supports network of fine blood vessels, including choroid plexuses Cranial meninges - spaces Extradural space –between the skull and dura –‘potential space’ (only the middle meningeal artery) Subdural space –Between dura and arachnoid –‘potential space’; contains a small amount of serous fluid Subarachnoid space –Between arachnoid & pia –True space; contains delicate trabeculae & Cerebrospinal Fluid –Large pools of CSF near the fissures – Arachnoid Cisterns **It is important to be aware of these spaces when learning pathology The ventricular system Within the brain is 4 irregular shaped communicating cavities (ventricles), filled with CSF The Ventricular System is formed of: – 2 lateral ventricles – 3rd ventricle – 4th ventricle CSF is produced and secreted by choroid plexuses (capillary networks) in the walls of lateral and fourth ventricles, and the roof of the third ventricle Cerebrospinal fluid (CSF) Clear, colourless liquid Similar composition to blood – water, mineral salts, glucose, plasma proteins, creatinine & urea Circulates around the brain within the ventricular system and subarachnoid spaces Functions of CSF: –Support & protect the brain (‘cushions’ the brain along with meninges) –Maintain a uniform pressure –Act as a cushion & shock absorber –Keep brain & spinal cord moist; exchange nutrients & waste Flow of CSF around the brain Blood supply to the brain The brain receives 15% of cardiac output The blood supply to the brain is from the internal carotid arteries and the vertebral arteries. Internal carotid arteries Arise from common carotid bifurcation Enter carotid canals and course anteriorly cavernous sinuses Divide into the anterior and middle cerebral arteries Vertebral arteries Arise from R brachiocephalic and L subclavian arteries Pass through the transverse foramina of the first 6 cervical vertebrae, through the foramen magnum At the level of the pons, unite to form the basilar artery (anterior to pons) At the top of the pons, the artery divides into the posterior cerebral artery Cerebral Arterial Circle (of Willis) Located at the base of the brain- forms a vital anastomosis between the arteries that supply the brain Therefore if one aspect of the circle becomes obstructed the blood can flow the other way around the circle meaning cerebral blood flow can be maintained (vital to avoid cell death Formed by the posterior cerebral, posterior communicating, internal carotid, anterior cerebral, anterior communicating arteries The circle of Willis Dural Venous Sinuses The dural venous sinuses are endothelial-lined spaces between the periosteal and meningeal layers of the cranial dura. Large veins from the surface of the brain empty into these sinuses. Ultimately all the blood from the brain drains through them into the internal jugular vein. Venous sinuses Main venous sinuses are: Superior sagittal sinus (x1) Inferior sagittal sinus (x1) Straight sinus (x1) Transverse (lateral) sinus (x2) Sigmoid sinus (x2) The spinal cord and cranial nerves Learning Outcomes You will be expected to know the following with regard to the spinal cord Location Function Gross anatomy Internal structure Protections Number of spinal nerves Awareness of related pathologies  Function Nervous tissue link for nerve impulses travelling to and from the brain Spinal nerves leave/enter the cord at the appropriate level and pass to the structures they supply (motor and sensory impulses) The major reflex centre and conduction pathway Processes reflex responses in response to environmental changes Independent of the brain Location The spinal cord & spinal nerve are located within the vertebral canal Continuous with the medulla oblongata superiorly extends from the foramen magnum to lower border of L1 (variable) Anchored by the filum terminale, to the coccyx Gross Anatomy Cylindrical in shape Slightly flattened from anterior to posterior It is a tube neural tube Medulla oblongata to L2 42 – 45 cm long ¾” diameter ( about the size of your little finger Tapers to form the medullary cone at L1/L2 Gross Anatomy Cauda Equina (horses tail) Loose bundle of spinal nerve roots arising from the lumbar enlargement and medullary cone Terminal filum Arises from the tip of the medullary cone; attaches to the dorsum of the coccyx. It is an anchor for the inferior part of the spinal cord and meninges Gross Anatomy Internal Structure The cord is enlarged in 2 regions in relationship to innervation of the limbs Cervical enlargement Extends from C4 through to the T1 segment of the spinal cord Most of the anterior rami arising from it form the brachial plexus Lumbosacral enlargement Extends from T11 through to S1 Anterior rami arising from this enlargement make up the lumbar and sacral plexuses that innervate the lower limbs Internal Structure Divided into 2 equal parts by: Anterior median fissure Posterior median fissure Composed of grey matter in the centre, surrounded by white matter. (opposite to the brain)  Grey Matter Central area of grey matter is H or butterfly shaped 2 posterior, 2 anterior, 2 lateral columns (one each side of the midline) Centre of this commisure is the central canal containing CSF (which is continuous with the 4th ventricle above) Consists primarily of nerve cell bodies: Sensory (receives impulses from body) Motor (transmit impulses to muscle) Connector (reflex arc)  White Matter Arranged into 3 columns anterior, posterior, lateral Ascending tracts – sensory axons that conduct impulses to the brain Descending tracts – motor axons carrying nerve impulses down the cord from the brain Spinal cord Protection Bony Vertebrae (contained within vertebral canal) Surrounded by: Cushion of CFS Spinal meninges (similar to the brain) 1. Dura mater 2. Arachnoid mater 3. Pia mater Easy way to remember order of the meninges (inner to outer) “the meninges PAD the brain” Pia; Arachnoid; Dura Dura Mater Outermost covering membrane Tough layer of fibrous and elastic tissue Forms the spinal dural sac (only 1 layer – brain has 2)  Arachnoid Mater Middle covering Delicate, avascular membrane Ensheaths spinal cord and nerve roots Connected to pia mater by arachnoid trabelculae Lines the dural sac  Pia Mater Innermost covering Thin transparent layer of connective tissue closely follows the contours of the spinal cord Covers spinal nerve roots Contains small blood vessels that nourish the cord Level of L2, the pia mater extends as the filum terminale to attach on to the coccyx  Pia Mater The spinal cord is suspended within the dural sac by 21 pairs of Denticulate ligaments thickenings of pia mate that extend laterally, fuse with arachnoid mater and secure the cord in place  Epidural Space Between the bony wall of the vertebrae and the dura mater Contains cushioning of fat, blood vessels and connective tissue Runs from the length of the vertebral canal (NB there is NO epidural space around the brain) Subarachnoid Space Between the arachnoid and the pia mater Spanned by arachnoid trabelculae Filled with Cerebrospinal fluid (CSF) sagittal view of cord in situ 1. Intervertebral disc 2. Vertebral body 3. Dura mater 4. Epidural space 5. Spinal cord 6. Subarachnoid space  Spinal Nerves Peripheral Nervous System (PNS) = spinal nerves and cranial nerves 31 pairs of spinal nerves Arise from both sides of the spinal cord Emerge through the intervertebral foramina Names/grouped according to associated vertebrae  Spinal Nerves Cervical x 8 First spinal nerve emerges between C1 and occipital bone Thoracic x12 Lumbar x5 Cauda equina = sheaf of nerves Sacral x5 Coccygeal x1  Nerve Roots Each nerve is formed by the union of an anterior (motor) and posterior (sensory) nerve root, and is therefore a MIXED nerve (when leaving the spinal cord the nerve roots are covered in dura and arachnoid – these terminate when they join) Spinal cord Spinal Nerves Cranial Nerves Learning Outcomes By the end of this session you should be able to:- Identify the 12 cranial nerves by Name Number Type Function Peripheral Nervous System PNS consists of:- 1. Sensory neurons (Sometimes called afferent neurons) Carrying impulses from receptors in the ‘periphery’ to the CNS 2. Motor neurons (sometimes called efferent neurons) Carrying impulses from the CNS to muscles and glands Peripheral Nervous System PNS can be subdivided into:- Somatic Nervous System (voluntary) 12 pairs of cranial nerves – sensory, motor or mixed 31 pairs of spinal nerves – mixed Ganglia (groups of nerve cell bodies) Autonomic Nervous System (involuntary) Viscera (organs) of the body are supplied by fibres from two divisions Sympathetic division – increases organ activity Para-sympathehtic division – decreases organ activity Cranial Nerves Peripheral Nervous System 12 pairs Each has both a number (in roman numerals) and a name numbered from superior to inferior, from which they arise Name designates its distribution or function 10 originate from the brain stem 2 (CNI and CNII) are extensions of the forebrain Some are purely sensory, some motor and some are mixed All emerge through the foramina or fissures in the cranium  Cranial Nerves (12) I. Olfactory VII. Facial II. Optic VIII. Vestibulocochlear III. Oculomotor IX. Glossopharangeal IV. Trochlear X. Vagus V. Trigeminal XI. Accessory VI. Abducens XII. Hypoglossal On On On They Travelled And Found Voldemort Guarding Very Ancient Horcruxes  CNI. Olfactory Nerve (S) Nerve of the sense of smell Olfactory nerve fibres pass from the nasal cavity through the cribiform plate to synapse with the olfactory bulb The olfactory tracts the then proceeds to the temporal lobe, the area of perception of smell (also involves the limbic system) Lesions of the nerve result in parosmia ( altered sense of smell) or anosmia (loss of smell) Function test – smelling common objects  Nerve of sense of sight Sensory nerve cells arise from the retina and CNII Optic Nerve (S) converge at the posterior eye to form the optic nerve Passes through the optic canal The optic nerves join at the optic chiasm anterior to pituitary stalk, where the fibres from the medial side of the retina cross to the opposite side –allows binocular vision The optic nerves terminate in the thalmus, but optic radiations continue to the visual cortex Function test – charts for acuity, visual field, colour Lesions of the visual pathway result in blindness and pupillary abnormalities CNIII Oculomotor (M) Movement of the eyeball (elevation, adduction) superior, inferior, medial rectus muscle Focusing; regulating pupil size Ciliary muscles; circular muscles CN IV Trochlear (M) Movement of the eyeball (depression) Superior oblique muscles  CNV Trigeminal Nerves (mixed) Largest of the cranial nerves Primarily involve in sensation in the face, but also chewing, biting & swallowing (mastication) Three main branches Opthalmic – sensory Maxillary – sensory Mandibular - mixed CN VI Abducent (M) Movement of the eyeball (abduction) lateral rectus muscle CN VII Facial (Mixed) Facial Expression; Sense of Taste sensory fibre to tongue motor fibre to face  CN VIII Vestibulocochlear (S) Passes through the internal auditory canal Has 2 sets of fibres: Vestibular branch – impulses from the semi-circular canals to areas of the cerebellum that aid balance and posture Cochlear branch – impulses from the inner ear to the areas in cerebral cortex that interpret sound Function tests – tuning fork(hearing); closing eyes (balance)  CN IX Glossopharangeal (mixed) Taste; secretion of salvia; movement of the Pharynx Parotid Gland Back of tongue CN X Vagus (mixed) Distributed in the head, neck, thorax and abdomen Taste; talking & swallowing; secretion Sensory – taste & sensations from throat; BP & O2 monitoring; regulates breathing; visceral sensations from organs in thorax and abdomen Motor – swallowing; coughing; voice production (parasympathetic) – smooth muscles of GI tract; slowing of heart rate; digestive sections CN XI Accessory (M) Cranial & spinal root (originates from both brain and spinal cord) Swallowing (cr); Movement of head and shoulders (SC) Pharynx & larynx Sternocleidomastoid & trapezius muscles CN XII Hypoglossal (M) Tongue movement Base Of Skull A. Optic canal B. Foramen rotundum C. Foramen ovale D. Foramen spinosum E. Foramen magnum F. Hypoglossal canal G. Jugular foramen H. Internal Acoustic Meatus(IAM) I. Foramen lacerum J. Cribriform plate P234, Bones and Joints – review the foramen through which each CN nerve passes