Brain and Cranial Nerves PDF

The Brain and Cranial Nerves Chapter 14 Development of the Brain Neural To understand the terminology used for the principal parts of plate the brain, it is helpful to understand how...

The Brain and Cranial Nerves Chapter 14 Development of the Brain Neural To understand the terminology used for the principal parts of plate the brain, it is helpful to understand how the brain develops Notochord Day ~20 Embryonic Development Ectoderm Blastodisc Neural groove Primitive streak Neural fold Yolk sac Amniotic Mesoderm Endoderm cavity Neural tube Day ~12 Day ~21 Blastocyst implanted in uterus Development of the Brain Lateral ventricles Third ventricle Cerebral aqueduct Fourth ventricle Central canal Major Parts of the Brain The brain is composed of Sagittal four major parts: plane Brainstem Cerebrum Cerebellum Diencephalon Diencephalon: Cerebrum Thalamus Hypothalamus Brain stem: Midbrain Pons Medulla oblongata Cerebellum Spinal cord ANTERIOR Protective Coverings of the Brain Protection provided by: Boney cranium Cranial meninges Also provide supporting framework for arteries / veins Contain and circulate cerebrospinal fluid Form some of the veins that drain blood from the brain Cerebrospinal fluid (CSF) Protective Coverings of the Brain SUPERIOR Frontal plane Skin Parietal bone Periosteal layer Meningeal Cranial meninges: layer Dura mater Subarachnoid Arachnoid mater space Pia mater Arachnoid granulation Cerebral cortex Dural fold Anterior view of frontal section through skull showing the cranial meninges Protective Coverings of the Brain Potential spaces appearing only under pathological conditions Extradural or epidural space (dura mater – skull interface) Subdural space (dura mater – arachnoid mater interface) Subarachnoid space (arachnoid mater – pia mater interface) Actual space containing cerebrospinal fluid (CSF), arteries and veins Cranial Dural Septa Four cranial dural septa partitions the brain providing stabilization and support: Falx cerebri Tentorium cerebelli Falx cerebelli Diphragma sellae Dural venous sinuses run within the margins of the dural septa Cerebrospinal Fluid Fluid‐filled cavities containing cerebrospinal fluid (CSF) provides: Mechanical protection: Buoyancy: reduces weight of brain from 1400g (3 lbs) to 25‐50g Shock absorption: liquid cushion Chemical protection: ensures accurate neuronal signaling Circulation: transports nutrients and removes waste products There are four ventricles Two lateral ventricles, one in each cerebral hemispheres (separated by septum pellucidum) 3rd ventricle found in the diencephalon 4th ventricle lies between the pons and the cerebellum Brain Ventricles Circulation of CSF Dural venous sinus Arachnoid granulations Pia mater Produced by the choroid plexus in all ventricles Rate of 500ml / day ~150 ml continually bathes the CNS Lateral & median apertures allow CSF to flow into subarachnoid space Interventricular foramen CSF removed through arachnoid Dura mater Lateral granulations that act as a one‐way (periosteal layer) aperture Dura Median mater valve aperture Subarachnoid Dura mater space (meningeal layer) Arachnoid granulation Arachnoid villi Pia mater Dural venous sinus Regional Brain Structures Brainstem | Cerebellum | Diencephalon | Cerebrum Brainstem Connects prosencephalon (forebrain) and cerebellum to spinal cord Contains many autonomic centers and reflex centers required for survival Houses nuclei of many of the cranial nerves Three regions form the brainstem: Midbrain Pons Medulla oblongata Medulla Oblongata All comm. between the brain and spinal cord passes through the medulla Relay stations for sensory or motor pathways Houses nuclei of cranial nerves: VIII, IX, X, XI, and XII Notable structural region: pyramids Decussation of pyramids marks the crossing over of corticospinal tracts Medulla Oblongata Houses autonomic centers for: Cardiovascular | respiratory | swallowing | coughing | vomiting | sneezing | hiccupping Inferior olivary nucleus directs input from the cerebrum, midbrain, and spinal cord to the cerebellum Enables cerebellum to adjust muscle activity Cuneatus and gracilis nuclei relay sensory information to the thalamus Touch, pressure, vibration, and conscious proprioception Pons Latin for bridge, connects: Right and left side of the cerebellum Descending tracts Pneumotaxic center Contains ascending sensory and Apneustic center Ascending descending motor tracts tracts Houses nuclei of cranial nerves: Transverse V, VI, VII, and VIII fibers Cerebellum Fourth Pontine respiratory group (pneumotaxic and ventricle apneustic areas), help control respiration along with the respiratory center in the Medulla oblongata medulla Reticular formation Midbrain Cerebral peduncles, composed of descending (motor) tracts from the cerebral cortex to the spinal cord, pons, and medulla Tectum (= roof) houses corpora quadrigemina (reflex centers) Superior colliculus regulates reflexive eye, head, and neck movements to visual stimuli Inferior colliculus regulates reflexive head, neck, and trunk movements to auditory stimuli Superior colliculus The tectum is also referred to as the Inferior colliculus tectal plate Midbrain Substantia nigra, darkly pigmented nucleus associated with subconscious control of muscle activity Loss of the neurotransmitter dopamine from these neurons linked to Parkinson’s disease Superior colliculi Red nuclei (appearance due to rich blood supply) Reticular formation Tectum receives input from cerebrum and cerebellum to help control upper limb movements (particularly reaching Tegmentum movements) Tegmentum is the ventral part (floor) of the midbrain (vs tectum, roof) Includes periaqueductal gray matter, red nucleus, Red nuclei and substantia nigra Substantia nigra Cerebral CN III peduncle Reticular Formation Cluster of gray matter spanning brainstem, neurons provide both: Ascending (sensory) function: Reticular Activating System (RAS) Influences state of consciousness (wakefulness or alertness) Inactivity produces sleep Descending (motor) function Help regulate muscle tone, influences cardiovascular and respiratory centers Cerebellum Accounts for approx. one tenth of the brain mass but contains ~ ½ of all neurons in brain Functions in the coordination of skeletal muscle contractions and in the maintenance of normal muscle tone, posture, and balance Does not initiate movement but assists in the coordination of movements Receives extensive proprioceptive feedback from muscles and joints Cerebellar Anterior lobe hemisphere Vermis Posterior lobe Folia Diencephalon Thalamus Thalamus Relay station for sensory information reaching the primary sensory cortex of the cerebrum Relays motor commands from cerebellum and basal nuclei to primary motor cortex of the cerebrum Output to the limbic system (emotions, memory & olfaction) Links to learning and cognition Helps in the maintenance of consciousness Interthalamic adhesion Diencephalon Hypothalamus Considered to be part of both the nervous and endocrine systems Control of autonomic nervous system Production of hormones Posterior hypothalamus releases neurohormones Anterior hypothalamus mediate activity of pituitary gland Regulation of emotional and behavioral patterns Regulation of eating and drinking Control of body temperature Regulation of circadian rhythms (day‐night cycles) Infundibular Pituitary stalk gland Diencephalon Epithalamus Pineal gland Habenular nuclei Pineal Secretes melatonin, promotes rhythmic changes in sleep, gland wakefulness, body temperature, and hormone secretion Melatonin helps regulate cortisol, growth hormone, luteinizing and follicle‐stimulating hormones, insulin, and thyroid hormones Thalamus Habenular nuclei Stores memories linked to odors Inferior colliculi  Cerebrum Cortex (2‐4 mm thick gray matter) Contains neuron cell bodies and their associated dendrites versus white matter that contains myelinated axons Longitudinal fissure Left Right Hemisphere Hemisphere Cortex Precentral Gyrus (primary motor cortex)  Neurons direct voluntary movements by Gyri controlling somatic motor neurons in the (L = “circle”) brainstem and spinal cord Lateral Central Sulcus fissure Postcentral Gyrus (primary somatosensory cortex)  Neurons receive somatic sensory information for Sulci touch, pressure, pain, taste, and temperature (L = “furrow”) from the dorsal columns and spinothalamic tracts Coronal section Cerebrum Motor and sensory cortex homunculus (Latin for “little man”, used to refer to any representation of a human being) Disproportionate association of the cortex with different areas of the body Precentral gyrus Postcentral gyrus Primary motor Primary cortex somatosensory cortex Lobes of the Cerebrum Central Sulcus Insula Frontal section  Cerebral White Matter Association tracts connect cortical areas within the same hemisphere Commissural tracts connect cortical areas in one hemisphere to corresponding area in the other hemisphere Corpus callosum Anterior and posterior commissure Commissural tracts Projection tracts connect cerebrum to / from lower parts of the CNS ex. Internal capsule Projection tracts Association tracts Decussation in pyramids Cerebral White Matter Commissural tracts Corpus callosum Anterior commissure Posterior commissure  Corpus Striatum (Basal Nuclei) aka cerebral nuclei or basal ganglia Masses of gray matter embedded in the white matter of the cerebrum Consist of: Caudate nucleus | Globus pallidus | Putamen | Claustrum Head of Septum caudate nucleus pellucidum Claustrum Lateral sulcus Lentiform Putamen nucleus Globus pallidus Internal capsule Anterior commissure Frontal section Limbic System More of a functional organization than an anatomical one Limbic system forms a ring around the diencephalon Function: Establishing emotional states (“emotional brain”) Pain | pleasure | docility | affection | anger Linking conscious intellectual functions of cerebral cortex with unconscious, autonomic functions of brain stem Facilitate memory storage and retrieval Direct links to olfaction  Limbic System Cingulate gyrus Fornix Dentate gyrus Septal nuclei Mammillary body Amygdala Olfactory bulb Hippocampus Temporal lobe Parahippocampal gyrus Posterior‐inferior view of the left hemisphere of the cerebrum Cranial Nerves 12 pairs numbered with roman numerals (CN I ‐ XII) beginning anteriorly Named generally related to: Primary function Origin Pathway Destination Fiber composition is either sensory, motor or both (mixed)  CN I Olfactory Function: entirely sensory, smell Pathway: cribriform plate of ethmoid Destination: olfactory tracts terminate in the temporal lobe Olfactory bulb Olfactory Tract Olfactory bulb Cribriform plate Olfactory nerves Cribriform plate Olfactory Axon epithelium Olfactory sensory neurons are bipolar with Olfactory a lifespan of ~2 months epthelium CN II Optic Function: entirely sensory, vision Pathway: optic canal of sphenoid Destination: thalamus, brainstem, occipital lobe  CN III Oculomotor Function: entirely motor; extraocular (SNS) and pupillae muscles (PNS) Origin: anterior midbrain (mesencephalon) Pathway: superior orbital fissure of sphenoid Trochlear nerve Optic nerve Oculomotor nerve Abducens nerve Ciliary ganglion  CN IV Trochlear Function: entirely motor, controls extraocular muscles Origin: posterior midbrain (mesencephalon) Pathway: superior orbital fissure of sphenoid Trochlear nerve Optic nerve Oculomotor nerve Abducens nerve CN V Trigeminal Function: mixed, sensory and motor Ophthalmic branch Sensory: touch, temperature, and pain Motor: muscles of mastication Maxillary branch Origin: pons Mandibular branch Sensory ‐ scalp, forehead, Pons eyebrows, eyelids & nose Sensory ‐ lower eyelids, upper lip, cheeks, nose, upper gums, teeth & palate Trigeminal Trigeminal ganglion Motor (Mastication m.) nerve Sensory (gums, teeth) CN V Trigeminal Function: mixed, sensory and motor Sensory: touch, temperature, and pain Motor: muscles of mastication Origin: pons Superior orbital fissure Sensory ‐ scalp, forehead, eyebrows, eyelids & nose Foramen rotundum Sensory ‐ lower eyelids, Foramen ovale upper lip, cheeks, nose, upper gums, teeth & palate Motor (Mastication m.) Sensory (gums, teeth)  CN VI Abducens Function: entirely motor, controls extraocular muscle Origin: pons Pathway: superior orbital fissure of sphenoid Trochlear nerve Optic nerve Oculomotor nerve Abducens nerve CN VII Facial Function: Mixed (sensory and motor) Sensory: taste (anterior ⅔ of the tongue) and skin around ear Motor: muscles of facial expression; lacrimal, palatine, salivary glands Origin: pons Pathway: internal acoustic meatus of temporal bone Nasal and Palatine glands (produce mucous) Tongue (taste) Facial nerve Salivary glands (submandibular and sublingual) CN VIII Vestibulocochlear Function: sensory, balance and hearing Origin: pons Pathway: internal acoustic meatus of temporal bone Semicircular Internal Tympanic cavity canals Vestibular branch acoustic Vestibulocochlear (middle ear) meatus nerve Pons Tympanic Auditory Cochlea Cochlear branch membrane tube CN IX Glossopharyngeal Function: mixed, sensory and motor Sensory: taste (posterior ⅓ tongue), lining of the pharynx and soft palate Motor: muscles that assists swallowing; Passes through parotid salivary gland jugular foramen Pons Origin: medulla oblongata Glossopharyngeal nerve Pathway: jugular foramen Otic ganglion Inferior (petrosal) Superior (jugular) ganglion ganglion Lingual branch Pharyngeal branches Parotid salivary gland Carotid sinus branch Carotid body (chemoreceptors) Carotid sinus (baroreceptors) Common carotid artery  Carotid sinus CN X Vagus Carotid body Function: mixed, sensory and motor Aortic bodies Larynx Sensory: visceral sensation from CN IX tongue, throat, heart, esophagus, abdominal viscera, and intestine Motor: muscles of the throat, heart, lungs, larynx, trachea, and most abdominal organs Origin: medulla oblongata Pathway: jugular foramen Vagus nerve Pancreas Pancreas (behind stomach) Small Large intestine intestine CN XI Accessory Function: Motor, controls the SCM, trapezius, and some pharynx muscles Origin: Medulla oblongata Pathway: jugular foramen Medulla oblongata Accessory Sternocleidomastoid nerve Trapezius muscle muscle CN XII Hypoglossal Function: motor, controls tongue muscles Origin: medulla oblongata Pathway: hypoglossal canal of occipital bone  CN I Mnemonic aid to remember name and function Names Functions Oh ‘S’ome CN II Optic chiasm Oh ‘S’ay CN III Oh ‘M’arry CN IV To ‘M’oney CN V Touch ‘B’ut CN VI And ‘M’y CN VII Feel ‘B’rother CN VIII Very ‘S’ays CN IX Green ‘B’ad CN X Vegetables ‘B’oys CN XII Ah ‘M’arry CN XI Heaven ‘M’oney Aging and the Nervous System Brain development Double in size in the first year of life Achieve 80% of adult brain by age 3; 90% by age 5; development stops early 30s Age‐related effects involve loss of neurons, decreased transmission capabilities and processing of information Diminished synaptic contacts Neurons shrink and dendrites retract Other effects include decreased conduction velocity, slowing of voluntary motor movements, and increased reflex time. Deterioration of myelin sheath Degenerative changes and disease states involving the sense organs can alter vision, hearing, taste, smell, and touch.