Ch 15 Pathophysiology PDF

UNIT 2 STUDY GUIDE NU 545- Pathophysiology Ch. 15 CHAPTER 15- Structure & Function of the Neurologic System Afferent (ascending) is used to describe things like nerves, blood vessels, and arteries that lead TOWARD or bring things (like...

UNIT 2 STUDY GUIDE NU 545- Pathophysiology Ch. 15 CHAPTER 15- Structure & Function of the Neurologic System Afferent (ascending) is used to describe things like nerves, blood vessels, and arteries that lead TOWARD or bring things (like blood, in the case of arteries) to an organ, such as the heart or brain. Efferent (descending) is used to describe parts that carry or lead things AWAY from organs or other parts. Support cells of the Nervous System: CNS: Astrocytes: Form specialized contact between neuronal surfaces and blood vessels Provide rapid transport for nutrient and metabolites Thought to form an essential component of blood brain barrier Appear to have scar-forming cells of CNS, which may be foci for seizures Appear to work with neurons in processing information and memory storage Oligodendroglia (oligodendrocytes) Formation of myelin sheath in CNS Microglia Responsible for cleaning cellular debris (phagocytic properties) and the key immune cell in the CNS Ependymal Cells Serve as a lining for ventricles and choroid plexuses involved in production of CSF Peripheral Nervous System: Schwann cells o Formation of myelin sheath within PNS Nonmyelinating Schwann Cells o Provide neuronal metabolic support and regeneration in PNS Satellite glial cells o Surround sensory, sympathetic and parasympathetic nerve cell bodies and ganglia to provide protection and promote cellular communication (similar to astrocytes in CNS) What nerves are capable of regeneration? Mature neurons do not divide and injury in the CNS causes permanent loss of damaged neurons. Crushed nerves recover better than cut nerves. Myelinated fibers in the PNS can repair themselves through axonal reaction Local changes occur when the axon is severed: 1. Cut ends retract and the axolemma covers the cut ends, diminishing the escape of axoplasm 2. Macrophages and Schwann cells begin to phagocytize damaged tissue 3. The cell body undergoes chromatolysis with swelling, loss of Nissl bodies, and the lateral migration of the nucleus 4. Antegrade (Wallerian) degeneration occurs in the distal axon 5. A characteristic swelling appears in the axon terminal and it degenerates and loses contact with the post synaptic membrane within 7 days 6. Macrophages and Schwann cells phagocytize the remnants of the axon terminal 7. Schwann cells proliferate, forming a column or tube of Schwann cells enclosed by the original basal lamina of the endoneurium. 8. Retrograde changes occur at the proximal end of the injured axon and are similar to antegrade changes but only back to the next node of Ranvier. Approximately 7-14 days after the injury, new terminal sprouts project from the proximal segment guided by Schwann cells and enter the sustaining substrate of a more detailed representation of these events o This process is very slow, about 1mm/day, and is limited to myelinated fibers in the PNS. o The closer the injury is to the cell body of the nerve, the greater the chances that the nerve cell will die and not regenerate  o Peripheral nerves injured close to the spinal cord recover poorly and slowly because of the long distance between the cell body and the peripheral termination of the axon. The regeneration of axonal constituents in the CNS is limited by an increased incidence of glial scar formation (gliosis) and the different nature of myelin formed by the oligodendrocyte Nerve regeneration depends on many factors: o Location of the injury o The type of injury: crushing injury allows recovery more fully than does a cut injury ▪ Crushed nerves sometimes fully recover, whereas cut nerves often form connective tissue scars that block or slow regenerating axonal branches o The presence of inflammatory responses o The process of scarring Cranial Nerve Origin & Course Function I. Olfactory Fibers arise from nasal Purely sensory; carries impulses for sniff aromatic substances identify them olfactory epithelium & form sense of smell synapses with olfactory bulbs that transmit impulses to temporal lobe II. Optic Fibers arise from retina of eye Purely sensory; carries impulses for Vision and visual field tested with an eye chart to form optic nerve, which vision and by testing point at which person first sees an passes through sphenoid bone; object (finger) moving into visual field; inside of two optic nerves then form eye is viewed with ophthalmoscope to observe optic chiasma (with partial blood vessels of eye interior crossover of fibers) III. Oculomotor Fibers emerge from midbrain Contains motor fiber to inferior Pupils examined for size, shape, and equality; & exit from skull & extend to oblique & to superior, inferior & pupillary reflex tested with a penlight (pupils eye medial rectus extraocular muscles should constrict when illuminated); ability to that direct eyeball; levator muscles of follow moving objects eyelid; smooth muscles of iris & ciliary body; and proprioception (sensory) to brain from extraocular muscles IV. Trochlear Fibers emerge from posterior Proprioceptor & motor fibers for Tested in common with cranial nerve III relative midbrain & exit from skull to superior oblique muscles of eye to ability to follow moving objects run to eye (extraocular muscles) V. Trigeminal Fibers emerge from pons and Both motor & sensory for face; Sensations of pain, touch, and temperature tested form three divisions that exit conducts sensory impulses from with safety pin and hot and cold objects; corneal from skull and run to face and mouth, nose, surface of eye, and dura reflex tested with a wisp of cotton; motor branch cranial dura mater mater; also contains motor fibers that tested by asking subject to clench teeth, open stimulate chewing muscles mouth against resistance, and move jaw from side to side VI. Abducens Fibers leave inferior pons and Contains motor fibers to lateral rectus Tested in common with cranial nerve III relative exit from skull, and extend to muscle and proprioceptor fibers from to ability to move each eye laterally eye same muscle to brain VII. Facial Fibers leave pons and travel Mixed: (1) supplies motor fibers to Anterior two-thirds of tongue tested for ability to through temporal bone & muscles of facial expression and to taste sweet (sugar), salty, sour (vinegar), and bitter extend to face lacrimal and salivary glands and (2) (quinine) substances; symmetry of face checked; carries sensory fibers from taste buds subject asked to close eyes, smile, whistle, and so of anterior part of tongue on; tearing tested with ammonia fumes VIII. Fibers run from inner ear Purely sensory; vestibular branch Hearing checked by air and bone conduction by Vestibulocochlear (hearing & equilibrium transmits impulses for sense of use of a tuning fork; vestibular tests: Bárány and receptors in temporal bone) to equilibrium; cochlear branch caloric tests enter brainstem just below pons transmits impulses for sense of hearing IX. Glossopharyngeal Fibers emerge from midbrain Mixed: (1) motor fibers serve Gag and swallow reflexes checked; subject asked and leave skull and extend to pharynx (throat) and salivary glands, to speak and cough; posterior one-third of tongue pharynx, salivary glands and and (2) sensory fibers carry impulses may be tested for taste tongue from pharynx, posterior tongue (taste buds), and pressure receptors of carotid artery X. Vagus Fibers emerge from medulla, Fibers carry sensory & motor Same as for cranial nerve IX (IX and X are tested pass through skull, and impulses for pharynx; a large part of in common) because they both serve muscles of descending through neck region this nerve is parasympathetic motor the throat into thorax and abdominal fibers, which supply smooth muscles region of abdominal organs; receives sensory impulses from viscera XI. Spinal Accessory Fibers arise from medulla & Provides sensory & motor fibers for Sternocleidomastoid and trapezius muscles superior spinal cord & extend to sternocleidomastoid and trapezius checked for strength by asking subject to rotate muscles of neck & back muscles of soft palate, pharynx, and head and shrug shoulders against resistance larynx XII. Hypoglossal Fibers arise from medulla & Carries motor fibers to muscles of Subject asked to stick out tongue, and any exit from skull & extend to tongue & sensory impulses from position abnormalities are noted tongue tongue to brain Review the anatomy of the brain.  The Brain: allows individuals to reason, function intellectually, express personality and mood, and interact with the environment. Weighs approximately 3 lbs. but receives 15%-20% of total cardiac output THREE MAJOR DIVISIONS OF THE BRAIN PRIMARY VESICLES SECONDARY VESICLES ASSOCIATED STRUCTURES FOREBRAIN (prosencephalon) Cerebral hemispheres Telencephalon Cerebral cortex Rhinencephalon (olfaction) Basal ganglia Epithalamus Diencephalon Thalamus Hypothalamus Subthalamus MIDBRAIN Mesencephalon Tectum (corpora quadrigemina) Connects the Pons to the Tegmentum diencephalon Red nucleus Substantia nigra Cerebral peduncles HINDBRAIN Mentencephalon Cerebellum (rhombencephalon) Pons Myelencephalon Medulla Oblongata BRAINSTEM Comprised of the midbrain, pons, and medulla oblongata Connects the left / right hemispheres, cerebellum, and spinal cord Reticular formation / reticular activating system SPINAL CORD Spinal cord  THE CEREBRAL HEMISPHERE The Cerebral Hemispheres. A) Left hemisphere of cerebrum, lateral view B) Functional areas of cerebral cortex, midsagittal view C) Functional areas of the cerebral cortex, lateral view FOREBRAIN (prosencephalon)  Telencephalon Frontal Lobe Prefrontal area 1. Goal-oriented behavior 2. Short term memory 3. Concentration 4. Elaboration of thought 5. Inhibition on limbic area (emotional region of the brain) 6. Executive attention functions (problem solving, planning) Premotor area 1. Programs motor movement: (Brodmann area 6) a. Contains cell bodies that form part of the basal ganglia system - extrapyramidal system 2. Controls eye movement a. Brodmann area 8 b. Middle frontal gyrus Primary motor area 1. Primary voluntary motor = somatotopic organization (Brodmann area 4) (Homunculus = little man) 2. Cerebral cortex → central impulses control the opposite side of the body = contralateral control Broca speech area 1. Motor aspect of speech (Brodmann area 44, 45) 2. Speech and language processing area **most important in the 3. Dysfunction (damage from CVA) may result in inability left hemisphere to form words → expressive aphasia or dysphasia Parietal Lobe Somatic sensory input 1. Provides communication between motor and sensory (Brodmann areas 3, 1, 2) areas 2. Storage, analysis, and interpretation of stimuli Temporal Lobe Primary auditory cortex (Brodmann area 41) Wernicke area 1. Sensory speech area (Brodmann area 22) 2. Reception and interpretation of speech (superior temporal gyrus) 3. Dysfunction / damage may result in receptive aphasia or dysphasia 4. Secondary function of balance Memory consolidation and smell Occipital Lobe Primary visual cortex Receives input from the retinas (Brodmann area 17) Remainder of lobe Visual association (Brodmann areas 18, 19) Corpus Callosum Bundle of myelinated fibers that connects the two cerebral hemispheres (conveying contralateral projection) which is essential in coordinating activities between hemispheres Limbic System Located between the 1. Mediates emotion and long-term memory through connections in telencephalon and the prefrontal cortex diencephalon and 2. Primitive behavioral responses and visceral reaction to emotion, surrounding the corpus feeding behaviors, biologic rhythms and sense of smell callosum 3. Expression of affect (emotion and behavioral state) → mediated by connections with limbic system and prefrontal cortex 4. Consolidation of memory → reverberating circuit Diencephalon (Interbrain) Surrounded by the cerebrum and sitting on top of the brainstem; has four divisions Epithalamus Forms the roof of the 3rd 1. Controls vital functions and visceral activities ventricle; composes the 2. Closely associated with the limbic system most superior portion Thalamus Largest component of the 1. Major center for afferent (SENSORY) impulses to the cerebral diencephalon; surrounds cortex the third ventricle 2. Cortical processing = interpretation of sensations 3. Relay center for information from the basal ganglia and cerebellum to appropriate motor area Hypothalamus Forms ventral part 1. Main functions: (a) Maintains constant internal environment (b) Implements behavioral patterns 2. Visceral and somatic responses 3. Affectual responses 4. Hormone synthesis (endocrine function) 5. Sympathetic / Parasympathetic control (autonomic nervous system function) 6. Body temperature regulation 7. Feeding responses 8. Regulation of physical expression of emotions 9. Sexual behavior 10. Pleasure-punishment centers 11. Level of arousal or wakefulness Subthalamus Lateral to hypothalamus Important basal ganglia center for motor activities MIDBRAIN (mesencephalon) Connects the frontal lobe with the hindbrain; composed of 3 structures Tectum (corpora Roof of the midbrain; 1. Superior colliculi – voluntary and involuntary visual motor quadrigemina) includes superior colliculi movements and inferior colliculi a. Ability for the eyes to track moving objects in the visual field 2. Inferior colliculi – similar motor activities but involve movements affecting the auditory system (positioning the head to improve hearing) a. Major relay center along the auditory pathway Tegmentum Floor of the midbrain; 1. Provides communication between motor and sensory areas includes red nucleus and 2. Storage, analysis, and interpretation of stimuli substantia nigra Red nucleus 1. Receives ascending sensory information from the cerebellum and projects a minor motor pathway (rubrospinal tract) to the cervical spinal cord Substantia nigra 1. Synthesizes dopamine 2. Dysfunction of dopaminergic neurons in the substantia nigra is associated with: a. Parkinson disease and schizophrenia Cerebral peduncles Anterior midbrain; made 1. Contains nuclei of the cranial nerves III & IV up of fibers that link to 2. Cerebral aqueduct (aqueduct of Sylvius) = carries CSF cortex of the brainstem between 3rd and 4th ventricles →obstruction of the aqueduct is common cause of hydrocephalus HINDBRAIN Mentencephalon Cerebellum Composed of two lobes 1. Responsible for reflexive, involuntary fine-tuning of of gray and white motor control (conscious and unconscious muscle matter; divided by energy) central fissure; 2. Maintaining balance and posture (via connections with connected by the vermis the medulla and the midbrain) 3. Control of the body = ipsilateral (same side) 4. Damage to the cerebellum is characterized by loss of equilibrium, balance, and motor coordination on the same side Pons “bridge” 1. Transmits information from the cerebellum to the below the midbrain and brainstem (between the two hemispheres) above the medulla 2. Contains nuclei of the 5th-8th (V-VIII) cranial nerves 3. Aids in controlling respirations Myelencephalon Medulla Oblongata Lowest portion of the 1. Aids in controlling reflex activity: brainstem a. Heart rate b. BP c. Respirations d. Coughing e. Sneezing f. Swallowing g. Vomiting 2. Contains nuclei of the IX through XII cranial nerves 3. Sleep-wake rhythms BRAINSTEM Comprised of the midbrain, pons, and medulla oblongata Connects the two hemispheres, cerebellum, and spinal cord Reticular Large network of 1. Controls vital reflexes: Formation diffuse nuclei that a. Cardiovascular connect the brainstem to b. Respiration function the cortex 2. Vomiting, yawning, and hiccups = reflex-like motor responses “Reticular Reticular formation + 1. Essential for maintaining consciousness/wakefulness Activating Cerebral cortex and attention System” Which portion is responsible for keeping you awake, controlling thought, speech, emotions and behavior, maintaining balance and posture? Reticular Formation Prefrontal area Broca speech area Wernicke area (Brainstem) (Forebrain) (Forebrain) (Forebrain-temporal lobe) Regulates vital reflexes Goal-oriented behavior Motor aspects of speech Reception and (cardiovascular function (i.e. ability to (usually on left interpretation of speech and respiration) concentrate) hemisphere); (superior temporal gyrus) RAS: Short-term or recall Damage to this area (ex. Secondary function of Essential for maintaining memory CVA) results in inability balance wakefulness. to form words, called Elaboration of thought expressive aphasia or Damage to this area dysphasia. results in difficulty Inhibition on the limbic understanding words or (emotional) areas of the written language, called CNS. receptive aphasia or Limbic system Hypothalamus Cerebellum (Hindbrain) dysphasia. (Forebrain) (Forebrain) Primitive behavioral Maintenance of a Conscious and responses constant internal unconscious muscle environment synergy Visceral reaction to emotion Implementation of Maintaining balance and behavioral patterns posture Feeding behaviors Integrative centers Damage to the Biologic rhythms control function of the cerebellum is ANS characterized by Sense of smell ipsilateral (same side) Regulation of body loss of equilibrium, Expression of affect temperature balance, and motor (emotional and coordination behavioral states) Regulation of endocrine system Consolidation of memory Regulation of emotional expression What part of the brain must be functioning for cognitive operations? The neural systems essential to cognitive function are: o Attentional systems that provide arousal and maintenance of attention over time o Memory and language systems by which information is communicated  o Affective or emotive systems that mediate mood, emotion, and intentions. Cognitive cerebral functions require a functioning reticular activating system → regulates aspects of attention, information processing, and maintains consciousness. Awareness (content of thought) encompasses all cognitive functions (including awareness of self, environment, and affective states – moods) Awareness is mediated by the core networks (selective attention and memory) under the guidance of executive attention networks (the networks that involve abstract reasoning, planning, decision making, judgment, error correct, and self-control) Each attentional function is not localized in a single brain area but is a network of interconnected brain circuits. Prefrontal cortex is involved in cognitive functions such as planning and evaluating outcomes, and consequences for actions o The prefrontal area mediates several cognitive functions (executive attention functions – planning, problem solving, goal-setting) It is responsible for goal-oriented behavior (i.e., ability to concentrate), short-term or recall memory, and elaboration of thought and inhibition on the limbic (emotional areas of the CNS) Which part of the brain controls movement of the eye? Six extrinsic eye muscles (attached to the outer surface of each eye) allow gross eye movements and permit the eyes to follow a moving object. o These muscles arise from the common tendinous ring in the orbit, the eye cavity, and attach to the eyeball. o The six muscles are: 1. Lateral rectus muscle 2. Medial rectus muscle 3. Inferior rectus muscle 4. Superior rectus muscle 5. Inferior oblique muscle 6. Superior oblique muscles o When muscles contract it causes movement of the eyeball, by pulling the eyeball towards the muscle. The frontal eye fields (lower portion of Brodmann area 8): o Controlling eye movements, are in the middle frontal gyrus The superior colliculi of the midbrain: o Voluntary and involuntary visual motor movements o e.g. the ability of the eyes to track moving objects in the visual field Abnormal ocular movements occur because of oculomotor, trochlear, or abducens cranial nerve dysfunction (e.g., strabismus, nystagmus, and paralysis of individual extraocular muscles) o Oculomotor: fibers emerge from midbrain (oculomotor nucleus) o Trochlear: fibers emerge from posterior midbrain (trochlear nucleus) o Abducens: fibers leave inferior pons (abducens nucleus) Occipital lobe lies caudal to the parietooccipital sulci and superior to the cerebellum. Primary visual cortex (Brodmann area 17) is in this region and receives input from the retinas. Much of the remainder of this lobe is involved in visual association (Brodmann areas 18, 19). Discuss the types of mid-brain dysfunction and its physical symptoms. Midbrain: a relay center for some motor and sensory tracts, as well as a center for auditory and visual reflexes, temperature control, sleep-wake cycles, arousal, and attention. o Damage to the midbrain can result in: ▪ A wide variety of movement disorders ▪ Difficulty with vision and hearing ▪ Trouble with memory Tectum (Corpora Quadrigemina) (roof of the midbrain): o Disorders of selective attention related to visual orienting behavior are produced by disease that involves portions of the midbrain ▪ Superior colliculi: responsible for involuntary and voluntary visual motor movements (i.e. ability to track moving objects in the visual field); disease manifests as slowness in orienting attention ▪ Inferior colliculi: responsible for movement affecting the auditory system (i.e. positioning head to improve hearing); relay center along the auditory pathway Tegmentum (floor of the midbrain): o Red nucleus: receives ascending sensory information from the cerebellum → minor motor pathway (rubrospinal tract) → cervical spinal cord o Substantia nigra (inferior portion of the basal ganglia): ▪ Synthesizes dopamine (neurotransmitter and precursor of norepinephrine) ▪ Dysfunction of this structure is associated with Parkinson’s disease Schizophrenia Huntington’s disease Drug addiction Multi-system atrophy o Damage to tegmentum near hypothalamus and third ventricle → akinetic mutism (neither to move [akinesia] nor speak [mutism]) Cerebral peduncles (anterior midbrain): o Made up of efferent fibers of the corticospinal, corticobulbar, and corticopontocerebellar tracts (tracts that link the cortex to the brainstem) o Cerebral aqueduct (aqueduct of sylvius): ▪ Carries CSF between 3rd / 4th ventricle → obstruction → hydrocephalus Because the midbrain houses the hypothalamus, it also plays a major role in automatic body functions. Other notable structures include: o Nuclei of the third and fourth cranial nerves (pupils) → mid-position pupils o CNS damage or disease affecting lower midbrain →Central reflex hyperpnea (brainstem breathing pattern) o Severe damage to midbrain/upper pons → decerebrate (abnormal posturing – internal rotation with hyperpronation of forearms) Syndromes associated with midbrain pathology include the Weber, Claude, Benedikt, Nothnagel, and Parinaud syndromes  o Parkinsonism is a neurologic condition characterized by tremors, rigidity, hypokinesia, and postural instability because of degeneration of the corpus striatum or substantia nigra. What is the function of the CSF? CSF is a clear, colorless fluid like blood plasma and interstitial fluid. Intracranial and spinal cord structures float in the CSF and are thereby partially protected from jolts and blows, and the buoyant properties of CSF also prevent the brain from tugging on meninges, nerve roots, and blood vessels. Where is CSF produced? Where is CSF absorbed? CSF is produced by the choroid plexus (rich network of blood vessels supplied arising from the pia mater) function to produce cerebrospinal fluids (CSF) o Lies in close contact with ventricular ependymal cells o Tight junctions of the choroid blood vessel providing a limiting barrier between the CSF and blood that functions similarly to the Blood-Brain Barrier CSF does not accumulate and is reabsorbed by means of a pressure gradient between the arachnoid villi and the cerebral venous sinuses. CSF is derived from the blood, and after circulating throughout the CNS, it returns to the blood Know the function of the arachnoid villi. Protrude from the arachnoid space, through the dura mater, and lie within the blood flow of the venous sinuses. The villi function as one-way valves, directing CSF outflow into the blood but preventing blood into the subarachnoid space CSF reabsorbed between arachnoid villi & cerebral venous sinuses Review blood flow to the brain. The brain receives approx. 20% of the cardiac output or 800 to 1000 mL of blood flow per minute CO2 serves as the primary regulator for blood flow (CO2 = powerful vasodilator that effects ensures adequate blood supply) Brain derives arterial blood supply from two systems: Internal carotid arteries (anterior circulation)  o Greater amount of blood flow (80% of blood blow to brain) o Originate from common carotid arteries → enter through cranium (base of skull) →cavernous sinus → divide into: ▪ Anterior cerebral artery ▪ Middle cerebral artery Vertebral arteries (posterior circulation) (supplies 20% of blood flow to brain) o Originate at subclavian →pass through the transverse foramina of the cerebral vertebrae →entering the cranium (through the foramen magnum)→ join at the junction of the pons and medulla oblongata →form the basilar artery o Basilar artery divides at the midbrain to form three paired posterior cerebral arteries (perfuse cerebellum and brainstem): ▪ Posterior inferior cerebellar artery ▪ Anterior inferior cerebellar artery ▪ Superior cerebellar arteries o Basilar artery also gives rise to small pontine arteries The larger arteries on the surface of the brain and their branches are called the superficial arteries (or conducting arteries), with the small branches that project into the brain called projecting arteries (or nutrient arteries) Circle of Willis (arterial circle) provides alternative route for blood flow when a contributing artery is obstructed and is comprised of: posterior cerebral arteries posterior communicating arteries internal carotid arteries anterior cerebral arteries anterior communicating artery