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NU 545 Unit 2 Study Guide
CHAPTER 15 (p. 434-465) STRUCTURE OF THE NEUROLOGICALSYSTEM
1. Review the anatomy of the brain. Which portion is
responsible forkeeping you awake, controlling
thought, speech, emotions and behavior, maintaining
balance and posture?
- Allows individuals to reason, function intellectually, express personality and mood, and interact with the environment.
- Approx. 3 lbs. and consistency of tofu or custard
- Receives 15%-20% of total cardiac output
- Three major divisions : 1) Forebrain, 2) Midbrain, and 3) Hindbrain 1. Forebrain (F) (prosencephalon) which includes the telencephalon and diencephalon, two cerebral hemispheres Telencephalon: a. frontal lobe i. Prefrontal area: goal-oriented behavior, short-term memory, concentration, elaboration of thought, and inhibition on limbic areas(emotion region of brain) ii. Premotor area: programs motor movement (extrapyramidal system); Controls eye movement iii. Primary motor area: primary voluntary motor, somatotopicorganization (homunculus), Controls lowers limbs/feet iv. Broca Speech Area: motor aspect of speech – damage to this area results in the ability to form words (expressive dysphasia or aphasia), Speech & language processing area b. Parietal lobe i. Somatic sensory input: provides communication between motor andsensory areas; storage, analysis, and interpretation of stimuli c. Temporal lobe i. Primary auditory cortex ii. Wernicke area: reception and interpretation of speech iii. Involved in long-term memory and secondary function (balance, taste,and smell) d. Occipital lobe i. Primary visual cortex: receives input from retinas
ii. Remainder of lobe: visual association e. Corpus callosum: massive white matter pathway that connects the two
3. Hindbrain (H) (metencephalon & myelencephalon) includes the cerebellum, pons, and medulla
a. Cerebellum i. Conscious and unconscious muscle synergy ii. Maintains balance and posture b. Pons ( Bridge ) i. Aids in controlling respirations ii. Cranial nerves V – VIII c. Medulla oblongata i. Aids in controlling reflex activity (heart rate, respirations, BP, coughing, sneezing, swallowing, and vomiting) ii. Cranial nerves IX – XIII iii. Controls sleep wake rhythms
- Brainstem is comprised of the midbrain, medulla oblongata, and pons, andconnects the hemispheres of the brain, cerebellum, and spinal cord.
- Reticular formation : collection of nuclei within the brainstem; regulates vital reflexes, such as cardiovascular function and respiration, and is essential for maintaining wakefulness. o In conjunction with the cerebral cortex = reticular activating system.
- Prefrontal area (F): 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.
- Broca speech area (F): responsible for motor aspects of speech (usually on left hemisphere); damage to this area (ex. CVA) results in inability to form words, called expressive aphasia or dysphasia.
- Wernicke area (F): responsible for reception and interpretation of speech (superior temporal gyrus); damage to this area results in receptive aphasia or dysphasia.
- Limbic system (F): principal effects are believed to be involved with primitive behavioral responses , visceral reaction to emotion , feeding behaviors , biologic rhythms, and the sense of smell. Expression of affect (emotional and behavioral states) is mediated by extensive connections with the limbic system and prefrontal cortex. One of its major functions is the consolidation ofd memory through a reverberating circuit.
- Hypothalamus (F): responsible for two major functions: 1) maintenance of a constant internal environment, and 2) implementation of behavioral patterns. Integrative centers control function of the ANS, regulation of body temperature, function of the endocrine system, and regulation of emotional expression.
- Cerebellum (H): responsible for conscious and unconscious muscle synergy, and for maintaining balance and posture. Damage to the
4. What is the function of the CSF? Where is it produced?
Where is itabsorbed?
- 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,
andblood vessels.
- The choroid plexus in the lateral, third, and fourth ventricles produce themajor portion of CSF. The plexuses are characterized by a rich network of blood vessels, supplied by the pia mater, that lies in close contact with ventricular ependymal cells that secrete and absorb CSF.
- The CSF does not accumulate and is reabsorbed by means of a pressure gradient between the arachnoid villi and the cerebral venous sinuses – it is
reabsorbed into the venous circulation through the arachnoid villi
- The CSF is formed from the blood and after circulating through the CNS it returns to the blood
5. Review blood flow to the brain.
- The brain receives approx. 20% of the cardiac output or 800 to 1000 mL ofblood flow per minute.
- Derives arterial blood supply from two systems:
- Internal carotid arteries (anterior circulation) o After entering the skull, divide into anterior and middle cerebral arteries
- Vertebral arteries (posterior circulation) o Originate at subclavian arteries and pass through the transverse foramina entering the cranium through the foramen magnum o Join to form the basilar artery. Basilar artery divides at the midbrainto form paired posterior cerebral arteries. ▪ Three major paired arteries perfuse the cerebellum andbrainstem: (originate from the basilar) - The posterior inferior cerebellar artery - Anterior inferior cerebellar artery - Superior cerebellar arteries
- Circle of Willis (arterial circle) provides alternative route for blood flow when a contributing artery is obstructed. Formed by the posterior cerebral arteries, posterior communicating arteries, internal carotid arteries, anterior cerebral arteries, and anterior communicating artery. **Provides an alternative route for blood flow when one of the attributing arteries is obstructed.
6. What is the gate control theory of pain?
- Gate control theory (GCT) integrates and builds upon features of other theories (specificity theory, pattern theory, etc.) to explain the
“gate.” The spinal gate regulates pain transmission to higher centers in the CNS.
- Large myelinated A-delta fibers and small, unmyelinated C fibers respond toa broad range of painful stimuli (mechanical, thermal, and chemical) – these fibers terminate on interneurons in the substantia gelatinosa (laminae in the dorsal horn of the spinal cord). ▪ Nociceptive transmissions on these fibers “open” the spinalgate and increase the perception of pain.
- Non-nociceptive stimulation carried on larger, A-beta fibers, creates closure or partial closure of the spinal gates, and decreases pain perception.
7. Know the type of nerve fibers that transmit pain impulses.
Nociceptors are free nerve endings in the afferent peripheral nervous system that selectively respond to different chemical, mechanical and thermal stimuli. When stimulated they cause nociceptive pain. Nociceptors are categorized according to the stimulus to which they respond and by the properties of the axons associated with them. Nociception has four phases: transduction, transmission, perception, and modulation.
- A-delta (Aδ) fibers are lightly myelinated, medium-sized fibers that are stimulated by severe mechanical deformation or by mechanical deformation and/or extremes of temperature. o Transmit sharp, well-localized “fast” pain sensations. o Responsible for reflex withdraw of affected body part from the stimulus ▪ Ex: Pulling a hand away from a hot stove
- Unmyelinated C fibers are polymodal are stimulated mechanical, thermal,and chemical nociceptors. o Slowly transmit dull, aching, or burning sensations that are poorlylocalized and longer lasting.
- A-beta (Aβ) fibers are large myelinated fibers that transmit touch andvibration sensations. o Do NOT normally transmit pain o Play a role in pain modulation
8. Where in the CNS does pain perception occur?
Pain perception is the conscious awareness of pain that occurs primarily in the reticular and limbic systems and the cerebral cortex. Three systems interact to produce the perception of pain and it changes with age. o Sensory-discriminative system - medicated by the somatosensory cortex andis responsible for identifying the presence, character, location, and intensity of pain.
o Affective-motivational system - determines an individual’s conditioned
o Neuropathic pain- chronic pain initiated or caused by primary lesion or dysfunction in the nervous system and leads to long-term changes in painpathway structures and abnormal processing of sensory information.
o Peripheral neuropathic pain- caused by peripheral nerve lesions and anincrease in the sensitivity and excitability of primary sensory lesions neurons and cells in the dorsal root ganglion. o Central neuropathic pain- caused by a lesion or neuroplastic changes inthe brain or spinal cord. o Chronic pain syndromes include specific and nonspecific spinal pain, myofascial pain syndrome, chronic postoperative pain, cancer pain, central poststroke pain, phantom limb pain, complex regional pain syndrome.
10. Know endogenous opioids.
Endogenous Opioids are a family of morphine-like neuropeptides that inhibit transmission of pain impulses in the spinal cord, brain, and periphery. Their receptors play a role in various central nervous, gastrointestinal, immune, and other organ system disorders. There are 4 types of opioid neuropeptides that act as neurotransmitters by binding to one or moreG-protein-coupled opioid receptors.
- Enkephalins- most prevalent of the natural opioids; binds to the δ receptors; concentrated in the hypothalamus, the PAG matter, the nucleusraphe magnus of the medulla, and the dorsal horns of the spinal cord. Two types: i) Methionine-enkephalin (ratio to leucine-enkephalin is 4:1) ii) Leucine-enkephalins
- Endorphins (endogenous morphine)-produced in the hypothalamus and pituitary gland; binds to μ receptors in the hypothalamus and pituitary gland;produces the greatest sense of exhilaration as well as substantial natural painrelief.
- Dynorphins- most potent endogenous neurohormone, binding strongly with the κ receptors to impede pain signals in the brain; plays a role in mooddisorders and drug addiction and paradoxically in stimulating chronic pain. 4) Endomorphins- Endomorphins-1 and -2 bind with μ receptors throughoutthe brain, brainstem, and gastrointestinal tract and have analgesic, immune, and anti-inflammatory responses.
- Found to bind to almost all tissue in the body and thus affect numerousbiological functions.
thermal stimuli. When stimulated, they cause nociceptive pain. Nociceptors are categorized according to the stimulus to which they respond, and the properties associated with them.
- A-delta fibers are lightly myelinated, medium-sized fibers that are stimulatedby severe mechanical deformation or by mechanical deformation and/or extremes of temperature. o Rapidly transmit sharp, well-localized “fast” pain sensations - Unmyelinated C fibers are polymodal and stimulated by mechanical, thermal, and chemical nociceptors. A-beta fibers are large myelinated fibers that transmit touch and vibration sensations. o Slowly transmit dull, aching, or burning sensations that are poorlylocalized and longer lasting - Pain transmission is the conduction of pain impulses along the A-delta and C fibers in the dorsal horn of the spinal cord. Here they form synapses with the excitatory or inhibitory interneurons that branch int o the ascending or descending collaterals for one or two cord segments in the neuronal projectionscalled the dorsolateral tract. 12. What is the relationship between epinephrine and body temperature? Epinephrine causes vasoconstriction (improves thermal regulation), stimulatesglycolysis, and increases metabolic rate, thus increasing body heat. Heat is distributed by the circulatory system. - Heat production: hypothalamus + endocrine system hypothalamic hormone called thyroid stimulating hormone release hormone TSH-RH stimulates anterior pituitary to release TSH acts on thyroid gland to stimulate release of thyroxine (T1) acts on adrenal medulla causing release of epinephrine into the bloodstream - Body Heat is produced by the chemical reactions of metabolism and skeletalmuscle tone and contractions. The heat-producing mechanism begins with the hypothalamic thyrotropin-stimulating hormone-releasing hormone (TSH-RH) which stimulates the anterior pituitary to release thyroid-stimulating hormone (TSH), which acts on the thyroid gland and stimulates the release of thyroxine. Thyroxine then acts on the adrenal medulla, causing the release of epinephrine into the bloodstream.
13.Know mechanisms of heat
production andheat loss.
- In human, body temperature is maintained around 37C (98.6F) and rarelyexceeds 41C. The normal range is 36.2C to 37.7C.
- Temperature regulation (thermoregulation) is mediated by the hypothalamus;
d. Vasodilation: peripheral vasodilation increases heat loss by diverting core- warmed blood to the surface of the body. As the core-warmed blood passes through the periphery, heat is transferred by conduction to the skin surface and from the skin to the surrounding environment. Occurs in response to
autonomic stimulation under the control of the hypothalamus. e. Decreased muscle tone: to decrease heat production, muscle tone may be moderately reduced and voluntary muscle activity curtailed; this may explain in part the “washed-out” feeling associated with high temperaturesand warm weather. f. Evaporation: evaporation of body water from the surface of the skin and the linings of the mucous membranes is a major source of heat reduction. Insensible water loss accounts for about 600ml of water loss per day. Sweating may result in 2.2L of fluid lost per hour. Electrolytes are also lost. Large volume loss through sweating may result in decreased plasma volume,decreased BP, weakness, & fainting. Heat loss by sweating/evaporation is affected by: i. Sympathetic neural activity. ii. Favorable temperature difference between the body and theenvironment. iii. Humidity: when high, sweat does not evaporate and instead remainson the skin or drips, when low, evaporates quickly. g. Increased pulmonary ventilation: exchanging air with the environment through the normal pulmonary ventilation provides some heat loss, althoughit is minimal in humans. This normal process occurs faster at higher body temperatures through and increase in ventilator rates; thus, hyperventilation is associated with hyperthermia. h. Voluntary mechanisms: in response to high body temperatures, people physically “stretch out,” thereby increasing the body surface area availablefor heat loss. They also “take it easy,” thereby decreasing skeletal muscle work, and they “dress for warm weather” in garments that reflect heat and promote convection, conduction, and evaporation (light-colored, loose- fitting clothes). i. Heat adaptation: the body of an individual who goes from a cooler to a muchwarmer climate undergoes a period of adjustment, a process that takes several days to several weeks.
14. Know heat exhaustion and heat stroke?
- Heat exhaustion : or collapse , (most common heat related injury) is theresult of prolonged high core or environmental temperatures. o High temperatures cause the appropriate hypothalamic response ofprofound vasodilation and profuse sweating.
