Chapter 11/12 short answers
List four chemical classes of neurotransmitter. Give an example of each and a brief description of how it works or what it's known for. ALSO: What are the most important inhibitory and excitatory central nervous system neurotransmitters?
1. ACETYLCHOLINE: All neurons stimulating skeletal MUSCLES, some in autonomic nervous system. example: nicotinic Ach receptors. (Located on muscular junctions, that bind substances and release others) 2. BIOGENIC AMINES: These are in-direct neurotransmitters and do not bind to receptor channels. Instead, bind to G-protein receptors. example: Dopamine. This is a reward/positive behavior neurotransmitter. 3. AMINO ACIDS: Located in central nervous system and always in the blood. example: Glutamate. Important in learning and memory. Found in the spinal cord and brain. **Glutamate - the most abundant EXCITATORY neurotransmitter in the CNS **Glycine - the most abundant INHIBITORY neurotransmitter in the CNS 4. PEPTIDES: These are short chains of amino acids. Example:Endorphins reduce perception of pain "natural opiates" by minding morphine.
An 86-year-old patient with Alzheimer's disease was admitted to the hospital with dehydration. Her daughter states that her mother has been very confused and combative lately. What are the MAIN PARTS of the diencephalon and what are their functions? Explain why the patient developed dehydration.
Alzheimer's disease is a neurodegenerative disease characterized by progressive neuron death and loss of brain function. The main components of the diencephalon are the thalamus and the hypothalamus. Functions of the Thalamus: -Relay between ascending inputs and cerebral cortex -Inputs from all sensory neurons, basal nuclei, hypothalamus, premotor cortex, cerebellum Outputs - primary somatosensory cortex, premotor cortex, many parts of the cerebrum Sorts edits and enhances sensory information -Roles in sensation, motor activity, cortical arousal, learning, memory Hypothalamus -caps brain stem, forms floor of third ventrical -mammillary bodies bulge from inferior surface - olfactory relays -Visceral control center Inputs: limbic system (emotional state), thalamus, cells that sense blood pressure, body temp, plasma osmolarity Outputs: medulla oblongata (cardiovascular and respiratory centers), pituitary gland Autonomic control center - blood pressure, heart rate, respiration, GI tract Visceral response to emotional state Body temp - causes sweating, shivering, blood vessel constriction or dilation Hunger/Food intake - senses glucose, amino acid levels Thirst - water balance Sleep cycle Endocrine system - connects to pituitary gland In this case, the patient has become severely dehydrated. The hypothalamus, which controls thirst, may have become damaged by the Alzheimer's; also, other cerebral regions may be involved, affecting her motivation or even ability, to follow through and get water.
Because all action potentials are alike, how does the brain distinguish between situations that require immediate attention from ordinary "positional" inputs (the feather versus the hammer stimuli)?
Graded potentials are the strength signals depending on the intensity of the stimuli. So.... the graded potentials on sensory neuron and post-synaptic neuron dendrites are DEPOLARIZATIONS that are proportional to the stimulus INTENSITY. If the depolarization reaches THRESHOLD at the axon hillock, an action potential will occur and travel down the axon; as long as the hillock remains at or above threshold, action potentials will continually be produced. The greater stimulus INTENSITY, the greater the graded DEPOLARIZATION, and the more FREQUENT the action potentials. So, stimulus intensity is encoded as action potential FREQUENCY.
What is gray matter in the cerebral cortex? What are nuclei in the central nervous system? Which white matter tracts connect the cerebrum to the lower brain areas? Which connects the hemispheres of the cerebrum?
Gray matter called the cerebral is made up of neuron cell bodies. Nuclei in the central nervous system are regions deep to the cortex also made up of neuron bodies. The white matter containing axon tracts connecting the cerebrum to lower brain areas are called projection fibers. Fibers connecting the hemispheres of the cerebrum make up the corpus callosum, as well as the anterior and posterior commissures.
Diagram the divisions of the nervous system, indicating in each case the direction of information flow. ( the different divisions of the nervous system)
Information flows between the Central nervous system and the peripheral nervous system. Central nervous system CNS: brain and spinal cord, integration/control centers Peripheral nervous system PNS: Cranial nerves and spinal nerves, communication throughout body PERIPHERAL NERVOUS SYSTEM breaks into sensory division and motor division Sensory division: somatic and visceral sensory nerve fibers. Conducting impulses to CNS Motor division: motor nerve fibers. Conducting impulses from CNS THEN MOTOR DIVISION breaks into somatic and autonomic nervous system Somatic nervous system: voluntary Autonomic nervous system: involuntary THEN AUTONOMIC NERVOUS SYSTEM breaks into sympathetic division and parasympathetic division Sympathetic division: mobilizes body system during activity Parasympathetic division: Conserves energy and promotes functions at rest
11. Be able to identify on a drawing the following areas, and explain the main function of each: primary motor cortex, premotor cortex, primary somatosensory cortex, somatosensory association cortex, visual and auditory areas, prefrontal cortex, and Broca's area.
LABELINGGGGG. Primary motor cortex: transfer neuron signals to the body and its movement Premotor cortex: helps in integrating sensory and its motor information Primary somatosensory cortex: It receives sensory information from the senses. It is responsible for processing somatic sensations. Somatosensory association cortex: responsible for retrieving and processing sensory information. Visual and auditory areas: Perceives sight and sound Prefrontal cortex: cognitive control. As well as intelligence and memory. Broca's area: where speech is produced. It also regulates breathing.
A patient is admitted to the hospital with exacerbation (flare-up) of multiple sclerosis (MS). What is the disease process in MS, and what is the role and mechanism of action of the normal structures?
Multiple sclerosis (MS) is an AUTOIMMUNE disease characterized by DESTRUCTION of the myelin sheath of myelinated neuron axons. The myelin sheath serves to greatly INCREASE the rate of action potential conduction, and insulate axons from one another. The result is compromised axon conduction SPEED, and severe sensory and motor impairment. Under NORMAL conditions, the myelin sheath SPEEDS the transmission of action potentials along the axon. The sodium and postassium channels are found only at the gap of the myelin sheaths, so that's where action potentials (rapid depolarization) occur. Because the myelin sheath prevents ions from crossing the membrane, the depolarization can spread very QUICKLY from node to node by local currents WITHOUT dying out; the AP appears to skip from node to node along the axon.
Imagine a neuron that has several hundred axonal knobs impinging on it. The majority of these axonal knobs are shown to be "firing." However, the neuron in question DOES NOT transmit an impulse. Give a valid explanation of WHY this could occur, using details. When would such a neuron have an action potential?
Neurotransmitters that activate Na+/K+ channels lead to membrane depolarizations known as excitatory post-synaptic potentials (EPSP) AND those that open potassium channels cause hyperpolarization of the membrane, or inhibitory post-synaptic potentials (IPSP). The COMBINED summation of multiple synaptic events may yield net depolarization, no change, or net hyperpolarization, depending on the number and FREQUENCY of EPSPs and IPSPs. SOOO.. there could be a great deal of activity at many synapses, but no action potentials produced in the post-synaptic neuron.
What is conus medullaris? What clinical procedure takes advantage of its location? What is the cauda equina and why is it given this name?
The conus medullaris represents the inferior-most extent of the spinal cord, and is located in the upper lumbar region of the spinal column. Spinal tap, a procedure for sampling the cerebrospinal fluid for microorganisms or chemicals, is performed by inserting a needle between lumbar vertebrae 3 and 4, below the conus medullaris, eliminating the risk of spinal cord injury during the lumbar puncture. The cauda equina is an array of nerves that continues inferiorly from the conus medullaris, and that gives rise to the lower lumbar, sacral, and coccygeal spinal nerves.
Explain the process of forming long-term memories, including the major brain structures involved. What are some physical changes that occur during memory formation? List factors that can enhance the transfer of information from short-term memory to long-term memory.
Process of long term memories: 1. Starts with sensory in SOMATOSENSORY CORTEX 2. Signals to HIPPOCAMPUS AND AMYGDALA: Where it stores memories with other memories. creates mechanism for later access. 3. Then to the THALAMUS, BASAL FOREBRAIN and PREFRONTAL CORTEX 4. signals from BASAL FOREBRAIN complete a lisp back to SENSORY CORTEX. (process is repeated because rehearsal strengthens memory) 5. recalling it stimulates the same neurons. Which involved prefrontal cortex, hippocampus (learning) and amygdala (which links memories with emotions) PHYSICAL CHANGES: -new neurons appear in hippocampus with learning -Changes occur in hippocampus -dendrites change shape for neurons to form new connections LAST PART OF QUESTION: LIST FACTORS THAT ENHANCE TRANSFER OF INFO FROM SHORT TO LONG -called memory consolidation -emotional state affects it -association helps
Describe the 3 phases of an action potential and the ionic changes that occur with each phase. i.e. which channels are opening and closing, and what happens as a result. Explain how an action potential is self-propagating.
Resting membrane: - at rest, the cell is negatively charged inside relative to the outside -there is an electrical potential difference, or voltage, across the membrane, called resting membrane potential. THREE PHASES: 1. DEPOLARIZATION Phase: sodium fast channels open, increasing sodium permeability of the membrane. Sodium enters the cell down its electrochemical concentration gradient, making the membrane LESS NEGATIVE inside (depolarizing the membrane) 2. REPOLARIZATION Phase: Sodium fast channels "inactivate" (close and are temporarily blocked) Potassium slow channels open, allowing potassium ions to leave the cell, making the interior more negative again (repolarizing the membrane) 3. REFRACTORY period: During and after an action potential, there is a delay. (called the refractory period) before another action potential can be triggered: - when the sodium gates are "inactivated", they cannot be reactivated for a brief period -during repolarization, the membrane actually becomes momentarily hyperpolarized, making it harder to reach threshold
What is a stroke, and are the two main types? What are the primary preventive measures to prevent these two types? A patient is admitted to the rehabilitation unit five days after having a stroke. The nurse assesses his muscle strength and determines that he has right-sided weakness. Based on this assessment data, what part of the brain was injured?
Strokes cause injury the brain, and are of two main types: Hemorrhagic - hypertension (high blood pressure) and atherosclerosis (artery disease) lead to blood vessel rupture, and bleeding, which kills neural tissue. Ischemic (insufficient blood flow) - blood clots that form in the circulation and later break free become lodged in the blood vessels of the brain, blocking flow to parts of the cerebrum, resulting in tissue injury and death. Strokes are prevented by treating hypertension, and by administration of anticoagulants to prevent blood clots in people with atrial fibrillation. The finding of right-sided muscle weakness suggests the stroke caused damage to the primary motor cortex in the left hemisphere; the upper motor neurons decussate, or cross over, on the anterior medulla oblongata.
What is the reticular formation, and where is it found? What is its role in cerebral function? Describe the role of the reticular activating system in cortical arousal and stimulation.
The Reticular Formation is a loose collection of neurons running through the BRAIN STEM. ROLE: Sensory inputs: visual and auditory Ouputs: hypothalamus, thalamus, cerebellum, spinal cord FUNCTION: -arousal of the brain as a whole - maintains alertness, consciousness RAS - reticular activating system The more sensory inputs it receives, the more it elevates the level of activity in the cortex. filters sensory inputs (weak, repetitive, familiar)
Which brain areas lack a blood-brain barrier, and what purpose does this absence serve? Name the three main parts of the brain stem, and describe some prominent features/functions of each.
The blood brain barrier is absent in: 1) the vomiting center (brainstem), which allows access to irritants and toxins 2) parts of the hypothalamus, which needs access to plasma to regulate water balance, body temperature, and metabolic activity The Brain Stem - includes the midbrain, pons, medulla oblongata 1.MIDBRAIN: -cerebral peduncles -cerebral aquaduct -visual reflex center -auditory center -reflex center -substantia nigra PONS: Deep - fibers from higher brain to spinal cord Superficial - relay (nuclei) motor cortex to cerebellum Cerebellar peduncles - connections between the cerebrum and the cerebellum MEDULLA OBLONGATA: fourth ventrical - fluid filled space on the ventral surface - decends into central canal of spinal cord Functions: Cardiovascular center - blood pressure Respiratory center - rate and depth of breathing, rhythm (with pons)
Parkinson's disease involves a decreased level of the neurotransmitter dopamine in the brain. However, Parkinson's patients can't take dopamine itself as a drug, because it cannot reach the brain. What anatomic structures prevent the drug from reaching the brain? How are the same structures beneficial under different circumstances? In what two areas of the brain is the brain much more accessible, and why?
The dopamine is prevented from reaching the brain extracellular fluid by the BLOOD BRAIN BARRIER. This barrier does NOT let most circulating chemicals into the CNS, such as neurotransmitters. Structures of the blood brain barrier that are beneficial: 1. endothelium (cells lining blood vessels) in CNS - many tight junctions 2. Thick capillary basement membrane 3. Astrocytes - "feet" wrap capillaries, capturing solutes that do escape the capillaries However, the blood brain barrier is incomplete in at least two areas of the brain: 1) vomiting center (aka posterior medulla) - allows sensation of irritants/toxins so the body knows to get rid of toxic stomach contents 2) hypothalamus - regulates water balance based on solute concentration (osmolarity) of plasma
Shannon was the pitcher on her softball team. During one game, a sharply hit ball ricocheted off the left side of Shannon's head, knocking her temporarily unconscious. She eventually regained consciousness, but experienced severe pain near her left temple. Within a few hours, Shannon had trouble moving her right upper limb, and became lethargic. Her team captain brought her to the emergency room, where the physician diagnosed her with epidural hematoma. Between what two structures had blood accumulated? Why did Shannon experience problems with her right upper limb - what brain structure was the hematoma most likely impinging upon?
The hematoma refers to hemorrhage into the space around the dura mater. The accumulation of blood was probably imposing pressure in the CEREBRUM, interfering with function. The particular location was the left primary motor cortex, interfering with the control of her right arm. The motor neurons cross over at the anterior medulla oblongata, so paralysis due to pressure on the motor cortex in the left hemisphere occurs on the right side, in this case, the right arm muscles.
Multiple sclerosis (MS) is a disease in which the myelin sheaths are destroyed. Describe the functions of the myelin sheath, and explain how it promotes impulse transmission. What would be the consequence of the disease changes associated with MS?
The myelin sheath insulates neuron axons to prevent crossing of impulses from one axon to another, and INCREASES the speed of impulses. Action potentials occur only at the gaps in the myelin sheath, because this is the only place where the sodium fast channels and potassium slow channels are located. Then, because of the myelin sheath, the depolarization spreads very quickly from node to node. Local currents do dissipate, but the action potential depolarization is renewed at each node. Autoimmune destruction of the myelin sheaths with MS greatly slows, and eventually eliminates, neuron action potential transmission, progressively impairing nervous system function.
Describe the mechanisms that give rise to the negative resting membrane potential typical of neurons.
sodium-potassium pump: Transports sodium out of the cell, and potassium into the cell. The pumping action creates concentration gradients for these ions: Na+ concentration is high outside the cell and low inside the cell, and potassium concentration is low outside the cell and high inside. Permeability: The cell is slightly permeable to these ions, and because of the gradients set up by the pumps, the ions leak across the membrane. At rest, its more permeable to potassium. so they initially leak out of the cell faster than sodiums leak in. As the positively charged K+ leave the cell, the cell interior is left with more negative charges than positives.
