A&P Exam 4 (chap 11 & 12)

CNS tells difference between a weak and strong stimulus by

*FREQUENCY* -frequency is the number of impulses (action potentials) recieved per second -higher frequencies mean stronger stimulus

spinal nerves

carry impulses to and from spinal cord

cranial nerves

carry impulses to and from the brain

primary somatosensory cortex of cerebral cortex

-located in the postcentral gyri of the parietal lobe, just posterior to the primary motor cortex -receive info from general (somatic) sensory receptors in the skin and proprioceptors (located in a joint, muscle, or tendon; concerned with locomotion, posture, and muscle tone) -spatial discrimination: identification of body region being stimulated -somatosensory homunculus, just like the primary motor cortex --->face and fingers most sensitive

vestibular (equilibrium) cortex of cerebral cortex

-located in the posterior part of the insula and adjacent parietal cortex -responsible for conscious awareness of balance (position of head in space)

primary (somatic) motor cortex

-located in the precentral gyrus of the frontal lobe of each hemisphere -made of *pyramidal cells*: large neurons that allow conscious control of precise, skilled, skeletal muscle movements --->form pyramidal tracts which project long axons down the spinal cord -somatotopy: all muscles of the body can be mapped to area on primary motor cortex --->motor homunculi: upside-down caricatures represent contralateral motor innervation of body regions

somatosensory association cortex of cerebral cortex

-located just posteriorly to the primary somatosensory cortex -integrates sensory inputs (temp, pressure, etc), relayed to it via the primary somatosensory cortex, to produce understanding of an object being felt (size, texture, and relationship of parts) -draws from memories to recognize things without seeing them

frontal eye field of cerebral cortex

-located partially in and anterior to the premotor cortex and superior to Broca's area -controls voluntary eye movements

retrograde amnesia

-loss of old memories -can form short term memories

cytoskeletal elements

-maintain cell shape and integrity -contain microtubules and neurofibrils (bundles of intermediate filaments)

neuronal pathways

-major spinal tracts are part of multineuron pathway that connect the brain and the body periphery -4 key points about spinal tracts and pathways 1. decussation: most pathways cross from one side of CNS to other side at some point 2. relay: consist of chain of two or three neurons 3. somatotopy: precise spatial relationship in CNS correspond to spatial relationship in body 4. symmetry: pathways are paired symmetrically with a member of the par present on each side of the spinal cord or brain

arachnoid mater

-middle layer with spiderweb like extensions -separated from dura mater by subdural space -subarachnoid space contains CSF and largest blood vessels of brain -arachnoid granulations protrude through dura mater into superior sagittal sinus --->permit reabsorption to CCSF back into venous blood

theta waves

-more irregular -common in children -uncommon in awake adults, but may appear when concentrating

memory

-storage and retrieval of info -different kinds of memory --->declarative (fact) memory: names, faces, words, dates --->procedural (skills) memory: playing piano --->motor memory: riding a bike --->emotional memory: ponding heart when you hear a rattlesnake nearby

polarized

Electrical condition of the plasma membrane of a resting neuron

secondary 5 brain vessicles

Forebrain divides into 1. telencephalon ("endbrain") 2. diencephalon ("interbrain") 3. Midbrain remains undivided hindbrain forms 4. metencephalon ("afterbrain") 5. myencephalon ("spinal brain") each of the five vesicles then divide rapidly to produces the major structure of the adult brain

parethesias

abnormal sensations (damage to dorsal roots)

propagation *nonmyelinated axons*

allows action potential to be transmitted from origin down entire axon length toward terminals

pia mater

-delicate connective tissue -contains many blood vessels -clings tightly to brain like seran wrap -small arteries entering the brain tissue carry ragged sheaths of pia mater inward with them for a short distance

Brain Wave Patterns and the EEG

-EEG = electroencephalogram -brain waves reflect electrical activity of higher mental functions -4 categories 1. alpha 2. beta 3. theta 4. delta 0brain waves with frequencies too high or too low suggest problems with cerebra cortical functions, and unconsciousness happens at both ends

diencephalon

-part of the forebrain between the cerebral hemispheres and the midbrain -3 main structures 1. thalamus 2. epithalamus 3. hypothalamus -enclose the third ventricle

synapse

-a junction that mediates info transfer from one neuron to the next or from a neuron to its effector cell, it's where the action is -the junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron

descending pathways and tracts

-deliver efferent impulses from brain to spinal cord -2 groups 1. direct pathways: pyramidal tracts 2. indirect pathways: all others -motor pathways involve 2 neurons 1. upper motor neurons: pyramidal cells in primary motor cortex 2. lower motor neurons: ventral horn motor neurons, innervate skeletal muscles

depolarization

-*relative to resting membrane potential* -decrease in membrane potential (moving toward 0 and above) --->the inside of the membrane becomes *less negative* than the resting potential --->probability of producing impulse increases

hyperpolarization

-*relative to resting membrane potential* -increase in membrane potential (moves farther from zero) --->the inside of the membrane becomes *more negative* than resting membrane potential --->probability of producing impulse decreases

declarative memory

-2 stages 1. short-term memory: temporary holding of info (limited to seven or eight pieces of info 2. long-term memory: limitless capacity, but memories can be forgotten, and declines with age -4 factors that influence transfer of short-term to long-term 1. emotional state: best if alert, motivated, surprised, or aroused (norepinephrine [neurotransmitter involved in memory] released) 2. rehearsal: repetition and practice helps us remember 3. association: tying "new" info to "old" info already stored in long term memory 4. automatic memory: subconscious info stored in ltm -memory consolidation: involves fitting new facts into categories already stored in cerebral cortex --->hippocampus, temporal cortical areas, thalamus, and prefrontal cortex are involved in consolidation

meninges

-3 connective tissue membranes that lie just external to the CNS 1. dura matter 2. arachonid mater 3. pia mater -the meninges 1. cover and protect the CNS 2. protect blood vessels and enclose venous sinuses 3. contain cerebrospinal fluid 4. form partitions in the skull

brain stem

-3 regions 1. midbrain 2. pons 3. medulla oblongata -each about an inch long -collectively account for only 2.5% of total brain mass -tissue organized similarly to spinal cord (deep gray matter surrounded by white matter fiber tracts), but has neuclei of gray matter embedded in the white matter -produce rigidly programmed, automatic behaviors necessary for survival -located between the cerebrum and spinal cord -provides a pathway for fiber tracts running between higher and lower neural centers -associated with 10 of the 12 cranial nerves

cerebellum

-accounts for 11% of brain mass -located dorsal to pons and medulla oblongata and intervening fourth ventricle -protrudes under the occipital lobes of the cerebral hemispheres -processes input from cortex, brain stem, and sensory receptors to provide precise, coordinated movements of skeletal muscles (for smooth, coordinated movements needed for daily living--driving, typing, and for some, tuba) -also plays major role in balance -bilaterally symmetrical -cerebral hemispheres connected by wormlike vermis -heavily convoluted with fine, transversely oriented pleatlike gyri, folida -each hemisphere has 3 lobes 1. anterior 2. posterior 3. flocculondular lobes -contains thin cortex of gray matter with distinctive treelike pattern of white matter called arbor vitae -contains purkinje cells: large, extensively branched dendrites, only cortical neurons that send axons through the white matter to synapse with the central nuclei of the cerebellum -humunkulli --->The medial portions influence the motor activities of the trunk and girdle muscles. --->The intermediate parts of each hemisphere influence the distal parts of the limbs and skilled movements. --->The lateralmost parts of each hemisphere integrate information from the association areas of the cerebral cortex and appear to play a role in planning movements rather than executing them. --->The flocculonodular lobes receive inputs from the equilibrium apparatus of the inner ears, and adjust posture to maintain balance. -ipsilateral: fibers are from and to the same side -3 paired fiber tracts connect cerebellum to brain stem 1. superior cerebellar peduncles: connect cerebellum to midbrain 2. middle cerebellar peduncles: connect pons to cerebellum 3. inferior cerebellar peduncles: connect medulla to cerebellum -cerebellum fine-tuned motor activity as follows 1. recieves impulses from cerebral cortex of intent to initiate voluntary muscle contraction 2. receives signals from proprioceptors throughout body, as well as visual and equilibrium pathways that continuously "inform" cerebellum of body's position and momentum 3. cerebellar cortex calculates the best way to smoothly coordinate muscle contraction 4. send "blueprint" of coordinated movement to cerebral motor cortex and brain stem nuclei -neuroimaging suggests that it also plays a role in thinking, language, and emotion -as in motor system, may compare actual output of these systems with expected output and adjust accordingly

oligodendrocytes

-also branch, but have fewer processes than astrocytes -line up along the thicker nerve fibers in the CNS and wrap processes tightly around the fibers producing insulating covering called myelin sheath

neuron cell body

-also called perikaryon or soma -consists of a spherical nucleus surrounded by cytoplasm -plasma membrane acts as part of the receptive region that receives info from other neurons -major biosynthetic center and metabolic center -contains 3 structures a. protein- and membrane-making machienery b. cytoskeletal elements c. pigment inclusions -most located in the CNS where they are protected by bones of the skull and vertebral column -clusters of cell bodies in CNS are called nuclei -clusters along the PNS are called ganglia

indirect pathways

-also referred to as multineuronal pathways -complex and multisynaptic -includes brain stem motor nuclei and all motor pathways except pyramidal pathways -these pathways regulate 1. axial muscles, maintaining balance and posture 2. muscles controlling coarse limb movements 3. head, neck and eye movements that follow objects in visual field -consist of 4 major pathways 1. reticulospinal and vestibulospinal tracts -maintain balance by varying tone of posteral muscles 2. rubrospinal tracts: control flexor muscles 3. tectospinal tracts: originate from superior colliucli and mediate head movements in respinse to visual stimuli

how sleep is regulated

-alternating cycles of wakefulness reflect natural circadian rhythm --->hypothalamus responsible for this -RAS (reticular activating syatem) activity is inhibited during sleep, but RAS also mediated sleep stages -superchiasmatic and preoptic nuclei of hypothalamus time sleep cycle --->releases orexins to help wake you up (to cortex)

axonal transport

-anterograde movement --->movement away from cell body --->substances include mitochondira, cytoskeletal elements, membrane components, and enzymes -retrograde movement --->movement toward the cell body --->subtances in this direction are mostely organelles returning to cell body to be degraded or recycled --->important for intracellular communication --->delivers vesicles to the cell body containing signal molecules

8 sensory areas of cerebral cortex

-areas of cortex concerned with conscious awareness of sensation -occur in parietal, insular, temporal, and occipital lobes 1. primary somatosensory cortex 2. somatosensory association cortex 3. visual areas 4. auditory areas 5. vestibular cortex 6. olfactory cortex 7. gustatory cortex 8. visceral sensory area

hypothalamus of diencephalon

-below the thalamus -caps the brain stem and forms the inferolateral walls of the third ventricle -extends from the optic chiasma to the posterior margin of the mammilary bodies -between optic chiasma and mammillary bodies is the infundibulum -main visceral control center of the body, virtually important to overall body homeostasis -chief roles --->controls autonomic nervous system -------->influences blood pressure, rate and force of heartbeat, digestive tract motility, eye pupil size, and more visceral activities --->initiate physical responses to emotions -------->heart of limbic system: perceives pleasure, fear, rage, biological rhythms, drives (sex) --->regulate body temp -------->shivering/sweating --->regulate food intake -------->based on blood levels (glucose/amino acids) or hormones --->regulates water balance and thirst -------->release ADH --->regulate sleep-wake cycles --->control endocrine system function -------->releasing and inhibiting hormones control secretion of hormones by the anterior pituitary -------->supraotic and paraventricular nuclei produce the hormones ADH and oxytocin -disturbances cause obesity, body wasting, sleep disturbances, etc

Inhibitory Synapses and IPSPs

-binding neurotransmitters at inhibitory synapses reduces a postsynaptic neuron's ability to generate an action potential

pigment inclusions

-black melanin (red iron-containing pigment) -lipofucin (golden-brown pigment --->by-product of lysosomal activity, called aging pigment seen in old people

gray matter and spinal roots

-cross section of cord resembles butterfly or letter "H" -three areas of gray matter are found on each side of center and are mirror images 1. dorsal horns: interneurons that receive somatic and visceral sensory input 2. ventral horns: some interneurons; somatic motor neurons 3. lateral horns (only in thoracic and superior lumbar regions): sympathetic neurons -gray commissure: bridge of gray matter that connects masses of gray matter on either side --->encloses central canal -ventral roots: bundle of motor neuron axons that exit the spinal cord -dorsal roots: sensory input to cord -dorsal root (spinal) ganglia: cell bodies of sensory neurons -spinal nerves: formed by fusion of dorsal and ventral roots -spinal gray matter is divided into four groups based on somatic or visceral innervation 1. somatic sensory (SS) 2. visceral sensory (VS) 3. visceral (autonomic) motor (VM) 4. somatic motor (SM)

electrochemical gradient

-determines the direction and ion moves (in or out of the cell) -2 components 1. concentration gradient: ions move from an area of higher concentration to area of lower concentration 2. electrical gradient: ions move toward an area of opposite electrical charge -do not usually work together, the stronger gradient wins and drives the net flow of ions in its direction

spinal cord

-bundle of nervous tissue that runs from the brain to the first to third lumbar vertebrae and provides a conduction pathway to and from the brain -provides a two way conduction pathway to and from the brain -major reflex center: reflexes are initiated and completed at spinal cord -protected by bone, meninges, and cerebrospinal fluid -spinal dura mater is one layer thick --->does not attach to vertebrae -between vertebrae and spinal dura mater is an epidural space, filled with a soft padding of fat and a network of veins -CSF fills the subarachnoid space between the arachnoid and pia matter meninges -dural and arachnoid membranes extend to sacrum, beyond end of cord at L1 or L2 --->site of lumbar puncture/tap -spinal cord terminates in a cone-shaped structure called conus medullaris -filum terminale extends to coccyx --->fibrous extension of conus covered by pia mater --->anchors spinal cord -denticulate ligaments: extentions of pia mater that secure cord to dura mater --->cervical and lumbar enlargements: areas where nerves servicing upper and lower limbs arise from spinal cord -31 pairs of spinal nerves attach to the cord by paired roots --->each spinal cord segments is designated by the paired spinal nerves that arise from it -because the cord does not reach the end of the vertebral column, the spinal cord segments are located superior to where their corresponding spinal nerves emerge through the intervertebral foramina -cauda equina: collection of nerve roots at inferior end of vertebral canal

anterograde amnesia

-can't form new memories -old memories not lost

each cerebral hemisphere has 3 basic regions

-cerebral cortex (gray matter superficially) -white matter (internally) -basal nuclei (deep within white matter)

ascending neural pathways

-conduct sensory pathways upward through a chain of three neurons 1. first order neuron -conducts impulses from cutaneous receptors and proprioceptors -branches diffusely as it enters spinal cord or medulla -synapses with second-order neuron 2. second order neuron -reside in dorsal horn of spinal cord or in medullary nuclei -transmit impulses o the thalamus or to the cerebellum where they synapse -interneuron 3. third order -interneuron -cell bodies in thalamus -relay impulses to the somatosensory cortes of cerebrum (no third order in cerebellum) -somatosensory signals travel along 3 main pathways on each side of spinal cord --->2 pathways transmit somatosensory info to sensory cortex vi athalamus 1. dorsal column-medial lemniscal pathways 2. spinothalamic pathways --->these both provide for discriminatory touch and conscious proprioception --->both decussate-first in medulla and second in spinal cord --->thrid pathway, spinocerebellar tract terminate in the cerebellum

axon functional characteristics

-conducting region of the neuron -generates nerve impulses and transmits them (typically away from the cell body along the plasma membrane or axolemma) -in motor neurons, nerve impulse is generated at initial segment of the axon and conducted along the axon terminals --->axon terminals are the secretory region of the neuron -when the impulse reaches the axon terminals, it causes neurotransmitters to be released in extracellular space -contains same cytoplasmic organelles as dendrites and cell bodies but lacks rough ER and golgi aparatus -quickly decay id cut or severed because not getting proteins from cell body

peripheral nervous system (PNS)

-consists mostly of nerves (bundles of axons) that extend from the brain and spinal cord, and ganglia (collections of neuron cell bodies) -the nerves serve as communication lines that link all parts of the body to the CNS

thalamus of diencephalon

-consists of bilateral egg-shaped nuclei --->form the superolateral walls of the third ventricle -interthalamic adhesion (intermediate mass) connects the nuclei in most people --->*the* relay station for info coming into the cerebral cortex --->nuclei project and receive fibers from cerebral cortex -80% of dienceohalon -main function to act as relay station for info coming into cortex --->sorts, edits, and relays ascending input such as -------->impulses from hypothalamus for regulating emotion and visceral function -------->impulses from cerebellum and basal nuclei to help direct motor cortices -------->impulses for memory or sensory integration -overall, acts to mediate sensation, motor activities, cortical arousal, learning, and memory

central nervous system (CNS)

-consists of the brain and spinal cord -integrating and control center of the nervous system -interprets sensory info and dictates motor output based on reflexes, current conditions, and past experiences

brain ventricles

-continuos with one another and with the central canal of the spinal cord -hollow chambers filled with cerebrospinal fluid -lined by ependymal cells (a type of neuroglia) -paired *lateral ventricles* are large, C-shaped chambers located deep in each hemisphere --->pair separated by membranous *septum pellucidum* on the anterior part -lateral ventricles communicate with narrow *third ventricles* --->located in the diencephalon --->lateral ventricles connected to third ventricles by *interventricular foramen* -third ventricle connected to *fourth ventricle* --->via canal-like *cerebral aqueduct* --->lies in hindbrain dorsal to the pons and superior to the medulla --->continuous with the central canal of the spinal cord inferiorly -3 openings connect the fourth ventricle to the *subarachnoid space* (a fluid-filled space surrounding the brain) --->paired *lateral apertures* in side walls --->*median aperture* in roof

4 motor areas of the cerebral cortex

-control voluntary movement -lie in the posterior part of the frontal lobes 1. primary motor cortex 2. premotor cortex 3. Broca's area 4. frontal eye field

paralysis

-damage to ventral root -2 types 1. flaccid: nerve impulses do not reach the affected muscle causing them to be unable to move both voluntarily or involuntarily, without stimulation, muscle atrophizes --->damage to ventral root 2. spastic: spinal motor neurons remain intact and spinal reflex activity continues to stimulate muscles irregularly, muscles remain healthy longer, but their movements are no longer subject to voluntary control, many times muscles shorten permanently --->if only upper motor neurons of primary cortex are damaged -transection of spinal cord at any level results in total motor and sensory loss in regions inferior to cut 1. paraplegia: transection between T1 and L1 2. quadriplegia: transection in cervical region

lateralization of cortical functioning

-division of labor between hemispheres -cerebral dominance: the hemisphere that is dominant for language --->dominant in about 90% of people --->working when we compose a sentence, add numbers, and memorize a list -the other hemisphere (usually right) --->more free-spirited, more involved in visual-spatial skills, intuition, emotion, and artistic/musical skills (poetic, creative, and insightful side) -two hemispheres have almost instantaneous communication with each other via connecting fiber tracts

neuron processes

-extend from cell body -CNS contains cell bodies and processes, whereas the PNS contains mostly neuron processes -2 kinds a. dendrites b. axons

reticular formation

-extends through the central core of the medulla oblongata, pons, and midbrain -composed of loosely clustered neurons in what is otherwise white matter -neurons form 3 broad columns along the length of the brain stem 1. raphe nuclei: midline 2. medial (large cell) group: laterally flank the raphe nuclei 3. lateral (small cell) group: also laterally flank? -has far-flung axonal connections with hypothalamus, thalamus, cerebral cortex, cerebellum, and spinal cord --->connections allow it to govern brain arousal -reticular activating system (RAS) --->sends a continuous stream of impulses to the cerebral cortex, keeping it alert and conscious --->filters out repetitive, familiar, or weak stimuli (~99% of all stimuli is not relayed to consciousness) -inhibited by sleep centers, alcohol, drugs -severe injury can result in permanent unconsciousness (coma) -motor function of reticular formation helps control coarse limb movements via reticulospinal tracts -reticular autonomic centers regulate visceral motor functions --->vasomotor centers --->cardiac center --->respiratory centers

neural tube

-fetal structure that gives rise to the brain, spinal cord, and associated neural structures -formed from ectoderm by day 23 of embryonic development -as soon as it forms, its anterior (rostral) end begins to expand and constrictions appear that mark off the three primary brain vessicles

relative refractory period

-follows the absolute refractory period -most Na+ channels have returned to their resting state -some K+ channels are still open -repolarization is occuring -threshold for action potential is substantially elevated --->a stimulus that would normally generate action potential is no longer sufficient -only an exceptionally string stimulus can re-open the Na+ channels that have already returned to their resting state and generate another action potential --->stronger stimuli trigger more frequent Action potentials by introducing into the relative refractory period

cerebral hemispheres

-form the superior part of the brain -accounts for about 83% of the total brain mass

myelination in the PNS

-formed by schwann cells --->wrap around self like a jelly roll -wrapping is initially loose, but the schwann cell cytoplasm is gradually squeezed from between the membrane layers -thickness depends on the number of spirals -nucleus and cytoplasm end up in a bulge just external to the myelin sheath (outer collar of perinuclear cytoplasm) -no channel and carrier proteins (making it a good electrical insulator) -presence of specific protein molecules that interlock to form molecular velcro between adjacent myelin membranes -myelin sheath gaps or nodes of Ranvier -sometimes surround peripheral nerve fibers but the coiling does not occur (but considered nonmyelated and typically thin fibers)

cerebrospinal fluid (CSF)

-forms a liquid cushion of constant volume around the brain -reduces brain weight by 97% and prevents brain from crushing under own weight -protects brain from blows and other trauma -helps to nourish brain, with evidence that it carries chemical signals from one part of the brain to another -composed of watery solution formed from blood plasma, but with less protein and different ion concentrations from plasma -chorid plexus: cluster of capillaries that hangs from roof of each ventricle, enclosed by pia mater and surrounding layer of ependymal cells --->CSF is filtered from plexus at constant rate --->ependymal cells use ion pumps to control composition of CSF and help cleanse CSF by removing wastes --->cilia of ependymal cells helps to keep CSF in motion -normal adult CSF volume of ~150 ml is replaced every 8 hours

limbic system

-group of structures located on the medial aspect of each cerebral hemisphere and dienceohalon -amygdaloid body: almond shaped nucleus that sits on the tail of the caudate nucleus and other parts of the rhinencephalon --->recognizes angry or fearful facial expressions, assesses danger, and elicits fear response -formix: fiber tracts that link limbic system regions -cingulate gyrus: plays role in expressing emotions via gestures and resolves mental conflict -put emotional response to odor -most output relayed via hypothalamus --->play a role in psychosomatic illnesses: disorders with physical symptoms that originate from emotional causes (high blood pressure, heart burn) -limbic system interacts with prefrontal lobes --->allows us to react emotionally to things we consciously understand to be happening --->makes up consciously aware of emotional richness in out lives --->explains why emotions can sometimes override logic, and why reason can stop us from expressing our emotions inappropriately -hippocampus and amygdala body play a role in memory

surface marking of cerebral hemispheres

-gyri: ridges -sulci: shallow groves -fissures: deep grooves --->longitudinal fissure: separates two hemispheres --->transverse cerebral fissure: separates cerebrum and cerebellum

protein- and membrane-making machienery

-have organelles needed to synthesize proteins -rough endoplasmic reticulum, free ribosomes, and golgi aparatus -rough ER also called chromatophilic substance stains dark with basic dyes

midbrain of brain stem

-located between the diencephalon and pons -on ventral aspect has two cerebral peduncles that form vertical pillars that seem to hold up cerebrum --->contains a large pyramidal motor tract descending toward the spinal cord -cerebral aqueduct: runs through midbrain and connects the third and fourth ventricles -periaqueductal gray matter: nuclei that play a role in pain suppression and fight-or flight response --->contain nuclei that control cranial nerve III and IV -midbrain nuclei scattered throughout white matter --->corpora quadrigemina: paired dorsal protrusions on midbrain surface -------->superior colliculi: visual reflex centers that coordinate head and eye movements when following a moving object -------->inferior colliculi: part of auditory relay from the hearing receptors if the ear to the sensory cortex, act in reflexive response such as startle reflex that makes you turn your head toward unexpected noise --->substantia nigra: functionally linked to basal nuclei (axons project to the putamen) -------->degeneration of these is the ultimate cause of parkinson's --->red nucleus: relay nuclei for some descending limb fexion motor pathways (part of reticular formation)

blood brain barrier

-helps maintain stable environment of brain --->chemical variations could lead to uncontrollable neuron firings -substances from blood must first pass through continuous endothelium of capillary walls before gaining entry into neurons --->tight junctions ensure substances pass through, not around endothelial cells --->feel of astrocytes and smooth muscle-like pericytes surround endothelial cells ------>help to promote tight junction formation in endothelial cells -substances move through endothelial cells via 1. simple diffusion: allows lipid-soluable substances, as well as blood glasses to pass freely through cell membrane 2. specific transport mechanisms: facilitated diffusion moves substances important to the brain such as glucose, amino acids, and specific ions --->transcytosis moves larger substances into and out of brain -thick basement membrane surrounding capillaries is last part of barrier substances must pass through --->contains enzymes that destroy certain chemicals (epinephrine and norepinenphrine)n that would activate brain neurons -absent in some areas, such as vomiting center and hypothalamus --->necessary to monitor chemical composition and temperature of blood -injury to brain may result in localized breakdown of blood brain barrier

delta waves

-high amplitude -seen during sleep and when the reticular activating system is suppressed (such as anesthesia) -in awake adults, indicate brain damage

commissural fibers

-horizontal fibers that connect gray matter of the two hemispheres -allow two hemispheres to function as a whole -corpus callosum: largest commissure, lies superior to the lateral ventricles, deep within the longitudinal fissue -less prominent, anterior and posterior

association fibers

-horizontal running fibers that connect different parts of the same hemisphere -short ones connect adjacent gyri -long ones are bundled into tracts and connect different cortical lobes

differences in plasma membrane permeability

-impermeable to large anionic proteins -slightly permeable to Na+ (through leakage channels) -25x more permeable to K+ than sodium (more leakage channels) --->potassium diffuses out of cell down concentration gradient -quite permeable to CL- -K+ diffuse out of cell along their concentration gradient easier than Na+ ions can enter the cells along their concentration gradient --->K+ flowing out of the cell causes it to become more negative inside, making the interior more negative at resting membrane potential (this is because K+ can leave much more easily than Na+ can enter) -sodium-potassium pump (Na+/K+ ATPase) stabilizes the resting membrane potential --->maintains concentration gradients for Na+ and K+ --->3 Na+ are pumped out of cell while 2 K+ are pumped back in

direct (pyramidal) pathways

-impulses from pyramidal neurons in precentral gyri pass through pyramidal (lateral and ventral corticospinal) tracts -descend directly without synapsing until axon reaches end of tract in spinal cord -in spinal cord, axons synapse with interneurons (lateral tract) or ventral horn motor neurons (ventral tract) -direct pathway regulates fast and fine (skilled) movements

anterior association area of cerebral cortex

-in frontal lobe -also called prefrontal cortex -most complicated cortical region -involved with intellect, complex learning abilities (cognition), recall, and personality -contains working memory, necessary for abstract ideas, judgement, reasoning, persistence, and planning -matures slowly and depends heavily on feedback from social environment

limbic association area of cerebral cortex

-includes the cingulate gyrus, parahippocampal gyrus, and hippocampus -part of the limbic system -provides emotional impact that makes a scene important to us -hippocampus establishes memories that allow us to remember incidents

differences in ionic composition

-intracellular fluid contains lower concentration of Na+ and higher concentration of K+ than the extracellular fluid -in intracellular fluid, negatively charged (anionic) protons help to balance the positive charges of intracellular cations (primarily K+) -in extracellular fluid, positive charges of Na+ and other cations chiefly balanced by chloride ions (Cl-)

action potential is an all or none phenomenon

-it either happens completely or doesn't happen at all -action potential is generated and propagated whether or not the stimulus continues

premotor cortex of the cerebral cortex

-just anterior to the precentral gyrus in the frontal lobe -helps plan movements -controls learned, repetitious, or patterned motor skills -coordinates simultaneous or sequential actions by sending activating impulses to the primary motor cortex --->also influences motor activity more directly by supplying about 15% of pyramidal tract fibers (staging area for skilled motor activities) -controls voluntary actions that depend on sensory feedback --->such as feeling for a light switch in the dark

language

-language implementation system association cortex of left hemisphere -2 main area's 1. broca's: involved with speech production 2. wernike's: involved in understanding spoken and written words -corresponding areas on right side are involved with nonverbal language components --->body language --->tone of voice --->emotional content of what we hear

posterior association area of cerebral cortex

-large region encompassing parts of the temporal, parietal, and occipital lobes -plays a role in recognizing patterns and faces and localizing us in space, and binding different sensory inputs into coherent whole -attention to an area of space or an area of one's own body -involved in understanding written and spoken language (including Wernicke's area)

spinothalamic pathways

-lateral and ventral spinothalamic tracts -transmit pain, temp, course toach, and pressure impulses within lateral spinothalamic tract

Broca's area of cerebral cortex

-lies anterior to the inferior region of the premotor cortex -present in only one hemisphere (usually left) -motor speech area that directs muscles of speech production -active in planning speech and voluntary motor activities

pons of brain stem

-located between midbrain and medulla oblongata -fourth ventricle separates pons from cerebellum -composed of conduction tracts 1. longitudinal fibers connect higher brain centers and spinal cord 2. transversal/dorsal fibers relay impulses between motor cortex and cerebellum -origin of cranial nerves V, VI, and VII -some nuclei play a role in the reticular formation, and some help maintain normal rhythm of breathing

gustatory cortex of the cerebral cortex

-located in the insula just deep to the temporal lobe -involved in perceiving taste stimuli

chemical synapses

-most common type of synapse -specialized to allow the release and reception of chemical messengers known as neurotransmitters -made up of two parts a. *axon terminal of presynaptic neuron*: contains many tiny, membrane bound synaptic vesicles carrying thousands of neurotransmitters b. *receptor region on postsynaptic neuron's membrane*: usually located on a dendrite pr the cell body (soma) --->separated by a synaptic clef: fluid filled space at a synapse (30-50 nm wide) -is like a lake that the two neurons shout across -electrical signal gets converted into chemical signal at cleft, then back to electrical -transmission across synaptic cleft --->synaptic cleft prevents nerve impulses from directly passing from one neuron to the next --->chemical event --->depends on release, diffusion, and receptor binding of neurotransmitters --->ensures unidirectional communication between neurons

epithalamus of the diencephalon

-most dorsal portion of the diencephalon -forms the roof of the third venricle -extending from its posterior border and visible externally is the pineal gland --->secretes hormone melatonin, and helps regulate sleep-wake cycle -posterior commissure forms the caudal border of it

medulla oblongata of brain stem

-most inferior part of brain stem -blends into the spinal cord at the foramen magnum of the skull -contains fourth ventricle --->together with the pons forms the ventral wall of the fourth ventricle --->contains choroid plexus: capillary-rich membrane that forms cerebral spinal fluid -3 structures 1. pyramids 2. decussation of the pyramids 3. olives -cranial nerves VIII, IX, X, and XII -vestibular and cochlear nuclei: mediate responses that maintain equilibrium -nucleus cuneatus and nucleus gracilis: relay ascending sensory info from spinal cord -autonomic reflex center -functions overlap with hypothalamus, as it relays its instructions through medullary reticular centers (medulla) -3 functional groups 1. cardiovascular center --->cardiac center adjusts force and rate of heart contraction --->vasomotor center adjusts blood vessel diameter for blood pressure regulation 2. respiratory centers --->generate respiratory rhythm --->control rate and depth of breathing (with pontine centers) 3. various other centers regulate --->vomiting, hiccuping, swallowing, coughing, sneezing

electrical synapses

-much less common -consist of gap junction -electrically coupled neurons --->channel proteins (connexons) connect to the cytoplasm of adjacent neurons and allow ions and small molecules to flow directly from one neuron tot he next --->transmission/communication across synapse is very rapid, may be unidirectional or bidirectional -found in regions of the brain responsible for certain stereotyped movements, such as the normal jerky movements of the eyes, and in axoaxonal synapses in the hippocampus, a brain region involved in emotions and memory -more abundant in embryonic nervous tissue, helping neural development so neurons can properly connect with one another -get replaced by chemical synapses -like a doorway: messages (ions) can move directly from one room (neuron) to another

white matter of spinal cord

-myelinated and nonmyelinated nerve fibers allow communication between parts of spinal cord, and spinal cord and brain -run in three directions 1. ascending: up to higher centers (sensory inputs) 2. descending: from brain to cord or lower cord levels (motor outputs) 3. transverse: form one side to the other (commissural fibers) -white matter is divided into 3 white columns (funiculi) on each side 1. dorsal (posterior) 2. lateral 3. ventral (anterior) -each funiculus contains several fiber tracts, and each tract is made up of axons with similar destinations and functions

neuron

-nerve cells -structural units of nervous system -conduct messages in the form of nerve impulses from one part of the body to another

Excitatory synapses and ESPSs

-neurotransmitter binding depolarizes the postsynaptic membrane -chemically gated ion channels open on postsynaptic membranes (those of dendrites and cell bodies or soma) --->allows simultaneous flow of Na+ ad K+ in opposite directions --->because the electrochemical gradient for sodium is much steeper than for potassium, Na+ influx is greater than K+ efflux and net depolarization occurs -postsynaptic membranes generally do not generate action potentials --->the dramatic polarity reversal doesn't happen because of the opposite movements of K+ and Na+, preventing excessive positive charge from accumulating inside the cell -for this reason, instead of action potentials, depolarizing graded potentials called *excitatory postsynaptic potentials (EPSPs) occur at excitatory post synaptic membranes --->lasts a milisecond and goes back to resting potential --->only function is to help trigger an action potential distally at the initial segment of the postsynaptic neuron;s axon --->can travel to axon hillock and trigger opening of voltage-gated channels, causing action potential to be generated

dendrites

-of motor neurons, are short, tapering, diffusely branching extensions -100s of these near cell body -main receptive or input regions -provide enormous surface area for receiving signals from other neurons bristle with dendritic spines which represent close contact with other neurons (in brain) -convey incoming messages toward the cell body -graded potentials

myelination in the CNS

-oligodendrocytes that form myelin sheaths -can coil as many as 60 axons at the same time -myelin sheath gaps -lack an outer collar of pernuclear cytoplasm because cell extensions so the coiling and the squeezed out cytoplasm is forced back toward the centrally located nucleus in stead of peripherally -shor axons not myelinated

axon structure

-only one per neuron -comes from a cone shaped area of the cell body called the axon hillock -for some the axon is very short or absent, but for others it accounts for nearly the entire length of the neuron -long axons called nerve fiber -bundles of axons are called tracts in the CNS and nerves in the PNS -can have branches called axon collaterals -usually branches profusely at end called terminal branches -the knoblike distal endings of the terminal branches are called axon terminals

cerebral cortex

-outer gray matter region of the cerebral hemispheres -"executive suite" of the nervous system -where conscious mind is found -enables us to --->be aware of ourselves and our sensations --->to communicate --->remember --->understand --->and initiate voluntary movement -composed of gray matter: neuron cell bodies, dendrites, associated glia and blood vessels, but no fiber tracts -billions of neurons arranged in 6 layers -only 2-4mm thick -about 40% of total brain mass --->its convolutions effectively triple its surface area

mammillary bodies of the hypothalamus

-paired anterior nuclei -act as olfactory relay stations

consciousness

-perception of sensation -voluntary initiation and control of movement -capabilities associated with higher mental processing (memory, logic, judgment, etc) -continuum that grades behavior in response to stimuli --->alertness --->drowsiness or lethargy (proceeds to sleep) --->stupor --->coma -current suppositions about consciousness --->consciousness involves simultaneous activity of large areas of the cerebral cortex --->superimposed on other types of neural activity --->is holistic and totally interconnected

absolute refractory period

-period following stimulation during which no additional potential can be evoked -begins with the opening of Na+ channels, and ends when those channels begin to reset to their original resting state -ensures that each action potential is an all or nothing event -enforces a one-way transmission of nerve impulses --->only travel down the axon

decussation of the pyramids of medulla oblongata

-point where pyramidal tracts cross over to opposite side of body -controls voluntary movements of the opposite side

visceral sensory area of cerebral cortex

-posterior to gustatory cortex -conscious perception of visceral sensations --->upset stomach, full bladder, feeling in lungs that they will burst when you hold your breath too long

olfactory cortex of cerebral cortex

-primary olfactory cortex -located on the medial aspect of the temporal lobe in a small region called the piriform lobe, which is dominated by the hooklike uncus -conscious awareness of different odors -part of primitive rhinencephalon(remainder becomes limbic system), including the protruding olfactory tracts and bulbs that extend to the nose --->why smells can bring up emotions

action potential

-principle way neurons send signals --->means of long-distance neural communication -occur only in muscle cells and axons of neurons -brief reversal of membrane potential with a change in voltage of about 100mv --->depolarization followed by repolarization and often a short period of hyperpolarization -*do not decay over distance as graded potentials do* -in neurons also referred to as a nerve impulse (typically only generated in axons) --->involves opening a specific voltage-gated channel -takes place in the initial segment of the axon

ependymal cells

-range in shape from squamous to columnar and many are ciliated -line the central cavities of the brain and the spinal cord -form a fairly permeable barrier between the cerebrospinal fluid that fills those cavities and the tissue fluid bathing the cells of the CNS -beating of their cilia helps to circulate the cerebrospinal fluid that cushions the brain and spinal cord

multimodal association areas of cerebral cortex

-receives input from multiple sensory areas -sends outputs to multiple areas -allows us to give meaning to info received, store it in memory, tie it to previous experiences, and decide what action to take --->sends decisions to the premotor cortex which sends it to the motor cortex -where sensations, thoughts, and emotions become conscious (makes us ho we are) -divided into 3 parts 1. anterior association area 2. posterior association area 3. limbic association area

alpha waves

-relatively regular and rhythmic -low amplitude -synchronous waves -indicate brain "idling" -calm and relaxed state of wakefulness

beta waves

-rhythmic, but less regular than alpha -higher frequency -occur when we are mentally alert, as when concentrating on some problem or visual stimulus

cerebral white matter

-second of three basic regions of cerebral hemispheres -provides communication between cerebral areas and lower CNS centers -consists of myelinated fiber bundled into large tracts -classified according to direction they run 1. association 2. commissural 3. projection

astrocytes

-shaped like delicate branching sea anemones -most abundant and versatile -numerous radiating processes cling to neurons and their synaptic endings and cover nearby capillaries -support and brace the neurons and anchor them to their nutrient supply --help determine capillary permiability -control the chemical environment around neurons, where their most important job is "mopping up"leaked potassium ions and recapturing and recycling released neurotransmitters -connected by gap junctions, they signal each other with slow-paced intracellular calcium pulses, and releasing extracellular chemical messengers -influence neuronal functioning and therefore participate in information processing in the brain

graded potentials

-short lived, localized changes in membrane potential, usually in dendrites of the cell body -stronger the stimulus, the more voltage changes and the further current flows -triggered by stimulus that opens gated ion channels --->can be depolarization or hyperpolarization -given differnet names depending on where they occur and the function they preform 1. receptor potential or generator potential: produced when a sensory receptor is excited by a stimulus --->graded potential in receptors of sensory neurons 2. postsynaptic potential: produced when the stimulus is a neurotransmitter released by another neuron (in synapse) --->neuron graded potntial -positive ions migrate toward more negative areas (the direction of cation movement is the direction of current flow), and negative ions simultaneously move toward more positive areas

sleep and sleep-wake cycles

-sleep: state of partial unconsciousness from which person can be aroused by stimulation -cortical activity is depressed, but brain stem activity doesn't change -2 major types of sleep 1. non-rapid eye movement (NREM) --->broken into 3 stages --->during first 30-45 mins of sleep cycle, pass through the first 2 stages (slow wave sleep is stages 3 and 4), frequency of EEG waves declines, but amplitude increases, blood pressure and heart rate also decrease --->about 90 mins after sleep begins, after reach stage 4, the EEG patterns change abruptly and goo back up to REM 2. rapid eye movement (REM) --->more oxygen used in this state than awake state -stage 4 sleep declines steadily as we age and may disappear by age 60

importance of sleep

-slow wave sleep (stages 3 and 4) presumed to be restorative stage -people deprived of REM become moody and depressed -REM sleep may: 1. give brain opportunity to analyze day's events and work through emotional events or problems 2. eliminate unneeded synapses that were formed (dream to forget)

microglial cells

-small and ovoid with relatively long "thorny" processes -processes touch nearby neurons, monitoring their health, and when they sense that certain neurons are injured or in other trouble, the microglial cells migrate towards them -turn into special macrophage that phagocytizes microorganisms or neural debris --->super important because immune system cells have limited access to CNS

dura mater

-strongest -made of two layers of fibrous connective tissue 1. peristeal layer: attaches to inner surface of skull --->found only in brain, not spinal cord 2. meningeal layer: true external covering of brain --->extends into vertebral canal as spinal dura mater -two layers fused together in all areas, except those to form dural venous sinuses --->sinuses collect venous blood from brain, empty into jugular veins of neck -extends inward in many areas to form flat partitions that divide cranial cavity --->referred to as dural septa --->act to limit excessive movement of brain -3 main septa 1. falx cerebri: in longitudinal fissur; attached to crista galli 2. falx cerebelli: along vermis of cerebellum 3. tentorium cerebelli: horizontal dural fold over cerebellum and in transverse fissure

schwann cells (nerolemmocytes)

-surround all nerve fibers in the PNS -form myelin sheaths around the thicker nerve fibers -functionally similar to oligodendrocytes -vital to the regeneration of damaged peripheral nerve fibers

satellite cell

-surround neuron cell bodies located in the peripheral nervous system -thought to have many of the same functions inf the PNS as astrocytes in the CNS -looks like moons around planets

olives of medulla oblongata

-swellings caused by underlying inferior olivary nuclei that relay stretch info from muscles and joints to cerebellum

resting membrane potential

-the electrical charge of a neuron when it is not active -minus sign represents that the membrane is negatively charged relative to the outside -membrane said to be polarized -2 factors generate resting membrane potential 1. differences in the ionic composition of the intracellular and extracellular fluids 2. differences in the plasma membrane's permeability to those ions

basal nuclei

-third basic region of each hemisphere -primarily involved in the control of movement -each hemisphere's nuclei include 3 things 1. caudate nucleus 2. putamen 3. globus pallidus -caudate nucleus (comma-shaped) + putamen = striatum -functionally associated with the subthalamic nuclei (located in the later "floor" of the diencephalon) and the substantia nigra of the midbrain -receive input from entire cerebral cortex, as well as other subcortical nuclei -no direct access to motor pathways -play a role in --->motor movements (overlap with those of cerebellum) --->cognition and emotion --->regulate intensity of slow or sterotyped movements --->filter out incorrect/inappropriate responses --->inhibit antagonistic/unnecessary movements -huntington's and parkinson's are diseases of basal nuclei

synaptic delay

-time required for a signal to cross a synapse between two neurons (time neurotransmitters to be released, diffuse across synapse, and bind to receptors) -typically lasts .3-5 ms, making transmission across the chemical synapse the rate-limiting (slowest) step of neural transmission -explains why transmission along neural pathways involving only two or three neurons occurs rapidly, but transmission along multisynaptic pathways typical of higher mental functioning occurs much more slowly -these are not actually noticeable because they are still super fast

epileptic seizure

-torrent of electrical discharges by groups of neurons -occurs in 1% of pop -absence seizures: mild seizures of young children, blank expression -tonic-clonic seizures: grand mal, very big

dorsal column-medial lemniscal pathways

-transmit input to somatosensory cortex for discriminative touch and vibrations -composed of paired tracts of the dorsal white column of the spinal cord- fasciculus cuneatus and fasciculus gracilis in spinal cord and medial lemniscus in brain (medulla to thalamus)

spinal cord cross sectional anatomy

-two lengthwise grooves that run length of cord partially divide it into right and left halves 1. ventral (anterior) median fissure 2. dorsal (posterior) median sulcus -gray matter is located in core, white matter outside -central canal runs length of cord --->filled with CSF

pyramids of medulla oblongata

-two ventral longitudinal ridges formed by pyramidal tracts from motor cortex -formed by large pyramimdal tracts descending from the motor cortex -cross over to other side before going to spinal cord

threshold typically reached when the membrane has been depolarized by 15 to 20 mv from the resting value

-unstable equilibrium state -if one more Na+ enters, further depolarization occurs and more Na+ gates open, allowing more Na+ to enter -if one more K+ leaves, membrane potential driven away from threshold, Na+ channels close, and K+ continues to diffuse outward until resting value reached

spinocerebellar paths

-ventral and dorsal tracts -convey info about muscle or tendon stretch to cerebellum --->used to coordinate muscle activity

projection fibers

-vertical fibers that connect hemispheres with lower brain or spinal cord -sensory info reaches the cerebral cortex and motor output leaves it through these projection fibers -tie the cortex to the rest of the nervous system and to the body's receptors and effectors 1. internal capsule: passes between the thalamus and some of the basal nuclei, projection fibers on either side of the brain stem that form a compact band 2. corona radiata: projection fibers that radiate through cerebral white matter to cortex

myelin sheath

-whitish, fatty -long or large in diameter typically covered -protects and electrically insulates fibers -increases transmission speed of nerve impulses -only associated with axons (dendrites are ALWAYS nonmyelinated)

6 steps involved in info transfer across chemical synapses

1. *action potential arrives at axon terminal of presynaptic neuron* 2. *voltage gated Ca2+ channels open, and Ca2+ enters axon terminal* -flows down electrochemical gradient from extracellular fluid to inside the axon terminal 3. *Ca2+ entry causes synaptic vesicles to release neurotransmitter by exocytosis* -Ca2+ acts as intracellular message and causes synaptotagmin protein to react with SNARE proteins that control fusion and synaptic vesicles with axon membrane -fusion to axon membrane results in exocytosis of neurotransmitters into synaptic cleft -Ca2+ then quickly removed from terminal either taken up into the mitochondria or ejected from neuron by active Ca2+ pump -the higher the impulse frequency (more intense the stimulus), the more vesicles exocytose (more vesicles release contents), leading to a greater effect on the postsynaptic cell 4. *neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane* -often chemically gated ion channels 5. *binding of neurotransmitter opens ion channels, creating graded potentials -binding causes receptor protein to change shape, which causes ion channels to open --->creates graded potentials in postsynaptic cell ------>can be excitatory or inhibitory event --->some receptor proteins are also ion channels 6. *neurotransmitter effects are terminated* -as long as the neurotransmitter is bound to a postsynaptic receptor, a neurotransmitter continues to affect membrane permeability and block reception of additional signals from presynaptic neurons -effects from neurotransmitters only last a few milliseconds before being terminated in one of 3 ways a. *reuptake*: by astrocytes or presynaptic terminals, where it is stored or destroyed by enzymes b. *degradation*: by enzymes associated with the postsynaptic membrane or present in the synaptic cleft c. *diffusion*: away from the synapse

4 main steps to generating an action potential

1. *resting state: all voltage-gated Na+ and K+ channels are closed* -only leakage channels open maintaining resting membrane potential -each Na+ channel has 2 voltage sensitive gates a. activation gates: closed at rest, opened with depolarization, allowing Na+ to enter the cell b. inactive gates: open at rest, block channel once it is open to prevent more Na+ from entering the cell -each K+ channel has has a single voltage-sensitive gate --->closed in resting state and opens slowly in response to depolarization 2. *depolarization: Na+ channels open* -depolarizing local currents open voltage-gated Na+ channels and Na+ rushes into the cell -Na+activation and inactivation gates open due to influx of Na+ (depolarizes that patch) -Na+ influx causes more depolarization, which opens more Na+ channels --->as a result, intercellular fluid becomes less negative -at threshold (-55 to -50 mv), positive feedback causes opening of all Na+ channels --->Na+ permeability 1000x greater than a resting neuron --->results in large action potential spike ---> membrane polarity jumps to +30mv because becomes more and more less negative -positive feedback cycle: increasing Na+ permeability due to increased channel openings leads to greater depolarization, which increases Na+ permeability, and so on 3. *repolarization: Na+ channels are inactivating, and voltage-gated K+ channels open -Na+ channel inactivation gates close --->membranes permeability to Na+ declines to resting state --->action potential spike stops rising -slow voltage gated K+ channels open --->K+ exits cell down its electrochemical gradient --->restores internal negativity of the resting neuron -repolarization: membrane returns to resting membrane potential 4. *hyperpolarization: some K+ channels remain open, and Na+ channels reset* -some K+ channels remain open, allowing excessive K+ efflux --->increased permeability for K+ lasts longer than needed to restore resting state --->inside the membrane becomes more negative than in resting state -this causes hyperpolarization of the membrane (slight dip below resting potential voltage) -Na+ channels also begin to rest

depending on the effect of chemical synapse on the membrane potential on the postsynaptic neuron, there are two types of postsynaptic potentials

1. EPSP: excitatory postsynaptic potentials 2. IPSP: inhibitory postsynaptic potentials

4 types of neuroglia in the CNS

1. astrocytes 2. microglial cells 3. ependymal cells 4. oligodendrocytes

rate of impulse (action potential) propagation depends on 2 factors

1. axon diameter: the larger the axon diameter, the faster it conducts impulses -less resistance to local current flow, so have faster impulse connection and bring adjacent areas of membrane to threshold more quickly 2. degree of myelination: the presence of myelin sheath dramatically increases the speed of propagation -conduction velocity increases with degree of myelination (lightly myelinated fibers conduct more slowly than heavily myelinated fibers)

neuron structure

1. cell body (perikaryon or soma) 2. neuron processes a. dendrites b. axons 3. myelin sheath

major sulci that divide the lobes

1. central sulcus: separates *precentral gyrus* of the frontal lobe and the *postcentral gyrus* of the parietal lobe 2. parieto-occipital sulcus: separates occipital and parietal lobes 3. lateral sulcus: outlines temporal bone, separates it from the parietal and frontal lobes -insula buried deep within this and forms part of its floor

4 brain regions

1. cerebral hemispheres 2. diencephalon 3. brain stem 4. cerebellum

3 types of gated channels

1. chemically gated channel (ligand-gated): open when the appropriate chemical binds 2. voltage gated channel: open and close in response to changes in membrane potential 3. mechanically gated channels: open in response to physical deformation of the receptor (as in sensory receptors for touch and pressure)

membrane potential can change when

1. concentrations of ions across membrane change 2. membrane permeability to ions changes --->only permeability important foe transferring info

2 types of conduction based on if the fiber is myelinated or not

1. continuos connection: nonmyelinated axons, voltage agted channels in the membrane are immediately adjacent to each other -RELATIVELY SLOW 2. saltatory conduction:transmission of an action potential along a myelinated fiber in which the action potential appears to leap from gap to gap -30X FASTER -myelin sheaths insulate and prevent leakage of charge (about 1mm) -voltage-gated Na+ channels are located at myelin sheath gaps -action potentials generated only at gaps

2 types of synapses

1. electrical 2. chemical

3 special characteristics of neurons

1. extreme longevity: given good nutrition, they can function optimally for a lifetime 2. amitotic: when they get their role of communicators for the nervous system, they lose ability to divide (high price because neurons cannot be replaced if damaged) 3. high metabolic rate: require continuos and abundant supplies of oxygen and glucose

sulci divide each hemisphere into 5 lobes

1. frontal 2. parietal 3. temporal 4. occipital 5. insula

changes in membrane potential can produce two types of signals

1. graded potentials: usually incoming signals operating over short distances that have variable (graded) strength 2. action potentials: long-distance signals of axons that always have the same strength

nerve fibers may be classified according to diameter, degree of myelination, and conduction speed, 3 types

1. group A fibers -mostly somatic sensory and motor fibers --->skin, skeletal muscles, and joints -largest diameter -thick myelin sheaths -conduct impulses at speeds up to 150 m/s (over 300 miles per hour) 2. group B fibers -lightly myelinated fibers -intermediate diameter -transmit impulses at an average rate of 15 m/s (about 30 miles per hour) 3. group C fibers -nonmyelinated -smallest diameter -incapable of saltatory conduction -conduct impulses at leisurely pace of 1 m/s (2 miles per hours) or less *B and C fiber groups include ANS motor and sensory fibers that serve visceral organs, and the smaller somatic sensory fibers that transmit sensory impulses from the skin (such as pain and small touch fibers)

5 analysis of higher mental functions

1. language 2. memory 3. brain waves and EEGs 4. consciousness 5. sleep and sleep-wake cycles

neurotransmitter receptors cause graded potentials that vary in strength based on

1. mount of neurotransmitter released 2. time neurotransmitter stays in cleft

3 structural classification of neurons

1. multipolar neurons -3 or more processes, 1 axon, and the rest dendrites -most common type (more than 99% of neurons in this class) -the major neuron type in the CNS 2. bipolar neurons -2 processes, 1 axon, and 1 dendrite (each extend from opposite end of cell body) -rare, only found in special sense organs such as the retina of eye and olfactory mucosa 3. unipolar neurons -single short process that emerges from the cell body and divides T-like into proximal and distal branches -the more distal process is associated with a sensory receptor -central process enterd the CNS -pseudounipolar neurons found chifely in ganglia in the PNS where they function as sensory neurons -central process=axon (conducts impulses away from cell body -no dendrites, receptor endings

nervous tissue made of 2 principle cell types

1. neuroglia (glial cells): small cells that surround and wrap the more delicate neurons 2. neurons: nerve cells that are excitable (respond to stimuli by changing their membrane potential) and transmit electrical signals

auditory areas of cerebral cortex

1. primary auditory cortex -located in superior margin of temporal lobe next to the lateral sulcus -interprets info from inner ear as pitch, loudness, and location 2. auditory association area -posterior to the primary auditory cortex -permits the perception of the sounds stimulus (speech, scream, music, etc) -stores memories of sound for future reference

visual areas of cerebral cortex

1. primary visual (striate) cortex -located on the extreme posterior tip of the occipital lobe, but most is buried deep in the calcarine sulcus in the medial aspect of the occipital lobe -largest cortical sensory area -receives info that originates on the retina of the eye 2. visual association area -surrounds the primary visual cortex and covers much of the occipital lobe -communicates with the primary visual cortex to interpret visual stimuli (color, form, movement) by using past visual experiences --->such as facial recognition -complex processing uses entire posterior half of cerebral hemispheres

primary 3 vesicles of the brain

1. prosencephalon or forebrain 2. mesencephalon or midbrain 3. rhombencephalon or hindbrain the remaining caudal (toward the tail) or posterior portion of the neural tube becomes the spinal cord

2 kinds of neuroglia in the PNS

1. satellite cells 2. schwann cells

3 steps to the nervous system

1. sensory input: uses millions of sensory receptors to monitor changes inside and outside the body 2. integration: processes those inputs and determines what should be done at each moment based on them 3. motor output: activates effector organs (muscles and glands) to cause a response to the sensory info and integration

2 functional subdivision of the PNS

1. sensory or afferent division: consists of nerve fibers that convey impulses to the central nervous system from sensory receptors located throughout the body 2. motor or efferent division: transmits impulses from the CNS to effector organs (muscles and glands)

3 functional classification of neurons

1. sensory or afferent neurons -transmit impulses from sensory receptors in the skin or internal organs toward or into the CNS -almost all are unipolar -cell bodies located in sensory ganglia outside the CNS -most distal part act as receptors and peripheral processes long 2. motor or efferent neurons -carry impulses away from the CNS to the effector organs (muscles and glands) -multipolar -most cell bodies located in the CNS 3. interneurons -association neurons -lie between motor and sensory neurons in neural pathways and shuttle signals through CNS pathways where integration occurs -most confined within CNS -make up over 99% of neurons in the body, including those in the CNS -almost all multipolar

2 kinds of sensory fibers for sensory divison

1. somatic fibers: convey impulses from skin, skeletal muscles, and joints 2. visceral sensory fibers: transmits impulses from the visceral organs

2 main parts of the PNS

1. somatic nervous system: composed of somatic nerve fibers that conduct impulses from the CNS to skeletal muscles, often referred to as voluntary nervous system because it allows us to consciously control our skeletal muscles 2. autonomic nervous system: consists of visceral motor nerve fibers that regulate the activity of smooth muscles, cardiac muscles, and glands, called the involuntary nervous system because it controls activities we cannot control

2 components of autonomic nervous system

1. sympathetic: mobilizes body systems during activity (fight or flight) 2. parasympathetic: conserves energy, promotes house-keeping functions during rest

4 generalizations of the cerebral cortex

1. the cerebral cortex contains 3 kinds of functional areas a. motor areas b. sensory areas c. association areas 2. each hemisphere is chiefly concerned with sensory and motor functions of the contralateral (opposite) side of the body 3. although largely symmetrical in structure, the two hemispheres are not entirely equal in function, instead, there is lateralization (specialization) of cortical functions 4. gross oversimplification, no functional area of the cortex acts alone, and conscious behavior involves the entire cortex in one way or another

how the cerebral hemispheres fit into the brain

1. the frontal lobes lie in the anterior cranial fossa 2. anterior parts of the temporal lobes fill the middle cranial fossa 3. brain stem and cerebellum fill the posterior cranial fossa -the occipital lobes are well superior to this cranial fossa

multiple sclerosis

A chronic disease of the central nervous system marked by damage to the myelin sheath (turns them to hardened lesions called scleroses). Plaques occur in the brain and spinal cord causing tremor, weakness, incoordination, paresthesia, and disturbances in vision and speech

white matter

myelinated axons

in general info flows

sensory receptors ---> primary sensory cortex ---> sensory association cortex ---> multimodal association cortex

gray matter

short, nonmyelinated neurons and neuron cell bodies

infundibulum of hypothalamus

stalk that connects to pituitary gland

axosomatic synapses

synapses between axon endings of one neuron and the cell body (soma) of another neuron

axoaxonal

synapses between axons (less common)

somatodendritic

synapses between cell bodies (soma) and dendrites (less common)

dendrodendritic

synapses between dendrites (less common)

axodendritic sunapses

synapses between the axon endings of one neuron an the dendrites of another neuron

current

the flow of electrical charge from one point to another

resistence

the hinderance to charge flow provided by substances through which the current must pass (higher resistance are insulators, lower resistance are conductors)

voltage

the measure of potential energy generated by separated electrical charges

presynaptic neuron

the neuron conducting impulses toward the synapse

postsynaptic neuron

the neuron transmitting the electrical signal away from the synapse -outside the CNS, this may be another neuron or an effector cell (muscle or gland)

potential difference or potential

voltage measured between two points (the greater the difference in charge between two points, the higher the voltage)