Higher Functions of the Nervous System PDF

Higher Functions of the Nervous System I. Electroencephalogram (EEG) A. introduction 1. recordings of potential oscillations recorded from electrodes on scalp 2. EEG recorded in humans from grid of standard sites 3. diagnostic tool in clinical neurology and epilepsy B. EEG wave compositio...

Higher Functions of the Nervous System I. Electroencephalogram (EEG) A. introduction 1. recordings of potential oscillations recorded from electrodes on scalp 2. EEG recorded in humans from grid of standard sites 3. diagnostic tool in clinical neurology and epilepsy B. EEG wave composition 1. EEG wave forms a. result of extraellular currents from cortical EPSPs & IPSPs b. EEG spike does not result from cortical action potentials (1) reflects activity of many cortical pyramidal cells (2) size or polarity of EEG wave does not reflect excitation or inhibition of cells 2. dominant frequency effected by: a. age b. state of conciousness c. recording site d. drug action e. disease 2. wave classification a. alpha waves, 8 – 13 Hz (1) recorded in posterior brain when awake and undisturbed (2) awake relaxed individual with eyes closed b. beta waves, more than 13 Hz (1) present when nervous system active (2) occurs during sensory input and mental activity  c. theta waves, 4 – 7 Hz (1) commonly observed in sleep and in young children (2) occur with many mental disorders d. delta waves, less than 4 Hz (1) occur in adults, only in deep sleep (2) common in awake, young children 3. brain death = persistent isoelectric EEG in absence of depressants C. evoked potential 1. EEG change elicited by a stimulus a. visual, acoustic, or peripheral nerve stimulus b. waveform largest over appropriate brain region 2. used clinically to determine integrity of sensory pathway II. Sleep-wake cycle A. cyclic (circadian) process 1. endogenous 25 hr cycle 2. interrupted by time zone or environmental shift B. sleep stages (general) 1. non-REM sleep a. initial stage of sleep, muscles relax b. heart rate & GI activity decrease c. EEG synchronized and slow d. awake easily 2. REM (rapid eye movement) sleep a. occurs approximately every 90 min of sleep b. phasic contraction of selected muscles (e.g. eyes) c. changes in temp, HR, blood pressure, respiration d. desynchronized EEG e. most dreams occur 3. non-rem sleep stages a. stage 1 - drowsy (theta waves) b. stage 2 - light sleep (slow waves interspersed with sleep spindles & K complexes) c. stage 3 - muscle tone decreases, heart rate slows (some delta waves) d. stage 4 - deepest sleep, difficult to arouse (delta waves) 4. REM character a. periods increase in length with sleep duration b. In newborns, 50% of sleep is REM, decreases with age c. believed to be period most dreams ocxcur 5. mechanism and purpose of sleep a. purpose unknown, however, lack is debilitating b. levels of serotonin, norepinephrine, and acetylcholine can effect sleep wake cycle II. Cerebral Dominance A. introduction 1. each hemisphere receives & analyzes information 2. however, each is dominant for certain functions a. left hemisphere dominant for speech, writing, analytical & computational activities b. non-dominant hemisphere specializes in non-verbal, emotional, artistic, and intuitive activities. B. early studies 1. anatomic asymmetry a. 65% of individuals have larger left temporal lobe than right 2. sodium amytal (fast acting barbituate) test a. injected into rt. and lt. carotid, while patient counts aloud b. demonstrates speech dominant hemisphere (1) majority of both lt. and rt. handed people have left hemisphere speech (2) lateralization is weak or absent in some lt. handed people 3. split brain experiments a. commissurotomy used for severe epileptic patients (1) sever corpus callosum and anterior commissure (2) prevents spread of epileptic activity (3) each hemisphere functions independently b. no obvious changes in patients following procedure c. Lashley (1950) proposed the function of the commissures was mechanical, to keep lobes from sagging. 4. classical studies with commissurotomized patients a. presentation of objects to isolated visual fields. (1) picture presented to left visual field (LVF) is processed by contralateral hemisphere (right) i. patient can locate object only with ipsilateral (to image) hand ii. denies seeing anything (2) picture presented to right visual field (RVF) is processed in left hemisphere i. patient can describe and locate object with hand ii. left hemisphere has speech center b. presentation of conflicting images (1) when left visual field was presented with word “Rub” a. left hand scratched right hand b. when asked what command was patient stated “ Oh... itch” (2) right figure a chicken claw, left a snow scene a. when asked to find images left hand finds a snow shovel, right a chicken b. when asked to explain what happened patient states “I saw the claw so picked a chicken and you need a shovel to clean up. (3) chimeric image (a) a split brain patient is told to focus on the chimeric image below and asked to vocalize what they see they will say (b) when asked what they see will say “a man” (c) when asked to point to a similar face in a series of faces, they will point to a women (d) which hemisphere gains control depends upon that most suited for task ) C. Summary 1. we have essentially two brains, each with their own strengths and weaknesses 2. when separated they develop mechanisms to work together 3. you tube video of spilt brain patient experiment www.youtube.com/watch?v=ZMLzP1VCANo V. Biological Basis of Learning and Memory - Introduction A. Within first six months of life, human brain has full neuron complement. 1. brain growth results from: a. addition of processes (both axons and dendrites) b. supportive and protective cells (glia) B. We are not hard-wired like a computer! 1. neuron process elaboration continues until death 2. neuron processes and synaptic connections are dynamic. Processes strengthen when utilized and regress when inactive. (neuron plasticity) 3. an important part of learning may be the stabilization of useful circuits.. brains our modular both anatomically and functionally 1. We can listen to a lecture, take notes, look at the figures, and be thinking about lunch. 2. When interest, need, or curiosity prompts us to pay attention, the frontal lobe becomes active. 3. Axons have been shown to functionally connect with other axons, hyperpolarizing or depolarizing their contacts (gating signals). a. When we are concentrating, frontal neurons attenuate signals from sources of distraction, auditory or visual. b. gating signals can also promote passage to gnostic areas in frontal cortex Memory A. qualitative categorization 1. declarative – storage and retrieval of material to conscious mind 2. procedural – motor (not available to conscious mind) B. temporal categorization 1. short-term memory (a) anterior portion of frontal lobe and thalamus (b) depends on ongoing neural activity (c) easily disrupted 2. recent memory (a) hippocampus (b) recalled easily, past days events 3. long term memory (a) result of repeated recall (b) stored diffusely in both hemispheres  3. engram a. site of change in nervous system associated with learning instance b. hippocampus (1) profound memory deficits occur with hippocampal lesion (2) short term declarative memory particularly effected (3) animal studies indicate hippocampus may store spatial map 4. stages of memory a. input processed into short term memory store (inhibitors of protein synthesis have no effect) b. short term memory converted to long term by “long term potentiation” (LTP) (1) blocked by inhibitors of protein synthesis (2) requires gene induction B. learning 1. neural circuitry involved in learning in mammals is complex 2. cellular basis studied in invertebrate systems, e.g. aplysia a. gill-tail-siphon withdrawal reflex (monosynaptic) (1) tactile or electrical stimulation leads to withdrawal of siphon, gills and tail (2) subject to short term and long term potentiation b. single tail shock (1) activated serotonergic neurons (2) increases sensory neuron transmitter release (a) increase cAMP dependent phosphokinase A (b) decrease K conductance (c) depolarize neurons (increase sensitivity) b. long term potentiation (1) stimuli over 1 1/2 hrs induce sensitization that lasts for days to wks (2) activation of DNA regulatory proteins, increased RNA transcription (3) induced protein synthesis (4) potential long term result (a) increased neuronal cell adhesion molecules (NCAMs) (b) increase dendritic density (c) increased second messenger activity (d) long term facilitated transmitter release