Download Physiology Ch 58 p711-720 [4-25

Physiology Ch 58 711-720
Behavioral and Motivational Mechanisms – Limbic System/Hypothalamus
Activating-Driving Systems of the Brain – compression of brainstem can cause coma because
cerebrum needs signals from lower brain to survive
-nerve signals in brainstem directly activate basal level of neuron activity in brain and activate
neurohormonal systems that release specific facilitatory/inhibitory hormone neurotransmitter
Control of Cerebral Activity by Continuous Excitatory Signals from Brain Stem
Reticular Area of Brain Stem – the driving component of brain activity is an excitatory area in
the reticular substance of the pons and mesencephalon, also called bulboreticular facilitory
area; sends signals up to thalamus  cerebral cortex
-signals through thalamus are type types:
1. Rapid transmitted action potential exciting cerebrum for few ms, originating in cell bodies
throughout brainstem reticular area; release acetylcholine which serves as excitatory agent
2. Second type originates from small neurons throughout reticular excitatory area passing
through thalamus by small, slow-conducting fibers synapsing in intralaminar nucleus of
thalamus  small fibers distributed everywhere in cortex; excitatory effect lasts minutes
Excitation of Excitatory Area by Peripheral Sensory Signals – activity of excitatory brainstem is
determined by number and type of sensory signals entering brain from periphery
-pain tends to increase activity in excitatory area to excite brain to attention
-if cutting the brainstem above where 5th cerebral nerve enters pons (where highest nerves exist
transmitting somatosensory signals to brain), level of brain activity diminished abruptly
-if cut below the 5th nerves, many sensory signals remain, and coma is averted
Increased Activity of Excitatory Area Caused by Feedback Signals Returning from Cerebral
Cortex – feedback signals also return from cerebral cortex back to same area; cortex sends
signals to brain stem excitatory area  back to cerebral cortex to maintain level of excitation of
cerebral cortex during thought processes/motor processes (Positive Feedback)
Thalamus is Distribution Center that Controls Activity in Specific Regions of the Cortex – every
area of cerebral cortex connects with its own highly specific area in the thalamus; therefore,
electrical activation of a specific area of the thalamus activates a specific region of the cortex
A Reticular Inhibitory Area is Located in the Lower Brain Stem – the reticular inhibitory area,
located medially and ventrally in the medulla, can inhibit reticular facilitory area and decrease
activity of superior brain through serotonergic neurons
Neurohormonal Control of Brain Activity – excitatory or inhibitory neurotransmitter hormone
agents in the brain can control activity; (1) norepinephrine system, (2) dopamine system, (3)
serotonin system
-norepinephrine is excitatory hormone, serotonin is inhibitory, and dopamine is both excitatory
and inhibitory depending on the location
-norepinephrine spreads to every brain area, but serotonin/dopamine directly to specific
regions; dopamine to basal ganglia and serotonin to midline structures
Neurohormonal Systems in Human Brain – norepinephrine, serotonin, dopamine, acetylcholine
1. Locus ceruleus and Norepineprhine System – locus ceruleus is located
bilaterally/posteriorly between pons and mesencephalon; fibers spread norepinephrine
throughout the brain to increase neuron activity; plays a role in REM sleep
2. Substantia nigra and Dopamine System – substantia nigra is anterior in superior
mesenceophalon, and neurons send fibers to caudate nucleus and putamen of cerebrum,
secreting dopamine (inhibitory neurotransmitter in basal ganglia)
3. Raphe Nuclei and Serotonin – midline of pons and medulla are several nuclei called raphe
nuclei, neurons from which secrete serotonin to diencephalon and cerebral cortex + spine.
Serotonin has ability to suppress pain, and in diencephalon/cerebrum causes sleep
4. Gigantocellular neurons of Reticular Excitatory Area and Acetylcholine – giant cells in the
reticular excitatory area of pons and mesencephalon secrete acetylcholine to higher brain
areas and down reticulospinal tract into spinal cord for excitatory functions; acutely awake
and excited nervous system
Other Neurotransmitters and Neurohormonal Substances Secreted in the Brain – many other
hormonal systems are used in the brain: encephalin, GABA, glutamate, vasopressin, ACTH,
melanocyte stimulating hormone, neuropeptide Y, epinephrine, histamine, endorphine,
angiotensin and neurotensin
Limbic System – limbic means border, used to describe border structures around basal
cerebrum; limbic system controls emotional behavior and motivation drives
-hypothalamus is major controller of internal conditions of body, temp, osmolality, and appetite,
all called vegetative functions of brain, and their control is closely related to behavior
Functional Anatomy of Limbic System (Hypothalamus) – hypothalamus is in the middle of the
limbic system structures, surrounded by the subcortical structures: septum, paraolfactory area,
anterior nucleus of thalamus, basal ganglia, hippocampus, and amygdala
-surrounding the subcortical structures is the limbic cortex, composed of a ring of cerebral
cortex in each side of the brain:
1. beginning in orbitofrontal area in ventral areas of frontal lobes
2. extending upward into subcallosal gyrus
3. over the top of corpus callosum onto medial aspect cerebral hemisphere in cingulate gyrus
4. passing behind corpus callosum into ventromedial surface of temporal love to the
parahippocampal gyrus and uncus
-on the medial/ventral surface of each hemisphere there is a paleocortex, surrounding group of
deep structures associated with behavior and emotions; limbic cortex connects it to neocortex
-many hypothalamic signals for controlling autonomic nervous system transmitted in brainstem
-an important route of communication between limbic system and brainstem is the medial
forebrain bundle, which extends from septal and orbitofrontal regions of cortex through middle
of hypothalamus and brainstem reticular formation
Hypothalamus, Major Control Headquarters for Limbic System – hypothalamus has 2-way
communication system throughout limbic system and sends output signals in 3 directions:
1. backward and downward to brainstem (reticular areas of mesencephalon, pons,
medulla and into peripheral nerves)
2. up to higher areas of diencephalon and cerebrum (ant thalamus/limbic portions of
cortex)
3. into hypothalamic infundibulum to control posterior/anterior pituitary
-hypothalamus controls most of the vegetative and endocrine functions of body and many
aspects of emotional behavior
Vegetative and Endocrine Control of Hypothalamus – controls arterial pressure, thirst and
water conservation, appetite, temperature, and endocrine control
-a large, lateral hypothalamic area is present on each side important for thirst, hunger, emotion
Cardiovascular Regulation – hypothalamus increases arterial pressure and heart rate through
stimulation of posterior and lateral hypothalamus, however stimulation of the preoptic area
causes decreases in arterial pressure/heart rate  transmitted through reticular regions
Regulation of Body Temperature – anterior portion of hypothalamus (preoptic area) regulates
body temperature; increase in blood temperature activates temp-sensitive neurons, whereas a
decrease in blood temp decreases those activities
Regulation of Body Water – hypothalamus regulates H2O in two ways: creating sensation of
thirst and controlling excretion of H2O in urine
-a thirst center is located in the lateral hypothalamus; when fluid electrolytes in this center
becomes too concentrated, animal develops desire to drink until electrolytes return to normal
-control of renal excretion of H2O is through the supraoptic nuclei; when fluids become
concentrated, neurons here are stimulated and project down to posterior pituitary to secrete
antidiuretic hormone (vasopressin) which is absorbed into blood and acts on kidney to increase
reabsorption of H2O, decreases loss of water but increases excretion of electrolytes to decrease
the concentration of body fluids
Regulation of Uterine Contractility and Milk Ejection – stimulation of the paraventricular nuclei
causes their neuronal cells to secrete oxytocin to increase uterine contractility and contraction
of myoepithelial cells surrounding breast alveoli to empty milk through nipples
-at the end of pregnancy, large amounts of oxytocin are secreted to promote labor contractions
Gastrointestinal and Feeding Regulation – stimulation of several areas of hypothalamus causes
animal to experience hunger; such as the lateral hypothalamic area
-the ventromedial nucleus has a satiety center that opposes hunger center and causes animal
to stop eating
-mamillary bodies control patterns of feeding reflexes, like licking lips and swallowing
Control of Endocrine Hormone Secretion – stimulation of hypothalamus causes anterior
pituitary to secrete endocrine hormones; anterior pituitary receives blood from blood that first
flows through lower hypothalamus and then through anterior pituitary vascular sinuses; so
hormones can be released into this blood that reach the pituitary to act on glandular cells
Behavioral Functions of Hypothalamus –
Effects Caused by Stimulation of Hypothalamus – stimulation of hypothalamus has profound
effects on emotion/behavior, such as:
1. stimulation of lateral hypothalamus causes thirst/eating and increases general activity
level leading to overt rage and fighting
2. stimulation of ventromedial nucleus opposes lateral hypothalamic stimulation to cause
sense of satiety, decreased eating, and tranquility
3. stimulation of thin zone of periventricular nuclei next to 3rd ventricle leads to fear and
punishment reactions
4. sexual drive can be stimulated from anterior and posterior hypothalamus
Effects Caused by Hypothalamic Lesions – opposite effects to stimulation effects
1. bilateral lesions of lateral hypothalamus will decrease drinking/eating and cause
extreme passivity of animal with loss of drives
2. bilateral lesions of ventromedial areas will oppose those lesions in lateral hypothalamus;
excessive drinking/eating, hyperactivity and continuous savagery with rage
Reward and Punishment Function of Limbic System – several limbic functions are concerned
with affective nature of sensory sensations, whether they are pleasant or unpleasant; also
called reward or punishment, or satisfaction/aversion
Reward Centers – found to be located along course of medial forebrain bundle, especially in the
lateral and ventromedial nuclei of hypothalamus
-lateral hypothalamus strong signals cause rage, weak signals cause reward
-less potent centers are the septum, amygdala, and areas of thalamus/basal ganglia
Punishment Centers – most potent areas for punishment and escape have been found in the
central gray area surrounding the aqueduct of Sylvius in mesencephalon and into periventricular
zones of hypothalamus and thalamus
-less potent areas are amygdala and hippocampus
-stimulation of punishment centers will inhibit reward centers; punishment/fear takes
precedence over reward and pleasure
Rage – emotional pattern involved in punishment centers of hypothalamus and other limbic
structures has been characterized as follows:
-STRONG stimulation of punishment centers in periventricular zone of hypothalamus and
lateral hypothalamus causes defense posture, extend claws, lift tail, hiss, spit, growl,
piloerection, wide-open eyes, dilate pupils
-normal rage phenomenon held back by inhibitory signals from ventromedial nuclei of
hypothalamus, hippocampus, and anterior limbic cortex
-Placidity and Tameness – exact opposite
Importance of Reward or Punishment on Behavior – reward and punishment control body
activities, drives, aversions, and motivations
-Effect of Tranquilizers on Reward/Punishment Centers – tranquilizers such as chlorpromazine
inhibits both reward and punishment centers and decreases reactivity of animal
Importance of Reward of Punishment in Learning and Memory – experience that causes
neither reward nor punishment is hardly remembered at all; repeated stimulus without reward
punishment causes habituation and extinction of response
-if stimulus DOES cause reward or punishment, cortical response becomes increased upon
repeated stimulation, and response is reinforced
Specific Functions of Other Parts of Limbic System –
Functions of Hippocampus – hippocampus is elongated portion of cortex with an amygdaloid
nuclei on one end, and its lateral border fuses with parahippocampal gyrus, which his cerebral
cortex on ventromedial outside of temporal lobe
-hippocampus and its structures are called hippocampal formation and has many connections
to cortex and limbic system; any sensory experience causes hippocampal activation
-hippocampus distributes outgoing signals to thalamus, hypothalamus and other limbic
structures, especially through the fornix
-stimulation of hippocampus can cause pleasure, rage, passivity, or sex driv
-hippocampus can become HYPEREXCITABLE, and weak stimulation can cause small epileptic
seizures in small areas of hippocampi
-during hippocampal seizures, person experiences psychomotor effects: including olfactory,
visual, auditory, tactile, and other types of hallucinations
-hippocampus only has 3 nerve cell layers, where other areas have 6
Role of Hippocampus in Learning –
Effect of Bilateral Removal of Hippocampi – Inability to Learn – people with removal of
hippocampi bilaterally can recall previously learned memories but are unable to learn new
information based on verbal symbolism (names of people), but they CAN remember what goes
on during activities
-capable of short term memory for seconds up to a minute, but no ability to establish long term
(greater than 1 min) memory; called anterograde amnesia
Theoretical Function of Hippocampus in Learning – hippocampus originated as part of olfactory
cortex, and played a role in determining whether animal ate particular food; if hippocampus
signals that a neuronal input is important, information is likely to be committed to memory
-hippocampus provides drive that translates short-term memory into long-term memory
Functions of Amygdala – amygdala is a complex of small nuclei beneath cerebral cortex with
abundant bidirectional connections with hypothalamus and other limbic structures
-in lower animals, it deals with olfactory stimuli and interrelations
-olfactory tract terminates in portion of amygdala called corticomedial nuclei
-in humans, the basolateral nuclei in amygdala plays a big role
-amygdala receives signals from limbc cortex, neocortex of temporal, parietal, and occipital
lobes, especially from auditory and visual association areas
-amygdala sends signals to hippocampus, septum, cortical areas, thalamus, and hypothalamus
Effects of Stimulating Amygdala – stimulation of amygdala can cause changes in arterial
pressure, heart rate, GI motility, defecation/micturition, pupillary dilation, piloerection,
secretion of anterior pituitary hormones, especially gonadotropins and adrenocorticotropics
-besides hypothalamic mediated effects, amygdala stimulation can cause involuntary
movement, such at tonic movements (raising head/bending body), circling movements, clonic,
rhythmical movements, olfactory movements and eating (licking, chewing, swallowing)
-stimulation of amygdala can cause rage, escape, punishment, pain, and fear, but also reward
-finally, stimulation of amygdala can cause erection, ejaculation, ovulation, uterine activity, and
premature labor
Effects of Bilateral Ablation of Amygdala (Kluver-Bucy Syndrome) – animal is not afraid of
anything, extreme curiosity, forgets rapidly, tendency to place everything in mouth, strong sex
drive
-amygdalas function semiconsciously and project to limbic system
Function of the Limbic Cortex – most poorly understood portion of limbic system is the ring of
cerebral cortex around the limbic structures; functions as transitional zone through which
signals are transmitted from remainder of brain and back; functions as an association area for
control of behavior
Ablation of Anterior Temporal Cortex – Kluver-Bucy Syndrome occurs as listed above (curiosity,
sex drive, loses fear)
Ablation of Posterior Orbital Frontal Cortex – causes animal to develop insomnia associated
with intense motor restlessness, becoming unable to sit still and move about continuously
Ablation of Anterior Cingulate Gyri and Subcallosal Gyri – these portions communicate
between prefrontal cerebral cortex and subcortical limbic structures, and destruction of these
releases rage centers of septum and hypothalamus from prefrontal inhibitory influence; animal
becomes ANGRY