THE LIMBIC SYSTEM

LEARNING OBJECTIVES Define limbic system Know the different parts and function of Limbic system Describe the functions of various parts of Hypothalamus

LIMBIC SYSTEM Limbic means the structure which lies on medial rim of brain between cerebral cortex & hypothalamus Limbic system is a set of brain structure including hippocampus, amygdala, ant. thalamic nuclei and limbic cortex

Limbic System Not a separate structure but a ring of forebrain structures that surround the brain stem Responsible for Emotions , long term memory, olfaction Basic, inborn behavioral patterns related to survival and perpetuation of the species Plays important role in motivation and learning

Schematic of the Limbic System Components

Location of the Limbic System

Hypothalamus major output pathway of the limbic system vegetative functions: neurogenic control of arterial pressure regulation of body temperature regulation of fluid volume regulation of endocrine gland secretion growth hormone, thyroid hormone, glucocorticoid secretion, sex hormones

Behavioral Functions of the Hypothalamus and Related Areas lateral hypothalamus eating, thirst, general level of activity, rage ventromedial nucleus satiety, tranquillity periventricular nucleus fear, punishment reactions anterior and posterior hypothalamus sexual drive

Functional Areas of the Hypothalamus

Hypothalamus Brain area most involved in directly regulating internal environment Functions Controls body temperature Controls thirst and urine output Controls food intake Controls anterior pituitary hormone secretion Produces posterior pituitary hormones Controls uterine contractions and milk ejection Serves as a major ANS coordinating center Plays role in emotional and behavioral patterns Participates in sleep-wake cycle

Behavior and its Control Almost all behaviors are associated with either reward or punishment. Several limbic structures are concerned with the affective nature of the sensory experience–is it pleasant or unpleasant? Reward center - located around medial forebrain bundle (the lateral and ventromedial hypothalamus). Punishment center - located in central gray around the aqueduct and extending into periventricular zones of hypothalamus and thalamus. Punishment always takes precedent over reward

Function of Other Limbic Areas Amygdala receives input from other areas of limbic system as well as most areas of the cortex sends output back to cortex as well as into hippocampus, septum, and hypothalamus functions in behavioral awareness at the semiconscious level projects into limbic system one’s status with respect to the surroundings and current thoughts helps pattern behavior appropriate for the each occasion

Function of Other Limbic Areas Hippocampus originated as part of the olfactory cortex in lower animals the sense of smell is an important determinant of behavior (is it good to eat, does it smell like danger, is it sexually inviting) therefore, the early hippocampus was involved in decision making by determining the importance of the incoming information

Hippocampus memory and learning, (in remembring recent events) damage causes anterograde amnesia reward and punishment determine whether or not information will be stored as memory a person becomes habituated to indifferent stimuli but learns any sensory experience that causes pain or pleasure hippocampus provides the drive to rehearse and consolidate these sensory experiences

Limbic Cortex cerebral association area, Role in anger, fear and emotional behavior with sexual behavior stimulation of various portions of this area can elicit almost all types of behavior in an animal

Functions of limbic system Part Function Amygdala aggression & fear Cingulate gyrus autonomic functions Hippocampus recent memory Mammilary body long memory Prefrontal cortex personality

Malfunction of limbic system Leads to psychiatry disorders e.g. Schizophrenia, depression and senile dementia Lesions in hippocampus: loss of recent memory, in Alzheimer’s disease there is extensive degeneration of hippocampus Lesions in Amygdaloid nucleus: loss of aggressive behavior, fear and anger

References Human physiology by Lauralee Sherwood, seventh/eighth edition Text book physiology by Guyton &Hall, 12th edition Text book of physiology by Linda .s contanzo, third edition