Limbic System Flashcards
what is the limbic system?
A collection of cortical and subcortical structures located in the medial and ventral regions of the cerebral hemispheres
What is defined as the limbic cortex/lobe?
The cingulate gyrus and parahippocampal gyrus
What are the four main functions of the limbic system?
Homeostasis, olfactory, memory, emotion (HOME)
List the many components of the limbic system
- Limbic cortex
- Hippocampal formation
- Amygdala
- Olfactory cortex
- Diencephalon
- Septal nuclei
- Brain stem
- Basal ganglia
- Basal forebrain
What are the functions of the limbic cortex?
Cingulate gyrus: memory, emotional processing, afferent nervous system
Parahippocampal gyrus: Memory processing
What are the three parts of the hippocampal formation and do they receive input or send output?
Located on the medial temporal lobe
1. Dentate gyrus: afferent input
2. Subiculum: efferent output
3. Hippocampus: efferent output
What is the amygdala responsible for and what nuclei are involved?
Functions: emotion, behavior, emotional response to smell
Nuclei: corticomedial nucleus (olfaction), central nuclei (autonomic control), basilar nuclei group (all other emotions)
What are the nuclei involved in the limbic system within the hypothalamus?
Mamillary bodies: main nuclei involved in limbic pathways
ANS nuclei: give rise to parasympathetic and sympathetic pathways
What are the nuclei involved in the limbic system within the thalamus?
Anterior nucleus of the thalamus: involved in the Papez Circuit and memory
Mediodorsal nucleus of the thalamus: emotions and behaviors
How is the septal area involved in the limbic system?
- It is connected to the Habenula which is part of of the epithalamus
- Part of the reward pathways and involved in dopamine and serotonin
What is the association cortex?
- Part of the cerebral cortex that is not directly involved with sensation or movements
- Found in prefrontal cortex and temporal cortex
- Helps associate motor and sensation to emotions
Match the limbic system function acronym HOME with the key structure responsible for the function
Homeostasis: hypothalamus
Olfaction: olfactory cortex
Memory: hippocampal formation
Emotion: amygdala
What vasculature supplies blood to the limbic system?
Anterior cerebral artery: medial surface of frontal and parietal lobe
Posterior cerebral artery: medial and inferior surface of the temporal lobe
Anterior choroidal artery: cingulate gyrus, parahippocampal formation, and amygdala
Branches of circle of willis: hypothalamus, anterior commissure
List the tracts involved in the limbic system
- Medial and lateral olfactory stria
- Fornix
- Stria terminalis
- Ventral amygdala fugal pathway
- Mammillothalamic tract
- Medial forebrain bundle
Describe the medial and lateral olfactory stria
- Involved in olfaction
- Receives input from olfactory tracts
- Sends output to the primary olfactory cortex, orbital frontal olfactory cortex, corticomedial nucleus of the amygdala (smell evoked emotion), parahippocampal gyrus (smell evokes memory)
Describe the fornix
- Involved in memory pathways
- Signals sent between septal areas in deep center of brain, hippocampal formation, and mamillary bodies of the hypothalamus
Describe the mammillothalamic tract
- Involved in memory pathways
- Sends input to the anterior nucleus of the hypothalamus
Describe the stria terminalis
- Involved in the amygdala pathway (long way to reach septal area because it travels along the wall of the lateral ventricle)
- Signals between the septal area, amygdala (fornix), and hypothalamus
Describe the ventral amygdalofugal pathway
- Involved in the amygdala pathway (short way to reach septal area)
- Signals between septal area, amygdala, hypothalamus, and mediodorsal nucleus of the thalamus
Describe the medial forebrain
- Involved in sending information about behaviors, emotions, and personality to the brainstem and back (two way connection)
- Signals sent from amygdala to hypothalamus, to brainstem and back
What is olfaction?
- Function: smell contributes to the sensation of odors and taste
- Single odor molecule activates olfactory receptors, this results in a infinite number of different odors
- The only sensation that bypasses the thalamus
How is smell detected?
Smell stimulus > activation of olfactory receptors > olfactory nerves > through cribiform plate of ethmoid bone > olfactory bulb > olfactory tract > medial and lateral olfactory stria
Which part of the brain is responsible for declarative memory specifically?
- Hippocampal formation
- Medial temporal lobes (parahippocampal gyrus, entorhinal cortex)
How can memory influence decision making?
There is an important connection between the hippocampal formation and the prefrontal association cortex that allows you to consult your memory during decision-making to ensure you are making the correct decision
Describe the pathway of the Papez circuit
- Responsible for memory processing and learning
- Signals from the subiculum of the hippocampus sent to the mammillary bodies of the hypothalamus via the fornix
- Mamillary bodies send signals to the anterior nucleus of the thalamus via the mammillothalamic tract
- Anterior nucleus of the thalamus sends signals to the cingulate gyrus and pre-frontal association cortex
- The cingulate gyrus sends signals to the parahippocampal gyrus
- The parahippocampal gyrus sends signals to the dentate gyrus of the hippocampus, signals then make their way back to the subiculum
What are the three types of memory processes?
- Encoding: acquiring information
- Storage: maintaining information (medial temporal lobe)
- Retrieval: recalling information (communication with prefrontal cortex and other association cortices)
What is retrograde amnesia?
Type of declarative memory failure in which there is a loss of memories that occurred before the trauma or disease
What is anterograde amnesia?
Type of declarative memory failure in which there is a loss of memory that occur after the trauma or disease
How may someone with amnesia learn new things?
Through implicit memory they may have a change in performance without conscious awareness, there may be an improvement in perceptual skills (face and pattern recognition) and cognitive skills (reasoning and logic)
What is Wernicke Encephalopathy/Wernicke Korsakoff Syndrome?
- Disorder of hippocampal function
- Destruction of mammillary bodies of the hypothalamus due to thiamine (B1) deficiency
- Symptoms: profound memory loss, confabulation, impulsive, eye movement abnormalities, ataxia
What is Alzheimer’s disease?
- Disorder of hippocampal function
- Bilateral hippocampal, temporal, and basal forebrain structures have disruptions of cholinergic neurons resulting is progressive dementia/memory loss
What is psychogenic amnesia?
- Disorder of hippocampal formation
- Memory loss for events of particular emotional significance
What is a seizure?
High frequency electrical discharge and firing of neurons in the brain resulting in abnormal experience of behavior
What are the phases of a generalized seizure?
Tonic: all muscles stiffen and person falls over
Clonic: rhythmic bilateral jerking
Ictal (during the seizure): autonomic response of tachycardia, HTN, hypersalivation, and pupillary dilation
Post-ictal (after the seizure): fatigue, amnesia, headache, deep breathing to compensate for acidosis
What are the two types of partial seizure?
Simple: person is aware during the seizure and symptoms depend on the area of the brain that is affected (ex. right motor cortex hand area = hand twitching, visual association cortex = hallucinations)
Complex: impaired consciousness and increased symptoms
Describe the common symptoms for a seizure that occurs in the medial temporal lobe
- Aura is common
- Memory loss (anterograde amnesia) if repeated, resulting in hippocampal sclerosis
- Contralateral dystonia (basal ganglia typically involved)
- Ipsilateral automatisms: repetitive behaviors such as limb patting or stroking, or lip smacking
What is the cause of a medial temporal lobe seizure? What is the treatment?
Cause: genetics, fever, head trauma, CVA, infection, electrolyte abnormality
Treatment: medications, surgery, ketogenic diet, neurostimulation, hemispherectomy if pt is under 2-3 years old
What is the function of the amygdala?
- Emotional responses: occurs in a situation where you feel fear, anger, rage, sadness and the amygdala must communicate with other structures
- Involved in motivation, behavior, personality, etc.
Why are there connections between the amygdala and the association cortex and temporal lobe?
- Decision making influenced by memory and emotions
- The ability to regulate emotion
Describe the signal between the amygdala and hypothalamus regarding appetite
- Sadness pertaining to appetite depending on where in the hypothalamus the synapse occurs
- Ventromedial nucleus of the hypothalamus: satiety, too sad to eat
- Lateral hypothalamic nucleus: hunger, i need to eat my sorrows away
Describe the signal between the amygdala and hypothalamus regarding sexual behavior
- Good feelings
- Periventricular nucleus of hypothalamus: releases oxytocin which increases sexual drive and blood flow to organ
- Medial preoptic nucleus of the hypothalamus: releases gonadotropin releasing hormone to increase sex drive
What are the two areas involved in the amygdala’s reward seeking pathway and what are the clinical implications?
- Medial prefrontal cortex
- Ventral striatum
- Implications: sense of euphoria with drug use leading to abuse and addiction
Describe the mesolimbic pathway as it pertains to reward-seeking
Ventral tegmental area > dopaminergic neurons > nucleus accumbens (ventral striatum on basal ganglia)
Describe the cortico-basal ganglia-thalamus circuit as it pertains to reward-seeking
Ventral tegmental area > dopaminergic neurons > medial dorsal thalamic nuclei > medial prefrontal cortex
What is addiction?
- Loss of behavioral control in response to a stimulus combined with continued use of a substance regardless of negative consequences
- Those effected have lower levels of dopamine
What specific functions is the hypothalamus responsible for in the limbic system?
- Emotional influences on autonomic pathways
- Homeostasis including immune function
- Homeostasis as it pertains to motivation and reproduction
What are some examples of homeostatic changes can be seen based on emotions?
- Really scared: shaking, pilo erection
- Embarrassed: cheeks get red (vasodilation)
- Nervous: blotchy, sweaty
Describe how the homeostasis pathway can create an autonomic response
- Central nuclei of the amygdala senses an emotion of fear and anxiety and sends it to the hypothalamus via the stria terminalis or the ventral amygdalofugal pathway
- Descending autonomic fibers send signals from the hypothalamus to the brainstem via the medial forebrain bundle
- Fibers synapse on the parasympathetic nuclei in the brainstem and sacral region, and on sympathetic nuclei in the thoracolumbar region
- Increase HR, glucose secretion, vasoconstriction to LEs for running, increase respiratory rate
What makes up the diencephalon?
- Thalamus
- Hypothalamus
- Epithalamus
- Subthalamus
Why is the hypothalamus essential to survival?
- Homeostasis: circadian rhythm, appetite, thirst, drive
- Endocrine control: release hormones and stimulatory/inhibitory factors to pituitary gland
- Autonomic: descending projections influence sympathetic and parasympathetic divisions of the ANS via medial forebrain bundle
- Limbic system: involved in the stria terminalis, ventral amygdalofugal pathway, fornix, and mammillothalamic tract (limbic = emotions and memory)
What hormones are released from the anterior pituitary gland and what are their functions?
- Adrenocorticotropic hormone: stimulates adrenal cortex to produce corticosteroid hormones, important for BP and electrolyte regulation
- Growth hormone: stimulates organs to secrete hormones to promote growth in long bones and other tissues
- Prolactin: mammillary glands to produce milk
- Luteinizing hormone and follicle stimulating hormone: regulates ovarian hormone for menstruation and ovulation in females, regulates testicular hormones and spermatogenesis in males
What hormones are released from the posterior pituitary gland and what are their functions?
- Antidiuretic hormone: increases reabsorption of water in the kidney, allows for concentration of urine
- Oxytocin: stimulates smooth muscle in the uterus for labor and delivery, elicits milk expulsion in lactating females
What symptoms can arise with pituitary tumors?
- Headaches
- Nausea/vomiting
- Irregular menstruation and lactation
- Sexual dysfunction
- High BP
- Increased glucose
- Acromegaly: growth hormone disorder causing enlargement of the head, hands, and feet
- Cushing’s disease: excessive adrenocorticotropic hormone causing abnormal deposits of face and trunk fat
- Bitemporal hemianopia: compression of optic chiasm
