Lecture 2-6 notes exam prep material PDF

Preview

Summary

The medical model: abnormal behaviour is a disease Mental illness, psychopathology, neurobehavioural disorders E., Parkinson’s Disease, Autism Spectrum Disorder, Major Depressive DisorderUseful as an analogy in treatment/prevention of mental illness Diagnosis: Which illness is it? Etiology: What cau...

Description

The medical model: abnormal behaviour is a disease Mental illness, psychopathology, neurobehavioural disorders E.g., Parkinson’s Disease, Autism Spectrum Disorder, Major Depressive Disorder Useful as an analogy in treatment/prevention of mental illness Diagnosis: Which illness is it? Etiology: What caused it? Prognosis: What are the short / long-term consequences? How common are neurobehavioural disorders? Epidemiology: study of the distribution of disorders in the population Prevalence: Percentage of the population that exhibits a disorder during a specified time period 1969 – David L. Rosenhan (Psychology professor at Swarthmore College) Voices in head, “empty, thud, hollow” Diagnosis: schizophrenia “On Being Sane in Insane Places” (Science, 1973) Conclusion: psychiatrists did not have a valid way to diagnose mental illness The nervous system is organized into the central and peripheral divisions. Central Nervous System (CNS) Brain Spinal cord Peripheral Nervous System (PNS) Somatic Nervous System Autonomic Nervous System The PNS has two divisions, each of which has its own sub-divisions: Somatic nervous system: Efferent (outgoing) nerves: Motor nerves that connect the CNS to the skeletal muscles. Afferent (incoming) nerves: Sensory nerves that carry information from the sense organs to the CNS. Autonomic nervous system: Regulates homeostasis. Sympathetic nervous system (SNS): Arousing. “Fight or flight.” Parasympathetic nervous system (PNS): Calming. “Rest and digest.” The brain and spinal cord are protected by special membranes called meninges. When these membranes are infected, meningitis results. Cerebrospinal fluid (CSF) fills the ventricles and circulates around the brain and spinal cord. Like plasma, CSF contains glucose, various salts, and minerals, but unlike plasma it contains very little protein. CSF possesses a similar density to the brain. This allows the brain to float comfortably in the skull. Neurons The basic information processing units of the brain. Approximately 80 billion in the human brain.

Glial cells – “glue (G.)” Support and modulate neurons’ activities. Creates the myelin sheath.

Approximately 100 billion in the human brain. Neurons are specialized cells that are specialized for transferring information from one place to another. Neurons have specialized structures for this purpose. Dendrites – “tree (G.)” Gather information from other neurons. Cell body Core region; contains the nucleus and DNA. Axon hillock Junction of the cell body and axon, where the action potential begins. Axon Carries information to be passed onto other cells. Terminal button Knob at the tip of an axon that conveys information to other neurons. Connects with dendrites of other neurons. Axons, especially longer ones, are usually covered with a myelin sheath. Myelin is a fatty substance produced by glial cells. Myelin insulates the axon, increasing the speed and efficiency of electrical signal conduction. The fatty nature of myelin gives white matter its color. Grey matter Areas of the nervous system composed of cell bodies and blood vessels. Ex. Cerebral cortex, subcortical nuclei, etc., White matter Areas of the nervous system rich in fat-sheathed neural axons. Ex. Subcortical white matter, corpus callosum, etc., Grey matter Areas of the nervous system composed of cell bodies and blood vessels. Ex. Cerebral cortex, subcortical nuclei, etc., White matter Areas of the nervous system rich in myelinated neural axons. Ex. Subcortical white matter, corpus callosum, etc., Tract Large collections of axons in the CNS are called tracts. Tracts connect nuclei to each other in the brain. White matter consists mostly of tracts (myelinated axons) Nerve A large collection of axons forming connections in the PNS. Examples: Phrenic nerve (arising from C3-C5, it controls the diaphragm). Nucleus (pl. nuclei) A distinct cluster of neural cell bodies (grey matter) forming a functional group. Nuclei can be distinguished by their structure, chemical composition, and function. Examples: Ventral Tegmental Area (VTA), Arcuate Nucleus (ARC) etc., The brain’s outer layer of grey matter is called the cerebral cortex - “bark (L.)” It is often just called ‘the cortex’ for short. The cerebral cortex is part of a larger structure called the cerebrum. The cortex is the site of our higher level functions, consciousness, and many other important things.

Neurons in the cortex tend to have a uniform, grid-like organization. This is rather like how suburbs are organized. The comparison makes sense because both suburbs and the cerebral cortex are the most recently developed parts of cities and brains respectively.

On the other hand, neurons in subcortical and brainstem nuclei tend to have a more irregular organization. To continue the analogy, this is like how the innermost parts of old cities often have a confusing and sporadic layout. The inner city, like the deepest regions of the brain, shows evidence of an ancient history. The cerebral cortex has a characteristically wrinkled appearance. This is a space-saving tactic. By crumpling up, the cortex is able to fit more grey matter into the same amount of space. Gyrus (pl. gyri) – “ring, circle (G.)” A bump or convolution between grooves. Sulcus (pl. sulci) – “furrow, trench (L.)” A groove between gyri. Cerebrum - “brain (L.)” Major structure of the forebrain consisting of two virtually identical hemispheres (left & right). Cerebellum – “little brain (L.)” Involved in motor coordination, and possibly other mental processes. Brainstem Comprises the deep structures of the brain. Connects the brain to the spinal cord. Critical for sustaining life (respiration, blood pressure, etc.,) The cerebral cortex is divided into two hemispheres, each of which has four lobes. Frontal lobe Motor control. Executive functions. Occipital lobe – “back of skull (L.)” Vision Parietal lobe – “wall (L.)” Touch sensation. Sense of self in space. Temporal lobe Auditory sensation. Language perception. Gustatory (taste) functions. The limbic system – “edge/border (L.)” – is important for emotions, memories, and can be affected by psychological disorders and drug addiction. It consists of three major parts. Cingulate cortex – “encircling/belt (L.)” Involved in emotional processing and memory.

Amygdala – “almond (G.)” Involved in fear, aggression, and emotionally charged memories. Hippocampus – “seahorse (G.)” Involved in the formation of long-term memories. The basal ganglia are involved in controlling movement. They are also important in learning and memory, and in particular learning “habits”. The basal ganglia consist of three main parts: The caudate nucleus – “tail (L.)” - and putamen – “shell (L.)” - are together known as the striatum – “striped (L.)”. The globus pallidus – “pale globe (L.)” The substantia nigra – “black substance (L.)” - is part of the midbrain. It contains numerous dopaminergic neurons that project into the basal ganglia. Parkinson’s Disease involves the death of DAergic neurons in the substantia nigra. The brainstem is divided into three basic regions. Diencephalon: Thalamus – “inner chamber (L.)” All sensory information (except smell) passes through the thalamus en route to the cortex. Hypothalamus – “below/under (G.) thalamus” Controls homeostasis, regulates hormone secretion from the pituitary gland. Midbrain: Contains neurons that produce dopamine that project to various other brain regions. Hindbrain: Pons – “bridge (L.)” Connects the cerebellum to the brainstem. Medulla – “marrow (L.)” Controls breathing & heart rate. Connects the brain to the spinal cord. The brain, like everything else in the body, is a product of evolution. By its nature, evolution does not tend to remove old things that still work. It may add new improvements on top of the old standbys, but it typically leaves old things alone as long as they aren’t causing any problems. Newly evolved regions like the cortex sit atop older regions (the limbic system), and those in turn sit atop even older regions (the brainstem). Inevitably, things do not work perfectly in this system. The brain was not engineered all at once – it was built up bit by bit and the end result of this is a very fragile and rickety machine. As we will see, our brains and genes are not always well-suited to the modern world. This is often the source of our troubles… In 1849, A.A. Berthold (1803-1861) noted that removing the testes from a developing rooster caused it to become a docile capon. Capons lack many male-type behaviors and anatomical traits (they look more like hens).

Berthold found that if you put some other testes back into a capon, its male-type behaviors and anatomical traits would return. Importantly, this worked even though Berthold did not re-connect the nerves. This suggested to him that the testes secreted a substance into the blood Testosterone Hormones: chemicals secreted by one cell group that travel through the bloodstream to act on targets (other organs, cells) Hormones are released typically by glands Endocrine glands release hormones within the body Exocrine glands use ducts to secrete fluids such as tears and sweat outside the body Synaptic or neurocrine signaling involves chemical release and diffusion across a synaptic cleft. Endocrine signaling involves hormones being released into the bloodstream to act on target tissues. Hormones act in a gradual fashion Hormones act by changing the probability or intensity of a behavior (not like on/off switch) The relationship between behavior and hormones is reciprocal Hormones change behaviours and behaviours change hormone levels A hormone may have multiple effects and one behavior can be affected by several hormones Hormones often have a pulsatile secretion pattern – in bursts Example: Growth Hormone (GH) shows pulsatile release during the day, higher release at night, and maximum levels during puberty. Example: estrogen and progesterone show changes over the roughly month long menstrual cycle. Some hormones are controlled by circadian clocks Hormones can interact with other hormones and change their effects E.g., cortisol can affect levels of luteinizing hormone, ghrelin Hormonal communication is similar to neural communication in three basic ways: Neurons and endocrine glands produce and store chemicals (neurotransmitters or hormones) and release them upon stimulation. Neurotransmitters and hormones both bind to receptors to stimulate target cells. Some chemicals can act as either hormones or neurotransmitters, depending on where they are released. For example: norepinephrine is a neurotransmitter associated with alertness in the CNS, but it is also a hormone released by the adrenal glands under conditions of stress or anxiety. Differ in 4 basic ways: Neural communication travels to precise destinations. Hormonal communication spreads throughout the body, and is picked up by cells with the proper receptor Neural messages are rapid, measured in milliseconds. Hormonal messages are slower, measured in seconds and minutes Distance traveled varies – the synaptic cleft is small while hormones may travel over a meter Neural communications are sometimes under voluntary control, while hormones are involuntary Classified on basis of chemical composition, not function Peptide/Protein hormone – a string of amino acids

E.g., Insulin Monoamine hormones – a modified amino acid, found in brain as neurotransmitters as well E.g., norepineprine Steroid hormones – four rings of carbon atoms E.g., testosterone Unlike many neurotransmitter receptors, hormone receptors are not ion channels. Rather than affecting the membrane potential, when hormones bind to their receptors they trigger the release of intracellular second messengers. Hormones are considered first messengers These second messengers spread throughout the cell and cause a variety of physiological changes. Changes in metabolism, hormone release, receptor trafficking, cell growth, etc. Second messenger mediated effects inside the cell are rapid. Steroid hormones (like testosterone, estrogen, cortisol, etc.,) are all made from cholesterol, a fatty substance. Consequently, steroid hormones are lipophilic and can easily pass through the cell membrane. Steroid hormone receptors are inside the cell, usually floating freely within the cytoplasm. The steroid-receptor complex binds to DNA and acts as a transcription factor – controlling gene expression. Transcription factor mediated mechanisms are slow, however their effects are long-lasting. These mechanisms usually take hours to kick in. Hormones act throughout the body in many ways. These can be generalized into three basic categories: Hormones may promote proliferation, growth and differentiation of cells. Example: Growth hormone promotes growth of the long bones (during childhood and adolescence). Hormones may modulate cell activity and metabolism. Example: Insulin increases glucose uptake by muscle, fat, and liver. Example: Thyroid hormones increase glucose and fat metabolism in all tissue. Hormones may modulate hormone secretion from endocrine glands. Example: ACTH causes the release of cortisol from the adrenal glands. Example: Negative feedback. Four Levels Hypothalamus Pituitary Gland Target Endocrine Glands Target Organs and Tissues Hormones affect almost every neuron in the brain Can also influence genetic expression, synthesis of proteins The pituitary gland – “mucus, phlegm (L.)” – is the “master gland” of the body, secreting hormones that affect function of glands and organs throughout the entire body. The pituitary gland is located at the base of the brain and connected to the hypothalamus to by the pituitary stalk.

There are two parts of the pituitary gland: Anterior pituitary: connected to the hypothalamus by blood vessels. Posterior pituitary: directly connected to the hypothalamus by axons extending from hypothalamic neurons. Major neural system activated during stress Hypothalamus: releases Corticotropin-releasing hormone (or factor; CRH) Pituitary: Acts on anterior pituitary to release adrenocorticotropic releasing hormone (ACTH) Adrenal: Acts on adrenal gland, which releases glucocorticoids, e.g., cortisol The endocrine system is capable of self-regulation. The various hormonal systems use negative feedback to control their function. The principle of negative feedback loops is critical in maintaining homeostasis. Broadly speaking, negative feedback is the counteraction or reduction of an effect that occurs as a result of the effect itself. The hypothalamus determines a set point for the hormone level. In this case, the set point is a medium level of the hormone. 1. The hypothalamus detects circulating hormone levels. If they are too low, the hypothalamus orders the secretion of more of that hormone. 2. The blood level of the hormone goes up. 3. At a certain point, the hormone levels approach (or slightly overshoot) the set point. In response, the hypothalamus orders hormone secretion to stop. 4. Hormone levels begin to decline again. The system loops back to step 1. 5. The hypothalamus determines a set point for the hormone level. In this case, the set point is a medium level of the hormone. 6. The hypothalamus detects circulating hormone levels. If they too low, the hypothalamus orders the secretion of more of that hormone. 7. The blood level of the hormone goes up. 8. At a certain point, the hormone levels approach (or slightly overshoot) the set point. In response, the hypothalamus orders hormone secretion to stop. 9. Hormone levels begin to decline again. The system loops back to step 1, and the cycle repeats. A huge number of processes in the brain are governed by negative feedback loops. Real-world applications of this concept often involve several extra steps, but the basic process remains the same. Stressors are stimuli that challenge the body’s homeostasis and trigger a response. psychological or physical May be real, perceived, or imagined threats. If a stimulus causes a stress response, it can be considered a stressor. The stress response is the body’s response to the challenge of a stressor. The stress response involves physiological and behavioral changes that attempt to cope with or escape the stressor. All stressors (psychological or physiological) produce a similar pattern of physiological changes. While major stressors (war, disaster, death, divorce, etc.,) are clearly problematic, researchers are finding that minor stressors (waiting in line, paying bills, other daily hassles,) add up as well. Additionally, major stressors can produce minor stressors The major life event divorce can lead to a lot of smaller hassles: finding a lawyer, separating belongings, moving, arguing, etc.,

Routine, daily stressors may have a significant impact on health. This may be an especially big problem in modern times, when daily hassles are inescapable. Our everyday experience attests to the fact that stress exists. But why does it exist? What possible benefit could there be in getting stressed? Does the stress response really help us? To begin to answer this, we have to think about the big picture. It’s been said that ‘generals are always prepared for the last war’, and similarly our brains are always prepared for the challenges of our ancestors. If we cannot see the wisdom in the stress response in then modern era, then we have to look back in time at the conditions in which we evolved. Think about an animal with a much simpler life, say a zebra*. What are some realistic scenarios that might stress a zebra? Getting chased by a lion. Getting chased by a bear (if bears ever invaded the African savanna.) Starvation, illness, etc., There are more, but the basic idea here is that for most animals (zebra included), stressors are episodic and shortlived. If a zebra is stressed by a lion, within a few minutes it either escapes or gets eaten. In the wild, survival is a high-stakes game and there is no point in ‘holding anything back’. When animals encounter a stressor, they use it as a cue to dump all of their body’s resources into survival. Wouldn’t you do the same in a life or death situation? Given that most stressors in wild animals are short-lived, life or death scenarios, we can begin to see why the stress response works the way it does. In general, the stress response accomplishes two things: 1) Temporarily puts the brain and body into ‘overdrive’ in order to deal with the stressor. 2) Suspends bodily repair, construction and growth in order to conserve energy. Hans Selye (1907-1982) is often credited with being the first scientist to characterize the concept of stress. He proposed a three stage model called general adaptation syndrome. Alarm: Initial reaction to stressor. “Fight or flight (SNS)” activated. Resistance: Physiological adaptations take place to help cope with prolonged stressors. Involves cortisol and the HPA axis. Exhaustion: Physiological resources are depleted as the body becomes unable to cope with the prolonged stressor. This is where diseases can begin to appear. This basic progression is the same regardless of the type of stressor. Physical and psychological stressors of all types produce these effects. The stress response involves two separate pathways: The sympatho-adrenomedullary axis (SAM axis) – The “fast pathway” Mediates the initial “alarm” phase of the stress response. The hypothalamic-pituitary-adrenal axis (HPA axis) – The “slow pathway”

Mediates the physiological adaptations involved in dealing with prolonged stress. The adrenal glands - “of or near kidney (L.)” – sit atop the kidneys. The adrenal glands are critical for the stress response. The adrenal glands are actually two glands in one. The adrenal medulla secretes epinephrine (aka adrenaline) and norepinephrine (aka noradrenaline). The adrenal cortex secretes cortisol. There are two steps in SAM activation: Neural circuits in the hypothalamus project to the spinal cord, where they synapse with neurons of the sympathetic nervous system (SNS). SNS neurons project to the adrenal medulla. The adrenal medulla releases the catecholamines epinephrine and norepinephrine into circulation. The catecholamines epinephrine and norepinephrine bind to adrenergic receptors located throughout the body. Epinephrine and norepinephrine have a number of rapid effec...