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• There are four major parts of the brain: The most “primitive” part of the brain is the brainstem The diencephalon is an “outgrowth” of the brainstem The cerebellum coordinates complex movements The cerebrum is the “newest” part of the brain, and is involved in “higher” brain function The Brain Comparative Physiology: The Vertebrate Brain Protective Mechanisms of the Brain • The brain is covered by the same three meninges as the spinal cord: Dura mater Arachnoid mater Pia mater • Extensions of the dura mater separate parts of the brain: The falx cerebri separates the two cerebral hemispheres The falx cerebelli separates the two cerebellar hemispheres The tentorium cerebelli separates the cerebrum and the cerebellum Protective Mechanisms of the Brain • The blood brain barrier (BBB) prevents substances in the blood from entering the brain • It consists in part of tight junctions in endothelial cells of capillaries, and a thick basement membrane • It also consists of processes of astrocytes which press up against the endothelial cells • Glucose crosses the BBB by special transport • Most water soluble substances cannot cross the BBB • Most lipid soluble substances can cross the BBB Cerebrospinal Fluid (CSF) and Ventricles • CSF protects the brain, and carries O2, glucose, and ions • CSF circulates continuously in the subarachnoid space of the brain and spinal cord • CSF fills cavities called ventricles: Lateral ventricles (separated by the septum pellucidum) 3rd ventricle (between halves of thalamus) 4th ventricle (between brain stem and cerebellum) • CSF is generated in the choroid plexuses • CSF is reabsorbed into the blood through the arachnoid villi Structures of the Brainstem • The medulla oblongata is continuous with the spinal cord • It regulates heart rate, blood vessel diameter, and breathing • It controls several survival oriented reflexes for vomiting, coughing, hiccuping, sneezing, and swallowing • It contains the pyramids and the olives ~90% of the descending corticospinal tracts cross in the pyramids This is known as the decussation of the pyramids The inferior olivary nuclei convey proprioceptive information The medulla contains nuclei for cranial nerves VIII - XII Structures of the Brainstem • The pons is the “bridge” between the brain stem and the cerebellum The pneumotaxic and apneustic areas help regulate breathing • The pons contains nuclei for cranial nerves V - VIII • The midbrain lies between the pons and the diencephalon The tectum consists of the superior and inferior colliculi The superior colliculi function as visual reflex and tracking centers The inferior colliculi function as auditory reflex and transmission centers The cerebral aqueduct passes through the midbrain, connecting the 3rd and 4th ventricles • Structures of the Brainstem The midbrain also contains the substantia nigra: So named because of its dark color Dopaminergic neurons send axons into the putamen and caudate nuclei Degeneration of these neurons leads to Parkinson’s disease • The midbrain also contains the red nuclei Once again named for their color Cell bodies for the rubrospinal tract, function with the cerebellum to coordinate movements • The midbrain contains nuclei for cranial nerves III and IV • The ascending reticular activation system (ARAS) helps regulate sleep and wakefulness Structures of the Diencephalon • The diencephalon lies superior to the brain stem • The thalamus is the relay station, switchboard, or network router of the brain It routes incoming sensory information to the appropriate locations in the cerebrum Involved in crude pain, temperature, and pressure sensations • The pineal gland releases melatonin, an indoleamine related to serotonin, which is involved in regulating sleep • The habenular nuclei (not shown) are involved in olfaction and emotional responses to smell Structures of the Diencephalon • The hypothalamus lies inferior to the thalamus Involved in the 4 F’s Major regulator of homeostasis Monitors blood glucose, blood pressure, and many hormones Controls the ANS Controls circadian rhythms • The pituitary gland is connected to the hypothalamus by the infundibulum • The posterior pituitary is an extension of the hypothalamus, the anterior pituitary is the “master gland” of the endocrine system • The pituitary is situated in the hypophyseal fossa of the sella turcica The Cerebellum • Posterior to the pons and medulla • Second largest structure in the brain • Accounts for only 10% of the brain’s mass, but 50% of the neurons • Connected to the brain stem by the cerebellar peduncles • Sends feedback signals to the motor cortex to regulate balance and posture • Monitors and coordinates complex skilled movements, such as speaking, dancing, juggling, riding a bicycle, skipping, flipping a pancake, playing a musical instrument, hitting a baseball, playing a video game, skating, etc. • The cerebellum is one of the first brain structures affected by alcohol The Cerebrum: Lobes • Involved in cognition, memory, learning, problem solving, and “higher functions” • Divided into two lateral hemispheres connected by the corpus callosum • Divided into 4 lobes: The frontal lobe is involved in planning, organizing, personality, attention, speech, movement (motor cortex), emotions, problem solving, and more. The occipital lobe is the primary visual center of the brain The parietal lobe includes the sensory cortex and association cortex The temporal lobe is involved in auditory and visual processing, and memory • Deep folds of the cerebrum, not seen from the surface, are called insula The Cerebrum: Basal Ganglia • Three nuclei deep within the cerebral hemisphere • Globus pallidus and putamen together known as the lentiform nucleus • Together with caudate nucleus known as the corpus striatum • Linked to substantia nigra and subthalamic nuclei • Regulate muscle tone and subconscious movements • Involved in the initiation and termination of movement • Axons from the substantia nigra synapse with neurons in the caudate nucleus • Degeneration of these neurons lead to Parkinson’s Disease The Cerebrum: Basal Ganglia • Parkinson’s patients often have a stooped posture, rigid limbs, and a fixed facial expression • They walk with an unsteady, shuffling gait (the “Parkinson’s shuffle”), and have little arm swing The Cerebrum: Famous Parkinson’s Patients The Cerebrum: White Matter • The corpus callosum is the largest fiber bundle in the brain, with ~300 million fibers • The corpus callosum, anterior commissure, and posterior commissure connect the two hemispheres of the cerebrum • In the past, some patients who had various forms of epilepsy underwent a cerebral commissurotomy, which severed the corpus callosum • This was sometimes knows as “split brain” surgery, because patients experienced a dissociation of the left and right sides of their brains • This created peculiar problems for some patients in which one side of the brain seemed not to know what the other side of the brain was doing The Cerebrum: Split Brain Phenomenon • In one type of procedure, split brain patients were shown two words, each visible to only one visual field • A group of objects, including the objects corresponding to the two words, were placed behind a screen, out of view of the patient • The patient could grab the objects with the left hand • When asked to speak the word that was seen, the patient responded only with the word which registered in the left hemisphere • When asked to grab the object named by the word, the patient grabbed the object corresponding to the word which registered in the right hemisphere The Cerebrum: Limbic System • A group of diverse structures implicated in emotions and memory formation • Also involved in sensations of pleasure and pain • Includes the dentate gyrus, parahippocampal gyrus, amygdala, septal nuclei, mammilary bodies, olfactory bulbs, fornix, and hippocampus • Damage to the hippocampus and amygdala may result in the inability to form new memories • This may result from physical injury, or from chemical injury (e.g. Korsakoff’s Syndrome) The Cerebrum: Sensory & Motor Cortex • Incoming sensory signals register in the primary somatosensory cortex on the postcentral gyrus • Outgoing motor signals arise from the primary motor cortex on the precentral gyrus • A representation of the body can be “mapped” onto these cortexes • This representation is known as a homunculus (“little man”) • Areas such as the face and hands have disproportionately large representations, while regions such as the back have disproportionately small representations • Larger area means more neurons devoted to that region, and so more sensitivity & control The Cerebrum: The Homunculus The Cerebrum: Speech Areas • Speech areas are usually located in the left hemisphere of the cerebrum • Broca’s area is located in the frontal lobe, and is associated with the primary motor cortex • Wernicke’s area is located in the temporal and parietal lobes, and is associated with other auditory processing areas • Broca’s area is involved in the production of speech, Wernicke’s area is involved in speech comprehension • Damage to Broca’s area may result in the inability to form complete sentences • Damage to Wernicke’s area may result in the inability to understand what is being said An Overview of Memory Memory Long Term (“permanent”) Declarative (Explicit) (facts & events) Semantic (facts) e.g. Who is George Washington? Short Term (last 30 sec) Procedural (Implicit) (skills) e.g. Knowing how to ride a bicycle Episodic (events) e.g. What did I have for dinner yesterday? Did you have dinner last night with George Washington, the first President of the United States? Where Is The Following Information Stored? 1. Where you left your car keys. 2. How to make your bed. 3. The meaning of the word beautiful. 4. The capital of North Carolina. 5. How to throw a curve ball. 6. When Columbus “discovered” America. 7. Your best friend in fifth grade. 8. How to drive a manual transmission. 9. Where you went on your first date. 10. When World War II ended. A Review of Memory Amnesia in the Movies No short term memory??? Amnesia Humor Amnesia Definitions • Amnesia is the loss of memory, the inability to remember past events • In many cases, amnesia centers around a traumatic event • Retrograde amnesia is the inability to remember events before the trauma • Anterograde amnesia is the inability to remember events after the trauma Types of Amnesia • Based on its source, amnesia can be divided into two types: organic and psychogenic • Organic amnesia results from some sort of physical trauma to the brain: Head injury Drug toxicity Alcohol blackout Disease (e.g. epilepsy, encephalitis, Alzheimer’s, etc.) ECT (electroconvulsive therapy) Hypoglycemia • Psychogenic amnesia results from some sort of psychological trauma: War, violent crime, etc. Depression Embarrassment, public offense, etc. • Amnesia can be transient or persistent Types of Amnesia • Neither type of amnesia typically affects procedural memory Victims can still drive a car, ride a bicycle, play a musical instrument, etc. • Both types of amnesia may have effects on episodic and semantic memory, but they are characteristically different Organic amnesia Most victims still know who they are Victims usually have continuous and systematic gaps in episodic memory Psychogenic amnesia Victims often don’t know who they are Victims have selective gaps in episodic memory • Most “movie” amnesia doesn’t exist • Many organic amnesia victims confabulate • Anterograde amnesia is an encoding problem, typically involving the limbic system, particularly the hippocampus Information is unable to pass from short term memory into long term memory The memory is not forgotten, it is in fact never even formed