Neuroscience1202 (Module 1) - Lecture 3-7 - week 1-3 - w/ kim hellemans PDF

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Module 1 - NeuroanatomyTe r m s Diagnosis : which illness is it? Etiology : What caused it? Prognosis : What are the short / long-term consequences? Epidemiology : study of the distribution of disorders in the population Prevalence : Percentage of the population that exhibits a disorder during a spe...

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Module 1 - Neuroanatomy Terms! • • • • •

Diagnosis: which illness is it? " Etiology: What caused it?" Prognosis: What are the short / long-term consequences?" Epidemiology: study of the distribution of disorders in the population Prevalence: Percentage of the population that exhibits a disorder during a specified time period"

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Lecture 3 - Organization of the nervous system Structures of the Nervous System! Directional Terminology In biology, directional terms are given with respect to the organism’s body axis. These terms are important for navigating creatures with unusual body plans or lifestyles." Dorsal - atop of the brain" Ventral - towards bottom of the brain" Anterior - towards the front" Posterior - towards the back" Medial - towards the middle" Lateral - towards the side"

Coronal section: is cut in a vertical plane, from the crown of the head down, yielding a frontal view of the brains internal structures - a frontal view." Horizontal section: is a slice from the anterior to the posterior, viewed looking down on the brain from above - a dorsal view." Sagittal view: is cut lengthways from the front to the back and is viewed from the side - a medial view. Separates left and right hemispheres."

Organization of the nervous system

- Organized into the central and peripheral divisions" • Central Nervous System (CNS)" – Brain – Spinal cord • Peripheral Nervous System (PNS)" – Somatic Nervous System – Autonomic Nervous System" Sensory connections to the receptors in the skin" Skin connects to body muscles (motor connections)" Sensory and motor connections to internal body organs (autonomic system)" Consists of nerves flowing out of spinal cord (Somatic nerves, optic nerves, auditory nerves)"

Organization of the Peripheral Nervous System The PNS has two sub-divisions: " • Somatic (body) 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 (autonomous from your control) nervous system: Regulates homeostasis. – Sympathetic nervous system (SNS): Arousing. “Fight or flight.” – Parasympathetic nervous system (PNS): Calming. “Rest and digest.”

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Ventricular System The brain is cushioned and supported by a series of interconnected hollow spaces called “ventricles” —>" When the brain is stressed you lose grey matter (cell loss) cerebral spinal fluid increases (enlarged cerebral ventricles) to compensate for “shrinking of the brain” (sign of autism, schizophrenia, certain dementias) CFS circulates and contains certain salts to nourish the cells. It also circulates outside of the brain; meninges."

The Meninges and CPF • 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."

Blood-Brain Barrier • The tight gaps between endothelial layer (cells that line the blood vessels) prevent large molecules from passing into the brain • One of the protective mechanisms of the nervous system; prevents potentially lethal substances from entering the brain" • Not perfect"

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Brain Cells - Two types of brain cells" • 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 (more populous)"

Neurons Transmitting Information • Neurons are specialized cells that are specialized for transferring information from one place to another."

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• 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." Oligodendrocytes myelinate axons in the CNS

•The fatty nature of myelin gives white matter its colour."

Schwann cells myelinate axons in the PNS

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Grey Matter & White Matter • 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. Sub cordial white matter, corpus callous, myelin sheath, etc.,"

Grouping of axons: tracts & nerves • 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 "

Grouping of cell bodies: nuclei • 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.,"

Groupings of cell bodies: cortex The brain’s outer layer of grey matter is called the cerebral cortex - “tree bark”" – 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 form networks •

Neurons in the cortex tend to have a uniform, gridlike 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.

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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.

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Contrasting cortex with other brain regions The cerebral cortex has a characteristically wrinkled appearance." !

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This is a space-saving tactic. By crumpling up, the cortex is able to fit more grey matter into the same amount of space."

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• Gyrus (pl. gyri) – “ring, circle (G.)” – A bump or convolution between grooves." • Sulcus (pl. sulci) – “furrow, trench (L.)” – A groove between gyri."

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External features of the brain

• Cerebrum - “brain”

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– Major structure of the forebrain consisting of two virtually identical hemispheres (left & right). • Cerebellum – “little brain” – 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.,)"

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The Cerebral Cortex

• The cerebral cortex is divided into two hemispheres, each of

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which has four lobes. • Frontal lobe – Motor control. – Executive functions. • Occipital lobe – “back of skull” – Vision • Parietal lobe – “wall” – Touch sensation. – Sense of self in space. • Temporal lobe – Auditory sensation. – Language perception. – Gustatory (taste) functions."

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The Corpus Callosum

- The corpus callosum - “firm body” - connects the two cerebral hemispheres, allowing both sides of the brain to work together."

- 2 More Distinct systems The Limbic System (*FORM & FUNCTION*)"

• The limbic system – “edge/border” – is important for emotions, motivations, memories, and can be affected by psychological disorders and drug addiction. It consists of three major parts:"

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• Cingulate cortex – “encircling/belt – Involved in emotional processing and memory."

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• Amygdala – “almond (G.)” – Involved in fear, aggression, and emotionally charged memories."

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• Hippocampus – “seahorse (G.)” – Involved in the formation of long-term memories."

The Basal Ganglia (motor tasks) • 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” - and putamen – “shell” - are together known as striatum – “striped”. • The globus pallidus – “pale globe” • The substantia nigra – “black substance” - 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."

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The Brainstem

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• The brainstem is divided into three basic regions.

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• 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.

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• 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."

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Module 2 - Communication in the Brain - Lecture 4 - Neurophysiology

Neurons are built for communication

- Neurons organize themselves in various patterns forming circuits in the brain" • How do signals move from one end of a neuron to the other? (cell body to terminal buttons • How do signals move from one neuron to another neuron? (terminal buttons to dendrites)" • How do neural circuits process signals? (not dressed in this course)"

Simply moving a signal from one place to the next cannot account for all that our brains are able to do"

• The possibility that animal movement may involve electricity was first suggested by Luigi Galvani (1737-1798), and elaborated upon by Alessandro Volta (1745-1827)." – Galvani noted that a dead frog’s legs could be made to twitch by touching them with a metal probe. – Volta correctly suggested that this was due to a small electric current created by the probe. • Muscles could be stimulated directly, but the effect was even stronger if the nerve leading to the muscle were stimulated." – It was not until the development of atomic theory that a plausible mechanism for this was possible."

Electrical Signalling • Electricity is simply the movement of electrically charged particles from one place to another." – The tendency to move is called electrical potential and is measured in volts (named for Alessandro Volta)" • A general rule of nature is that if you separate things, or move them out of equilibrium, they will tend to re-equilibrate. A circuit will force equilibrium" – As things move toward equilibrium, their movement can be used to do work or carry a message"

Electrophysiology of the Neuron • •

Neurons are like small batteries. Instead of maintaining an electric charge across two poles (as a battery does), neurons maintain an electric charge across their membrane.! Neurons have more negatively charged ions (wanderer – G.) inside their membrane than outside. For this reason, we say that the neuron is polarized. ! – The converse is true by necessity: neurons have more positively charged particles outside their membrane than inside." • If you were to use a voltmeter to measure the neuron’s electrical potential, you’d find it to be -70mv while the neuron is at rest. In other words, -70mv is the resting potential.! – The neuron does not have positive or negative poles like a battery. Instead, you place one electrode inside the neuron, and the other outside." •The neuron uses a combination of active and passive mechanisms to maintain the resting potential. ! – This process consumes energy. When the neuron dies, this process stops and ions quickly re-equilibrate. The resting potential is lost, just like a dead battery."

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As it stands, we know the neuron that is negatively charged compared to its surroundings. But how does this help it quickly send a message from one side to the other?" If you poked holes in the membrane (semipermeable), ions would quickly slip through the holes and move toward equilibrium" So any changes in membrane potential would be temporary at best. But this is a good thing, since signals are supposed to be temporary

The Action Potential • Neurons send signals using action potentials. Action potentials are like the counterpart to the resting potential. – The action potential is a short-lived, spreading, localized change in membrane polarity. – During an action potential, membrane potential briefly goes up to around +30mv."

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• Action potentials take place when ion channels in the neuron’s membrane open, allowing positive ions to flood in." – This flood of positive ions more than cancels out the negative resting potential, leading to a temporary positive charge. • However, action potentials are local and very short lived." – Ion channels quickly clamp shut, and the original resting potential re-establishes itself." • Since the neuron is said to be polarized when it’s at the -70mv resting potential, any change that reduces this is called a depolarization. – When the membrane is depolarized, it moves toward being positively charged. • Action potentials are therefore spreading depolarizations. • Depolarization can propagate, because depolarization in one area stimulates adjacent areas to depolarize as well. – This is example of a positive feedback loop; a single point of depolarization can trigger a chain reaction that spreads across the entire membrane."

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• Action potentials travel at a speed of 30-120m/s. Myelinated axons have a faster rate of conduction." • Information always flows in the same direction in neurons:" – Dendrites > Cell body > Axon > Axon terminal • Action potentials are fast, directional, and can travel virtually limitless distances." – They therefore satisfy our first question “How do signals move from one end of a neuron to the other?”

What triggers the action potential?! Not the dendrites but the axon hillock (soma)! How do signals move from one end of a neuron to the other?! The Synapse Small gap that is between one axon terminal button and the dendrite of an other neuron! • – “to clasp” – are the points of contact between two neurons. The site of inter-neuron information transfer." • While action potentials transfer signals rapidly by altering membrane electrical potential, synapses transfer signals by passing chemicals from neuron to an other • Because synaptic communication relies on chemical interactions, synapses are frequent tar for exogenous chemical stimulation (ie. drugs).

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• The cell on the receiving end of the synapse called the post-synaptic neuron." •The cell sending the signal is called the pre-synaptic neuron." •The synaptic cleft is an empty space found between the two opposing neurons. Chemical messages are sent across this gap.

Excitatory Post-Synaptic Potentials (EPSP) & IPSP NTs

ynapt c transm ss on n 4 steps 1. Neurotransmitters are synthesized and stored in the presynaptic axon terminal by instructions from the nucleus.! 2. Action potentials stimulate the release of neurotransmitters into the synaptic cleft.! 3. Neurotransmitters bind to receptors – specialized proteins embedded into the postsynaptic membrane.! 4. Receptors are often coupled to ion channels that open when bound to a neurotransmitter. The influx of ions changes the membrane potential of the post-synaptic neuron, causing a post-synaptic potential (PSP).

Triggering an Action Potential • Neurons receive hundreds of inputs. One their own, each input has a relatively small impact on the probability of an action potential. – The neuron integrates the combined input from all of its synapses. " • Each EPSP moves the neuron a little closer to the threshold potential of -50mv. • If there are a sufficient number of EPSPs happening close together in time or space, then an action potential is triggered. – If EPSPs are too far apart, then the neuron has time to return to its resting potential, cancelling out the effect of the EPSP.

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Neural Signalling in 5 steps

How are EPSP’s different from AP’s EPSP’s" • Graded/analog" • Occur dendritic tree/synapses on soma/dendrites" • Chemically-driven due to ligandgated activation of ion channels" • Communication between 2 neurons" • Signals can dissipate"

AP’s" • All or none (digital)" • Occur on axon hillock" • Electrically driven due to activation of voltagegated ion channels" • Communication within a neuron" • Once started, will go all the way down the axon"

Major Classes of Neurotransmitters Each has a unique chemical structure, but a few patterns emerge:

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1) PSPs are elicited on the cell body and dendrites.! 2) PSPs are conducted decrementally to the axon hillock" 3) If the threshold potential (-50mv) is reached at the axon hillock, an action potential is triggered." 4) The action potential is conducted in an “all-or-none” fashion down the axon." 5) The action potential arrives at the terminal buttons and triggers the release of neurotransmitters into the synapse.!

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• Amino acids: Glutamate (Glu), Glycine (Gly) ,γ-aminobutyric acid (GABA) • Monoamines: Dopamine (DA), Norepinephrine (NE), Epinephrine (EP), Serotonin (5-HT)

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• Peptides: Vasopressin, Oxytocin, Neuropeptide Y

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• Others: Acetylcholine (Ach), Adenosine, Anandamide, Nitric Oxide"

Fs and Ligands • Ligands are molecules that bind to and activate receptors. Neurotransmitters and hormones are ligands for their receptors. • The interaction between a receptor and its ligand – “to bind/tie (L.)” - somewhat resembles a lock and key. • The receptor protein is shaped in such a way as to only accept binding from certain types of molecules. The molecular interaction between receptor and ligand is still not well understood. • Drugs and poisons often work by interacting with receptors in a way that is similar to, but not

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Deactivating Neurotransmitters Neurotransmitters do not stay in the synaptic cleft indefinitely. They must be removed somehow, otherwise they would continue to stimulate the postsynaptic neuron. This can be accomplished in four ways.

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Diffusion: some of the neurotransmitter diffuses away from the synaptic cleft.

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Degradation: specialized enzymes break neurotransmitters down into inactive molecules.

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