Topic 1 - Structure and Function - F23.pdf

Topic 1 Structure and Function • Neurons and Glia • Flow of Neuronal Information • Neuronal Circuits and Circuit Dynamics • Divisions of the Nervous System • Visualizing Structure and Function The neuron Neurons - basic units of the nervous system The Neuron Doctrine: • The brain is composed of...

Topic 1 Structure and Function • Neurons and Glia • Flow of Neuronal Information • Neuronal Circuits and Circuit Dynamics • Divisions of the Nervous System • Visualizing Structure and Function The neuron Neurons - basic units of the nervous system The Neuron Doctrine: • The brain is composed of independent cells. • Information is transmitted from cell to cell across synapses. Zooming in on the Human Brain Neuronal communication Two basic types: • Action potential (AP) – communication within a neuron • Neurotransmission – between neurons Wikipedia (Laurentaylorj) Wikipedia (Thomas Splettstoesser) Functional zones of the neuron Input — Dendrites receive signals via neurotransmission Integration — Cell body (soma) combines input signals, initiates APs Conduction — Axon transmits APs Output— Axon terminals send signals via neurotransmission Classifying by shape Multipolar—one axon, many dendrites • most common type Bipolar—one axon, one dendrite Unipolar—a single extension branches in two directions • receptive pole • output zone Classifying by function Motor neurons stimulates muscles or glands. Sensory neurons respond to environmental stimuli (light, odor, touch, etc). Interneurons receive input from and send output to other neurons. Glia Support and enhance neuronal function Four major types • • • • Oligodendrocytes Schwann cells Astrocytes Microglia Astrocytes Astrocytes — star-shaped glia • Functions: • Maintain extracellular environment • Transport nutrients/oxygen • Contributes to blood brain barrier Oligodendrocytes and Schwann cells Myelin – fatty insulation layer around axons • Speeds up conduction of APs Formed by: • Oligodendrocytes - brain and spinal cord (CNS) • Schwann cells peripheral nerves (PNS) White vs gray matter White matter — bundles of myelinated axons Technology networks Gray matter — mostly cell bodies and dendrites Robert Ludlow, UCL Institute of Neurology Microglia Microglia - brain’s resident immune cells. • Remove debris from injured or dead cells. • “Immune sentinels” See them in action! The flow of neuronal information Axon hillock - coneshaped area of the soma that gives rise to the axon; site of integration. Healthline The flow of neuronal information Axons can divide into collaterals, allowing a neuron to innervate more than one postsynaptic cell. Neuronal connections Neuronal connections Presynaptic membrane Postsynaptic membrane Synaptic cleft Presynaptic terminal Synaptic vesicles • Contain neurotransmitters (NTs) • Those involved in communication concentrated at active zone. Takikawa & Nishimune, 2022 Postsynaptic membrane Neurotransmitter receptors detect NTs • Concentrated at the postsynaptic density (PSD) Carl Zeiss AG Synaptic transmission 1. Action potential reaches axon terminal 2. Synaptic vesicles release NTs into synapse 3. NTs bind to receptors 4. Receptors excite or inhibit postsynaptic neuron 5. NTs release from receptors and are cleared from the synapse How are neurons organized? Average brain = ~86 billion neurons (equal number of glia) Neuronal connections are functional Neural circuit – interconnected neurons that carry out a specific function when activated. Example: Myotatic reflex circuit Neurons in myotatic reflex Sensory neuron: muscle spindle  spinal cord Motor neurons: spinal cord  muscles Interneurons in spinal cord transform signal, communicate status Neuron action in a functional circuit Common neural connection dynamics Topographic projection – neighboring neurons project to neighboring neurons Common neural connection dynamics Divergence (blue) – axons split into multiple branches, project to different targets Convergence (green) – neurons receive input from two or more other neurons Common neural connection dynamics Reciprocal projection – “forward” projections from one brain area to another are reciprocated by “backward” projections Easy circuit dynamic visualization Divergence Convergence Topographical Reciprocal Projections Projections Circuit dynamics in real brain circuits! Nervous system divisions Central nervous system (CNS) - brain and spinal cord Peripheral nervous system (PNS) - nervous system outside the CNS Nervous system divisions Somatic nervous system – between CNS and muscles/sensory systems Autonomic nervous system (ANS) – between CNS and visceral organs Gray’s Anatomy Queensland Brain Institute 99Designs Somatic nervous system Cranial nerves — head, neck, and visceral organs Spinal nerves — rest of body Medical Gross Anatomy Somatic nerves Autonomic nervous system Autonomic nervous system (ANS) - controls body’s organs and glands. • Three subdivisions: • Sympathetic nervous system • Parasympathetic nervous system • Enteric nervous system Sympathetic nervous system Prepares the body for action/evasion • “fight, flight, or freeze” Innervates organs with NT norepinephrine (NE) Parasympathetic nervous system Helps the body relax and recuperate • “rest and digest”, “feed and breed” Innervates organs with NT acetylcholine (ACh) Enteric nervous system local, somewhat autonomous network of neurons that governs gut function • Some CNS input • Maintains fluid and nutrient balance (homeostasis) Divisions of the Nervous System Nervous System Central Peripheral Somatic Autonomic Sympathetic Parasympathetic Enteric Visualizing Structure Computerized axial tomography (CAT or CT) – measures X-ray absorption at several positions around the head • maps tissue density Visualizing Structure Magnetic resonance imaging (MRI) - high-resolution images using powerful magnetic fields and radio frequency energy Visualizing Structure Diffusion tensor imaging (DTI) use of modified MRI methodology to study white matter tracts • DTI measures ease of water diffusion - water diffuses easier along white matter tracts Visualizing Function Positron emission tomography (PET) -produces images of brain activity PET scan using flurodeoxyglucose (FDG) – radioactive glucose to show metabolic activity • Combines CT with injections of radioactive dyes to show neural activity associated with specific brain functions. Visualizing Function Functional MRI (fMRI) shows how networks of brain structures collaborate • detects small regional changes in brain metabolism during brain activity • Blood-oxygen-leveldependent (BOLD) signal Comparing imaging methods Speed-accuracy trade-off – limitation of imaging techniques that forces choice between spatial resolution and temporal resolution • fMRI - high spatial resolution (high structural detail) but low temporal resolution (slow at making images) Visualizing Function Electroencephalograms (EEGs) - records electrical activity from surface of brain • Excellent temporal resolution, terrible spatial resolution Magnetoencephalography (MEG) – measure magnetic fields generated by active neurons • Very good temporal resolution, better spatial resolution Your action items: • Course website issues hopefully resolved today! • Quiz 1 (Structure and Function) likely on Thursday • Read Breedlove, Ch 2 • Email or schedule a meeting with me if you have questions, concerns, or comments