3 Neuroscience at the Cellular Level.pdf

Neuroscience at Cellular Level Dr. Meeyoung Kim Neurosciences Physiotherapy Dept. University of Sharjah Contents Neurons Synapse Glia Action Potential Generation  Neurons 1 μm = 1×10−6 m =1x10-3mm nm = 1×10−9 m Motor neuron cell body = 100 μm, Axon length =...

Neuroscience at Cellular Level Dr. Meeyoung Kim Neurosciences Physiotherapy Dept. University of Sharjah Contents Neurons Synapse Glia Action Potential Generation  Neurons 1 μm = 1×10−6 m =1x10-3mm nm = 1×10−9 m Motor neuron cell body = 100 μm, Axon length = 1 m  Neurons are the fundamental functional units of the nervous system. They have several roles: Process information by conduct the impulses Sense environmental changes & React to chemical and sensory stimuli Communicate changes to other neurons Command body response Emit specific chemical regulators Basic Parts of a Neuron -Cell body (Soma) -Neurites (Process): Dendrites, axon  Classifying Neurons Classification based on number of neurites Single neurite Unipolar Two or more neurites Bipolar: two Multipolar: more than two Where is each types of neuron located? https://en.wikipedia.org/wiki/Neuron  Neuron Parts: Dendrites and Cell body Dendrite: receives stimuli and carry it to the cell body Cell body: site of cellular activity  Dendrites “Antennae” of neurons Dendritic tree Synapse—receptors Dendritic spines Postsynaptic (receives signals from axon terminal) Neurites Composed of the dendrites and cell axon. The dendrites carry impulses from another neuron to the cell body and impulses then travel down the axon. Axons can either be myelinated (an insulating sheath that aids impulse conduction) or unmyelinated. Schwann cells form the myelin sheath. Neuron Part: Axons Carry impulses away from the cell body  Myelin Schwann cells wrapped around the axon of some neurons appear as multiple lipid-protein layers are actually a continuous cell increase the speed of action potential conduction  Nodes of Ranvier Gaps between Schwann Cells impulse jumps from node to node saltatory conduction (from the Latin saltare, to hop or leap  Synapses Axon terminal, synaptic cleft, postsynaptic membrane (with receptors)  Synapse is the Junction between the dendrites of one neuron and the axon of a second neuron Nerves communicate by releasing chemical messenger at synapse Electrical-to-chemical-to-electrical transformation Important structures are the presynaptic terminals, the synaptic cleft and the post synaptic membrane. Presynaptic terminals They can be described as excitatory or inhibitory. Neurotransmitters Activity: Search excitatory and inhibitory neurotransmitters  The synaptic cleft is a fluid filled space between the presynaptic terminal and the postsynaptic membrane (effector neuron). The impulses -> at axon terminal: membrane depolarises -> neurotransmitter release -> cross the synaptic cleft -> bind on the postsynaptic membrane. The chemical neurotransmitter signals are then reverted back to impulses, which are then transmitted away from the synapse down the neuron (=Electrical-to-chemical-to-electrical transformation)  Glia (=Neuroglia) Glia insulate, support, and nourish neurons.  The function of neuroglia cells is to ensure structural support, nourishment and neuron protection. Types of Neuroglia cells: Oligodendrocytes Schwann Astrocytes Ependyma (ventricle cells) Microglia as phagocytes (immune function)  Astrocytes Most numerous glia in the brain Fill spaces between neurons Influence neurite growth Regulate chemical content of extracellular space Myelinating glia Oligodendroglia (in CNS) Schwann cells (in PNS) Insulate axons Cross section of myelinated nerve fibers  Glia are different from neurons 1. Neurons have TWO "processes (neurite)" called axons and dendrites. Glial cells only have ONE. 2. Neurons CAN generate action potentials. Glial cells CANNOT, however, do have a resting potential. 3. Neurons HAVE synapses that use neurotransmitters. Glial cells do NOT have chemical synapses. 4. Neurons do NOT continue to divide. Glial cells DO continue to divide. 5. There are many MORE (10-50 times more) glial cells in the brain compared to the number of neurons. Action Potential Generation https://www.youtube.com/watch?v=oa6rvUJlg7o Pop up questions Resting Membrane Potential A state where no impulse is being initiated. The different levels of potassium and sodium -> a charge difference: -70mV. Semi permeable membrane. Outer: Na+, Cl- Inner: K+ Voltage gates are shut in the resting state. A pump mechanism (ion) Na+ / K + Pump Membrane bound proteins Utilizes ATP Maintains resting membrane potential Establishes sodium & potassium concentration gradients  Generating Action Potentials (AP) The action potential generated at the axon hillock propagates as a wave along the axon. Voltage gated ion channels sodium channels open -- sodium in sodium channels close -- stops inward flow of sodium potassium channels open -- potassium out AP: electrical impulse or nervous impulse AP Peak: around +50 mV Generation of Action Potentials: A Closer Look An action potential can be considered as a series of stages Resting state -> Depolarization (Rising phase of AP) -> Overshoot (Rising phase of AP) -> peak of AP -> Repolarization (Falling phase of AP) -> hyperpolarization (Undershoot) At resting potential 1. Most voltage-gated sodium (Na+) channels are closed; most of the voltage-gated potassium (K+) channels are also closed  Key Na+ K+ +50 Membrane potential 0 (mV) Threshold −50 1 Resting potential −100 Time OUTSIDE OF CELL Sodium Potassium channel channel INSIDE OF CELL Inactivation loop 1 Resting state  When an action potential is generated 2. Voltage-gated Na+ channels open first and Na+ flows into the cell 3. During the rising phase (Depolarization, Overshoot), the threshold is crossed, and the membrane potential increases 4. During the falling phase (Repolarization), voltage-gated Na+ channels become inactivated; voltage-gated K+ channels open, and K+ flows out of the cell  Key Na+ K+ +50 Membrane potential 0 (mV) Threshold 2 −50 1 2 Depolarization Resting potential −100 Time OUTSIDE OF CELL Sodium Potassium channel channel INSIDE OF CELL Inactivation loop 1 Resting state Figure 48.11-3 Key Na+ K+ 3 Rising phase of the action potential +50 Action potential Membrane potential 3 0 (mV) Threshold 2 −50 1 2 Depolarization Resting potential −100 Time OUTSIDE OF CELL Sodium Potassium channel channel INSIDE OF CELL Inactivation loop 1 Resting state Figure 48.11-4 Key Na+ K+ 4 Falling phase of the action potential 3 Rising phase of the action potential +50 Action potential Membrane potential 3 0 (mV) Threshold 4 2 −50 1 2 Depolarization Resting potential −100 Time OUTSIDE OF CELL Sodium Potassium channel channel INSIDE OF CELL Inactivation loop 1 Resting state 5. During the undershoot (Hyperpolarization), membrane permeability to K+ is at first higher than at rest, then voltage- gated K+ channels close and resting potential is restored Figure 48.11-5 Key Na+ K+ 4 Falling phase of the action potential 3 Rising phase of the action potential +50 Action potential Membrane potential 3 0 (mV) Threshold 4 2 −50 1 5 1 2 Depolarization Resting potential −100 Time OUTSIDE OF CELL Sodium Potassium channel channel INSIDE OF CELL Inactivation loop 1 Resting state 5 Undershoot  +50 Action potential Membrane potential the membrane potential becomes positive is referred to as overshoot 3 0 (mV) 2 4 Threshold −50 1 1 5 Resting potential −100 Time What are names of each periods from 1 to 5?  During the refractory period after an action potential, a second action potential cannot be initiated The refractory period is a result of a temporary inactivation of the Na+ channels Discussion board (screenshot of your test results): https://www.physiologyweb.com/daily_qu iz/physiology_quiz_QBTakR5k4CTyBTLXoKGaSzdZ1bz2N7cq_neuronal_action_potential.html All or None Law when a neuron reaches threshold it generates an action potential which is conducted the length of the axon without any voltage change. Summation of Action Potentials Temporal Summation additive effect of successive st imuli from an axon Spatial Summation additive effect of stimuli from various axons  Any questions? Dendrites Stimulus Useful site for today’s topic Neurons & the Nervous System Axon hillock Nucleus http://people.eku.edu/ritchisong/301notes2.htm#:~:text= Neurons%20are%20able%20to%20respond,of%20cells%2 0like%20muscle%20cells).&text=The%20nucleus%20of%2 0a%20neuron,processes%20called%20dendrites%20and% Cell 20axons. body Action potentials Presynaptic https://opentextbc.ca/anatomyandphysiology/chapter/12- Axon 4-the-action- cell potential/#:~:text=Potassium%20ions%20reach%20equilib rium%20when,the%20K%2B%20channels%20are%20open. Signal direction Synapse Synaptic terminals Synaptic terminals Postsynaptic cell Neurotransmitter