Nerve Cells, Nerve Impulse, Neurotransmitters PDF

Nerve Cells Neuron and Glia Nervous system Central Nervous System (CNS) Brain and Spinal Cord Peripheral Nervous System (PNS) Connects brain and spinal cord to the rest of the body (cranial, spinal, and autonomic nerves) Somatic Nervous System Autonomic Nervous System Two ty...

Nerve Cells Neuron and Glia Nervous system Central Nervous System (CNS) Brain and Spinal Cord Peripheral Nervous System (PNS) Connects brain and spinal cord to the rest of the body (cranial, spinal, and autonomic nerves) Somatic Nervous System Autonomic Nervous System Two types of nerve cells Neurons Receive information and convey the information to other cells. Glia Enhance and modify the activity of neurons in many ways. Neurons Neurons are separated from each other. There are small gaps between the tips of two neuron fibers. Santiago Ramon y Cajal found out about this in late 1800s by staining cells from infant brains using Golgi’s method (staining nerve cells with silver salts) Snell, R. S. (2010). Clinical Neuroanatomy 7th Edition. LWW.  Neurons are some of Neurons the longest-lived cells in the body. Cells in the cerebral cortex has the same life span as you currently have. Neurons vary in size, shape, and function. The shape determines its connection to other cells which Snell, R. S. (2010). Clinical Neuroanatomy 7th Edition. LWW. determines its function. Neurons Neurons are irreplaceable. Most neurons are amitotic (cannot divide). Neurons have huge appetite. They need constant and abundant glucose and oxygen. Snell, R. S. (2010). Clinical Neuroanatomy 7th Edition. LWW. Parts of neurons Parts of neurons Cell Body or Soma Dendrites Axons Cell body or soma Metabolic center of neurons Contains the following o Nucleus o Ribosomes o Mitochondria Axon Hillock – connects soma to axon Dendrites Receives nerve impulses DRT – dendrite=receive impulse=toward cell body Always naked/not myelinated o Synaptic Receptors – lines the dendrite’s surface, receives information from other neurons o Dendric Spines – increase surface of dendrites. axons Transport impulses towards neurons/organs/muscle ATA – axons=transport impulse=away from cell body Myelinated or with myelin sheath Longer, Microns to meters o Myelin Sheath o Nodes of Ranvier o Presynaptic Terminal axons Myelin Sheath – insulating material Nodes of Ranvier – interruptions between myelin sheaths Presynaptic Terminal / Axon Terminal Bulb / end bulb / bouton – points where axon releases chemicals that cross through the junction from one neuron to another cell. Functional classification Intrinsic / Sensory / Afferent Motor / Efferent Interneuron Away from CNS to Organs or sensory Neurons between organs, muscle, or receptors to CNS sensory and motor glands. neurons. Every sensory neuron is Every motor neuron is afferent to the rest of Dendrites and axons efferent from the the nervous system are within a single nervous system. structure. A – Admit E – Exit. Most abundant Two types of nerve cells Neurons Receive information and convey the information to other cells. Glia Enhance and modify the activity of neurons in many ways. Glia or neuroglia Component of nervous system that has many functions From Greek word glia meaning “glue” – old idea that glia glue neurons together. Central Nervous System Peripheral Nervous (CNS) System (PNS) Astrocytes Oligodendrocytes Satellite Cells Ependymal Cells Schwann Cells Microglial astrocytes Found in CNS Star-shaped Functions: 1. Shields neurons from chemicals surrounding it. Part of Blood Brain Barrier (BBB). Secretes growth factors that stimulates endothelial cells to make more tight junctions (controls permeability) 2. Regulates ions and transmitters that helps in synchronized sending of messages in waves. 3. Glycogen reserve that helps in bringing nutrients to the brain. 4. Increase interactions of synapses between neurons by releasing chemicals that magnify or modify the message to next neurons Satellite Cells Found in PNS – Sensory and Autonomic ganglia (cluster of nerves) Astrocytes of PNS Myelin Sheath – Insulating material that covers the axons which is a combination of lipids and proteins. Increases action potential Oligodendrocytes Schwann Cells Found in PNS Found in CNS Function: Myelinate axons Function: Myelinate axons in PNS in CNS 1 Schwann cell to 1 axon Myelinate multiple axons or multiple Schwann cells (30-60 axons) to 1 axon Damages cannot be Damages can be regenerated. regenerated. Demyelination leads to Demyelination leads to multiple sclerosis. Guillian-Barre Syndrome (immune system attacks the nerves) Ependymal cells Found in CNS Functions: part of Blood Cerebrospinal Fluid Barrier – Controls movement across the Blood CSF Barrier and also creates CSF – Cushion and shock absorber between the brain and the skull – Maintains homeostasis of the brain such as regulating temperature. Microglia Located in CNS Function: Part of immune system – Destroys pathogens (viruses and fungi) that attacks or damages the neurons. – Removes damaged neurons – Removes weakest synapses (synaptic pruning) NERVE IMPULSE Neural communication Osmosis from Elsevier. (2016 , December). Neuron action potential - physiology [Video. YouTube. https://www.youtube.com/watch?v=BbUcWbtVjT4. Osmosis from Elsevier. (2016 , December). Neuron action potential - physiology [Video. YouTube. https://www.youtube.com/watch?v=BbUcWbtVjT4. Things to remember: → There are ions or electrical charges inside and outside of the cell → Cell membrane separates the electrical charges between the outside of the cell and inside of the cell Things to remember: → The membrane is composed of two layers of phospholipids molecules → Embedded in the phospholipids are protein molecules which some chemicals could pass. → The protein molecules where chemicals can pass are called ion channels. → Ion channels are very selective. Things to remember: Types of Ion Channel A. Leaky / Passive Channels – Always open B. Gated Channels – could be opened or closed based on signals Things to remember: Types of Gated Channels 1. Voltage-gated channels – opens and closes in response to changes in membrane potential (charges) 2. Ligand-gated channels – opens when a neurotransmitter latches onto the receptor 3. Mechanically-gated channels – opens in response to physically stretching of the membrane Resting Membrane Potential (RMP) → Voltage difference across cell membrane when the cell is at rest → Cell at rest is slightly negative -- Polarized → RMP = -70MV Osmosis from Elsevier. (2016 , December). Neuron action potential - physiology [Video. YouTube. https://www.youtube.com/watch?v=BbUcWbtVjT4. Osmosis from Elsevier. (2016 , December). Neuron action potential - physiology [Video. YouTube. https://www.youtube.com/watch?v=BbUcWbtVjT4. Resting Membrane Potential (RMP) Sodium-Potassium Pump 3 NA+ gets out, 2 K+ gets in Cell becomes a little negative Generates concentration gradient – difference in distribution of ions across the membrane Inside the cell Outside the cell  K+  NA+  NA+  K+ Graded Potential Ligand-Gated Channels Presynaptic → Neurotransmitter → Excites the ligand-gated channel → gates open → ions get in → voltage goes up (-55MV) Graded Potential When the cell depolarizes and reaches the threshold (-55MV), it triggers the Action Potential Osmosis from Elsevier. (2016 , December). Neuron action potential - physiology [Video. YouTube. https://www.youtube.com/watch?v=BbUcWbtVjT4. All or None Principle The fact that a neuron fires an Electrical charges have only impulse of the same strength one strength but may vary in frequency or speed. whenever its action potential is → Weak stimulus triggers triggered. less frequent action potential → Strong stimulus triggers more frequent action potential Osmosis from Elsevier. (2016 , December). Neuron action potential - physiology [Video. YouTube. https://www.youtube.com/watch?v=BbUcWbtVjT4. Propagation of Action Potential → Passive Conduction in unmyelinated axons, the action potential must be replicated at each successive segment. → Salutatory Conduction in myelinated axons action potential is much faster because action potentials occur only at the nodes of Ranvier. Things to remember: → When neurons is stimulated, it fires electrical charges down the axon. → The axon regenerates an impulse at each point --- the impulse travels along the axon without weakening.  Refractory Period → Cell resists the production of further action potentials → The sodium channels are closed, and potassium is flowing out of the cell at a faster-than-usual rate.  Release of Neurotransmitter Action Potential → Ca2+ voltage-gated channel opens → Ca2+ gets in the cell → Exocytosis Exocytosis: the process in which the synaptic vesicles fuse with the membrane of the axon terminal and release neurotransmitter molecules to the synaptic gap Ca2+ have higher concentration outside the cell Ca2+ voltage-gated channels are mostly located in the axon terminal membrane Neurotransmitters are stored in synaptic vesicles prior to exocytosis. Exocytosis may have partial release called “kiss and run” or full release. This is still being researched. Osmosis from Elsevier. (2016 , December). Neuron action potential - physiology [Video. YouTube. https://www.youtube.com/watch?v=BbUcWbtVjT4. References Freberg, L. (2010). Discovering biological psychology. Wadsworth, Cengage Learning. J., P. J. P., & Barnes, S. (2018). Biopsychology. Pearson. Kalat, J. W. (2019). Biological psychology. Cengage. Osmosis from Elsevier. (2016 , December). Neuron action potential - physiology [Video. YouTube. https://www.youtube.com/watch?v=BbUcWbtVjT4 Neurotransmitter Neurotransmitter Neurotransmitter Neurotransmitter  NEUROTRANSMITTER A chemical messenger that communicates across a synapse. Substances released by one cell at a synapse that produce a reaction in a target cell  NEUROTRANSMITTER Classification (effect on neurons) Excitatory Neurotransmitter – promotes action potential Inhibitory Neurotransmitter - prevent action potential Ionotropic Receptor  Termination of Chemical Signals Diffusion Deactivating Enzyme Reuptake The presynaptic membrane uses The neurotransmitter The neurotransmitter its own set of receptors known as diffuses away from areas molecules are deactivated transporters to capture of high concentration to in the synapse by enzymes molecules of neurotransmitter areas of low in the synaptic gap substance and return them to the concentration. interior of the axon terminal.  Effects of drugs to synaptic transmission: Agonist – enhance activity of neurotransmitter Antagonist – reduce activity of neurotransmitter  ACETYLCHOLINE (ACh) Functions Movement – Muscle contractions Autonomic function Learning and memory Location Neuromuscular junction – synapse between neuron and a muscle fiber Autonomic Nervous System – preganglionic synapses, postganglionic synapses in parasympathetic division Brain – Hippocampus ACh - linked with increased salivation, muscle weakening, blurred vision, and paralysis  ACh - linked to learning and memory impairments; possible links to dementia and Alzheimer’s  Neurotransmitter Release Agonist – produces greater than normal release of neurotransmitter Example: Black Widow Spider venom Black widow spider venom is cholinergic agonist which leads to high release of ACh at neuromuscular junction. High ACh overstimulates muscle fibers, which leads to convulsions. In sever cases, the pace of release becomes too much, and neuron cannot produce and package ACh. This leads to convulsion followed by muscle paralysis  Neurotransmitter Release Antagonist – prevents release of neurotransmitter Example: Clostridium botulinum bacteria Clostrridium botulinum bacteria can be found in spoiled food. This prevents release of ACh at the neuromuscular junction and at synapse of autonomic nervous system. This leads to botulism – rapid paralysis and death Example: Botox Botox is the trade name of one of botulinum toxins. It paralyzes muscles to prevent the formation of wrinkles and to treat a variety of medical conditions involving excess muscle tension. Dopamine Building block: Dopa decarboxylase (enzyme) acting on L-dihyroxyphenylalanine (L-Dopa) Functions Voluntary movement Reinforcement - perception of pleasure Planning, learning, and memory Location: Substantia nigra projecting to basal ganglia Ventral tegmentum projections to hippocampus, amygdala and nucleus accumbens Ventral tegmentum projections to parts of frontal lobe of cerebral cortex Dopamine - addiction (reward, pleasure), hallucination, disturbance of thoughts and emotions  Dopamine - links to depression, muscle tremors, and uncoordinated body movements (Parkinson’s disease) Schizophrenia – may have more receptor sites for dopamine on CNS areas for emotional responding.  Neurotransmitter Release Antagonist – blocks the synaptic activity by blocking the receptors. Example: Phenothiazines Phenothiazines are drugs used to treat schizophrenia. It inhibits the dopamine to take action in the synapse by blocking its receptors. It may have side effects that are Parkinson-like. Norepinephrine formerly known noradrenaline Building block: Dopamine-hydroxylase – DBH (enzyme) acting on Dopamine Functions Arousal and vigilance Mood Fight-or-flight response Learning and memory Eating Location: Brainstem Norepinephrine - High blood, excessive sweating, and anxiety  Norepinephrine - low energy level, lacking concentration, contributes to depressive feelings  Neurotransmitter Release Agonist – promote activity of neurotransmitter by allowing the released substance to stay active in synapse for longer period by preventing reuptake. Example: Amphetamines and coccaine Amphetamines increases the production of norepinephrine and dopamine that leads to persistent arousal. Both amphetamines and cocaine prevents reuptake of the neurotransmitters that leads to their build up and longer activity in the synapse Serotonin Building block: Step 1: Tryptophan hydroxylase (enzyme) acting on Tryptophan (from dietary source like grains, meat, and dairy products) to produce 5-Hydroxytryptophan (5-HTP) Step 2: 5-HTP decarboxylase (enzyme) acting on 5-HTP to produce Serotonin Functions Sleep Appetite Mood – emotional arousal Location: Pons – raphe nucleus Projected widely in brain and spinal cord Serotonin - restlessness, hallucinations, and confusion  Serotonin - depression, alcoholism, aggression, eating disorder, sadness, fatigue, suicidal thoughts, and anxiety  Reuptake effects and Enzymatic Degradation Agonist – promote activity of neurotransmitter by allowing the released substance to stay active in synapse for longer period. Example: Flouxetine (Prozac) Prozac acts as reuptake inhibitors for serotonin. This leads for serotonin to remain active in the synapse for longer time, providing some relief from symptoms of depression. GABA (gamma-aminobutyric acid) Most frequently used inhibitory neurotransmitter in CNS Building block: Glutamic acid decarboxylase – GAD (enzyme) acting on Glutamate Functions Inhibition Mood Seizure threshold  GABA - hypersomnia (oversleeping) and a lack of energy  GABA - poor impulse control and could lead to seizures in the brain. May also result to bipolar disorder and mania.  Reuptake effects and Enzymatic Degradation Agonist – promote activity of neurotransmitter by allowing the released substance to stay active in synapse for longer period. Example: Alcohol and tranquilizers Alcohol and tranquilizers binds with GABA receptors and amplify its effects. This helps in calming anxiety reactions. Endorphins Functions Pain reduction Feelings of euphoria Reward processing Body’s natural painkillers. Works and functions like narcotic morphine.