![]() Repolarization occurs once the membrane potential reaches a certain positive voltage. The myelin sheath made of protein and fatty substances surrounds the axons of certain nerve cells and acts as an insulator, allowing actional potentials to move more quickly down the axon. As the voltage increases along the axon, additional sodium channels open, propagating the signal. This causes an influx of positive sodium ions into the cell, raising the voltage and depolarizing the membrane. When the neuron is triggered, it activates voltage-gated sodium channels at the beginning of the axon. Opening and closing ion channels changes the membrane potential. There is a greater sodium ion concentration outside of the cell and a greater potassium ion concentration inside the cell. In the resting state, when it is not sending a signal, a neuron’s membrane is polarized, with the inside of the cell being more negatively charged than the outside (negative membrane potential). 4Īn action potential goes through three phases following a triggering event: depolarization, repolarization, and hyperpolarization. However, because they don’t use neurotransmitters, electrical synapses are less modifiable than chemical ones. For this reason, electrical synapses work faster than chemical ones and allow for impulses to travel in either direction within the neuron. ![]() The synaptic cleft in an electrical synapse is much smaller, making it possible for neurons to pass ion currents directly through gap junctions. 3Įlectrical synapses are less common than chemical synapses and are mainly found in the CNS. Researchers have identified more than 100 types of neurotransmitters-the most common include glutamate, acetylcholine, glycine, norepinephrine, serotonin, dopamine, and gamma-aminobutyric acid (GABA). Once they traverse the gap between neurons (synaptic cleft), neurotransmitters interact with excitatory or inhibitory receptors on the receiving cell to generate excitatory or inhibitory signals. 1Ĭhemical synapses communicate by releasing neurotransmitters-signaling molecules that are stored and released from neurons via synaptic vesicles in response to action potentials and voltage-gated calcium channels. Lower motor neurons originate in the spinal cord and directly or indirectly control voluntary movement of certain targets such as muscles, eyes, the face, and tongue. Upper motor neurons generally begin in the brain’s motor cortex and interact with spinal interneurons to initiate the neural circuits that generate movement. 1Ī motor neuron’s cell body is also often located either in the spinal cord or the brainstem with projections that interact with organs such as muscles and glands. For example, they can detect changes in the blood’s chemical properties or respond to potentially damaging stimuli by causing the perception of pain. Internal receptors respond to changes inside the body. External receptors respond to stimuli outside of the body and include olfactory receptors, taste receptors, photoreceptors, cochlear hair receptors, thermoreceptors, and mechanoreceptors. Specifically, sensory neurons are activated by a sensory input via specific external and internal receptors. The cell bodies of sensory neurons are located in the dorsal root ganglia-cell body clusters just outside the spinal cord-whereas their peripheral extensions travel throughout the body. In general, neurons in the PNS receive and carry signals in the body while neurons in the CNS analyze information. ![]() The CNS consists of the brain and spinal cord whereas the PNS includes neurons that branch off from the CNS and connect to the rest of the body. The nervous system is broadly divided into two sections: the central nervous system (CNS) and the peripheral nervous system (PNS). Multiple interconnected neurons form a neural circuit and use electrical and chemical signals to quickly transmit information throughout an organism. Nerve cells, or neurons, are the basic functional units of the nervous system. Stay up to date on the latest science with Brush Up Summaries. ![]()
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