Synapses connect neurons in the brain to neurons in the rest of the body and from those neurons to the muscles. This is how the intention to move our arm, for example, translates into the muscles of the arm actually moving. Synapses are also important within the brain, and play a vital role in the process of memory formation , for example. There are two different types of synapses, the electrical and the chemical, and they work very differently. The simpler type is the electrical synapse, in which there are essentially no gaps between the cells.
Instead, ions travel through what are called gap junctions and transfer an electrical charge to the next neuron. These gap junctions may actually be better understood in other areas of the body, as they are not unique to neurons. There are other cells, like in the heart, that also have gap junctions that transmit electrical signals.
Soma cell body — this portion of the neuron receives information. Dendrites — these thin filaments carry information from other neurons to the soma. Axon — this long projection carries information from the soma and sends it off to other cells. It normally ends with a number of synapses connecting to the dendrites of other neurons. Axons vary in length a great deal.
Some can be tiny, whereas others can be over 1 meter long. The longest axon is called the dorsal root ganglion DRG , a cluster of nerve cell bodies that carries information from the skin to the brain.
Some of the axons in the DRG travel from the toes to the brain stem — up to 2 meters in a tall person. Efferent neurons — these take messages from the central nervous system brain and spinal cord and deliver them to cells in other parts of the body. Afferent neurons — take messages from the rest of the body and deliver them to the central nervous system CNS. If a neuron receives a large number of inputs from other neurons, these signals add up until they exceed a particular threshold.
Once this threshold is exceeded, the neuron is triggered to send an impulse along its axon — this is called an action potential. Neurons at rest are more negatively charged than the fluid that surrounds them; this is referred to as the membrane potential.
It is usually millivolts mV. When the cell body of a nerve receives enough signals to trigger it to fire, a portion of the axon nearest the cell body depolarizes — the membrane potential quickly rises and then falls in about 1,th of a second.
This change triggers depolarization in the section of the axon next to it, and so on, until the rise and fall in charge has passed along the entire length of the axon. After each section has fired, it enters a brief state of hyperpolarization, where its threshold is lowered, meaning it is less likely to be triggered again immediately. Ions move in and out of the axons through voltage-gated ion channels and pumps.
The strength of a stimulus is transmitted using frequency. For instance, if a stimulus is weak, the neuron will fire less often, and for a strong signal, it will fire more frequently.
Myelin is created by Schwann cells in the peripheral nervous system and oligodendrocytes in the CNS. There are small gaps in the myelin coating, called nodes of Ranvier. The action potential jumps from gap to gap, allowing the signal to move much quicker. Multiple sclerosis is caused by the slow breakdown of myelin. Neurons are connected to each other and tissues so that they can communicate messages; however, they do not physically touch — there is always a gap between cells, called a synapse.
Synapses can be electrical or chemical. In other words, the signal that is carried from the first nerve fiber presynaptic neuron to the next postsynaptic neuron is transmitted by an electrical signal or a chemical one. Once a signal reaches a synapse, it triggers the release of chemicals neurotransmitters into the gap between the two neurons; this gap is called the synaptic cleft. The neurotransmitter diffuses across the synaptic cleft and interacts with receptors on the membrane of the postsynaptic neuron, triggering a response.
Synaptic pruning, a phase in the development of the nervous system, is the process of synapse elimination that occurs between early childhood and the onset of puberty in many mammals, including humans.
During pruning, both the axon and dendrite decay and die off. New connections are continually created while synapses that are no longer in use degenerate. Researchers only recently found out that even in the adult brain , not only do existing synapses adapt to new circumstances, but new connections are constantly formed and reorganized.
Brain Growth Lessons At about week 12 of a pregnancy, a human fetus starts to undergo a tremendous growth in the number of synapses in the brain. This period is known as exuberant synaptogenesis and lasts roughly until eight or nine months after birth.
The timing of synaptic pruning varies by brain region. Some synaptic pruning begins very early in development, but the most rapid pruning happens between roughly age 2 and Synaptic pruning is thought to help the brain transition from childhood, when it is able to learn and make new connections easily, to adulthood, when it is a bit more settled in its structure, but can focus on a single problem for longer and carry out more complex thought processes.
Synaptic pruning refers to the process by which extra neurons and synaptic connections are eliminated in order to increase the efficiency of neuronal transmissions. There are two main types of neuroplasticity: Functional plasticity: The brain's ability to move functions from a damaged area of the brain to other undamaged areas.
Structural plasticity: The brain's ability to actually change its physical structure as a result of learning. Science has made huge strides in understanding the human brain and how it functions. For example, we know that the frontal lobes are the center of rational thinking and of self control. Lesions or damage to the frontal lobes and to other parts of the brain can and affect impulses and impulsive behaviors. Research has shown that in fact the brain never stops changing through learning.
Plasticity is the capacity of the brain to change with learning. Changes associated with learning occur mostly at the level of connections between neurons: New connections form and the internal structure of the existing synapses change.
On an evolutionary time scale, selective ecological pressures shape the sensory and motor capacities as well as the body and behavior.
Correspondingly, in development, behavior acts in concert with the environment to cause structural changes in the brain lasting a lifetime. Neuroplasticity is the ability of the brain to change its physical structure and function based on input from your experiences, behaviors , emotions, and even thoughts. It used to be believed that except for a few specific growth periods in childhood, the brain was pretty much fixed.
The brain's anatomy ensures that certain areas of the brain have certain functions. Part of the body's ability to recover following damage to the brain can be explained by the damaged area of the brain getting better, but most is the result of neuroplasticity — forming new neural connections. Neuroplasticity, or the capacity for our brain cells to change in response to our behavior, can help us more thoughtfully engage in activities that will contribute to our well-being—no matter our age.
Neuroscientists used to think that the brain stopped developing in adolescence. The same neuroplasticity which allows not-so- good -for-you habits to be carved into your brain also gives you the ability to change your brain and life for the better.
By making conscious choices and leveraging neuroplasticity , you really can change yourself and your life for the better. You have a use or lose it brain. In other words, it can continue developing and changing throughout life. Therapy and rehabilitation can help your brain relearn this ability by repairing old pathways or creating new ones. Something as simple as taking a walk three times a week can rewire your brain to be more positive. Add in some mindfulness into your walk, and those positive feelings are certain to increase.
Psst: Studies have even shown that three thirty-minute brisk walks can improve recovery from clinical depression.
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