The Nervous System. The NERVOUS SYSTEM controls and coordinates functions throughout the body and responds to internal and external stimuli. NEURONS are cells that transmit messages, called IMPULSES , through the nervous system.
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The Nervous System
NEURONSare cells that transmit messages, called IMPULSES, through the nervous system
The AXON carries impulses away from the cell body. The axon is covered in a membrane called the MYELIN SHEATH. There are gaps in the myelin sheath, called NODES. The signal can jump from node to node, increasing the speed of the impulse.
A RESTING NEURON is one that is not transmitting an impulse. Na+/K+ gates pump three Na+ ions out of the cell membrane and two K+ ions in through the cell membrane, creating a net negative charge inside the cell. This charge configuration is called the RESTING POTENTIAL of the neuron.
When the neuron receives a signal from the environment or another neuron, the ion gates at the leading edge of the cell open and Na+ is pumped into the the axon, and K+ is pumped out. This creates an ACTION POTENTIAL, which creates a current that moves down the axon.
In order for a neuron to send an impulse in response to a stimulus, the stimulus must overcome the THRESHOLD POTENTIAL, the minimum potential needed in order to create an action potential.
A neuron can transfer a signal to another cell at locations called SYNAPSES. At the synapse, chemicals called NEUROTRANSMITTERS are released, which sends the impulse to receptors in an adjacent cell.
The Brain Stem:
Peripheral Nervous System
Light is focused through the LENS onto the RETINA. Images are transmitted from the retina to the brain through the OPTIC NERVE
HEARING – vibrations from noise in the air are sensed by three tiny bones in the ear, the HAMMER, ANVIL, and STIRRUP. These create pressure waves in the fluid of the COCHLEA, which contains tiny hairs that wave back and forth. The motion of these hairs produce the nerve impulses that are sent to the brain
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