基本神经元类型
Neurons come in many sizes. For example, a single sensory neuron from your fingertip has an axon that extends the length of your arm, while neurons within the brain may extend only a few millimeters.
They also have different shapes depending on their functions.Motor neuronsthat controlmusclecontractions have acellbody on one end, a long axon in the middle and dendrites on the other end.Sensory neuronshave dendrites on both ends, connected by a long axon with a cell body in the middle.Interneurons, orassociative neurons,carry information between motor and sensory neurons.
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These fundamental members of the nervous system also vary with respect to their functions.
- Sensory neuronscarry signals from the outer parts of your body (periphery) into the central nervous system.
- Motor neurons(motoneurons) carry signals from the central nervous system to the outer parts (muscles, skin, glands) of your body.
- Interneuronsconnect various neurons within the brain and spinal cord.
The simplest type of neural pathway is amonosynaptic(single connection)reflex pathway, like the knee-jerk reflex. When the doctor taps the right spot on your knee with a rubber hammer, receptors send a signal into the spinal cord through a sensory neuron. The sensory neuron passes the message to a motor neuron that controls your leg muscles. Nerve impulses travel down the motor neuron and stimulate the appropriate leg muscle to contract. The response is a muscular jerk that happens quickly and does not involve your brain. Humans have lots of hardwired reflexes like this, but as tasks become more complex, the pathway circuitry gets more complicated and the brain gets involved.