Overview of neuron structure and function
How do you know where you are right now?
The human nervous system
- The central nervous system (CNS) consists of the brain and the spinal cord. It is in the CNS that all of the analysis of information takes place.
- The peripheral nervous system (PNS), which consists of the neurons and parts of neurons found outside of the CNS, includes sensory neurons and motor neurons. Sensory neurons bring signals into the CNS, and motor neurons carry signals out of the CNS.
Classes of neurons
The basic functions of a neuron
- Receive signals (or information).
- Integrate incoming signals (to determine whether or not the information should be passed along).
- Communicate signals to target cells (other neurons or muscles or glands).
Anatomy of a neuron
- The dendrites tend to taper and are often covered with little bumps called spines. In contrast, the axon tends to stay the same diameter for most of its length and doesn't have spines.
- The axon arises from the cell body at a specialized area called the axon hillock. In motor neurons and interneurons, it's at the axon hillock that the action potential is initiated.
- Finally, many axons are covered with a special insulating substance called myelin, which helps them convey the nerve impulse rapidly. Myelin is never found on dendrites.
Variations on the neuronal theme
Neurons form networks
The knee-jerk reflex
- Motor neuron innervating the quadriceps muscle. The sensory neuron activates the motor neuron, causing the quadriceps muscle to contract.
- Interneuron. The sensory neuron activates the interneuron. However, this interneuron is itself inhibitory, and the target it inhibits is a motor neuron traveling to the hamstring muscle on the back of the thigh. Thus, the activation of the sensory neuron serves to inhibit contraction in the hamstring muscle. The hamstring muscle thus relaxes, facilitating contraction of the quadriceps muscle (which is antagonized by the hamstring muscle).