Almost 400,000 people in the United States have multiplesclerosis, and it is the most common disease of the nervous system in young adults.
The first symptoms usually occur in the 20s and 40s.
There is no cure for the disease, so affected individuals must deal with their condition for the rest of their lives.
In almost 45% of cases, the disease is not severe and can be controlled with medication.
The nervous systems of cnidarians, planarians, and annelids are compared.
Complex animals rely on the nervous system to seek food and mates and to avoid danger.
It continuously monitors internal and external conditions.
The evolutionary trends that led to the nervous system of mammals are shown in a comparative study.
The simplest multicellular animals, such as sponges, do not have a nervous system.
The most common example is the closing of the osculum in response to various stimuli, as their cells can respond to their environment and communicate with each other.
The nerve net of the hydras is composed of contractile cells in the body wall and neurons in contact with one another.
They are able to contract and extend their bodies, and even turn somersaults.
Sea anemones and jellyfish seem to have two nerve nets, a fast-acting one that allows major responses in times of danger, and a slower one that coordinates slower and more delicate movements.
In a flatworm, the nerve cords have the appearance of a ladder.
The earthworm has a brain and a solid nerve cord.
There is a peripheral nervous system.
The nervous system of the crab is similar to that of annelids, but the ganglia are larger.
The squid has a brain with giant nerve fibers that allow it to move quickly.
The central nervous system of a cat is similar to that of other animals.
Planarians have bilateral symmetry and the organization of their nervous system reflects it.
The cerebral ganglia and nerve cords are connected to the eyespots.
Concentration of nervous tissue in the anterior or head region has happened.
The movement of the two sides of the brain is coordinated by the two nerve cords.
Bilateral symmetry and cephalization are two important organizational trends in the development of the nervous system that allow it to adapt to an active way of life.
Annelids and arthropods are complex animals with a nervous system.
There is a brain and a nerve cord.
The brain, which normally receives sensory information, controls the activity of the ganglia and assorted nerves so that the muscle activity of the entire animal is coordinated.
The anterior end of the squid's body has a well-defined brain and well-developed sense organs.
The cephalopods are considered to be the most intelligent of all the animals, and some of them, such as the octopus, have been observed to collect, transport, and assemble coconut shells for later use as a shelter.
There are more neurons in vertebrates than in invertebrates.
A cat's nervous system may contain many thousand times the number of neurons as that of an insect.
Some species of whales may have more than 100 billion brain cells.
The nervous system is controlled by the brain.
The hindbrain, midbrain, and forebrain are usually divided into the hindbrain, midbrain, and forebrain.
When an animal is sleeping, the lungs and heart work.
The cerebellum became the center of coordination of motor activity associated with limb movement, posture, and balance.
The brain is divided into three parts.
The eyes, ears, and olfactory structures allow the animal to gather information from the environment.
The anterior end of the animal is where the sense organs are located.
The midbrain was once a center for coordinating reflexes involving the eyes and ears.
The sense of smell was the main concern of the forebrain.
The forebrain processes sensory information from the beginning.
The thalamus evolved to receive sensory input from the hindbrain and the cerebrum, the part of the forebrain in animals.
In the forebrain, the hypothalamus is concerned with homeostasis and is able to communicate with other parts of the body.
The brain and spine are part of the central nervous system.
The nerves and ganglia are outside the central nervous system.
Sections 37.3 and 37.4 give more detail on the CNS and PNS.
The central nervous system is made up of the brain and spinal cord, while the peripheral nervous system is made up of nerves.
Nerves in the PNS send impulses from the skin and internal organs to the central nervous system.
Motor impulses travel through the sympathetic and parasympathetic divisions in the autonomic system.
The single, long axon, branches only near its tip.
The sensory neuron has structures projecting from the axon.
The cortex of the cerebellum has very branched dendrites.