31.2 The Central Nervous System Lesson Overview 31.2 The Central Nervous System

THINK ABOUT IT The nervous system contains billions of neurons, each capable of carrying impulses and sending messages. What keeps them from sending impulses everywhere and acting like an unruly mob? Is there a source of order in this complex system, a central place where information is processed, decisions are made, and order is enforced?

Types of Neurons Neurons can be classified into three types according to the direction in which an impulse travels. Sensory neurons carry impulses from the sense organs, such as the eyes and ears, to the spinal cord and brain. Motor neurons carry impulses from the brain and the spinal cord to muscles and glands. Interneurons process information from sensory neurons and then send commands to other interneurons or motor neurons.

Structure of Neurons The largest part of a typical neuron is its cell body, which contains the nucleus and much of the cytoplasm.

Structure of Neurons Spreading out from the cell body are short, branched extensions called dendrites.

Structure of Neurons Dendrites receive impulses from other neurons and carry impulses to the cell body.

Structure of Neurons The long fiber that carries impulses away from the cell body is the axon.

Structure of Neurons An axon ends in a series of small swellings called axon terminals.

The Synapse At the end of the neuron, the impulse reaches an axon terminal, which may pass the impulse along to another cell. A motor neuron, for example, may pass impulses to a muscle cell, causing the muscle cell to contract. The point at which a neuron transfers an impulse to another cell is called a synapse. A space, called the synaptic cleft, separates the axon terminal from the adjacent cell.

The Brain and Spinal Cord Where does processing of information occur in the nervous system?

The Brain and Spinal Cord Where does processing of information occur in the nervous system? Each of the major areas of the brain—the cerebrum, cerebellum, and brain stem— is responsible for processing and relaying information. The spinal cord is the main communication link between the brain and the rest of the body. This makes up the CENTRAL NERVOUS SYSTEM

Cerebrum The largest region of the human brain is the cerebrum. The cerebrum is responsible for the voluntary, or conscious, activities of the body. It is also the site of intelligence, learning, and judgment.

Cerebellum The second largest region of the brain is the cerebellum. Information about muscle and joint position, as well as other sensory inputs, is sent to the cerebellum.

Brain Stem The brain stem connects the brain and spinal cord. The brain stem includes three regions— the midbrain, the pons, and the medulla oblongata. Each of these regions regulates the flow of information between the brain and the rest of the body. Functions such as regulation of blood pressure, heart rate, breathing, and swallowing are controlled by the brain stem. The brain stem keeps the body functioning even when you have lost consciousness due to sleep or injury.

PERIPHERAL NERVOUS SYSTEM: nerves branched off the spinal cord and brain.

Nervous System Function: Recognizes and coordinates changes in internal and external environments. Control center of the body. Invertebrate Organs Nerve nets, ganglia, nerve rings Vertebrate Organs Main organs Brain Spinal cord Peripheral nerves Think about this… Describe internal and external conditions that an organism would respond to? Which organs allow you to respond? How does the body perceive or “know” what is occurring?

Nervous System: Response to the environment All animals respond to their environment through specialized cells called nerve cells (neurons). In most animals nerve cells hook together to form the nervous system. Nervous systems can range from fairly simple to extremely complex. The arrangement of nerve cells from phylum to phylum can be dramatically different.

Figure 29–12 Invertebrate Nervous Systems Section 29-2 Arthropod Brain Ganglia Ganglia Brain Nerve Cells Think about this… Cnidarian Flatworm Which nervous system seems to be the simplest? Why? Mollusk What is “Ganglia” ? How does it differ from a brain? Hint: You will need to look this up

The Human Brain: Control center of the Nervous System Figure 35-9 The Brain Section 35-3 Pons Pituitary gland Hypothalamus Cerebrum Medulla oblongata Spinal cord Cerebellum Pineal gland Thalamus Discuss the brains function in sensory perception and action control. Brain stem

Human Nerve Cell: Messenger of the nervous system Discuss how nerve cells line up, how impulses are sent throughout the body. Think about this… What role does the neuron (nerve cell) play in response to a stimulus?

Craniate Brains (con’t) Figure 15.15: Dorsal view of craniate brains (book figure 16.14).

Fish Cerebrum Primitive sensory Motor area Pallium- dorsal area Motor area Subpallium- ventral area Globus pallidus (Striatum) Figure 15.16: Globus pallidus of fish; left cerebral hemisphere (book figure 16.25).

Amphibian Cerebrum Similar pallium and globus pallidus Split left and right hemispheres Figure 15.17: Globus pallidus of amphibian; left cerebral hemisphere (book figure 16.25).

Reptile Cerebrum Cerebrum is huge compared to amphibians Increase of lateral walls Pushes into lateral ventricle Dorsal ventricular ridge forms Receives visual, auditory, and sensory stimuli Figure 15.18: Globus pallidus of reptile and bird; left cerebral hemisphere (book figure 16.25).

Bird Cerebrum Similar to reptiles Avian ridge (hyperstiatum) Stratum of neurons that capped ridge Processes visual information Important to instinctive stereotypic behavior Migration and courtship

Mammal Cerebrum Lateral ventricles extremely expanded Neocortex Higher mental facilities Grooves (sulci) Folds (gyrae) Figure 15.19: Neocortex of mammalian brain.

Mammal Cerebrum (con’t) Figure 15.20: Ventral view of human brain (book figure 16.17).