The Nervous System Part II

Objectives: Describe and recognize nervous system structures in other organisms Understand and explain the structures and functions of the central nervous system. Identify the major structures within the brain.

How do single celled organisms such as the amoeba respond to stimuli? The image on the left shows an amoeba engulfing a bacteria by phagocytosis. How is it that the amoeba can detect, chase, and engulf its prey without any nervous system structures?

Response to stimuli in single celled organisms is achieved by membrane receptors. Single celled organisms such as protists and bacteria can detect changes in their environment and respond to stimuli using receptor proteins embedded in their cell membranes. For example, an amoeba can follow a bacteria based on the trail of metabolic wastes the bacteria is giving off. These waste molecules bind to the amoeba’s chemoreceptors allowing the amoeba to chase and capture the bacteria.

Evolution of a nervous system

Nerve Net in Hydra and Jellyfish The nervous system of the hydra and jellyfish is in the form of an irregular network of neurons called a nerve net. This nerve net allows the muscles of the hydra to move in a coordinated manner.

The Nervous System of the Earthworm is a Bit More Complex The earthworm has a central nervous system and a peripheral nervous system. The central nervous system is made up of a primitive brain connected to a pair of nerve cords. The nerve cords connect to a ganglion in each segment. A ganglion is a “mini-brain” made up of interneurons that switch, relay, and coordinate nerve impulses.

Earthworm regulation The peripheral nervous system of the earthworm is made up of nerves branching off of the cns to all parts of the worm’s body. The earthworm contains sensory and motor neurons. They have specialized structures for detecting light, chemicals, vibration and heat.

Regulation in the grasshopper The nervous system of the grasshopper is similar to that of the earthworm. The CNS is made up of a brain in the head region, nerve cords that run the length of the body, and ganglia. Peripheral nerves branch from the ganglia to all other parts of the body. Sense organs of the grasshopper are more highly developed than that of the earthworm.

Terms you will need to define and know. - Central Nervous System - Hypothalamus - Peripheral Nervous System - Reflex - Meninges - Gray matter - Cerebrospinal Fluid - White matter -Cerebrum - Ganglia -Cerebral Cortex -Cerebellum -Brain Stem - Thalamus

Two Divisions of the Human Nervous System Neurons do not act alone. Instead they are joined together to form a complex network—the nervous system. The nervous system is separated into two major divisions. 1.The Central Nervous System (CNS) 2.The Peripheral Nervous System (PNS)

The Central Nervous System Consists of the brain and the spinal cord. The skull protects the brain and the vertebrae protect the spinal cord Both the brain and spinal cord are wrapped in three layers of connective tissue called meninges.

Meninges and Cerebrospinal Fluid There are three layers of meninges that surround and protect the brain and spinal cord. Between two of the layers is a space filled with cerebrospinal fluid which acts as a shock absorber for the CNS.

Blood Brain Barrier Contains extensive capillaries Protects brain: Limits what can contact the brain and what cannot. Contains many glucose transporters

Summary of CNS Protective Structures Skull and Vertebrae 3 Layers of Meninges Cerebrospinal Fluid Blood-Brain Barrier

The Brain The brain is the main processing area of the Central Nervous System. The brain helps to relay messages, process and analyze information. The brain consists of: –Cerebrum –Cerebellum –Brain stem

The Brain

The Cerebrum The cerebrum is the largest and most prominent region of the human brain. It is responsible for the voluntary, or conscious activities of the body. It is the site of intelligence, learning, and judgment. A deep groove divides the cerebrum into right and left hemispheres. Corpus callosum is the band of tissues that connects the two hemispheres

The Cerebrum Each half of the cerebrum deals mainly with the opposite side of the body. The right hemisphere is thought to be associated with artistic ability and creativity. The left hemisphere may be associated with mathematical ability, logic, and analysis.

The Cerebrum Folds and groves on the surface of each hemisphere greatly increase the surface area of the cerebrum. Each hemisphere of the cerebrum is divided into lobes. The lobes are named for the bones of the skull that cover them.

The Cerebrum – Cerebral Cortex The cerebrum consists of two surfaces. The outer surface of the cerebrum is called the cerebral cortex and consists mostly of gray matter. Gray matter consists mainly of densely packed neuron cell bodies. The cerebral cortex processes information from the sense organs and controls body movements

The Cerebrum The inner surface of the cerebrum consists of white matter, which is made up of bundles of axons with myelin sheaths. The myelin sheaths give the white matter its characteristic color.

White Matter and Gray Matter

The Cerebellum The second largest region of the brain is the cerebellum, which is located in the back of the skull. Although the commands to move muscles come from the cerebral cortex, the cerebellum coordinates and balances the actions of the muscles so the body can move gracefully and efficiently.

The Brain Stem The brain stem connects the brain and the spinal cord. The brain stem consists of two regions, the pons and the medulla oblongata. Each of these regions acts as a neural “switchboard” regulating the flow of information between the brain and the rest of the body. Blood pressure, heart rate, breathing, and swallowing are controlled by the brain stem.

Thalamus and Hypothalamus Thalamus: receives messages from the sense organs and relays information to the cerebrum for processing. Hypothalamus: control center for recognition and analysis of hunger, thirst, fatigue, anger, and body temperature. Thalamus Hypothalamus

Summary of Brain Structures

The Spinal Cord The spinal cord is the major nerve pathway to and from the brain. It is protected by the vertebral column and the meninges. 31 pairs of spinal nerves branch out from the spinal cord, connecting the brain to the body. Certain kinds of information, such as reflexes, are processed directly in the spinal cord. A reflex is a quick, automatic response to a stimulus. It allows the body to respond to danger immediately.

The Spinal Cord