Chapter 8 The Nervous System

Outline of the Nervous System The nervous system is divided into two major parts: 1.The central nervous system 2.The peripheral nervous system

Central Nervous System Consists of the brain and spinal cord The brain is the principal organ of the nervous system The brain weighs only about three pounds The brain communicates to the body through the spinal cord.

Central Nervous System The spinal cord has nerves attached to it There are 31 pairs of spinal nerves and serve to transmit to and from the body all information There are 12 pairs of cranial nerves which branch from the brain stem to send signals to the eyes, ears, mouth, face, and scalp.

Central Nervous System The spinal cord and brain are covered by a triple protection layer of tissues called meninges The outer layer is the dura mater The middle layer is the arachnoid The inner layer is the pia mater

Central Nervous System Cerebrospinal fluid circulates through the fibers of the arachnoid to cushion the brain.

Central Nervous System The brain and spinal cord is made of two types of cells: 1.Glial cells – support/protect nerve tissue 2.Neurons – actual nerve cells

Neurons The cell body of each neuron contains a nucleus and cytoplasm. Extending from the cell body are dendrites and axons

Neurons Dendrites receive nerve impulses Axons send nerve impulses

Neurons Gray matter – found within the brain Gray matter consists largely of cell bodies White matter of the brain is composed of axons and glial cells. White matter is white because is has myelin (a fatty covering)

Neurons Nerve cell bodies are found only in the brain, the spinal cord, or in a ganglion A ganglion is a mass of cell bodies Ganglion in a large mass are called a plexus You have a plexus in the back of the neck and shoulder

Neurons A group of nerve cells in the brain or spinal cord is a nerve center. The nerve center in the medulla oblongata of the brain stem controls your breathing.

Neurons There are three types of neurons: 1.Sensory neurons –transmit info from the senses (and pain as well) 2.Motor neurons – relay info to body from the central nervous system 3.Interneurons – relay signals between neurons or groups of neurons – responsible for processing info in the brain

Peripheral Nervous System Consists of nerves The twelve nerves branching from brain The thirty-one pairs of spinal nerves Most nerves contain both sensory and motor nerves

Sensory Nerve Fibers Sensory nerve fibers carry messages of light, taste, sound, touch, and pain from other parts of the body to the spinal cord and brain for analysis. Motor nerve fibers carry messages of action from the brain and spinal cord to the muscles and organs.

Nerves and How They Work Nerve cells – unlike other cells of the body, neurons do not reproduce. When a nerve cell dies it is not replaced

Nerves and How They Work The axons that extend from the nerve cell bodies in peripheral nerves are surrounded by special glial cells called Schwann cells which produce layers of myelin sheath. The myelin sheath has gaps called “nodes of Ranvier”

Transmitting a nerve Impulse

The Brain The brain has three parts: 1.The cerebrum – upper brain – coordinates thought, memory, and learned behaviors 2.The cerebellum – lower part of the brain – controls balance and coordinates voluntary muscle activity 3.The brain stem – connects spinal cord – controls the involuntary muscles and activities of autonomic nervous system.

Cerebrum The cerebrum is the largest part of your brain and is the physical organ that helps you in the areas of Consciousness Memory Voluntary Action Thinking Intelligence

Cerebrum The cerebrum consists of two halves: The right hemisphere The left hemisphere They are spilt by a longitudinal fissure (a deep groove)… The left side of the hemisphere is connected to the right side of the body… The right side of the hemisphere is connected to the left side of the body…

Cerebrum The two sides of the cerebrum are not equal or identical…they perform different functions… The left seems to specialize in details, known procedures and logic… The right seems to specialize in “the big picture”…creativity, intuitive approach to problems…

Cerebrum The two hemispheres communicate with each other through a mass of nerve fibers called the corpus callosum, located in the base of the cerebrum.

Cerebrum The cerebrum consists of two layers: 1. Grey matter 2. White matter

Cerebrum The brains grey matter is located in the cerebral cortex…the outer layer of the cerebrum.

Cerebrum Cerebral lobes: the convolutions of each of the cerebral hemispheres are divided by shallow grooves into various regions, or lobes… They are: 1. the frontal lobe 2. the parietal lobes 3. the temporal lobes 4. the occipital lobes

Cerebrum 1. Frontal Lobes: Associated with personality, judgment, and self control Rear portion called motor area – it controls the voluntary movement of skeletal muscle.

Cerebrum 2. Parietal Lobes: Behind frontal lobe – analyses sensations (touch and pain)

Cerebrum 3. Occipital Lobes Vision is interpreted here Located in back of brain

Cerebrum 4. Temporal Lobes Associated with senses of hearing, taste, and touch

Cerebellum Second largest part of the brain Lies behind the brain stem and below occipital lobe It is divided into a left and right hemisphere Like the cerebrum it is organized into grey and white matter

Cerebellum The function of the cerebellum is to coordinate skeletal muscle activity.

Cerebellum The cerebellum is trained to operate your muscles habitually. Most complex muscle coordination is handled by the cerebellum. Damage to the cerebellum means even the simplest tasks are difficult.

Brain Stem Located between the cerebellum and the spinal cord. The brain stem has three parts: The medulla oblongata The pons The midbrain

Brain Stem Medulla Oblongata The lowest part of the brain stem. Monitors and regulates breathing, heartbeat, blood pressure, and other bodily functions.

Brain Stem The Pons Links cerebrum and cerebellum Assists in breathing regulation Coordinates some eye movement and facial expressions

Brain Stem The Midbrain Adjust the eye pupils in response to light… Operate lens muscles to focus eyes…

Brain Stem The reticular formation Serves as the master switch of the cerebrum It brings you to consciousness