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Publication Date: July 2005.
Welcome to "Neuroscience: Anatomy and Physiology."
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Click on the Course Notes button to download a PDF version of the course. The course notes contain all the text associated with the course, including objectives, transcripts, and progress checks.
Date Published: July 2005
The nervous system is the master control and communication system of the body. Every sensation, action, thought, instinct, and emotion reflects its activity. In order to carry out its functions, the various components of the nervous system communicate with each other to integrate and act upon sensory information gathered from the body and external environment. This course describes the anatomy and physiology of the nervous system and how individual nerve cells communicate with one another. The course concludes with a presentation of the different imaging techniques currently in use to study nervous system physiology and disease.
The course is divided into four sections.
The first section, General Histology, provides an overview of the main subdivisions of the nervous system. This is followed by a description of the principal cell types that make up the nervous system.
The second and third sections, Neuroanatomy I and II, describes the organisation and associated functions of the major components of the central and peripheral nervous systems.
The fourth section, Neurotransmission, describes how nerve impulses are generated and how individual neurons communicate with each other.
The final section, Imaging Techniques, highlights the various imaging techniques currently in use to assess neurophysiology and neuropathology.
Anatomically, the nervous system has two main divisions: the central nervous system (CNS), which is composed of the brain and spinal cord, and the peripheral nervous system (PNS), which is composed of the peripheral nerves that connect the brain and spinal cord to all other parts of the body. At the cellular level, the structures of the nervous system are made up of two distinct classes of cells: nerve cells (or neurons) and glial cells (or glia). This section introduces the components and divisions of the CNS and the PNS. This is followed by a description of the unique structural features and properties of neurons and glia.
These are the objectives for this section. You will be tested on these objectives in the final assessment.
After you finish this section, you should be able to:
The CNS is the site of information processing in the nervous system. It interprets and integrates incoming sensory information and dictates voluntary and involuntary motor responses. This lesson introduces the components of the CNS.
The central nervous system or CNS consists of the brain and the spinal cord. The brain is encased in the upper bones of the skull, collectively called the cranium. The spinal cord extends from the base of the skull and runs down the neck and back within the vertebral column. The bones of the cranium and the vertebral column help to protect the brain and spinal cord from injury. The peripheral nerves consist of the cranial nerves that originate from the brain, and the spinal nerves that originate from the spinal cord.
The brain can be further divided into four anatomically distinct regions. These are the cerebral hemispheres, the diencephalon, the brain stem and the cerebellum. The cerebral hemispheres, known collectively as the cerebrum, form the uppermost portion of the brain. The cerebrum covers the diencephalon and the top of the brain stem. Note that the spinal cord is continuous with the brain stem.
Two sets of directional terms are important with respect to describing the organisation of the nervous system. The components of the central nervc ous system are organised along what is referred to as a rostral-to-caudal (also called anterior-to-posterior or head end-to-tail end) axis. The higher brain regions lie rostrally or toward the nose, whereas the inferior parts of the CNS lie caudally or toward the tail.
A second directional axis is the dorsal-to-ventral axis. In the brain dorsal refers to the top and ventral refers to the bottom. In the spinal cord dorsal is toward the back of the body and ventral is toward the front.
The peripheral nervous system is responsible for relaying information between the CNS and the rest of the body. This lesson identifies the components and main divisions of the peripheral nervous system.
The peripheral nervous system or PNS is the part of the nervous system outside the CNS and consists of the nerves that extend from the brain and the spinal cord. These peripheral nerves serve as essential lines of communication that link all regions of the body to the central nervous system. Twelve pairs of cranial nerves carry signals to and from the brain and 31 pairs of spinal nerves carry signals to and from the spinal cord.
Sensory or afferent nerve fibres carry signals to the CNS from various specialised sensory receptors throughout the body. Examples of such receptors include touch receptors in the skin of the fingertips, odorant receptors in the nasal epithelium and stretch receptors in the smooth muscle surrounding the urinary bladder.
Motor or efferent nerve fibres carry signals away from the CNS to muscles and glands in the periphery, causing these organs to contract or secrete. The motor pathways are further partitioned into the somatic nervous system, which relays commands to the skeletal muscles and the autonomic nervous system, which stimulates the glands, internal organs, and smooth muscles of the body.
The nervous system is a highly complex communication system. This communication is conducted through an elaborate circuitry of neurons, which are the basic functional unit of the nervous system. This lesson describes the unique structural features of a neuron and their role in facilitating the flow of information.
Neurons are specialized cells that are the basic functional unit of the nervous system. Unlike other cells, neurons are unique in that they establish connections with one another and conduct electrical impulses to communicate. A typical neuron consists of three components: the cell body, also called the soma, and two types of processes sprouting off the cell body known as dendrites and axons.
The cell body is the metabolic centre of the neuron and contains the nucleus. The axon hillock is a cone shaped region of the cell body from which the axon arises.
Axons carry electrical impulses away from the nerve cell body. Unlike dendrites which are usually numerous, a neuron has only one thin axon that can range in length from several micrometers up to a meter or more. The axon is the main conducting unit of the neuron and conveys information to other neurons or target tissues. Although a neuron has only one axon, it can give rise to multiple branches allowing a single neuron to project to multiple targets.
Dendrites conduct electrical impulses toward the nerve cell body. A neuron usually has several dendrites. These branch out in tree-like fashion and serve as the main apparatus for receiving inputs from other neurons. The dendrites provide a large area for contact with other neurons, and a single neuron can receive inputs from multiple neurons.
The three functional classifications of neurons are discussed in this lesson.
Chemical messengers are needed to make communication between a neuron and another neuron or target cell possible. These chemical messengers are called neurotransmitters.
Neurons can be classified functionally into three major groups: sensory neurons, motor neurons and interneurons. The axons of sensory or afferent neurons carry information into the CNS for conscious perception and motor coordination. The axons of motor or efferent neurons carry commands to muscles and glands. The peripheral nerves that relay information to and from the CNS are bundles of motor axons, sensory axons or both.
Interneurons are found in the central nervous system and constitute by far the largest class of neurons. They process information locally or convey information from one site in the CNS to another. Interneurons with long axons, called projection interneurons, relay information over great distances from one region of the central nervous system to another. Interneurons with short axons convey information locally and are called local interneurons.
Glial cells outnumber neurons in the CNS by 50 to 1, and make up about half the mass of the brain, and have many important supporting roles in the nervous system. Like neurons, glial cells have branching processes and a central cell body. There are three distinct classes of glial cells based on their appearance under the microscope.
Star-shaped astrocytes are the most abundant glial cells in the CNS. They have irregularly shaped cell bodies that give rise to many radiating processes with bulbous ends. Many of these endings form tight seals with the cells lining the blood vessels in the brain, creating the blood-brain barrier that protects the brain from toxic substances in the blood. Astrocytes also help maintain the ionic balance in the CNS environment by taking up excess potassium.
Microglia are the smallest and least abundant type of glial cell in the CNS. They typically have elongated cell bodies and cell processes with many pointed projections, like a thorny bush. The microglia are phagocytes, the macrophages of the CNS. They engulf and remove invading microorganisms and injured or dead neurons. .
Oligodendrocytes have fewer and shorter processes than astrocytes. Oligodendrocytes line up in small groups along the thicker axons in the CNS and wrap their cell processes around these axons to produce a fatty covering around the axon called myelin sheaths. The myelin sheath insulates the axon and allows for faster rates of electrical conduction along the length of the axon. Short gaps in the myelin sheath are referred to as the nodes of Ranvier.
Schwann cells are a type of glial cell found in the PNS. They function in a manner similar to the oligodendrocytes in the CNS by providing the myelin coverings for axons bundled in the peripheral nerves.
Roll your cursor over the names of cell types to review their features.
Rollover Text: Astrocytes (in CNS)
Rollover Text: Microglia (in CNS)
Rollover Text: Oligodendrocytes (in CNS)
This "drag and drop" progress check will test your knowledge of the information presented in this section. Because your score will not be recorded, you may take the progress check as many times as you would like.
Match the terms with the correct definitions. Not all terms are used. Use the "rewind" button to reset.
Match the terms with the appropriate groups. Not all terms are used. Use the "rewind" button to reset.
Use the terms to label the diagram. Not all terms are used. Use the rewind" button to reset.