Lecture 3 - Structure And Function Of A Neuron by Matt Wilson

Psychology and Counselling: Neuropsychology

Photo source: Paul De Koninck - http://www.greenspine.ca/media/mGFP_neuron2.jpg

ÂŠ Matt Wilson 2010

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Psychology and Counselling: Neuropsychology

Aim: To explain the structure and function of a neuron. Objectives: (TSSBAT…) • Explain how a neuron functions, and name the 3 common types of neuron. • Differentiate between the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). • Identify and label the main parts of a typical neuron. • Construct a neuron structure out of modelling clay.

Psychology and Counselling: Neuropsychology

The neuron is the basic unit of information processing and the building block of the brain and works together with other neurons and cells throughout the body, allowing us to think, feel, move and breathe. A single sensory neuron from your fingertip has an axon that extends the length of your arm, while neurons within the brain may be only a few millimetres long.

Adapted from: http://www.childrenshospital.org/research/Site2029/mainpageS2029P23sublevel51.html

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Psychology and Counselling: Neuropsychology

A neuron works like a computer processor, operating as a single "gate": It has a digital output (it's either on or off), and it is able to instantly receive the outputs of many other cells, process this information, and determine whether or not to generate its own signal -- a pulse of electrical energy. This signal is then passed on to other neurons (sometimes as many as 10,000!) or to muscle or gland cells. A neuron can display varying levels of excitability, firing slowly when less excited and rapidly when more excited. Adapted from: http://www.childrenshospital.org/research/Site2029/mainpageS2029P23sublevel51.html

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Psychology and Counselling: Neuropsychology

Neurons are similar to other cells in the human body in a number of ways, but there is one key difference, neurons are specialized to transmit information throughout the body. Neurons are responsible for communicating information in both chemical and electrical forms. Adapted from: http://psychology.about.com/od/biopsychology/f/neuron01.htm

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Psychology and Counselling: Neuropsychology

There are also several different types of neurons responsible for different tasks in the human body: • Sensory neurons - carry information from the sensory receptor cells in the outer parts (periphery) of your body to the brain and central nervous system. • Motor neurons - transmit information signals from the brain and central nervous system to the outer parts of your body (muscles, skin, glands etc) Adapted from: http://psychology.about.com/od/biopsychology/f/neuron01.htm

Psychology and Counselling: Neuropsychology

There are also several different types of neurons responsible for different tasks in the human body: • Interneurons - are responsible for communicating information between different neurons in the body by connecting various neurons within the brain and spinal cord. • Receptors – are part of a neuron cell that sense the environment (chemicals, light, sound, touch) and encode this information into electrochemical messages that are then transmitted by sensory neurons. Adapted from: http://psychology.about.com/od/biopsychology/f/neuron01.htm

Psychology and Counselling: Neuropsychology

The central nervous system (CNS) is comprised of the brain and spinal cord. The CNS receives sensory information from the nervous system (neurons) and controls the body's responses. The peripheral nervous system (PNS) involves all of the nerves outside of the brain and spinal cord that carry messages to the CNS. Source: http://psychology.about.com/od/cindex/g/def_cns.htm

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Psychology and Counselling: Neuropsychology

The simplest type of neural pathway is a reflex pathway, like the knee-jerk reflex. We will look at the different stages of this reaction on the next slide!

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Psychology and Counselling: Neuropsychology

When the doctor taps the right spot on your knee with a rubber hammer; 1) Receptors send a signal into the spinal cord through a sensory neuron. 2) The sensory neuron passes the message to a motor neuron that controls your leg muscles. 3) Nerve impulses travel down the motor neuron and stimulate the appropriate leg muscle to contract. 4)The response is a muscular jerk that happens quickly and does not involve your brain. ÂŠ Matt Wilson 2010 Create PDF files without this message by purchasing novaPDF printer (http://www.novapdf.com)

Psychology and Counselling: Neuropsychology

• Provides the link between the brain and the rest of the body • Is attached to the brain and emerges from an opening in the base of the skull

Psychology and Counselling: Neuropsychology

Diagram of a typical neuron

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Psychology and Counselling: Neuropsychology

There are three basic parts of a neuron: • the dendrites, • the cell body, • the axon. However, all neurons vary somewhat in size, shape, and characteristics depending on the function and role of the neuron. Some neurons have few dendritic branches, while others are highly branched in order to receive a great deal of information. Some neurons have short axons, while others can be quite long. The longest axon in the human body extends from the bottom of the spine to the big toe and averages a length of approximately three feet! © Matt Wilson and Holly Donohoe 2010 Create PDF files without this message by purchasing novaPDF printer (http://www.novapdf.com)

Psychology and Counselling: Neuropsychology

Dendrites are tree like extensions at the beginning of a neuron that help increase the surface area of the cell body and are covered with synapses. These tiny protrusions receive information from other neurons and transmit electrical stimulation. Dendrite Characteristics • Most neurons have many dendrites. • Short and highly branched. • Transmits information to the cell body. Source: http://psychology.about.com/od/biopsychology/ss/neur onanat_2.htm

Psychology and Counselling: Neuropsychology

The axon is the elongated fibre that extends from the cell body to the terminal endings and transmits the neural signal. The larger the axon, the faster it transmits information. Some axons are covered with a fatty substance called myelin that acts as an insulator. These myelinated axons transmit information much faster than other neurons. Axon Characteristics • Most neurons have only one axon. • Transmit information away from the cell body. • May or may not have a myelin covering. Source: http://psychology.about.com/od/biopsychology/ss/neuronanat_5.htm

Psychology and Counselling: Neuropsychology

The axon terminals are located at the end of the neuron and are responsible for sending the signal on to other neurons. At the end of the terminal is a gap known as a synapse. A nerve impulse CANNOT go backward across a Synapse. ÂŠ Matt Wilson 2010 Create PDF files without this message by purchasing novaPDF printer (http://www.novapdf.com)

Psychology and Counselling: Neuropsychology

Neurotransmitters are used to carry the signal across the synapse to other neurons. A nerve impulse arriving at the axon terminal of one neuron stimulates release of a chemical neurotransmitter, which crosses the synapse to the adjoining neuron in milliseconds. Many chemicals are believed to act as neurotransmitters, including DOPAMINE and SEROTONIN. Some neurotransmitters activate neurons; others inhibit them. Some mind-altering drugs act by changing synaptic activity. Source:http://www.answers.com/topic/neurotransmitter

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Psychology and Counselling: Neuropsychology

Schwann Cell: Any of the cells that cover the axons in the peripheral nervous system and form the myelin sheath Nodes of Ranvier: Small gaps in the myelin sheath of myelinated axons

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Psychology and Counselling: Neuropsychology

The myelin sheath aids in the rapid and efficient transmission of impulses along the nerve cells and is present in both the central nervous system and the peripheral nervous system. Without the myelin sheath, we cannot function. This is demonstrated by the devastating effects of Multiple Sclerosis, a demyelinating disease that affects bundles of axons in the brain, spinal cord and optic nerve, leading to: • lack of co-ordination • lack of muscle control • difficulties with speech and vision. Source: http://vision.about.com/od/eyeanatomy/g/Myelin.htm

Psychology and Counselling: Neuropsychology

An interactive explanation and demonstration of how a neuron functions can be found here:

http://www.childrenshospit al.org/research/_neuron/in dex.html

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