PSYA01H3 Chapter Notes - Chapter 3.2: Axon Hillock, Myelin, Axon Terminal
eModule 3.2- How the Nervous System Works: Cells and Neurotransmitters
Neural Communication
-Neurons: cells in nervous system responsible for receiving and sending messages throughout
body
The Neuron
-Primary purpose is to receive input from one group of neurons and to transmit that information
to other neurons leading to some form of behaviour
-All neurons have a cell body (soma) which is the part that contains the nucleus (cell’s genetic
material)
oGenes in cell body synthesize proteins that form chemicals allowing neuron to function
oActivity of these genes can be influenced by input coming from other cells
▪This input is received from dendrites: small branches radiating from the cell
body that receive messages from other cells and transmit those messages
toward the rest of the cell
oImpulses from other cells travel to the base of cell body called axon hillock; if this
receives enough stimulation from other neurons, it will initiate a chemical reaction that
will flow down rest of neuron
oAxon: transports information in the form of electrochemical reactions from the cell body
to the end of the neuron
▪When activity reaches end of axon, it will arrive at axon terminals (extensions
filled with vesicles) which contain neurotransmitters- the chemicals that
function as messengers allowing neurons to communicate with each other- thus
releasing neurotransmitters and allowing neural communications
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-Sensory neurons: receive information from bodily senses and bring it toward brain. NEURONS
THAT RESPOND TO TOUCH OR PAIN SENSATIONS OF THE SKIN BRING THE MESSAGE TOWARD
THE SPINAL CORD AND BRAIN.
-Motor neurons: carry messages away from the brain and spinal cord and towards muscles in
order to control their flexion and extension.
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Fig 3.13 Sensory and Motor Neurons: sensory neurons carry information toward the spinal cord and the
brain whereas motor neurons send messages to muscles of the body. The interneuron links the sensory
and motor neurons. This is the pathway of a simple withdrawal response to a painful stimulus.
-Some cells have few, if any, dendrites extending from the cell body; these cells do not perform
tasks requiring a lot of interactions with other neurons and vice versa
-Physical structure of a neuron is related to the function it performs
Glial Cells
-Specialized cells of the nervous system that are involved in mounting immune responses in the
brain, removing waste, and synchronizing the activity of the billions of neurons that constitute
the nervous system
-Critical function is to insulate the axon of a neuron
oMyelin: fatty sheath that insulates axons from one another, resulting in increased speed
and efficiency of neural communication
oMyelin protects impulse from decay thus reducing how often impulse needs to be
regenerated
oAxons without myelin transfer information 0.5-10m/s, axons with myelin 150m/s
oDamage to a small group of axons can lead to impairments in brain areas
▪Ex. when the myelin sheath is damaged, the efficiency of axon decreases
example, Multiple Sclerosis is a disease in which the immune system does not
recognize myelin and attacks it thus destroying the nervous system
The Neuron’s Electrical System: Resting and Action Potentials
-Neural activity is based on changes in the concentrations of charged atoms called ions
-When neuron is not transmitting information= outside of neuron has high concentration of
positively charged ions while interior of axon has fewer positively charged ions and high
concentration of negatively charged chloride ions
-Resting potential is the stable state during which the cell is not transmitting messages
oThis stable state involves a lot of tension because of
▪Electrostatic gradient: inside and outside of cell have different charges
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Document Summary
Emodule 3. 2- how the nervous system works: cells and neurotransmitters. Neurons: cells in nervous system responsible for receiving and sending messages throughout body. Primary purpose is to receive input from one group of neurons and to transmit that information to other neurons leading to some form of behaviour. Sensory neurons: receive information from bodily senses and bring it toward brain. That respond to touch or pain sensations of the skin bring the message toward. Motor neurons: carry messages away from the brain and spinal cord and towards muscles in order to control their flexion and extension. Fig 3. 13 sensory and motor neurons: sensory neurons carry information toward the spinal cord and the brain whereas motor neurons send messages to muscles of the body. The interneuron links the sensory and motor neurons. This is the pathway of a simple withdrawal response to a painful stimulus.
