Chapter 3: Biology of behaviour
NEURONS:
• Individual cells in the nervous system that receives, integrates and transmit information.
• They are basic chains of communication within the nervous system.
• Most neurons communicate only with other neurons. However, some neurons also receive
signals from outside the nervous system (sensory neurons) or carry messages from the
nervous system to the muscles that move the body (motor neurons)
OVERVIEW OF THE NEURON:
• Sensory neuron
Sensory neurons are nerve cells within the nervous system responsible for converting external
stimuli from the organism's environment into internal electrical impulses.
• Motor neuron
A motor neuron (or motoneuron or efferent neuron [1]) is a neuron whose cell body is in the motor
cortex, brainstem or the spinal cord, and whose axon (fibre) projects to the spinal cord or outside of
the spinal cord to directly or indirectly control effector organs, mainly muscles and glands.
STRUCTURE
• Soma
-Contains the nucleus and most of the other structures common to most cells.
• Dendrites
-Parts of a neuron that are specialised to receive information.
, • Axon
-A long, thin fibre that transmits signals away from the soma to other neurons, or to muscle
glands.
-Vary in length.
• Myelin
-A high concentration of a white, fatty substance that usually wraps the axon.
• Myelin Sheaths
-Acts as insulating material and aids in accelerating the transmission of signals that move along
axons.
• Terminal buttons
-When the axon ends in a cluster
• Neurotransmitters
-Small knobs that secrete chemicals.
-Transmit information from one neuron to another- aid in the communication across synaptic
clefts.
• Synapse
-A junction where information is transmitted from one neuron to another.
• Summary:
-information is received at the dendrites
-passed through the soma and along the axon
-and transmitted to the dendrites of other cells at meeting points called synapses
GLIA
• Cells found throughout the nervous system that provide various types of support for neurons.
• Glia (GLIAL FOR PLURAL) tends to be much smaller than neurons but are much more abundant
within the human brain.
• Glial cells account for over 50% of the brains volume.
• Functions of Glial cells are:
-Provision of certain nutrients for neurons
-Insulation
-Removal of waste products
- also play a complicated role in the development of the nervous system in the human embryo.
-Play a role in sending and receiving chemical signals
• The myelin sheaths that encase some axons are derived from special types of glial cells.
USING ENERGY TO SEND INFORMATION
• The neuron at rest: A tiny battery
-The neural impulses is a complex electrochemical reaction (can consist of a number of electron
transfer steps, with some chemical steps preceding or succeeding the electron transfer steps or
taking place in between them)
-Both inside and outside the neuron are Ions (fluids containing electrically charged atoms and
molecules)
- Positively charged sodium and potassium ions and negatively charged chloride ions flow back
and forth across the cell membrane, but they do not cross at the same rate.
- The difference in flow rates leads to a slightly higher concentration of negatively charged ions
inside the cell, creating a negative charge within the neuron.
, - The neuron at rest can therefore be thought of as a tiny battery, a store of potential energy.
- The resting potential of a neuron is its stable, negative charge when the cell is inactive. This
charge is about –70 millivolts, roughly one-twentieth of the voltage of a torch battery
• The neural impulse
-The electrochemical properties of the neuron allow it to transmit signals.
-The electric charge of a neuron can be measured with a pair of electrodes connected to an
oscilloscope.
• The action potential: How neurons fire
-As long as the voltage of a neuron remains constant, the cell is quiet and no messages are being
sent.
-When the neuron is stimulated, channels in its cell membrane open, briefly allowing positively
charged sodium ions to rush in.
-An action potential shift in a neuron’s electrical charge that travels along an axon, like water
traveling through a hosepipe, but much faster.
• The absolute refractory period
-The minimum length of time after an action potential before another action potential can
begin.
-This ‘down time’ is brief (1/2 milliseconds).
-It’s followed by a brief relative refractory period during which the neuron can fire but its
threshold for firing is elevated, so more intense stimulation is required to start an action
potential.
NEURONS:
• Individual cells in the nervous system that receives, integrates and transmit information.
• They are basic chains of communication within the nervous system.
• Most neurons communicate only with other neurons. However, some neurons also receive
signals from outside the nervous system (sensory neurons) or carry messages from the
nervous system to the muscles that move the body (motor neurons)
OVERVIEW OF THE NEURON:
• Sensory neuron
Sensory neurons are nerve cells within the nervous system responsible for converting external
stimuli from the organism's environment into internal electrical impulses.
• Motor neuron
A motor neuron (or motoneuron or efferent neuron [1]) is a neuron whose cell body is in the motor
cortex, brainstem or the spinal cord, and whose axon (fibre) projects to the spinal cord or outside of
the spinal cord to directly or indirectly control effector organs, mainly muscles and glands.
STRUCTURE
• Soma
-Contains the nucleus and most of the other structures common to most cells.
• Dendrites
-Parts of a neuron that are specialised to receive information.
, • Axon
-A long, thin fibre that transmits signals away from the soma to other neurons, or to muscle
glands.
-Vary in length.
• Myelin
-A high concentration of a white, fatty substance that usually wraps the axon.
• Myelin Sheaths
-Acts as insulating material and aids in accelerating the transmission of signals that move along
axons.
• Terminal buttons
-When the axon ends in a cluster
• Neurotransmitters
-Small knobs that secrete chemicals.
-Transmit information from one neuron to another- aid in the communication across synaptic
clefts.
• Synapse
-A junction where information is transmitted from one neuron to another.
• Summary:
-information is received at the dendrites
-passed through the soma and along the axon
-and transmitted to the dendrites of other cells at meeting points called synapses
GLIA
• Cells found throughout the nervous system that provide various types of support for neurons.
• Glia (GLIAL FOR PLURAL) tends to be much smaller than neurons but are much more abundant
within the human brain.
• Glial cells account for over 50% of the brains volume.
• Functions of Glial cells are:
-Provision of certain nutrients for neurons
-Insulation
-Removal of waste products
- also play a complicated role in the development of the nervous system in the human embryo.
-Play a role in sending and receiving chemical signals
• The myelin sheaths that encase some axons are derived from special types of glial cells.
USING ENERGY TO SEND INFORMATION
• The neuron at rest: A tiny battery
-The neural impulses is a complex electrochemical reaction (can consist of a number of electron
transfer steps, with some chemical steps preceding or succeeding the electron transfer steps or
taking place in between them)
-Both inside and outside the neuron are Ions (fluids containing electrically charged atoms and
molecules)
- Positively charged sodium and potassium ions and negatively charged chloride ions flow back
and forth across the cell membrane, but they do not cross at the same rate.
- The difference in flow rates leads to a slightly higher concentration of negatively charged ions
inside the cell, creating a negative charge within the neuron.
, - The neuron at rest can therefore be thought of as a tiny battery, a store of potential energy.
- The resting potential of a neuron is its stable, negative charge when the cell is inactive. This
charge is about –70 millivolts, roughly one-twentieth of the voltage of a torch battery
• The neural impulse
-The electrochemical properties of the neuron allow it to transmit signals.
-The electric charge of a neuron can be measured with a pair of electrodes connected to an
oscilloscope.
• The action potential: How neurons fire
-As long as the voltage of a neuron remains constant, the cell is quiet and no messages are being
sent.
-When the neuron is stimulated, channels in its cell membrane open, briefly allowing positively
charged sodium ions to rush in.
-An action potential shift in a neuron’s electrical charge that travels along an axon, like water
traveling through a hosepipe, but much faster.
• The absolute refractory period
-The minimum length of time after an action potential before another action potential can
begin.
-This ‘down time’ is brief (1/2 milliseconds).
-It’s followed by a brief relative refractory period during which the neuron can fire but its
threshold for firing is elevated, so more intense stimulation is required to start an action
potential.
