International Student Edition
Biological Psychology
James W. Kalat
,Chapter 1: The Major Issues
Chapter 2: Nerve Cells and Nerve Impulses
Module 2.1: The Cells of the Nervous System
Anatomy of Neurons and Glia
The nervous system consists of 2 kinds
of cells:
1) neuron: cell that receives information and
transmits it to other cells by conducting
electrochemical impulses ---> 3 types of
neurons: a) motor neurons (= efferent):
neuron that receives excitation from other
neurons through its dendrites and conducts
impulses from its soma in the spinal cord to
muscles or gland cells. b) sensory neuron (=
afferent): specialized to be highly sensitive to a
specific type of stimulation. c) interneuron:
neuron whose axons and dendrites are all
confined within a given structure ---> structure:
• neurons contain the same internal structures
as other animal cells (zie fig. 2.2). • neurons
have 4 major parts: soma (cell body),
dendrites (branching fibers that emanates from a
neuron, growing narrower as it extends from the cell
body toward the periphery), an axon (single thin fiber of
constant diameter that extends from a neuron) and
presynaptic terminals (tip of an axon, the point from
which the axon releases chemicals) (zie hiernaast voor
motor neuron (boven) en sensory neuron (onder)).
2) glia: type of cell in the nervous system that, in contrast
to neurons, does not conduct impulses to other cells --->
different types of glia: a) astrocytes: relatively large, star-
shaped, glia cell that wraps around a group of functionally
related axons ---> enables neurons to send messages in
waves, removes waste material & control amount of blood flow to each brain area. b) microglia: very
small cells that remove waste materials and microorganisms from the central nervous system. c)
oligodendrocytes: glia cells that surround and insulate certain axons in the vertebrate brain and
spinal cord ---> build myelin sheaths. d) Schwann cells: glia cells that surround and insulates certain
axons in the periphery of the vertebrate body ---> build myelin sheaths. e) radial glia: type of glia
cells that guides the migration of neurons and the growth of their axons and dendrites during
embryological development.
The Blood-Brain Barrier
Blood-brain barrier: the unbroken wall of endothelial cells that surround the blood vessels of the
brain and spinal cord and that keeps many viruses and dangerous chemicals out of the brain --->
chemical that cross the barrier: a) passively: • small uncharged molecules (oxygen, water, ). •
molecules that dissolve in the fats of the membrane. b) by active transport: protein mediated
process that expends energy to pump chemicals from the blood into the brain (glucose, amino acids,
purines, choline, a few vitamins, iron, certain hormones).
2
, The Nourishment of Vertebrate Neurons
Neurons depend almost entirely on glucose: a simple sugar, the main fuel of vertebrate neurons --->
problem glucose shortage, = inability to use glucose (deficiency in thiamine: vitamin B).
Module 2.2: The Nerve Impulse
The Resting Potential of the Neuron
Membrane of a neuron maintains an electrical
polarization, a difference in electrical charge between
the inside and the outside of a cell ---> resting
potential: difference in voltage when a neuron is not
being stimulated (the inside of a resting neuron has a
negative charge of -70mV with respect to the outside) -
--> is maintained because of the sodium-potassium
pump: mechanism that actively transports 3 sodium
ions out of the cell while drawing in 2 potassium ions
(zie fig. 2.15) ---> is effective only because of the
selective permeability (ability of certain chemicals to
pass more freely (e.g. potassium) than other (e.g. sodium) through a membrane): without selective
permeability, electrical gradient (difference in positive and negative charges across a membrane) &
concentration gradient (difference in distribution of ions across a membrane) would push sodium
into the cell ---> the sodium-potassium pump is an active transport requiring energy.
The Action Potential
Stimulation of the neuron: a) negative ---> hyperpolarization: increased polarization across a
membrane. b) positive ---> depolarization: reduction in the level of polarization across a membrane -
--> depolarization beyond the threshold of excitation produces action potential: rapid depolarization
and slight reversal of the usual polarization caused by stimulation beyond the threshold ---> all-or-
none law: the size, velocity and amplitude of the action potential are independent of the intensity of
the stimulus that initiated it ---> after action potential, the cell is in a refractory period: a) absolute
refractory period: time immediately after an action potential when the sodium gates close and the
membrane cannot produce an action potential in response to a stimulation of any intensity. b)
relative refractory period: time after the absolute refractory period, when potassium gates remain
open wider than usual, requiring a stronger that usual stimulus to initiate an action potential.
Propagation of the Action Potential
Propagation of the action potential: transmission of an action potential down an axon ---> (stimulus ---
> voltage-gated channels open ---> depolarization ---> depolarization beyond threshold --->
rush in ---> peak ---> peak flows down the axon ---> voltage-gated channels shut, voltage gated
channels open ---> flows out ---> membrane returns to resting potential)
The Myelin Sheath and Saltatory Conduction
Myelin sheath: insulating material composed of fats and proteins that covers many vertebrate axons
---> faster impulse conduction ---> saltatory conduction: jumping of action potentials form one node
of Ranvier to another by the flow of positive ions.
Local Neurons
Local neurons: small neuron with no axon or a very short one ---> graded potentials: membrane
potential that varies in magnitude without following the all-or-none law.
3
Biological Psychology
James W. Kalat
,Chapter 1: The Major Issues
Chapter 2: Nerve Cells and Nerve Impulses
Module 2.1: The Cells of the Nervous System
Anatomy of Neurons and Glia
The nervous system consists of 2 kinds
of cells:
1) neuron: cell that receives information and
transmits it to other cells by conducting
electrochemical impulses ---> 3 types of
neurons: a) motor neurons (= efferent):
neuron that receives excitation from other
neurons through its dendrites and conducts
impulses from its soma in the spinal cord to
muscles or gland cells. b) sensory neuron (=
afferent): specialized to be highly sensitive to a
specific type of stimulation. c) interneuron:
neuron whose axons and dendrites are all
confined within a given structure ---> structure:
• neurons contain the same internal structures
as other animal cells (zie fig. 2.2). • neurons
have 4 major parts: soma (cell body),
dendrites (branching fibers that emanates from a
neuron, growing narrower as it extends from the cell
body toward the periphery), an axon (single thin fiber of
constant diameter that extends from a neuron) and
presynaptic terminals (tip of an axon, the point from
which the axon releases chemicals) (zie hiernaast voor
motor neuron (boven) en sensory neuron (onder)).
2) glia: type of cell in the nervous system that, in contrast
to neurons, does not conduct impulses to other cells --->
different types of glia: a) astrocytes: relatively large, star-
shaped, glia cell that wraps around a group of functionally
related axons ---> enables neurons to send messages in
waves, removes waste material & control amount of blood flow to each brain area. b) microglia: very
small cells that remove waste materials and microorganisms from the central nervous system. c)
oligodendrocytes: glia cells that surround and insulate certain axons in the vertebrate brain and
spinal cord ---> build myelin sheaths. d) Schwann cells: glia cells that surround and insulates certain
axons in the periphery of the vertebrate body ---> build myelin sheaths. e) radial glia: type of glia
cells that guides the migration of neurons and the growth of their axons and dendrites during
embryological development.
The Blood-Brain Barrier
Blood-brain barrier: the unbroken wall of endothelial cells that surround the blood vessels of the
brain and spinal cord and that keeps many viruses and dangerous chemicals out of the brain --->
chemical that cross the barrier: a) passively: • small uncharged molecules (oxygen, water, ). •
molecules that dissolve in the fats of the membrane. b) by active transport: protein mediated
process that expends energy to pump chemicals from the blood into the brain (glucose, amino acids,
purines, choline, a few vitamins, iron, certain hormones).
2
, The Nourishment of Vertebrate Neurons
Neurons depend almost entirely on glucose: a simple sugar, the main fuel of vertebrate neurons --->
problem glucose shortage, = inability to use glucose (deficiency in thiamine: vitamin B).
Module 2.2: The Nerve Impulse
The Resting Potential of the Neuron
Membrane of a neuron maintains an electrical
polarization, a difference in electrical charge between
the inside and the outside of a cell ---> resting
potential: difference in voltage when a neuron is not
being stimulated (the inside of a resting neuron has a
negative charge of -70mV with respect to the outside) -
--> is maintained because of the sodium-potassium
pump: mechanism that actively transports 3 sodium
ions out of the cell while drawing in 2 potassium ions
(zie fig. 2.15) ---> is effective only because of the
selective permeability (ability of certain chemicals to
pass more freely (e.g. potassium) than other (e.g. sodium) through a membrane): without selective
permeability, electrical gradient (difference in positive and negative charges across a membrane) &
concentration gradient (difference in distribution of ions across a membrane) would push sodium
into the cell ---> the sodium-potassium pump is an active transport requiring energy.
The Action Potential
Stimulation of the neuron: a) negative ---> hyperpolarization: increased polarization across a
membrane. b) positive ---> depolarization: reduction in the level of polarization across a membrane -
--> depolarization beyond the threshold of excitation produces action potential: rapid depolarization
and slight reversal of the usual polarization caused by stimulation beyond the threshold ---> all-or-
none law: the size, velocity and amplitude of the action potential are independent of the intensity of
the stimulus that initiated it ---> after action potential, the cell is in a refractory period: a) absolute
refractory period: time immediately after an action potential when the sodium gates close and the
membrane cannot produce an action potential in response to a stimulation of any intensity. b)
relative refractory period: time after the absolute refractory period, when potassium gates remain
open wider than usual, requiring a stronger that usual stimulus to initiate an action potential.
Propagation of the Action Potential
Propagation of the action potential: transmission of an action potential down an axon ---> (stimulus ---
> voltage-gated channels open ---> depolarization ---> depolarization beyond threshold --->
rush in ---> peak ---> peak flows down the axon ---> voltage-gated channels shut, voltage gated
channels open ---> flows out ---> membrane returns to resting potential)
The Myelin Sheath and Saltatory Conduction
Myelin sheath: insulating material composed of fats and proteins that covers many vertebrate axons
---> faster impulse conduction ---> saltatory conduction: jumping of action potentials form one node
of Ranvier to another by the flow of positive ions.
Local Neurons
Local neurons: small neuron with no axon or a very short one ---> graded potentials: membrane
potential that varies in magnitude without following the all-or-none law.
3
