Transcript The Nervous System - Gordon State College

Chapter 2
Neural and Genetic Bases of Behavior
Overview of Nervous System
LO 2.1 What Are the Nervous System, Neurons, and Nerves?
 Nervous System: an extensive network
of specialized cells that carry
information to and from all parts of the
body
 Neuroscience: deals with the structure
and function of neurons, nerves, and
nervous tissue
– relationship to behavior and learning
An Overview of the Nervous
System
Organization of the
Nervous System
Nervous
system
Central
(brain and
spinal cord)
Peripheral
Autonomic (controls
self-regulated action of
internal organs and glands)
Skeletal (controls
voluntary movements of
skeletal muscles)
Sympathetic
(arousing)
Parasympathetic
(calming)
Nervous System
 Central Nervous System (CNS)
–the brain and spinal cord
 Peripheral Nervous System (PNS)
–the sensory and motor neurons
that connect the central nervous
system (CNS) to the rest of the
body
Central nervous system (CNS)
– Spinal cord: slender, tube-shaped part of the (CNS)
that connects the brain to the body via the peripheral
nervous system
 The spinal cord transmits information from sensory
neurons to the brain, and from the brain to motor
neurons that initiate movement.
 The upper segments of the spinal cord control the
upper parts of the body, while the lower segments
control the lower body.
 The spinal cord also controls some automatic,
involuntary responses to sensory stimuli called
reflexes.
Reflex
 a simple, automatic, inborn response to a
sensory stimulus
Brain
Sensory neuron
(incoming information)
Muscle
Skin
receptors
Motor neuron
(outgoing
information)
Interneuron
Spinal cord
Peripheral Nervous System
LO 2.4 Somatic and Autonomic Nervous Systems
 Peripheral nervous system (PNS): all
nerves and neurons that are not
contained in the brain and spinal cord
but that run through the body itself
– divided into the:
somatic nervous system
autonomic nervous system
The Peripheral Nervous System
 Peripheral nervous system: All the nerves located
outside the brain and spinal cord.
– Its function—to connect the brain and spinal
cord with the organs and tissues of the body.
– The peripheral nervous system is composed of
two major divisions:
The somatic/skeletal nervous system
 The autonomic nervous system
– Sympathetic nervous system
– Parasympathetic nervous system

The Peripheral Nervous System
Somatic Nervous System
LO 2.4 Somatic and Autonomic Nervous Systems
 Soma = “body”
 Somatic nervous system: division of the
PNS consisting of nerves that carry
information from the senses to the CNS
and from the CNS to the voluntary
muscles of the body
– sensory pathway: nerves coming from
the sensory organs to the CNS
consisting of sensory neurons
Somatic Nervous System
LO 2.4 Somatic and Autonomic Nervous Systems
 Somatic Nervous System (cont’d)
– motor pathway: nerves coming from
the CNS to the voluntary muscles,
consisting of motor neurons
Autonomic Nervous System
LO 2.4 Somatic and Autonomic Nervous Systems
 Autonomic Nervous System (ANS)
– division of the PNS consisting of
nerves that control all of the
involuntary muscles, organs, and
glands; sensory pathway nerves
coming from the sensory organs to
the CNS consisting of sensory
neurons
Autonomic Nervous System
LO 2.4 Somatic and Autonomic Nervous Systems
– sympathetic division (fight-or-flight
system): part of the ANS that is
responsible for reacting to stressful
events and bodily arousal
– parasympathetic division: part of the
ANS that restores the body to normal
functioning after arousal and is
responsible for the day-to-day
functioning of the organs and glands
Functions of the Parasympathetic and Sympathetic
Divisions of the Nervous System
The Endocrine System Communicates
by Secreting Hormones
 The endocrine system is interconnected with—but not
part of—the nervous system.
– consists of a network of glands that make and
secrete hormones - chemical messengers.
– The pituitary gland (master gland), in the base of
the brain, releases about 10 different hormones
and is controlled by the hypothalamus.
– Other endocrine glands include the thyroid gland,
the adrenal glands, and the gonads.
The Endocrine Glands
The Endocrine Glands
LO 2.5 How Hormones Interact with the Nervous System and Affect Behavior
 Pineal gland: endocrine gland located
near the base of the cerebrum that
secretes melatonin
 Thyroid gland: endocrine gland found in
the neck that regulates metabolism
 Pancreas: endocrine gland that controls
the levels of sugar in the blood
The Endocrine Glands
LO 2.5 How Hormones Interact with the Nervous System and Affect Behavior
 Gonads: the sex glands that secrete
hormones that regulate sexual
development and behavior as well as
reproduction
– ovaries: the female gonads
– testes: the male gonads
The Endocrine Glands
LO 2.5 How Hormones Interact with the Nervous System and Affect Behavior
 Adrenal glands: endocrine glands
located on top of each kidney that
secrete over thirty different hormones to
deal with stress, regulate salt intake,
and provide a secondary source of sex
hormones affecting the sexual changes
that occur during adolescence
The Neuron
 Neurons are specialized cells in the
nervous system that send and receive
information throughout the body.
– Neurons are the nervous system’s
building blocks.
A Neuron
The nervous system contains 90 to 180 billion neurons (98.8
percent in the brain and 1.2 percent in the spinal cord).
Each neuron transmits information to about a thousand
other neurons; there are trillions of different neural
connections in the brain.
Structure of the Neuron
LO 2.1 What Are the Nervous System, Neurons, and Nerves?
 Parts of a Neuron
– dendrites: branch-like structures that
receive messages from other neurons
– soma: the cell body of the neuron,
responsible for maintaining the life of
the cell
– axon: long, tube-like structure that
carries the neural message to other
cells
Neuron
Structure of a Neuron
There are three basic types of
neurons:
 Sensory
neurons: send information
from sensory receptors to the brain
 Motor neurons: send commands
from the brain to glands, muscles,
and organs
 Interneurons: connect other
neurons to one another
Structure and Operation
of the Neuron
Neural
Communication
 Action Potential
– a neural impulse; a brief electrical charge
that travels down an axon
– generated by the movement of positively
charged atoms in and out of channels in
the axon’s membrane
 Threshold
– the level of stimulation required to trigger a
neural impulse
 Firing is all or none
Generating the Message: Neural
Impulse
 All-or-none: a neuron either fires
completely or does not fire at all
 The message is electrical
 To fire, the neuron must reach threshold
 Firing (or not-firing) messages come in
on the dendrites
 Firing is down the axon
The Neural Impulse Action Potential
In the graph below, voltage readings are shown at a
given place on the neuron over a period of 20 or 30
milliseconds
(thousandths of a second). At first the cell is resting;
it then reaches threshold and an action potential is
triggered. After a brief hyperpolarization period, the
cell returns to its resting potential.
Threshold
Generating the Neural Impulse
 Ions: charged particles
– inside neuron: negatively charged
– outside neuron: positively charged
 Resting potential: the state of the neuron
when not firing a neural impulse
 Action potential: the release of the neural
impulse consisting of a reversal of the
electrical charge within the axon
– allows positive sodium ions to enter the cell
The Neural Impulse Action Potential
Synapses: Points of Chemical
Transmission between Neurons
– Axon terminal buttons contain round sacs
called synaptic vesicles.
– When an action potential arrives, it causes
these vesicles to release chemical
messengers, called neurotransmitters,
which travel across the synaptic cleft.
– These neurotransmitters fit into the
receiving dendrites’ receptor sites, like
keys fit into locks (based on molecular
shape).
Synaptic Transmission
Synapses: Chemical Transmission
between Neurons
After locking into receptor sites,
neurotransmitters either excite or inhibit firing
of the receiving neuron.
Excitatory messages increase the probability of
an action potential.
Inhibitory messages reduce the likelihood of
neural firing.

Whether the neuron fires will depend on which
type of message is in greater abundance.
Synapses: Chemical Transmission
between Neurons
 After neurotransmitters deliver their
messages they are either:
– Repackaged into new synaptic
vesicles in a process known as
reuptake or
– Broken down by enzymes and
removed from the synaptic cleft in a
process called enzyme deactivation.
Synaptic Transmission—Reuptake
Synaptic Transmission— Enzyme
Deactivation
Chemical Neurotransmitters
About 75 neurotransmitters have been
identified, including:

Acetylcholine (ACh): involved in muscle
contraction, cognition, and memory formation

Dopamine (DA): controls large muscle
movements; influences pleasure and motivation

Endorphins: important in the experience of
pleasure and control of pain

Serotonin: involved in regulating emotional states
such as depression, sleep cycles and dreaming,
aggression, and appetite
Agonists and Antagonists
Neurotransmitter
molecule
Receptor site on
receiving neuron
Receiving cell
membrane
Agonist mimics
neurotransmitter
Antagonist
blocks
neurotransmitter
Neuron Communication
LO 2.2 How Neurons Use Neurotransmitters to Communicate
– agonists: mimic or enhance the
effects of a neurotransmitter on the
receptor sites of the next cell,
increasing or decreasing the activity
of that cell
– antagonists: block or reduce a cell’s
response to the action of other
chemicals or neurotransmitters