Chapter 37
Nervous System
Nervous System-receives and relays information
about activities within the body and monitors and
responds to internal and external changes
Three main functions of the
nervous system
• 1. Sensory Input
• 2. Integration
• 3. Motor Output
Three main functions of the
nervous system
Structures of the central Nervous
system (CNS)
• 1. brain
• 2. spinal nerve cord
in vertebrates
Motor output is the conduction of
signals from the CNS to the effector
cells such as muscles
How are signals conducted
• Signals are conducted by nerves
• Nerves are bundles of neurons which are
wrapped in connective tissue
Sensory and motor neurons are
collectively called the peripheral
nervous system
Neuron-structural and functional
unit of the nervous system
Four main parts of a neuron
• 1. Cell body
• 2. Dendrites
• 3. Axon (action potential is generated here
number 20)
• 4. Axon terminals
Synapse-The site of contact between a synaptic
terminal of a neuron and a target, such as another
neuron, a muscle cell, or a gland, is called a
Pre-synaptic cell and post-synaptic
cells of a synapse
Reflex arc-the simplest type of
nerve circuit
Has to be at
least one
neuron and
one motor
Ganglia and nuclei
Collections of cell bodies of neurons.
Ganglia are found in the peripheral
nervous system
Nuclei are found within the brain.
Schwann Cells
Cells that form the insulating sheaths
around axons
Located outside the Central Nervous
It is made of myelin
Membrane potential
All cells have an electrical charge difference
across their plasma membrane called the
membrane potential
It exists because the different concentration of
certain ions across the cell membrane
The membrane potential of an unstimulated
neuron is called the resting membrane
These ions move across the membrane either
by being pumped by membrane proteins or by
simple diffusion through ion channels.
Membrane potential
Resting membrane potential
All cells have a membrane potential
However, only certain cells such as
neurons and muscle cells have the ability
to generate large changes in their
membrane potential
These cells are called excitable
Action Potential
• If a sufficiently strong stimulus causes
depolarization to reach “threshold
potential” it triggers a different type of
response called an action potential
Two factors that affect the speed at
which an action potential travels
down an axon
• The diameter of the axon, the larger the
diameter the faster the action potential
• The presence of myelin around the axon,
myelin insulates the axon and allows the
action potential to travel quicker
The “motor division” of the peripheral nervous system is
divided into two functional divisions, called the somatic and
autonomic nervous systems
What do they do?
• The somatic nervous system carries
signals to skeletal muscle
• The autonomic nervous system carries
signals to cardiac muscle, smooth muscle,
and glands
Sympathetic and Parasympathetic
of the Autonomic nervous system
• The autonomic nervous system consists of two
divisions that act on body organs with opposite
• The Sympathetic Division correlates with an
activation of the fight or flight response
• The Parasympathetic Division causes a calming
effect and a return to an emphasis on selfmaintenance functions

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