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The Nervous System
• Components:
–Brain, spinal cord, nerves, sensory receptors
• Responsible for…
–Sensory perceptions, mental activities, stimulating muscle movements,
secretions of many glands
• Subdivisions:
–Central Nervous System (CNS)
–Peripheral Nervous System (PNS)
Central Nervous System
• Consists of brain and spinal cord
• The structural & functional center of the entire nervous system which integrates
incoming pieces of information & initiates an outgoing response
Peripheral Nervous System
• All other nerves
• All pathways going toward and away from the CNS
Nervous System Organization
LZHS McGraw Hill – Chapter 11 Notes
Anatomy H
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Cells of Nervous System
• Neurons or nerve cells
–Receive stimuli and transmit action potentials
–Organization
• Cell body or soma
• Dendrites: input
• Axons: output
• Neuroglia cells
–Support and protect neurons
Types of Neurons
• Functional Classification
–Sensory or afferent: action potentials toward CNS (receives stimuli; could
be a special sense organ)
–Motor or efferent: action potentials away from CNS (attached to a muscle
or gland)
–Interneurons or association neurons: within CNS from one neuron to another
Myelinated and Unmyelinated Axons
• Myelinated axons
–Myelin protects and insulates axons from one another
–Not continuous
• Nodes of Ranvier
• Impulse “jumps” from node to node
• Fast impulse
• Unmyelinated axons
–Slower impulse
Electrical Signals
• Cells produce electrical signals called action potentials
• Transfer of information from one part of body to another
• Electrical properties result from ionic concentration differences across plasma
membrane and permeability
LZHS McGraw Hill – Chapter 11 Notes
Anatomy H
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Nerve Impulses
• A wave of electrical fluctuation that travels along the plasma membrane; due to
changes in chemical concentrations.
Impulse
+++-++++++-++++-+
---+---+-----------+--+
++++++-+++-++-+++++-++++++++
----+----+--+--------+
++++-++++++-+++++-
-----+----+-------+--+-------+--------
----+----+---+----------
++++++++-++-++++-++
++++++-++-+++++++
--------+--++----------+----
----+-----++-----------+-----+------+--+++++++-+++++++--++++++++-+++
Resting Potential
Action Potential
Resting Potential
“Polarized”
“Depolarized”
“Repolarized”
Resting Membrane Potential
• Characteristics
–Number of charged molecules and ions inside and outside cell nearly equal
–Concentration of K+ higher inside than outside cell- negative proteins in also,
Na+ higher outside than inside
–At equilibrium there is very little movement of K+ or other ions across
plasma membrane
Action Potentials
• Series of permeability changes when a local potential causes depolarization of
membrane
• Phases
–Depolarization
• More positive
–Repolarization
• More negative
• All-or-none principle
–Neuron will fire or it won’t
LZHS McGraw Hill – Chapter 11 Notes
Anatomy H
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The Synapse
• Junction between two cells
• Electrical message transferred across the synapse by chemicals called
neurotransmitters
Stimulus
• Any change in your environment.
–Temp, sound, smell
• You may or may not respond to a specific stimulus
Reflex
• A predictable response to a stimulus which may or may not be conscious
–A reflex consists of either muscle contraction or glandular secretion
–Neurons involved in reflex
• Afferent neuron- sensory
• Interneuron
• Efferent neuron- motor
Sensory Receptors
• In order for a stimulus to be detected, it must be strong enough to elicit an
impulse
–It must be at the threshold level- the minimum stimulus to start an impulse
• The all-or-none response means that either a neuron will fire or it won’t, there is
no partial impulse
• Sensation- the brain’s interpretation of what the stimulus is
Characteristics of Sensations
• Projection- brain refers a sensation to the point of stimulation
• Adaptation- loss of sensation even though the stimulus is still applied
LZHS McGraw Hill – Chapter 11 Notes
Anatomy H
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• Afterimage- persistence of a sensation even though the stimulus is removed
• Referred pain- felt in the skin near or around the organ sending the impulse
• Phantom pain- sensation of pain in a limb that has been amputated
Classification of Receptors
1. Mechanoreceptors- activated by mechanical stimuli or deformation of the
receptor
2. Chemoreceptor- changing of the chemical concentrations around the body
3. Thermoreceptors- detect hot and cold
4. Nociceptors- any stimuli that can cause tissue damage; sensation of pain
5. Photoreceptors- respond to light
Somatic Senses - pain, temperature and touch
• These sensations can be felt throughout the body, yet they are distributed
unevenly through the skin
• Exteroceptors- sense receptors located on body surfaces
• Proprioceptors- found in the muscles and joints
• Visceroceptors- found in internal organs
• Nociceptors- pain receptors; free nerve endings
Review
• Meissner’s corpuscles- touch
• Krause’s End Bulbs- touch
• Ruffini’s corpuscles- continuous touch
• Pacinian corpuscles- deep pressure
LZHS McGraw Hill – Chapter 11 Notes
Anatomy H
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