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Nervous System
Central Nervous System (CNS): brain and
spinal cord.
CNS contains tracts
Peripheral Nervous System (PNS): nerves of
the body
PNS contains nerves
-- Includes 31 pairs of spinal nerves
-- And 12 pairs of cranial nerves
Basic Divisions of the Nervous System
Figure 12.2
THREE BASIC FUNCTIONS OF THE NERVOUS SYSTEM
• Sensory - gathers info
• Integrative - information is brought together
• Motor - responds to signals, homeostasis
Peripheral Nervous System
Afferent - transmits action
potentials from sensory organs to
the CNS
Efferent - transmits action
potentials from the CNS to effector
organs such as muscles - glands
Peripheral Nervous System
Efferent divided further
SOMATIC NERVOUS SYSTEM skeletal muscles, under voluntary control
AUTONOMIC NERVOUS SYSTEM smooth muscles, glands, involuntary
Peripheral Nervous System
Autonomic divided further
Sympathetic – Fight or Flight
Parasympathetic – Rest and Digest
Common Neurotransmitters
• Epinephrine/Adrenaline
• NorEpinephrine/Noradrenaline
• Acetylcholine
Neurons
Factors Affecting Nerve Impulse
Velocity
• Diameter of the neuron
• Temperature
• Myelinated or Unmyelinated
Neuroglial Cells
- support cells for the neurons
1. Microglial : scattered throughout, digest
debris or bacteria
2. Oligodendrocytes: provide insulation around
the axons
3. Astrocytes: connect blood vessels to neurons
4. Ependymal Cells: form a membrane that
covers brain-like parts
5. Schwann cells: form the insulating sheath
around the neurons within the PERIPHERAL
nervous system
Neurilemma = thin, membranous covering over
Schwann cells that allows cells to slowly
repair/regenerate themselves if injured
*Myelin Sheaths - necessary for insulation of
neurons
Supporting Cells in the CNS
Microglial cells
respond to
immunological
alarms
Supporting Cells in the CNS
Creates the myelin sheath
that insulates axons
Supporting Cells in the CNS
Astrocytes connect
neurons to blood vessels
Supporting Cells in the CNS
Figure 12.12a
Supporting Cells in the CNS
Supporting Cells in the CNS
Supporting Cells
Neuron Structure
• Neurofibril - fibers
• Chromatophilic substance (rough ER) transport system
• Myelin -insulation surrounding axons
• Nodes of Ranvier - gaps in the insulation
White vs Grey Matter
Myelinated (white matter) – myelinated axons
Unmyelinated (grey matter) - unmyelinated
Label
NEURON (main cell of the nervous system)
• All neurons do three things:
• Receive a signal. Can be any type of stimulus (change in
environment, signal from another neuron, etc).
• Transmit a signal to another location. E.g. finger touching
something • signal to spinal cord or brain.
• Stimulate another cell
o
o
o
Another neuron • transmit signal
Muscle • contraction
Gland • secretion
The Neuron
• Other special characteristics
Longevity – can live and function for a lifetime
Do not divide – fetal neurons lose their ability to
undergo mitosis; neural stem cells are an exception
o High metabolic rate – require abundant oxygen and
glucose
o
o
Types of Neurons
Functional:
Sensory, Motor,
Interneurons
Structural:
(A) Bipolar
(B) Unipolar
(C) Multipolar
Nerve Impulses
Nerve Impulses
At rest, the inside of a neuron's membrane
has a negative charge. As the figure
shows, a Na+ / K+ pump in the cell
membrane pumps sodium out of the cell
and potassium into it. However, because
the cell membrane is a bit leakier to
potassium than it is to sodium, more
potassium ions leak out of the cell. As a
result, the inside of the membrane builds
up a net negative charge relative to the
outside.
Animations of Nerve Impulses
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter14/anim
ation__the_nerve_impulse.html
http://outreach.mcb.harvard.edu/animations/actionpotenti
al.swf
The Synapse
Synapse - junction between two
communicating neurons
Nerve pathway - nerve impulse
travels from neuron to neuron
Synaptic Transmission
Dendrite ' cell body ' along axon '
synapse (gap)
To complete the signal, a
NEUROTRANSMITTER is
released at the gap to signal the
next neuron
Structure of a Synapses
Figure 12.8a, b
Neurotransmitters
Excitatory - increase membrane permeability,
increases chance for threshold to be achieved
Inhibitory - decrease membrane permeability,
decrease chance for threshold to be achieved
Types of Neurotransmitters
• Acetylcholine - stimulates muscle contraction
• Monoamines - Norepinephrine & Dopamine (sense
of feeling good, low levels = depression)
• Serotonin (sleepiness)
• Endorphins (reduce pain, inhibit receptors)
Drugs that Affect Synapses and Neurotransmitters
•
•
•
•
•
Curare
Strychnine
Cocaine, morphine, alcohol, ether and chloroform
Mescaline and LSD
Ecstasy
Antidepressants
• Zoloft is part of a class of drugs called selective
serotonin reuptake inhibitors, or
• SSRIs for short. SSRIs act on a specific chemical
within the brain known as serotonin. This is one of
several chemicals used to send messages from one
nerve cell to another.
Impulse Processing
Neuronal pool - groups of neurons that make
hundreds of synaptic connections and work together
to perform a common function
Types of Nerves
Dorsal Root/Sensory Nerves - conduct impulses into the
brain or spinal cord
Ventral Root/Motor Nerves - carry impulses to muscles
of glands
Mixed Nerves - contain both sensory and motor nerves
Problem
• If Mary has a spinal cord injury to just her ventral
portion of the spinal cord what would happen to
her?
• HINT** Will she lose feeling, movement or
both?
Neurons Classified by Function: Sensory vs. Motor Neurons
Figure 12.11
Nerve Pathways
•
•
•
•
Reflex arc - only includes a few neurons
Reflex Behavior - automatic, subconscious responses
Knee-jerk reflex - maintains uprightedness
Withdrawal reflex - avoidance of painful stimuli