THE NERVOUS SYSTEM
Divisions of the NS
• Central Nervous
System (CNS)
• Peripheral Nervous
System (PNS)
Fig. 11.32
Sensory vs. Motor Nerves
• SENSORY nerves:
– Body  CNS
• MOTOR nerves:
Fig. 10.2
– CNS  Body
2 Different Types of Motor Nerves
• Somatic NS
– consciously controlled
effectors
• Autonomic NS
– involuntary effectors
Cells of the Nervous System
• NEURONS
vs.
• NEUROGLIAL
CELLS
NEUROGLIAL CELLS
•
•
•
•
Fill spaces
Provide structure
Produce myelin
Phagocytize bacteria
& cellular debris
• Outnumber neurons
• Can divide (mitosis)
Neuron Anatomy Overview
• Dendrites  Cell
body  Axon 
Synaptic knobs at
axon terminals 
Effector
Neuron Anatomy
• Schwann cells
– type of neuroglial
cell
– myelin sheath
• Nodes of Ranvier
Fig. 10.3
Classification of Neurons
THE DIRECTION
THEIR SHAPE
Fig. 10.6
Sensory, Motor, and Interneurons
(Direction)
• Sensory neurons
– PNS  CNS
• Motor neurons
– CNS  PNS
• Interneurons
– in between sensory
and motor neurons
Fig. 10.7
Shapes of Neurons
Fig. 10.6
Neuron vs. a “Nerve”
Fig. 11.24 • Neuron = a cell
• Nerve = bundles of
neuron axons, and
neuroglial cells bound
together
– outside brain/spinal
cord
Neuron Physiology
• Sending neuron impulses = action potential
– change in electrical charge in cell membrane
– depends on electrolytes
• potassium (K+) and sodium (Na+)
First Things First: Creating a Resting
Potential
• Protein pumps
– open and close
– let ions through
• Active pumps
– against a gradient
Fig. 10.13
Na+/K+ Pump
• Passive pumps
– with the gradient
Resting Potential
Fig. 10.14
Action Potential
Fig. 10.15
Action Potential
A Nerve Impulse- a series of action
potentials
Fig. 10.16
Computer activity
http://outreach.mcb.harvard.edu/animations/actionpotential.swf
Action Potential
Fig. 10.18
Action Potential Zoomed Out
What happens when the nerve
impulse reaches the end of the axon?
• axon terminals
– next to another
neuron (as shown) or
a muscle or gland
• Gap called a synapse
Synapse
Fig. 10.11
The Synapse
•
•
•
•
Neurotransmitters
Synaptic cleft
Receptors
Send a message
Fig. 10.12
Neurotransmitters
Classification of
Neurotransmitters
• EXCITATORY =
depolarize the next
neuron
• It tells the next
neuron/muscle/gland
to GO
• INHIBITORY =
hyperpolarize the next
neuron
– prevent the nerve
impulse from
continuing
• It tells the next
neuron/muscle/gland
to STOP
Acetylcholine (ACH)
• First neurotransmitter
discovered (1921)
• Mostly excitatory
• Skeletal muscle
neuromuscular junctions
& synapses between the
brain and spinal cord
• Message =
– muscles contract or
– continue sending impulses
Acetylcholine cont.
• Nicotine
– Activates acetylcholine receptors
– Releases dopamine (coming later…)
• Alzheimers
– Memory loss, depression, disorientation,
dementia, hallucinations,death
– Deficient acetylcholine
Glutamate
• Generally excitatory
– helps send messages in the
brain
• Involved in learning and
memory
• Alcohol inhibits glutamate
receptor function
• Monosodium Glutamate
(MSG)
– food additive
– stimulates glutamate
receptors in the taste buds
Serotonin
• Found in the brain
• Primarily inhibitory
• Sleep, mood and
temperature regulation
• Insomnia – deficient
serotonin
• Antidepressants
(Prozac, Zoloft, Paxil,
etc)
– “SSRI’s” or Selective
Serotonin Reuptake
Inhibitors
– Serotonin accumulates
in the synapse
– feel more content
• LSD blocks serotonin
• MDMA releases
excess serotonin
Dopamine
• AKA “the brain reward”
• Regulates emotions, moods
and subconscious control of
skeletal muscle
• Nicotine
– excess dopamine release
• Cocaine
– blocks reuptake (leaves more in
the synapse)
• Methamphetamine
– excess dopamine release
Dopamine - cont’d
• Dopamine also sends
signals that help
coordinate your skeletal
muscle movements
• Parkinson’s Disease
– deficient dopamine
production
– tremors
GABA
• Found in the brain
• Generally inhibitory
• Prevents the receptor
nerve from being
overstimulated
• When it accumulates it
has a sedative effect
• Valium, Xanax and
Ativan work by
allowing GABA to
accumulate
• Huntington’s Disease
– deficient GABA
Norepinephrine
• Found in the brain
• Alertness, regulation of
moods
• Ritalin & Adderallincrease level of norepi
and dopamine
• Strattera- increase only
norepi
• Clinical depression – low
norepi
Endorphins
• Flood the synaptic cleft during pain or stress
– Usually inhibit neurons from firing, causing an
analgesic effect
– At lower levels can excite the next neuron
• Reduces pain and makes one feel good
• “Opiates” (heroin, codeine, morphine,
oxycodone, hydrocodone, etc)
– bind to endorphin receptors and mimic
endorphins
Anandamide
• Involved in working memory, regulation of
feeding behavior, generation of motivation and
pleasure
• Anandamide receptors are called cannabinoid
receptors
– A lot of cannabinoid receptors in the hippocampus
(short term memory), cerebellum (coordination) and
basal ganglia (unconcious muscle movement) of brain
• THC (found in marijuana) mimics anandamides
and binds to cannabinoid receptors
Peripheral Nervous System
• 12 pairs cranial nerves
• 31 pairs spinal nerves
PNS Flow Chart
Peripheral Nervous System
Motor
nerves
Somatic
nerves
Sensory
nerves
Autonomic
nerves
Sympathetic
nerves
Parasympathetic
nerves
PNS cont.
• Motor nerves are divided
into
– Somatic n.s.- conscious
activities
– Autonomic n.s. –
unconscious activities
• Autonomic n.s is divided
into
– sympathetic and
– parasympathetic
divisions.
PNS cont.
SYMPATHETIC
PARASYMPATHETIC
• “fight or flight”
responses
• speeds up heart rate,
breathing and other
functions vital to
survival
• Digestion and other
less essential functions
will be slowed for
awhile.
• when the body is not
mobilized and active in
fight or flight.
• speeds up digestion and
other essential functions
• When the body is in this
mode, heart rate and
breathing are calm.
The Central Nervous System
• The Brain
• The Spinal Cord
Central Nervous System - Spinal
Cord
Figs11.5, 11.6, & 11.7
Reflexes
Fig. 11.8
Central Nervous System: The Brain
• Cerebrum
– Largest part
– Sensory & motor functions
– Higher mental functions
(memory, reasoning, etc)
• Brainstem
– Connects the cerebrum to
the spinal cord
• Cerebellum
– Coordinates voluntary
muscle movements
• Diencephalon
– Processes sensory info
Fig. 11.15
The Cerebrum
• Divided into right and left
cerebral hemispheres
• Covered by folds called
convolutions/gyri and
grooves called sulci (little
groves) and fissures (big
grooves)
• Connected by the corpus
callosum
• It has a cortex: an outer
covering about 2 mm thick
• Gray matter vs. white
matter
The Cerebrum cont.
• The cerebral cortex is
divided into LOBES
which control various
functions
• FPOT
Fig. 11.16 & 11.17
The Cerebrum cont.
• FRONTAL LOBE –
– “Primary Motor Area”
• controls voluntary
muscles
– “Broca’s Area”
• motor speech
• usually L hemisphere
– Voluntary eye
movement
– Concentration,
planning, problem
solving, analysis
The Cerebrum cont.
• PARIETAL LOBE
– Sensory info: touch, taste, pressure, pain
• interpretation of sensory info, “awareness”
of body
– “Wernicke’s Area”
• sensory speech, understanding written &
spoken language
• usually L hemisphere
The Cerebrum cont.
• OCCIPITAL LOBE
– visual senses
– analyzing visual patterns, combining visual
images with other info (i.e. recognizing a
person)
• TEMPORAL LOBE
– sensory smell and hearing
– interpretation of sensory experiences
(understanding speech, reading)
Cerebral Hemispheres
• Hemisphere = half of
sphere (brain)
• The right side of the
brain controls the left
side of the body and
vice versa
• Corpus callosum
The Cerebellum
• Integrates sensory info
– Balance,
coordination of
skeletal muscle,
posture
Brainstem
Fig. 11.21
• Brainstem: Connects the
cerebrum to the spinal cord
– Midbrain: visual and
auditory reflex center
– Pons: transfer nerve
impulses
– Medulla Oblongata:
• Cardiac center- heart
rate
• Vasomotor centersmooth muscle in blood
vessels/blood pressure
• Respiratory centerbreathing rate
• Coughing, sneezing,
swallowing and
vomiting reflexes
1. Thalamus-
Diencephalon
Receives all sensory
impulses (except smell)
and relays them to the
appropriate region of the
cerebral cortex
2. Hypothalamus –
– Maintain homeostasis
– Links the nervous
system to the endocrine
system
3. Pituitary & pineal
glands
Fig. 11.19
Diencephalon cont.
• The limbic system is a
collection of structures
involved in emotional
behavior and your
feelings
– Includes the amygdala
and hippocampus
MEMORY
•
•
Primarily occurs in the
cerebrum and the
hippocampus (in the
diencephalon)
3 main types of memory:
1. Sensory memory = lasts
momentarily and involves input
from senses
2. Short term memory = lasts from
a few seconds or minutes to
hours (varies)
Memory cont.
3. Long term memory = the neurons actually
change shape (dendrites extend, more are
made, etc) and connect with other neurons.
Lasts days to years (varies).