Download 1. Somatic nervous system

Nervous System
Topic 14
I. Functional Units of the Nervous
System
• A. neuron – functional unit of the nervous
system
• B. neurons are specialized cells that transmit
information in the form of electrochemical
signals called action potentials
• C. signals are generated when the neuron alters
the voltage found across its plasma or cell
membrane
• D. neurons have an excitable membrane which
allows them to carry an action potential
• E. parts of the neuron
– 1. cell body – contains the nucleus and most of
the organelles – also the site for protein synthesis
and energy production
– 2. dendrites – receive chemical information from
other neurons as changes in membrane potential
and carry this information to the cell body
– 3. axon – a long, slender projection of the neuron
that transmits the action potential from the cell
body to the target the neuron is to communicate
with – can be short or as long as a meter
• F. Resting potential – all cells have a voltage across
their plasma membrane that is generated through
the actions of a protein called the Na+ / K+ ATPase –
using the hydrolysis of ATP for energy, this protein
pumps sodium ions out of the cell and potassium
into the cell – it also maintains the osmotic balance
in cells – some of the potassium leaks back out of
the cell through an ion channel called the potassium
leak channel – with more positive ions on the
outside of the cell, a net negative voltage of about
-70 mV is found across the plasma membrane and is
called the resting potential
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• G. Action potential – a wave of electrochemical
information that moves through axons and muscle
tissue creating a response in those target tissue –
neurons and muscle cells have a protein in their
plasma membrane that lets sodium ions through the
membrane in response to a decrease in the
membrane potential – this protein is called a voltagegated sodium channel and gives neurons an
excitable membrane
• (continued on next slide)
• – if the membrane voltage becomes less negative
than the resting potential, changing from -70 mV to
-50 mV, then the voltage-gated sodium channels in
the neuron’s plasma membrane will open – the
voltage at which the voltage-gated channels open is
called the threshold potential – when these channels
are open, sodium will diffuse freely through the
channel to cross the plasma membrane, flowing
down a gradient from the outside of the cell into the
cytoplasm – the opening of these channels in one
region of the membrane and the entry of sodium
through the channels cause membrane
depolarization
• (continued on the next slide)
• After the voltage-gated sodium channels
have opened and depolarization is complete,
the channels close – potassium channels
open and potassium rushes out allowing the
membrane voltage to return to its normal
negative voltage – this is called
repolarization – the sodium/potassium pump
puts the sodium and potassium back to their
original positions and the axon is now ready
for a new action potential
Action Potential
Graph of an Action Potential
http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter45/animat
ions.html#
• H. Size and Frequency of Action
Potentials
– 1. every action potential in a neuron is the
same size
– 2. neurons do not have half of a
depolarization or half of an action potential –
it is all or nothing
– 3. the strength of the stimulus does not
change the size of the action potential or the
duration
– 4. the difference is in the frequency of the
action potential
• (a) weak – may only trigger one action potential in
a second
• (b) strong – may trigger many more in the same
period
– 5. the membrane cannot fire again
immediately – it must first depolarize and then
repolarize – the time before it can fire again is
called the refractory period
Action Potential Rules
• I. Synapses – spaces between neurons
and their target cells – the membrane
potential is converted into a chemical
signal or neurotransmitter – the gap
between the neuron and the target cell is
called the synapse or synaptic cleft – the
synapse between a neuron and a muscle
is called the neuromuscular junction
Synapse
Neuromuscular Junction
http://www.youtube.com/watch?
v=9FF6UKvDgeE
• J. turning off signals is as important as
turning it on – ways to remove
neurotransmitters
– 1. diffuse into the surround fluid
– 2. an enzyme degrades the neurotransmitter
– 3. cells in the synapse take the
neurotransmitter up
II. Nervous Regulation
• A. stimuli - any change in the
environment that causes a response
• B. receptors and effectors - receptors
are the senses which detect stimuli effectors are muscles and glands which
respond to the stimuli
III. Adaptations for nervous
control
A. protozoans - paramecium have fibrils which
transmit impulses to cilia
B. hydra - have a nerve net - impulses may
travel in any direction
Hydra – nerve net
C. Earthworm - has a “brain” or mass of
ganglia (group of neurons), a ventral
nerve cord and nerve branches
Earthworm
• D. grasshopper - similar to earthworm
plus sensory organs – eyes, antennae,
tympannum
IV. Human Nervous System
A. neurons - units of the nervous system three types of neurons
– 1. Sensory neurons - transmit impulses from
sense organs or receptors to the brain and spinal
cord
– 2. Motor neurons - transmit impulses from the
central nervous system(brain and spinal cord) to
muscles or glands(effectors)
– 3. Interneurons - transmit impulses between
sensory and motor neurons
• B. nerves - bundles of neurons
• C. Central Nervous System – Brain and
Spinal Cord
– 1. Structure and location - thick nerve that
is found inside the vertebrae
– 2. Functions - transmits impulses between
the brain and the rest of the body
•
D. brain
– 1. Structure and location - large mass made mostly of interneurons
found inside the cranium
– 2. Functions
• a. cerebrum - voluntary movement, memory, reasoning – also
called the cerebral cortex
• b. cerebellum - balance
• c. medulla - involuntary movement (breathing, heartbeat, blood
pressure, digestion)
• D. olfactory lobe – smells
• E. thalamus – relays info to the cerebral cortex
• F. hypothalamus – hunger, thirst, pain, temp. reg., water
balance
• G. pons – relays info from cerebrum to cerebellum
• H. reticular activating system – brain stem – process sensory
inputs
Brain
• E. peripheral nervous system - nerves that extend
away from the brain and spinal cord
– 1. Somatic nervous system - consists of nerves
that control the voluntary muscles
– 2. Autonomic nervous system - consists of nerves
that control heart muscles, glands, and smooth
muscles
• (a) sympathetic nervous system – uses
norepinephrine – fight or flight – increases
heart rate
• (b) parasympathetic nervous system –
acetylcholine – deactivate or slow down
activities of muscles and glands – rest and
digest response
• F. human behavior
– 1. Involuntary behavior
• a. simple reflexes - inborn, automatic patterns
of behavior - goes from receptor to sensory
neuron to interneuron to a motor neuron to an
effector
Reflex Arc
• G. some malfunctions of the nervous system
– 1. Meningitis - inflammation of the meninges
(membranes around the brain and spinal cord)
– 2. Cerebral palsy - damage to the motor centers of
the brain
– 3. Stroke - damage to the nerve cells in the brain blockage of artery
– 4. Polio - virus of the spinal cord
V. Sensory Organs
•
A. Eye – parts and functions
– 1. cornea – transparent – bends and focuses light rays
– 2. pupil – opening
– 3. iris – muscle that controls the opening and closing of the pupil –
responds to the intensity of light
– 4. lens – suspended behind pupil – light travels through here and is
focused on the retina
– 5. retina – contains photoreceptors that transduce light into action
potentials – image is actually upside down but revision and
interpretation in the cerebral cortex result in the perception of the image
right-side up
– 6. optic nerve – conduct visual information to the brain
– 7. cones and rods
• a. cones – sensitive to color
• b. rods – night vision – light and dark
•
B. Ear – parts and functions
– 1. outer ear
a. Auricle (pinna)
b. Auditory canal
– 2. middle ear
a. Tympanic membrane (eardrum) – vibrates at the same frequency as the
incoming sound
b. Three bones or ossicles – amplify the stimulus and transmit it through the
oval window which leads to the fluid-filled inner ear
1. Malleus (hammer)
2. Incus (anvil)
3. Stapes (stirrup)
– 3. inner ear
a. Cochlea – contains the organ of Corti which has specialized sensory cells
called hair cells – hair cells vibrate – transduce pressure into action
potentials
b. Semicircular canals – used for balance
• C. Taste and Smell
– 1. taste buds – chemical sensory cells located
on the tongue – sour, salty, sweet, and bitter
– 2. olfactory receptors – chemical sensors
found in the olfactory membrane in the upper
part of the nostrils – axons join to form the
olfactory nerves