Transcript Nervous System

The Nervous System
AP Biology
Why do animals need a nervous
• Because the world
system?
is always coming
at you!
Remember…
Poor
thinkbunny!
about
the bunny…
The Nervous System
• Function: environment is
constantly changing – nervous
system detects those changes
and helps the organism
respond/adapt
• Irritability: ability to respond to a
stimulus
The Nervous System
• Nervous System detects
(sensory input), processes
(integration), and responds
(motor output)
• Peripheral Nervous System
detects and responds
• Central Nervous System
processes information
Nervous System
cerebrum
cerebellum
spinal cord
• Central nervous
system
– brain & spinal cord
• Peripheral nervous
system
– nerves from senses
– nerves to muscles
cervical
nerves
thoracic
nerves
lumbar
nerves
femoral
nerve
sciatic
nerve
tibial
nerve
The Neuron (Nerve Cell)
• Three types of neurons:
–Sensory – carry impulses from
the sense organs (receptors) to
the CNS
–Motor – carry impulses from the
CNS to the muscles or glands
(effectors)
–Interneurons – connect and
carry impulses between
sensory and motor neurons
Neurons
1. Cell body – largest part; most
metabolic activities take place
here; contains nucleus
2. Dendrites – carry impulses from
the environment or other
neurons toward the cell body
Neurons
3. Axon – long fiber that carries
impulses away from the cell
body
• Terminal branches –
branching of axon
• Synaptic knobs – ends of
axon; contain vesicles with
neurotransmitters
Fun facts about neurons
• Most specialized cell in
animals
• Longest cell
– blue whale neuron
• 10-30 meters
– giraffe axon
• 5 meters
– human neuron
• 1-2 meters
Nervous system allows for
1 millisecond response time
The Nerve Impulse
• Resting potential – a nerve cell has
an electric potential because
OPPOSITELY charged ions are on
each side of the membrane
• Anions are mainly on the inside of
the the cell; cations on the outside
++++++++++++++++++++++++
-----------------------------------------
The Nerve Impulse
• Ungated ion channels allow ions to
diffuse across the plasma membrane
–These channels are always open
• This diffusion does not achieve an
equilibrium since sodium-potassium
pumps transport these ions against
their
gradients
Hyperpolarization
• Gated K+ channels
open  K+ diffuses
out of the cell 
the membrane
potential becomes
more negative
Depolarization
• Gated Na+
channels open 
Na+ diffuses into
the cell  the
membrane
potential becomes
less negative
The Nerve Impulse
• Action Potential – a rush of Na+ flow
into the membrane causing an
imbalance in the charge on each side
of the membrane
• This causes the POLARITY to shift
and a wave (impulse) moves down
the length of the neuron
+++++++++++++++++--------------------------------------+++++++
+
Step 1: Resting State
Step 2: Threshold
Step 3: Depolarization
Step 4: Repolarizing
Step 5: Undershoot
Na+ gates close & K+
gates open
Na+
gates open
Stimulus
K+ gates close
• During hyperpolarization or
undershoot, Na+ channels are closed
–Neuron cannot depolarize in
response to another stimulus:
refractory period
–The refractory period assures
impulse conduction is
unidirectional
Myelin
• Is composed of 80% lipid and 20%
protein
• Used for insulation and to help
speed up the nerve impulse
• Wraps around the axon of some
neurons
Myelin
• Gaps in myelin sheath cells
called Nodes of Ranvier – allow
impulses to move more quickly
down neurons
Myelin
• In Saltatory Conduction, only the
Nodes of Ranvier depolarize and
therefore conduct an impulse
faster
The Synapse
• SYNAPSE: the space between the
axon of one neuron and the dendrite
of another
• Axon terminals have vesicles
containing chemicals:
NEUROTRANSMITTERS
• These chemicals are secreted from
the axon of one neuron  stimulates
receptor sites on the effector or the
dendrite of the next neuron
Neurotransmitter Action at Synapse
1. Action potential arrives at axon
terminal of presynaptic neuron
2. Synaptic vesicles rupture, releasing
neurotransmitter into synapse
3. Neurotransmitter diffuses across
synapse & binds to receptor protein
on postsynaptic cell
4. Postsynaptic cell is excited or
inhibited
5. Neurotransmitter in synapse is
deactivated
Synapse
Junction between nerve cells
– 1st cell releases chemical to
trigger next cell
– where drugs affect nervous
system
synapse
• Neurotransmitters are the chemicals
which allow the transmission of signals
from one neuron to the next across
synapses.
• They are also found at the axon endings
of motor neurons, where they stimulate
the muscle fibers.
• They and their close relatives are
produced by some glands such as the
pituitary and the adrenal glands.
• They are chemicals that communicate
information throughout our brain and
body.
• The brain uses neurotransmitters to tell
your heart to beat, your lungs to
breathe, and your stomach to digest.
• They can also affect mood, sleep,
concentration, weight, and can cause
adverse symptoms when they are out of
balance.
• Neurotransmitter levels can be depleted
many ways.
• Stress, poor diet, neurotoxins, genetic
predisposition, drug (prescription and
recreational), alcohol and caffeine
usage can cause these levels to be out
of optimal range.
Types of Neurotransmitters
• Two kinds of neurotransmitters –
INHIBITORY and EXCITATORY.
• Excitatory neurotransmitters are not
necessarily exciting
– stimulate the brain.
• Inhibitory - calm the brain and help
create balance are called .
– balance mood and are easily
depleted when the excitatory
neurotransmitters are overactive.
Small molecule neurotransmitters
Type
Neurotransmitter
Acetylcholine
Amino acids
Biogenic amines
Postsynaptic effect
Excitatory
Gamma aminobutyric
Inhibitory
acidGABA
Glycine
Inhibitory
Glutamate
Excitatory
Aspartate
Excitatory
Dopamine
Inhibitory
Nor adrenaline
Excitatory
Serotonin
Inhibitory
Histamine
Excitatory
ACETYLCHOLINE
• Acetylcholine was the first
neurotransmitter to be discovered.
• It is responsible for much of the
stimulation of muscles, including the
muscles of the gastro-intestinal
system.
• It is also found in sensory neurons and
in the autonomic nervous system, and
has a part in scheduling REM (dream)
sleep.
• There is a link between acetylcholine
and Alzheimer's disease: There is
something on the order of a 90% loss of
acetylcholine in the brains of people
suffering from Alzheimer's, which is a
major cause of senility.
• Outside the brain, acetylcholine is the
main neurotransmitter in the
parasympathetic nervous system – the
system that controls functions such as
heart rate, digestion, secretion of saliva
and bladder function.
• The plant poisons curare cause
paralysis by blocking the acetylcholine
receptor sites of muscle cells.
• The well-known poison botulin works by
preventing the vesicles in the axon
ending from releasing acetylcholine,
causing paralysis.
SEROTONIN
• SEROTONIN is an inhibitory
neurotransmitter – which means that it
does not stimulate the brain.
• Adequate amounts of serotonin are
necessary for a stable mood and to
balance any excessive excitatory
(stimulating) neurotransmitter firing in
the brain.
• If you use stimulant medications or
caffeine in your daily regimen – it can
cause a depletion of serotonin over
• Low serotonin levels leads to an
increased appetite for carbohydrates
(starchy foods) and trouble sleeping,
which are also associated with
depression and other emotional
disorders. It has also been tied to
migraines, irritable bowel syndrome,
and fibromyalgia.
• Low serotonin levels are also
associated with decreased immune
system function.
• In addition to mood control, serotonin
has been linked with a wide variety of
functions, including the regulation of
sleep, pain perception, body
temperature, blood pressure and
hormonal activity
• Largest amount of serotonin is found in
the intestinal mucosa.
• Although the CNS contains less than
2% of the total serotonin in the body,
serotonin plays a very important role in
a range of brain functions. It is
synthesized from the amino acid
tryptophan.
• Gamma amino butyric acid(GABA) is the
major inhibitory neurotransmitter that is
often referred to as “nature’s VALIUMlike substance”. When GABA is out of
range (high or low excretion values), it
is likely that an excitatory
neurotransmitter is firing too often in
the brain. GABA will be sent out to
attempt to balance this stimulating
over-firing.
• People with too little GABA tend to
suffer from anxiety disorders, and drugs
like Valium work by enhancing the
effects of GABA. Lots of other drugs
influence GABA receptors, including
alcohol and barbiturates. If GABA is
lacking in certain parts of the brain,
epilepsy results.
HISTAMINE
• Amino acid Histidine is the precursor of
an important neurotransmitter
histamine.
• Histamine is present in venom and
other stinging secretions.
• Histamine is a biogenic amine involved
in local immune responses
• Regulate physiological function in the
gut
• Act as a neurotransmitter.
• Triggers the inflammatory response.
Nervous System Organization
• Cnidaria - nerve net
–loose organization of
bi-directional neurons
–no centralization
• Flatworms - ladder
–2 anterior ganglia (rudimentary
brain) with paired,
longitudinal nerve cords
–paired sensory organs
(eyespots)
Nervous System Organization
• Segmented worms - advanced ladder
–prominent brain
–solid, fused, ventral
nerve cord
–segmentally arranged
ganglia
Nervous System Organization
• Arthropods
–prominent brain
–solid, fused, ventral
nerve cord
–extensive fusion of ganglia
–well-developed sensory organs
–exhibit complex behaviors
Organization of the NS
• The human nervous system is
divided into 2 major divisions:
–Central Nervous System (CNS)
• Control center of body, brain and
spinal cord
–Peripheral Nervous System (PNS)
• Nerves (bundles of axons)
CNS: Parts of the Brain
• Forebrain
• Midbrain
• Hindbrain
Hindbrain
• Cerebellum
–coordinates muscular movements
• Medulla oblongata
–regulates heart rate, blood
pressure and breathing
–contains reflex centers for
vomiting, swallowing, sneezing,
hiccupping, and coughing
• Pons
–helps regulate respiration
Forebrain
• Thalamus – switching station for
sensory input for all senses but
smell; relays sensory info to
cerebrum and motor info from the
cerebrum
• Hypothalamus – control hunger,
thirst, fatigue, anger, and body temp;
regulates pituitary gland
Forebrain
• Cerebrum – divided
into left and right
hemispheres
• Corpus callosum –
major connection
between hemispheres
–Left hemisphere primarily
responsible for right side of body;
right hemisphere primarily
responsible for left side
Forebrain
• Cerebral cortex – outer covering of
gray matter
–The more convoluted the surface,
the more surface area, the more
neurons
Forebrain
• Cerebrum – divided into frontal,
temporal, parietal, and occipital
lobes
• Frontal lobe
–Contains the
primary motor
cortex
(controls
actions of skeletal muscles) and
olfactory cortex (smell)
Forebrain
• Parietal lobe
–Contains the primary
somatosensory cortex and
gustatory cortex (taste)
• Temporal lobe
–Contains
auditory cortex
(sound)
• Occipital lobe
–Contains visual
cortex (sight)
PNS
• Sensory – transmits impulses
from the sense organs (such as
the ears and taste buds) to the
CNS
• Motor – transmits impulses from
the CNS to the muscles or
glands (somatic or autonomic)
• Somatic – conscious movement
of the body
• Autonomic – regulates activities
that are automatic or involuntary
–Sympathetic (stress, high
energy) and Parasympathic
(leisure, rest) are antagonistic
systems that turn an autonomic
response on or off
Sympathetic effects:
• dilates pupil
• accelerates heartbeat & respiration
• inhibits stomach & intestine activity
• relaxes urinary bladder
Parasympathetic effects:
• constricts pupil
• slows heartbeat & respiration
• stimulates stomach & intestine activity
• contracts urinary bladder
Reflex Arc
• Some actions don’t/can’t wait for
your brain to interpret the signal
• Reflexes are involuntary actions;
they travel from ____ to ____:
–Receptors (nerve “endings”)
–Sensory neurons
–Interneurons
–Motor neurons
–Effectors (muscles or glands)
Types of Sensory Receptors
• Thermoreceptors – detect heat and
cold
• Pain receptors (nocioceptors) –
detect chemicals released from
injured cells
• Mechanoreceptors –
detect mechanical
energy (touch,
pressure, vibration)
Types of Sensory Receptors
• Chemoreceptors – detect chemicals
• Photoreceptors – detect light energy
• Electroreceptors – detect electrical
fields
How are sounds sensed?
• The ear captures, transmits, and
converts sound into electrical
signals
• Ear has three basic parts:
1. Outer ear
2. Middle ear
3. Inner ear
How are sounds sensed?
• Outer ear: external ear (pinna) and
auditory canal
–Funnels sound
–Sound waves vibrate the
tympanic membrane
How are sounds sensed?
• Middle ear
–Tympanic membrane (ear drum)
–Three tiny bones: malleus
(hammer), incus (anvil), stapes
(stirrup); transfer vibrations to
the oval window on the cochlea
–Eustachian tube – equalize
pressure; connects middle ear to
pharynx
How are sounds sensed?
• Inner ear: cochlea
–converts vibrations into
electrical signals
–As the oval window vibrates, it
sets the cochlear fluid in motion
–Moving fluid brushes over hairs
–Bending of hairs is sensed by
mechanorecptors and sends the
signal to the brain (auditory
nerve)
Equilibrium
• Equilibrium is maintained by the
semicircular canals
Equilibrium
• The semicircular canals are
arranged in the X, Y, and Z planes
–Therefore, any movement in any
direction will be perceived
• Fluid in the canals brushes over
hairs
• Movement of hairs is sensed and
the signal is sent to the brain
Equilibrium
• Dizziness can be due to the
momentum of the fluid in the
canals
–You’ve stopped moving, but the
movement of the fluid in the
semicircular canals makes you
think you’re still moving
Fish “Hearing” – Lateral Lines
• Contains mechanoreceptors that
function similarly
to mammalian
inner ear
• Gives info about
direction and
velocity of water
flowing over fish’s
body
How is light sensed?
• Sclera – tough, white layer
• Conjunctiva – external cover of
sclera; keeps eye moist; conjuctivitis
(pink
eye)
How is light sensed?
• Cornea – transparent covering in
front of eye
• Choroid – thin, pigmented layer
lining interior surface of the sclera;
prevents light rays from scattering
and distorting the image
• Iris regulates size of pupil/amount of
light into eye
How is light sensed?
• Lens focuses light on retina
• Retina – Contains photoreceptors
(Except at the optic disk where the
optic nerve attaches)
–Rods: Black and White
–Cones: Color
• Optic nerve takes electric signals
from eye to brain
Rods and Cones
• ~ 125 million rod cells
–Rod cells are light sensitive but do
not distinguish colors
• ~ 6 million cone cells
–Not as light sensitive as rods but
provide color vision
–Most highly concentrated on the
fovea – area of retina lacking rods
How are scents sensed?
• Insects smell through their legs
and antennae
Male silkworm moth
Bombyx mori
Sensory hairs on
antennae detect
pheromones
released by female
How are scents sensed?
• Olfactory nerves are stimulated
when chemicals touch them
• Different chemicals create
different responses in the
olfactory nerves; hence we detect
different smells
How are tastes sensed?
• Taste buds on tongue act just like the
olfactory nerves
–Different chemicals stimulate the
nerves in the taste buds differently;
hence we detect different tastes
• Four “primary” tastes
are bitter, sour, salty,
and sweet