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Chapter 28 The Nervous System
1) Receive sensory input, interpret it, send out
commands
a) Nervous systems
i)
most intricately organized data processing system on
Earth
ii) neurons
(1) nerve cells specialized for carrying signals from one
location to another (wires)
(2) 50 million in a cubic centimeter in your brain
(3) one neuron may communicate with 1000s other neurons
(a)learn, remember, perceive our surrounding, move, etc
(4) cell body plus long, thin extensions called neuron fibers
iii) Three interconnected functions
(1) sensory input (sensory neurons)
(a)conduction of signals from sensory receptors (light
sensors of eye, pressure sensors of skin, etc…) to
integration centers
(2) integration (interneurons)
(a)interpretation of the sensory signal and formulation of
a response
(3) Motor output (motor neurons)
(a)conduction of signals from integration center to
effectors (muscle cells or gland cells) – cells that
perform the responses
iv) Two main division
(1) central nervous system (CNS)
(a)site of most integration
(b) brain and spinal cord (vertebrates)
(2) peripheral nervous system (PNS)
(a)communication lines (nerves) that carry signal to and
from CNS
nerves
(i) bundles of neurons wrapped in connective tissue
(c)ganglia
(i) clusters of neuron cell bodies in the nerves
v)
knee jerk reflex (Fig. 28.1B)
(1) circles are cell bodies
(2) lines are neuron fibers
(3) three types of neurons
(a)sensory neurons
(i) convey signal from sensor to CNS
(b) interneurons
(i) located within CNS, integrate data, relay to other
interneurons and motor neurons
(c)motor neurons
(i) convey signal from CNS to effector
(4) tap knee -> sensory receptor detects stretch in muscle > signal conveyed to CNS (spinal cord) -> straight to
motor neuron and interneuron -> send signal to contract
quads and not contract hams
(5) this is over simplified since there would be MANY of
each type of neuron working here
vi) neurons are the functional units of nervous systems
(1) vary widely in shape
(2) Figure 28.2 – motor neuron
(a)cell body
(i) houses nucleus and other organelles
(b) neuron fibers
(i) dendrites (dendron is tree in greek)
1. extend from cell body
2. short, numerous, highly branched
3. receive incoming messages from sensory or
interneurons and send to cell body
(ii) axon
1. single fiber on many neurons
(b)
conducts signal toward another neuron or
effector
3. can be very long
a. lower part of spinal cord to toes
4. ends in cluster of branches (typically hundreds
to thousands of branches)
a. synaptic knob
i. on the end of each branch
ii. relay signal to another neuron or effector
(3) supporting cells
(a) outnumber neurons 50 to 1 in nervous system
(b) protect insulate and reinforce neurons
(i) Ex. Schwann cells
1. forms the myelin sheath of many axons that
require rapid transmission of signals (insulator)
2. wrap the axon
3. nodes of Ranvier
a. spaces b/w Schwann cells
b. only place where signal can transmit
c. so signal jump from node to node
d. signals travel at 150 m/s (330 miles/hr)
e. without myelin only 5 m/s
4. Multiple sclerosis (MS)
a. autoimmune diseases
b. destroys Schwann cells
c. progessive loss of signal conduction, muscle
control and brain function
d. treat with drugs that suppress immune sys
2) Nerve signals and their transmission
a) resting neurons
i)
contain potential energy
(1) electrical charge difference across PM
(2) cytoplasm is slightly negative and fluid outside positive
(3) resting potential
2.
(a)voltage
across PM = -70mV
ii) what causes resting potential?
(1) proteins kept in cell tend to be more neg.
(2) sodium-potassium pumps
(a)ACTIVELY transport 3 Na+ out for every 2 K+ in
(3) sodium not allowed to come back in
(4) potassium allowed to diffuse out down conc. grad.
b) nerve signal begins as a change in membrane potential
i)
stimulus
(1) any factor that causes a nerve signal to be generated
(a)light, sound, touch, chemicals from another neuron
ii) Hodkins and Huxley
(1) worked out signal transmission details using giant
axons in squids in the 1940’s
iii) The action potential (Fig. 28.4) -name for nerve signal
(takes only a few milliseconds)
(1) resting potential (-70mV)
(2) apply stimulus
(a)some Na+ channels open
(b) K+ closed
(c)voltage might rise to “threshold” potential (-50mV)
(3) IF threshold is reached, action potential is triggered
(a)additional Na+ channels open (these are voltagegated)
(b) K+ closed
(c)inside becomes positive compared to outside
(4) membrane repolarizes
(a)Na+ channels close and inactivate (close at high
voltage)
(b) K+ channels open (open at high voltage)
(i) K+ rushes out down electrochemical gradient
(5) undershoot
(a)K+ channels slow to close
iv) Na+ and K+ channels are voltage-gated channels
c) action potential propagates itself along the neuron
i)
action potential is a local event
ii) this event must travel along neuron
iii) Figure 28.5
(1) each action potential generates another next door
(domino effect)
(2) why do they only flow in one direction?
(a)Na+ channels are inactivated while K+ is diffusing
out
(b) If they can’t open, there can’t be an action potential
iv) action potentials are all-or-none
(1) they are always the same
(2) there is no such thing as a strong or weak one
(3) so how do we tell if something hurts a little or a lot?
(a)frequency of action potentials
d) How are signals passed b/w neurons?
i)
synapse
(1) junction or relay point b/w two neurons or b/w neuron
and effector
(2) electrical synapse
(a)action potential itself passes b/w neurons
(b) frequency of action potentials remains the same
(c)common in heart and digestive tract
(3) chemical synapses
(a)found in most other organs (skeletal muscles and
CNS where signaling is more complex and varied)
(b) synaptic cleft
(i) narrow gap b/w synaptic knob of sending neuron
and the receiving neuron
(c)electrical signal must convert to a chemical signal
(d) neurotransmitters
(i) the chemical signal
(ii) generate action potential in receiving cell
(iii)Figure 28.6
(iv) contained in vesicles at knob
(v) Action P. causes vesicles to fuse with PM
(vi) neurotransmitter
released into cleft
(vii)
diffuse across cleft and bind to receptors
(viii)
chemically-gated ion channels open
(ix) a new action P. might be generated if threshold is
reached
(x) neurotransmitter broken down by enzyme or taken
back up and recycled by sending neuron and
channels close
ii) how is a one-way signal ensured at synapse
e) chemical synapses make complex information processing
possible
i)
Figure 28.7
(1) many inputs on a single neuron (can be 1000’s)
(2) each sending neuron can secrete:
(a)different quantity of neurotransmitter
(b) different kind of neurotransmitter
(i) excitatory – open Na+ channels
(ii) inhibitory – open Cl- (flows in) or K+ (flows out)
channels
(3) rate of signaling is summation of all the signals
(4) contrast excitatory and inhibitory synapses in how they
change a receiving cell’s membrane potential relative to
triggering an action potential.
f) variety of small molecules function as neurotransmitters
i)
dozens are known and there are likely many more
ii) most are small nitrogen-containing molecules
(1) acetylcholine
(a) brain signaling
(b) motor neuron to muscle signaling
(c)can be excitatory or inhibitory
(i) depends on receptors
(ii) makes skeletal muscles contract, but slows rate of
heart muscle contraction
(2) biogenic amines
(a)group of neurotrans. derived from amino acids
Include (all function as hormones also)
(i) epinephrine
(ii) norepinephrine
(iii)serotonin
(iv) dopamine
(c)important in CNS
(i) serotonin and dopamine – effect sleep, mood,
attention and learning
(d) Parkinson’s disease
(i) associated with lack of dopamine in brain
(e)schizophrenia
(i) associated with excess dopamine
(f) depression
(i) associated with reduced levels of norepinephrine
and serotonin
(3) amino acids
(a)aspartate, glutamate, glycine and GABA (gamma
aminobutyric acid)
(i) important in CNS
(ii) asp and glu – excitatory
(iii)gly and GABA – inhibitory
(iv) GABA – 100X more in brain than any other
(4) peptides
(a)substance P
(i) excitatory – underlies perception of pain
(b) endorphins (also a hormone)
(i) decreases perception of pain
(5) dissolved gases
(a)nitric oxide (NO)
(i) memory storage and learning
(ii) relaxes smooth muscle
1. leads to penis engorging and erection
2. Viagra – promotes effect of NO
iii) What determines if a neuron is affected by a specific
neurotransmitter?
(b)
g) many drugs act at chemical synapses
i)
Caffeine
(1) counters effects of inhibitory neurotranmitters
ii) Nicotine
(1) binds to and activates acetylcholine receptors
(stimulant)
iii) alcohol
(1) depressant believed to increases inhibitory effect of
GABA
iv) Prozac (fluoxetine) - antidepressant
(1) blocks removal of serotonin from synapse
v)
Valium and Xanax - tranquilizers
(1) activate receptors for GABA – increasing its effect
vi) Some drugs block receptors
(1) antipsychotic drugs used to treat schizophrenia
vii) amphetamines and cocaine – stimulants
(1) increase release and availability or norepinephrine and
dopamine at synapses
viii) LSD and mescaline
(1) activate serotonin and dopamine receptors leading to
hallucinations
ix) Opiates – morphine, codeine, and heroin
(1) bind endorphin receptors – reduces pain and produces
euphoria
x)
abuse of any of these drugs may change the brain’s
chemical synapses and reduce normal syn. of neurotrans.
xi) drugs alter a fine-tuned brains in way we do not
understands and many time permanently.
(1) It has been evolving for millions of years, it knows
better than you
3) Nervous systems
a) organization usually correlates with body symmetry
i)
sponges (porifera)
(1) no nervous system
ii)
radial symmetry
(1) Hydra (cnidaria)
(a)nerve net – one of simplest
(i) weblike system of neurons extending through
body
(ii) no head or brain
(iii)no central or peripheral divisions
(b) somersaults, glides slowly, most of time stationary
(c)simple life = simple system
(2) echinoderms (phylum of sea stars, brittle stars, sand
dollars, sea urchins)
(a)radial nerves up each arm from central nerve ring
iii) bilateral symmetry
(1) head and tail
(2) head first to encounter stimuli (head first)
(a)brain located here with sense organs
(3) flatworms (planaria) – phylum playthelminthes
(a)cephalization
(i) concentration of nervous system at head
(b) centralization
(i) presence of a CNS distinct from PNS
(c)small brain and 2 parallel nerve cords = CNS
(4) leech (annelid)
(a) higher conc. of neurons in brain
(b) segmented ganglia in ventral nerve cord
(5) insect (arthropoda)
(a)
(6) squid and octopus (molluska)
(a)most
complicated invertebrate nervous system
(b) large brain, large image forming eyes, rapid
signaling along giant axons
(c)rivals some vertebrates
(d) correlates with active predatory life
(e)but clams (molluska also) have no cephalization and
simple sense organs
b) Vertebrate nervous systems are highly centralized and
cephalized
i)
diverse in structure and level of sophistication
(1) humans and dolphins vs. frogs and fish
ii) All have CNS and PNS (centralized)
iii) All highly cephalized
iv) spinal cord
(1) lies inside vertebral column (spine)
(2) receives sensory info from skin and muscles
(3) can integrate simple responses to certain stimuli
(a)knee jerk reflex
v)
brain
(1) master control center
(2) homeostatic centers
(3) sensory centers
(4) centers of emotion and intellect (in humans at least)
(5) blood vessels service CNS
(a)very selective as to what gets to brain
(b) blood-brain barrier
(i) blocks metabolic waste and other chemicals
(ii) nutrients and O2 flow freely
vi) brain and spinal cord are hollow
(1) ventricles – fluid filled spaces of brain continuous with
central canal (fluid filled space of spinal column)
(a)cluster of capillaries in each ventricle that secretes
cerebrospinal fluid
(i) circulates through central canal and ventricles
(ii) drains back into veins
(iii)cushions CNS, supplies with nutrients, hormones,
WBC’s
vii) Meninges
(1) three layers of connective surrounding CNS
(2) protective function
viii) Two distinct areas within CNS
(1) White matter
(a)mainly
axons (myelin sheaths are whitish)
(2) gray matter
(a) nerve cell bodies and dendrites
(b) in mammalian brain, most in cerebral cortex (outer
layer and center for higher brain functions)
ix) ganglia and nerves of PNS
(1) cranial nerves (12 of them)
(a) carry signals to and from brain directly
(b) eyes, nose, ears, etc…
(2) spinal nerves
(a) carry signals to and from spinal cord
(b) muscles and skin
c) PNS is a functional hierarchy
i)
Figure 28.12A
ii) PNS broken into two division
(1) sensory division
(a)sensing external environment (eyes, ears, nose – the
five senses)
(b) sensing internal environment (blood pH, etc…)
(c)pain
(i) senses by both sets
(ii) warning that your suffering tissue damage
(iii)nerves from internal organs or from skin synapse
with same neurons in CNS
1. result – internal pain feels like it is on body
surface
a. called referred pain (Fig. 28.12B)
b. extremely important for diagnosis
(2) motor division
(a)broken further into two systems
(i) somatic
1. carry signals to skeletal muscle in response to
external stimuli
a. ex. touch a stove
2. voluntary system
(ii) autonomic
involuntary
a. controls smooth and cardiac muscle
b. organs of dig., circulatory, excretory and
endocrine systems
2. broken into two division
a. sympathetic
b. parasympathetic
d) opposing actions of sympathetic and parasympathetic
neurons regulate the internal environment (Fig. 28.13)
i)
parasympathetic division
(1) primes body for digesting food and resting
(a)gain and conserve energy
ii) sympathetic division
(1) opposite effect
(2) prepares body for intense, energy consuming activities
(3) fight or flight, competing in sports, etc…
iii) bodies normally operate in between both
(1) receive signals from both divisions
(a)liver and adrenal glands are exceptions
(b) ex. salivary glands – just enough to keep mouth
moist
(i) parasym want to increase activity
(ii) sym wants to shut off
iv) sym and parasym nerves
(1) emerge from different regions of CNS
(a)parasym – from brain and lower part of spinal cord
(b) sym – middle regions of spinal cord
(2) use different neurotransmitters
(a)parasym – acetylcholine
(b) sym – norepinephrine
v)
Where are all the sym and parasym signals coming
from…the brain!
e) vertebrate brain develops from three anterior bulges of the
neural tube
1.
i)
brain and spinal cord develop from dorsal hollow
nerve cord
ii) embryonic brain regions in ALL vertebrates
(1) forebrain
(a)cerebrum – birds and mammals have large cerebrums
(i) sophisticated behavior correlates with this
(ii) porpoises, whales and primates have largest of
mammals
(2) midbrain
(3) hindbrain
4) The Human Brain
a) The structure of a living supercomputer: The human brain
i)
100 billion neurons, more supporting cells
ii) more powerful than most sophisticated computer by
far
iii) brainstem
(1) Three parts
(a)medulla oblongata
(b) pons
(c)midbrain
(2) all sensory and motor neuron signal to and from brain
pass through brainstem
(a)serves as a sensory filter
(i) selects which info goes through
(3) regulates sleep and arousal
(4) coordinates body movements like walking
iv) cerebellum
(1) planning center for body movements
(2) learning and remembering motor responses
(3) receives info about position of limbs, length of muscles,
info from auditory and visual systems, motor pathways
about which actions are being sent from cerebrum
(a)all about coordination of movement and balance
ex. step off curb – cerebellum evaluates body
position and sends cerebrum a plan for smoothly
getting rest of body to follow
v)
cerebrum, thalamus and hypothalamus (forebrain)
(1) most sophisticated integrating region
(2) thalamus
(a)contains most cell bodies that send info to cerebrum
(b) sorts data into categories
(i) ex. all the touch signals from hand (your getting
tons of signals all the time)
(c)suppresses some signals and enhances others
(d) sends signals to appropriate location in higher brain
(cerebrum)
(3) hypothalamus
(a)we already saw its control over pituitary
(b) also…
(i) body temperature
(ii) blood pressure
(iii)hunger and thirst
(iv) sex drive
(v) fight-or-flight
(vi) emotions such as rage or pleasure
1. “pleasure center” – addiction center
(vii)
biological clock
1. receives visual input from eyes
2. maintains daily rhythms like sleep and hunger
(4) cerebrum
(a)largest and most sophisticated part
(b) right and left cerebral hemispheres
(c)corpus callosum (CC)
(i) connects two hemispheres so they can process
information together
(d) basal ganglia (basal nuclei)
(i) clusters of neuron cell bodies below CC
(ii) important in motor coordination
(b)
(iii)damage
can result in immobilization
(iv) degeneration occurs in Parkinson’s
b) The cerebral cortex is a mosaic of specialized, interactive
regions
i)
>80% of total brain mass
ii) 10 billion neurons and 100s of billions of synapses
iii) reasoning, math skills, language, imagination, artistic
talent, personality traits, creates our sensory perceptions
using info from five senses, regulates voluntary
movements
iv) each hemisphere receives info and controls movement
of opposite side of body
(1) CC communicates between the two sides
v)
4 lobes on each side (Fig. 28.16)
(1) frontal
(2) parietal
(3) occipital
(4) temporal
vi) motor cortex
(1) sends commands to skeletal muscles in response to
sensory stimuli
vii) somatosensory cortex
(1) receives and partially integrates signals from touch,
pain, pressure and temperature receptors
viii) association areas
(1) areas of higher mental activities…thinking
(2) frontal association area
(a)evaluates consequences
(b) make considered judgements
(c)plan for the future
(3) reading
(a)visual centers send visual signals of words on paper
to speech and reading centers or parietal lobe. If to
be read aloud, signals will be organized and sent to
speech center in frontal lobe which tells motor cortex
how to move tongue, lips, etc… to form words.
ix) lateralization
(1) different sides of brain become specialized
(2) left hemisphere
(a)language, logic, math
(3) right side
(a)pattern/face recognition, music, emotional processing
(4) roles are switched in 10% of people
c) How do we know how the brain works?
i)
injury, illness and surgery
(1) if you want to know how something works, break a
small bit of it and see the outcome
(2) Phineas Gage – 1848 –
(a)accidentally exploded a dynamite charge as a railroad
construction foreman.
(b) Three foot long spike went through his head.
(c)he survived with his intellect
(d) however, he had new propensities toward meanness,
vulgarity, irresponsibility, inability to control
behavior
(e)preserved Gage’s skull and spike allowing group in
1994 to produce a computer model of injury (Fig.
28.17)
(i) pierced both frontal lobes
(3) brain surgery
(a)cortex lacks cells that detect pain
(b) operate on patients while awake
(c)stimulate parts of cortex with electrical current
(4) corpus callosum cut to treat epileptic seizures
(a)patients unable to verbalize sensory info received by
only right hemisphere
(5) hemispherectomy
(a)removal of ½ of brain excluding deep structures
(b) patients recover quick, leaving hospital in 2 weeks
done to alleviate severe seizures
(c)intellectual capacities undiminished
(d) partial paralysis on opposite side of body
(e)other side takes over missing functions
d) Several parts of brain regulate sleep and arousal
i)
arousal
(1) state of awarness of outside world
ii) sleep
(1) continue to receive stimuli, but not conscious of them
iii) hypothalamus with other brain regions helps regulate
sleep-wake cycles
(1) pons and medulla contain centers that produce sleep
when stimulated
(2) midbrain has center that causes arousal
iv) serotonin
(1) may be neurotransmitter that induces sleep
(2) drink milk before bed – lots of tryptophan – amino acid
used to make serotonin.
v)
reticular formation
(1) extends through brainstem
(2) receives data from sensory receptors
(3) filters out unimportant sensory info (repetitive)
(4) more input, the more alert and aware we are
vi) EEG – electroencephalogram
(1) records electrical signals in brain – brain waves
(2) look at Fig 28.18C
(3) REM sleep – rapid-eye-movement
(a)eyes move rapidly under closed lids
(b) brain is highly active
(i) may consume more O2 than when awake
(c)most dreams during REM
(d) occurs six times a night for 5-50 minutes each
(4) slow-wave sleep
e) The limbic system is involved in emotions, memory and
learning
(i)
i)
Figure 28.19
(1) nurturing of infants
(2) emotional bonding
(3) laughter and crying
ii) amygdala
(1) recognize emotional content of facial expression
(2) laying down emotional memories
iii) hippocampus
(1) formation of memories and their recall
iv) “scent memories”
(1) certain odors bring back memories and emotions
(2) olfactory bulb is connected to limbic system
v)
memory
(1) ability to store and retrieve information of previous
experience
(a)short-term memory
(i) lasts only a few minutes
(ii) dial phone number after just looking it up
(b) long-term memory
(i) if you can recall number weeks later
(2) transfer from short to long enhanced by
(a)rehearsal
(b) positive or negative emotional states mediated by
amygdala
(c) association of new data with previously learned data
already in long term memory
(3) factual memories and different from skill memories
(tying shoe)
(a)difficult to unlearn skill memories
f) cellular changes underlying memory and learning probably
occur at synapses
i)
long-term depression (LTD)
(1) decreased responsiveness to an action potential
ii) long-term potentiation
(1) enhanced responsiveness to an action potential