Transcript CHAPTER 13 THE NERVOUS SYSTEM

CHAPTER 13
THE NERVOUS SYSTEM
Introduction: Christopher
Reeve’s injury
A. The
Nervous System is the ultimate
coordinator of homeostasis
B. Two parts of the nervous
system
1. central nervous system = brain and
spinal cord (CNS)

these two interpret sensory information
and coordinate a response
2. peripheral nervous system (PNS) =
nerves that carry messages coming in
to and going away from the CNS
These two systems work together and
are connected
Functions of the Nervous System
1. Receives sensory input (PNS)

Sensory receptors all over the body pick up
information about changes around and
inside of us and send signals through
nerves to the CNS
2. integration (CNS)
 The
brain and spinal cord
process information from the
receptors and decide what to do
3. Generates motor output (PNS)
 Nerve
messages from the CNS
go to effectors (muscles and
glands)
Nervous Tissue
2 types of cells = neurons and neuroglia
A. Neuron structure:
A.
three parts of a neuron are...
 1. Dendrites- carry impulses to
cell body
 2. cell body – central part of cell
 3. Axon – carries impulses away
from the cell body
Sensory Neuron Function
Carries messages from receptors
to the central nervous system
(CNS)
Incoming information
Interneuron Function
Found inside the brain and spinal
cord
Carry messages inside the CNS
Integration: “thinking” and
processing
Motor Neuron Function
Carries messages from CNS to
muscles or glands (effectors)
Outgoing instructions
B. Myelin Sheath covers some
axons in the PNS & CNS
myelin is a lipid substance that
insulates and protects neurons
The myelin sheath is made by
neuroglial cells
myelin also helps with nerve
regeneration
the disease, multiple sclerosis
(MS) develops when the myelin
sheath becomes hardened and
interferes with nerve conduction
It is an autoimmune disease
Leukodystrophy disorders are
similar in that they are caused by
destruction of the myelin sheath,
but their cause is genetic
C. The Nerve Impulse
is an electrochemical signal passed
along the neurons
Electrical  it involves + and – charges
Chemical  it involves elements like
Na+ and Cl-
Nerve Impulse Conduction
1. Resting Potential – the inside of the
axon is neg. compared to outside
 sodium-potassium
difference at rest
“pump” maintains this
A Neuron at Rest is
Polarized!!
2. Action Potential – rapid change in
polarity across the membrane when
the impulse occurs. (all or none)
* threshold = minimum stimulation
needed to cause an impulse to start
A Neuron Carrying a Message
is Depolarized!!
3. Refractory Period –
the membrane is restored to its
resting potential
Neuron cannot be stimulated during
the refractor period
During the Refractory Period
the Membrane is Repolarized!
Ch.12animations\nerveimpulseswf_lw22_-.swf
D. Transmission Across a
Synapse
Neurons do not touch each other
so messages have to be sent from
one neuron to the next…
synapse
space between the axon of one
neuron and the dendrites or cell
body of another neuron
 (also between axons and muscle
cells)
neurotransmitter =
chemical stored at the ends of axons
that is responsible for transmission
across a synapse

(can stimulate or inhibit responses)
http://www.youtube.com/watch?v=90cj4
NX87Yk
Ch.12animations\chemical_syna
pse-swf_ch.swf
* at least 100 known
* examples are acetylcholine (ACh)
and norepinephrine (NE)
* drugs that affect the nervous
system can... (page 306)
1. promote action of
neurotransmitters

Xanax, valium, prozac for anxiety
2. decrease action of
neurotransmitters

Caffeine, antipsychotic drugs
3. mimic the action of a
neurotransmitter

Codeine, heroin, morphine for pain relief
integration
the sum of inhibitory and excitatory
signals received by a neuron
(threshold or not ??) Does the
message get through or not??
The Central Nervous
System
(brain and spinal cord)
A. Protectors of the CNS are...
1. skull and vertebrae
2. meninges
3. cerebrospinal fluid (CSF)
Meningitis
Any inflammation of the meninges
Usually caused by bacteria or virus
Swelling causes brain damage and
death
* hydrocephalus
“water on the brain”
Birth defect where brain swells due to a
build up of fluid that isn’t circulating
correctly
Can cause permanent brain damage if
not repaired
Hydrocephalus
CNS has gray matter and
white matter... difference?
Gray matter has no myelin sheath

Used for processing information and
memory
White matter has a mylein sheath

Used for sending messages
B. Spinal Cord has…
pairs of spinal nerves (PNS) which
leave between vertebrae
- because the white matter tracts cross
as they enter the brain... The right side
of the brain senses and controls the left
side of the body and vice versa
Functions of spinal cord
1. communication between brain and
PNS
2. center for reflex arcs (internal and
external)
C. Brain
Cerebrum
– largest part of human brain
- sensory input and motor output
- learning, memory, language
* divided into two sides or
hemispheres
* connected by corpus callosum
* lobes are named the same as the
skull
 Frontal, temporal, parietal,
occipital
Association areas are places where
integration occurs
Parkinson Disease
due to lack of dopamine, a
neurotransmitter
cells making dopamine are being
destroyed (autoimmune disease)
Gradual loss of motor control
Stem cell research may be the best
hope for a cure
2. Diencephalon
hypothalamus helps maintain
homeostasis and controls the pituitary
gland
 (links nervous and endocrine
systems)
 Controls hunger, thirst, rage, sex
drive, body temperature, etc.
thalamus receives sensory information
and sends it to the proper area of the
cerebrum
also helps integrate memory and
emotions
Gray matter
pineal gland releases
melatonin
Melatonin helps regulate our sleep
and wake cycles
Puberty??
3. Cerebellum
maintains posture and balance
- muscle coordination

Cerebrum actually sends the signals that
tell the muscles to contract
“rote” muscle movements like tying
shoes and typing are
“programmed” here
4. Brain Stem
midbrain acts as a relay station and
reflex center
- pons is the “bridge” between
cerebellum and CNS and helps control
breathing and reflex head movements
medulla oblongata
basic life support center
 Breathing, heart rate, etc.
also reflexes like coughing,
sneezing, etc. are triggered here
reticular formation
regulates alertness
- Severe Coma can be caused by
damage to this area
-
-
Anesthetics often work here
The Limbic System and
Higher Mental Functions
Limbic System
blends primitive emotions with higher
mental functions
- a series of tracts that run through the
cerebrum and diencephlalon
Alzheimer’s disease
Affects this part of the brain first,
affecting short-term memory
1. Alzheimer Disease – gradual loss of
reason due to plaques around axons
and tangles around axons
Cause unknown, diagnosis difficult
Some new drugs are slowing the
progression
Memory is the ability to hold a
thought or recall events
1. short-term memory
2. long-term memory is a mix of
semantic (numbers, words, etc.)
and episodic memories (persons,
events, etc.) NEED BOTH
3. Skill memory helps us do
automatic motor activities
like...walking, playing an
instrument, typing, driving, etc.
Learning is retaining and
using past memories !!!
Language and Speech
are combinations of recall, knowing
what and how to say something and
actually forming the words – all different
parts of the brain.
Left Brain
verbal, logical, analytical, rational
Right Brain
nonverbal, visual-spatial, intuitive,
creative
The Peripheral Nervous
System (PNS)
A. Nerves are bundles of axons

they can be sensory (incoming) or motor
(outgoing) from the CNS or a mixture of
these
C. Cranial nerves
(12 pair)
are connected directly to the brain
nervous system
peripheral nervous
system
"nerves"
central nervous
sytem
brain
spinal cord
somatic nervous
system
voluntary: skeltal
muscles
autonomic nervous
system
involuntary:cardiac,
smooth and glands
sympathetic emergency
parasympatheti normal
they send/receive messages
to/from things like....
Seeing, hearing, tasting
Muscles of the head and neck
Sensations in the head and neck
D. Spinal nerves
(31 pair)
are connected to the spinal cord
they send/receive messages
to/from things like...
Sensations below the neck
Motor activity below the neck
E. Somatic System
is the voluntary and muscle reflex
part of the PNS
it receives sensory information and
takes messages to skeletal
muscles
Reflex Arc...
Reflex = a rapid, involuntary response
to a stimulus
Reflex arc is the pathway that an
impulse follows in a reflex from the
receptor to the CNS and back out to the
effector
Locate the parts on the diagram
on page 303 in the book
A. sensory receptor
B. sensory neuron
C. interneuron
D. motor neuron
E. effector (muscle or gland)
A stimulus is received by a sensory
receptor
Which initiates an impulse in the
sensory neuron
The impulse travels through the sensory
neuron to the spinal cord and transmits
it to the interneuron
This neuron passes the impulse to the
motor neuron
Whose axons take the message to an
effector which reacts to the stimulus.
F. Autonomic System
controls cardiac muscle, smooth
muscle and glands
system is divided into sympathetic and
parasympathetic divisions
Sympathetic
“emergency response” system
Speeds heart rate, sends more
sugar and blood to muscles, slows
digestion, dilates pupils, releases
adrenaline, etc.
When we are under STRESS, this
system is too much in charge
Parasympathetic
“normal” system
Increases digestive activity, slows
heart and breathing, etc.
- both function automatically
- both have nerves in all internal
organs
both control reflexes involving
homeostasis
Comparison on page 305
Drug Abuse
drugs can cause physical or
psychological dependence and
withdrawal
Alcohol
metabolized in the liver
(damage from fat build up = cirrhosis)
Brain and liver damage
CNS depressant (decreases activity at
synapses)
Nicotine
excess of neurotransmitter dopamine
(mood) and mimics Ach
CNS stimulant
complications in pregnancy
Caffeine
CNS stimulant affecting many
neurotransmitters

Dopamine, seratonin, noradrenaline

Increases brain metabolism but decreases
blood flow to the brain??
Cocaine
prevents uptake of dopamine so
stimulation is constant
body stops making its own
neurotransmitters so the “crash”
greater risk of stroke and heart attack
Methamphetamine
Keeps neurotransmitters in
synapses so constant stimulation
causes agitation, wakefulness and
psychosis
Tolerance increases with addiction
Heroin
opium derived as pain medication
mimics the endorphins or “feel good”
chemicals of brain
body stops making its own so
withdrawal is extreme
Marijuana
wide ranging neurological effects, some
dependence
Mimics a neurotransmitter
Homeostasis
A. the nervous and endocrine systems
are most important in maintaining
homeostasis