Transcript nervous system

NERVOUS SYSTEM
Nervous System Overview
Role: Maintain homeostasis
1.
2.
3.
Sense changes (____ neurons)
Integrate information (_______)
Respond (______ neurons)
Basic Anatomy
1.
Mass = ____ lbs 3% total body mass
Main Subdivisions
1.
2.
Central Nervous System (CNS)
Peripheral Nervous System (PNS)
CELLS OF THE NERVOUS SYSTEM
 2 Types of cells found in the N S:
 1.
NEURONS: nerve cells
 2.NEUROGLIA
(Glia): specialized
connective tissue
NEURONS
 Motor neurons

Also called ________ neurons.
 Interneurons
 Also
called _______neurons.
 Sensory neurons
 Also
called _______neurons.
STRUCTURE OF NEURON
 AXON: is surrounded by segmented
wrapping called _______.
- It is:
Axon - long
section, transmits
impulses
Dendrite - small
extensions from
the cell body;
receive information
Neurofibrils - fibers
within the axon
Interesting Facts about the Neuron
Longevity – can live and function for a lifetime
•
•Do not divide – fetal neurons lose their ability to undergo
mitosis; neural stem cells are an exception
•High metabolic rate – require abundant oxygen and glucose
The nerve fibers of
newborns are
unmyelinated - this causes
their responses to stimuli
to be course and
sometimes involve the
whole body. Try surprising
a baby!
GLIA
 Glia or neuroglia: They are special types of supporting
cells
- Function: is to:
* Large cells look like stars: astrocytes
* Smaller cells are Microglia
Example: Oligodendrocytes: helps hold fibers together,
produce the fatty myelin sheath that envelops nerve
fibers in the brain and spinal cord
NERVES
 Nerve is a group of peripheral nerve
fibers (axons) bundled together like
the strands of a cable.
 Myelin is found on nerves and is
white.
 Nerves are referred to as _____
matter of the PNS and also the CNS.
 Unmyelinated axons and dendrites
are called ________. (because of
their color)
Brain = Gray over White
Spinal Cord = White over Gray
REFLEX ARC
 Nerve impulses are conducted from receptors to
effectors over neuron pathways known as
___________
 This results in a _______. (a contracted muscle or
secretion from a gland)
 2 types of reflex arcs:
- two-neuron arcs: spinal cord and motor neuron
- three-neuron arcs: sensory neurons, interneurons
and motor neurons
Animation
 http://www.youtube.com/watch?v=Y5nj3ZfeYDQ
 http://bcs.whfreeman.com/thelifewire/content/chp
46/46020.html
RECEPTORS
 Impulse conduction normally starts
in the_______.
 Found at the beginning of the
dendrites of sensory neurons
 Location:
MS (MULTIPLE Sclerosis)
DAMAGE TO MYELIN
 Hard lesions replace the
destroyed Myelin
 As the myelin is lost,
nerve conduction is
______
 Causing weakness, loss in
coordination, visual
impairment, speech
disturbances
 No known cure, occurs
most in women ages 2040.
Synapse
 A microscopic space from the axon ending of one
neuron to the dendrite of another neuron.
 The nerve impulse stops, chemicals are sent across
the gap, the impulse continues alone the dendrites.
Neurotransmitters
 Chemicals by which neurons communicate
 Some help us sleep, inhibit pain, make us energetic
 Examples
 Acetylcholine
Norepinephrine and Dopamine-

Serotonin-

Endorphins-
Neurotransmitters
Excitatory - increase membrane permeability,
increases chance for threshold to be achieved
Inhibitory - decrease membrane permeability,
decrease chance for threshold to be achieved
The Action Potentialan All-or-None
Electrical Signal
Cell Membrane Potential
At rest, the inside of a neuron's
membrane has a negative charge. As the
figure shows, a Na+ / K+ pump in the
cell membrane pumps sodium out of the
cell and potassium into it.
However, more potassium ions leak out
of the cell. As a result, the inside of the
membrane builds up a net negative
charge relative to the outside.
Animations of Nerve Impulses
http://highered.mcgrawhill.com/sites/0072495855/student_
view0/chapter14/animation
__the_nerve_impulse.html
Action Potential Overview
Signals or impulses of communication

Travel along axons
Are “all-or-none” events

Threshold must be reached
Two phases
1.
2.
Depolarization
Repolarization
Axon Diameter and Action Potentials
 Recall that axons are also called nerve fibers
 Larger fibers propagate impulses faster
 Larger fibers usually myelinated
 Smallest fibers are unmyelinated and therefore
propagate impulses slower
Resting Membrane Potential
 Recall that there is a separation of charges across the
membrane of excitable cells.
 Extracellular fluid contains more sodium ions than
are found inside a cell
 Cytosol contains more anions and negatively charged
proteins
 Thus sodium ions cling to the outside cell surface
Resting Membrane Potential
 Cell somewhat permeable to potassium
 Much less permeable to sodium
 Sodium quick to rush in when gates open
 following both electrical and concentration gradients
 Potassium not quick to rush out
 only has concentration gradient to drive flow
Resting Membrane Potential
• small build-up of anions in cytosol
• equal build-up of cations in extracellular fluid
Change in Membrane Potential
 Na+ channels open
 Fast Na+ influx
 Inside of cell becomes less negative

If change is +15mV action potential occurs
Ongoing Research
 Improve environment for spinal cord axons to bridge
injury gap
 Find ways to stimulate dormant stem cells to replace
lost, damaged, or diseased neurons
 Develop tissue cultured neurons that can be used for
transplantation purposes.
Drugs that Affect Synapses and Neurotransmitters
Strychnine poisoning can be fatal to
humans and animals and can occur
by inhalation, swallowing or
absorption through eyes or mouth
Strychnine is a neurotoxin which acts
as an antagonist of acetylcholine
receptors. It primarily affects the motor
nerves in the spinal cord which control
muscle contraction. An impulse is
triggered at one end of a nerve by the
binding of neurotransmitters to the
receptors.
Strychnine use by athletes?
Drugs that Affect Synapses and Neurotransmitters
•Cocaine, morphine, alcohol, ether and chloroform
•Ecstasy
LSD (hallucinogen)
Dangers of Ecstasy (MDMA)
The neurotransmitter serotonin is
vital in regulating many of our
basic functions. Serotonin is,
among other things, the feel good
neurotransmitter and helps to
regulate body temp.
Our brain cells are constantly
trying to bring some amount of
serotonin back into the cells and
out of the synapse using
serotonin reuptake transporters.
Ecstasy essentially takes these
upkeep transporters and reverses
their roles. This causes a massive
flood of serotonin from the brain
cells into the synapse.
The most common cause of
Ecstasy-related death is
overheating
(hyperthermia). MDMA
interferes with the body's
ability to regulate its own
body temperature and to
see other warning signs
allowing the body to
overheat without
discomfort especially
when dancing for hours
in hot clubs.
LSD; lysergic acid diethylamide
Actions/Effects: LSD alters the action of the neurotransmitters
serotonin, norepinephrine, and dopamine, triggering extreme
changes in brain function. Physical effects include increased body
temperature, heart rate, and blood pressure. Psychological effects
include perceptual and thought distortions, hallucinations, delusions,
and rapid mood swings.
Cocaine blocks reuptake
of dopamine
Central Nervous System



Integrates and correlates incoming sensory
information
Source of thoughts, emotions, memories
Most motor signals originate in CNS
CNS (CENTRAL NERVOUS SYSTEM)
Spinal Cord and Brain
 4 Divisions of the brain:
 Brainstem
 Cerebellum
 Diencephalon
 Cerebrum
.
BRAINSTEM
* Medulla
Oblongata: largest part of
the brainstem.
- extension of the _________
- Location: lies below the _______
- Functions: reflex center
-It controls:
DIENCEPHALON
 Hypothalamus:
- Structure:
- Function: Acts as the major center for
controlling the _____. (function of internal
organs)
- Controls _____________
- Centers for controlling:
DIENCEPHALON
 THALAMUS:
- Structure: dumbbell shaped mass
of gray matter in each cerebral
hemisphere
- Function:
- Produces emotions of
pleasantness and unpleasantness
associated with sensation
CEREBELLUM
 Second largest part of the brain
 Structure:
 - composed of _____in outer layer
and _______in the inner layer
• Function:
CEREBRUM
 Largest part of the brain
 Structure: Structures: Series of ridges and
grooves
-Ridges are called convolutions or ____
-Grooves are called _____ (deepest sulci are
called fissures)
-Divided into two halves- ________
-Hemispheres connected by the _________
CEREBRUM
 HEMISPHERES: Divided into lobes
 Lobes are named after bones that lie over them.
CEREBRUM
 Function: mental process of all types
 Sensations
 Consciousness
 Thinking
 Memory
 Willed Movements
Cerebrum
 Specific areas have specific functions
 Temporal lobe’s auditory areas interpret incoming nervous
signals as specific sounds
 Visual area of the occipital lobe helps you understand and
identify images
 If a specific part of the brain is damaged, for example
the Primary Taste Area, you would not be able to
taste things.
__________CEREBRUM
SPINAL CORD
 Structure: Outer part composed of white
matter
- Interior part composed of gray matter
 Function: center of all spinal cord
reflexes
- sensory tracts conduct impulses ___
the brain.
- motor tracts conducts impulses ____
the brain
Cutting the Cord
 Completely severing the spinal cord produces a loss
of sensation for all areas below the cut, called
anesthesia.
 It also produces a loss of the ability to make
voluntary movements, called paralysis.
Peripheral Nervous System (PNS)
Cranial and Spinal Nerves
 Function:
 Cranial Nerves:
- 12 pairs of cranial nerves
- Functions vary
SPINAL NERVES
 Structure: contain dendrites of sensory
neurons and axons of motor neurons
 Function: conduct impulses necessary for
sensations and voluntary movements
Autonomic Nervous System (ANS)
 Structure: Consists of motor neurons that




conduct impulses from spinal cord or brainstem to:
1. Cardiac Muscle tissue
2. Smooth muscle tissue
3. Glandular epithelial tissue
Function:
2 Divisions of ANS
 1. Sympathetic nervous system:
-Structure:
-Function:
2 Divisions of ANS
 2. Parasympathetic Nervous System:
 Structure:
 Function:
Autonomic Neurotransmitters
 Each division of the ANS signals its effectors with a
different neurotransmitter.
 This is how an organ can tell which division is
stimulating it.

Ex. The heart responds to acetylcholine from the
parasympathetic division by slowing down. If norepinephrine,
from the sympathetic division, is present, the heart speeds up.
ANS as a Whole
 Regulates the body’s autonomic
functions in ways that maintain
HOMEOSTASIS