Download The Nervous System

The Nervous System
True or False?
1. A bigger brain is better
2. Alcohol kills brain cells
3. Drugs destroy brain
tissue
4. Humans use about
10% of their brain
5. Humans are either
right or left brained
6. Intelligence is solely
determined by genes
Introduction to The Nervous System
A. Neurons = nerve cells that transmit signals to
other nerves, tissues or cells
Basic Structure of a Neuron
Dendrites - shorter, more
numerous, receive information
Cell Body - contains the nucleus
and two extensions
Axons - single, long fiber which transmits
impulses away from the cell body
CNS and PNS
The nervous system is divided into two parts:
1. Central
Nervous
System (CNS)
- brain and
spinal cord.
Integrates
sensory
information to
make
decision.
2. Peripheral
Nervous
System (PNS) –
nerves that
originate from
spine or brain,
but branch off
throughout the
body. Nerves
that initially
detect external
signals.
Basic Functions of Nervous System
1. Sensory Function - Gathers info, carries message
to the CNS (brain). Afferent.
2. Integrative Function - Info brought together and
decisions are made
3. Motor Function - Responds to stimuli, carries
message away from brain. Efferent.
The 3 basic functions:
Sensory – Integrative - Motor
• 1. Sensory Function - gathers info about
changes occurring within and around the body
- Sensory receptors, at ends of peripheral
nerves send signals (nerve impulses) to the
CNS.
The 3 basic functions:
Sensory – Integrative - Motor
• 2. Integrative Function - information is
"brought together," interpreted, to create
sensations, create thoughts, add to memory,
make decisions, etc. Association neuron or
interneuron
The 3 basic functions:
Sensory – Integrative - Motor
• 3. Motor Function - responses to signals
(impulses). Signals sent from the CNS to
effectors (muscles or glands). The goal is
usually to maintain stable conditions
(Homeostasis) .
Motor Functions: Somatic & Autonomic
- Somatic Nervous System = Signals from CNS
effect skeletal muscles, voluntary. Example:
talking, running, chewing, ect.
- Autonomic Nervous System = Signals from CNS
effect smooth muscles & glands, involuntary.
Example: shaking when cold, increase saliva
production when eating, slowing heart rate
before bed.
- Autonomic Nervous System
- Can be divided into Parasympathetic and Sympathetic
Parasympathetic:
Control the body's
response while at
rest.
Sympathetic:
Control the body's
response during
perceived threat.
(Integrative)
Neuron
Neuroglial Cells (Support cells for neurons)
1. Microglial Cells: scattered
throughout, digest debris or bacteria.
Immune response.
Neuroglial Cells (p 208)
2. Oligodendrocytes:
makes the myelin
sheath around the
axon of neuron
Neuroglial Cells (p 208)
3. Astrocytes: connect
blood vessels to
neurons. Supplies
nutrition for neuron
to function.
I connect to
blood
vessels
Neuroglial Cells (p 208)
4. Ependymal Cells: form a membrane that
covers brain and spinal cord.
5. Schwann cells: form the insulating myelin
sheath around the neurons
MYELIN SHEATHS
- serve as insulation around the axon.
Allows signal to travel long distances.
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!
Supporting Cells - NEUROGLIA
Supporting Cells- NEUROGLIA
Neurons
Axon - long section,
transmits impulses
Dendrite - small
extensions from the
cell body; receive
information
Neurofibrils - fibers
within the axon
neurofibrils
•Chromatophilic substance (rough ER) - transport
system
•Myelin -insulation surrounding axons
•Nodes of Ranvier - gaps in the insulation
•Axon Terminal – sends impulse to next neuron
White vs Grey Matter
Grey matter – short neurons with unmyelinated axons.
Also contains support cells (neuroglial cells).
White matter – long myelinated axons with no dendrites or
cell bodies. Function to connect gray matter. (Think of
this as an extension cord)
Cannabis effects on Gray Matter
- Heavy exposure to THC has been shown in many studies to reduce gray matter
- This affect is drastically seen in maturing brains under the age of 25.
- Researchers also have seen a decrease in IQ scores in long time cannabis users
- Heavy Cannabis use (2-3 times daily) does not shrink brain as studies claim,
but the brain compensates by increase the wiring of the brain (White matter)
Label
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
Types of Neurons
Functional:
Sensory, Motor,
Interneurons
Structural:
(A) Bipolar
(B) Unipolar
(C) Multipolar
Transmission of
Nerve Impulses
The electrical signal (nerve impulse)is sent in this order:
Dendrite  cell body  along axon  axon terminal  synapse (gap)
How is a nerve impulse like a
simple electrical circuit?
If the wire is connected to a battery,
then the light will illuminate.
If a neuron is connected to another
neuron with neurotransmitter, then
the nerve will function.
A neuron sending a signal down the axon.
“I dunno man, I haven’t skied in years. I’ll fall on my face!”
“It’s like riding a bike, it will be easy to do it again!”
Once you learn a skill (physical,
emotional or academic) and you
practice it enough it becomes
second nature.
Some call this “muscle memory”
for physical activities.
In reality, you have lots of gray
matter neurons working at the
same time. You have trained your
brain to make those connections
required for balance, coordination,
or strength.
Many top level athletes have
mental trainers for this reason.
Train your brain, and you can
achieve more physically.
Tying your shoes or riding
a bike is now easy
because of Neuronal
pools.
Neuronal pool - groups
of neurons that make
hundreds of synaptic
connections and work
together to perform a
common function.
Types of Neurotransmitters
•Acetylcholine – naturally stimulates muscle contraction
•Monoamines - Norepinephrine & Dopamine (sense of
feeling good, low levels = depression)
•Serotonin - sleepiness and positive mood
Endorphins
Produced during exercise, excitement, pain, love and they resemble the
opiates (opium) in their abilities to produce a feeling of well-being.
The name “endorphin” comes from endo- and -orphin; intended to
mean "a morphine-like substance originating from within the body.
Drugs that Affect Synapses and Neurotransmitters
Curare –
Poison made from frog skin and
causes paralysis by blocking
Acetylcholine receptors at the
neuromuscular junction.
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
Allows motor neurons to be more easily
activated. Spastic muscle contractions
occur that eventually lead to respiratory
failure and death.
Drugs that Affect Synapses and Neurotransmitters
Cocaine, morphine, alcohol, ether and chloroform
Anaesthetize (lose consciousness or feeling) nerve fibers.
Cocaine specifically keeps dopamine (good mood
hormone) in one place and user feels pleasurable for
longer periods of time.
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.
Produce their hallucinatory
effect by interfering with
Adrenaline & serotonin
Antidepressants
•Zoloft is part of a class of drugs called selective
serotonin reuptake inhibitors, or SSRIs for short.
• SSRIs act on a specific chemical within the brain
known as serotonin. This is one of several chemicals
used to send messages from one nerve cell to another.
Cell Membrane Potential
What is it?
Different ions (charged atoms) are allowed to enter the neuron
cell. This causes neurotransmitters to be released and the
neuron to communicate with the next.
Nerve Impulse
A: 1st Neuron (Presynaptic)
B: 2nd Neuron (Postsynaptic)
1. Mitochondria
2. Neurotransmitter
3. Calcium Pump
4. Synaptic cleft
5. Neurotransmitter receptor
6. Sodium/Potassium Pump
7. Fused vesicle releasing neurotransmitter
8. Neurotransmitter re-uptake pump
The Steps of Neurotransmission
1. Electrical impulse called an action potential
travels down the axon of 1st neuron (A).
2. This action potential opens a Na/K pump (6)
in the cell membrane. Na+ ions enter neuron.
3. Build up of Na+ ions signals the opening of
another channel, a Ca2+ (3).
4. The Calcium ions bond to the
neurotransmitters (2) and force them to release
their contents into the synaptic gap. (7)
5. The neurotransmitters then stimulate the
dendrite of the second neuron. (5)
Nerve impulse speed
Speed of an impulse is proportionate to the DIAMETER of the
AXON. Practicing a skill increases this diameter.
Greater diameter = faster speed
Myelinated Axons conduct faster than unmyelinated ones
The Synapse
Synapse - junction between
two communicating neurons
Nerve pathway - nerve
impulse travels from neuron
to neuron
Dendrite → cell body →
along axon -> synapse (gap) →
dendrite
The Synapse
To complete the signal, a
NEUROTRANSMITTER is
released at the gap to signal
the next neuron.
Receptors on the dendrite
receive the chemical
message
Neurotransmitters
Excitatory - increase membrane permeability,
increases chance for threshold to be achieved
Inhibitory - decrease membrane permeability,
decrease chance for threshold to be achieved
9.9 Types of Nerves
Sensory Nerves - conduct impulses into the brain or
spinal cord (afferent)
Motor Nerves - carry impulses to muscles of glands
(efferent)
Mixed Nerves - contain both sensory and motor nerves
Neurons Classified by Function: Sensory vs. Motor Neurons
Figure 12.11
9.10 Nerve Pathways
•Reflex arc - only includes a few neurons
•Reflex Behavior - automatic, subconscious responses
•Knee-jerk reflex - maintains uprighted-ness
•Withdrawal reflex - avoidance of painful stimuli