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Anatomy & Physiology: Nervous Tissue

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james donahue

on 29 November 2016

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Transcript of Anatomy & Physiology: Nervous Tissue

access
socrative.com

choose
student login

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421193
Neurons
Nucleus!
How is a neuron's structure related to its function?

Why are neurons an “animals only” phenomenon?
Big Questions
Characteristics of a nervous system

fast
accurate
reset quickly
Structure fits function
many entry points for signal
one path out
transmits signal
Most specialized cell in animals
Longest cell
blue whale neuron
10-30 meters
giraffe axon
5 meters
human neuron
1-2 meters
Fun facts about neurons
Think dominoes!
1.
start the signal
-
Knock down line of dominoes by tipping 1st one.
2.
propagate the signal
-
Do individual dominoes move down the line?
3.
reset the system
-
To repeat, you have to set up dominoes again.
1. Wave: nerve impulse travels down neuron
Change in charge opens next Na+ gates down the line
Na+ ions continue to diffuse into cell
the “wave” moves down neuron = action potential
1.
Resting potential
2.
Stimulus reaches threshold potential
3.
Rising (Depolarization): Na+ channels open; K+ channels closed
4.
Falling (Repolarization): Na+ channels close; K+ channels open
5.
Undershoot (Hyperpolarization): K+ channels close slowly, Na+/K+ pump reestablishes resting membrane potential
Axon coated with
Schwann cells
insulates axon, speeds signal

Signal hops from node to node

Saltatory conduction
myelinated axon velocity > 100 m/sec (223.7 mph)
vs.
unmyelinated axon velocity < 2 m/sec (4.5 mph)
Impulse has to jump the synapse!
junction between neurons
has to jump quickly from one cell to next
Events at synapse
action potential depolarizes membrane
opens Ca++ channels
neurotransmitter vesicles fuse with membrane
release neurotransmitter to synapse diffusion
neurotransmitter binds with protein receptor
ion-gated channels open
neurotransmitter degraded or reabsorbed
Acetylcholine
transmit signal to skeletal muscle

Epinephrine (adrenaline) & norepinephrine
fight-or-flight response

Dopamine
widespread in brain
affects sleep, mood, attention & learning
lack of dopamine in brain associated with Parkinson’s disease
excessive dopamine linked to schizophrenia

Serotonin
widespread in brain
affects sleep, mood, attention & learning
Weak point of nervous system:
Any substance that affects neurotransmitters or mimics them affects nerve function
gases:
nitrous oxide
carbon monoxide
mood altering drugs:
stimulants
amphetamines, caffeine, nicotine
depressants
quaaludes, barbiturates
hallucinogenic drugs: LSD, peyote
SSRIs: Prozac, Zoloft, Paxil
poisons
Differentiate between the different glial cell
Explain how each glial cell maintains homeostasis for the nervous system
Compare the regulatory structures and functions of the nervous and endocrine systems
Diagram the processes by which nervous signals are transmitted by and between neurons.
Label all parts of a neuron
Explain the causes and effects of major disruptions to neuron function
Make Sure You Can
The need for fast,
long-distance messages
Dendrites
Neurons Do These Things!
sensory neuron Interneuron Motor Neuron
Signal moves from
black
to
red
Glial cells help neurons
neurons stained with "Brainbow" flourescence
Incoming signals enter here (
afferent
).
Each dendrite is connected to another neuron at a synapse
Cell Body
Axon Hillock
Myelin Sheath
Schwann Cell
Node of Ranvier
Nerve Terminals
Axon
Lots of pump proteins and ion channels
Maintain concentrations of ions

Reset concentrations following nerve signal

Different kinds of "gates" control the openings to the channels:
mechanical gates
voltage gates
ligand gates
Summary
Action Potential
A nerve signal
Electrical (change the charge)
Binary (all or nothing)
Action Potential Propagation
Types of Incoming Impulses:

Excitatory or Inhibitory
An "All or None" Signal
For an action potential to be
generated, the membrane must be depolarized to a "
threshold
" potential.
Action Potential Generation
0. Neuron at rest (polarized):
All gated channels are closed
1. Neuron
De
polarizes:
Na+ gated channels begin to open
2. Rising Phase of AP:
Na+ gated channels all open
3. Peak of Action Potential
Na+ gates open, K+ begin opening
4. Neuron
Re
polarizes:
Na+ gates shut. K+ gates open
5. Undershoot / Hyperpolarizes:
K+ gates begin to close
Na+/K+ pump restores resting potential
Action potential travel by jumping ("saltations") between
Schwann cells.
Multiple Sclerosis:
Results from De-mylenation of motor neurons
Layers of Myelin insulate neurons.
Speeds Transmission of AP's
Saltatory Conduction
Major Neurotransmitters
Cone Snail Venom Blocks Na+ channels on post synaptic neurons
(
motor neurons in fish but sensory neurons in humans
)
Why are axons so long?
Why have synapses at all?
How do “mind altering drugs” work? (caffeine, alcohol, nicotine, marijuana…)
Do plants have a nervous system?
Do they need one?
Any Questions?
Yes!
So Cool!
Contains all organelles for the neuron. Signals move from Dendrites to cell body to axon to nerve terminals

Where an Action Potential begins (
if
it's going to).
The Action Potential moves through the
Nodes of Ranvier
by
saltatory conduction
3. But now both Na+ and K+ moved toward equilibrium
Na+ and K+ need to move "uphill"
this requires ENERGY!
the Na+/K+ pump accomplishes this
2. After firing a neuron has to re-set itself
Na+ needs to move back out
K+ needs to move back in
WHY?
to reestablish the resting membrane potential
diffusion won't accomplish this
The start of the axon.
Neuroglia
Astrocytes (CNS)
most common
anchors nerves to blood vessels
forms blood brain barrier
Microglia (CNS)
physically touches nerves
monitors health
change into phagocytes
Ependyma (CNS)
line cavities of CNS
ciliated
circulate CSF
Oligodendrocytes (CNS)
"few branches"
insulate nerves
create myelin
Schwann cells (PNS)
insulate nerves
create myelin
"saltatory conduction"
How do nervous cells that don't conduct an electrical impulse help the nervous system?
Big Question
Be sure you can:
www.youtube.com/watch?v=8xAbAeZ-Gog
Perception of Reality
Can you trust your eyes?
www.youtube.com/watch?v=iYhCn0jf46U
www.youtu.be/GyJDPVGwXI0
www.youtu.be/z7JRmq49aRw
www.youtube.com/watch?v=8-AL1pEonvs
Pay Attention
Inattentional Blindness
www.youtube.com/watch?v=t1nwSuWr_q8
Water Intoxication
Refractory
Period
www.youtube.com/watch?v=_kceXThkwyQ
Resting Membrane
Potential
There are more Na+ outside the neuron
There are more K+ inside the neuron
Both Na+ and K+ are positive, right?
Anions and proteins (made by the nerve) cannot diffuse out of the nerve
What is the difference in charge?
But, why does the Na+ or K+ move at all?
You see, back when I was a kid...
Therefore, the inside is more negative
What if the
threshold
is not reached?
Review
- please open Socrative
www.youtube.com/watch?v=A0Z78rFPFCA
Stopping NT action
1.
Diffusion
2. Enzymatic degredation
3. Reuptake
How can we us this pharmaceutically?
SSRI - Prozac, Paxil
SNRI - Cymbalta, Effexor
SDRI - Zyban, Meridia
Full transcript