Transcript Introduction to Anatomy

Nervous Tissue
A. Nervous system divisions
B. Functional anatomy of
nervous tissue
1. Neuroglia
a. Types of neuroglia
b. Myelination
2. Neurons
a. Parts of a neuron
b. Classification of
neurons
3. Gray and white matter
C. Neurophysiology
1. Resting membrane potential
2. Ion channels
3. Action potential (impulse)
a. Depolarization
b. Repolarization
c. Refractory period
d. Propagation (conduction) of
action potentials
e. The all-or-none principle
f. Saltatory conduction
4. Transmission at synapses
a. Chemical synapses
b. Excitatory and inhibitory
postsynaptic potentials
c. Spatial and temporal
summation of PSPs
d. Removal of neurotransmitter
5. Neuronal circuits
The nervous system is the body's control
center and communicates network.
It serves three broad functions:
1. senses changes in the environment
2. integrates and interprets
3. responds
Nervous Systems Divisions
1. central nervous
system
a. brain
b. spinal cord
2. peripheral nervous
system
a. somatic division
b. autonomic division
(1) sympathetic vs
(2) parasympathetic
Neuroglia
1.
2.
3.
4.
5.
astrocytes
oligodendrocytes
microglia
ependyma
neurolemmocytes
(Schwann cells)
6. satellite cells
Neuron
1. cell body
a. nucleus
b. nucleolus
c. Nissl substance
2. dendrite
3. axon
a. axon hillock
b. trigger zone
c. axon collaterals
d. telodendrion
e. end bulbs
Myelination
1. PNS = neurolemmocytes
CNS = oligodendrocytes
2. process
3. myelin sheath
4. neurolemma
5. nodes of Ranvier
Structural Classification of Neurons
1. multipolar neuron
2. bipolar neuron
3. unipolar neuron
a. central process
b. receptor
Functional Classification of
Neurons
1. sensory (afferent) neurons
2. association neurons (interneurons)
3. motor (efferent) neurons
Some Terminology
1.
2.
3.
4.
5.
6.
nerve fiber
nerve vs. tract
tract
ganglion vs. nucleus (center)
gray matter
Gray matter
white matter
White matter
Neurophysiology
Communication by neurons depends upon two
basic properties of their cell membranes:
1. There is an electrical voltage, called the
resting membrane potential, across the cell
membrane.
2. Their cell membranes contain a variety of
ion channels (pores) that may be open or
closed.
Resting Membrane Potential
1. build-up of ions
2. separation of charges =
potential energy (mV)
3. membrane potential = -70 mV
+++++
4. polarized membrane
+++++
----------------
Two Main Factors Contribute to
the RMP
1. distribution of ions across the cell membrane.
a. extracellular fluid is rich in Na+ and Clb. intracellular fluid is rich in K+ and anions
such as organophosphates and proteins
2. relative permeability of the cell membrane to
Na+ and K+
a. moderately permeable to K+ and Clb. slightly permeable to Na+
c. impermeable to the intracellular anions
Ion Channels(Pores)
1. non-gated (leakage)
2. gated (regulated)
a. open in response to stimulus
(chemical, voltage change, light, mechanical)
b. excitable cells have them
c. found in trigger zones
How do chemically gated ion
channels open?
extracellular fluid
Na+
Na+
ACh
Na+
Na+
+++++++
Na+
Na+
extracellular fluid
Na+
Na+
+++++++++++++
Na+
Na+
Na+
Na+
+++++++
+++++++++++++
cell membrane
cell membrane
Na+
-------
- - - - - - - - - - - --
-------
Na+
Na+
- - - - - - - - - - - -Na+
Na+
Na+
intracellular fluid
CHEMICALLY-GATED Na+ CHANNEL
closed
intracellular fluid
CHEMICALLY-GATED Na+ CHANNEL
open
Chemically gated channel
How do voltage-gated channels open?
extracellular fluid
Na+
Na+
Voltage
Na+
Na+
+++++++
Na+
Na+
extracellular fluid
Na+
Na+
+++++++++++++
Na+
Na+
Na+
Na+
+++++++
+++++++++++++
cell membrane
cell membrane
Na+
-------
- - - - - - - - - - - --
-------
Na+
Na+
- - - - - - - - - - - -Na+
Na+
Na+
intracellular fluid
VOLTAGE-GATED Na+ CHANNEL
closed
intracellular fluid
VOLTAGE GATED Na+ CHANNEL
open
3. Mechanically-gated channels, light-gated channels
An Action Potential
Action Potential-Depolarization
1. threshold stimulus
2. voltage-gated Na+ channels open
3. Na+ influx (-70 ---> +30 mV)
_____________________________
4. positive feedback
Action Potential-Repolarization
1.
2.
3.
4.
voltage-gated K+ channels open
K+ efflux (-90 <--- +30 mV)
hyperpolarization
Na-K pumps restore ions
Action Potential Summary
Refractory Period
1. absolute
2. relative
POSITIVE FEEDBACK OF AN ACTION POTENTIAL
CONTROLLED CONDITION
A stimulus or stress disrupts membrane
homeostasis by causing a threshold
depolarization
NO RETURN TO HOMEOSTASIS
Opening of the voltage-gated Na+
channels causes depolarization in
adjacent membrane, opening more
voltage-gated Na+ channels
RECEPTOR
The receptors in this case are
voltage-gated Na+ channels in their
resting state
CONTROL CENTER
The shape of the voltage-gated Na+
channel depends on membrane voltage
change
EFFECTORS
Voltage-gated Na+ channels are also
effectors. Threshold depolarization
causes shape changes in the channel
All of None Principle
Each time an action potential is formed, it
has a constant and maximum strength
for the existing conditions.
Continuous Conduction
1. trigger zone to synapse
2. propagation
3. one direction only
Saltatory Conduction
1.
2.
3.
4.
5.
myelin sheath
nodes of Ranvier
"jumping" impulse
0.5 vs 130 m/sec
energy conservation
Transmission at Synapses
1. "synapsis" means connection
2. synapses integrate and filter information
3. signals are transmitted or inhibited
4. presynaptic vs postsynaptic neurons
Chemical Synapses
1.
2.
3.
4.
5.
6.
7.
arrival of action potential
Ca++ influx
synaptic vesicle rupture
NT release
NT diffusion
NT/receptor interaction
postsynaptic potential
Postsynaptic Potentials can be
excitatory or inhibitory
1. excitatory (EPSP)
a. facilitation
b. summation
(1) spatial
(2) temporal
2. inhibitory (IPSP)
a. hyperpolarization
Postsynaptic Potentials
Facilitation and Summation
1. spatial
2. temporal
___________
net effects
1. facilitation
2. summation (impulses)
3. inhibition (hyperpolarization)
EXAMPLE OF SYNAPTIC INTEGRATION
postsynaptic neuron
excitatory presynaptic neuron
inhibitory presynaptic neuron
TYPES OF NEUROTRANSMITTERS
Acetylcholine
Most common neurotransmitter; In a class by itself chemically; Mostly excitatory,
depending on location and function; Brain, spinal cord, neuromuscular and
neuroglandular synapses of the periphery
Excitatory amino acids
Glutamate – 75% of excitatory synapses in
brain
Asparate – spinal cord
Inhibitory amino acids
Glycine – most common in spinal cord
GABA (gamma amino butyric acid) – most common in
brain
Monoamines (biogenic amines)
Catecholamines – norepinephrine, epinephrine, dopamine
Other amines – serotonin, histamine
Neuropeptides – substance P, enkephalines and endorphins, cholecystokinin
Removal of Neurotransmitter from
Synaptic Cleft
1. diffusion
2. enzymatic degradation
3. uptake into the cell
Neuronal Circuits
1.
2.
3.
4.
5.
simple series
diverging
converging
reverberating
parallel after-discharge