Download Neurophysiology-Organization of central nervous system

Neurophysiology-Organization of central nervous system
Introduction- lec1
Date of lec.11\4
Dr. Faisal Mohammad
Lec. # 30
This lec. Is introduction & all the topics will be taken later in details so
don't spend many time reading it (15 min. is enough).
*Homeostasis: the ability to keep almost any variable in the body almost
constant and each system we discussed until now contributes to
homeostasis in away or another…
Ex:
1)the cardiovascular sys. Contributes to homeostasis by:
-keeping the blood pressure almost constant
-distributing the blood and trying to maintain constant body temp.
,nutrients &hormones.
2)the respiratory sys. Keeps conc. of CO2,O2 &maintain pH.
*remember that we have 2 control sys. In the body:
Endocrine sys. & nervous sys.
*objective of this lecture:
1- state the parts of CNS.
2- describe the organization of CNS.
3- list function of CNS.
4- compare endocrine & nervous sys.
5- describe the anatomy of the functional unit of nervous sys.(neurons).
6- determine the area of communication in CNS.
*First: parts of CNS: brain &spinal cord.
*Second: organization of CNS:
1-sensory part: sensation transmitted by sensory(afferent)neuron from
receptors
they enter the spinal cord for integration
the brain: - if they reach the cerebral cortex
- if they don't
toward
conscious perception
they don't reach our consciousness
#types of sensation: tactile, visual, auditory, olfactory, thermal &
nociceptive (pain sensation).
2-integration part: for processing of information, In the CNS(brain or
spinal cord).
3-motor part: orders from motor areas in the cerebral cortex or other
motor areas transmitted by motor (efferent) neurons toward muscles or
glands to cause muscle contraction or glandular secretion.
SO they response to sensation by muscle contraction or gland secretion.
*NOTES:
1) Somatosensory pathway: from sensory receptors (like pain,
temperature, touch, pressure receptors) to the primary sensory area or
other sensory areas in the brain.
2) receptors in muscles called muscle spindles or stretch receptors they
sense how much length or tension in the muscle.
3) joint receptors: tell our body how much the angle of the joint (is it
flexed or extended).
4) receptors are very specific.
5) transducer receptors: they transconvert any type of energy [ex:
heat(thermal energy), pressure(physical),chemical energy] into electrical
energy.
They either part of afferent or very close to afferent neurons.
When they convert these energy into electrical energy, they transmit
action potential through afferent neuron bcoz what reach cerebral cortex
only nerve impulse (action potential) wither the sensation was touch,
pressure,……….. etc.
BUT how can I discriminate this kind of sensation as touch or
temperature or……….?
By the specificity of the receptors=(they respond to 1 type of energy &
they have 1 type of tract extend from the receptor to the cerebral
cortex),they may respond to other types of energy but the threshold will
be very high .ex:
Pain receptors respond to pain (there threshold to pain is very low)
they respond to pain very fast.
they can respond to very high or very low temperature but still feel it as
pain (bcoz they are pain receptors) &the threshold of this thermal
sensation is very high.
6)remember: collection of axons in PNS= nerves
collection of axons in CNS=tracts
7)ascending tracts(sensory tracts) have many stop points (synapses) in
the spinal cord or thalamus before they reach the cerebral cortex, these
synapses are very important in regulating the sensory impulses by
stimulate them or inhibit them=>so more than 90 % of the sensation we
don't feel them bcoz they inhibited at level of synapses before they reach
the cerebral cortex. (we will talk about this later in this lec.)
8)remember : precentral gyrus=primary motor area
Postcentral gyrus=primary sensory area
9)stimulation of the 1˚motor area end with contraction of a single muscle
fiber so when we need sequential contraction of muscles to make specific
movement, we need programmed sys. may located in the 2˚,3˚ or
association area.
10)cortecospinal tract: descending tract from cerebral cortex to spinal
cord & form synapse with α motor neuron.
11)α motor neurons called final common pathway bcoz they receive
impulses from most descending tracts & the resultant stimulus will go to
the muscle or gland.
12)types of neurons:
1-α neuron: the largest
2-β neuron
3-γ neuron: the smallest
Also there are: A= myelinated , C=non myelinated
So Aα >Aβ >Aγ
* Aα go to the muscle itself
* Aγ go to the muscle spindle
*third:comparing endocrine & nervous system:
1)the nervous sys.:
- uses neurons which carry nerve impulses (action potential=fire grade).
- these impulses are very fast (in some neurons the speed might reach
120m\sec.).
-the response is either contraction of muscle or secretion of gland.
-it regulates our behavior(memory).
-the gain isn't very large.
2)the endocrine sys.:
-uses chemicals (hormones) secreted from glands.
-most of these hormones are proteins that synthesized in the ER, packed
in Golgi apparatus, carried by vesicles to the membrane & secreted by
exocytosis =>so it takes long time to reach the target cell =>slow.
-it regulates our metabolic rate (ex:T3,T4 increase the basal metabolic
rate).
-very large gain.
*note: any control system has gain.
Gain=correction\error.
Ex: the mean arterial pressure=100 mm Hg
If the blood pressure increase to 120 mm Hg
The baroreceptors (neural)will respond very quickly & bring blood
pressure into 105 mm Hg  the correction=15 &the error=5
Gain=15\5=3 (not large)
BUT hormones like Angiotesin II, Aldosterone, ADH…will bring blood
pressure into 100,0001 mm Hg
Gain=19.9999\0 =∞ (very large)
*Forth: the area of communication in CNS: the synapse
We new that not only 1 neuron transmit the sensation from the receptor to
the cerebral cortex (usually 3 neurons), these neurons stop in stations &
make synapses, these synapses modulate the sensation by stimulate or
inhibit them.
so synapses are very imp. Areas for regulation of impulses &these
areas where dugs act on.
(We will take this in details in 3 lectures Later)
*Fifth : levels of control:
1) level of spinal cord:
-It is area of reflexes
-reflex: involuntary motor movement as response to stimulus
ex: stretch reflex
-reflexes used in walking circuit, supporting (antigravity muscles)!! ……
2)lower brain level:
-includes medulla, pones, mesencephalon, hypothalamus, thalamus,
cerebellum & basal ganglia.
-control subconscious body activity.
3)higher brain level:
- the cerebral cortex
-large memory store home, essential for processing each process in the
NS(sensory or motor) like special sensation, hearing, smelling, tasting….
*Finally: anatomy & functional unit of the neuron:
-The NS is like a computer: u give it inputs (sensory information)
these inputs go to the CPU for processing(integration)it give u
output(motor)
-neurons resemble the hand: the palm is the soma, the fingers are the
dendrites & the forearm is the axon.
#4 parts of the neuron:
1=the cell body(the soma):it contains organelles except to the
centrosomes (bcoz it doesn't divide)& it contains nissel granules .
*NOTE: nissel granules in soma like ER in other cells: they synthesis
proteins(neurotransmitters) these proteins composed of a,a such as γ
amino glutaric acid, glutarate, aspartate,……..)
When these neurotransmitters synthesized, they aren't used by the
soma they are transported in away called axonal transport , but this
transport is very slaw!! So they are used in very minimal amounts to be
more effective & faster..
2=dendrites: they have very small diameter &don't contain organelles.
3=axons: as we said they might be myelinated or non myelinated.
4=axon terminals: sight of releasing of neurotransmitters & recycling
of Ach.
*NOTE: when Ach is secreted, it will be broken down into acetate+
choline by proteases (peptidases),it is the only neurotransmitter that is
recycled..
DONE BY:SALAM NAYFEH
***love u kokisyano elsa3'eeer(popesia kooty),love u Mam & Dad***