synapses and transmitter substances

8/3/2019 Synapses and Transmitter Substances

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SYNAPSES AND TRANSMITTER SYNAPSES AND TRANSMITTER

SUBSTANCES SUBSTANCES

ORGANIZATION OF THE NERVOUSSYSTEM


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IN GENERAL

The NERVOUS SYSTEM controls the rapidactivities of the body such as musclecontractions, rapidly changing visceralevents, and rates of secretion of majorendocrine organs

It receives millions of bits of informationfrom the different sensory organs andintegrates all these to determine theresponse to be made by the body


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O N THE O THER HAND.

The ENDOCRINE SYSTEMregulates principally themetabolic functions of the body


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NEUR O NS

The basic functional unit of the CNS Incoming signal =) enters the neuron through

the SYNAPSES on the dendrites or cell body The synapses can be as many as hundreds to

200,000 from the input fibers The output signals =) travels by way of single

axon leaving the neuron This axon has many separate branches to other

parts of the nervous system or peripheral body


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NEUR O N


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TW O MAJ O R DIVISI O NS

Sensory Division- carried out by theSENSORY RECEPTORS

Motor Division carried out by theEFFECTORS


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SENS O RY DIVISI O N

Activities of the NS start form inputs emanating from the sensory receptors

The input can either bring or cause animmediate reaction, or its memory can bestored in the brain for minutes, weeks, or yearsand eventually can help determine bodilyreactions at some future date


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SENS O RY DIVISI O N

The somatic portionsomatic portion of the neuron transmits the sensoryinformation from the receptors

The information then enters the CNS thru the peripheral

nerves conducted to multiple sensory areas in the:1.1. Spinal cord at all levelsSpinal cord at all levels2.2. Reticular substance of the medulla,Reticular substance of the medulla, pons pons, ,

mesencephalonmesencephalon

3.3. CerebellumCerebellum4.4. ThalamusThalamus5.5. SomestheticSomesthetic areas of the cerebral cortexareas of the cerebral cortex


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M O T O R DIVISI O N

Carried out by the EFFECTORS which are themusclesmuscles and the glandsglands

Primary and ultimate role of the NS: control thecontrol the

various bodily activitiesvarious bodily activities Achieved thru :Achieved thru :1)1) Contraction of skeletal muscles throughout theContraction of skeletal muscles throughout the

bodybody

2)2) Contraction of the smooth muscle in the internalContraction of the smooth muscle in the internalorgansorgans3)3) Secretion of both exocrine and endocrine glandsSecretion of both exocrine and endocrine glands


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This division operates in parallel also toanother similar system: the AUTONOMICNERVOUS SYSTEM WHICH ALSO ACTS TOCONTROL THE SMOOTH MUSCLE, GLANDS ANDOTHER INTERNAL ORGANS


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The Skeletal Muscle can be controlled frommany levels of the CNS:

a) Spinal cordb) Reticular substance of the pons, medulla, and

mesencephalon

c)Basal ganglia

d) Cerebellum

e) Cerebral motor cortex


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The lower regions/level of the CNS (a, b, c, d)are concerned primarily with the automatic,instantaneous motor responses of the body tothe sensory stimuli

The higher region/level (cerebrum) areconcerned with the deliberate movementscontrolled by the thought process


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MAJ O R LEVELS OF THE CNS

The SPINAL CORD level The LOWER BRAIN level

The HIGHER BRAIN LEVELE ach level has a specific functional attributesE ach level has a specific functional attributes


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SPINAL C O RD LEVEL

Neuronal circuits in the cord can cause thefollowing:

1. Walking movements2. Reflexes that withdraw portions of the body

from painful objects3. Reflexes that stiffen the legs to support the

body against gravity4. Reflexes that control local blood vessels and

GIT movements


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L O WER BRAIN LEVEL

Composed of the: MEDULLA, PONS,MESENCEPHALON, HYPOTHALAMUS,THALAMUS, CEREBELLUM, and BASALGANGLIA

Functions: generally controls all thesubconscious activities


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SPECI F IC F UNCTI O NS OF THE L O WER

BRAIN

a) Control of the arterial pressure and respiration in the medulla and pons

b) Control of equilibrium combined function of the

cerebellum and the reticular substance of thepons and medullac) Feeding reflexes (e.g. salivation in response to

the food and licking of the lips) controlled byareas in the pons, medulla, amygdala,hypothalamus

d) Emotional patterns like anger, excitement, sexualresponse, reaction to pleasure


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L O WER BRAIN


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HIGHER BRAIN LEVEL O R C O RTICAL

LEVEL

Predominantly the CEREBRAL CORTEX The cerebral cortex is an extremely large memory

storehouse

The cerebral cortex is essential for most of ourthought processes However, the cerebral cortex never functions alone

but always in association with the lower centers(the functions of the lower brains are oftenIMPR EC ISE) , and it is the cortex that convertsthese functions to determinative and preciseoperations


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CEREBRAL C O RTEX


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PR O CESSING OF IN FO RMATI O N

The NS needs to process incoming information insuch a way that appropriateappropriate motor responsesoccur

Sensory information that are the brain receivesare all filtered and selected after the IMPORTANTsensory information has been selectedchanneled into the proper motor regions of thebrain to cause the desired responses

This channeling of information is the INTEGRATIVEINTEGRATIVEFUNCTION of the NSFUNCTION of the NS


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R O LE OF SYNAPSES.

In processing information Junction point from one neuron to another =>

advantageous site for control of signal

transmission Synapses determine the directions that thenervous signals spread in the NS

Some synapse can transmit signals with easewhile others with difficulty

Also there are facilitatory and inhibitory signalsfrom other areas of the NS that can controlsynaptic transmission


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R O LE OF SYNAPSE

Generally Synapse perform a selective action, oftenSynapse perform a selective action, often

blocking the weak signals, while allowing theblocking the weak signals, while allowing thestrong signals to pass, often selecting andstrong signals to pass, often selecting andamplifying certain weak signals, andamplifying certain weak signals, andchanneling channeling the signals in many directionsthe signals in many directionsrather than in one directionrather than in one direction


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SPECIAL F EATURE OF THE

SYNAPSE

FOR MOST SYNAPSE, the signal normallypasses only in the forward directionforward direction except inrare conditions

T his allows the signals to be conducted in theT his allows the signals to be conducted in therequired directions for performing necessary required directions for performing necessary nervous functionsnervous functions

Neurons are organized into a great multitude of NEURAL NETWORKS that determine thefunctions of the nervous system

synapses and transmitter substances

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