Download - DETECTING AND RESPONDING TO SIGNALS
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DETECTING AND RESPONDING TO SIGNALS
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The communication systems
ENDOCRINE- Chemical messengers secreted by cells and carried via a transport system, finally diffusing into extra cellular fluid surrounding a target cell
NERVOUS- System of specialised cells providing rapid and precise signalling via the transmission of electric impulses
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Neurons receive, conduct and transmit electrical signals.
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3 main types of nerve cells
sensory neurone
inter neurone
motor neurone
90% of our neurons are inter neurons
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TYPES OF SIGNALS PHYSICAL
lightheatTouch
CHEMICAL – specific signalling moleculesnutrient molecules (glucose)hormonesneurotransmitterspheromones
ELECTRICAL SIGNALS
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Receptor types ChemoreceptorDetect chemical stimulus: taste, smell, co2 levels, blood
glucose levels MechanoreceptorsDetect changes in pressure, touch, balance PhotoreceptorsDetect changes in light ThermoreceptorsDetect changes in temperature Pain receptorsFree nerve endings in the skin
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Detecting and responding to signals
STIMULUS Receptor
Effectors
RESPONSE
Transmission by nerves
Transmission by nerves or hormones
-physical, chemical, internal or external
Receive the signals
Feedback-the stimulus is
changed because of the response
Take action in response to the
stimulus
Communication systems
-nervous and endocrine systems
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Negative vs. Positive feedback
Stimulus
Receptor
Brain/Spinal Cord
Effector
Response
Negative feedback- response reduces stimulus
Positive feedback- response increases stimulus
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Action PotentialsThe membrane of any nerve cell is polarised
Signals are sent along a nerve cell when (+) particles are pumped inside the membrane
As (+) ions move inside the membrane, they stimulate neighbouring (+) to following causing a “domino effect”
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“all or nothing reaction” a signal will not be sent along an axon unless it reaches approx -55 mV (this is caused by Na+ ions crossing the membrane)
If this threshold is not reached, the neighbouring Na+ ions are not stimulate to cross the membrane, and the signal stops
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Refractory Period Brief period of time between the
triggering of an impulse and when it is available for another. NO NEW action potentials can be created
during this time.
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Conduction Velocity:
impulses typically travel along neurons at a speed of anywhere from 1 to 120 meters per second
the speed of conduction can be influenced by: the diameter of a fiber the presence or absence of myelin
Neurons with myelin (or myelinated neurons) conduct impulses much faster than those without myelin.
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THE SYNAPSE “Bridging the gap”
impulse impulse
Neurotransmitters stored in vesicle at the end of axon, released from synaptic cleft through exocytosis (there are various types of neurotransmitters)
1.Neurotransmitter released upon stimulus from pre synaptic axon
2.Neurotransmitters cross synapse
3.Neurotransmitters bind to receptors on dendrite of post synaptic neuron
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SIGNALLING ALONG THE NERVOUS SYSTEM
Electric Electric Electric
Chemical Chemical
Synapses
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Reflex Arc - act first, think later
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Reflex Arc Many of the bodies essential systems
operate through reflex arcs (eg. The heart, the liver, the stomach, etc)
Fight or Flight responses employ reflex arcs in order to decrease response time
The reflex arc involves signals being processed by the spinal cord rather that in the cerebrum, this creates a shorter response time
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