receptors energy transducers they detect a change in a particular form of energy ( eg . light)
DESCRIPTION
Receptors Energy transducers They detect a change in a particular form of energy ( eg . light) This change is called the stimulus The receptors then convert this energy into a form of electrical energy call a nervous impulse . How are nervous impulses generated? (1) - PowerPoint PPT PresentationTRANSCRIPT
Receptors
•Energy transducers•They detect a change in a particular form of energy (eg. light) •This change is called the stimulus•The receptors then convert this energy into a form of electrical energy call a nervous impulse
Receptor StimulusLight sensitive cells in the retina
Sound receptors in the inner ear
Olfactory receptors in the nasal cavity
Taste buds on the tongue
Pressure receptors in the skinMuscle spindles
Receptor StimulusLight sensitive cells in the retina
Light intensity and wavelength
Sound receptors in the inner ear
Olfactory receptors in the nasal cavity
Taste buds on the tongue
Pressure receptors in the skinMuscle spindles
Receptor StimulusLight sensitive cells in the retina
Light intensity and wavelength
Sound receptors in the inner ear
Vibrations of air particles
Olfactory receptors in the nasal cavity
Taste buds on the tongue
Pressure receptors in the skinMuscle spindles
Receptor StimulusLight sensitive cells in the retina
Light intensity and wavelength
Sound receptors in the inner ear
Vibrations of air particles
Olfactory receptors in the nasal cavity
Presence of volatile chemicals
Taste buds on the tongue
Pressure receptors in the skinMuscle spindles
Receptor StimulusLight sensitive cells in the retina
Light intensity and wavelength
Sound receptors in the inner ear
Vibrations of air particles
Olfactory receptors in the nasal cavity
Presence of volatile chemicals
Taste buds on the tongue Presence of soluble chemicals
Pressure receptors in the skinMuscle spindles
Receptor StimulusLight sensitive cells in the retina
Light intensity and wavelength
Sound receptors in the inner ear
Vibrations of air particles
Olfactory receptors in the nasal cavity
Presence of volatile chemicals
Taste buds on the tongue Presence of soluble chemicals
Pressure receptors in the skin
Pressure on skin
Muscle spindles
Receptor StimulusLight sensitive cells in the retina
Light intensity and wavelength
Sound receptors in the inner ear
Vibrations of air particles
Olfactory receptors in the nasal cavity
Presence of volatile chemicals
Taste buds on the tongue Presence of soluble chemicals
Pressure receptors in the skin
Pressure on skin
Muscle spindles Length of muscle fibres
How are nervous impulses generated? (1)
•Neurones have channels in their membranes
•There are two types or channels, which are specific to either sodium or potassium ions. Normally these are closed
•There are also sodium potassium pumps which pump sodium out of the cell and potassium in
•More sodium is pumped out than potassium is pumped in, so overall the inside of the cell is negative relative to the outside. We say it is polarised
• The difference in charge across the membrane is called a membrane potential
How are nervous impulses generated? (2)
•Nervous impulses are generated by changing the permeability of the membrane by opening the sodium channels
•Na+ moves into the cell, making it less negative, relative to the outside – we say it is depolarised.
•In receptor cells the stimulus causes sodium channels to open allowing Na+ into the cell.
•If a few channels open there will be only a small change in the membrane potential – we call this a generator potential
•If the stimulus is large a lot of channels open more Na+ will enter the cell causing a large enough change in the potential difference to stimulate a nervous impulse or an action potential
Resting potential
•The inside of the neurone is negative relative to the outside
•The potential difference is about -70mV
http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter11/animation__the_nerve_impulse.html
How is the impulse transmitted along the neurone?
•An action potential in a region of the neurone creates “local currents” around it
•These “local currents” stimulate the sodium channels ahead of the action potential to open.
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Myelinated and non myelinated neuronesMyelinated neurones
•Have a myelin sheath made of individual neurones
•About 1/3 of neurones in the peripheral nervous system
Myelinated and non myelinated neurones
Myelinated neurones
•Have a myelin sheath made of individual neurones
•About 1/3 of neurones in the peripheral nervous system
•Impulse is transmitted much faster than in non myelinated neurones
Myelinated and non myelinated neurones
Myelinated neurones
•Have a myelin sheath made of individual schwann cells
•About 1/3 of neurones in the peripheral nervous system
•Impulse is transmitted much faster than in non myelinated neurones
•Carry impluses over longer distances, between receptors and the CNS and between the CNS and the effectors
Myelinated and non myelinated neurones
Non Myelinated neurones
•Still associated with schwann cells, but one schwann cell can be loosely wrapped over several neurones
•No saltatory conduction, action potential moves continuously along the neurone
•Slower transmission
•Usually shorter and so carry impulses over shorted distances
•Often use in co-ordination of functions like the action of the digestive system and breathing
