Nerves Flashcards
Where are photoreceptors found (light intensity + wavelength)?
Eyes
Where are mechanoreceptors found (sound) ?
Chochlea- ear
Where are mechanoreceptors found (pressure)?
Pacinian corpuscle- skin
Where are thermoreceptors found (temperature)?
Skin
Where are chemoreceptors found (volatile chemicals)?
Olfactory cells- nasal cavity
Where are chemoreceptors found (soluble chemicals)?
Taste buds
What do sensory receptors do?
They convert specific types of stimuli to generator potentials by causing geated sodium ion channels to open, creating a potential difference across the cell membrane.
What can generator potentials lead to?
Generator potentials can lead to an action potential being initiated- a nerve impulse.
What is a pacinian corpuscle?
A mechanoreceptor that responds to pressure.
How does a pacinian corpuscle respond to pressure?
1) Pressure applied to layers
2) Gated sodium channels open
3) A generator potential is created.
4) If enough channels open, an action potential is produced.
What are the 3 types of neurone?
Sensory, relay and motor
What is the direction of nerve impulse transmission in sensory neurones?
From receptor to central nervous system (CNS)
What is the direction of nerve impulse transmission in relay neurones?
Between sensory and motor neurones, within the CNS.
What is the direction of nerve impulse transmission in motor neurones?
From the CNS to an effector, e.g. muscle or gland.
Describe a sensory neurone
Has 1 long myelinated dendron and a short axon with a myelinated sheath.
Describe a motor neurone
Has a long axon with a myelinated sheath. Has lots of short unmyeliated dendrites.
What is an action potential?
An action potential is a depolarisation of the cell membrane so the inside becomes more positive than the outside.
What is a nerve impulse?
The transmission of an action potential along a neurone.
What is the resting potential?
IT is maintained at about -60mV inside the cell compared to outside the cell.
What happens when the stimulus is intense?
When a stimulus has a high intensity a large number of action potentials are generated and it is these that are brain interprets, for instance, as a bright light or loud sound.
What is a refractory period?
When a region of the neurone is hyperpolarised, no further action potentials can be produced.
Why does a refractory period take place?
This is because the Na+ and K+ need to be re-distributed so that a resting potential can be re-established.
Explain how the myelin sheath speeds up a nerve impulse
The myelin sheath insulates the neurone. Na+ and K+ can only pass across the membrane in the gaps between the Schwann cells - nodes of Ranvier. This leads to the action potentials jumping from one node to the next- saltatory conduction.
What are synapses?
Junctions between neurones where chemicals called neurotransmitters are used to pass on action potentials.
Describe the action of neurotransmitters across a synapse
1) Action potential arrives at synaptic knob.
2) Calcium-gated channels open and calcium ions diffuse in.
3) Calcium ions cause neurotransmitter vesicles to fuse with the presynaptic membrane.
4) Acetylcholine diffuses across the synaptic cleft to bind with receptors on sodium ion channels.
5) Sodium ion channels open and a generator potential is created (EPSP- excitatory post-synaptic potential).
6) If the EPSP is of sufficient magnitude an action potential is produced.
What are the important roles of synapses in summation and control?
Allow for convergence of signals from many neurones to one neurone
Allow for the divergence of signals from one neurone to many neurones.
What are the other roles of synapses?
Ensure impulses travel in one direction only
Filter out low-level stimuli
Amplify low-level stimuli
Allow new (neuronal) pathways to occur- the basis for conscious thought and memory.
What is summation?
Summation refers to the way several small potential changes can combine to produce one large potential difference. It can be temporal or spatial and allows low-level stimuli to be amplified.
