Topic 8: Grey Matter Flashcards
What does the CNS consist of? (5)
- brain
- spinal cord
- optic nerve
- relay neurons
- protected by bones and meninges
What is the role of the CNS?
Integrate information and initiate responses
What does the PNS consist of? (2)
- sensory nerves
- motor nerves
What is the role of the PNS?
Connects CNS to limbs and organs
Describe the structure of a motor neuron (3)
- cell body in CNS
- axon extends out of CNS
- Schwann cells (myelin)
Describe the structure of a sensory neuron (4)
- cell body and dendrons outside CNS
- axon extends into CNS
- cell body found in dorsal root ganglia
- myelinated
Describe the structure of a relay neuron (2)
- found in CNS
- not myelinated
What is the role of Schwann cells? (2)
- protect neuron from damage
- speed up transmission of nerve impulses
What is a nerve and what is its role? (2)
- bundle of nerve fibres (axons/dendrons) in PNS
- blood vessels to supply glucose and oxygen to neurons
What is a reflex?
Immediate, involuntary response to a stimulus
What is the pathway in the reflex arc?
- Stimulus
- Receptor
- Sensory neuron
- Relay neuron
- Motor neuron
- Effector
- Response
How is a reflex arc different to normal neural pathways?
- sensory neurons synapse with relay in spinal cord rather than passing to brain
- brain receives sensory input and analysis happens after response
What happens to a pupil in dim light?
- radial muscles contract
- circular muscles relax
- pupil dilates (sympathetic)
What happens to a pupil in bright light?
- radial muscle relaxes
- circular muscles contract
- pupil constricts (parasympathetic)
How is an AP propagated along an axon?
Membrane at site of AP has opp charge to adjacent resting membrane.
+ve ions attracted to -ve area, creating a local electric current.
Resting membrane depolarised, generated AP as channels open
What are the factors affecting speed of impulse conduction?
- Diameter of axon: larger axon, higher speed of prop
- Myelination: conduct nerve impulses faster
- Temperature: higher increases speed of prop because higher rate of diffusion
- Concentration of Na+ in tissue fluid: more Na+, faster conduction
What is meant by saltatory conduction?
Impulse jumps from node of Ranvier to other node because Ap’s can’t form where myelin is present. This speeds up propagation
What is an action potential?
Rapid reversal of potential difference across neuron membrane from -70 to +40 to -70
What is a nerve impulse?
AP propagated in one direction along an axon as a wave of depolarisation
Describe what happens at resting potential (4)
- Na+/K+ pump creates conc. gradient: 3Na+ out, 2K+ in
- K+ diffuse out through channel along conc gradient. Na+ channel closed
- Positive charge builds up outside cell
- K+ conc gradient and electrical gradient counteract so no net movement of K+
What happens when the membrane is depolarised?
Stimulus changes shaped of V-gate Na+ channels so they open and diffuse into axon along electrochemical gradient (-70 to +40)
What happens when the membrane is repolarised?
V-gated Na+ close and K+ channels open. K+ diffuse out of axon due to electrochemical gradient (+40 to -70)
What happens when the membrane is hyperpolarised?
K+ channels are open so membrane is more permeable so K+ continues to diffuse out (-90)
How does the membrane return to resting potential?
V-gated K+ close but non V-gated still open so K+ diffuses into axon
What is a refractory period?
The time after an AP when membrane cannot react to a new stimulus
Why is a refractory period needed?
- limit to frequency of impulses
- ensure nerve impulses are only in 1 direction
What is the threshold to generate an action potential?
-55 to -50mV or it doesn’t happen at all
Why do some stimuli not cause an AP?
Only a small number ot V-gated Na+ channels open so depolarisation doesn’t reach -55 to -50mV
How can a stronger stimulus affect action potential?
- does not trigger higher AP as size is always the same
- frequence of AP increased as more neurons conduct impulse
- electrical activity increased
