5.3 Neuronal Communication Flashcards
What are sensory receptors?
detect stimuli and are energy transducers, converting one form of energy to electrical energy as a nerve impulse
What receptors respond to changes in pressure? How? What are some features?
Pacinian Corpuscles
- when pressure on skin changes, it deforms the ring. Sodium channels open, allowing them to diffuse into the cell and produce a generator potential.
- the movement across the membrane creates a change in potential difference.
- if a large enough stimulus is detected and enough gates are opened, the potential difference changes significantly = depolarisation and an action potential.
- rings of connective tissue around end of nerve cell
- fibroblasts producing connective tissue
What is the function of the motor neurone?
carry action potentials from CNS to an effector
What is the structure of a motor neurone?
- cell body with dendrites
- axon hillock
- very long axon with myelin sheath
- synaptic endings/ axon terminals
What is the function of the relay neurone?
connect sensory and motor neurones
What is the structure of a relay neurone?
- cell body with dendrites
- VERY short axon, with synaptic endings
What is the structure and function of sensory neurones?
- carry APS from receptors to CNS
- may have dendrites to sensory receptor
- dendron with myelin sheath
- cell body
- axon with myelin sheath
- synaptic endings
What are similarities in the structures of all the neurones?
- plasma membrane has many gated ion channels and Na+/K+ pumps
- cell body with nucleus, mitochondria and ribosomes
- ## dendrites carry impulses towards body, and axons away
What are the differences between the neurones?
- motor: cell body in CNS and has LONG axon to effector, sensory has LONG dendron to cell body which is outside of CNS. Short axon into CNS
- relay: short dendrities + short axon. CNS
- third of peripheral nervous system neurones MYELINATED. Rest in PNS, and the CNS, ARE NOT.
- sensory and motor contain nodes of ranvier, relay dont
What does myelination look like on a neurone? What is the purpose?
- Schwann cells that make up fatty sheath. Cytoplasm wrapped around axon.
- Gaps are nodes of Ranvier. The movement of ions can only occur here
- Jumping of impulse = rapid = increased speed of transmission over long distances
What occurs in non myelinated neurones? What is the purpose?
- AP moves along in a wave
- Schwann cells loosely wrapped around multiple axons instead
- Shorter distances, coordinating functions where speed isn’t so important
What is happening when neurones are at rest?
- Gated sodium ion channels are kept closed
- ATP is used to actively pump 3 Na+ ions out for every 2K+ ions inside
- Some potassium channels are open meaning the membrane is more permeable to them, and they tend to diffuse out.
- The cell cytoplasm also contains many large anions
- Membrane is POLARISED - more negative compared to outside = resting potential at about -60mV
What are the stages of an action potential?
- Resting potential
- A few sodium ion channels open (due to a stimulus in receptor cells, or diffusion in neurones) and some sodium ions diffuse into the cell
- Membrane reaches about -50mV - the THRESHOLD
- Positive feedback causes nearby voltage gated sodium ion channels to open and loads of ions flood in = DEPOLARISATION
- Potential difference reaches +40mV, where the sodium ion channels now close and potassium channels open.
- Potassium ions diffuse OUT of the cell bringing the potential difference back to negative = REPOLARISATION
- The potential difference overshoots slightly = HYPERPOLARISATION
- K+ ion channels close. Original resting potential is restored via the pump.
What is the refractory period?
after each AP it is impossible to reach another for some time -> allows the cell to recover and ensures APs are transmitted in one direction.
How are local currents formed?
- Sodium ion channel opens during depolarisation allowing Na+ to diffuse into the neurone
- Localised increase in conc of Na+ inside the neurone -> AP
- Sodium ions diffuse sideways along the axon/dendron away to a region of lower concentration.
- Causes slight depolarisation of the membrane further down and causes opening of Na+ channels further down the neurone at a node of Ranvier.
- The open channels allow rapid influx of sodium ions in, causing a full depolarisation along the neurone = another AP.