5.1.3 NEURONAL COMMUNICATION
- Created by: geaninec
- Created on: 21-09-17 01:54
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- 5.1.3 NEURONAL COMMUNICATION
- a) the roles of mammalian sensory receptors in
converting different types of stimuli into nerve
impulses
- SENSORY RECEPTORS are specialised tissues in the body that detect changes in the environment. They work by converting energy - acting as transducers - from one form into electrical energy, which relays a signal to another part of the body.
- b) the structure and functions of sensory, relay and
motor neurones
- SENSORY NEURONES: carry AP from sensory receptor to CNS, lond dendron, short axon
- RELAY NEURONES: connects sensory and motor neurones, many short dendrites, short axon
- MOTOR NEURONES: carry AP from CNS to effrectors (muscles, glands) cell body is within CNS, long axon
- Myelinated neurones: can transmit impulses at up to 100 metres per second (vs. 1 metre per second in non-myelinated). Myelin sheath - electrical insulator.
- c) the generation and transmission of nerve
impulses in mammals
- ACTION POTENTIAL
- 1. Neurone has a resting potential - not transmitting an impulse. Some potassium ion channels are open (mainly non voltage-gated) but some sodium voltage-gated ion channels are closed
- 2. Energy of the stimulus triggers some sodium voltage-gated ion channels to open = membrane more permeable to sodium ions ? Sodium ions diffuse into axon down electrochemical gradient ? inside neurone is less negative
- 3. Change in charge = more sodium ion channels open ? more sodium ions diffuse into axon. [POSITIVE FEEDBACK]
- 4. Potential difference reaches approx. +40mV ? voltage-gated sodium channels close and voltage-gated potassium ion channels open ? sodium can no longer enter axon, but membrane is now more permeable to potasasium ions
- 5. Potassium ions diffuse out of the axon down their electrochemical gardient ? reduces the charge - the inside of the axon more negative than the outside
- 6. Initially, lots of potassium ions diffuse out of the axon, resulting in the inside of the axon becoming more negative (relative to the outside) than its normal resting state ? HYPERPOLARISATION. VOltage-gated potassium channels close ? sodium-potassium pump causes sodium ions to move out of the cell, and potassium ions move in ? axon returns to resting potential [REPOLARISED]
- All-or-nothing principle
- If threshold value is reached, it always triggers a response. No matter how large the stimulus is, the same sized action potential will always be triggered.
- Greater stimulus intensity = more frequent action potentials
- If threshold value is reached, it always triggers a response. No matter how large the stimulus is, the same sized action potential will always be triggered.
- ACTION POTENTIAL
- d) the structure and roles of synapses in neurotransmission.
- a) the roles of mammalian sensory receptors in
converting different types of stimuli into nerve
impulses
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