Neural Communication Flashcards
Action potential
A brief reversal of the potential across the membrane of a neurone, causing a peak of +40mV compared to the resting potential of -60mV
Positive feedback
A mechanism that increases a change taking the system further away from the optimum
Resting potential definition
The potential difference across the membrane while the neurone is at resting
Resting potential
About -60mV
Pacinian corpuscle
A pressure sensor found on the skin
Sensory receptors
Cells/sensory nerve endings that respond to a stimulus in the internal or external environment of the organism - can create action potentials
Transducer
A cell that converts one form of energy into another
What do most energy transducers do?
Convert one form of energy to another
Stimulus
A change in the environment that elicits a response
How do sensory receptors respond to a stimulus
Respond by creating a signal in the form of electrical signal
What does a change in light intensity result in
Light sensitive cells (rods and cones) in the retina (sensory receptor) convert light to electrical signals
What does a change in temperature result in?
Temperature receptors in the skin and hypothalamus detect the change and convert heat to electrical energy
What does changes in pressure on the skin result in?
The Pacinian corpuscles in the skin detect the change and convert movement to electrical energy
What does a change in sound result in?
Vibration receptors in the cochlea of the ear detect the change and convert movement to electrical energy
What does a change of chemicals in the air result in?
Olfactory cells in epithelium lining the nose detect the presence of a chemical and create an electrical nerve impulse
Describe the structure of the Pacinian corpuscles
- An oval shaped structure
- Consists of a series of concentric rings of connective tissue wrapped around the end of a nerve cell
How does the Pacinian corpuscles detect the stimulus?
-When pressure on the skin changes this deforms the rings of connective tissue, which push against the nerve ending
Energy transducer
Transforms one mode of energy into another e.g. Chemical to electrical
What are neurones more specialised channels specific to?
Sodium and potassium
Approximately what is the potential difference across a resting neurone?
-65 millivolts (mV)
What is the cell membrane said to be when the cell is inactive?
Polarised (negatively charged inside compared to the outside)
How many sodium ions are transported across the cell membrane for how many potassium?
3 sodium out for 2 potassium in
What do cells associated with the nervous system have?
Specialised channel proteins e.g. Sodium channels are specific for sodium
What will happen if protein channels are permanently open?
Ions will diffuse across the membrane until their concentrations on either side reach an equilibrium
What happens across a membrane due to sodium channels being sensitive?
- As they are so sensitive to small movements across the membrane, when the membrane is deformed by the changing pressure the sodium channels open.
- This allows sodium ions to diffuse into the cell producing a generator potential (receptor potential)
What is the role of the sodium/potassium pump?
How is a nerve impulse created?
By altering the permeability of the nerve cell membrane to sodium ions
How is the creation of a nerve impulse achieved?
- By opening the sodium ion channels
- As the sodium ion channels open, the membrane permeability is increased and sodium ions can move across the cell membrane down their concentration gradients into the cell
- Movement of ions across the membrane creates a change in the potential difference across the membrane
- Inside of cell becomes less negative (depolarisation)
What happens if only a small stimulus is detected?
Only a few sodium channels will open
The larger the stimulus…..
The more gated channels will open
What happens if enough sodium gates are open?
Enough sodium ions will enter the cell, the potential difference across the cell membrane changes significantly and will initiate an impulse or action potential.
Motor neurones
Neurones that carry an action potential from the CNS to the effector muscle
Myelinated neurones
Has an individual layer of myelin around it. Myelin sheath
Non-myelinated neurones
Has no individual layer of myelin
Relay neurones
Join sensory neurones to motor neurones
Sensory neurones
Neurones that carry an action potential from the sensory receptor to the CNS
What does the cell body of all neurones contain?
Many mitochondria, a nucleus and ribosomes
What is different about motor neurones?
- Motor neurones have their cell body in the CNS and have a long axon that carries an AP out to an effector
What is different about sensory neurones to other neurones?
- Sensory neurones have a long dendron carrying the AP from the sensory receptor to the cell body, which is positioned just outside the CNS
- Have a short axon carrying the AP into the CNS
What is different about relay neurones to other neurones?
- Relay neurones connect the sensory and motor neurones together
- Have many short dendrites and a short axon
- No. Of dendrites and divisions of the axon is variable
Structures that are the same in all neurones
- long so to transmit action potential over a long distance
- cell surface membrane with many gated ion channels
- sodium/potassium pump that uses ATP to actively transport ions
- maintain a potential difference across the membrane
- axon carries impulse away from cell body
- axon surrounded by myelin sheath
What are the advantages of myelination?
- Myelinated neurones can transmit AP much quicker, typically 100-120 ms-1
- Myelinated tend to be longer and can so carry APs further
