Neuronal communication Flashcards
What is the role of the cerebellum?
Back of the head
Coordinates muscular movement.
Involved in posture/balance
Links with cerebrum as it is responsible for motor control.
What is the role of the cerebrum?
Controls voluntary actions
Involved in conscious thoughts
Personality/Memory
Learning
What is the role of the hypothalamus?
Homeostasis
Monitors internal environments
Produces hormones to coordinate environment at stable levels.
Main control of autonomic nervous system.
Branches into sympathetic and parasympathetic.
What is the role of the medulla oblongata?
Role in autonomic nervous system.
Heart rate
Ventilation
Describe role of pituitary gland:
Master gland
Posterior = stores + releases hormones made by hypothalamus
Anterior (front part)
= produces hormones
Describe the general structures of neurones?
Dendron = sends impulse to cell body
Dendrites = branches off dendron
Cell body = release neurotransmitters
Axon = sends impulse away from cell body
Myelin sheath = layer of plasma membrane —->
acts as insulating layer
Nodes of ranvier –> Non-myelinated gaps –> speed up transmission
Schwann cell –> produces myelin sheath
Describe 3 types of neurones:
Sensory: transmit impulse from receptor –> relay neurone
Relay: transmits impulse between 2 neurones
Motor: transmits impulse from relay –> effector
What are sensory receptors?
Give examples
Specific to 1 type of stimulus
Acts as transducers
4 types:
Mechanoreceptors: pressure
Chemoreceptors: chemicals
Thermoreceptors: heat
Photoreceptors: light
What are transducers?
Turn stimulus into an electrical impulse
Impulse known as generator potential
What is the general structure of a pacinian corpuscle?
Capsule on outside
Connective tissues = transmit vibrations
Sensory neurone ending containing stretch-mediated sodium ion channels
~~>Closed
Resting potential = -70mV
More Na+ on outside
Membrane = polarised
What happens when pressure is applied to pacinian corpuscle?
Pressure applied
Shape changes
Causes neurone membrane to stretch as well
Opens stretch-mediated Na+ channels
Na+ diffuse into sensory neurone through channels down electrochemical gradient
Depolarises membrane
~>initiates generator potential
—> leads to action potential to be propagated (spread) down neurone.
What does resting potential refer to?
State at which cell membrane can be stimulated.
What does polarised membrane mean?
Uneven distribution of ions across membrane.
Generates potential difference
What happens in the resting potential of a cell?
Sodium-potassium pump moves 3 Na+ ions out and 2 K+ in by active transport. (uses ATP)
Na+ channels = closed –> prevent re-entry of ions
K+ channels opened to allow K+ ions to leave cell by facilitated diffusion
Permeant negative ions inside cell
~~>resting potential of -70mV
What is an action potential?
Stimulus temporarily reverses charges on axon membrane.
How is an action potential generated?
Depolarisation
First sodium channels open by energy transferred from initial stimulus
energy not enough to open subsequent voltage-gated Na+ channels
Only open when membrane depolarised to -55mV (threshold potential)
~~>big influx of Na+
(positive feedback)
Until +40mV reached
How does cell go back to resting potential?
Repolarisation
At +40mV Na+ channels close
K+ channels open
K+ leaves via facilitated diffusion
Drop in voltage causes K+/Na+ channels to reopen.
Regenerate concentration
What is hyperpolarisation?
Overshoot of potential difference
Potential difference lower than -70mV
What is the wave of depolarisation?
Resting potential:
Overall concentration of + ions greater outside membrane
~~>membrane polarised
Action potential:
Stimulus causes sudden influx of Na+ = charge reversed
Membrane depolarised
Potassium ions leave cell –> hyperpolarisation
Propagated along axon = O.G charged state = repolarisation
Returns to resting potential for new stimulus
What is the refractory period?
Short period when axon cannot be excited again
Voltage-gated sodium ion channels remain closed.
Why is the refractory period important?
Prevents propagation of action potential backwards + forwards
Makes sure action potential unidirectional
Ensures action potentials do not overlap
What is saltatory conduction?
When action potential jump from one node to another
Myelinated axons transfer electrical impulses faster than non-myelinated axons.
Depolarisation can only occur in nodes of ranvier
More energy efficient
What are other factors that affect speed at which axon potential travels?
Axon diameter = bigger diameter = faster impulse
~~> less resistance to flow of ions in cytoplasm
Temperature = higher = faster nerve impulse
Ions diffuse faster at higher temps
What is the all-or-nothing principle?
Threshold value always triggers response
if threshold reached = action potential generated
No matter how large stimulus –> same action potential triggered
Larger stimulus = higher frequency of action potential generated
