NEURONAL COMMUNICATION Flashcards
State the basic plan of a nervous system
Change in enviro of receptor stimulus Receptor generates nerve impulses Sensory neurone Relay neurones in CNS Motor neurone Effector (muscle of GLAND) Response
What is a neurone
Specialised cells that transmit an ACTION POTENTIAL from one part of the body to another
- protect body
- maintain homeostasis
What are dendrites
Small extensions on cell body, creating larger SA carrying impulses towards cell body
-one= dendron
What is the axon
Single long fibre carries impulse AWAY from cell body
Function of axon terminals
Large SA
Lots of connections
What does the cell body contain
Nucleus and other organelles
Benefits of having long neurones
Transmit action potential over long distance
Benefits of sodium potassium pumps
Actively transport sodium out of the cell and potassium into the cell (ATP)
3 sodium out, 2 potassium in
Benefits of gated ion channels
Controls entry/exit of sodium/potassium/calcium ions
Ions= polar= repelled by bilayer
Benefits of organelles in the cell body
Mitochondria, nucleus, ribosomes, ER, Golgi- for production of neurotransmitters
Benefits of the myelin sheath
Fatty sheath insulates neurone from other electrical activity
20-30 layers of schwa cell membrane
Describe the myelin sheath
Wrap themselves around the axon
Made of myelin (lipid)
1/3 of cells are myelinated (speeds up conduction, 1ms-100ms)
What are gaps between schwa cells called
Nodes of Ranvier
2-3 um wide
Function of sensory neurone
Carry an action potential from sensory receptor to CNS
Function of motor neurone
Carry action potential from CNS to an effector (e.g. muscle or gland)
Function of relay neurone
Connect sensory and motor neurone
Sensory neurone:
Position of cell body
Length of dendrites
Length of axon
Outside CNS
Long, dendrites end axon
Short- outside CNS- inside CNS (spinal cord)
Motor neurone:
Position of cell body
Length of dendrites
Length of axon
Inside CNS
Many short dendrites
Long (outside CNS- effector)
Relay neurone:
Position of cell body
Length of dendrites
Length of axon
Within CNS
Short
Short
What is a nerve impulse
Temporary reversal of the electrical potential difference across the neurone membrane
What is the resting potential
Potential difference across the neurone cell membrane while membrane is at rest
Polarised membrane approx -70mV
How is the resting potential maintained
Phospholipid bilayer impermeable to ions
Sodium-potassium pump actively transports (ATP) 3NA+ out, 2K+ in
Potassium can diffuse back through open channel proteins
Sodium channels are closed, diffusion of potassium is passive- down a concentration gradient
Cytoplasm contains negatively charged ions (e.g. protein molecules)
Interior of neurone= negative
Function of channel proteins
Voltage gated- whether open or closed depends on voltage across membrane, changes of ion concentration changes protein shape
Stimulus sensitive- increase pressure, increase NA+ channels open
What is the action potential
Brief reversal of the potential across the membrane of a neurone causing a peak of +40mV compared to resting potential -70mV
Explain the concept of all or nothing
Below threshold value, no impulse generated
Above threshold, impulse generated
AP is the same size
Larger stimulus= more frequent the impulses
What is the refractory period
Follows AP, short period of time where another AP is impossible
V-gated Na+ channels are closed
Keeps AP going in one direction
Separates AP
