Summary Action potentials and the nervous system

ACTION POTENTIALS AND NEURONAL
RESPONSES:
Nervous tissues contain two types of cells:
1. Nervous: electrical signalling and communication
2. Glial cells: supporting cells with a range of functions

THE NEURONE:
CELL BODY  Metabolic functions
DENDRITES  Carry signals to the cell body
AXONS  Carry signals away from the cell body

Cell bodies make up the grey matter  CNS: nuclei PNS: ganglion
Axons make up the white matter  CNS: tract PNS: nerve

Axon hillock is where the axon begins it is where the contents of the neurone begin to differ.

AXON:
There are NO organelles in the axon and the cytoplasm is replaced with the AXOPLASM
- Axons are surrounded by an insulating MYELIN SHEATH which is deposited by GLIAL
CELLS.
Myelin sheath is not continuous but has GAPS along its length called NODES OF RANVIRER
which play a role in movement of electrical impulses across the neurone.

TYPES OF NEURONES:
We class neurones dependent on:
1. Location
2. Function
3. Neurotransmitters (chemical signalling molecules)
4. Shape
- UNIPOLAR (normally sensory)
- BIPOLAR (not common and found in the olfactory epithelium and retina)
- MULTIPOLAR (Most common!)




CELL MEMBRANE

, Ions are polar molecules and as the fatty acid tails are Non-Polar, they repel any
polar/charged molecule.
Therefore, require carrier proteins or channel proteins to allow ions pass through the cell
membrane




LIGAND
GATED CHANNELS
A group of transmembrane ion channels that open or close
in response to the binding of a chemical messenger (ligand)
such as a neurotransmitter.
The neurotransmitter attaches to the receptor causing ions to move in response to the
gradient.


MECHANICALLY GATED CHANNELS
They open because of a physical distortion of the cell membrane.
Many channels associated with the sense of touch (somatosensation)
are mechanically gated.
e.g. pressure applied to skin allows these channels to open and allow
ions to enter the cell.
Other examples are channels opening on the basis of temperature
changes such as in the shower.

VOLTAGE GATED CHANNELS:
Only open due to changes in the electrical properties of the
membrane.
The inner portion of the membrane is at a negative voltage
and when it becomes less negative, the channel begins to
allow ions to cross the membrane

LEAKAGE CHANNELS:
They are randomly gated meaning they open and close at random.
There is no event which opens the channel instead there is an
intrinsic rate of switching between open and closed states.


SODIUM POTASSIUM PUMP:
The sodium/potassium pump in the cell membrane play a major role in regulating ionic
content inside and outside the cell.