1. Neurons, Synapses & Signalling
The Brain & Nervous System
Neurons, Synapses & Signalling

2. Nervous System- 2 parts Brain & spinal cord
Located down centre of body
Connection from central to outside world
Voluntary (somatic)… under conscious control
Involuntary (autonomic)… runs internal organs, peristalsis, etc
Central Nervous System (CNS)
Peripheral Nervous System (PNS)

3. Neurons Nerve cells NOT nerves  nerves are “bundles” of nerve cells
Have THREE main parts: dendrites, cell body and axon

4. Parts of a Neuron Dendrites: Highly branched
Receive signals from other neurons
Cell Body:
Organelles & nucleus of neuron located here
Axon:
Transmits signals to other cells
Often longer than dendrites
Each end of an axon transmits to another cell at a junction called the SYNAPSE
Glial Cells nourish neurons and insulate the axon

5. 3 Main Types of Neurons Sensory Neurons Input to spine
Transmit information from sensors (ex. eyes, nose, etc) to brain for processing
Long dendrite, short axon

6. Motor Neurons
From spine outwards
Transmit signals to muscle cells
Long axon, short dendrites
Interneurons
Connect sensory & motor neurons
In CNS
For REFLEX = short axon, short dendrite
To BRAIN = short dendrite, long axon

7. Nerve Impulse Transmission
Membrane Potential: Also called resting potential; not sending any signals (between -60 and -80 mV)
Action Potential: Impulse as it moves along a neuron
Inputs from stimuli change membrane potential act as signals
These are moved along neurons to the CNS for processing!

8. Sodium Potassium Pump
Each ion (Na+ and K+) has concentration gradient across membrane of neuron
K+ concentration highest INSIDE cell
Na+ concentration highest OUTSIDE cell
Gradients maintained by sodium-potassium pump
Use energy of ATP hydrolysis to actively move Na+ OUT and K+ INTO the cell
3 Na+ and 2 K+ moved at a time

9. The Pump at Work

10. Resting potential maintained by movement through ion channels
Any net movement of +’ve or –’ve charge will generate membrane potential (voltage)
Gated ion channels open or close in response to stimuli

11. Increase in magnitude of membrane potential
Inside of membrane becomes more NEGATIVE
Increases outflow of positive ions OR inflow of negative ions
Reduction in magnitude of membrane potential
Involves gated sodium channels
Hyperpolarization
Depolarization

12. Action Potential Graph