Neurons, Synapses & Signalling The Brain & Nervous System Neurons, Synapses & Signalling
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)
Neurons Nerve cells NOT nerves nerves are “bundles” of nerve cells Have THREE main parts: dendrites, cell body and axon
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
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
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
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!
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
The Pump at Work
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
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
Action Potential Graph