The Nervous System

1. The Nervous System

2. At the End of the Lecture, You Should be Able to: • Understand the components of the human nervous system • Know the structure of a motor neuron • Know the different neurons and their function • Know resting and action potential • Explain how a nerve impulse travels along a non-myelinated neuron

3. Stimulus • A change in the environment (internal or external) that is detected by a receptor and elicits a response

4. Response • Action resulting from the perception of a stimulus

5. Receptors • Receive information from the (internal or external) environment

6. Effectors • Muscle or gland that produces the response to a stimulus

7. Action vs. Resting potential • Resting potential • The electrical potential (measured in millivolts, mV) across a cell membrane when not propagating an impulse • Action potential • The localised reversal and then restoration of the electrical potential across the membrane of a neuron as the impulse passes along it

8. Neurons • The cells of the nervous system • Carry rapid electrical responses • 3 types • Sensory Neuron • Relay Neuron • Motor Neuron

9. Sensory Neuron • Sensory neurons receive action potentials from receptors and conduct them towards the Central Nervous System (CNS brain and spinal cord). There they connect to relay neurons.

10. Relay neurons • Receive action potentials from sensory neurons and pass them to other parts of the central nervous system or directly to motor neurons in the case of a reflex arc

11. Motor Neuron • A motor Neuron is a nerve cell which transmits impulses from the brain to a muscle or gland • Take action potentials from the central nervous system to muscles or glands Weem, Biology 2007

12. Human Nervous System • Central Nervous System • Brain and Spinal Cord • Peripheral nerves • Carry messages from receptors or to effectors Weem, Biology 2007

13. Reflex Arc • A neural pathway that allows a quick reaction Weem, Biology 2007

14. The Nerve Impulse • Receptors convert a stimulus into an impulse in a nerve fiber which is carried to the central nervous system

15. Resting Potential vs. Action Potential • Resting Potential • The electrical potential (measured in millivolts, mV) across a cell membrane when not propagating an impulse. • Action Potential • The localized reversal and then restoration of the electrical potential (measured in mV) across the membrane of a neuron as the impulse passes along it.

16. A nerve impulse along a non-myelinated neuron • Depolarization • Na+ channels open, the electrical forces and diffusion flood the interior of the cell with Na+ • Repolarization • K+ channels open, electrical forces and diffusion cause K+ ions to diffuse out of the axon.

17. The Action Potential Since Na+ and K+ are both positively charged, it’s Cl- and other – ions that create the polar environment during the resting potential Weem, Biology 2007

18. The Action Potential Weem, Biology 2007

19. Synapses – Two kinds • Electrical Synapse • Membranes of neurons are pressed together and minute pores, called gap junctions, which permit an action potential to jump to another neuron • Chemical synapse • Slower • Calcium flows into synaptic knob which forces the release of a neurotransmitter, causing an action potential in the neighboring neuron

20. Synapses A chemical synapse: • The junction, or space, between two connecting neurons across which an impulse is transmitted Weem, Biology 2007