Unit 2 Notes: Nerves & Nerve Impulses

(1) Nerves Nerves are bundles of neuron axons. There are 3 Types of Nerves: Afferent  Transmit impulses from Sensory (Unipolar) Neurons Efferent  Transmit impulses from the Motor (Multipolar) Neurons Combination  Transmit impulses in both directions to/from the central nervous system Nerve Structure: Each individual neuron axon is wrapped in the Endoneurium tissue. Bundles of neuron axons are called Fascicles. Each fascicle is wrapped in the Perineurium tissue. Each nerve is wrapped in the Epineurium tissue.

(2) Nerve Impulse Basics Refers to the “messages” sent to and from the central nervous system. The result of the movement of Sodium (Na+) and Potassium (K+) ions, in and out of the axons of neurons, triggering the release of a neurotransmitter and a RESPONSE or another NERVE IMPULSE.

(3) Resting Potential of Neurons Resting Potential: Refers to the natural state and set-up of neurons when they aren’t doing anything. A neuron’s axon is naturally POLARIZED (meaning it has an imbalance of charges inside vs. outside). The outside is naturally more POSITIVE, and has Na+ ions. The inside is naturally more NEGATIVE, and has K+ ions.

(4) Nerve Impulse Steps Neurotransmitter binds to the dendrites of neuron. Depolarization of Axon. Repolarization of Axon. Release of a Neurotransmitter. Regain Resting Potential.

(5) Depolarization Na+ channels open Na+ ions move INTO the axon Temporary depolarization (or temporary balancing of charges)

(6) Repolarization K+ channels open K+ ions move OUT of the axon Temporary repolarization of axon (except the K+ is on the outside, and Na+ is on the inside)

(7) Regaining Resting Potential ATP binds to the axon channels. Na+ and K+ are ACTIVELY TRANSPORTED to their appropriate locations (Na+ forced back out, and K+ forced back in).