ANATOMY Unit 1 Notes: Nerve Impulses & Reflexes
ANATOMY
Unit 1 Notes:Nerve
Impulses & Reflexes
(1) What is a Nerve Impulse?
• Chain reaction of chemical events, allowing your neurons to send “messages”.
• Synonymous Terms:– Neuron Message– Nervous System Response– Depolarization & Repolarization
(2) The Basic Steps
1. Neurotransmitter binds to neuron.
2. Depolarization.
3. Repolarization.
4. Repeat #2 and 3 until reaching axon terminal.
5. Release of another neurotransmitter from axon terminal.
6. Regain resting potential.
NeurotransmitterBinds
Depolarization & RepolarizationDown The Axon
Release a neurotransmitter +
Stimulate next move
(3) Resting Potential
• “Resting Potential”:The natural state of a neuron when it’s not doing anything.
• At Rest There is…– Potassium (K+) on the inside of axon.– Sodium (Na+) on the outside of axon.–More cations on the outside than inside.
*This means that the outside is naturally more positive than the inside (making the axon polar).
(4) Depolarization
• De = withoutPolar = uneven charge
• Depolarization: To remove the imbalance of charge.
• What Happens?– Sodium pumps open.– Sodium ions fly thru channels into axon.– Temporarily increases positive charge inside
axon, removing polarization.
(5) Repolarization
• Re = repeatPolar = uneven charge
• Repolarization: To regain the charge imbalance.
• What Happens?– Potassium pumps open.– Potassium ions fly thru channels out of axon.– Temporarily increases positive charge back on
the outside of the axon, regaining polarization.
(6) Reaching the Terminals
• A neurotransmitter will be released.
• This neurotransmitter will:– Bind to another neuron or organ.–Make something else happen (muscle
contraction or another nerve impulse).
(7) Regaining Resting Potential
• Even though the axon is polarized at the end, the ions are on the wrong sides of the axon.
• Must actively transport ions:– Sodium must go back out.– Potassium must go back in.
• Requires ATP.
…Let’s Review All That Again…
(8) Myelin Sheath
• Where Is It?– Covers the outside of the axon.– Wraps around Na/K pumps.
• What Is Its Purpose?– Block some of the Na/K pumps.– Increases the speed of nerve impulse.
• How Does It Work?– Just like main-roads versus the freeway.– Main Roads = Axon without myelin sheath.– Freeway = Axon with myelin sheath.
(9) Reflexes
• Automatically programmed response to a specific stimulus.
• All reflexes are involuntary, however do not need to travel through the individual nervous system divisions.
• Reflex Arc Path:–Stimulus triggers nerve impulse.– Impulse sent to CNS, but at spinal cord
routes directly back out to effector organ.
(10) Types of Reflexes
• Somatic:A reflex which stimulates a response in the skeletal muscle.–Example: Retracting your arm from a hot
stove.
• Autonomic:A reflex which stimulates a response in smooth muscle.–Example: Your stomach releasing gastric
juice and churning once food is dropped in.