Biology Powerpoint #3 Unit 8 – Chapter 35 Nervous System Biology Powerpoint #3 Unit 8 – Chapter 35

Structures of the Nervous System: Brain Spinal Cord Peripheral Nerves: Neurons

Function of Nervous System: Coordinates the body’s response to changes in its internal and external environments.

1. The Central Nervous System Relays messages, processes information and analyzes information. Brain Spinal Cord

2. Peripheral Nervous System: Sensory Division: transmits impulses from sense organs to central nervous system. What are sense organs? Organs designed to pick up stimuli.

Peripheral Nervous System: Motor Division: transmits impulses from the central nervous system to muscles. Network of Neurons makes up the peripheral Nervous System.

Neurons Structure and Conduction of a Nerve Impulse

Basic Organization Sensory Input triggered by stimuli Integration sensory receptor (sensory input)  integration  (motor output)  effector Sensory Input triggered by stimuli conduction of signals to brain Integration interpretation of sensory signals by brain Motor output conduction of signals to effector cells (i.e. muscles, gland cells)

Neuron Dendrite - conducts “signal” toward the cell body -- [input zone] often short, numerous & highly branched signal comes from sensory cell or neighboring neuron Axon - usually a single fiber -- [conducting zone] conducts signal away from cell body to another neuron or effector cell Axon Ending a cluster of branches (100’s to 1000’s) relays signal to next neuron / effector cell

How a nerve impulse is transmitted 1) Resting - The neuron is POLARIZED. There is a slightly negative charge on the inside, and a positive charge on the outside The outside contain excess Na+ (sodium) The inside contain excess K+ (potassium) This balance is maintained by the sodium-potassium pump

Cells have voltage! – – + + Opposite charges on opposite sides of cell membrane membrane is polarized negative inside; positive outside charge gradient stored energy (like a battery) + This is an imbalanced condition. The positively + charged ions repel each other as do the negatively - charged ions. They “want” to flow down their electrical gradient and mix together evenly. This means that there is energy stored here, like a dammed up river. Voltage is a measurement of stored electrical energy. Like “Danger High Voltage” = lots of energy (lethal). – – +

How a nerve impulse is transmitted 2) Action Potential - stimulus causes opening of Na+ gates & closing of K+ gates, allowing Na+ to rush in This changes the neuron from polarized to de- polarized This is all-or-none, meaning a stimulus must exceed a threshold for the action potential to occur

How does a nerve impulse travel? Stimulus: nerve is stimulated reaches threshold potential open Na+ channels in cell membrane Na+ ions diffuse into cell charges reverse at that point on neuron positive inside; negative outside cell becomes depolarized – + Na+

How does a nerve impulse travel? Wave: nerve impulse travels down neuron change in charge opens next Na+ gates down the line “voltage-gated” channels Na+ ions continue to diffuse into cell “wave” moves down neuron = action potential Gate + – channel closed channel open – + Na+ wave 

How a nerve impulse is transmitted 3) Repolarization – K+ moves outside, Na+ stays inside 4) Refractory period – When the Na+/K+ balance returns to normal During this time the neuron will not respond to new impulses

How does a nerve impulse travel? Re-set: 2nd wave travels down neuron K+ channels open K+ channels open up more slowly than Na+ channels K+ ions diffuse out of cell charges reverse back at that point negative inside; positive outside + – Na+ K+ wave  Opening gates in succession = - same strength - same speed - same duration

How does a nerve impulse travel? Action potential propagates wave = nerve impulse, or action potential brain  finger tips in milliseconds! + – Na+ K+ wave  K+ gates open more slowly than Na+ gates

Nerve Impulse Transmission

The Synapse Action potential happens Neurons DON’T touch The gap between the axon of one neuron, and the dendrites of another is called the SYNAPSE Action potential happens Neurotransmitter is released by axon ending Neurotransmitter is a chemical that sends a signal Neurotransmitter binds to dendrite membrane of next neuron Excitation or inhibition of the membrane occurs Neurotransmitter is ‘recycled’

The Synapse

Myelin Sheath Resembles chain of beads Allows signal to travel faster because impulse “jumps” from node of Ranvier to node of Ranvier (with myelin sheath (225 mph / without 11 mph) MS  destruction of myelin sheath by own immune system (progressive loss of signal conduction, muscle control & brain function) Myelin Sheath