Neurons- The matter of the nervous system

Chapter 7: Pgs 120-133

The Nervous system controls the entire body

• It is the interface between stimulus and response

• Allows animals to interact with their environment

• Brain and spinal cord: central nervous system (CNS)

• Other nerves: peripheral nervous system (PNS)

The nervous system is the interface between stimulus and response

The Neuron is the base unit of the nervous system

Neurons are large cells supported by a variety of glial cells

• Human neurons can be 1m in length

• Potentially thousands of glial cells support a single neuron

• Provide nutrition, support, insulation

• Schwann cells are an example

Schwann cells are glial cells which protect neurons with myelin

The 3 kinds of neurons work together to

interface between stimulus and response

• The reflex arc is the simplest neural circuit

• Consists of – 1 sensory neuron– 1 interneuron– 1 motor neuron

The synapse is the connection point between

neurons• Vesicles sit in

axon terminals, loaded with neurotransmitters

Some important neurotransmitters

• Acetylcholine- Neuromuscular

• Dopamine-Exitatory• Norepinephrine • GABA- Inhibitory• Serotonin-Regulatory

Many Drugs copy the action of neurotransmitters

• Methamphetamine is structurally similar to dopamine

• Dopamine involved in learning and reward systems

Dopamine

Methamphetamine

Many synapses make complex information processing possible

• Cell interactions form logic circuits

• AND, NOT, etc. gates are formable

• Human Brain: 100 billion neurons

• Up to 10,000 synaptic connections/neuron

Which one of the following statements is false?

A) Sensory neurons convey signals from the CNS to

sensory receptors. B) Motor neurons convey signals from the CNS to

effector cells. C) Interneurons integrate data and relay

appropriate signals to other interneurons or to motor neurons.

D) The PNS includes nerves and ganglia. E) The CNS consists of the brain and spinal cord.

The Nerve impulse

The nervous system runs on electricity

• Current- The movement of charge (electrons or ions)

• Voltage- potential energy stored in a charge disparity over distance

• Nervous system uses ions (Na+, K+, Cl-, Ca++) to send signals from one neuron to another

At rest, neurons must be ready to respond in milliseconds

Water behind a dam is stored potential energy

Charge and concentration gradients hold potential chemical energy

Neurons have a resting membrane potential

• Negatively charged• Keeps the neuron

poised for instant action• -70mV• Maintained by constant

active transport of ions

Pumps maintain gradients, channels activate cells

• Which of the following statements about the sodium-potassium pump is false?

• A) It is a membrane protein. • B) It keeps the concentration of sodium low

inside the cell. • C) It moves sodium across the membrane and

into the cell. • D) It helps maintain the resting membrane

potential. • E) It actively transports potassium into the cell

Two kinds of ion channels

Ligand-gated ion channels open when bound to a ligand (a neurotransmitter)

Voltage gated ion channels open when the voltage in the cell changes

Neurons can respond in milliseconds, giving us quick reflexes

Neurotransmitters are the chemical signals with which neurons

communicate across a synapse• Neurotransmitters bind

to gated ion channels in the cell membrane of the next neuron

• Binding opens the ion channel

• Hydrolysis or reuptake removes the neurotransmitter

The Nerve Impulse step by step

Step 1- depolarization causes vesicles to fuse

Step 2- Fused vesicles release neurotransmitter into the synapse

Step 3- Neurotransmitters open gated sodium channels, depolarizing cell

Step 5- Voltage-gated sodium channels pass the signal down the axon

Voltage-gated channels sit at nodes of Ranvier, making the signal travel faster

Step 6- Change in voltage at the axon terminal passes the signal on

Step 7- Potassium channels are opened, re-polarizing the cell for its next response

Step 8- Ion balance is restored using active transport- the Na+/K+ pump

What is the functional unit of the nervous system?

• A) dendrite • B) cell body • C) neuron • D) axon • E) synapse

Depolarization is the activation event

• Depolarization is caused by opening of gated sodium channels

• When depolarized, neurons respond in milliseconds

Action potentials normally travel along an axon

• A) toward the cell body. • B) away from the cell body. • C) in either direction, depending on the needs

of the animal. • D) away from the synapse. • E) from axons into dendrites.

Step 0.5: Vesicles were marched down the axon previously by kinesin

Antidepressants can block reuptake of neurotransmitters

• SSRI- “Selective Serotonin Reuptake Inhibitors”

• Prozac, Paxil, Zoloft, etc.- all SSRI’s

Sarin nerve gas is an Acetylcholinesterase Inhibitor

• How does it work?• How does it kill people?

The reflex arc is the most basic neural circuit

The Ganglion splits the signal to notify the brain

The human brain has 3 major regions

Higher thought is compartmentalized to the cerebrum

Regions of the cerebral cortex are themselves compartmentalized

A homonculus shows the area of the brain devoted to regions of the body