Structure of a Vertebrate Neuron

Basic Tasks of the Nervous System

Sensory Input: Monitor both external and internal environments.

Integration: Process the information and often integrate it with stored information.

Motor output: If necessary, signal effector organs to make an appropriate response.

A system that controls all of the activities of the body.

The nervous system is made of:

The brain The spinal cord

The sensesThe nerves

The Central Nervous System is made of the brain and the spinal

cord.

The Central Nervous System controls everything in the body.

The Outer Nervous System is made of the nerves and the sense organs.

Nerves Sense organs

Myelinated Neurons

• Many vertebrate peripheral neurons have an insulating sheath around the axon called myelin which is formed by Schwann cells.

• Myelin sheathing allows these neurons to conduct nerve impulses faster than in non-myelinated neurons.

What is An Action Potential?

Saltatory Conduction in Myelinated Axons

Myelin sheathing has bare patches of axon called nodes of Ranvier

Action potentials jump from node to node

Fig. 48.11

How does a signal move from one neuron to another?

• A synape divides 2 neurons• The action potential will not move

across the synape• Neuro transmitters

–Released by the signal cell to the receiver cell

–Move by diffusion

Detail of Axon

Terminal

Source: Gray

Transmission Across the Synapse

A chemical synapse

Neurotransmitter molecules

(e.g., Acetylcholine or Dopamine)

Postsynaptic membrane

Detail of the Synapse Itself

Review the Synapse

• What is a synapse?

• A synapse is the “gap” between the axon of one nerve and the dendrite of the next one.

• The average neuron has 1,000 synapses with other neurons.

Neurotransmitters

• There are dozens of different neurotransmitters (NT) in the neurons of the body.

• NTs can be either excitatory or inhibitory• Each neuron generally synthesizes and

releases a single type of neurotransmitter • The major neurotransmitters are indicated

on the next slide.

Major Neurotransmitters in the BodyNeurotransmitter Role in the Body

Acetylcholine A neurotransmitter used by the spinal cord neurons to control muscles and by many neurons in the brain to regulate memory. In most instances, acetylcholine is excitatory.

Dopamine The neurotransmitter that produces feelings of pleasure when released by the brain reward system. Dopamine has multiple functions depending on where in the brain it acts. It is usually inhibitory.

GABA(gamma-aminobutyric acid)

The major inhibitory neurotransmitter in the brain.

Glutamate The most common excitatory neurotransmitter in the brain.

Glycine A neurotransmitter used mainly by neurons in the spinal cord. It probably always acts as an inhibitory neurotransmitter.

Norepinephrine Norepinephrine acts as a neurotransmitter and a hormone. In the peripheral nervous system, it is part of the flight-or-flight response. In the brain, it acts as a neurotransmitter regulating normal brain processes. Norepinephrine is usually excitatory, but is inhibitory in a few brain areas.

Serotonin A neurotransmitter involved in many functions including mood, appetite, and sensory perception. In the spinal cord, serotonin is inhibitory in pain pathways.

NIH Publication No. 00-4871

Examples of chemical neurotransmitters found in

synapse

• Acetylcholine: neuromuscular junctions, glands, brain and spinal cord

• Norepinepherine: affects brain regions concerned with emotions, dreaming

The Brain On Drugs

• http://www.thirteen.org/closetohome/science/html/animations.html

Higher Brain function

Vision

Speech, memory, hearing

Spatial

Motor control-Posture & equilibrium

Autonomic Functions: breathing, heartbeat, respiration, etc,

Put It all Together

- Stimulus- temperature/pressure on skin light- sound- eyes and ears correct shape molecule taste buds /nose- Action Potential proagates along axon- Neurotransmitter released into synapse- New action potential begins in adjoining

nerve or muscle cell