•  R E V I E W O F N E U R O N S •  H O W D O N E U R O N S C O M M U N I C A T E ? !

Chapter 28: The Nervous System

The Neuron

  3 types of neurons:   1. Sensory neurons: Neurons located near receptor

organs (skin, eyes, etc.)  Function: Receive incoming stimuli from the environment

  2. Motor neurons: send signals to muscles to control movement. Neurons located near effectors (muscles and glands)  Function: Carry impulses to effectors to initiate a response

  3. Interneurons: connect the sensory neurons and motor neurons  Most of the neurons in the brain& spinal cord = interneurons

 Average human brain ~100 billion neurons

Structure of the Neuron

Structure of the Neuron

 Cell Body (soma): the central part of the neuron, contains the nucleus  regulates cell functioning

 Dendrites: the branching part of the neuron that receives messages from other neurons and relays them to the cell body

Structure of the Neuron

 Axon: the long, cable-like extension that delivers messages (impulses) to other neurons

 Myelin Sheath: layer of fatty tissue that insulates the axon and helps speed up message transmission

 Knobs (axon terminal buttons): structure at the end of one of the axon’s branches that releases chemicals into the space between neurons, when the neuron is fired

S O Y O U W A N T T O T A L K T O A N O T H E R N E U R O N … ?

Neural Communication

Neurons

REMEMBER!! A MESSAGE CARRIED BY A

NEURON IS CALLED AN IMPULSE!

Neurons

REMEMBER!!  Dendrites receive messages from other neurons and send

them to the cell body  Axons carry messages away from the cell body to dendrites

of other neurons

From Neuron to Neuron

 There are ~100 billion neurons in a human brain, connected to an average of 10,000 others; some up to 100,000

 How do neurons communicate impulses to one another?  Synapse: the small space where an axon of one

neuron meets with the dendrite/cell body of the receiving neuron.  The tiny gap at this junction (where the axon of one

neuron meets the cell body/dendrite) is called the synaptic gap or synaptic cleft

From Neuron to Neuron

http://www.med.harvard.edu/publications/On_The_Brain/Volume7/Number1/images/Neuron.jpg

http://mhln.com

An impulse moves in only one direction across a synapse - from an axon to the dendrites or cell body of another neuron.

From Neuron to Neuron

 Neurotransmitters: a chemical that sends signals from one neuron to another over the synapse  When released by the

sending neuron, neurotransmitters travel across the synapse and bind to receptor sites on the receiving neuron

From Neuron to Neuron

  Neurotransmitters are stored in vesicles in the knobs (axon terminal buttons), and bind to receptors on the cell membrane of the next neuron.  Each receptor can

only bind with one kind of neurotransmitter.

(Some) Neurotransmitters Neurotransmitter Function Examples of

malfunctions Acetylcholine

(ACh) Enables muscle action,

learning & memory Alzheimer’s disease

less ACh production Dopamine Influences movement,

learning, attention, & emotion

Excess schizophrenia

Undersupply Parkinson’s disease

Serotonin Affects mood, hunger, sleep, and arousal

Undersupply depression

Norepinephrine Helps control alertness & arousal

Undersupply depressed mood

Glutamate Excitatory neurotransmitter involved in memory

Excess overstimulation of

brain, seizures

Pulling it All Together

1.  An impulse is released from the cell body 2.  The impulse travels down the axon until it reaches

the knobs (axon terminal) 3.  Impulse releases a neurotransmitters from vesicles 4.  Neurotransmitter enters the synaptic gap & flows

across the synapse 5.  Neurotransmitter binds to receptors on the

receiving neuron, stimulating the impulse in the dendrite of the next neuron

6.  Impulse moves from neuron to neuron

Path of an Impulse