chapter 28: the nervous system - ms. beels...
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• 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