Transcript Neurons & Neurotransmitters

Neurons & the Nervous
System
Chapter 2: The Brain and
Behavior
The Nervous
System
Peripheral
Somatic
Central
Autonomic
Sympathetic
Parasympathetic
Central v. Peripheral
• Central contains brain & spinal cord
– In a computer, this is your central
processing unit (CPU)
• Peripheral – sensory & motor neurons
that transmit messages between brain
and muscles & glands
– In a computer, this includes your keyboard,
mouse, CD-ROM, printer, etc.
Autonomic v. Somatic
• Somatic – voluntary - controls purposeful
body movements, movements for balance
& posture
– Consciously perceived sensations
• Autonomic – involuntary – automatic
activities such as heartbeat, respiration,
digestion, dilation of pupils, etc.
– Some can be under conscious control (i.e.
respiration)
– Smooth & cardiac muscle, some glands
Sympathetic v. Parasympathetic
• Sympathetic = “Fight-or-flight” response
– Uses energy reserves to cope with stress or
emergency
– Adrenaline!
• Parasympathetic = “Rest and digest”
– Conserves & builds up stored energy
reserves
Today’s Goal  You will be able to….
• Identify the parts of a neuron and their
functions in creating & sending neural messages.
Parts of the Neuron
• Neurons: nerve cells
• Dendrites: branch-like end of neuron which
receives messages
• Cell body (soma): contains nucleus
• Axon: long tail-like end of neuron which
transmits (sends) messages
• Myelin: fatty substance that speeds up
transmission of impulse
• Terminal buttons: bulb-shaped structure
at end of axon
Types of Neurons
• Afferent (sensory) neurons:
send messages from sensory
receptors to the spinal cord &
brain
• Efferent (motor) neurons: relay
messages from brain & spinal
cord to muscles & glands
• Interneurons: transmits neural
stimulus between sensory &
motor neurons
Reflex Arc
• Communication goes directly from interneurons in spinal cord
to motor neurons to move (reflexively) at the same time the
info is going to the brain to be perceived
Neural Networks
• Clusters of neurons that form a network of
cells
• The learn together as a team
Today’s Goal  You will be able
to….
• Describe how a neural impulse is
generated and how neurons communicate
in the brain and throughout the body.
The Synapse
• Synapse (synaptic cleft): gap between
dendrites of one neuron and axon of another
• Receptor sites: parts of dendrite which receive
neurotransmitters
• Neurotransmitters:
chemical substances
involved in sending
neural impulses
Neural Impulse: electrochemical
firing of a nerve cell
• Resting potential: electric potential when
neuron not firing (-70 millivolts)
• Depolarization: neuron reduces resting potential
by becoming positively charged
• Action Potential: neuron fires when it reaches
+30-40 millivolts
• Repolarization: internal charge becomes more
negative
• Refractory period: phase after firing an
impulse, neuron will not fire
• All-or-none principle: neuron will fire or not fire,
no in-between
• Threshold: level of stimulation required to
trigger a neural impulse (excitatory – inhibitory
= threshold)
Resting potential
Substances that Affect
Neurotransmitters
• Agonist: similar to the NT, mimics its effects
• Antagonist: inhibits the release of NT by
sending neuron, or blocks receptor site for
NT on receiving neuron
Neurotransmitters
• Excitatory NT: increases the likelihood
that postsynaptic neuron will fire
• Inhibitory NT: decreases likelihood that
postsynaptic neuron will fire
Neurotransmitters
• Acetylcholine (ACh)
Function: Muscle contractions,
learning, memory
EXCITATORY (sometimes inhibitory)
Malfunctions: Alzheimer’s Disease
Neurotransmitters
• Dopamine (DA)
Function: Voluntary movement,
sensations of pleasure & reward
Malfunctions: Too little  Parkinson’s,
Too much --> Schizophrenia
• Agonists  cocaine & amphetamines
• Antagonists  Ritalin, alcohol
Neurotransmitters
• Serotonin
Function: Mood, appetite, sleep,
impulsivity, concentration
Malfunctions: Depression,
Eating Disorders
• Agonists  LSD, Prozac
Neurotransmitters
• Norepinephrine
Function: Alertness, arousal,
mood, heart rate/appetite
Inhibitory & excitatory
Malfunctions: Depression
• Agonists  Cocaine, amphetamines
• GABA (most prevalent inhibitory NT)
Function: Decrease anxiety, sleep, reduce
seizures
Malfunctions: Anxiety disorders,
tremors, insomnia
• Glutamate (main excitatory NT)
Function: Memory & learning
Malfunctions: Migraines, seizures, addictions
• Endorphins
Function: Pain control
Malfunctions: None