CH. 2: Neuroscience Flashcards
What we will learn about the nervous system
- The organization of the human nervous system
- The components of the nervous system
- The functioning of the nervous system
- The role of hormones and neurotransmitters in behavior
- How the brain is studied
Phineas Gage
Phineas Gage’s traumatic accident allowed researchers to investigate the functions of the frontal lobe and its connections with emotion centers in the subcortical structures.
How Many Neurons Are in the Brain?
86 Billion! (Previous estimates were around 100 million)
Components of the Neuron
Cell body: Coordinates information-processing tasks and keeps the cell alive
Dendrite: Receives information from other neurons and relays it to the cell body
Axon: Transmits information to other neurons, muscles, or glands
Myelin sheath: Provides insulating layer of fatty material
Glial cells: Support cells found in the nervous system (makes up myelin sheath)
Synapse: Junction or region between the axon of one neuron and the dendrites or cell body of another
Axon> Synapse> Dendrite> Axon
Psychologist Donald Hebb’s “assembly theory”
Theory of how the brain achieves the feat of keeping neurons together, best summarized by the idea that “neurons that fire together wire together.” The idea is that neurons responding to the same stimulus connect preferentially to form “neuronal ensembles.”
The glial cells of Myelin also help keep the neurons physically together
Myelin and Nodes of Ranvier
Myelin is formed by a type of glial cell, and it wraps around a neuron’s axon to speed the movement of the action potential along the length of the axon. Breaks in the myelin sheath are called the nodes of Ranvier. The electric impulse jumps from node to node, thereby speeding the conduction of information down the axon. Myelin is white while grey matter is unmyelinated
Myelin
- Made up of Glial cells
- The glial cells help hold neurons in place
- Surface of brain is cell bodies and hence gray matter
- Inside is pinkish or white and myelinated axons
3 types of Neurons Specialized by Function
Sensory neurons, motor neurons, and interneurons
Sensory Neurons
- Receive information from the external world; convey this information to the brain via the spinal cord
- Receive signals for light, sound, touch, taste, and smell
Motor Neurons
- Carry signals from the spinal cord to the muscles to produce movement
- Often have long axons that reach to muscles at our extremities
Interneurons
- Connect sensory neurons, motor neurons, or other interneurons
Electrochemical Action
Communication of information within and between neurons proceeds in two stages: conduction and transmission
Conduction
Movement of electronic signal within neurons
Transmission
Movement of electrochemical signal from one neuron to another due to signaling across the synapse involving (chemical) neurotransmitters to the dendrites.
The action potential direction
a. In response to a signal, the soma end of the axon becomes depolarized.
b. The depolarization spreads down the axon. Meanwhile, the first part of the membrane repolarizes. Because Na* channels are inactivated and additional K* channels have opened, the membrane cannot depolarize again.
c. The action potential continues to travel down the axon.
Resting Potential
Balance of positively charged and negatively charged ions
Action Potential
All or none strength electrical impulse along axon to synapse
Refractory Period
Period of time until the nerve cell can fire again
Chemical Signaling: Transmission Between Neurons
Information is passed between neurons through chemicals called neurotransmitters.
Terminal buttons: Knoblike structures that branch out from an axon
Neurotransmitters: Chemicals that transmit information across the synapse to a receiving neuron’s dendrites
Receptors: Parts of the cell membrane that receive the neurotransmitter and initiate or prevent a new electric signal
Synaptic Transmission
(1) The action potential travels down the axon and (2) stimulates the release of neurotransmitters from vesicles.
(3) The neurotransmitters are released into the synapse, where they float to bind with receptor sites on a dendrite of a postsynaptic neuron, initiating a new action potential.
The neurotransmitters are cleared out of the synapse by (4) reuptake into the sending neuron, (5) being broken down by enzymes in the synapse, or (6) binding to autoreceptors on the sending neuron.
Acetylcholine (ACh)
- Enables muscle action, learning, and memory
- With Alzheimer’s disease, ACh-producing neurons deteriorate.
Dopamine
- Influences movement, learning, attention, and emotion
- Oversupply linked to schizophrenia. Undersupply linked to tremors and decreased mobility in Parkinson’s disease.
Serotonin
- Affects mood, hunger, sleep, and arousal
- Undersupply linked to depression. Some drugs that raise serotonin levels are used to treat depression.
Norepinephrine
- Helps control alertness and arousal
- Undersupply can depress mood.