nerve cells run through our entire body and communicate with each other. neurons are like a tree...
TRANSCRIPT
Chapter 2Neuroscience and Behavior
Neuron
Nerve cells Run through our entire body and
communicate with each other. Neurons are like a tree
› Have branches, trunk, roots and they lie among one another.
3 types
Types of Neurons
Types of Neurons
Sensory Neuron: conveys information to the brain from specialized receptor cells in sense organs and internal organs
Motor Neuron: Signals muscles to relax or contract
Interneuron: communicates information from one neuron to the next› Most neurons in the body are interneurons
The Cell Body (Soma)
Contains the cell’s nucleus› round, centrally located structure › contains DNA› controls protein manufacturing › directs metabolism› no role in neural signaling
Dendrites
• Information collectors• Receive inputs from neighboring
neurons• Inputs may number in thousands• If enough inputs, the cell’s AXON may
generate an output
Dendritic Growth
• Mature neurons generally can’t divide • But new dendrites can grow• Provides room for more connections to
other neurons• New connections are basis for learning
Axon
• The cell’s output structure• One axon per cell, 2 distinct
parts› tubelike structure › branches at end that connect to dendrites
of other cells
Myelin Sheath
• White fatty casing on axon • Acts as an electrical insulator • Not present on all cells• When present, increases the speed of
neural signals down the axon
Glial Cells Support cells that assist neurons by providing structural
support, nutrition, and removal of cell wastes, manufacture myelin.
Glial Cells• Outnumbering brain neurons by about 10 to 1, glial
cells provide support and nutrition for neurons.
• Astrocytes are one type of glial cell that provides connections between neurons and blood vessels in the brain.
• Glial cells are much more actively involved in regulating neuronal communication and activity than previously believed.
How Neurons Communicate
• Neurons communicate by means of an electrical signal called the action potential
• Action potentials are based on the movements of ions between the outside and inside of the cell
• When an action potential occurs, a molecular message is sent to neighboring neurons
Stimulus Threshold: the minimum level of stimulation to activate the neuron.
Polarized Neuron
There is a difference in the electrical charge between the inside and the outside of the axon.
Greater concentration of negative ions inside than out.› Negative inside/positive outside
There are different concentrations of potassium and sodium.› Fluid surrounding the axon contains a larger
concentration of sodium.› The fluid in the neuron has a larger concentration of
potassium.
Communication•Resting Potential: At rest, the inside of the cell is at -70 microvolts
•When sufficiently stimulated by other neurons the neuron depolarizes; starting the action potential.
•Figure shows resting axon being approached by an action potential
Depolarization Ahead of AP•Action potential opens cell membrane, opens for a mere thousandth of a second, to allow sodium (Na+) in•Potassium channels open next allowing potassium to flow out of the axon into the surrounding area. •Inside of cell rapidly becomes more positive than outside to +30 millivolts.•Causes a brief electrical impulse that moves down the axon.
Repolarization Follows
•After depolarization potassium (K+) moves out restoring the inside to a negative voltage•This is called repolarization•The rapid depolarization and repolarization produce a pattern called a spike discharge
Finally, Hyperpolarization
•Repolarization leads to a voltage below the resting potential, called hyperpolarization•Now, neuron cannot produce a new action potential•This is the refractory period
Communication
All-or-none law: either a neuron is sufficiently stimulated and an action potential occurs or a neuron is not sufficiently stimulated and an action potential does not occur.
Communication occurs of speeds up to 270 miles per hour – 2 miles per hour.
Neuron to Neuron
• Synapse: Point of communication between two neurons.
• Synaptic Gap: tiny space between the axon terminal of one neuron and the dendrite of an adjoining neuron.
• Axon terminals: Branches at the end of the axon that contain tiny pouches called synaptic vesicles.
• Neurotransmitters: Chemical messengers manufactured by a neuron.
Neuron to Neuron
Synaptic Transition: Process through which neurotransmitters are released by one neuron, cross the synaptic gap, and affect adjoining neurons.
Reuptake: Process by which neurotransmitter molecules detach from a postsynaptic neuron and are reabsorbed by a presynaptic neuron so they can be recycled and reused again.
Neurotransmitter Release
Action potential causes vesicle to open Neurotransmitter released into synapse Locks onto receptor molecule in
postsynaptic membrane› One way transaction
Neurotransmitter molecules have specific shapes
Receptor molecules have binding sites
Excitatory and Inhibitory Messages
• Excitatory message—increases the likelihood that the postsynaptic neuron will activate and generate an action potential.
• Inhibitory message—decreases the likelihood that the postsynaptic neuron will activate
Neurotransmitters
Disruptions of Acetylcholine Functioning
• Curare—blocks ACh receptors› paralysis results
• Nerve gases and black widow spider venom; too much ACh leads to severe muscle spasms and possible death
Cigarettes—nicotine works on ACh receptors› can artificially stimulate skeletal muscles, leading
to slight trembling movements
Dopamine
• Involved in movement, attention, and learning
• Dopamine imbalance also involved in schizophrenia
• Parkinson’s disease is caused by a loss of dopamine-producing neurons
Parkinson’s Disease
Results from loss of dopamine-producing neurons in the substantia nigra
Symptoms include› difficulty starting and stopping voluntary
movements› tremors at rest› stooped posture› rigidity› poor balance
Serotonin
• Involved in sleep• Involved in depression
› Prozac works by keeping serotonin in the synapse longer, giving it more time to exert an effect
GABA
• Causes inhibitory message to other neurons to help balance and offset excitatory messages.
• Found in brain• Too much impairs learning, motivation and
movement• Too little can lead to seizures• Alcohol makes people feel relaxed partly
because GABA is increased– reduces brain activity.
• Valium and Xanax increase GABA, which inhibits action potentials.
Endorphins
• Control pain and pleasure• Released in response to pain• Morphine and codeine work on
endorphin receptors• Runner’s high— feeling of pleasure
after a long run is due to heavy endorphin release
Drugs and Synaptic Transmission
Drugs increase or decrease the amount of neurotransmitters released.
Can block the reuptake of neurotransmitters.› Antidepressants SSRIs: Selective serotonin
reuptake inhibitors. Prozac, Zoloft, Paxil Drugs inhibit the reuptake of serotonin in certain
neurons. Increases the availability of serotonin in the brain.
› Cocaine interferes with the reuptake of dopamine.
Drugs and Receptors
Some drugs are shaped like neurotransmitters and mimic them.
Antagonists: fit the receptor and block the NT› Naloxone block opioid
receptor sites. Use for heroin overdose
Agonists: fit receptor well and act like the NT› Nicotine similar to
acetylcholine
Parts of the Nervous System
Central nervous system (CNS)› Brain and spinal
cord Peripheral nervous
system (PNS)› Carries messages
to and from CNS
Endocrine System• System of glands located throughout the body
that secrete hormones into the bloodstream• Hormones: Stimulate growth and different
reactions, such as activity levels and mood.› Have specific receptor sites just like
neurotransmitters.• Hypothalamus: Structure of the brain that
regulates the release of hormones from the pituitary gland.
Endocrine System
• Pituitary gland—attached to the base of the brain, secretes hormones that affect the function of other glands
• Adrenal glands—hormones involved in human stress response• Adrenal Cortex: outer portion of the adrenal glands;
secrete hormones that interact with the immune system.
• Adrenal Medulla: inner portion of the adrenal glands; secretes epinephrine and norepinephrine.
• Gonads (sex organs)—hormones regulate sexual characteristics and reproductive processes; testes in males, ovaries in females
Plasticity and Neurogenesis
Neuroplasticity: the brains ability to change function and structure.
Functional Plasticity: Brain’s ability to shift functions from damaged to undamaged brain areas.› Stroke victims relearn speaking, walking, or
reading. Undamaged areas assume the ability to process
and execute tasks. Structural Plasticity: Brain’s ability to change
its physical structure in response to learning, active practice, or environmental influence.
Neurogenesis
Development of new neurons. Stress, exercise, environment and
social status all affect the rate of neurogenesis.
New neurons are incorporated into the existing neural networks in the brain.
Brainstem
Region of the brain made up of the hindbrain and the midbrain.
Hindbrain: Region at the base of the brain that contains several structures that regulate basic life functions.
Hindbrain The Hindbrain:
› Made up of the Medulla, Pons, and the Cerebellum.
› Medulla: Involved in vital functions such as heart rate, blood pressure and breathing.
› Pons: connects the medulla to the two side of the cerebellum. Regulates body movement,
attention, sleep and alertness.› Cerebellum: two-sided structure at
the back of the brain. Involved in balance and
coordination.› Reticular Formation: nerve fibers
located in the center of the medulla that helps regulate attention, arousal, and sleep (reticular activating system)
Midbrain Located between the
hindbrain and the forebrain. Involved in vision and
hearing.› EX: eye movement
Substantia Nigra: motor control and contains a large concentration of dopamine-producing neurons.
Reticular activating system.› Important for attention,
sleep, and arousal.› Begins in the hindbrain and
rises through the midbrain into the lower part of the forebrain.
› Some drugs, such as alcohol reduce its activity.
Forebrain
Four key areas of the forebrain.› Thalamus› Hypothalamus› Limbic System› Cerebral
Cortex
Cerebral Cortex
Wrinkled outer portion of the forebrain, which contains the most sophisticated brain centers.› Composed of glial cells and neuron cell bodies and
axons- gives it a grayish color (gray matter) and white myelinated axons (white matter).
Cerebral Hemispheres: Nearly symmetrical left and right halves of the cerebral cortex.
Corpus Callosum: thick band of axons that connects the two cerebral hemispheres and acts as a communication link between them.
Lobes of the Cortex
• Frontal lobe—largest lobe, produces voluntary muscle movements; involved in thinking, planning, and emotional control
• Temporal lobe—primary receiving area for auditory information
• Occipital lobe—primary receiving area for visual information
• Parietal lobe—processes somatic information
Limbic System
Forms a fringe along the inner edge of the cerebrum.
Involved in learning and memory, emotion, hunger, sex, and aggression.
If damaged people can recall old memories, but cannot create new ones.
Damage can also make people act aggressively or passive.
The Limbic System
Hippocampus: Curved forebrain structure that is part of the limbic system and is involved in learning and forming new memories.
Amygdala: almond shaped cluster of neurons in the brain’s temporal lobe.› Involved in memory and emotional
response; especially fear.
Thalamus
Latin meaning “inner chamber”
Serves as a relay station for sensory stimulation.
Transmits sensory information to the parts of the brain that respond and interpret the information.
Relays sensory input from the eyes and the ears to the appropriate parts of the brain.
Hypothalamus
Contains nuclei involved in a variety of behaviors› sexual behavior› hunger and thirst› sleep› water and salt
balance› body temperature
regulation› circadian rhythms› role in hormone
secretion
Cortical Specialization
• Localization—notion that different functions are located in different areas of the brain
• Lateralization—notion that different functions are processed primarily on one side of the brain or the other
Language and the Brain
• Aphasia—partial or complete inability to articulate ideas or understand language because of brain injury or damage
• Broca’s area—plays role in speech production
• Wernicke’s area—plays role in understanding and meaningful speech
Cutting the Corpus Callosum
Split-brain operation: surgical procedure that involves cutting the corpus callosum.› Used to stop or reduce recurring seizures.› Contains seizures to one hemisphere.