 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

 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

 Contains the cell’s nucleus › round, centrally located structure › contains DNA › controls protein manufacturing › directs metabolism › no role in neural signaling

Information collectors Receive inputs from neighboring neurons Inputs may number in thousands If enough inputs, the cell’s AXON may generate an output

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

The cell’s output structure One axon per cell, 2 distinct parts › tubelike structure › branches at end that connect to dendrites of other cells

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

 Support cells that assist neurons by providing structural support, nutrition, and removal of cell wastes, manufacture myelin.

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.

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.

 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.

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

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.

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

Repolarization leads to a voltage below the resting potential, called hyperpolarization Now, neuron cannot produce a new action potential This is the refractory period

 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.

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.

 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.

 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 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

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

Involved in movement, attention, and learning Dopamine imbalance also involved in schizophrenia Parkinson’s disease is caused by a loss of dopamine-producing neurons

 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

Involved in sleep Involved in depression › Prozac works by keeping serotonin in the synapse longer, giving it more time to exert an effect

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.

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 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.

 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

 Central nervous system (CNS) › Brain and spinal cord  Peripheral nervous system (PNS) › Carries messages to and from CNS

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.

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

 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.

 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.

 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.

 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)

 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.

 Four key areas of the forebrain. › Thalamus › Hypothalamus › Limbic System › 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.

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

 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.

 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.

 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.

 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

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

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

 Split-brain operation: surgical procedure that involves cutting the corpus callosum. › Used to stop or reduce recurring seizures. › Contains seizures to one hemisphere.