Neuroscience and Behavior Chapter 2 Neuroscience and Behavior

Neurons and Synapses Types of Neurons Sensory Motor Interneurons Key words: Types of neurons; sensory neurons; motor neurons; interneurons; afferent nerves; efferent nerves

Sensory Neurons INPUT From sensory organs to the brain and spinal cord Drawing shows a somatic neuron Sensory Neuron Spinal Cord Key words: sensory neurons; afferent nerves; types of neurons Graphic from Hockenbury slides

Motor Neurons OUTPUT From the brain and spinal cord to the muscles and glands Spinal Cord Brain Sensory Neuron Motor Key words: Motor neurons; efferent nerves; types of neurons Graphic from Hockenbury slides

Interneurons Interneurons carry information between other neurons only found in the brain and spinal cord Spinal Cord Brain Sensory Neuron Motor Key words: interneurons; types of neurons Graphic from Hockenbury slides

Parts of a Neuron Key words: Neuron; structures of neurons Graphic From Image and lecture gallery

The Cell Body Contains the cell’s nucleus round, centrally located structure contains DNA controls protein manufacturing directs metabolism no role in neural signaling Graphic from Hockenbury slides Key words: Cell body; soma; cell nucleus Interesting facts: The DNA in the nucleus of the cell has lost its ability to divide. therefore, when a neuron dies,for the most part, the adult brain cannot simply grow new neurons. (Note there are a few exceptions to this rule.) The relative inability to grow new neurons leads to two interesting questions: Q1: How do brain tumors (cancer) occur? A: Unlike neurons, glial cells can divide and grow new cells throughout one's lifetime. Most brain tumors are limited to glial cells, not neurons. Q2: If a person cannot grow new neurons, how does the brain change in order to accommodate new learning? A: One mechanism by which the brain adapts to help you learn new information involves the structure on the next slide: the dendrites.

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 tube-like structure branches at end that connect to dendrites of other cells Hockenbury slides (Schulman) Key words: axon; action potentials Interesting facts: - The diameter of an axon may vary from approximately 1mm-20mm. - An axon may travel long distances to reach it's destination (longest axon is approximately 3 feet in humans and 10 feet in giraffes).

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 Graphic from Hockenbury slides Key words: myelin sheath; action potentials; axon Interesting facts: - The myelin sheath is NOT a part of the axon. The myelin sheath is actually formed of glial cells (oligodendricytes and Schwann cells) that wrap around the axon. - You may have often heard the brain referred to as either white matter or gray matter. The myelin sheath appears white in nature. Hence, the term white matter refers to areas of the brain that are myelinated. Gray matter refers to areas of the brain that are unmyelinated. - When you accidentally cut yourself, you often visually notice that you've cut yourself before you actually feel any pain from the cut. The reason for this is that visual information uses myelinated axons; whereas, pain information uses unmyelinated axons. - The loss of myelin is a significant factor in the disease multiple sclerosis (MS). When myelin is lost, the high-speed transmission of information is slowed down or blocked completely, which could lead the person with the inability to walk, write or speak.

How Neurons Communicate Neurons communicate by means of an electrical signal called the action potential. Action potentials are based on movements of ions between the outside and inside of the cell. When an action potential occurs, a molecular message is sent to neighboring neurons.

Action Potential Within a Neuron

Resting Potential Graphic, Hockenbury slides At rest, the inside of the cell is at -70 microvolts. With inputs to dendrites, the inside becomes more positive. If resting potential rises above threshold, an action potential starts to travel from cell body down the axon. Figure shows resting axon being approached by an AP.

Depolarization Ahead of AP Graphic from Hockenbury slides AP opens cell membrane to allow sodium (Na+) to enter. Inside of cell rapidly becomes more positive than outside. This depolarization travels down the axon as leading edge of the AP.

Repolarization follows Graphic from Hockenbury slides After depolarization, potassium (K+) moves out restoring the inside to a negative voltage. This step is called repolarization. The rapid depolarization and repolarization produce a pattern called a spike discharge.

Finally, Hyperpolarization Graphic from Hockenbury slides Repolarization leads to a voltage below the resting potential, called hyperpolarization. Now, the neuron cannot produce a new action potential. This is the refractory period.

Neuron to Neuron Axons branch out and end near dendrites of neighboring cells. Axon terminals are the tips of the axon’s branches. A gap separates the axon terminals from dendrites. The gap is called the synapse. Key words: axon terminal Graphic from Hockenbury slides .

Neurotransmitter Release Action potential causes vesicle to open. Neurotransmitter released into synapse. Neurotransmitter locks onto receptor molecule in postsynaptic membrane.

Excitatory and Inhibitory Messages Excitatory message — increases the likelihood that the postsynaptic neuron will activate Inhibitory message — decreases the likelihood that the postsynaptic neuron will activate.

Locks and Keys Neurotransmitter molecules have specific shapes. Receptor molecules have binding sites. When NT binds to receptor, ions enter. Graphic from Hockenbury slides

Some Drugs Work on Receptors Some drugs are shaped like neurotransmitters. Antagonists: fit the receptor but poorly and block the NT e.g., beta blockers Agonists: fit receptor well and act like the NT e.g., nicotine Graphic from Hockenbury slides

Types of Neurotransmitters Acetylcholine Dopamine Serotonin Norepinephrine GABA Endorphins

Found in neuromuscular junctions Involved in muscle movements Acetylcholine (Ach) Found in neuromuscular junctions Involved in muscle movements Involved in learning and memory Graphic, Hockenbury slides

Disruption 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

Disruptions in ACh Functioning Cigarettes — nicotine works on ACh receptors can artificially stimulate skeletal muscles, leading to slight trembling movements

Alzheimer’s Disease Deterioration of memory, reasoning, and language skills Symptoms may be due to loss of ACh neurons

Dopamine Involved in movement, attention, and learning Dopamine imbalance also involved in schizophrenia Loss of dopamine-producing neurons is cause of Parkinson’s disease

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 key words: Basal ganglia; Parkinson's disease; dopamine

Parkinson’s Disease Treatments L-dopa transplants of fetal dopamine-producing substantia nigra cells adrenal gland transplants electrical stimulation of the thalamus has been used to stop tremors L-Dopa facts: The purpose of this drug is to increase the amount of dopamine in the system. L-dopa is a precursor to dopamine. It will eventually be converted into dopamine. Question: Why not just give the patient dopamine? Answer: Dopamine cannot cross the blood brain barrier. If you take a dopamine pill, you will see increased levels of doapmine in the body, but not in the brain. L-dopa can enter the brain.

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

“Fight or flight” response Norepinephrine Arousal “Fight or flight” response

Endorphins Control pain and pleasure Released in response to pain Morphine and codeine work on endorphin receptors; involved in healing effects of acupuncture Runner’s high— feeling of pleasure after a long run is due to heavy endorphin release

GABA Inhibition of brain activity Huntington’s disease involves loss of neurons in striatum that utilize GABA Symptoms: jerky involuntary movements mental deterioration

Summary Neuron structure Action potentials Synapse Neurotransmitters Receptors and ions Agonists and antagonists Graphic from Hockenbury p.42 figure 2.2

Parts of the Nervous System Central Nervous System (CNS) Brain and spinal cord Peripheral Nervous System (PNS) Carries messages to and from CNS

Central nervous system Bloom, Nelson, and Lazerson, Brain, Mind, and Behavior Introduction to the Nervous System Figure 1.03 Peripheral nervous system

Discovering PSY p. 55 Figure 2.11

Sympathetic and parasympathetic divisions of the nervous system Kolb & Whishaw, An Introduction to Brain and Behavior How is the Brain Organized? Figure 2.29 Sympathetic and parasympathetic divisions of the nervous system

Endocrine System Pituitary gland — attached to the base of the brain, hormones affect the function of other glands Adrenal glands — hormones involved in human stress response Gonads — hormones regulate sexual characteristics and reproductive processes; testes in males, ovaries in females.

Brain Images Brainstem Forebrain Hindbrain Midbrain Limbic system Cortex Discovering PSY p. 65. Figure 2.16

Developing Brain Neural tube — beginning of nervous system develops at 2 weeks after conception Neurogenesis — development of new neurons

Hindbrain Structures Cerebellum Brainstem medulla reticular formation pons Discovering psy p 63 fig 2.14

Cerebellum Coordinated, rapid voluntary movements e.g., playing the piano, kicking, throwing, etc. Lesions to cerebellum jerky, exaggerated movements difficulty walking loss of balance shaking hands Hockenbury slides

Medulla Breathing Heart rate Digestion Other vital reflexes swallowing coughing vomiting sneezing Gray, 3e fig 5.6

Reticular Formation Network of neurons in the brainstem (and thalamus) Sleep and arousal Attention Myers, Exploring psy 4e Figure 2.10

Pons Helps coordinate movements on left and right sides of the body e.g., postural reflexes which help you maintain balance while standing or moving Gray, 3e fig 5.6

Forebrain Structures Thalamus Limbic System Cortex Bloom, Nelson, and Lazerson, Brain, Mind, and Behavior Introduction to the Nervous System Figure 1.07r

Thalamus Relay station in brain Processes most information to and from higher brain centers Gray, 3e fig 5.6

The Limbic System Hypothalamus Amygdala Hippocampus Discovering Psy p. 67 Fig 2.18

Hypothalamus Contains nuclei involved in a variety of behaviors sexual behavior hunger, thirst sleep water and salt balance body temperature regulation circadian rhythms role in hormone secretion The hypothalamus is made up different subregions or nuclei. These nuclei generally differ in terms of gross anatomy and function. Sexual behavior: The medial preoptic and medial anterior hypothalamic nuclei of the hypothalamus are heavily involved in mating behaviors of animals. Damage to these areas results in a loss of mating behaviors. Electrical stimulation of these areas (or insertion of sex hormones in these areas) can elicit sexual behaviors. Hunger: Lesions to the hypothalamus can lead to severe obesity or extreme weight loss, depending upon the region damaged. Thirst: Electrical stimulation of the hypothalamus can cause an animal to start drinking even in animals that have plenty of water in their systems. Neurons in the supraoptic nucleus of the hyopthalamus are sensitive to changes in the osmolarity of blood. These neurons control the secretion of vasopression, which is more commonly known as "anti-diuretic hormone" or ADH. ADH acts in the kidney to increase fluid retention. Sleep: Temperature regulation: Your body tries to keep the same body temperature regardless of how hot or cold it is outside. The hypothalamus helps maintain a constant body temperature. Hypothalamus contains temperature-sensitive neurons. Neurons in the posterior hypothalamus become active when you are cold; whereas, heat activates the anterior hypothalamus. Changes in body temperature can cause the hypothalumus to initiate such behaviors as shivering, hunger, adrenaline secretion and fever to help you get back to the proper body temperature. Circadian rhythms: the suprachiasmatic nucleus (or SCN) of the hypothalamus is thought to be involved in regulating the body's natural 24 hour rhythms.

Hypothalamus and Hormones Hypothalamus releases hormones or releasing factors which in turn cause pituitary gland to release its hormones Gray, psychology 3e fig 5.27

Amygdala and Emotion Identify emotion from facial expressions Amygdala damage makes this task difficult From Hockenbury slides (click on picture to advance photos)

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

Lobes of the Cortex Frontal lobe — largest lobe, produces voluntary muscle movements, involved in thinking, planning, emotional control Temporal lobe — primary receiving area for auditory information Occipital lobe — primary receiving area for visual information Parietal lobe — processes somatic information

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 Wernike’s area — plays role in plays role in understanding and meaningful speech

Discovering PSY 2e p74 table 2.2

Split brain operation—procedure used to reduces recurrent seizures of severe epilepsy Corpus callosum—thick band of axons that connects the two cerebral hemispheres