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Neuronal Communication: The Structure and Function of Neurons

Explore the biology of neurons and how they communicate with each other. Learn about the structure of a neuron, action potentials, synaptic communication, neurotransmitters, and the different parts of the nervous system. Discover how the brain and spinal cord work together to process information and control the body.

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Neuronal Communication: The Structure and Function of Neurons

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  1. Chapter 2 The Biology of Mind

  2. Neurons and Neuronal Communication:The Structure of a Neuron There are billions of neurons (nerve cells) throughout the body.

  3. Action potential:a neural impulse that travels down an axon like a wave Just as “the wave” can flow to the right in a stadium even though the people only move up and down, a wave moves down an axon although it is only made up of ion exchanges moving in and out.

  4. How neurons communicate (with each other): When does the cell send the action potential?... when it reaches a threshold The neuron receives signals from other neurons; some are telling it to fire and some are telling it not to fire. • When the threshold is reached, the action potential starts moving. • Like a gun, it either fires or it doesn’t; more stimulation does nothing. • This is known as the “all-or-none” response. The action potential travels down the axon from the cell body to the terminal branches. The signal is transmitted to another cell. However, the message must find a way to cross a gap between cells. This gap is also called the synapse. The threshold is reached when excitatory (“Fire!”) signals outweigh the inhibitory (“Don’t fire!”) signals by a certain amount.

  5. The Synapse The synapse is a junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. The synapse is also known as the “synaptic junction” or “synaptic gap.”

  6. Reuptake:Recycling Neurotransmitters [NTs] Reuptake: After the neurotransmitters stimulate the receptors on the receiving neuron, the chemicals are taken back up into the sending neuron to be used again.

  7. Neural Communication:

  8. Roles of Different Neurotransmitters

  9. Dopamine pathways Serotonin pathways Networks of neurons that communicate with dopamine are involved in focusing attention and controlling movement. Networks of neurons that communicate with serotonin help regulate mood.

  10. Hearing the messageHow Neurotransmitters Activate Receptors When the key fits, the site is opened.

  11. Keys that almost fit:Agonist and AntagonistMolecules An antagonist molecule fills the lock so that the neurotransmitter cannot get in and activate the receptor site. An agonistmolecule fills the receptor site and activates it, acting like the neurotransmitter.

  12. The Inner and Outer Parts of the Nervous System The central nervous system [CNS] consists of the brain and spinal cord. The CNS makes decisions for the body. The peripheral nervous system [PNS] consists of ‘the rest’ of the nervous system. The PNS gathers and sends information to and from the rest of the body.

  13. Types of Neurons Sensory neurons carry messages IN from the body’s tissues and sensory receptors to the CNS for processing. Interneurons(in the brain and spinal cord) process information between the sensory input and motor output. Motor neurons carry instructions OUT from the CNS out to the body’s tissues.

  14. The “Nerves” are not the same as neurons. Nerves consist of neural “cables” containing many axons. Nerves are part of the peripheral nervous system and connect muscles, glands, and sense organs to the central nervous system.

  15. The Central Nervous System • The brain is a web of neural networks. • The spinal cord is full of interneurons that sometimes have a “mind of their own.”

  16. Neural Networks These complex webs of interconnected neurons form with experience. Remember: “Neurons that fire together, wire together.”

  17. More Parts of the Nervous System

  18. The Peripheral Nervous System

  19. The AutonomicNervous System: The sympathetic NS arouses(fight-or-flight)The parasympatheticNS calms(rest and digest)

  20. The Endocrine System (The “Master Gland”) The endocrine system refers to a set of glands that produce chemical messengers called hormones.

  21. Studying cases of brain damage When a stroke or injury damages part of the brain, we have a chance to see the impact on the mind.

  22. Intentional brain damage: Lesions (surgical destruction of brain tissue) • performed on animals • has yielded some insights, especially about less complex brain structures • no longer necessary, as we now can chemically or magnetically deactivate brain areas to get similar information

  23. Split-Brain Patients • “Split” = surgery in which the connection between the brain hemispheres is cut in order to end severe full-brain seizures • Study of split-brain patients has yielded insights discussed at the end of the chapter

  24. Monitoring activity in the brain Tools to read electrical, metabolic, and magnetic activity in the brain: EEG: electroencephalogram PET: positron emission tomography MRI: magnetic resonance imaging fMRI: functional MRI

  25. EEG: electroencephalogram An EEG (electroencephalogram) is a recording of the electrical waves sweeping across the brain’s surface. An EEG is useful in studying seizures and sleep.

  26. PET: positron emission tomography The PET scan allows us to see what part of the brain is active by tracing where a radioactive form of glucose goes while the brain performs a given task.

  27. MRI: magnetic resonance imaging MRI (magnetic resonance imaging) makes images from signals produced by brain tissue after magnets align the spin of atoms. The arrows below show ventricular enlargement in a schizophrenic patient (right).

  28. Functional Magnetic Imaging Functional MRI reveals brain activity via changes in oxygenated blood flow. This fMRI scan shows increased activity in the visual cortex when a person looks at a photograph.

  29. The Brainstem: Pons and Medulla

  30. The Thalamus (“Inner Chamber”) • The thalamus is the “sensory switchboard” or “router.” • All sensory messages, except smell, are routed through the thalamus on the way to the cortex (higher, outer brain). • The thalamus also sends messages from the cortex to the medulla and cerebellum.

  31. Reticular (“Netlike”) Formation • The reticular formation is a nerve network in the brainstem. • It enables alertness, (arousal) from coma to wide awake. • It also filters incoming sensory information.

  32. Cerebellum (“little brain”) The cerebellum helps coordinate voluntary movement such as playing a sport. The cerebellum has many other functions, including enabling nonverbal learning and memory.

  33. The Limbic (“Border”) System The limbic system coordinates: • emotions such as fear and aggression. • the formation of episodic memories. The hippocampus (“seahorse”) • processes conscious, episodic memories. • works with the amygdala to form emotionally charged memories. The Amygdala (“almond”) • consists of two lima bean- sized neural clusters. • helps process emotions, especially fear and aggression.

  34. The Hypothalamus: Thalamus • lies below (“hypo”) the thalamus. • regulates body temperature and ensures adequate food and water intake (homeostasis), and is involved in sex drive. • directs the endocrine system via messages to the pituitary gland. The Hypothalamus as a Reward Center Riddle: Why did the rat cross the grid? Why did the rat want to get to the other side? Pushing the pedal that stimulated the electrode placed in the hypothalamus was much more rewarding than food pellets.

  35. Review of Brain Structures

  36. The Cerebral Cortex The lobes consist of: • outer grey “bark” structure that is wrinkled in order to create more surface area for 20+ billion neurons. • inner white stuff—axonslinking parts of the brain. • 180+ billion glial cells, which feed and protect neurons and assist neural transmission. 300 billion synaptic connections The brain has left and right hemispheres

  37. The Lobes of the Cerebral Cortex: Preview involved in speaking and muscle movements and in making plans and judgments • Frontal Lobes • Parietal Lobes • Occipital Lobes • Temporal Lobes include the sensory cortex • include the visual areas; they receive visual information from the opposite visual field • include the auditory processing areas

  38. Functions of the Brain: The Motor and Sensory Strips Output: Motor cortex (Left hemisphere section controls the body’s right side) Input: Sensory cortex (Left hemisphere section receives input from the body’s right side)  Axons receiving motor signals FROM the cortex Axons sending sensory information TO the cortex

  39. Using our knowledge of functions: Brain-computer interfaces and neural prosthetics • Here, a robotic arm is operated through controls embedded in the motor strip of the cortex. • We may soon be able to use computers to translate neural inputs into more commands and words than simply grabbing food.

  40. Association function of the cortex More complex animals have more cortical space devoted to integrating/associating information

  41. Frontal Lobes • The frontal lobes are active in “executive functions” such as judgment, planning, and inhibition of impulses. • The frontal lobes are also active in the use of working memory and the processing of new memories.

  42. Parietal Lobe Association Areas This part of the brain has many functions in the association areas behind the sensory strip: • managing input from multiple senses • performing spatial and mathematical reasoning • monitoring the sensation of movement

  43. Temporal Lobe Association Areas Some abilities managed by association areas in this “by the temples” lobe: • recognizing specific faces • managing sensory input related to sound, which helps the understanding of spoken words

  44. Plasticity: The Brain is Flexible If the brain is damaged, especially in the general association areas of the cortex: • the brain does not repair damaged neurons, BUT it can restore some functions • it can form new connections, reassign existing networks, and insert new neurons, some grown from stem cells This 6-year-old had a hemispherectomy to end life-threatening seizures; her remaining hemisphere compensated for the damage.

  45. The intact but lateralized brainRight-Left Hemisphere Differences Right Hemisphere Left Hemisphere Thoughts and logic Details such as “trees” Language: words and definitions Linear and literal Calculation Pieces and details Feelings and intuition Big picture such as “forest” Language: tone, inflection, context Inferences and associations Perception Wholes, including the self

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