Nervous System

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My AP Biology Thoughts

Unit 4 Cell Communication and Cell Cycle

Welcome to My AP Biology Thoughts podcast, my name is Saarim Rizavi and I am your host for episode # 83 called Unit 4 Cell Communication and Cell Cycle: The Nervous System. Today I will be discussing everything there is to know about the Nervous System. I’ll start off by giving a brief introduction into what the nervous system exactly is, the parts of the nervous system, what these parts themselves consist of, and the function of these parts. I will then get into how the nervous system develops as one grows older and the many life-debilitating and common diseases of the nervous system. I will finally place the nervous system into the broader topic of cell communication and the cell cycle by talking about the cells of the nervous system, the cell signaling pathway of the nervous system, and basically how neurons communicate with one another. So, basically, I’ll be talking about how the nervous system actually works. I actually want to study neuroscience in the future which is focused on the brain and its impact on behavior and our functions and the main focus of the field is how the brain sends messages throughout your body through the nervous system. So I’m happy to be talking about this topic and I hope you guys find it interesting too. Before I begin, I would like to give credit to some of the websites and resources that were used to create this podcast. These include, lumen learning, mayoclinic, the National Institute of Health, News-Medical.net, livescience.com, and Khan Academy.

Segment 1: Introduction to The Nervous System

  • What is the nervous system?
  • A complex network of nerves and cells that carry messages to and from the brain and spinal cord to different parts of the body
  • The main controlling, regulatory, and communicating system in the body and is known to be the most complex and highly organized body system
  • The center of all mental activity including thought, learning, and memory.
  • Responsible for maintaining and regulating homeostasis
  • Allows us to interact and understand our environment and surroundings, internally and externally
  • Has 2 main parts, the central nervous system and the peripheral nervous system
  • The Central Nervous System
  • Made up of the brain, spinal cord, and neurons
  • The brain controls many of the body’s functions including sensation, thought, movement, awareness, and memory
  • The surface of the brain is the cerebral cortex - associated with perception, memory, association, thought, and voluntary physical action
  • The largest part of the brain is the cerebrum - responsible for things such as memory, speech, voluntary behaviors, and thought.
  • The cerebrum is divided into the right and left hemispheres
  • The right hemisphere controls movements on the body’s left side, while the left hemisphere controls movements on the body’s right side
  • The hemispheres are divided into the frontal lobe, the occipital lobes, the parietal lobes, and the temporal lobes
  • The spinal cord connects to the brain via the brain stem and runs down through the spinal canal, located inside the vertebra.
  • The spinal cord carries information from various parts of the body to and from the brain and in the case of some reflex movements, responses are controlled by spinal pathways only
  • Neurons are the building blocks of the central nervous system.
  • Billions of these neurons can be found throughout the body and communicate with one another to produce physical responses and actions.
  • The Peripheral Nervous System
  • Made up of nerves that branch off from the spinal cord and extend to every part of the body
  • Main role of the peripheral nervous system is to connect the central nervous system to the organs, limbs, and skin
  • Nerves extend from the central nervous system to the outermost areas of the body
  • The peripheral nervous system allows the brain and spinal cord to receive and send information to other areas of the body, which then allows us to react to stimuli in our environment
  • Divided into the somatic nervous system and the autonomic nervous system
  • The somatic nervous system - responsible for carrying sensory and motor information to and from the central nervous system
  • Contains motor neurons, which carry info from the brain and spinal cord to muscle fibers throughout the body, and sensory neurons, which carry info from the nerves to the central nervous system
  • The autonomic nervous system - responsible for regulating involuntary body functions
  • It is divided into the parasympathetic nervous system and the sympathetic nervous system
  • The parasympathetic system helps control bodily functions when a person is at rest - digestion, metabolism, and just helping the body relax
  • The sympathetic nervous system prepares the body to expend energy to respond to environmental threats by regulating the flight-or-fight response
  • 3 parts of neuron - cell body, dendrites, axons
  • Glial cells - non-neuron cells that perform many important functions that keep the nervous system working such as supporting and holding neurons in place, regulating neurotransmitters, creating insulation called myelin which helps move nerve impulses, and more

Segment 2: More About The Nervous System

  • How the nervous system develops over time:
  • After the fetus is conceived, it takes around 3-4 weeks before one of the two cell layers of the human embryo begins to thicken and build up along the middle
  • The cells grow and form a flat area called the neural plate which has parallel ridges across its surface; these ridges fold in toward each other and fuse to form the hollow neural tube
  • The tube thickens at the top and forms three bulges that form the hindbrain, midbrain, and forebrain
  • The embryo has 3 layers that undergo many changes to form organs, bone, muscle, skin, and neural tissue
  • The skin and neural tissue arise from one of the layers called the ectoderm
  • Once the ectoderm starts becoming neural tissues due to specific signals, increased signaling interactions determine which type of brain cell forms - some form the neurons while others form the glial cells
  • The neurons, which are immature at this time, migrate and start making transient connections with other neurons before reaching their destinations - and they reach their destinations through using glial fibers and contractile proteins.
  • Neurons generally move from the central canal in the neural tube to the brain where they collect together and connect and form various brain structures.
  • The neurons move from the neural tube’s ventricular zone, or inner surface, to near the border of the marginal zone, which is the outer surface.
  • Once they stop dividing, they form an intermediate zone where they gradually accumulate as the brain develops.
  • Once the neurons reach their final locations, they must make proper connections for particular functions to occur.
  • Diseases of the nervous system (neurological disorders)
  • WHO: there is ample evidence that neurological disorders are one of the greatest threats to public health - nearly 1 in 6 of the world’s population, or 1 billion people, suffer from neurological disorders
  • 0.01 neurologists per 100,000 people in low income areas where these diseases are most prominent
  • Alzheimer’s disease
  • A progressive neurological disorder that causes the brain to shrink and brain cells to die
  • It is the most common cause of dementia, which is a continuous decline in thinking, behavioral and social skills, and a decline in the overall ability of a person to function independently
  • The causes of Alzheimer’s aren’t fully understood but at a basic level, brain proteins fail to function normally, which disrupts the work of neurons and triggers a series of toxic events in which neurons are damaged and lose connections to each other and eventually die
  • Scientists believe that for most, Alzheimer’s is caused by a combination of genetic, lifestyle, and environmental factors that affect the brain over time.
  • Parkinson’s disease
  • A brain disorder that leads to shaking, stiffness, and difficulty with walking, balance, and coordination
  • As the disease progresses, people may have trouble walking and talking; could also have mental and behavioral changes, sleep problems, depression, memory difficulties, and fatigue
  • The disease occurs when neurons in an area of the brain that controls movement become impaired and die - these neurons would have produced dopamine, an important brain chemical messenger that’s involved in reward, motivation, memory, attention, and the regulation of body movements
  • When these neurons die, less dopamine is produced which causes the movement problems seen in Parkinsons
  • Scientists still don’t understand what causes cells that produce dopamine to die
  • People with Parkinson’s lose the nerve endings that produce norepinephrine, the main chemical messenger of the sympathetic nervous system - the loss of norepinephrine may explain some of the non-movement features of Parkinson’s like fatigue, irregular blood pressure, and decreased movement of food through the digestive tract.
  • Epilepsy
  • Epilepsy is a neurological disorder in which brain activity becomes abnormal, causing seizures or periods of unusual behavior, sensations, and loss of awareness
  • Some people with epilepsy just stare blankly for a few seconds during a seizure, while others twitch their arms or legs repeatedly
  • At least 2 unprovoked seizures are required for an epilepsy diagnosis
  • Epilepsy has no identifiable causes in about half the people with the condition; in the other half, the condition may be traced to a variety of factors including genetic influence, head trauma, brain conditions, like brain tumors or strokes, infectious diseases, like meningitis and AIDS, prenatal injury, and developmental disorders, like autism.

Segment 3: Connection to the Course

  • Parts of a neuron
  • Cell body (soma) - contains a nucleus, smooth/rough ER, a golgi apparatus, mitochondria, and other cellular components
  • Dendrites - branch-like structures extending away from the cell body; their job is to receive messages from other neurons and allow those messages to travel to the cell body
  • Axons - tube-like structures that carry electrical impulses from the cell body or from another cell’s dendrites to the structures at the opposite end of the neuron, known as an axon terminal, which can then pass the impulse to another neuron
  • Synapses - chemical junctions between the axon terminals of one neuron and the dendrites of another; a space between two neurons where they can pass messages to communicate
  • Cell signaling/cellular communication in the nervous system
  • Neurons exist in a fluid environment - they are surrounded by extracellular fluid and contain intracellular fluid - the neuronal membrane keeps these two fluids separate which is important because the electrical signal that passes through the neuron develops on these intracellular and extracellular fluids being electrically different
  • This difference in charge across the membrane, called the membrane potential, provides energy for the signal
  • The electrical charge of the fluids is caused by ions dissolved in the fluid
  • The semipermeable nature of the neuronal membrane somewhat restricts the movement of these charged molecules - some of the charged particles tend to become more concentrated either inside or outside the cell
  • Between signals, the neuron’s membrane potential is in a state of readiness known as the resting potential.
  • In this state, ions are lined up on either side of the cell membrane, ready to rush across the membrane when the neuron goes active and the membrane opens its gates (sodium-potassium pump that allows the movement of ions across the membrane)
  • In the resting state, sodium ions are at a higher concentration outside the cell so they will tend to move into the cell while potassium ions are more concentrated inside the cell and so will move out of the cell
  • The inside of the cell is slightly more negatively charged compared to the outside of the cell in the resting state and so this also causes sodium to move into the cell
  • From this resting potential state, the neuron receives a signal at the dendrites, in the form of a chemical messenger known as a neurotransmitter binding to its receptors - as a result, small pores open on the neuronal membrane, allowing sodium ions to move into the cell - causes the internal charge of the cell to become more positive - the charge reaches a certain level called the threshold of excitation and then the neuron becomes active and the action potential begins
  • Many additional pores open, causing a massive influx of sodium ions and a positive spike in the membrane potential, known as the peak action potential.
  • At this peak, the sodium gates close and the potassium gates open and potassium ions leave the cell - this results in the neuron’s membrane returning to its resting state
  • The action potential is an electrical signal that moves from the cell body down the axon to the axon terminals - the action potential is propagated at its full strength at every point along the axon...

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