Nervous System Pt.1/ CH 7 Flashcards
Biology
What is the nervous system made up of?
made up of organs and structures that are composed of nervous tissues
What are the major functions of the nervous system?
- receiving external and internal stimuli (things that can trigger a response or reaction in an organism)
- transmitting electrochemical signals (action potentials)
- Integrating (combination/brought together) these electrochemical signals
- coordinating body functions
What are the nervous systems divisions for?
to categorize and understand the nervous system in different ways
What are the two different kinds of nervous system divisions?
- anatomical divisions
- functional division
Anatomical Division
- Central Nervous System (CNS): consists of brain and spinal cord
- Peripheral Nervous System: includes all the nervous tissue outside the brain and spinal cord
Functional Division
- Somatic Nervous System: innervates voluntary movements and innervates organs that we can consciously control, like the skeletal muscles
- Autonomic Nervous System: innervates involuntary functions and innervates organs you can’t consciously control, like the heart and digestive system
- Parasympathetic: associated with the “rest and digest” response, promoting relaxation and digestion
- Sympathetic: associated with the “fight or flight” response, preparing the body for intense physical activity or dealing with stress
What are neurons?
- functional unit of the nervous system
- responsible for synthesizing and transmitting electrochemical signals
What are the different parts of neurons?
- dendrites: receiving signals/stimuli from other neurons or sensory receptors
- soma: (cell body) carries out general cellular functions
- axon hillock: where the action potential is generated
- axon: transmits action potentials to other neurons or target cells
- axon terminals: transmit and amplify action potentials to communication with other neurons or muscles
morphological classification of neurons
- neurons can be classified based on the # of cellular projections they have:
1. Pseudounipolar neurons: have a short, singular projection
2. Bipolar neurons: have 2 projections (dendrite and axon)
3. Multipolar neurons: have multiple dendrites and a single axon
4. Anaxonic neurons: have multiple projections, but no distinct axon
Functional classification of neurons
Sensory (afferent) neurons: specialized to detect & respond to different types of sensory information (touch, smell, temperature)
Motor (efferent) neurons: relay motor signals from the central nervous system (CNS) to effectors, such as muscles or glands
- motor neurons can be further divided into somatic and autonomic neurons
- autonomic neurons are responsible for regulating involuntary bodily functions and can be further divided into parasympathetic and sympathetic divisions
Interneurons: responsible for integration within the nervous system. play a role in:
- regulating motor activity in response to sensory signals
- establishing complex networks that facilitate higher processing function like thought and memory
- interneurons are morphologically diverse, meaning they come in different shapes and forms
What do glial cells do?
fulfill various supporting roles in the nervous system, both in the central nervous system (CNS) and the peripheral nervous system (PNS)
What are the different kinds of glial cells and their functions ?
- Astrocytes: regulated the content of extracellular fluid and provide support to CNS neurons
- Satellite cells: control the content of extracellular fluid and support PNS neurons
- Ependymal cells: line the ventricles of the brain and the central canal of the spinal cord
- Microglia: play a role in immunity as phagocytes, helping to protect the nervous system
- Oligodendrocytes: produce the myelin sheath in the CNS, which helps with conduction of nerve impulses
- Schwann Cells: produce the myelin sheath in the PNS, also assisting with the conduction of nerve impulses
What roles do astrocytes have in the nervous system?
Protective and Regulatory roles in the nervous system
What is the astrocytes protective role in the nervous system?
- help form the blood-brain barrier, which protects the brain from harmful substances
- aid in the formation and maintenance of synapses (the connections between neurons)
- contribute to neurogenesis (the generation of new neurons)
What is the astrocytes regulation role in the nervous system?
- regulate the balance of excitatory and inhibitory action potentials by converting the neurotransmitter glutamate to glutamine
- control the concentration of neurotransmitters, potassium ions (K+), and the calcium (Ca2+)
- metabolize glucose into lactic acid and lactate to provide energy for neurons
What is myelin?
a substance that supports the conductivity of signals on the nervous system
How does myelin support the conductivity of signals on the NS?
it does this by maintaining the membrane potential in specific segments of the axon
- saxons can either be myelinated or unmyelinated, and the diameter of the axon is what differentiates them
What is nodes of randvier?
the unmyelinated portions of the axon that play a role in inducing changes in the membrane potential
In the peripheral nervous system, myelination is carried out by what?
schwann cells
Myelination in the PNS by Schwann cells:
- Neurilemma: layer of schwann cells that covers both myelinated and unmyelinated axons in the PNS
- myelin sheath: an insulating layer, that’s formed by multiple layers of the Schwann cell plasma membrane
- multiple schwann cells work together to cover or “envelop” different segments of the axon
In the central nervous system, myelination is carried out by what?
carried out by oligodendrocytes cells (oligodendrocytes form myelin sheath)
Myelination in the CNS by Oligodendrocytes cells:
- myelin sheath: an insulating layer made up of multiple layers of their plasma membrane
- one oligodendrocytes can myelinate multiple axons, unlike in the peripheral nervous system where each schwann cell myelinates a single axon
What is gray matter?
in CNS, unmyelinated soma and dendrites make up the gray matter
What is white matter?
myelinated axons form the white matter
What is transmembrane potentials?
refer to the difference in the concentration of charged molecules across a membrane
What is the resting membrane potential?
typically around -70mV, indicating a negative charge inside the cell compared to the outside
What does the Voltage determine?
determines the magnitude of this difference across the membrane
What are ways the membrane permeability can affect the membrane potential?
- Depolarization: there is a surge of positive ions, which can lead to a change in the membrane potential
- Repolarization: occurs when positive ions are released, bringing the membrane potential back to its resting state (negative)
- Hyperpolarization: involves a surge of negative ions, further increasing the difference in charge across the membrane
What is membrane permeability?
- How easily substances, such as ions, can pass through the cell membrane
- they send signals by changing the voltage across their cell membranes
How is membrane permeability achieved?
through the regulation of the influx (entry) and efflux (exit) of sodium ions (Na+) and potassium ions (K+) through specialized channels called voltage-gated ion channels
What are transmembrane potentials?
are all about the voltage across a neuron’s cell membrane
What are the different kinds of transmembrane potentials?
- Depolarization: this is when sodium ions (Na+) rush into the neuron, making the inside less negative and closer to zero millivolts (mV). the cell is getting ready to fire off a signal.
- Overshoot: if the Na+ keeps coming in, the inside of the cell gets even more positive, going past zero mV
- Repolarization: now, potassium ions (K+) start to leave the cell, which makes the inside less positive and moves the voltage back down towards the resting state of around -70mV
- Hyperpolarization: sometimes, too much K+ leaves the cell, making the inside even more negative than the resting potential of -70mV. Its like the cell is overshooting on its way back to rest
What’s the first propagation of action potentials?
- resting membrane potential: this is the initial state of the cell membrane, where the inside is negatively charged compared to the outside
What’s the second propagation of action potentials?
- when an inital signal reaches the membrane, it causes depolarization, which means the inside of the cell becomes less negative and more positive
What’s the third propagation of action potentials?
- as a result of depolarization, voltage-gates sodium (Na+) channels open first, allowing sodium ions to enter the cell. the further contributions to depolarization and helps propagate the action potential along the cell membrane
What’s the fourth propagation of action potentials?
- after the sodium channels open and sodium ions enter the cell, the next step is the opening of voltage-gated potassium (K+) channels. this allows potassium ions to leave the cell, leading to repolarization
What’s the fifth propagation of action potentials?
- as potassium ions leave the cell, the inside becomes more negative (less positive) and moves closer to the resting membrane potential (RMP) of around -70mV
What’s the sixth propagation of action potentials?
- this brings the cell back to its original state, completing the action potential
What’s the seventh propagation of action potentials?
- when an action potential occurs in one section of a neuron, the sodium ions (Na+) from that region will diffuse to the next region and start an action potential there. this allows the action potential to propagate along the entire length of the neuron
What’s the eighth propagation of action potentials?
- the concept of “all-or-none” means that if the axon hillock, which is the initial part of the neuron, reaches a threshold of -55mV, the action potential will always spread down the entire axon to the terminal
