Chapter 12 Nervous Tissue Flashcards
What are the three basic functions of the nervous system?
- Sensory (input)
- Integrative (process)
- Motor (output)
These functions allow the nervous system to sense stimuli, process information, and initiate responses.
Define the central nervous system (CNS).
The CNS consists of the brain and spinal cord.
The brain contains about 85 billion neurons, while the spinal cord contains about 100 million neurons.
What is the role of the peripheral nervous system (PNS)?
The PNS consists of all nervous tissue outside the CNS, including nerves and sensory receptors.
The PNS conveys sensory input to the CNS and motor output to effectors.
What are the two main divisions of the PNS?
- Sensory (afferent) division
- Motor (efferent) division
The sensory division conveys input to the CNS, while the motor division conveys output from the CNS.
Contrast the somatic nervous system and autonomic nervous system.
- Somatic nervous system: Voluntary control of skeletal muscles.
- Autonomic nervous system: Involuntary control of smooth muscle, cardiac muscle, and glands.
The autonomic nervous system is further divided into sympathetic and parasympathetic branches.
What is the function of sensory receptors?
Sensory receptors detect changes in the external or internal environment.
Examples include touch receptors, photoreceptors, and olfactory receptors.
Define neurons.
Neurons are specialized cells capable of conducting nerve impulses.
They possess electrical excitability and are essential for sensing, thinking, and controlling muscle activity.
List the three main parts of a neuron.
- Cell body
- Dendrites
- Axon
The cell body contains the nucleus, dendrites receive signals, and the axon transmits impulses.
What is the role of dendrites in a neuron?
Dendrites are the receiving or input portions of a neuron.
They contain receptor sites for binding chemical messengers from other cells.
What is an action potential?
An action potential is an electrical signal that propagates along the surface of a neuron’s membrane.
It is initiated by a stimulus and travels due to ion movement.
What distinguishes gray matter from white matter?
Gray matter contains neuronal cell bodies, while white matter contains myelinated axons.
The presence of myelin gives white matter its characteristic color.
Define neurotransmitter.
A neurotransmitter is a molecule released from a synaptic vesicle that excites or inhibits another neuron or effector cell.
Different neurotransmitters can have varying effects on the postsynaptic cell.
What is the function of neuroglia?
Neuroglia support, nourish, and protect neurons.
Unlike neurons, neuroglia continue to divide throughout an individual’s lifetime.
What is the significance of the axon hillock?
The axon hillock is where action potentials are initiated in a neuron.
It is located at the junction of the cell body and axon.
Fill in the blank: The _______ nervous system is responsible for rest-and-digest activities.
parasympathetic
The parasympathetic nervous system opposes the fight-or-flight responses of the sympathetic nervous system.
What is plasticity in the context of the nervous system?
Plasticity refers to the nervous system’s ability to adapt and reorganize itself.
This includes changes in neural pathways and synapses based on experience.
What is neurogenesis?
Neurogenesis is the process of generating new neurons.
This process occurs primarily during development but can also occur in certain brain regions in adults.
Describe the process of fast axonal transport.
Fast axonal transport moves materials along microtubules at speeds of 200–400 mm per day in both directions.
It uses motor proteins to transport organelles and synaptic vesicles.
True or False: Neurons typically undergo mitotic divisions throughout an individual’s lifetime.
False
Most neurons lose the ability to divide, unlike neuroglia.
What is the role of the enteric nervous system?
The enteric nervous system regulates the activity of the smooth muscle and glands of the gastrointestinal tract.
It contains over 100 million neurons and can function independently.
What happens during the integrative function of the nervous system?
The nervous system processes sensory information and makes decisions for appropriate responses.
This activity is crucial for generating appropriate motor responses.
What is the significance of the synapse?
The synapse is the site of communication between two neurons or between a neuron and an effector cell.
It is where neurotransmitters are released to transmit signals.
What is the size range of neuron cell bodies?
5 micrometers (μm) to 135 μm
The smallest neuron cell body is slightly smaller than a red blood cell, while the largest is barely visible to the unaided eye.
How are neurons structurally classified?
According to the number of processes extending from the cell body:
* Multipolar
* Bipolar
* Unipolar
Most neurons in the brain and spinal cord are multipolar, while sensory neurons are typically unipolar.
What are the characteristics of multipolar neurons?
Several dendrites and one axon
Most neurons in the brain and spinal cord, as well as all motor neurons, are of this type.
Where are bipolar neurons found?
In the retina of the eye, the inner ear, and the olfactory area of the brain
Bipolar neurons have one main dendrite and one axon.
What is a unique feature of unipolar neurons?
Dendrites and one axon are fused together to form a continuous process
These neurons are also known as pseudounipolar neurons.
What are the functional classifications of neurons?
- Sensory neurons (afferent)
- Motor neurons (efferent)
- Interneurons (association)
The classification is based on the direction of the nerve impulse concerning the CNS.
What is the role of sensory neurons?
Convey action potentials to the CNS from sensory receptors
Most sensory neurons are unipolar in structure.
What do motor neurons do?
Convey action potentials away from the CNS to effectors
Motor neurons are multipolar in structure.
What is the function of interneurons?
Integrate incoming sensory information and elicit a motor response
Most interneurons are multipolar and located in the CNS.
What is neuroglia?
Cells that support and protect neurons
Neuroglia make up about half the volume of the CNS and are more numerous than neurons.
What are the four types of neuroglia found in the CNS?
- Astrocytes
- Oligodendrocytes
- Microglial cells
- Ependymal cells
These cells have different functions and characteristics.
What is the function of astrocytes?
Support neurons and maintain the blood-brain barrier
Astrocytes also regulate ion concentration and neurotransmitter uptake.
What do oligodendrocytes do?
Form and maintain the myelin sheath around CNS axons
Unlike Schwann cells, oligodendrocytes can myelinate multiple axons.
What is the role of microglial cells?
Function as phagocytes to remove debris and damaged tissue
They help maintain the health of the nervous system.
What are ependymal cells responsible for?
Producing and assisting in the circulation of cerebrospinal fluid
They also line the ventricles of the brain.
What types of neuroglia are found in the PNS?
- Schwann cells
- Satellite cells
Schwann cells myelinate axons, while satellite cells surround the cell bodies of neurons.
What is myelination?
The process where axons are surrounded by a myelin sheath
This insulation speeds up the conduction of nerve impulses.
What is the function of the nodes of Ranvier?
Gaps in the myelin sheath that facilitate faster nerve impulse conduction
Each Schwann cell covers one segment of an axon between two nodes.
What is the difference between gray matter and white matter?
- Gray matter: neuronal cell bodies, dendrites, unmyelinated axons
- White matter: myelinated axons
White matter appears lighter due to the presence of myelin.
What is a ganglion?
A group of neuronal cell bodies found in the PNS
Ganglia are typically linked to cranial and spinal nerves.
What is a nucleus in the context of the nervous system?
A cluster of neuronal cell bodies located in the CNS
Nuclei serve as processing centers for information.
What are the two types of electrical signals generated by neurons?
- Graded potentials
- Action potentials
Graded potentials are for short-distance communication, while action potentials enable long-distance communication.
What is the resting membrane potential?
The electrical voltage difference across the plasma membrane
It is essential for the generation of action potentials.
What role do ion channels play in neuronal signaling?
Allow specific ions to pass through the plasma membrane
This movement of ions generates electrical currents necessary for signaling.
What is the role of ion channels in the plasma membrane?
Ion channels allow specific ions to flow through the plasma membrane, creating electrical currents in response to stimuli.
Ion flow generates current, altering membrane potential.
What are the two main components of the electrochemical gradient?
- Concentration Difference: Ions move from higher to lower concentration.
- Electrical Difference: Cations move toward negatively charged areas and anions toward positively charged areas.
What are the four types of ion channels?
- Leak Channels
- Ligand-Gated Channels
- Mechanically-Gated Channels
- Voltage-Gated Channels
How do leak channels operate?
Leak channels randomly switch between open and closed states, allowing ions to passively flow through.
They are more permeable to potassium than sodium.
What triggers ligand-gated channels to open?
The binding of specific chemical ligands, such as neurotransmitters or hormones.
What type of stimuli activate mechanically-gated channels?
Mechanical stimuli like touch, pressure, vibration, or tissue stretching.
What is the function of voltage-gated channels?
They open in response to changes in membrane potential, crucial for generating action potentials.
What is the resting membrane potential?
A slight accumulation of negative ions inside the cell and positive ions outside, typically around -70 mV in neurons.
What factors contribute to the resting membrane potential?
- Unequal Ion Distribution
- Inability of Anions to Leave
- Electrogenic Nature of Na⁺–Potassium ATPases
What is a graded potential?
A small change in the resting membrane potential that can hyperpolarize or depolarize the membrane.
What happens during hyperpolarizing graded potential?
The inside of the cell becomes more negative relative to the outside.
What occurs during depolarizing graded potential?
The inside of the cell becomes less negative or more positive.
What is the all-or-none principle in action potentials?
An action potential either occurs fully or not at all, depending on whether the threshold is reached.
What are the phases of an action potential?
- Depolarizing Phase
- Repolarizing Phase
- After-Hyperpolarizing Phase
What occurs during the depolarizing phase of an action potential?
Na+ channels open, allowing Na+ to enter the cell, making the membrane potential more positive.
What happens during the repolarizing phase?
Na+ channels close, K+ channels open, allowing K+ to exit the cell, restoring the negative membrane potential.
What defines the refractory period?
The time after an action potential when a cell cannot generate another action potential.
What are the two types of refractory periods?
- Absolute Refractory Period
- Relative Refractory Period
What influences the speed of action potential propagation?
- Amount of Myelination
- Axon Diameter
- Temperature
What is continuous conduction?
A step-by-step process where each segment of the membrane undergoes depolarization and repolarization, occurring in unmyelinated axons.
What is saltatory conduction?
The rapid propagation of action potentials along myelinated axons, where action potentials ‘leap’ from node to node.
What is the typical resting membrane potential range in neurons?
-40 mV to -90 mV, commonly -70 mV.
Fill in the blank: The _______ phase of an action potential occurs when the membrane potential becomes more negative than its resting level.
after-hyperpolarizing
What are the three main factors that affect the speed of action potential propagation?
- Amount of Myelination
- Axon Diameter
- Temperature
Myelinated axons conduct action potentials faster; larger diameter axons propagate faster; cooler temperatures slow propagation.
What are A fibers characterized by?
- Largest diameter (5–20 μm)
- Myelinated
- Conduct impulses rapidly (12 to 130 m/sec)
- Short absolute refractory period
- Carry sensory information related to touch, pressure, and pain
A fibers are critical for fast transmission of sensory information and motor impulses.
What are the characteristics of B fibers?
- Diameter of 2–3 μm
- Myelinated
- Conduct impulses at speeds up to 15 m/sec
- Longer absolute refractory period than A fibers
- Transmit sensory impulses from organs to the brain
B fibers are involved in autonomic functions and sensory transmission.
What are the defining features of C fibers?
- Smallest diameter (0.5–1.5 μm)
- Unmyelinated
- Conduct impulses slowly (0.5 to 2 m/sec)
- Longest absolute refractory periods
- Carry sensory information for pain and autonomic motor impulses
C fibers are crucial for slow pain transmission and autonomic control.
What are the two main types of electrical signals generated by excitable cells?
- Graded potentials
- Action potentials
These signals differ in distance of communication, membrane potential, duration, propagation speed, and other characteristics.
True or False: Action potentials allow for short-distance communication.
False
Action potentials are designed for long-distance communication, while graded potentials are for short distances.
What are the differences between graded potentials and action potentials in terms of amplitude?
Graded potentials vary in amplitude; action potentials are all or none and typically about 100 mV
This difference highlights how graded potentials can vary based on stimulus strength.
What is the role of the presynaptic neuron in a synapse?
Transmits a nerve impulse toward the synapse and sends the signal
The presynaptic neuron releases neurotransmitters to communicate with the postsynaptic cell.
What is an electrical synapse?
A synapse where action potentials travel directly between adjacent neurons through gap junctions
Electrical synapses enable rapid communication and synchronization between cells.
What is a chemical synapse?
A synapse where neurotransmitters are released into the synaptic cleft to communicate between neurons
Chemical synapses involve a synaptic delay of about 0.5 msec due to the processes involved.
What is an excitatory postsynaptic potential (EPSP)?
A depolarization of the postsynaptic membrane that makes it more likely to reach threshold for action potential
EPSPs result from the binding of excitatory neurotransmitters.
What is an inhibitory postsynaptic potential (IPSP)?
A hyperpolarization of the postsynaptic membrane that makes it harder to generate an action potential
IPSPs result from the binding of inhibitory neurotransmitters.
What are the two types of neurotransmitter receptors?
- Ionotropic receptors
- Metabotropic receptors
Ionotropic receptors are directly linked to ion channels, while metabotropic receptors are linked through G proteins.
Fill in the blank: The removal of neurotransmitters from the synaptic cleft is essential for normal _______.
[synaptic function]
Without removal, neurotransmitters could affect the postsynaptic cell indefinitely.
What are the two main types of summation in postsynaptic potentials?
- Spatial summation
- Temporal summation
These types of summation help integrate multiple signals received by a neuron.
What occurs if the excitatory effects exceed inhibitory effects and reach the threshold?
One or more nerve impulses (action potentials) are triggered
This firing continues as long as the EPSP remains above threshold.
What is the role of neurotransmitter transporters?
They actively transport neurotransmitters back into the neuron that released them or into neighboring neuroglia
These proteins are crucial for recycling neurotransmitters and maintaining synaptic function.
What happens if the excitatory effects exceed inhibitory effects in a neuron?
One or more nerve impulses (action potentials) are triggered. The neuron continues to fire if the EPSP remains above the threshold.
What does IPSP stand for and what does it signify?
Inhibitory Postsynaptic Potential; it indicates that inhibitory effects surpass excitatory effects, hyperpolarizing the membrane and preventing nerve impulse generation.
What is the primary function of dendrites?
Receive stimuli through activation of ligand-gated or mechanically-gated ion channels.
What occurs at the junction of the axon hillock and the initial segment of the axon?
It serves as the trigger zone in many neurons, integrating EPSPs and IPSPs to initiate action potentials if the depolarization reaches the threshold.
What is the primary role of the axon?
Propagates nerve impulses from the initial segment to axon terminals in a self-regenerating manner.
What triggers exocytosis of neurotransmitters at axon terminals?
Inflow of calcium caused by the depolarizing phase of a nerve impulse.
What are the two main classes of neurotransmitters based on size?
- Small-molecule neurotransmitters
- Neuropeptides
Which neurotransmitter is most studied and released by many neurons in the PNS?
Acetylcholine (ACh)
How does acetylcholine function at the neuromuscular junction?
Acts as an excitatory neurotransmitter by binding to ionotropic receptors, opening cation channels.
What is the role of acetylcholinesterase?
Breaks down ACh into acetate and choline to deactivate it.
Name two powerful excitatory neurotransmitters in the CNS.
- Glutamate
- Aspartate
What is the most common inhibitory neurotransmitter in the CNS?
Gamma-aminobutyric acid (GABA)
What effect do anti-anxiety medications like diazepam have on GABA?
Enhance GABA’s effects.
What are catecholamines and name three examples?
Chemically classified neurotransmitters containing an amino group and a catechol ring. Examples: * Norepinephrine
* Dopamine
* Epinephrine
What is the function of serotonin in the brain?
Involved in sensory perception, temperature regulation, mood control, appetite, and sleep induction.
What is neurogenesis?
The birth of new neurons from undifferentiated stem cells.
What inhibits neurogenesis in most areas of the brain?
- Inhibitory effects from neuroglia, especially oligodendrocytes
- Absence of growth signals from fetal development
What is Wallerian degeneration?
The breakdown of the axon and myelin sheath distal to the injury site.
What role do Schwann cells play in nerve regeneration?
Multiply, grow toward each other, and may form a regeneration tube across the damaged area.
What is substance P and its role in the nervous system?
A neuropeptide that transmits pain signals from peripheral pain receptors to the CNS, enhancing the perception of pain.
What are enkephalins and their function?
Neuropeptides that inhibit pain impulses by suppressing the release of substance P.
Fill in the blank: The enzyme that breaks down catecholamines is _______.
Monoamine oxidase (MAO) or Catechol-O-methyltransferase (COMT)
True or False: Neuropeptides can only act as neurotransmitters.
False; many neuropeptides also function as hormones.
What is the role of nitric oxide in the nervous system?
Acts as an important excitatory neurotransmitter produced on demand.
What is the role of the regeneration tube in nerve repair?
It helps guide the new axon across the injury site.
What happens if the gap at the site of nerve injury is too large?
New axons cannot grow.
What are the components of the central nervous system (CNS)?
Brain and spinal cord.
What does the peripheral nervous system (PNS) consist of?
All nervous tissue outside the CNS, including nerves and sensory receptors.
What are the two divisions of the PNS?
- Sensory (afferent) division
- Motor (efferent) division
What is the function of the sensory division of the PNS?
Delivers sensory input into the CNS from sensory receptors.
What does the motor division of the PNS do?
Delivers motor output from the CNS to effectors (muscles and glands).
What are the subdivisions of the efferent division of the PNS?
- Somatic nervous system
- Autonomic nervous system
What does the autonomic nervous system control?
- Smooth muscle
- Cardiac muscle
- Glands
What are the three divisions of the autonomic nervous system?
- Sympathetic division
- Parasympathetic division
- Enteric plexuses
What is the primary function of the nervous system?
Helps maintain homeostasis and integrates all body activities.
What are the two main types of cells in nervous tissue?
- Neurons
- Neuroglia
What is the property of electrical excitability in neurons responsible for?
Sensing, thinking, remembering, controlling muscle activity, and regulating glandular secretions.
What are the three main parts of a neuron?
- Dendrites
- Cell body
- Axon
What is the function of synapses?
Site of functional contact between two excitable cells.
What are the two types of axonal transport?
- Slow axonal transport
- Fast axonal transport
How are neurons classified based on structure?
- Multipolar
- Bipolar
- Pseudounipolar
What types of neurons are functionally classified?
- Sensory (afferent) neurons
- Motor (efferent) neurons
- Interneurons
What is the role of neuroglia?
Support, nurture, and protect neurons.
What types of neuroglia are found in the CNS?
- Astrocytes
- Oligodendrocytes
- Microglial cells
- Ependymal cells
What types of neuroglia are found in the PNS?
- Schwann cells
- Satellite cells
What is white matter composed of?
Aggregates of myelinated axons.
What does gray matter contain?
- Cell bodies
- Dendrites
- Axon terminals
- Unmyelinated axons
- Neuroglia
What are graded potentials used for?
Short-distance communication.
What is the typical resting membrane potential of a neuron?
−70 mV.
What causes the resting membrane potential?
- Unequal distribution of ions
- Inability of most cytosolic anions to leave the cell
- Electrogenic nature of the Na+/K+ ATPases
What is an action potential characterized by?
A constant size impulse generated if a stimulus is strong enough.
What is saltatory conduction?
Nerve impulse propagation that ‘leaps’ from one myelin sheath gap to the next.
How is the intensity of a stimulus encoded in nerve impulses?
- Frequency of nerve impulses
- Number of sensory neurons recruited
What are the two types of synapses?
- Electrical synapses
- Chemical synapses
What is the function of neurotransmitters?
Transmit signals across a synapse.
What are the two major types of neurotransmitter receptors?
- Ionotropic receptors
- Metabotropic receptors
What are the three ways neurotransmitter is removed from the synaptic cleft?
- Diffusion
- Enzymatic degradation
- Uptake by cells
What is summation in the context of synapses?
The combined effect of neurotransmitters from several presynaptic end bulbs generating a nerve impulse.
What is required for axon repair in the PNS?
- Intact cell body
- Functional Schwann cells
- No rapid scar tissue formation
