Neuroscience Chapter 5 Quiz

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Questions and Answers

What type of receptors adapt slowly or not at all?

Phasic receptors

Chemical receptors

Tonic receptors (correct)

Electrical receptors

Which of the following best describes the role of first-order neurons in sensory pathways?

They modulate pain signals within the brain.

They relay information from receptors to the spinal cord. (correct)

They transmit signals directly to the brainstem.

They carry signals from the thalamus to the cerebral cortex.

What enhances sensory acuity by suppressing neighboring signals?

Lateral inhibition (correct)

Receptor potential

Adaptation

Signal amplification

Which type of nociceptor is specifically activated by extreme temperatures?

Thermal receptors Signup and view all the answers

What neurotransmitters are primarily used in the autonomic nervous system?

Acetylcholine and norepinephrine Signup and view all the answers

What is the correct sequence of information flow in sensory pathways?

Receptors -> Spinal cord -> Thalamus -> Cerebral cortex Signup and view all the answers

Which type of fibers transmits pain signals more quickly?

A-delta fibers Signup and view all the answers

The sympathetic nervous system is associated with which response?

Fight or flight Signup and view all the answers

What is the typical range for resting membrane potential in neurons?

-70 to -90 mV Signup and view all the answers

During which phase of the action potential do Na+ ions rush into the cell?

Depolarization Signup and view all the answers

What is hyperpolarization primarily caused by?

Increased Cl- entry or K+ exit Signup and view all the answers

What characterizes graded potentials?

Their spread is decremental and they are local. Signup and view all the answers

What initiates neurotransmitter release at chemical synapses?

Ca²⁺ influx Signup and view all the answers

What mechanism is used for faster conduction of action potentials in myelinated axons?

Saltatory conduction Signup and view all the answers

Which type of neurotransmitter is mainly inhibitory?

GABA Signup and view all the answers

What is the consequence of reaching the threshold potential of approximately -55 mV?

An action potential is triggered. Signup and view all the answers

What is the primary function of endorphins in the nervous system?

Modulate pain perception and aid in digestion Signup and view all the answers

What distinguishes temporal summation from spatial summation?

Temporal summation involves multiple signals from the same neuron over time. Signup and view all the answers

Which of the following correctly describes the role of cocaine in the nervous system?

Blocks dopamine reuptake. Signup and view all the answers

The central nervous system (CNS) is composed of which of the following structures?

Brain and spinal cord Signup and view all the answers

What is the primary function of astrocytes in the CNS?

Support and repair neurons Signup and view all the answers

Which component is responsible for cushioning the brain and spinal cord?

Cerebrospinal fluid (CSF) Signup and view all the answers

The primary function of ependymal cells in the CNS is to:

Line cavities and circulate cerebrospinal fluid Signup and view all the answers

What characterizes the nervous system's response compared to the endocrine system?

Precise, immediate, and short-lived effects Signup and view all the answers

What type of neurotransmitter is primarily released by the sympathetic nervous system?

Norepinephrine Signup and view all the answers

Which of the following is NOT a response associated with the sympathetic nervous system?

Slower heart rate Signup and view all the answers

What type of receptor binds acetylcholine in the parasympathetic nervous system?

Muscarinic receptors Signup and view all the answers

Which statement about dual innervation is true?

Most organs receive signals from both sympathetic and parasympathetic divisions. Signup and view all the answers

At the neuromuscular junction, what triggers the release of acetylcholine?

Voltage-gated calcium channel opening Signup and view all the answers

What is the role of acetylcholinesterase at the neuromuscular junction?

To break down ACh Signup and view all the answers

What is the effect of curare at the neuromuscular junction?

Blocks ACh receptors Signup and view all the answers

What distinguishes the somatic nervous system from the autonomic nervous system?

It controls voluntary skeletal muscles. Signup and view all the answers

What is the role of tropomyosin in muscle contraction?

To block actin-myosin interaction Signup and view all the answers

What initiates the release of Ca²⁺ from the sarcoplasmic reticulum?

Action potential in a somatic motor neuron Signup and view all the answers

During which phase of a muscle twitch does the muscle fiber actually generate force?

Contraction phase Signup and view all the answers

Which muscle fiber type is primarily responsible for endurance activities?

Slow oxidative (type I) Signup and view all the answers

What is a key factor in the sliding filament mechanism?

Myosin pulling actin inward during power stroke Signup and view all the answers

What defines a large motor unit?

It includes many muscle fibers innervated by one motor neuron. Signup and view all the answers

Which type of contraction occurs when a muscle generates tension without shortening?

Isometric contraction Signup and view all the answers

What primarily causes muscle fatigue during prolonged exercise?

Accumulation of lactic acid and inorganic phosphate Signup and view all the answers

Study Notes

Resting Membrane Potential

The resting membrane potential of a typical neuron is approximately -70 mV, with a range of -40 to -90 mV.
The membrane is polarized, with a positive charge on the outside and a negative charge on the inside.
This is maintained by a higher concentration of sodium ions (Na+) outside the cell and potassium ions (K+) inside the cell.

Electrical States of Membranes

Polarization: Any membrane potential other than 0 mV.
Depolarization: The membrane potential becomes less negative (closer to 0 mV).
Repolarization: The membrane potential returns to the resting potential after depolarization.
Hyperpolarization: The membrane potential becomes more negative than the resting potential.

Types of Signals

Graded potentials: Short-distance signals that vary in strength and duration based on the stimulus.
Action potentials: Long-distance, all-or-none signals that travel along axons with a constant magnitude and speed.

Ion Permeability and Membrane Potential

Depolarization: Sodium ions (Na+) flow into the cell, making the inside more positive.
Repolarization: Potassium ions (K+) flow out of the cell, restoring the negative charge inside.
Hyperpolarization: Further exit of potassium ions (K+) or entry of negative ions (Cl-) makes the inside even more negative.

Graded Potentials

They are short-lived, localized changes in membrane potential.
Their amplitude and duration are proportional to the strength and duration of the stimulus.
They decrease in strength as they spread away from the point of origin.
Examples include postsynaptic potentials and receptor potentials.

Action Potentials

When the membrane potential reaches a threshold (around -55 mV), an action potential is triggered.
Phases:
- Depolarization: Sodium ions (Na+) rapidly enter the cell, causing a sharp increase in membrane potential to +30 mV.
- Repolarization: Potassium ions (K+) rapidly exit the cell, restoring the negative charge inside.
- Hyperpolarization: Potassium channels remain open slightly too long, causing the membrane potential to become more negative than the resting potential.
Refractory period: A period of time after an action potential where it is difficult or impossible to trigger another one, ensuring that action potentials travel in one direction.

Conduction of Action Potentials

Saltatory conduction: In myelinated axons, action potentials "jump" between gaps in the myelin sheath called Nodes of Ranvier, significantly speeding up transmission.
Myelin formation:
- CNS: Formed by oligodendrocytes.
- PNS: Formed by Schwann cells.
Axon diameter: Larger diameter axons conduct action potentials faster.

Synapses

Electrical synapses: Rare, direct electrical coupling of cells through gap junctions. They allow for rapid transmission of signals.
Chemical synapses: More common, involve the release of neurotransmitters across a synaptic cleft.
Steps of chemical synaptic transmission:
1. Action potential arrives at the presynaptic terminal.
2. Calcium ions (Ca²⁺) enter the presynaptic terminal.
3. Calcium ions trigger the release of neurotransmitters from vesicles.
4. Neurotransmitters bind to receptors on the postsynaptic membrane.
5. Binding of neurotransmitters can either excite (EPSP) or inhibit (IPSP) the postsynaptic neuron.

Neurotransmitters

Chemical types:
- Acetylcholine (ACh): Found at neuromuscular junctions and many synapses in the autonomic nervous system.
- Biogenic amines: Epinephrine, norepinephrine, dopamine, serotonin - involved in mood, arousal, and autonomic function.
- Amino acids: GABA (inhibitory), glycine (inhibitory), glutamate (excitatory) - major neurotransmitters in the brain and spinal cord.
- Peptides: Endorphins (pain relief), substance P (pain transmission) - often act as neuromodulators.
Functional types:
- Excitatory: Promote depolarization, increasing the likelihood of an action potential.
- Inhibitory: Promote hyperpolarization, reducing the likelihood of an action potential.

Summation

Temporal summation: Multiple signals from the same neuron arriving close together in time.
Spatial summation: Signals from multiple neurons converge on a single postsynaptic neuron.

Drugs and Diseases Affecting Synapses

Cocaine: Blocks the reuptake of dopamine, leading to increased dopamine levels and pleasurable effects.
Parkinson's Disease: Characterized by a deficiency of dopamine in the brain, causing problems with movement.
Strychnine: Blocks glycine receptors, leading to muscle spasms and seizures.
Tetanus toxin: Prevents the release of GABA, an inhibitory neurotransmitter, resulting in muscle rigidity and spasms.

Nervous vs. Endocrine Systems

Nervous system: Uses electrical signals transmitted along specific pathways to target specific effectors (skeletal muscles, glands). Rapid, precise, short-lived effects.
Endocrine system: Uses hormones, chemical messengers that travel through the bloodstream to target cells with specific receptors. Slower, longer-lasting effects.

Nervous System Overview

Central Nervous System (CNS): Brain and spinal cord, the control center for the nervous system.
Peripheral Nervous System (PNS): Connects the CNS to the rest of the body, made up of nerves and ganglia.
- Sensory (afferent) division: Carries sensory information from receptors to the CNS.
- Motor (efferent) division: Carries motor commands from the CNS to muscles and glands.
  - Somatic nervous system: Controls voluntary skeletal muscle movement.
  - Autonomic nervous system: Controls involuntary functions of smooth muscles, cardiac muscles, and glands.

Neuron Types

Afferent neurons (sensory neurons): Carry signals from sensory receptors to the CNS.
Efferent neurons (motor neurons): Carry signals from the CNS to muscles and glands.
Interneurons: Found entirely within the CNS, connect afferent and efferent neurons.

Glial Cells

Astrocytes: Support neurons, maintain the blood-brain barrier, and repair brain injuries.
Oligodendrocytes: Form myelin sheaths in the CNS.
Microglia: Immune defense cells in the CNS.
Ependymal cells: Line the cavities of the CNS and help circulate cerebrospinal fluid (CSF).

CNS Protection

Meninges: Three layers of protective membranes surrounding the brain and spinal cord:
- Dura mater: Tough, outermost layer.
- Arachnoid mater: Middle layer, contains cerebrospinal fluid.
- Pia mater: Delicate innermost layer, tightly attached to the brain and spinal cord.
Cerebrospinal fluid (CSF): Acts as a cushion and shock absorber, circulates in the ventricles of the brain and spinal cord.

Sensory Receptors

Receptors: Specialized cells or structures that detect changes in the internal or external environment.
- Stimulus Intensity: A stronger stimulus generates a larger receptor potential, which can increase the frequency of action potentials.
- Adaptation: Receptors can adjust to a sustained stimulus, decreasing the frequency of action potentials over time.
  - Tonic receptors: Adapt slowly or not at all (e.g., pain receptors).
  - Phasic receptors: Adapt quickly (e.g., Pacinian corpuscles for pressure/vibration).

Pathways to the CNS

Reflex arc: A simple neural circuit that produces a rapid, involuntary response to a stimulus.
Ascending pathways: Carry sensory information to the brain for conscious processing.
Somatosensory pathways: Transmit conscious sensory information from the body.
- First-order neurons: Relay information from receptors to the spinal cord.
- Second-order neurons: Carry the signal to the thalamus.
- Third-order neurons: Bring the information to the cerebral cortex.

Sensory Acuity and Receptive Fields

Acuity: The ability to discriminate between two closely spaced sensory stimuli.
Receptive field: The area of the body that, when stimulated, activates a particular sensory neuron.
Lateral inhibition: A process where neighboring neurons suppress each other, enhancing the perception of the stimulus and increasing acuity.

Pain Perception and Nociceptors

Nociceptors: Specialized pain receptors that detect and signal damage.
Mechanical receptors: Activated by physical damage.
Thermal receptors: Activated by extreme temperatures.
Polymodal nociceptors: Respond to multiple damaging stimuli.
Pain pathways: Pain signals travel along different types of fibers:
- Fast fibers (A-delta): Transmit sharp, localized pain quickly (30 m/s).
- Slow fibers (C fibers): Transmit dull, aching pain more slowly (12 m/s).
- Brain regions involved in pain processing: Somatosensory cortex (location), thalamus (relay), reticular formation (alertness), and various brain stem centers.
- Analgesic system: The brain has a descending pathway that can modulate pain signals through the release of endorphins.

Autonomic Nervous System (ANS)

Innervates: Cardiac and smooth muscles, exocrine and endocrine glands.
Neurotransmitters: ACh (acetylcholine) and norepinephrine.
Nerve pathway: Consists of two neurons:
- Preganglionic fiber: Connects the CNS to the autonomic ganglia.
- Postganglionic fiber: Connects the autonomic ganglia to the target organ.

Divisions of the ANS

Sympathetic Nervous System (SNS) ("fight or flight"):
- Origin: Thoracic and lumbar spinal regions.
- Preganglionic fibers: Short.
- Postganglionic fibers: Long.
- Neurotransmitter: Norepinephrine (adrenergic).
- Responses: Dilated pupils, increased heart rate, inhibited digestion, increased glucose production, sweating, vasoconstriction of blood vessels in most regions.
Parasympathetic Nervous System (PNS) ("rest and digest"):
- Origin: Cranial and sacral levels of the CNS.
- Preganglionic fibers: Long.
- Postganglionic fibers: Short.
- Neurotransmitter: Acetylcholine (cholinergic).
- Responses: Constricted pupils, slower heart rate, stimulated digestion, decreased glucose production, bronchoconstriction, vasodilation of blood vessels to digestive organs.

Dual Innervation

Most organs are innervated by both sympathetic and parasympathetic divisions, allowing for precise control of their functions.
Exceptions: Most blood vessels and sweat glands are only innervated by the sympathetic nervous system.

Receptors in the ANS

Cholinergic receptors (bind ACh):
- Nicotinic: Found in all autonomic ganglia, between pre- and postganglionic neurons.
- Muscarinic: Found in parasympathetic postganglionic neurons.
Adrenergic receptors (bind norepinephrine/epinephrine):
- Alpha receptors: Generally excitatory (alpha 1) or inhibitory (alpha 2).
- Beta receptors:
  - Beta 1: Excitatory (mainly in the heart).
  - Beta 2: Inhibitory (found in smooth muscles).

Drugs Affecting the ANS

Agonists: Mimic the effects of autonomic neurotransmitters.
Antagonists: Block the effects of autonomic neurotransmitters.

Somatic Nervous System

Controls voluntary skeletal muscle movement.
Nerve pathway: Single motor neuron from the spinal cord to the muscle fiber.
Neurotransmitter: Acetylcholine at the neuromuscular junction.

Neuromuscular Junction

Steps:
1. Action potential arrives at the axon terminal.
2. Voltage-gated calcium channels open, allowing calcium ions (Ca²⁺) to enter.
3. Calcium ions initiate the release of acetylcholine (ACh) from synaptic vesicles.
4. Acetylcholine binds to receptors on the muscle fiber membrane.
5. Binding of ACh causes sodium channels to open, leading to depolarization and an action potential in the muscle fiber.
6. Acetylcholinesterase breaks down ACh, terminating the signal.

Disruptions at the Neuromuscular Junction

Toxins:
- Black widow venom: Increases the release of ACh, causing muscle spasms.
- Botulinum toxin: Blocks the release of ACh, causing muscle paralysis.
Curare: Blocks ACh receptors, preventing muscle contraction.

Muscle Structure and Function

Muscles only contract - they cannot actively lengthen.
Skeletal muscle fiber: A large, elongated, cylindrical cell containing myofibrils.
Myofibrils: Bundles of protein filaments responsible for contraction.
- Thick filaments: Made of myosin.
- Thin filaments: Made of actin, troponin, and tropomyosin.
Sarcomere: The functional unit of a muscle fiber, spanning from one Z line to another.
- A band: Includes both myosin and actin filaments.
- H zone: The middle of the A band, contains only myosin.
- M line: Center of the A band.
- I band: Contains only actin filaments.

Proteins Involved in Muscle Contraction

Thick filaments: Myosin - has cross bridges that bind to actin and an ATPase activity for energy.
Thin filaments:
- Actin: Serves as the binding site for myosin cross bridges during contraction.
- Tropomyosin: Blocks the binding sites on actin when the muscle is relaxed.
- Troponin: Binds calcium ions (Ca²⁺) to move tropomyosin and expose the binding sites on actin.

Sliding Filament Mechanism

Myosin cross bridges attach to actin and pull the filaments inward, shortening the sarcomere.
This cycle of attachment, pulling ("power stroke"), and detachment is repeated as long as calcium ions (Ca²⁺) are present.
Energy for contraction: ATP is essential for myosin to detach from actin and reset for the next cycle.

Excitation-Contraction Coupling

Steps:
1. An action potential in a somatic motor neuron triggers the release of acetylcholine at the neuromuscular junction.
2. Acetylcholine initiates an action potential in the muscle fiber, which travels along the T-tubules.
3. The action potential in the T-tubules triggers the release of calcium ions (Ca²⁺) from the sarcoplasmic reticulum (SR).
4. Calcium ions bind to troponin, moving tropomyosin away from the binding sites on actin, allowing myosin to bind.
5. Myosin cross bridges bind to actin and initiate the sliding filament mechanism, resulting in muscle contraction.

Muscle Relaxation

Calcium ions (Ca²⁺) are actively transported back into the SR.
Tropomyosin blocks the binding sites on actin once again, stopping the sliding filament mechanism.

Motor Units

Motor unit: A single motor neuron and all the muscle fibers it innervates.
Size of motor units:
- Small motor units: Control fine movements (e.g., eye muscles).
- Large motor units: Control coarse movements (e.g., leg muscles).
Muscle tension: Determined by the number of motor units recruited and the frequency of action potentials.

Muscle Twitch

Twitch: A single contraction-relaxation cycle of a muscle fiber in response to a single stimulus.
- Phases:
  - Latent period: Short delay between stimulation and the start of contraction.
  - Contraction phase: Muscle develops tension and shortens.
  - Relaxation phase: Muscle returns to its resting length.
Twitch summation: Repeated stimuli delivered before the muscle can fully relax cause increased tension due to the accumulation of calcium.
Tetanus: When stimuli are delivered at a very high frequency, the muscle stays in a continuous, sustained contraction.

Types of Contraction

Isotonic contraction: Muscle shortens while lifting a load, the tension remains relatively constant.
Isometric contraction: Muscle develops tension but does not shorten, the load is greater than the force the muscle can generate.

Energy Sources for Muscle Contraction

Creatine phosphate: Provides immediate energy for a few seconds of intense activity.
Oxidative phosphorylation: Aerobic metabolism in mitochondria, provides ATP for sustained activity.
Glycolysis: Anaerobic metabolism, provides ATP for short bursts of intense activity, produces lactic acid.

Muscle Fiber Types

Slow oxidative fibers (type I): Adapted for endurance activities, rich in mitochondria and myoglobin, use aerobic metabolism primarily.
Fast oxidative fibers (type IIa): Intermediate in characteristics, can use both aerobic and anaerobic metabolism.
Fast glycolytic fibers (type IIb): Adapted for short bursts of intense activity, rely heavily on anaerobic metabolism, have fewer mitochondria and myoglobin.

Muscle Fatigue

Muscle fatigue: A decline in muscle force production, can be caused by:
- Lactic acid accumulation: Inhibits muscle function.
- Inorganic phosphate accumulation: Interfere with calcium release and reuptake.
- Depletion of energy stores: Limited ATP and glycogen.

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Test your understanding of key concepts in neuroscience, specifically Chapter 5. This quiz covers sensory pathways, nociceptors, neurotransmitters, and the role of neurons in the nervous system. Challenge your knowledge and see how well you grasp the intricacies of neural function.