Nervous System Functions and Neurons

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Questions and Answers

What is the primary function of the thalamus in the brain?

Controls voluntary muscle movement

Regulates pituitary hormone secretion

Integrates sensory inputs (correct)

Maintains body temperature

Which of the following is true about the sympathetic nervous system?

It stimulates digestion and gut activity.

It promotes relaxation and conservation of energy.

It operates only during sleep.

It is responsible for 'fight or flight' responses. (correct)

What type of neuron carries impulses from the CNS to effectors?

Efferent neuron (correct)

Afferent neuron

Sensory neuron

Interneuron

Which division of the peripheral nervous system is responsible for voluntary control of skeletal muscles?

Somatic nervous system Signup and view all the answers

Which of the following actions is NOT associated with the parasympathetic nervous system?

Increases heart rate Signup and view all the answers

The balance between sympathetic and parasympathetic nervous systems results in what?

Coordinated regulation of organs and glands Signup and view all the answers

The autonomic nervous system consists of which two major divisions?

Sympathetic and parasympathetic Signup and view all the answers

What is a function of the autonomic nervous system?

Regulation of involuntary bodily functions Signup and view all the answers

What is the resting membrane potential of a typical resting cell?

-70 mV Signup and view all the answers

What is primarily responsible for maintaining the concentration gradient of Na+ and K+ across the cell membrane?

Na+/K+ ATPase pump Signup and view all the answers

During depolarization, which ion primarily floods into the cell?

Na+ Signup and view all the answers

What is the typical peak value of the action potential after depolarization?

+40 mV Signup and view all the answers

What occurs during repolarization of an action potential?

K+ floods out of the cell Signup and view all the answers

What is the role of the synaptic cleft in a chemical synapse?

Acts as a gap for signal transmission Signup and view all the answers

Which type of cell is involved in transmitting signals away from a synapse?

Postsynaptic neuron Signup and view all the answers

What is the overshoot of the resting membrane potential called?

Hyperpolarization Signup and view all the answers

What type of synapse directly passes action potentials between neurons?

Electrical synapse Signup and view all the answers

What happens to the resting membrane potential after an action potential?

It returns to -70 mV Signup and view all the answers

What is the primary function of acetylcholinesterase (AChE) at the synapse?

To destroy acetylcholine for neurotransmitter clearance Signup and view all the answers

Which type of acetylcholine receptor directly opens membrane channels upon binding with acetylcholine?

Nicotinic receptors Signup and view all the answers

What effect can binding of acetylcholine to muscarinic receptors have?

Either an EPSP or an IPSP Signup and view all the answers

Which class of neurotransmitters does acetylcholine belong to?

Cholinergic neurotransmitters Signup and view all the answers

What is the result of spatial summation of excitatory postsynaptic potentials (EPSPs)?

Production of an action potential Signup and view all the answers

How are acetate and choline reused after acetylcholine is inactivated?

They are resynthesized to form acetylcholine again Signup and view all the answers

Which of the following is NOT a characteristic of muscarinic ACh receptors?

Directly open ion channels Signup and view all the answers

What role do cholinergic fibers play in the nervous system?

They release acetylcholine at synapses Signup and view all the answers

What triggers the release of neurotransmitters from presynaptic neurons?

Arrival of presynaptic action potential Signup and view all the answers

What occurs at the postsynaptic membrane after neurotransmitter binding?

Activation of ligand-gated ion channels Signup and view all the answers

What is the result of a strong enough excitatory postsynaptic potential (EPSP)?

Generation of action potentials in the axon Signup and view all the answers

What is an inhibitory postsynaptic potential (IPSP)?

Hyperpolarization of the postsynaptic membrane Signup and view all the answers

How can the strength of stimuli affect depolarization in postsynaptic neurons?

It leads to varying amounts of depolarization Signup and view all the answers

What happens when multiple presynaptic neurons release EPSPs simultaneously?

It can lead to generation of action potentials Signup and view all the answers

What is responsible for the removal of neurotransmitters from the synapse?

Enzymatic degradation Signup and view all the answers

What occurs when neurotransmitters are released into the synaptic cleft?

They diffuse across to the postsynaptic membrane Signup and view all the answers

What is the main function of the nervous system?

To sense, interpret, and respond to changes Signup and view all the answers

Which of the following structures is primarily responsible for receiving stimuli?

Dendrites Signup and view all the answers

What type of neuron carries signals from sensory receptors to the central nervous system?

Afferent neurons Signup and view all the answers

Which type of neuroglia is responsible for forming myelin sheaths in the peripheral nervous system (PNS)?

Schwann cells Signup and view all the answers

Which part of the nervous system consists of the brain and spinal cord?

Central nervous system Signup and view all the answers

What is the primary role of interneurons in the nervous system?

To connect afferent and efferent neurons Signup and view all the answers

Which centers are controlled by the medulla oblongata?

Cardiac and respiratory centers Signup and view all the answers

Which part of the brain is responsible for balance and posture?

Cerebellum Signup and view all the answers

The forebrain includes which of the following structures?

Cerebrum and diencephalon Signup and view all the answers

What function do astrocytes serve in the central nervous system?

Support neurons physically and help form the blood-brain barrier Signup and view all the answers

Which lobe of the brain is associated with decision-making and planning?

Frontal lobe Signup and view all the answers

What is the primary role of the spinal cord?

To transmit signals between the brain and the body Signup and view all the answers

Which structure serves as a protective barrier for the central nervous system?

Vertebral column Signup and view all the answers

Which neuroglial cell type is involved in defending the nervous system?

Microglia Signup and view all the answers

Which division of the peripheral nervous system is responsible for carrying impulses from receptors to the central nervous system?

Sensory (afferent) division Signup and view all the answers

What is the primary role of the hypothalamus in the brain?

Controlling pituitary hormone secretion Signup and view all the answers

In what situation is the sympathetic nervous system primarily activated?

In response to high stress or strong emotions Signup and view all the answers

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

Somatic system is responsible for voluntary control of skeletal muscles; autonomic system is involuntary. Signup and view all the answers

Which of the following is an action associated with the sympathetic nervous system?

Increasing secretion of epinephrine Signup and view all the answers

How do the sympathetic and parasympathetic systems generally work together?

They have opposing effects, balancing body functions. Signup and view all the answers

Which type of sensory neuron transmits information from internal organs to the central nervous system?

Visceral afferent neuron Signup and view all the answers

What is the impact of the autonomic nervous system on cardiac muscles?

It ensures that heart activity remains involuntary. Signup and view all the answers

What enzyme is responsible for the breakdown of acetylcholine in the synaptic cleft?

Acetylcholinesterase Signup and view all the answers

Which receptors directly open membrane channels when acetylcholine binds to them?

Nicotinic receptors Signup and view all the answers

What occurs when acetylcholine binds to muscarinic receptors?

It either results in an EPSP or hyperpolarization. Signup and view all the answers

What is a characteristic of nicotinic acetylcholine receptors?

They function as ion channels. Signup and view all the answers

What is the role of acetylcholinesterase in neurotransmission?

To inactivate acetylcholine after synaptic transmission. Signup and view all the answers

Which class of neurotransmitters does include serotonin and norepinephrine?

Biogenic amines Signup and view all the answers

What is the primary effect of excitatory postsynaptic potentials (EPSPs)?

They result in depolarization of the postsynaptic neuron. Signup and view all the answers

What happens to acetate and choline after acetylcholine is inactivated?

They are reused to resynthesize acetylcholine. Signup and view all the answers

What is the primary ion responsible for the depolarization phase of an action potential?

Na+ Signup and view all the answers

What mechanism is involved in restoring the resting membrane potential during repolarization?

K+ efflux Signup and view all the answers

What is the typical resting membrane potential (RMP) of a neuron?

-70 mV Signup and view all the answers

Which structure conducts signals away from a synapse?

Postsynaptic neuron Signup and view all the answers

What type of synapse uses neurotransmitters to transmit signals?

Chemical synapse Signup and view all the answers

What event occurs when an excitatory postsynaptic potential (EPSP) is strong enough?

An action potential is generated Signup and view all the answers

What occurs during hyperpolarization of a neuron?

Membrane potential drops below resting level Signup and view all the answers

What action does the Na+/K+ ATPase pump primarily accomplish?

Maintains resting membrane potential Signup and view all the answers

What best describes the 'all-or-none response' of action potentials?

Action potentials either occur or do not occur Signup and view all the answers

What is the function of gap junctions in electrical synapses?

To directly pass action potentials between neurons Signup and view all the answers

What role do dendrites play in a neuron?

They receive stimuli from the environment. Signup and view all the answers

Which type of neuron conducts signals from sensory receptors to the central nervous system?

Afferent neurons Signup and view all the answers

What is the main function of astrocytes in the central nervous system?

To help form the blood-brain barrier. Signup and view all the answers

Which part of the nervous system is responsible for involuntary reflex actions?

Spinal cord Signup and view all the answers

What is the primary role of the myelin sheath?

To increase the speed of conduction of action potentials. Signup and view all the answers

What part of the nervous system contains cranial and spinal nerves?

Peripheral nervous system (PNS) Signup and view all the answers

Which structure is not part of the brainstem?

Cerebellum Signup and view all the answers

What is one of the functions performed by the medulla oblongata?

Controlling the rate and depth of breathing. Signup and view all the answers

Which part of the cerebrum is responsible for high-level functions such as language and memory?

Cerebral cortex Signup and view all the answers

What is the role of microglia in the nervous system?

Acting as phagocytes for defense. Signup and view all the answers

What type of neuron connects afferent and efferent neurons within the central nervous system?

Interneurons Signup and view all the answers

Which lobe of the brain is primarily involved in planning and decision-making?

Frontal lobe Signup and view all the answers

What function do Schwann cells serve in the peripheral nervous system?

Forming myelin sheaths around PNS axons. Signup and view all the answers

What is the primary function of the hypothalamus?

Regulating autonomic nervous system functions. Signup and view all the answers

What is the primary role of calcium ions (Ca2+) during neurotransmitter release?

To initiate the release of neurotransmitters from vesicles Signup and view all the answers

Which potential is characterized by the inward diffusion of Na+ and results in depolarization?

Excitatory postsynaptic potential (EPSP) Signup and view all the answers

What occurs when EPSPs produced by multiple presynaptic neurons coincide?

Spatial summation leading to action potential generation Signup and view all the answers

What is the consequence of the postsynaptic membrane not reaching the threshold potential?

No action potential is generated Signup and view all the answers

Which process describes the periods of depolarization and hyperpolarization based on neurotransmitter activity on the postsynaptic membrane?

Graded potentials Signup and view all the answers

What triggers the removal of neurotransmitters from the synapse?

Enzymatic breakdown or reuptake mechanisms Signup and view all the answers

How does the strength of a stimulus affect postsynaptic depolarization?

Stronger stimuli create graded responses Signup and view all the answers

What defines an inhibitory postsynaptic potential (IPSP)?

It leads to hyperpolarization of the postsynaptic membrane Signup and view all the answers

Study Notes

Function of Nervous System

The nervous system detects internal and external changes.
It interprets these changes and responds appropriately.
The nervous system is also responsible for learning, memory, and intelligence.

Neuron

The neuron is the basic unit of the nervous system.
It consists of a cell body, dendrites, and an axon.
Dendrites receive stimuli.
Axons conduct nerve impulses away from the cell body.
Axons are covered in a myelin sheath, which speeds up signal transmission.
Myelin sheaths are interrupted by nodes of Ranvier, which help to facilitate signal transmission.

Types of Neurons

Afferent (sensory) neurons transmit signals from sensory receptors to the CNS.
Efferent (motor) neurons transmit signals from the CNS to effector organs (muscles and glands).
Interneurons connect afferent and efferent neurons within the CNS.

Neuroglia

Neuroglia support and assist neuron function.
They physically support neurons, form myelin sheaths, and regulate the extracellular fluid composition.

Types of Neuroglia

Schwann cells form myelin sheaths for axons in the PNS.
Oligodendrocytes form myelin sheaths for axons in the CNS.
Astrocytes help to form the blood-brain barrier.
Microglia function as phagocytic cells for defense.

Nervous System Organization

The nervous system consists of the central nervous system (CNS) and the peripheral nervous system (PNS).
The CNS includes the brain and the spinal cord.
The PNS includes nerves that extend from the CNS to the muscles, glands, and sensory organs.

Spinal Cord and Reflexes

The spinal cord transmits nerve impulses to and from the brain.
It also has reflex centers that control involuntary actions.

Brain

The brain is responsible for integrating information and higher-level functions.
It consists of the forebrain, brainstem, and cerebellum.

Brainstem

The brainstem controls involuntary movements.
It also integrates cardiovascular and respiratory activity.
The medulla oblongata is the lowest part of the brainstem; it contains the following centers:
- Cardiac center to control heart rate and strength.
- Respiratory center to control rate and depth of breathing.
- Vasomotor center to control blood vessel diameter.
- Autonomic reflex center to induce vomiting, coughing, and sneezing.

Cerebellum

The cerebellum is involved in maintaining posture, balance, and skeletal muscle function.
It also plays a role in some forms of learning.

Forebrain

The forebrain consists of the cerebrum and the diencephalon.

Cerebrum

The cerebrum has two hemispheres.
The cerebral cortex is the outermost layer of the cerebrum, and it is responsible for higher brain functions, including memory, learning, language, planning, and decision-making.
The cerebrum has four lobes: frontal, parietal, occipital, and temporal.

Diencephalon

The thalamus integrates sensory inputs.
The hypothalamus regulates pituitary hormone secretion and controls homeostatic functions, such as water balance and body temperature.

Peripheral Nervous System

The peripheral nervous system carries impulses from sensory receptors to the CNS and from the CNS to effector organs.
It is divided into the sensory (afferent) and motor (efferent) divisions.

Sensory (Afferent) Division

The sensory (afferent) division carries impulses from the receptors to the CNS.
It consists of somatic and visceral components.
Somatic: stimuli originates from the skin and skeletal muscles.
Visceral: stimuli originates from internal organs.

Motor (Efferent) Division

The motor (efferent) division carries impulses from the CNS to effectors.
It is divided into the somatic and autonomic nervous systems.
- Somatic: voluntary control of skeletal muscles.
- Autonomic: involuntary control of cardiac muscle, smooth muscle, and glands.
- The autonomic nervous system consists of the sympathetic and parasympathetic nervous systems.

Autonomic Nervous System

The autonomic nervous system is part of the PNS.
It consists of sympathetic and parasympathetic nerves.
These two divisions act antagonistically.
The balance between the two divisions regulates organ function.

Sympathetic Nervous System

The sympathetic nervous system is responsible for the "fight-or-flight" response.
It prepares the body to deal with stress or strong emotions.
Its functions include:
- Increasing heart rate.
- Dilating bronchi.
- Dilating arteries to muscles.
- Constricting arteries to the gut.
- Converting glycogen to glucose.
- Increasing epinephrine secretion.

Parasympathetic Nervous System

The parasympathetic nervous system promotes conservation and relaxation.
Its effects oppose the effects of the sympathetic system.
It is associated with the body's quiet state and well-being.

Neuron Function

Neurons transmit electrochemical signals.
This is accomplished through the generation and propagation of action potentials.

Resting Membrane Potential (RMP)

The RMP is a negative charge difference across the cell membrane.
This is maintained by the Na+/K+ ATPase pump.
The resting membrane is more permeable to potassium (K+) than sodium (Na+).
The RMP is approximately -70 mV.

Na+/K+ ATPase Pump

The Na+/K+ ATPase pump maintains and establishes the concentration gradient of Na+ and K+ across the cell membrane.
It pumps three Na+ ions out of the cell for every two K+ ions pumped in.

Action Potential (AP)

Action potentials are the electrochemical signals that travel along neurons.
They involve a rapid, localized change in the RMP that results in a brief reversal of the membrane potential.
An AP is characterized by a rapid depolarization phase, followed by a repolarization phase and a brief hyperpolarization phase.
AP's are all-or-none responses.
They can travel long distances without diminishing in strength.

AP Phases

Depolarization: The cell membrane becomes more permeable to Na+ ions, which flow into the cell due to their concentration gradient. This causes the RMP to move toward a positive value (+40 mV).
Repolarization: The cell membrane becomes less permeable to Na+ and more permeable to K+ ions, which move out of the cell due to their concentration gradient. This causes the RMP to return to its resting value (-70 mV).
Hyperpolarization: The membrane potential briefly becomes more negative than the RMP. This is caused by the K+ channels remaining open for a brief period after the repolarization phase.

Synapse

A synapse is the junction between a neuron and another neuron, muscle, or gland cell.
It is where neurotransmitters are released.
Presynaptic neuron: The neuron that transmits signals toward the synapse.
Postsynaptic neuron: The neuron that receives signals from the synapse.
Synaptic knob: The terminal of the presynaptic neuron where neurotransmitters are stored.
Synaptic cleft: The narrow gap between the pre- and postsynaptic neurons.

Types of Synapses

Electrical Synapse: Direct transfer of action potential through gap junctions between neurons.
Chemical Synapse: Transmission of signals by release of neurotransmitters from the presynaptic neuron to the postsynaptic neuron.

Neurotransmitter Release at a Chemical Synapse

An action potential arrives at the presynaptic terminal.
Voltage-gated Ca2+ channels open and Ca2+ flows into the presynaptic terminal.
Ca2+ triggers the release of neurotransmitters from synaptic vesicles via exocytosis.
Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane.
Binding of the neurotransmitter to its receptor activates ion channels, causing a postsynaptic potential.
After its action, neurotransmitters are removed from the synapse by enzymatic degradation or reuptake into the presynaptic terminal.

Synaptic Potentials

Synaptic potentials are postsynaptic depolarizations or hyperpolarizations caused by neurotransmitters.
Excitatory postsynaptic potential (EPSP): A depolarization of the postsynaptic membrane that brings the membrane potential closer to the threshold for firing an action potential.
Inhibitory postsynaptic potential (IPSP): A hyperpolarization of the postsynaptic membrane that makes the membrane potential more negative and less likely to fire an action potential.

Summation of Synaptic Potentials

Spatial summation: Multiple presynaptic neurons release neurotransmitters at the same time, and their EPSP's summate to reach the threshold for firing an action potential.
Temporal summation: A single presynaptic neuron releases multiple neurotransmitters in rapid succession, and their EPSP's summate to reach the threshold for firing an action potential.

Neurotransmitters

Acetylcholine (ACh): Important neurotransmitter at neuromuscular junctions.
Biogenic Amines: Includes norepinephrine, epinephrine, and serotonin.
Amino Acids: Includes glutamic acid and gamma-aminobutyric acid (GABA).
Neuropeptides: Includes endorphins and substance P.

Acetylcholine (ACh)

ACh is a common neurotransmitter at neuromuscular junctions.
Cholinergic fibers release ACh.
ACh is rapidly destroyed by the enzyme acetylcholinesterase (AChE) to terminate its effect at the synapse.

Types of ACh Receptors

Nicotinic ACh receptors: Found at neuromuscular junctions. They are ionotropic, meaning they are directly linked to ion channels that open upon binding of ACh. This leads to depolarization and EPSPs.
Muscarinic ACh receptors: Present in the heart, smooth muscle, and glands. They are metabotropic, meaning they indirectly activate second messenger systems. This can lead to either EPSPs or IPSPs.

Important Notes

The brain is comprised of more glial cells than neurons.
The nervous system is a vast and complex network that plays a vital role in regulating and coordinating the body's activities.
There are a variety of diseases that affect the nervous system, including Alzheimer's disease, Parkinson's disease, multiple sclerosis, and stroke.