Chapter 11: Efferent Division: Autonomic and Somatic Motor Control

Describe the role of efferent neurons in the peripheral
nervous system.

Efferent neurons carry commands from the Central Nervous System (CNS) to muscles and glands.

Define the two branches of the autonomic division.

The two branches are the sympathetic branch, which activates 'fight-or-flight'
responses, and the parasympathetic branch, which activates 'rest-and-digest' functions.

How do autonomic reflexes contribute to homeostasis?

Autonomic reflexes work in conjunction with endocrine and behavioral state systems to maintain homeostasis.

Explain the function of the hypothalamus in autonomic
reflexes.

The hypothalamus contains neurons that act as sensors for homeostatic regulation and houses homeostatic control centers. autonomic responses, endocrine responses, and behavioral responses such as drinking, food-seeking, and temperature regulation (getting out of the heat, putting on a sweater). These behavioral responses are integrated in brain centers responsible for motivated behaviors and control of movement.

What is the significance of spinal reflexes in the autonomic
system?

Some autonomic reflexes do not require integration in the brain, allowing for quicker responses.

These spinal reflexes include urination, defecation, and penile erection—body functions that can be influenced by descending pathways from the brain but do not require this input.

Describe antagonistic control in the autonomic division.

Most internal organs are under antagonistic control, where one branch is excitatory and the
other is inhibitory.

Identify exceptions to antagonistic control in the
autonomic division.

Exceptions include sweat glands and smooth muscles in most blood vessels, which operate
with only sympathetic innervation, termed tonic control.

What is cooperative control in the autonomic division?

Cooperative control involves different tissues working together to achieve a common goal.

How does neurotransmitter receptor type influence response
in target tissues?

The type of neurotransmitter receptor often determines the response in the target tissue

Define the role of the preganglionic neuron in
autonomic pathways.

The preganglionic neuron is the first neuron in the chain, with its cell body located in the CNS,
projecting to an autonomic ganglion.

What is the function of the postganglionic neuron in autonomic pathways?

The postganglionic neuron is the second neuron in the chain, with its cell body in the autonomic ganglion, projecting to the target tissue and synapses with the target cell

Describe a ganglion in the context of the nervous system.

A ganglion is a cluster of neuronal cell bodies located outside the central nervous
system (CNS) that acts as a miniintegration center.

Define the origin of the sympathetic division of the autonomic nervous system.

The sympathetic division originates from the thoracic and lumbar regions of the spinal cord.

How are sympathetic ganglia organized in the body?

Sympathetic ganglia are organized in two chains along each side of the vertebral column.

Describe the origin of the parasympathetic division.

The parasympathetic division originates in the brain stem and exits via cranial nerves.

Where are parasympathetic ganglia located?

Parasympathetic ganglia are located on or near target organs.

What is the role of the vagus nerve in the parasympathetic division?

The vagus nerve contains approximately 75% of all parasympathetic fibers and is responsible for transmitting sensory information from internal organs to the brain and output from the brain to organs.

Explain the chemical transmission in the autonomic nervous system.

Both sympathetic andparasympathetic preganglionic neurons release acetylcholine
(ACh) onto nicotinic cholinergic receptors (nAChR) on postganglionic cells.

What neurotransmitter do most sympathetic postganglionic
neurons secrete?

Most sympathetic postganglionic neurons secrete norepinephrine (NE) onto adrenergic receptors on target cells.

How do parasympathetic postganglionic neurons communicate with target cells?

Parasympathetic postganglionic neurons primarily release acetylcholine (ACh) on target cells through muscarinic receptors.

Define the role of the efferent division in the nervous system.

The efferent division is crucial for transmitting commands from the central nervous system (CNS) to effectors

How does the autonomic division maintain homeostasis?

The autonomic division maintains homeostasis through two opposing branches, each with distinct roles and neurotransmitter systems.

What is the significance of antagonistic control in the autonomic nervous system?

antagonistic control ensures balanced physiological responses, allowing the body to
maintain homeostasis.

Describe the organization of neurons in the autonomic
nervous system.

The organization into preganglionic and postganglionic neurons allows for a complex but efficient signaling system throughout the body.

What do postganglionic parasympathetic neurons
primarily secrete?

Postganglionic parasympathetic neurons primarily secrete acetylcholine (ACh) onto
muscarinic cholinergic receptors (mAChR) on target cells.

Identify an exception to the secretion pattern of postganglionic neurons in the sympathetic division.

An exception is sympathetic cholinergic neurons, which secrete acetylcholine (ACh) on
sweat glands.

Describe the role of nonadrenergic, noncholinergic
neurons.

They utilize other neurotransmitters instead of
adrenergic or cholinergic ones.

Define the neuroeffector junction.

It is the synapse between a postganglionic autonomic neuron and its target cell.

What is a varicosity in the context of autonomic neurons?

A varicosity is a swelling at the end of a postganglionic neuron.

How can the release of autonomic neurotransmitters be
modulated?

The release can be influenced by various factors, allowing for adjustments in neurotransmitter levels.

Explain where neurotransmitter synthesis occurs in autonomic neurons.

Neurotransmitter synthesis occurs in the axon of the neuron.

Describe the control exerted by autonomic pathways.

Autonomic pathways control smooth and cardiac muscle as well as glandular functions.

Identify the three types of autonomic pathways illustrated in figures.

The three types are the Parasympathetic Pathway, Sympathetic Pathway, and Adrenal Sympathetic Pathway.

How do autonomic varicosities function at the neuroeffector junction?

They release neurotransmitters over the surface of target cells.

Define the primary types of receptors in the autonomic system.

They are primarily G proteincoupled receptors with multiple subtypes.

What are alpha receptors and their subtypes in the sympathetic system?

Alpha receptors include a1-receptors, which cause muscle contraction or secretion, and a2-
receptors, which decrease cAMP leading to relaxation or decreased secretion.

Describe the response of beta receptors to catecholamines.

Beta receptors have varying affinities: b1-receptors respond equally to epinephrine and
norepinephrine, b2-receptors are more sensitive to epinephrine, and b3-receptors are more
sensitive to norepinephrine.

How do parasympathetic pathways interact with target cells?

They stimulate muscarinic receptors on target cells.

Describe the function of the adrenal medulla in the
autonomic system.

The adrenal medulla functions as neuroendocrine tissue and acts as a modified sympathetic ganglion.

How does the adrenal medulla secrete epinephrine?

It is innervated by sympathetic preganglionic fibers and its postganglionic neurons (chromaffin cells) lack axons, secreting
epinephrine into the bloodstream.

What characterizes the somatic motor division?

It consists of a somatic motor pathway made up of one neuron.

Where does the somatic motor division originate?

It originates in the CNS, either in the brain or the ventral horn of the spinal cord.

Describe the characteristics of somatic motor neurons.

Somatic motor neurons are myelinated, very long, and always excitatory. Their terminal branches are close to the target, with each terminal innervating a single skeletal muscle fiber.

Define the neuromuscular junction (NMJ).

The neuromuscular junction (NMJ) is defined as the synapse between a somatic motor neuron and a skeletal muscle fiber.

What are the key components of the neuromuscular junction?

The key components of the neuromuscular junction include the motor end plate on the
skeletal muscle cell membrane, acetylcholinesterase (AChE) present in the synaptic cleft, and ACh receptors on the postsynaptic membrane.

How do nicotinic receptors function in the NMJ?

Nicotinic receptors, identified as nAChR channels of skeletal muscle, are found in the
neuromuscular junction and are responsible for mediating excitatory responses.

Explain the function of ACh receptors on neurons.

ACh receptors on neurons function as chemically-gated channels, containing two binding sites for acetylcholine (ACh), and always result in an excitatory response leading to muscle contraction.

Describe the efferent divisions of the nervous system.

The efferent divisions of the nervous system comprise pathways that transmit impulses
from the central nervous system (CNS) to peripheral targets, divided into the somatic motor pathway and the autonomic
nervous system.

How do somatic motor neurons communicate with skeletal muscles?

Somatic motor neurons convey
signals from the CNS to skeletal muscles through the neuromuscular junction, where
they communicate with muscle fibers.

What occurs at the presynaptic terminal of the NMJ?

The presynaptic terminal contains synaptic vesicles filled with acetylcholine (ACh), which is
released into the synaptic cleft upon stimulation.

Describe the mechanism of action at the NMJ.

Upon stimulation, ACh is released from the presynmpatic terminal into the synamptic cleft, binds to ACh receptors on the postsynmpatic membrane, opening chemically gated channels that allow sodium ions (Na+) to enter the muscle fiber, leading to depolarization and triggering an action potential

What is the role of acetylcholinesterase (AChE) in
the NMJ?

Acetylcholinesterase (AChE) is present in the synaptic cleft and is responsible for breaking down acetylcholine (ACh) to terminate
the signal and prevent continuous stimulation of the muscle fiber.

Describe the role of ACh in muscle contraction.

ACh is crucial for the excitation contraction
coupling process in skeletal muscles, facilitating the transmission of signals that lead to muscle contraction.

How does acetylcholinesterase contribute to muscle relaxation?

Acetylcholinesterase breaks down ACh into acetate and choline in the synaptic cleft,
preventing continuous stimulation of the muscle and allowing for relaxation.

Define excitation-contraction coupling.

Excitation-contraction coupling is the physiological process that links the electrical stimulation of a muscle fiber to its contraction

Explain the significance of the somatic motor pathway.

The somatic motor pathway provides voluntary control over skeletal muscles, enabling precise movements.

What is synaptic transmission?

Synaptic transmission is the process of communication at the neuromuscular junction (NMJ), essential for the functioning of the muscular system.

Describe the importance of understanding ACh receptors in muscle movement.

Understanding ACh receptors and the mechanics of the neuromuscular junction is vital
for comprehending how the nervous system controls voluntary muscle movements.

What is the outcome of the action potential traveling along a muscle fiber?

The action potential traveling along the muscle fiber ultimately results in muscle contraction.

How does the interplay between neurons and muscle fibers affect movement?

The interplay between neurons and muscle fibers via ACh is fundamental to normal movement and the potential for neuromuscular disorders.

What is varicosity?

The swelling at the end of automatic postganglionic axons that contain vesicles filled with neurotransmitter

What is the neuroeffector junction?

The synapse between posganglionic automatic neuron and target cell

What are the two receptor types in postganglionic neurons?

Cholinergic and Adrenergic

Which of the two receptor types is found in the parasympathetic branch?

Cholinergic

What are the subdivision of Cholinergic receptor?

Muscarine and Nicotine

Which of the two receptor types is found in the sympathetic branch?

Adrenergic

What types of receptors you find in Adrenergic receptors?

A1, A2, B1, B2, and B3 receptors

Where are A1 receptors found in?

Most sympathetic target tissues

Where are A2 receptors found in?

Gastrointestinal tract and pancreas

Where are B1 receptors found?

Heart muscle and kidney?

Where are B2 receptors found?

Certain blood vessels and smooth muscles of some organ?

Where is B3 receptors found?

Adipose (fat) tissue

What is the sensitivity of A1 receptors?

NE>E

What is the sensitivity of A2 receptors?

NE>E

What is the sensitivity of B1 receptors?

NE=E

What is the sensitivity of B2 receptors?

E>NE

What is the sensitivity of B3 receptors?

NE>E

What is A1 receptor’s effect on second messenger?

Increases IP3 and intracellular Ca 2+ and increases PKC

What is A2 receptor’s effect on second messenger?

Decreases cAMP

What is B1 receptor’s effect on second messenger?

Increases cAMP

What is B2 receptor’s effect on second messenger?

increases cAMP

What is B3 receptor’s effect on second messenger?

Increases cAMP