Peripheral Nervous System Overview

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Questions and Answers

What type of receptors respond to stimuli from internal viscera and blood vessels?

Photoreceptors

Proprioceptors

Exteroceptors

Interoceptors (correct)

Which level of sensory processing involves the conversion of stimuli into electrical energy?

Perceptual level

Cortical level

Receptor level (correct)

Circuit level

What do proprioceptors primarily inform the brain about?

Pain from injuries

Movements of the body (correct)

Temperature fluctuations

Chemical changes in the blood

Adaptation in sensory processing refers to what phenomenon?

A decrease in responsiveness to a constant stimulus Signup and view all the answers

At which level does sensory integration culminate in the interpretation of stimulus meaning?

Cortical level Signup and view all the answers

What surrounds each individual axon in the central nervous system?

Endoneurium Signup and view all the answers

Which type of nerve transmits impulses from the spinal cord?

Motor (efferent) Signup and view all the answers

What is the primary function of cranial nerves?

To mainly provide sensation and movement for specific structures Signup and view all the answers

Which layer surrounds entire nerve bundles in the peripheral nervous system?

Epineurium Signup and view all the answers

Which classification correctly identifies cranial nerves based on impulse direction?

Motor and sensory Signup and view all the answers

What characterizes phasic receptors in terms of adaptation?

Become less responsive quickly. Signup and view all the answers

What is the role of the thalamus in sensory processing?

It guarantees sensory input reaches the correct region of the cerebral cortex. Signup and view all the answers

Which aspect of sensory perception involves identifying the intensity of a stimulus?

Magnitude estimation Signup and view all the answers

What does spatial discrimination allow an individual to do?

Identify the site or pattern of stimulation. Signup and view all the answers

Which type of receptors do nociceptors belong to?

Tonic receptors Signup and view all the answers

Which of the following best describes feature abstraction?

Identifying complex aspects and multiple stimulus properties. Signup and view all the answers

What is meant by quality discrimination?

Identifying submodalities of a sensation. Signup and view all the answers

What is the function of ascending pathways in sensory processing?

To transmit impulses toward the cerebral cortex. Signup and view all the answers

How do tonic receptors differ from phasic receptors in terms of response to stimuli?

Tonic receptors adapt slowly or not at all. Signup and view all the answers

Which process allows an individual to recognize patterns or familiar forms in sensory input?

Pattern recognition Signup and view all the answers

What is the primary function of the motor neuron in a reflex arc?

Conducts efferent impulses to the effector organ Signup and view all the answers

Which type of reflex involves more than one synapse in its integration center?

Polysynaptic reflex Signup and view all the answers

Which type of muscle is activated by autonomic (visceral) reflexes?

Both B and C Signup and view all the answers

Where is the integration center located in spinal reflexes?

In the spinal cord Signup and view all the answers

Which component of the reflex arc is responsible for the initial detection of a stimulus?

Receptor Signup and view all the answers

Which cranial nerve is responsible for taste and facial expression?

Facial Signup and view all the answers

What type of function does the Vagus nerve serve?

Motor and visceral organ sensation Signup and view all the answers

Which cranial nerve is primarily involved in eye movement?

Oculomotor Signup and view all the answers

How many cranial nerves are classified as 'motor' only?

4 Signup and view all the answers

What type of motor neurons innervate voluntary muscles?

Somatic motor neurons Signup and view all the answers

Which cranial nerve is responsible for hearing and balance?

Vestibulocochlear Signup and view all the answers

Which cranial nerve has both sensory and motor functions and is involved in chewing?

Trigeminal Signup and view all the answers

What distinguishes autonomic motor fibers from somatic motor fibers?

They do not form discrete junctions but release neurotransmitters from swellings. Signup and view all the answers

Identify the cranial nerve that is involved in swallowing and secretion of saliva.

Glossopharyngeal Signup and view all the answers

Which spinal nerve category has the largest number of pairs?

Cervical nerves Signup and view all the answers

Inborn reflexes differ from learned reflexes in that they are:

Rapid, involuntary, and predictable responses. Signup and view all the answers

Which cranial nerve controls the movement of the tongue during speech and swallowing?

Hypoglossal Signup and view all the answers

Where do spinal nerves exit the vertebral column?

Through intervertebral foramina Signup and view all the answers

What is the role of acetylcholine (ACh) in somatic motor endings?

To open chemically-gated ion channels. Signup and view all the answers

What is significant about the term 'synapse en passant' in relation to autonomic motor endings?

It describes how neurotransmitters are released along the axon. Signup and view all the answers

Which spinal nerve types are classified under mixed nerves?

Mixed nerves, containing both sensory and motor fibers Signup and view all the answers

Study Notes

Peripheral Nervous System (PNS)

The PNS has three key components: sensory receptors, nerves, and motor endings.
These components connect the Central Nervous System (CNS) to the rest of the body.

Sensory Receptors

Respond to changes in the environment (stimuli).
Activation results in graded potentials that may trigger nerve impulses.
Receptors are classified by stimulus type (modality), location, and structure.
Not all receptor structure and function will be discussed in this session.
Classification by Stimulus Type:
- Mechanoreceptors: Respond to touch, pressure, vibration, and stretch.
- Thermoreceptors: Respond to changes in temperature.
- Photoreceptors: Respond to light energy.
- Chemoreceptors: Respond to chemicals (taste/smell molecules or changes in blood chemistry).
- Nociceptors: Respond to potentially damaging stimuli (extreme heat/cold, excessive pressure, inflammatory chemicals)
- Itch receptors: Histamine-sensitive C-fibers, also sensitive to heat and capsaicin. Not identified until 1997.
Classification by Location:
- Exteroceptors: Respond to stimuli from outside the body. Examples: receptors in skin for touch, pressure, pain, temperature or special sense organs (vision, hearing, smell).
- Interoceptors (visceroceptors): Respond to stimuli from internal organs and blood vessels. Examples: chemical changes, tissue stretch, and temperature changes in internal organs
- Proprioceptors: Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings around bones and muscles. These receptors inform the brain about body position and movement.

Sensation and Perception

Sensation is the awareness of a stimulus.
Perception is the interpretation of a stimulus's meaning and is vital for survival. This occurs exclusively in the brain.
Sensory information is processed at three levels:
- Receptor level: Processing of sensory information by sensory receptors.
- Circuit level: Processing of sensory information in ascending pathways.
- Perceptual level: Processing of sensory information in cortical sensory areas.

Receptor Level Processing: Adaptation

Adaptation is a change in sensitivity in the presence of a constant stimulus.
Receptor membranes become less responsive to the constant stimulus.
Graded potentials decrease in frequency or stop.
- Phasic receptors: Rapidly adapt such as photoreceptors and Meissner's corpuscles
- Tonic receptors: Slowly or not at all adapt, such as nociceptors and most proprioceptors.

Circuit Level Processing

Ascending pathways carry impulses towards the cerebral cortex.
The thalamus ensures that sensory information reaches appropriate regions of the cerebral cortex.
Crude sensation occurs once signals reach the thalamus. Complex localization and discrimination occur in the cerebral cortex

Perceptual Level Processing

Perception of the sensory stimulus occurs at this level.
- Perceptual detection
- Magnitude estimation
- Spatial discrimination
- Feature abstraction
- Quality discrimination
- Pattern recognition

Nerves

Nerves are bundles of PNS axons enclosed by connective tissue.
Structure inside a nerve is called a tract in the CNS.
- Endoneurium: surrounds individual axons
- Perineurium: surrounds bundles of axons (fascicles)
- Epineurium: surrounds the entire nerve

Nerve Classification

Direction of Impulse Transmission:
- Sensory (afferent): Carries impulses toward the CNS
- Motor (efferent): Carries impulses away from the CNS
- Mixed: Contains both sensory and motor fibers
Origin:
- Cranial: Originates from cranial nerves
- Spinal: Originates from spinal nerves

Cranial Nerves

Most cranial nerves are named for the structure they serve or their function.
Specific lists of cranial nerves and functions provided.

Spinal Nerves

Spinal nerves are named based on the location where they emerge.
- Cervical (C1-C8)
- Thoracic (T1-T12)
- Lumbar (L1-L5)
- Sacral (S1-S5)
- Coccygeal (Co)
All spinal nerves are mixed nerves.
They do not directly attach to the spinal cord.

Motor Endings

Somatic Motor Endings: innervation of skeletal muscle
- Somatic motor neurons innervate voluntary muscles via neuromuscular junctions (NMJ)
- Acetylcholine (ACh) opens chemically-gated ion channels
Autonomic Motor Endings: innervation of visceral muscle and glands
- Neurotransmitter (ACh or norepinephrine) is released from swellings (varicosities) along the length of the axon
- These synapses are called synapses en passant.

Reflexes

Inborn (intrinsic) reflexes are rapid, involuntary, and predictable responses to a stimulus.
Learned (acquired) reflexes result from practice and repetition, such as driving a car.

Components of a Reflex Arc

Receptor: Site of stimulus action.
Sensory neuron: Transmits afferent impulses to the CNS.
Integration center: Region within the CNS.
Motor neuron: Conducts efferent impulses to the effector.
Effector: Responds to efferent impulses.

Reflex Types

Cranial reflexes: Integration center in the brain; utilizes cranial nerves.
Autonomic (visceral) reflexes: Activate smooth muscles, cardiac muscle, and glands.
Spinal reflexes: Integration center in the spinal cord; utilizes spinal nerves.
Somatic reflexes: Stimulate skeletal muscle.
Monosynaptic reflexes: One synapse in the integration center (Sensory neuron communicates directly with motor).
Polysynaptic reflexes: More than one synapse in the integration center (Interneurons are used).

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Description

This quiz covers the key components of the Peripheral Nervous System (PNS), including sensory receptors, their classifications by stimulus type, and their functions. Understanding these elements is crucial for grasping how the PNS connects the Central Nervous System to the body. Test your knowledge on mechanoreceptors, thermoreceptors, and more!