Chapter 6: The Peripheral Nervous System - Afferent Division; Special Senses

The PNS has nerve fibers that carry information between the CNS and body regions. Its ___ (sensory) division sends information about the external and internal environment to the CNS

afferent

__ are a connected series of neurons and fibers that transmit signals from one specific part of the nervous system to another, like a dedicated communication route.

Pathways

___ carries information towards the CNS (brain and spinal cord)

Afferent pathways

___ are organs in the body cavities, such as the abdominal cavity

Viscera

Afferent input derived from receptors located at the body surface or in the muscles or joints, typically reaching conscious awareness. This input is also known as ___. Categorized as somatic (body sense) sensation and special sense.

Sensory information

___ arises from the body surface, inclusion somesthetic sensation (sensation from the skin, such as touch, pressure, heat, cold, and pain) and proprioception (awareness of body’s position) from the muscle, joints, skin, and inner ear

Somatic sensation

___ is the incoming pathway for information derived from the internal viscera. Subconscious information (sometimes interchangeable with afferent information) like blood pressure, and the concentration of CO2 in the body fluids

Visceral afferent

___ is the incoming pathway for sensory information. Conscious information that we can sense.

sensory afferent

___ is the conscious awareness of the external world

Perception

Perception is created by the brain from a pattern of ___ sent to the brain from sensory receptors.

nerve impulses

The brain interprets an input. Human perception ___ replicate reality.

does not

___ (also just called receptors, though that word can apply broadly) are structures at the peripheral endings of afferent neurons. They detect stimuli and carry information toward the CNS. Classified by stimulus, location and structural complexity

Sensory receptors

Sensory receptors are classified by ___. Each type of receptor has a corresponding __. Types of receptors are: photoreceptor, mechanoreceptor, thermoreceptor, osmoreceptor, chemoreceptor, and nociceptor.

Stimulus

___ respond to visible wavelength of light

Photoreceptors

__ are sensitive to mechanical energy

mechanoreceptors

___ are sensitive to heat and cold

thermoreceptor

___ detect changes in the concentration of solutes in body fluids.

osmoreceptors

___ are sensitive to specific chemicals such as the concentration of oxygen in the blood

chemoreceptors

___ are pain receptors that are sensitive to tissue damage

nociceptors

Sensory receptors classified by ___: Exteroceptors (outside the body), interceptors (inside the body), proprioceptors (position in the body)

location

Sensory receptors classified by ___: simple (modified dendritic endings of sensory neurons), complex (special senses associations)

complexity

A stimulus alters the membrane permeability of the cells of a receptor (triggering event). This leads to production of a ___ receptor potential.

graded

The sensory receptor of an ___ neuron can be a specialized ending of an ___ neuron or a cell closely associated with the ___ ending of a neuron. So sometimes the receptor is attached and sometimes it's not.

afferent

A stimulus alters the membrane permeability of the cells of a receptor, producing a graded receptor potential. This change in membrane permeability can lead to the influx of sodium ions. This produces receptor (generator) potentials. The magnitude of the report potential represents the intensity of the stimulus. A receptor potential of sufficient magnitude can produce an action potential. This action potential is propagated along an ____ fiber to the CNS.

Afferent

Draw receptor connected and unconnected diagram

Draw receptor connected and unconnected diagram

By ___, receptors can adjust to sustained stimulation. With sustained stimulus length, the extent of receptor depolarization decreased. This ___ can be fast or slow.

adaptation

___ receptors adapt slowly or do not adapt. Important in situations where information about a stimulus must be maintained,  such as stretching

Tonic

___ receptors adapt rapidly. Most notably Pacinian corpuscle. Important for situations where it's important to signal a change in stimulus intensity rather than to relay status quo information. (ex: not consistently aware of the feeling of clothes on skin).

Phasis

The ___ (type of receptor) detects pressure and vibrations in the skin. Responds with a slight depolarization called the off response when the stimulus is removed. As a phasic receptor, it adapts rapidly.

Pacinian corpuscle

Draw pacinian corpuscle diagram

Draw pacinian corpuscle diagram

Afferent pathways reaching the spinal cord can be part of a ___ or can be __ to the brain by ascending pathways.

 reflex arc; relayed

___ are discrete chains of neurons

Labeled lines

___ pathways convey conscious somatic sensations. Consist of labeled lines synaptically interconnected in a particular sequence to accomplish progressively more sophisticated processing of the sensory information.

Somatosensory

A receptor detects a stimulus. A specific receptor detects a specific stimulus for each kind of ___.

sense modality

___ neuron is an afferent neuron with its peripheral (from PNS) receptor that first detects the stimulus. Sends a signal from the receptor to the spinal cord

first-order sensory

The first-order sensory neuron synapses with a second-order neuron in the ___ or __.

spinal cord; medulla

The second-order sensory neuron synapses with a third-order sensory neuron in the ___ and so on.

thalamus

Each afferent and ascending pathway excites a defined area of the ___

Cerebral cortex

The ___ is a circumscribed area of the skin surrounding the point of stimulation. Said stimulus information is sent from a somatosensory neuron.

receptive field

The smaller the receptive fields for a sense on the skin surface, the ___ (lesser or greater) the acuity (/ discriminative ability).

greater

___ also influences receptor acuity from the skin. The center of a stimulus inhibits less excited areas on the fringe of the stimulus.

Lateral inhibition

Draw receptive field diagrams

Draw receptive field diagrams

Draw acuity diagram

Draw acuity diagram

Draw lateral inhibition diagram

Draw lateral inhibition diagram

Stimulation of ___ produces the perception of pain. Because of their value to survival, nociceptors do not adapt to sustained or repetitive stimulation.

nociceptors

___ (such as withdrawal or defense) and ___ (such as crying or fear) responses also affect the perception of pain

Motivated behavioral response; emotional reaction

There are three categories of___: mechanical receptors, thermal receptors and polymodal nociceptors.

pain receptors

___ respond to mechanical damage, such as cutting, crushing, or pinching

Mechanical receptors

___ respond to temperature extremes

Thermal receptors

___ respond to damaging stimuli, including irritating chemical release from injured tissues

Polymodal nociceptors

There are fast and slow ___ pain fibers

afferent

A-delta (afferent) fibers fire at rates of _ meter per second (the fast pain pathway). Transmit mechanical and thermal nociceptors. Sharp initial pain

30

C (afferent) fibers fire at _ meters per second (slow pain pathway). Carry polymodal nociceptors. Dull aching pain that follows initial pain.

12

There is a higher-level processing of pain input. Such as the pain ___ , substance P

neurotransmitter

___ activates ascending pathways that transmit nociceptive signals to higher levels for further processing

Substance P

Ascending pathways for ___ are in the cortex, thalamus, and reticular formation.

pain

___ processing areas localize the pain, whereas other cortical areas participate in the other conscious components of the pain experience, such as deliberation about the incident.

Cortical somatosensory

Pain can still be perceived in the absence of the cortex, presumably at the level of the ___

thalamus

The ___ increases the level of alertness associated with the noxious encounter

Reticular formation

Interconnection from the ___ and __ to the hypothalamus and the limbic system elicit the behavioral and emotional responses accompanying the painful experience.

Thalamus; reticular formation

___ is a pain-suppressing system contained within the CNS. It suppresses transmission in the pain pathways as they enter the spinal cord.

Analgesic system