Peripheral Nervous System: General Sensations and Sensory Pathways

Flashcards covering the peripheral nervous system, general sensations, sensory modalities, sensory receptors, somatic sensations, somatic sensory pathways, somatic motor pathways, integrative functions of the cerebrum, learning and memory, and amnesia.

General Sensations

Sensory impulses reach the CNS, becoming part of a large sensory input pool that undergoes integration with other information.

Integration

The process where incoming sensory information combines with other arriving and previously stored information.

Sensation

A conscious perception or subconscious awareness that changes have occurred in the external or internal environment.

Sensory Modality

Each unique type of sensation (touch, pain, vision).

Somatic Senses

Tactile sensations (touch, pressure, vibration, itch, and tickle), thermal sensations (warm and cold), pain sensations, and proprioception (awareness of limb and joint position in space (body position)).

Visceral Senses

Information about conditions within internal organs (pressure, stretch, chemicals, nausea, hunger and temperature).

Sensory Receptor

Responds vigorously to one particular kind of stimulus.

Stimulation of Sensory Receptor

An appropriate stimulus must occur within the receptor’s receptive field.

Transduction of Stimulus

A sensory receptor transduces transform the energy of a stimulus into a graded potential.

Generation of Nerve Impulses

Occurs when a graded potential reaches threshold which triggers one or more nerve impulses which then propagate toward the CNS.

Integration of Sensory Input

Occurs when a particular region of the CNS integrates a number of sensory nerve impulses and results in a conscious sensation or perception.

Free Nerve Endings

Bare dendrites that lack structural specializations; receptors for pain, temperature, tickle, itch, and some touch.

Encapsulated Nerve Endings

Dendrites enclosed in a connective tissue capsule with a distinctive microscopic structure; used for pressure, vibration, and some touch.

Separate Cells

Sensory receptors for special senses that release neurotransmitters to produce receptor potentials. Examples include gustatory receptor cells, photoreceptors, and hair cells.

Exteroceptors

Located at or near the external surface of the body and respond to external stimuli; examples include hearing, vision, smell, taste, touch, pressure, temperature, and pain.

Interoceptors (Visceroceptors)

Located in blood vessels, organs, and muscles, producing impulses usually not consciously perceived, but may feel pain or pressure.

Proprioceptors

Located in muscles, tendons, joints, and the inner ear, providing information about body position, muscle length, and movement of joints.

Mechanoreceptors

Sensitive to deformation, stretching, or bending of cells; detect touch, vibration, and pressure.

Thermoreceptors

Detect changes in temperature.

Nociceptors

Respond to painful stimuli and tissue damage.

Photoreceptors

Detect photons of light striking the retina of the eye.

Chemoreceptors

Detect chemicals in the mouth (taste), nose (smell), and body fluids.

Osmoreceptors

Detect the osmotic pressure of body fluids.

Adaptation

Generator or receptor potential decreases in amplitude during a sustained or constant stimulus.

Rapidly Adapting Receptors

Receptors that quickly adapt, associated with pressure, touch, and smell.

Slowly Adapting Receptors

Receptors that continue to trigger impulses as long as the stimulus persists, associated with pain, body position, and chemical composition of the blood.

Somatic Sensations

Sensations arising from stimulation of sensory receptors in the skin or subcutaneous layer, mucous membranes, muscles, tendons, joints, and inner ear.

Cutaneous Sensations

Sensations arising from the skin surface.

Tactile Sensations

Touch, pressure, vibration, itch, and tickle.

A Fibers

Largest, fast, myelinated neurons that carry touch and pressure sensations, joint position; many motor neurons are also this type.

B Fibers

Medium size and speed; comprise myelinated visceral sensory & autonomic preganglionic neurons.

C Fibers

Smallest and slowest; comprise unmyelinated sensory and autonomic motor neurons.

Meissner Corpuscles of Touch

Located in hairless skin; rapidly adapting touch receptors enclosed by connective tissue.

Hair Root Plexuses

Found in hairy skin; free nerve endings wrapped around hair follicles.

Type I Cutaneous Mechanoreceptors (Tactile Discs)

Free nerve endings that make contact with Merkel cells of the stratum basale; slowly adapting touch receptors.

Type II Cutaneous Mechanoreceptors (Ruffini Corpuscles)

Encapsulated receptors located deep in the dermis, ligaments, and tendons; sensitive to stretching of skin; slowly adapting touch receptors.

Pressure

A sustained sensation felt over a larger area than touch, occurs with deformation of deeper tissues.

Pacinian Lamellated Corpuscle

Large oval structure composed of multilayered connective tissue capsule that encloses a dendrite; rapidly adapting pressure receptor.

Itch

Results from stimulation of free nerve endings by chemicals like bradykinin or antigens in mosquito saliva.

Tickle

Free nerve endings are thought to mediate this sensation, arises only when someone else touches you.

Cold Receptors

Free nerve endings located in the stratum basale of the epidermis; rapidly adapting thermoreceptors, sensitive to temperatures between 50-95 degrees F.

Warm Receptors

Free nerve endings located in the dermis; rapidly adapting thermoreceptors, sensitive to temperatures between 86-113 degrees F.

Nociceptors

Chemoreceptive free nerve endings activated by tissue damage from intense thermal, mechanical, or chemical stimuli; found in every tissue except the brain.

Fast Pain

Occurs rapidly due to impulses propagating along large-diameter, myelinated A fibers.

Slow Pain

Begins after a stimulus is applied and gradually increases in intensity; impulses conduct along small-diameter, unmyelinated C fibers.

Superficial Somatic Pain

Arises from stimulation of receptors in the skin.

Deep Somatic Pain

Results from stimulation of receptors in skeletal muscles, joints, tendons, and fascia.

Visceral Pain

Results from stimulation of nociceptors in visceral organs.

Referred Pain

Pain felt in or just deep to the skin that overlies the stimulated visceral organ, or in a surface area far from the stimulated organ.

Proprioceptive Sensations

Allow us to recognize that parts of our body belong to us and to know where our head and limbs are located and how they are moving.

Kinesthesia

Perception of body movements.

Proprioceptors

Receptors embedded in muscles and tendons; monitor body position.

Postcentral Gyri

Located on both parietal lobes of the brain; sites for the primary somatosensory area.

First-Order Neurons (FON)

Conduct impulses from somatic receptors into the brain stem or spinal cord.

Second-Order Neurons (SON)

Conduct impulses from the brain stem and spinal cord to the thalamus; axons decussate before ascending to the thalamus.

Third-Order Neurons (TON)

Conduct impulses from the thalamus to the primary somatosensory area of the cortex on the same side.

Relay Station

The thalamus.

Cerebellum Activities

Monitoring intentions for movement, monitoring actual movement, comparing command signals with sensory information, and sending out corrective feedback.

Wakefulness and Sleep

Relies on the reticular activating system (RAS).

Circadian Rhythm

A 24 hour cycle.

NREM Non-Rapid Eye Movement Sleep

Involves transition stage, light sleep, moderately deep sleep and then the deepest sleep.

REM Rapid Eye Movement Sleep

Occurs about every 90 minutes with each session gradually getting longer. Neuronal activity is high during this cycle.

Learning

The ability to acquire new information or skills through instruction or experience.

Memory

The process by which information already acquired through learning is stored and retrieved.

Immediate Memory

Lasts for only a few seconds; perspective to the present time.

Short-Term Memory

Lasts from a few seconds to minutes; remembering a phone number.

Long-Term Memory

Lasts from days to years; about 1% of all information that comes to our consciousness is stored this way.

Plasticity

The capability for change associated with learning.

Amnesia

Refers to the lack or loss of memory; a total or partial inability to remember past experiences.

Anterograde Amnesia

Inability to form new memories.

Retrograde Amnesia

Inability to recall the past.