Sensory pathways and tracts

What are sensory receptors?

Processes of specialized sensory neurons or cells monitored by sensory neurons.

What is the difference between sensation and perception?

Sensation is the arriving information, while perception is the conscious awareness of a sensation.

What are the general senses?

Sensitivity to temperature, pain, touch, pressure, vibration, and proprioception (body position).

What are the special senses?

Olfaction (smell), gustation (taste), vision (sight), equilibrium (balance), and hearing.

What is receptor specificity?

Each receptor has a characteristic sensitivity to specific stimuli.

What is a receptive field?

The area monitored by a single receptor cell; larger fields make it harder to localize a stimulus.

What is transduction in sensory receptors?

The conversion of an arriving stimulus into an action potential by a sensory receptor.

What is adaptation in sensory receptors?

The reduction of receptor sensitivity in the presence of a constant stimulus, which can be peripheral or central.

What are tonic receptors?

Always active and slow-adapting receptors that generate action potentials at a frequency reflecting the background level of stimulation.

What are phasic receptors?

Normally inactive receptors that respond strongly at first to a stimulus but then decrease activity; they are fast-adapting.

What are exteroceptors?

Sensory receptors that provide information about the external environment.

What are proprioceptors?

Sensory receptors that report the positions of skeletal muscles and joints.

What are interoceptors?

Sensory receptors that monitor visceral organs and functions.

What are nociceptors?

Pain receptors that are free nerve endings with large receptive fields, sensitive to temperature extremes, mechanical damage, and dissolved chemicals.

Where are cold receptors located?

In the dermis, skeletal muscles, liver, and hypothalamus; they are thermoreceptors that are more numerous than warm receptors.

What stimuli do thermoreceptors respond to?

They respond to temperature changes and sensations are conducted along pathways that also carry pain sensations.

What are mechanoreceptors?

Sensory receptors that respond to physical distortion.

What are chemoreceptors?

Sensory receptors that respond to chemical concentration.

What are mechanoreceptors sensitive to?

Physical stimuli that distort their plasma membranes, including stretching, compression, twisting, and other distortions.

What are the three classes of mechanoreceptors?

Tactile receptors, baroreceptors, and proprioceptors.

What sensations do tactile receptors provide?

Touch (shape or texture), pressure (degree of mechanical distortion), and vibration (pulsing pressure).

What do baroreceptors detect?

Pressure changes in blood vessels and in the digestive, respiratory, and urinary tracts.

What do proprioceptors monitor?

The positions of joints and skeletal muscles.

What are the characteristics of fine touch and pressure receptors?

They are extremely sensitive, have narrow receptive fields, and provide detailed information about the source of stimulation.

What do crude touch and pressure receptors provide?

Poor localization and little information about the stimulus due to their large receptive fields.

What are free nerve endings sensitive to?

Touch and pressure, situated between epidermal cells.

What do root hair plexus nerve endings monitor?

Distortions and movements across the body surface wherever hairs are located.

What are tactile discs sensitive to?

Fine touch and pressure, and they are extremely sensitive tonic receptors with very small receptive fields.

Where are bulbous corpuscles (Ruffini corpuscles) located?

In the reticular (deep) dermis, sensitive to pressure and distortion of skin.

What do lamellar corpuscles (Pacinian corpuscles) respond to?

Deep pressure and are most sensitive to pulsing or high-frequency vibrating stimuli.

What sensations do tactile corpuscles (Meissner corpuscles) perceive?

Fine touch, pressure, and low-frequency vibration, adapting quickly after contact.

What do chemoreceptors respond to?

Water- and lipid-soluble substances dissolved in body fluids, monitoring pH, carbon dioxide, and oxygen levels.

What is the role of first-order neurons in sensory pathways?

They deliver sensations to the central nervous system (CNS).

What is the function of second-order neurons?

Interneurons in the spinal cord or brainstem that receive information from first-order neurons and cross to the opposite side of the CNS.

What is the role of third-order neurons?

They are located in the thalamus and must receive information from second-order neurons for the sensation to reach awareness.

What are the major somatic sensory pathways?

Spinothalamic pathway, posterior column pathway, and spinocerebellar pathway.

What is phantom limb syndrome?

A condition where painful sensations are felt in an amputated limb.

What is referred pain?

Pain felt in an uninjured part of the body when pain originates at another location.

What is the sensory homunculus?

A functional map of the primary somatosensory cortex, showing areas devoted to body regions proportional to the density of sensory neurons.

What does the spinocerebellar pathway convey?

Information on positions of muscles, tendons, and joints from the spinal cord to the cerebellum.

What are the three major groups of proprioceptors?

Muscle spindles, Golgi tendon organs, and receptors in joint capsules.

What does the somatic nervous system control?

Contractions of skeletal muscles through somatic motor pathways involving at least two motor neurons.

What is the role of upper motor neurons?

They lie in a CNS processing center and synapse on lower motor neurons, facilitating or inhibiting their activity.

What is the function of lower motor neurons?

They innervate a single motor unit in a skeletal muscle, triggering contractions.

What are the three integrated motor pathways that control skeletal muscles?

Corticospinal pathway, medial pathway, and lateral pathway.