7.2 - Sensation to Response starts with Receptors

Sensation

Biochemical or electrochemical changes at the cellular level in a receptor cell that detect an imbalance in homeostasis or a change in the environment; information is sent as an impulse toward the CNS via afferent nerves

Perception

The identification, interpretation, and organization of a sensory signal by the CNS that allows for construction of an appropriate response

Response (effector)

The output triggered by the CNS via efferent signals; carried out by effectors after the CNS processes and perceives sensory input

Ascending tracts

Spinal cord tracts that carry sensory information upward from the PNS to the CNS (brain)

Descending tracts

Spinal cord tracts that carry motor output downward from the brain to the spinal cord and out to the periphery

Sensory pathway steps

Stimulus → receptor depolarization → action potential in afferent neuron → CNS processing/perception → motor response (voluntary/somatic or involuntary/autonomic)

Sensory receptors

Structures located in skin, organs, muscles, and tendons that detect a specific stimulus and convert it into electrochemical signals sent to the CNS

Nociceptors

Sensory receptors that detect pain caused by chemicals from tissue damage, intense mechanical stimuli, or extreme temperature changes; protect tissues from damage

Thermoreceptors

Sensory receptors sensitive to temperature above (heat) or below (cold) homeostatic body temperature; do NOT detect temperatures that cause pain or tissue damage (unlike nociceptors)

Mechanoreceptors

Sensory receptors that detect physical stimuli (light touch, pressure, vibration, sound, body position) by physical distortion of the cell membrane, which opens mechanically regulated ion channels

Meissner's corpuscles (Tactile corpuscles)

Mechanoreceptors in the skin that detect fine touch and vibration

Lamellar corpuscles (Pacinian corpuscles)

Encapsulated mechanoreceptors in the dermis that respond to deep pressure and touch; highest concentration in hands and feet

Root hair plexuses

Mechanoreceptors that wrap around hair follicles and detect movement of the hair

Baroreceptors

Free nerve ending mechanoreceptors in walls of organs and blood vessels (digestive, urinary, respiratory tracts) that sense pressure changes by detecting wall stretch and altering their rate of action potential firing

Proprioceptors

Mechanoreceptors located near moving body parts that interpret the position of tissues as they move; found in muscles and tendons to monitor tension and stretch and prevent tearing or overstretching

Golgi tendon organ (GTO)

A proprioceptor located in tendons that detects the rate of change in tendon tension; activated by stretch during muscle contraction; signals the brain if muscle tension is too high

Muscle spindle

A proprioceptor found within muscle tissue that provides information to the brain on muscle length; stimulated when the muscle stretches and lengthens

Chemoreceptors

Sensory receptors that detect specific chemical stimuli; includes taste (gustatory), smell (olfactory), and receptors in the brain and carotid arteries that monitor pH, CO₂, and O₂ levels in blood and CSF

Chemoreceptors of medulla oblongata

Detect changes in pH and CO₂ in cerebrospinal fluid; trigger reflexive adjustments in depth and rate of respiration

Chemoreceptors of carotid bodies

Detect changes in pH, CO₂, and O₂ in blood; signal via cranial nerve IX; trigger reflexive adjustments in respiratory and cardiovascular activity

Chemoreceptors of aortic bodies

Detect changes in pH, CO₂, and O₂ in blood; also involved in cardiovascular and respiratory regulation

Exteroceptors

Sensory receptors that detect stimuli from the external environment; examples include somatosensory receptors (touch, pressure, thermoreceptors, nociceptors), chemoreceptors for taste and smell, and telereceptors

Interoceptors

Sensory receptors that detect stimuli from internal organs and tissues; examples include baroreceptors, chemoreceptors, stretch receptors, osmoreceptors, and proprioceptors

Telereceptors

Specialized exteroceptors that detect stimuli from far distances; examples include photoreceptors (vision) and hair cells (hearing)

Osmoreceptors

A type of interoceptor primarily found in the hypothalamus that detects changes in solute concentration of blood (blood osmolality)

Baroreceptors of carotid sinus and aortic sinus

Interoceptors that provide information on blood pressure to cardiovascular and respiratory control centers

Baroreceptors of the lung

Interoceptors that provide information on lung expansion to respiratory rhythmicity centers to control respiratory rate

Baroreceptors of the digestive tract

Interoceptors that detect volume of tract segments and trigger reflex movement of materials along the tract

Baroreceptors of the colon

Interoceptors that detect volume of fecal material and trigger the defecation reflex

Baroreceptors of the bladder wall

Interoceptors that detect volume of urine in the bladder and trigger the urination reflex

Nociceptors vs. thermoreceptors — key difference

Both can respond to temperature, but thermoreceptors detect non-damaging temperature changes while nociceptors respond to extreme temperatures that cause pain or tissue damage

Exteroceptors vs. interoceptors — key difference

Exteroceptors detect stimuli from outside the body (environment); interoceptors detect stimuli from inside the body (organs, tissues, blood)