Sensory pathways & the somatic nervous system (Vocabulary Flashcards)

Vocabulary flashcards covering key concepts from sensory receptors, transduction, interpretation of sensory information, receptive fields, somatic nervous system, and neuromuscular transmission.

Receptor adaptation

Receptors become less sensitive to constant stimulation over time.

Tonic receptors

Adapt slowly or not at all; provide a constant signal during a stimulus.

Phasic receptors

Adapt quickly; respond best to changes in stimulus.

Receptor potential

Graded potential produced in a sensory receptor in response to a stimulus.

Sensory transduction

Conversion of stimulus energy into electrical energy (action potentials) in the nervous system.

Mechanoreceptors

Receptors that respond to mechanical stimuli such as touch, pressure, vibration, and proprioception.

Thermoreceptors

Receptors that detect changes in temperature (warmth and cold).

Nociceptors

Pain receptors that respond to mechanical, thermal, or chemical stimuli.

Chemoreceptors

Receptors that respond to chemical stimuli (e.g., CO2, pH).

Proprioceptors

Receptors that monitor the position and movement of joints and muscles.

Free nerve endings

Tactile receptors in the skin that respond to touch/pressure; slow adapting.

Root hair plexus

Receptor that detects movement of hair; fast adapting.

Tactile discs

Touch and pressure receptors in the epidermis; slow adapting.

Meissner’s corpuscles

Tactile receptors for light touch, pressure, and vibration; rapid adapting.

Pacinian (Lamellated) corpuscles

Deep pressure and vibration receptors; rapid adapting.

Ruffini endings

Deep sustained pressure receptors in the reticular dermis; slow adapting.

Two-point discrimination

Ability to distinguish two closely spaced points as separate stimuli.

Receptive field

Area monitored by a single sensory neuron.

Receptive field size variation

Fields are small in sensitive areas (e.g., lips) and large in less sensitive areas (e.g., back).

Primary somatosensory cortex

Cortex area where touch, pressure, and proprioceptive information is mapped.

Labelled lines

Distinct neural pathways that carry specific stimulus types to the cortex.

First-order neuron

Afferent neuron sending action potentials toward the CNS.

Second-order neuron

Neuron in the spinal cord or brainstem that relays to the thalamus or cerebellum.

Third-order neuron

Neuron from the thalamus to the cerebral cortex.

Stimulus type (labelled line concept)

The cortex identifies the type of stimulus based on the specific labelled line activated.

Stimulus intensity

Determined by the frequency of action potentials and the number of receptors activated.

Stimulus location

Determined by receptive field organization and cortical mapping of the area stimulated.

Receptive field

Area monitored by a single sensory neuron; size varies by body region.

Somatic nervous system

Division of the PNS that controls skeletal muscle.

Motor unit recruitment

Activation of more motor units to increase contraction strength.

Frequency of action potentials

Higher AP frequency increases muscle tension.

Neuromuscular junction (NMJ)

Synapse where the motor neuron communicates with a muscle fiber.

Acetylcholine (ACh)

Neurotransmitter released at the NMJ to trigger a muscle action potential.

Ca2+ in NMJ (presynaptic)

Ca2+ enters the presynaptic terminal triggering ACh release.

Ca2+ release in muscle (sarcoplasmic reticulum)

Ca2+ release into the cytosol from the SR triggers muscle contraction.

Troponin

Regulatory protein on actin that binds Ca2+ and moves tropomyosin away from myosin binding sites.

Tropomyosin

Regulatory protein that covers actin binding sites; moved by Ca2+-bound troponin.

Cross-bridge cycling

Myosin heads bind, pivot (power stroke), detach, and re-cock to pull actin.

Power stroke

Myosin head pivots to slide the thin filament toward the center of the sarcomere.

ATP in contraction

ATP provides energy for detachment and re-cocking of myosin heads.

Motor neuron action potential at NMJ

AP arrival opens voltage-gated Ca2+ channels; Ca2+ triggers ACh release.

ACh receptor-channel (nicotinic-like)

Ion channel at the motor end plate that opens to cations when ACh binds.

T tubules and SR in muscle

APs travel via T-tubules to trigger Ca2+ release from the sarcoplasmic reticulum.

Ca2+ reuptake

Ca2+ pumped back into the sarcoplasmic reticulum when APs stop, enabling relaxation.

Twitch

A single, brief muscle contraction in response to a single AP.

Tetanus (fused contraction)

A smooth, sustained contraction resulting from high-frequency stimulation.

A-delta fibers

Fast, myelinated nociceptive fibers conveying sharp pain.

C fibers

Slow, unmyelinated nociceptive fibers conveying dull, aching pain.