10: Neural Pathways and Somatic Reflexes

Flashcards covering the definitions of neural pathway components, various types of reflexes, sensory receptors, and the mechanical functions of somatic reflex arcs like the stretch and tendon reflexes.

Reflex

A fast, involuntary, automatic, predictable response to a particular stimulus.

Reflex Arc

The neural pathway that impulses take to produce a reflex.

Spinal Reflex

A reflex where integration occurs in the spinal cord gray matter with spinal nerves serving as both afferent and efferent nerves.

Cranial Reflex

A reflex where integration takes place in the nuclei of the brainstem with cranial nerves serving as the afferent and efferent nerves.

Inborn Reflexes

Reflexes that are unlearned and typically subconscious.

Acquired Reflexes

Reflexes that are learned and result from practice or repetition.

Somatic Reflex

A reflex where efferent impulses are delivered by somatic motor neurons to skeletal muscle effectors; the response is always excitatory.

Autonomic (Visceral) Reflex

A reflex where efferent impulses are delivered by visceral motor neurons to smooth muscle, cardiac muscle, or a gland.

Sensation

Awareness of a stimulus, whereas the interpretation of the stimulus meaning (perception) occurs in the brain.

Exteroceptors

Sensory receptors that detect stimuli from the external environment, such as touch, pressure, and special senses like vision.

Interoceptors (Visceroceptors)

Sensory receptors that monitor the internal environment, including biochemical changes, mechanical forces, and thermal states.

Interoception

The process by which the nervous system senses and integrates information about the inner state of the body.

Proprioceptors

A subtype of interoceptor located in muscles, tendons, and joints that detect body positions and movements.

Dorsal Root

The collection of afferent axons that enter the spinal cord dorsally (posteriorly).

Ventral Root

The collection of efferent axons that exit the spinal cord ventrally (anteriorly).

Dorsal Root Ganglion (DRG)

An enlarged region of the dorsal root where the cell bodies of all sensory neurons entering the spinal cord are bundled.

Monosynaptic Reflex

The simplest type of reflex involving a single synapse between a sensory neuron and a motor neuron.

Polysynaptic Reflex

A reflex involving one or many interneurons, creating multiple synapses between sensory and motor neurons.

Excitatory Postsynaptic Potentials (EPSPs)

Inputs that increase the likelihood of a neuron depolarizing to create an action potential.

Inhibitory Postsynaptic Potentials (IPSPs)

Inputs that decrease the likelihood of a neuron depolarizing.

Summation

The process of adding together all excitatory and inhibitory inputs at the axon hillock to determine if threshold is reached.

Threshold of Excitation

A positive deviation of approximately $15\,mV$ from the resting membrane potential ($RMP \approx -70\,mV$) required to generate an action potential.

Neuromuscular Junction (NMJ)

The specific synapse where a somatic motor neuron releases Acetylcholine ($ACh$) to a skeletal muscle fiber.

Stretch Reflex

A protective reflex that initiates contraction of a muscle to counteract rapid or maximal lengthening.

Muscle Spindles

Proprioceptors found within the perimysium that monitor changes in muscle length and initiate the stretch reflex.

Intrafusal Fibers

Specialized muscle fibers within a muscle spindle capsule that function as part of the receptor rather than producing tension.

Extrafusal Fibers

Normal skeletal muscle fibers used to create tension and force.

Alpha Motor Neurons

Motor neurons that innervate extrafusal muscle fibers to produce the contraction that resists muscle stretch.

Gamma Motor Neurons

Motor neurons that innervate the ends of intrafusal fibers to keep the muscle spindle taut and sensitive to stretch.

Agonist

A muscle that has the major responsibility for producing a specific movement.

Antagonist

Muscles that oppose, reverse, or slow a particular movement, typically located on the opposite side of the joint to the agonist.

Reciprocal Inhibition

The reflexive relaxation of antagonist muscles to allow the contraction of agonist muscles without opposition.

Tendon Organs (Golgi Tendon Organs)

Proprioceptors located at the musculotendinous junction that monitor changes in muscle tension.

Tendon Reflex

A reflex initiated by tendon organs that causes the same muscle to relax when excess tension is detected.