The Somatic Nervous System Practice Flashcards

These flashcards cover the key vocabulary regarding the somatic nervous system, sensory receptors, ascending sensory pathways, descending motor tracts, and various reflex mechanisms based on the Chapter 14 lecture notes.

Afferent division

A functional division of the Peripheral Nervous System (PNS) that carries sensory information from receptors in peripheral tissues and organs to the Central Nervous System (CNS).

Efferent division

A functional division of the PNS that carries motor commands from the CNS to peripheral effectors like skeletal muscles, smooth muscles, and glands.

Somatic motor (SMS)

A component of the efferent division that carries motor commands specifically to skeletal muscles.

Autonomic motor (ANS)

A component of the efferent division that carries motor commands to smooth muscles, cardiac muscle, glands, and adipose tissue.

Sensory neurons

Afferent neurons, typically unipolar, whose cell bodies are grouped in sensory ganglia and whose processes extend from sensory receptors to the CNS.

Monitor external environment

The primary function of somatic sensory neurons.

Motor neurons

Efferent neurons that carry instructions from the CNS to peripheral effectors via efferent fibers (axons).

Interneurons

Neurons located between sensory and motor neurons, responsible for the distribution of sensory information, coordination of motor activity, and higher functions such as memory and planning.

Ascending tracts

Sensory pathways consisting of a series of neurons that relay information up the spinal cord to the CNS.

Transduction

The process of turning a stimulus into an action potential.

Sensation

The arriving information in the form of action potentials reaching the CNS.

Perception

The conscious awareness of a sensation.

Proprioception

A general sense describing the awareness of body position.

Free Nerve Endings

Naked dendrites where action potentials result from membrane stimulation; they detect touch, pressure, pain, and temperature.

Encapsulated Nerve Endings

Dendrites covered in collagen fibers where action potentials result from membrane stimulation.

Specialized Receptor Cells

Cells, mostly found in special senses, that secrete neurotransmitters onto another cell to generate an action potential in a neuron.

Exteroceptors

Receptors located near the surface of the body that provide information about the external environment.

Proprioceptors

Receptors located in moving parts of the body, such as muscles and joints, that report the positions of skeletal muscles and joints.

Interoceptors

Receptors in visceral organs and tissues that monitor internal functions and organs.

Nociceptors

Sensory receptors that respond to pain, often consisting of free nerve endings with large receptive fields.

Thermoreceptors

Sensory receptors that respond to changes in temperature, located in the dermis, skeletal muscles, liver, and hypothalamus.

Mechanoreceptors

Sensory receptors sensitive to physical stimuli that distort plasma membranes by opening mechanically gated ion channels.

Osmoreceptors

Sensory receptors that respond to the solute concentration in body fluids.

Chemoreceptors

Sensory receptors that respond to water- and lipid-soluble substances dissolved in body fluids, monitoring levels of pH, $CO_2$, and oxygen.

Myelinated Type A fibers

Fibers that carry sensations of fast pain, such as prickling pain from an injection or deep cut, reaching the CNS quickly.

Unmyelinated Type C fibers

Fibers that carry sensations of slow pain, such as burning or aching, providing only a general idea of the affected area.

Carotid bodies

Clusters of chemoreceptors located near the origin of the internal carotid arteries.

Muscle spindles

Proprioceptors located inside skeletal muscles that monitor muscle length and trigger stretch reflexes.

Golgi tendon organs

Proprioceptors located at the junction between skeletal muscle and its tendon that monitor tension during contraction.

Root hair plexus nerve endings

Free nerve endings wrapped around hair follicles that monitor movement across the body surface.

Tactile discs (Merkel Discs)

Fine-touch and light pressure receptors in the epidermis sensitive to shape and texture.

Labeled line

A pathway that carries information about one specific sensory modality to the cortical neurons.

First-order neuron

A sensory neuron that responds to a stimulus and delivers sensations from the outside of the CNS to the spinal cord.

Second-order neuron

An interneuron in the spinal cord or brainstem that receives information from a first-order neuron and undergoes decussation.

Third-order neuron

A neuron in the thalamus that receives information from a second-order neuron to relay sensations to the cortex for awareness.

Decussation

The crossing of second-order neuron axons to the opposite side of the CNS.

Fasciculus gracilis

The medial tract of the dorsal column system that contains axons from the legs and lower body.

Fasciculus cuneatus

The lateral tract of the dorsal column system that contains axons from the upper body and arms.

Medial lemniscus

A bundle of second-order axons that leads from the medulla to the thalamus in the dorsal column system.

Sensory homunculus

A functional map of the primary somatosensory cortex where the size of a region is proportional to the density of sensory neurons.

Phantom limb syndrome

A condition characterized by the continued feeling of pain in an amputated limb due to abnormalities in the spinothalamic pathway.

Referred pain

Feeling pain in an uninjured part of the body when the pain actually originates at another location, such as a heart attack felt in the left arm.

Upper motor neuron

A motor neuron with its cell body in the CNS that descends to synapse on a lower motor neuron.

Lower motor neuron

A motor neuron with its cell body in the ventral gray horn of the spinal cord (or a motor nucleus in the brainstem) that projects to skeletal muscle.

Descending tracts

Motor pathways that begin in the brain and descend down the spinal cord to peripheral effectors.

Corticobulbar Tracts

Motor tracts extending from the primary motor cortex through cranial nerves to control muscles of the eye, face, mandible, neck, and pharynx.

Vestibulospinal Tracts

Motor tracts extending from the medulla to the anterior gray horns to regulate balance and muscle tone.

Tectospinal Tracts

Motor tracts extending from the midbrain tectum involved in visual and auditory reflexes for head, neck, and arm movements.

Reflex arc

The pathway of a neural reflex consisting of $5$ components: receptor, sensory neuron, CNS processing, motor neuron, and effector.

Innate reflexes

Basic neural reflexes formed before birth and genetically programmed, such as sucking or withdrawal.

Acquired reflexes

Rapid, automatic learned motor patterns enhanced by repetition, such as braking a car in an emergency.

Monosynaptic reflex

The simplest and fastest reflex arc involving a single synapse where a sensory neuron synapses directly with a motor neuron.

Polysynaptic reflex

A reflex arc involving at least one interneuron between the sensory and motor neurons; it is slower due to multiple synapses.

Stretch reflex

A monosynaptic reflex that regulates skeletal muscle length, such as the patellar reflex.

Reciprocal inhibition

The process where interneurons in the spinal cord inhibit antagonistic muscles so that a flexor reflex can function (e.g., extensors relax when flexors contract).

Crossed extensor reflex

A reflex coordinated with the flexor reflex that straightens the opposite limb to receive body weight before the injured foot is lifted.

Babinski reflex

A reflex in infants where stroking the lateral sole causes extension of the toes; in adults, it may indicate CNS damage.