chapter 13: the peripheral nervous system and reflex activity

Sensory receptor

A specialized structure that responds to changes in the internal or external environment.

Stimulus

A change in the internal or external environment that activates a sensory receptor.

Afferent pathway

A pathway that carries sensory information toward the CNS.

Mechanoreceptor

A receptor stimulated by mechanical forces such as touch, pressure, vibration, and stretch.

Thermoreceptor

A receptor that responds to changes in temperature.

Photoreceptor

A receptor that detects light.

Chemoreceptor

A receptor stimulated by chemicals, such as odorants, taste stimuli, or chemicals in body fluids.

Nociceptor

A receptor that responds to painful stimuli.

Exteroceptor

A receptor located at or near the body surface that detects stimuli coming from outside the body.

Interoceptor

A receptor associated with internal organs and blood vessels that monitors internal conditions such as chemical changes, stretch, and temperature.

Proprioceptor

A receptor found in skeletal muscles, tendons, joints, ligaments, and connective tissue that provides information about body movement.

Simple receptor

A general sensory receptor that may consist of a nonencapsulated or encapsulated dendritic ending.

Nonencapsulated dendritic ending

A free nerve ending that detects temperature, pain, itch, light touch, or stimuli at the base of hair follicles.

Encapsulated dendritic ending

A dendrite enclosed in a connective tissue capsule that detects discriminatory touch, pressure, and stretch.

Somatosensory system

The part of the sensory system that receives information from the body wall and limbs.

Receptor level

The first level of neural integration where a stimulus excites a receptor and produces graded potentials.

Circuit level

A level of neural integration where neural circuits process sensory information.

Perceptual level

The level of neural integration where sensory information is processed into a perception.

Receptive field

The area in which a stimulus can activate a particular sensory receptor.

Graded potential

A change in membrane potential produced when a sensory receptor is stimulated.

Generator potential

A graded potential produced when the receptor is part of a sensory neuron; it can trigger an action potential.

Receptor potential

A graded potential produced when the receptor is separate from the sensory neuron; it may cause a generator potential.

Sensory adaptation

A decrease in receptor responsiveness when a stimulus continues for a period of time.

Nerve

A cord-like organ consisting of parallel bundles of peripheral axons surrounded by connective tissue.

Endoneurium

The thin connective tissue layer surrounding each individual axon.

Perineurium

The connective tissue wrapping that surrounds groups of nerve fibers and forms fascicles.

Epineurium

The connective tissue layer that surrounds and bundles all fascicles into a nerve.

Fascicle

A bundle of nerve fibers surrounded by perineurium.

Mixed nerve

A nerve containing both sensory and motor fibers.

Sensory nerve

A nerve that carries impulses toward the CNS; also called an afferent nerve.

Motor nerve

A nerve that carries impulses away from the CNS; also called an efferent nerve.

Ganglion

A collection of neuron cell bodies located in the PNS.

Sensory ganglion

A ganglion containing the cell bodies of sensory neurons.

Motor ganglion

A ganglion containing mostly the cell bodies of autonomic motor neurons.

Nerve regeneration

The process by which a damaged PNS axon can regrow when its cell body remains intact.

Schwann cells

Cells that participate in the regeneration of damaged PNS axons.

Oligodendrocytes

CNS cells that have growth-inhibiting proteins that do not support axon regrowth.

Cranial nerves

Nerves that arise from the brain; there are 12 pairs.

Cranial nerve I — Olfactory

Responsible for smell.

Cranial nerve II — Optic

Responsible for vision.

Cranial nerve III — Oculomotor

Helps control movement of the eyeball.

Cranial nerve IV — Trochlear

Helps control movement of the eyeball.

Cranial nerve V — Trigeminal

Provides sensation from the face and controls muscles used for chewing.

Cranial nerve VI — Abducens

Helps control movement of the eyeball.

Cranial nerve VII — Facial

Controls muscles used for facial expressions.

Cranial nerve VIII — Vestibulocochlear

Responsible for hearing and balance.

Cranial nerve IX — Glossopharyngeal

Controls the tongue and pharynx.

Cranial nerve X — Vagus

Controls several visceral organs.

Cranial nerve XI — Accessory

Has a relationship with the vagus nerves.

Cranial nerve XII — Hypoglossal

Innervates muscles of the tongue.

Spinal nerves

31 pairs of mixed nerves that arise from the spinal cord and serve the entire body except the head and neck.

Ventral root

The connection between a spinal nerve and spinal cord that contains motor fibers.

Dorsal root

The connection between a spinal nerve and spinal cord that contains sensory fibers.

Rami

Lateral branches of spinal nerves that contain both motor and sensory fibers.

Dorsal rami

Branches of spinal nerves that innervate the back.

Ventral rami

Branches of spinal nerves that contain both motor and sensory fibers and supply much of the body.

Plexus

A network of spinal nerve fibers formed by branching and recombining of nerve fibers.

Cervical plexus

A plexus formed by the ventral rami of the first four cervical nerves.

Brachial plexus

A plexus located partly in the neck and partly in the axilla that gives rise to virtually all nerves innervating the upper limb.

Lumbosacral plexus

The lumbar and sacral plexuses, which overlap and are connected by the lumbosacral trunk.

Dermatome

The area of skin innervated by the cutaneous branches of a single spinal nerve.

Upper-limb dermatomes

Dermatomes of the upper limbs are innervated by ventral rami from C5–T1.

Lower-limb dermatomes

Dermatomes of the lower limbs are supplied by lumbar nerves on the anterior surface and sacral nerves on the posterior surface.

Afferent vs. efferent

Afferent carries information toward the CNS; efferent carries information away from the CNS.

Mechanoreceptor vs. thermoreceptor

Mechanoreceptors detect mechanical forces; thermoreceptors detect temperature.

Exteroceptor vs. interoceptor

Exteroceptors detect stimuli from outside the body; interoceptors monitor conditions inside the body.

Exteroceptor vs. proprioceptor

Exteroceptors detect external stimuli; proprioceptors provide information about body movement and position.

Endoneurium vs. perineurium vs. epineurium

Endoneurium surrounds one axon; perineurium surrounds a fascicle; epineurium surrounds the entire nerve.

Dorsal root vs. ventral root

Dorsal root contains sensory fibers; ventral root contains motor fibers.

Roots vs. rami

Roots connect spinal nerves to the spinal cord; rami are branches of spinal nerves that contain sensory and motor fibers.

PNS vs. CNS nerve regeneration

PNS axons can regenerate when the cell body remains intact; CNS nerve fibers almost never regenerate.