Chapter 13 - THE PERIPHERAL NERVOUS SYSTEM AND REFLEX ACTIVITY Flashcards
What is the peripheral nervous system (PNS)?
All neural structures outside the brain and spinal cord
Activation of sensory receptors from environmental changes (stimuli) causes what?
Graded potentials that trigger nerve impulses
Where does sensation and perception occur?
The brain
What kind of receptor is triggered from stimuli arising from outside the body?
Exteroceptors
What kind of receptor is in the skin that deals with touch, pressure, pain, and temperature?
Exteroceptors
What kind of receptor deals with the special senses?
Exteroceptors
What kind of receptor deals with the stimuli from internal viscera?
Interoceptors (visceroceptors)
What kind of receptor deals with chemical and temperature changes and tissue stretch?
Interoceptors (visceroceptors)
What kind of receptors sometimes since discomfort but of which we are usually unaware of?
Interoceptors (visceroceptors)
What kind of receptors occur in skeletal muscles, tendons, joints, and ligaments and in connective tissue coverings of bones and muscles?
Proprioceptors
What kind of receptors deal with touch, pressure, vibration, and stretch?
Mechanoreceptors
Are light touch receptors nonencapsulated or encapsulated?
Non-encapsulated
What do hair follicle receptors and tactile discs have in common?
They are non-encapsulated and they are light touch receptors
Almost all mechanoreceptors are encapsulated.
Yup
Tactile corpuscles, or Meissner’s corpuscles, are receptors for what?
Discriminative touch
Lamellar corpuscles, or Pacinian corpuscles, are stimulated by what?
Deep pressure
Bulbous corpuscles, or Ruffini endings, respond to what?
Deep continuous pressure
What do muscle spindles detect and then initiate?
They detect muscle stretch and initiate a reflex that resists the stretch
Tendon organs detect what and initiate what?
They detect compression of the nerve fibers when a muscle contraction stretches the tendon fibers. This initiates a reflex that causes the contracting muscle to relax.
Joint kinesthetic receptors provide information on what?
Joint position and motion, a sensation of which we are highly conscious
What kind of receptors detect changes in temperature?
Thermoreceptors
Are thermoreceptors encapsulated or not encapsulated?
Nonencapsulated
What kind of receptors respond to light energy?
Photoreceptors
What kind of sensory neurons are particularly abundant an epithelial and connective tissues?
Nonencapsulated (free) nerve endings
What do chemoreceptors detect?
Changes in chemicals, such as smell, taste, and changes in blood chemistry
What are nociceptors?
They are the pain-causing stimuli, such as extreme heat or cold, excessive pressure, and inflammatory chemicals. They are nonencapsulated.
What receptors does the somatosensory system receive inputs from?
Exteroceptors, proprioceptors, and interoceptors
What is transduction?
It is when the stimulus is changed to a graded potential
Do graded potentials have to reach a threshold?
Yes. They must.
What is it called when there is a change and sensitivity with a constant stimulus?
Adaptation
What are phasic receptors?
Fast-adapting receptors, they give bursts of impulses at the beginning and the end of the stimulus
What or tonic receptors?
They adapt slowly or not at all; nociceptors and most proprioceptors are tonic receptors because of the protective importance of their information
What are the three main levels of neural integration that operate in the somatosensory system?
The receptor level, the circuit level, and the perceptual level
What is the receptor level of neural integration in the somatosensory system?
Sensory receptors
What is the circuit level of neural integration in the somatosensory system?
Processing in ascending pathways
What is the perceptual level of neural integration in the somatosensory system?
Processing in cortical sensory areas
What is the ability to detect that a stimulus has occurred? This is the simplest level of perception.
Perceptual detection
What must happen to the inputs from several receptors for perceptual detection to occur?
Inputs must be summed
What is the ability to detect how intense a stimulus is?
Magnitude estimation
What allows us to identify the site or pattern of stimulation?
Spatial discrimination
What test determines how close together two points on the skin can be and still be perceived as two points rather than as one?
Two-point discrimination test
What is the mechanism by which a neuron or circuit is tuned to one feature, or property, of a stimulus in preference to others? It also enables us to identify more complex aspects of a sensation.
Feature abstraction
What is the ability to differentiate the sub-modalities of a particular sensation? For example, taste is a modality and its sub-modalities include sweet and bitter.
Quality discrimination
What is the ability to take in the scene around us and recognize a familiar pattern, an unfamiliar one, or one that has special significance for us?
Pattern recognition
Histamine, K+, ATP, acids, and bradykinin are what?
Among the most potent pain-producing chemicals
Some pain impulses are blocked by what?
Endogenous opioids such as endorphins and enkephalins
When we say that someone is “sensitive” to pain, we mean what?
That person has a low pain tolerance rather than a low pain threshold
Do we all have the same pain threshold?
Yes
What is the phenomenon in which pain stimuli arising in one part of the body are perceived as coming from another party?
Referred pain
What is a nerve?
A cordlike bundle of axons that conducts sensory and motor impulses. It is part of the peripheral nervous system.
Most nerves are what?
Mixed
What are ganglia?
Collections of neuron cell bodies associated with nerves in the PNS
What are nuclei?
Collections of neuron cell bodies in the CNS
What are the four types of fibers in mixed nerves?
Somatic afferent, somatic efferent, visceral afferent, visceral efferent
How are peripheral nerves classified?
Cranial or spinal
What do afferent nerve fibers contain?
Sensory neuron cell bodies
What do efferent nerve fibers contain?
Autonomic motor neurons
Do most CNS fibers ever regenerate?
Never
Why do most CNS fibers never regenerate?
Because CNS oligodendrocytes release proteins that inhibit growth and prevent axon regeneration. Astrocytes at the site of an injury form scar tissue blocking an axon.
How many cranial nerves attach to the forebrain?
Two
What is the olfactory nerve?
Nerve I. The sensory nerves of smell. They are purely sensory in function.
What is the optic nerve?
Nerve II. They arise from the retina and pass through the optic canals and cross over at the optic chiasma. Continues to the thalamus where they synapse. Purely sensory infunction.
What is the oculomotor nerve?
Nerve III. Controls four of the six extrinsic eye muscles. Parasympathetic. Primarily motor.
What is the trochlear nerve?
Nerve IV. It innervates the superior oblique muscle of the eyeball. Primarily motor. Directs eyeball.
What is the trigeminal nerve?
Nerve V. The largest cranial nerve. Fibers from pons to face. Sensory impulses from various areas of the face and supplies motor fibers for mastication.
What is the abducens nerve?
Nerve VI. Primarily motor. Innervates the lateral rectus muscle of the eyeball.
What is the facial nerve?
Nerve VII. Mixed nerve. Motor: facial expression, parasympathetic impulses to lacrimal and salivary glands. Sensory: taste from anterior 2/3 of tongue
What is the vestibulocochlear nerve?
Nerve VIII. Sensory. Afferent fibers from hearing receptors and equilibrium receptors.
What is the glossopharyngeal nerve?
Nerve IX. Mixed nerve. Motor: tongue and pharynx for swallowing, parasympathetic fibers to parotid salivary glands. Sensory: taste/general sensory impulses from pharynx and posterior tongue, and impulses from carotid chemo receptors and baroreceptors
What is the vagus nerve?
Nerve X. Mixed nerve. The only cranial nerve that extends beyond the head and neck region. Motor: parasympathetic fibers help regulate activities of the heart, lungs, abdominal viscera. Sensory: carry impulses from thoracic and abdominal viscera, baroreceptors, chemoreceptors, taste buds of posterior tongue and pharynx.
What is the accessory nerve?
Nerve XI. Motor. Innervates trapezius and sternocleidomastoid muscles.
What is the hypoglossal nerve?
Nerve XII. Motor. Innervates muscles of tongue that contribute to swallowing and speech.
Spinal nerves supply all body parts but what?
The head and part of the neck
How many pairs of spinal nerves are there?
31 pairs
Are spinal nerves sensory, motor, or mixed?
Mixed
What do the ventral roots innervate?
The skeletal muscles
What do the dorsal roots do?
They conduct impulses from the peripheral receptors
Dorsal and ventral roots unite to create what?
Spinal nerves, which emerge from the vertebral column
What do the dorsal roots do?
They bring sensory inputs to the spinal cord
What is the dorsal root ganglia?
Cell bodies of sensory neurons
What are the ventral horns?
Cell bodies of some interneurons and somatic motor neurons.
How do axons exit the spinal cord?
Via ventral roots
Where are the lateral horns found?
Only in the thoracic and superior lumbar regions
What are lateral horns?
Sympathetic neurons
All ventral rami except what form interlacing nerve networks called nerve plexuses?
T2-T12
What is Hilton’s law?
Any nerve serving a muscle that produces movement at a joint also innervates the joint and the skin over the joint.
Notice that only ventral rami form plexuses.
Yup
Why does each muscle in a limb receive its nerve supply from more than one spinal nerve?
Within a plexus, fibers from the various ventral rami criss-cross one another and become redistributed.
What nerves make up the cervical plexus?
Ventral rami of C1-C4
What is the phrenic nerve?
It is the major motor and sensory nerve of the diaphragm. Irritation causes hiccups.
What nerves make up the brachial plexus?
Ventral rami of C5-C8 and T1. Innervates the upper limb.
Roots form trunks which form divisions which form cords.
Yup
What is the ulnar nerve?
It supplies the flexor carpi ulnaris, part of the flexor digitorum profundus, most intrinsic hand muscles, skin of the medial aspect of hand, and wrist/finger flexion
What is the radial nerve?
It innervates essentially all extensor muscles, supinators, and the posterior skin of the limb.
What is the femoral nerve?
It innervates the quadriceps and the skin of the anterior thigh and medial surface of the leg.
What is the obturator nerve?
It passes through the obturator foramen to innervate the adductor muscles.
What nerves make up the lumbar plexus?
Arises from L1-L4. Innervates thigh, abdominal wall, and psoas muscle.
What nerves make up the sacral plexus?
Arises from L4-S4. Serves the buttock, lower limb, pelvic structures, and perineum.
What is the sciatic nerve?
It is the longest and thickest nerve of the body. It innervates the hamstring muscles, adductor magnus, and most muscles in the leg and foot. Composed of two nerves: tibial and common fibular.
What is the area of skin innervated by cutaneous branches of a single spinal nerve called?
Dermatome
Which spinal nerve does not participate in a dermatome?
C1
The extent of spinal cord injuries is determined by what?
The affected dermatomes
Why does the destruction of a single spinal nerve not cause complete numbness?
Because most dermatomes overlap
What are the three levels of motor control?
Segmental, projection, pre-command
Regarding motor control, what does the segmental level control?
Locomotion and often-repeated motor activity
Regarding motor control, what does the projection level control?
Precise start/stop movements, coordinate movement with posture, block unwanted movements, and monitor muscle town
Regarding motor control, what is the pre-command level control?
Initiates voluntary skeletal movements and keeps higher command levels informed
What are inborn (intrinsic) reflexes?
Rapid, involuntary, predictable motor responses to stimulus
What are learned (acquired) reflexes?
From practice or repetition
What are the components of a reflex arc?
In order: receptor, sensory neuron, integration center, motor neuron, effector
What is the site of a stimulus action called?
Receptor
What transmits afferent impulses to the CNS?
A sensory neuron
What is the monosynaptic or polysynaptic region within the CNS?
The integration center
What conducts efferent impulses from the integration center to an effector organ?
A motor neuron
What is a muscle fiber or gland cell responding to an efferent impulse by contracting or secreting?
Effector
What are autonomic (visceral) reflexes?
They activate visceral effectors (smooth/cardiac muscle or glands)
What are somatic reflexes?
They activate skeletal muscle
To smoothly coordinate skeletal muscle the nervous system receives proprioceptor input regarding:
Length of a muscle from the muscle spindles. Amount of TENsion in muscle from TENdon organs.
Muscle spindles are excited and two ways:
One, external stretch of muscle and muscle spindle. Two, internal stretch of a muscle spindle. Stretch yields an increased rate of impulses to the spinal cord.
What motor neurons cause stretched muscle to contract?
Alpha motor neurons
All stretch reflexes are monosynaptic and ipsilateral.
Yup
What do positive reflex reactions indicate?
Intact sensory and motor connections between the muscle and spinal cord and the strength of response indicates the degree of spinal cord excitability.
Why might a stretch reflex be hypoactive or absent?
If there is peripheral nerve damage or a ventral horn injury
Why might a stretch reflex be hyperactive?
If there are lesions of the corticospinal tract
What is the tendon reflex?
It is polysynaptic. Helps prevent damage due to excessive stretch. It is important for a smooth onset and termination of muscle contraction.
What is reciprocal activation?
It is when a contracting muscle relaxes and an antagonist muscle contracts
What is the flexor reflex?
It is the automatic withdrawal of a threatened body part by a painful stimulus. It is ipsilateral and polysynaptic. It is protective so it is important. The brain can override.
What is the crossed extensor reflex?
It occurs with flexor reflexes in a weight-bearing limb to maintain balance. It is an ipsilateral withdrawal reflex and contralateral extensor reflex.
What are superficial reflexes?
Gentle cutaneous stimulation. Best known: plantar reflex and abdominal reflex
What is an abnormal response to the plantar reflex?
Babinski’s sign
What superficial reflex tests the integrity of the spinal cord from L4 to S2?
Plantar reflex
What superficial reflex tests the integrity of the spinal cord from T8 to T12?
Abdominal reflex
Spinal nerves branch from what when the PNS is developing?
Developing spinal cord and neural crest cells
Peripheral nerves are viable throughout life unless subjected to trauma.
Yup
