CH13 Flashcards
(127 cards)
1
Q
- All neural structures outside the brain
- Sensory receptors
- Peripheral nerves and associated ganglia
- Motor endings
A
Peripheral Nervous System (PNS)
2
Q
- Specialized to respond to changes in their environment (stimuli)
- Activation results in graded potentials that trigger nerve impulses
- Sensation (awareness of stimulus) and perception (interpretation of the meaning of the stimulus) occur in the brain
A
Sensory Receptors
3
Q
Classification of Receptors
• Based on:
A
• Stimulus type
• Location
• Structural complexity
4
Q
respond to touch, pressure, vibration, stretch, and itch
A
**• Mechanoreceptors **
5
Q
sensitive to changes in temperature
A
**
• Thermoreceptors— **
6
Q
respond to light energy (e.g., retina)
A
**• Photoreceptors— **
7
Q
respond to chemicals (e.g., smell, taste, changes in blood chemistry)
A
• Chemoreceptors
8
Q
ensitive to pain-causing stimuli (e.g. extreme heat or cold, excessive pressure, inflammatory chemicals)
A
• Nociceptors—
9
Q
- Respond to stimuli arising outside the body
- Receptors in the skin for touch, pressure, pain, and temperature
- Most special sense organs
A
. Exteroceptors
10
Q
- Respond to stimuli arising in internal viscera and blood vessels
- Sensitive to chemical changes, tissue stretch, and temperature changes
A
**
Interoceptors (visceroceptors)**
11
Q
- Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles
- Inform the brain of one’s movements
A
Proprioceptors
12
Q
type of classificaton for receptor
• Vision, hearing, equilibrium, smell, and taste (Chapter 15)
A
Complex receptors (special sense organs)
13
Q
type of classification for receptor
- Tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sense
- Unencapsulated (free) or encapsulated dendritic endings
A
** Simple receptors for general senses:**
14
Q
Type of Unencapsulated Dendritic Endings
- Cold receptors (10–40ºC); in superficial dermis
- Heat receptors (32–48ºC); in deeper dermis
A
• Thermoreceptors
15
Q
Type of Unencapsulated Dendritic Endings
Respond to:
• Pinching
• Chemicals from damaged tissue
• Temperatures outside the range of thermoreceptors
• Capsaicin
A
• Nociceptors
16
Q
Type of Unencapsulated Dendritic Endings
- Tactile (Merkel) discs
- Hair follicle receptors
A
**
• Light touch receptors**
17
Q
Types of Encapsulated Dendritic Endings
• All are mechanoreceptors
A
- Meissner’s (tactile) corpuscles—discriminative touch
- Pacinian (lamellated) corpuscles—deep pressure and vibration
- Ruffini endings—deep continuous pressure
- Muscle spindles—muscle stretch
- Golgi tendon organs—stretch in tendons
- Joint kinesthetic receptors—stretch in articular capsules
18
Q
the awareness of changes in the internal and external environment
A
**• Sensation: **
19
Q
the conscious interpretation of those stimuli
A
**
• Perception: **
20
Q
Whe level is
the sensor receptors
A
** Receptor level **
21
Q
What level is
ascending pathways
A
** Circuit level— **
22
Q
What level is
neuronal circuits in the cerebral cortex
A
Perceptual level—
23
Q
Processing at the Receptor Level
• Transduction occurs when
A
• **Stimulus energy is converted into a graded potential called a receptor potential **
24
Q
• Conduct impulses from the receptor level to the second-order neurons in the CNS
A
• First-order neurons
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• Transmit impulses to the thalamus or cerebellum
## Footnote
**
• Second-order neurons**
## Footnote
** **
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• Conduct impulses from the thalamus to the somatosensory cortex (perceptual level)
## Footnote
• Third-order neurons
## Footnote
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• Aspects of sensory perception:
—ability to detect a stimulus (requires summation of impulses)
• Perceptual detection
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• Aspects of sensory perception:
intensity is coded in the frequency of impulses
• Magnitude estimation nation test)
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• Aspects of sensory perception:
identifying the site or pattern of the stimulus (studied by the two-point discrimination test)
• Spatial discrimination
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Main Aspects of Sensory Perception
## Footnote
—identification of more complex aspects and several stimulus properties
**• Feature abstraction **
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Main Aspects of Sensory Perception
—the ability to identify submodalities of a sensation (e.g., sweet or sour tastes)
•
**• Quality discrimination **
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Main Aspects of Sensory Perception
—recognition of familiar or significant patterns in stimuli (e.g., the melody in a piece of music)
**
• Pattern recognition **
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Structure of a Nerve
• Connective tissue coverings include:
_—loose_ connective tissue that _encloses axons and their myelin sheaths_
**• Endoneurium **
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Structure of a Nerve
• Connective tissue coverings include:
—_coarse_ connective tissue tha_t bundles fibers into fascicles
_
**• Perineurium **
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Structure of a Nerve
• Connective tissue coverings include:
—_tough fibrous_ _sheath around a nerve_
**• Epineurium**
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Regeneration of Nerve Fibers
that
_—remove debris_
**
• Macrophages **
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Regeneration of Nerve Fibers
• Involves coordinated activity among:
—form regeneration tube and secrete growth factors
**• Schwann cells— **
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Regeneration of Nerve Fibers
• Involves coordinated activity among:
_ regenerate damaged part_
**• Axons**
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bears growth-inhibiting proteins that prevent CNS fiber regeneration
• CNS oligodendrocytes
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* _Twelve pairs_ of nerves associated with the brain
* Most are mixed in function; _two pairs are purely sensory_
* Each nerve is _identified by a number (I through XII)_ and a name
**Cranial Nerves**
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• Arise from the olfactory receptor cells of nasal cavity
• _Pass through the cribriform plate of the ethmoid bone_
• Fibers synapse in the olfactory bulbs
• Pathway terminates in the primary olfactory cortex
_• Purely sensory (olfactory) function_
I: The Olfactory Nerves
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* Arise from the retinas
* Pass through the optic canals, converge and partially cross over at the optic chiasma
* Optic tracts continue to the thalamus, where they synapse
* Optic radiation fibers run to the occipital (visual) cortex
* _Purely sensory (visual) function_
**II: The Optic Nerves**
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* Fibers e_xtend from the ventral midbrain through the superior orbital fissures to the extrinsic eye muscle_s
* _Functions in raising the eyelid, directing the eyeball, constricting the iris (parasympathetic), and controlling lens shape_
* *III: The Oculomotor Nerves
* *
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* Fibers from the dorsal midbrain enter the orbits via the superior orbital fissures to innervate the superior oblique muscle
* _Primarily a motor nerve that directs the eyeball_
* *IV: The Trochlear Nerves
* *
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• Largest cranial nerves; fibers extend from pons to face
Three divisions
• _Ophthalmic (V1) passes through the superior orbital fissure_
• _Maxillary (V2) passes through the foramen rotundum_
* _Mandibular (V3) passes through the foramen ovale_
* _Convey sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for mastication_
**V: The Trigeminal Nerves**
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* Fibers from the inferior pons enter the orbits via the superior orbital fissures
* Primarily a motor, innervating the lateral rectus muscle
**VI: The Abducens Nerves**
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* Fibers _from the pons travel through the internal acoustic meatuses, and emerge through the stylomastoid foramina_ to the lateral aspect of the face
* Chief motor nerves of the face with 5 major branches
* _Motor functions include facial expression, parasympathetic impulses to lacrimal and salivary glands_
_• Sensory function (taste) from the anterior two-thirds of the tongue_
VII: The Facial Nerves
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* Afferent fibers from the hearing receptors (cochlear division) and equilibrium receptors (vestibular division) pass from the inner ear through the internal acoustic meatuses, and enter the brain stem at the pons-medulla border
* Mostly sensory function; small motor component for adjustment of sensitivity of receptors
**VIII: The Vestibulocochlear Nerves**
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* Fibers from the _medulla leave the skull via the jugular foramen and run to the throat_
* **Motor functions:** _innervate part of the tongue and pharynx for swallowing, and provide parasympathetic fibers to the parotid salivary glands_
* **Sensory functions:** fibers c_onduct taste and general sensory impulses from the pharynx and posterior tongue_, and _impulses from carotid chemoreceptors and baroreceptors _
IX: The Glossopharyngeal Nerves
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* The only cranial nerves that extend beyond the head and neck region
* Fibers from the medulla exit the skull via the jugular foramen
* Most motor fibers are parasympathetic fibers that help regulate the activities of the heart, lungs, and abdominal viscera
* Sensory fibers carry impulses from thoracic and abdominal viscera, baroreceptors, chemoreceptors, and taste buds of posterior tongue and pharynx
**X: The Vagus Nerves**
## Footnote
** **
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* _Formed from ventral rootlets from the C1–C5_ region of the spinal cord (not the brain)
* _Rootlets pass into the cranium via each foramen magnum_
_• Accessory nerves exit the skull via the jugular foramina to innervate the trapezius and sternocleidomastoid muscles_
* *XI: The Accessory Nerves
* *
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* Fibers from the medulla exit the skull via the hypoglossal canal
* I_nnervate extrinsic and intrinsic muscles of the tongue that contribute to swallowing and speech_
**XII: The Hypoglossal Nerves**
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* Contain motor (efferent) fibers from the ventral horn motor neurons
* Fibers innervate skeletal muscles)
* *• Ventral roots
* *
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* Contain sensory (afferent) fibers from sensory neurons in the dorsal root ganglia
* Conduct impulses from peripheral receptors
**• Dorsal roots**
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Spinal Nerves: Rami
• Each spinal nerve branches into mixed rami
**• Dorsal ramus**
**• Larger ventral ramus**
**• Meningeal branch**
**• Rami communicantes (autonomic pathways) join to the ventral rami in the thoracic region**
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forms interlacing nerve networks called plexuses (cervical, brachial, lumbar, and sacral)
**• All ventral rami**
**except T2–T12 **
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• The back is innervated by
• ** dorsal rami via several branches**
## Footnote
** **
58
• Ventral rami of T2–T12 as intercostal nerves supply
** muscles of the ribs, anterolateral thorax, and abdominal wall**
## Footnote
59
* Formed by ventral rami of C1–C4
* Innervates skin and muscles of the neck, ear, back of head, and shoulders
* Phrenic nerve
**Cervical Plexus**
60
• Major motor and sensory nerve of the diaphragm (receives fibers from C3–C5)
_***\*Primary for Breathing\****_
**• Phrenic nerve**
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* Formed by ventral rami of C5–C8 and T1 (and often C4 and T2)
* It gives rise to the nerves that innervate the upper limb
**Brachial Plexus**
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• Major branches of Brachial plexus:
** **
**
• Roots—five ventral rami (C5–T1)**
**• Trunks—upper, middle, and lower**
**• Divisions—anterior and posterior**
**•Cords—lateral, medial, and posterior **
63
Brachial Plexus: Nerves
—innervates the deltoid, teres minor, and skin and joint capsule of the shoulder
**• Axillary **
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Brachial Plexus: Nerves
—innervates the biceps brachii and brachialis and skin of lateral forearm
**
• Musculocutaneous **
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Brachial Plexus: Nerves
—innervates the skin, most flexors and pronators in the forearm, and some intrinsic muscles of the hand
**• Median **
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Brachial Plexus: Nerves
—supplies the flexor carpi ulnaris, part of the flexor digitorum profundus, most intrinsic muscles of the hand, and skin of medial aspect of hand
**• Ulnar **
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Brachial Plexus: Nerves
- innervates essentially all extensor muscles, supinators, and posterior skin of limb
• Radial
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* Arises from L1–L4
* Innervates the thigh, abdominal wall, and psoas muscle
* Femoral nerve
* Obturator nerve
**Lumbar Plexus**
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—innervates quadriceps and skin of anterior thigh and medial surface of leg
**• Femoral nerve **
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passes through obturator foramen to innervate adductor muscles
**
• Obturator nerve **
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* Arises from L4–S4
* Serves the buttock, lower limb, pelvic structures, and perineum
* Sciatic nerve
Sacral Plexus
72
* Longest and thickest nerve of the body
* Innervates the hamstring muscles, adductor magnus, and most muscles in the leg and foot
* Composed of two nerves: tibial and common fibular
**
• Sciatic nerve
**
73
Innervation of Skin
the area of skin innervated by the cutaneous branches of a single spinal nerve
**• Dermatome: **
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• All spinal nerves except ____ participate in dermatomes
**C1**
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• Most dermatomes overlap, so destruction of a single spinal nerve ***_will or will not_ ***
cause complete numbness
_* **will not***_ cause complete numbness
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Innervation of Joints
Any nerve serving a muscle that produces movement at a joint also innervates the joint and the skin over the joint is know as what?
**• Hilton’s law: **
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Motor Endings
• PNS elements that _activate effectors by releasing _what??
** neurotransmitters **
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Innervation of Skeletal Muscle
• Takes place at
* * a neuromusclular junction
* *
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Innervation of Skeletal Muscle
• Acetylcholine (ACh) is the
** neurotransmitter**
80
Innervation of Skeletal Muscle
• ACh binds to receptors, resulting in:
** • Movement of Na+ and K+ across the membrane**
**• Depolarization of the muscle cell**
**• An end plate potential, which triggers an action potential**
81
Innervation of Visceral Muscle and Glands.
• Autonomic motor endings and visceral effectors are
* * simpler than somatic junctions
* *
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Innervation of Visceral Muscle and Glands.
• Branches form
** synapses en passant via varicosities**
•
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Innervation of Visceral Muscle and Glands.
-----act indirectly via second messengers
**• Acetylcholine and norepinephrine **
84
Innervation of Visceral Muscle and Glands.
----are slower than somatic responses
**• Visceral motor responses **
85
Levels of Motor Control
**• Segmental level**
**• Projection level**
**• Precommand level**
86
* Central pattern generators (CPGs): segmental circuits that activate networks of ventral horn neurons to stimulate specific groups of muscles
* Controls locomotion and specific, oft-repeated motor activity
* The lowest level of the motor hierarchy
**Segmental Level**
87
Projection Level
• Consists of:
• **_Upper motor neurons that direct_ the direct _(pyramidal) system_ to _produce voluntary skeletal muscle movements_**
**• _Brain stem motor areas_ that _oversee the indirect (extrapyramidal)_ system to c_ontrol reflex and CPG-controlled motor actions_**
**• P_rojection motor pathways_ keep _higher command levels informed_ of what is happening**
88
Precommand Level
• Neurons in the cerebellum and basal nuclei
** • Regulate motor activity**
**• Precisely start or stop movements**
**• Coordinate movements with posture**
**• Block unwanted movements**
**• Monitor muscle tone**
**• Perform unconscious planning and discharge in advance of willed movements**
89
* Acts on motor pathways through projection areas of the brain stem
* Acts on the motor cortex via the thalamus
**• Cerebellum**
90
• Inhibit various motor centers under resting conditions
**• Basal nuclei**
91
Reflexes
: a rapid, involuntary, predictable motor response to a stimulus
**
• Inborn (intrinsic) reflex **
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Reflexes
* result from practice or repetition,
* Example: driving skills
**• Learned (acquired) reflexes **
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• Components of a reflex arc (neural path)
1. **Receptor**—site of stimulus action
2. **Sensory neuron**—transmits afferent impulses to the CNS
3. **Integration cente**r—either monosynaptic or polysynaptic region within the CNS
4. **Motor neuron**—conducts efferent impulses from the integration center to an effector organ
5. **Effector**—muscle fiber or gland cell that responds to the efferent impulses by contracting or secreting
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—site of stimulus action
•
**Receptor **
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—transmits afferent impulses to the CNS
** Sensory neuron **
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either monosynaptic or polysynaptic region within the CNS
** Integration center **
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conducts efferent impulses from the integration center to
** Motor neuron **
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—muscle fiber or gland cell that responds to the efferent impulses by contracting or secreting
** Effector **
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* Integration center is in the spinal cord
* Effectors are skeletal muscle
**• Spinal somatic reflexes**
100
• For skeletal muscle activity to be smoothly coordinated,
** proprioceptor input is necessary**
## Footnote
** **
101
• Muscle spindles inform the
**nervous system of the length of the muscle**
## Footnote
102
• Golgi tendon organs inform
** brain as to the amount of tension in the muscle and tendons**
## Footnote
103
• Composed of 3–10 short intrafusal muscle fibers in a connective tissue capsule
**Muscle Spindles**
104
• Intrafusal fibers
## Footnote
• Noncontractile in their central regions lack
** myofilaments **
105
* Intrafusal fibers
* Wrapped with **_two types of afferent_** endings:
** _primary sensory**_ endings of _**type Ia fibers_**
and **_secondary sensory**_ endings of _***type II fibers*_**
106
• Contractile end regions are innervated by
** gamma (γ) efferent fibers that maintain spindle sensitivity**
107
extrafusal fibers (contractile muscle fibers) are innervated by
** alpha (α) efferent fibers**
108
* Intrafusal fibers
* Excited in two ways:
1. External stretch of muscle and muscle spindle
2. Internal stretch of muscle spindle:
• ***_Activating the γ motor neurons stimulates the ends to contract, thereby stretching the spindle_***
109
• Stretch causes an increased rate
** of impulses in Ia fibers
• **
110
• Contracting the muscle reduces
**tension on the muscle spindle**
111
• Sensitivity would be lost unless
* * the muscle spindle is shortened by impulses in the γ motor neurons
* *
112
*
* α–γ coactivation maintains the tension and sensitivity of
** the spindle during muscle contraction**
113
• How a stretch reflex works:
** • Stretch activates the muscle spindle**
**• IIa sensory neurons synapse directly with α motor neurons in the spinal cord**
**• α motor neurons cause the stretched muscle to contract**
114
• All stretch reflexes are
** monosynaptic and ipsilateral **
115
• Reciprocal inhibition also occurs—
** IIa fibers synapse with interneurons that inhibit the α motor neurons of antagonistic muscles**
116
In the patellar reflex, the stretched muscle _(quadriceps) contracts_ and the
antagonists _(hamstrings) relax_
117
* Initiated by a painful stimulus
* Causes automatic withdrawal of the threatened body part
* Ipsilateral and polysynaptic
**• Flexor (withdrawal) reflex**
•
118
* Occurs with flexor reflexes in weight-bearing limbs to maintain balance
* Consists of an ipsilateral flexor reflex and a contralateral extensor reflex
* The stimulated side is withdrawn (flexed)
* The contralateral side is extended
**
• Crossed extensor reflex
**
119
* Stimulus: stroking lateral aspect of the sole of the foot
* Response: _downward flexion_ of the toes
* _Tests for function of corticospinal tracts_
* *• Plantar reflex
* *
120
\*Like Plantar Flexion
* Response: dorsiflexion of hallux and fanning of toes
* _Present in infants due to incomplete myelination_
• ***_In adults, indicates corticospinal or motor cortex damage
_***
• **Babinski’s sign
**
121
* Cause contraction of abdominal muscles and movement of the umbilicus in response to stroking of the skin
* Vary in intensity from one person to another
* Absent when corticospinal tract lesions are present
* *• Abdominal reflexes
* *
122
• Spinal nerves branch from the developing spinal cord and
** neural crest cells**
## Footnote
** **
123
• Supply both motor and sensory fibers to developing
** developing muscles to help direct their maturation
• **
124
• Cranial nerves innervate
** muscles of the head
• **
125
• Distribution and growth of spinal nerves correlate
** with the segmented body plan
• **
126
• Sensory receptors atrophy with age _and muscle tone lessens due to loss of _
** loss of neurons, decreased numbers of synapses per neuron, and slower central processing**
## Footnote
** **
127
• Peripheral nerves remain viable throughout life unless
** subjected to trauma**
## Footnote
