Chapter 13 Peripheral Nervous System (PNS)

The deepest layer of the meninges is
• Dura mater
• Arachnoid
• Pia mater
• Alma mater

Pia mater

The central nervous system consists of
• Brain
• Spinal cord
• Cranial nerves
• All of the above
• All of the above except C

All of the above except C

• brain and spinal cord!!!

peripheral nervous system

All neural structures outside the brain & Spinal
Cord

• Sensory receptors

• Peripheral nerves and associated ganglia

• Motor nerves

peripheral nervous system consists of

• sensory (afferent) division

  • approach

• motor (efferent) division

  • exit

sensory receptors

• 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

classifications of receptors are based on

• stimulus type

  • name indicates type of stimulus

  • ex) thermoreceptors

• location

  • respond to either internal or external stimuli

• structural complexity

  • general senses

    • simple

      • ex) touch, temp, pressure

  • special senses

    • complex

      • ex) vision, hearing, taste, smell

receptors that are classified by stimulus type

• mechanoreceptors

• thermoreceptors

• photoreceptors

• chemoreceptors

• nociceptors

mechanoreceptors

respond to touch, pressure, vibration, stretch, and itch

thermoreceptors

sensitive to changes in temperature

• touch hot item

photoreceptors

respond to light energy (e.g., retina)

chemoreceptors

respond to chemicals (e.g., smell, taste, changes in blood chemistry)

nociceptors

sensitive to pain-causing stimuli (e.g. extreme heat or cold, excessive pressure, inflammatory chemicals

receptors that are classified by location

• exteroceptors

• interoceptors

• proprioceptors

exteroceptors

respond to environment

• ex) someone taps ur shoulder, feeling the warmth of the sun

interoceptors

viscero, respond to internal

• stomach growling

proprioceptors

position, movement, orientation of body parts

• walking without looking at ur legs

sensation

the awareness of changes in the internal and external environment

• Input comes from sensory receptors

perception

the conscious interpretation of that stimuli

• This occurs in the brain

sensory integration consists of 3 levels

• receptor level

  • sensory reception and transmission to CNS

  • depolarization

• circuit level

  • processing in ascending pathways

  • spinal cord and brain stem (travels)

• perceptual level

  • neuronal circuits in cerebral cortex

  • ex) feeling warmth of sun and recognizing its a pleasant sensation

adaption of sensory receptors

is a change in sensitivity in the presence of a
constant stimulus (bright light)

• two types

  • phasic receptors (fast-adapting)

  • tonic receptors

phasic receptors

fast-adapting receptors signal the beginning or end of a stimulus, signals a change

• ex) receptors for pressure, touch, and smell
  (clothing)

tonic receptors

adapt slowly or not at all

• ex) nociceptors and most proprioceptor

• sitting in a chair and feeling the pressure of it, you don’t really notice it after a period of time but you can still maintain posture and adjust position if needed

structure of a nerve

Bundle of myelinated and unmyelinated peripheral axons enclosed by connective tissue

3 layers of connective tissue

• endoneurium

• perineurium

• epineurium

Endoneurium

loose CT that encloses axons and their myelin
sheaths

• innermost layer

Perineurium

coarse CT that bundles fibers into fascicles (binds)

Epineurium

tough fibrous sheath around a nerve

• outermost layer

classifications of nerves

• Most nerves are mixtures of afferent and efferent fibers:

  • Somatic afferent and somatic efferent

    • ex) hands sense something hot and responds by moving them away

  • Visceral afferent and visceral efferent

    • ex) stomach growls due to hunger and once you start to eat food the smooth muscles digest the food

• Peripheral nerves classified as cranial or spinal nerves

ganglia

collections/bundles of cell bodies in PNS

nuclei

collections/bundles of cell bodies in CNS

dorsal root ganglia

• sensory

  • sense signals related to things such as touch or pain

• somatic

  • control voluntary movement and sensory perception

autonomic ganglia

• motor

• visceral

  • involuntary movement of muscles like heart rate and digestion

Regeneration of Peripheral Nerve Fibers vs central nerve fibers

• Mature neurons are amitotic

  • doesn’t undergo cell division

• If the soma (cell body) of a damaged nerve is intact, axon will regenerate

• CNS oligodendrocytes bear growth inhibiting proteins that prevent CNS fiber regeneration

The neurotransmitter that is associated with
reward and pleasure is ...
A. Norepinephrine
B. Serotonin
C. Dopamine
D. Acetylcholine
E. Histamine

C. Dopamine

Which statements are correct about language and the brain?
A. Wernicki’s area is related to language expression and is located in the right frontal lobe
B. Broca’s area is related to language expression and is located in the left frontal lobe
C. Wernicki’s area is related to language comprehension and is located in the left temporal lobe
D. Broca’s area is related to language comprehension and is located in the right temporal lobe

B. Broca’s area is related to language expression and is located in the left frontal lobe
C. Wernicki’s area is related to language comprehension and is located in the left temporal lobe

both are on the left hemisphere

cranial nerves

• Twelve pairs (12) of peripheral nerves
  associated with the brain

• Most are mixed in function; two pairs are purely sensory (I and II)

deal with complex sensations

what are the 12 cranial nerves

“on occasion our trusty truck acts funny— very good vehicle anyhow”

• olfactory (I)

• optic (II)

• oculomotor (III)

• trochlear (IV)

• trigeminal (V)

• abducens (VI)

• facial (VII)

• vestibulocochlear (VIII)

• glossopharyngeal (IX)

• vagus (X)

• accessory (XI)

• hypoglossal (XII)

cranial nerve I: olfactory nerve

smell just sensory

cranial nerve II: optic nerve

vision just sensory

cranial nerves I and II are just

sensory, no motor function

cranial nerves relating to eye movement (just motor)

CN 3, 4 and 6

• oculomotor (III)

• trochlear (IV)

• abducens (VI)

cranial nerve III: oculomotor nerve

• pupil constriction

• all other eye movements ex) upwards

cranial nerve IV: trochlear nerve

downward and outward eye movement

cranial nerve VI: abducens nerve

outward lateral eye movements (abducts eyes)

palsy in cranial nerves III, IV and VI can result in

eye misalignment

cranial nerve V: trigeminal nerve

• Sensation of face

• Motor of mastication muscles

cranial nerve VII: facial nerve

• Motor of face – facial expression

• Sensory - taste

cranial nerve VIII: vestibulocochlear nerve

hearing and balance

trigeminal neuralgia

a type of chronic pain disorder that involves sudden attacks of severe facial pain

• very painful

vestibular nerve pathology

• directly affects vestibulocochlear (VIII) nerve which is responsible for balance and spatial orientation

• leads to

  • vertigo (dizziness)

  • imbalance

  • involuntary movement of eyes

  • spatial disorientation

cranial nerve IX: glossopharyngeal nerve

tongue and throat” – taste & swallowing

cranial nerve X: vagus nerve

“the wanderer”

• Only cranial nerve that leaves the head and neck

• Involved in Parasympathetic nervous system

• Help regulate the heart, lungs and abdominal viscera

cranial nerve XI: accessory nerve

moves head and neck (trapezius and SCM muscle)

SCM= sternocleidomastoid

cranial nerve XII: hypoglossal nerve

“under tongue” – moves tongue

cranial nerves XI and XII are just

motor

Neuroglial cells that protect against pathogens
in the brain are the ______.
• astrocytes
• ependymal cells
• microglia
• Schwann cells

microglia

Which cranial nerve detects sensation in the
face?
A. Cranial Nerve 4 Troclear Nerve
B. Cranial Nerve 5 Trigeminal Nerve
C. Cranial Nerve 7 Facial Nerve
D. Cranial Nerve 10 Vagus Nerve

Cranial Nerve 5 Trigeminal Nerve

• facial nerve is just motor

During repolarization of the action potential
which gates are opened?
A. Voltage gated Na
B. Voltage gated K
C. Leakage channels for Na
D. Leakage channels for K

B. Voltage gated K

• membrane potential going negative again

spinal nerves

31 pairs of mixed nerves named according to
their point of issue from the spinal cord

• 8 cervical (C1–C8)

• 12 thoracic (T1–T12)

• 5 Lumbar (L1–L5)

• 5 Sacral (S1–S5)

• 1 Coccygeal (C0)

sensory nerves enter the spinal cord vias dorsal or ventral horn?

dorsal horn

each spinal nerve connects to the spinal cord via

two roots

• ventral roots

• dorsal roots

ventral roots

• Contain motor (efferent) fibers from the ventral horn motor neurons

• Fibers innervate skeletal muscles

dorsal roots

• Contain sensory (afferent) fibers from sensory neurons in the dorsal root ganglia

• Conduct impulses from peripheral receptors

dorsal and ventral roots unite to form

spinal nerves

each spinal nerve branches into mixed rami

• dorsal ramus

  • sensory info

• larger ventral ramus

  • motor info

• Rami communicantes (autonomic pathways) join to the ventral rami in the thoracic region

roots lie

medial to spinal nerves

• either motor or sensory

rami lie

lateral to spinal nerves

• mixed

All ventral rami except T2–T12 form

networks called plexuses

(cervical, brachial, lumbar, and sacral)

the back is innervated by

dorsal rami via several branches

shingles

infection on dorsal rami

cervical plexus

most superior

• Formed by ventral rami of C1–C5

• Innervates skin and muscles of the neck, ear, back of head, and shoulders

phrenic nerve

• Major motor and sensory nerve of the diaphragm (receives fibers from C3–C5)

• Irritation of phrenic nerve causes hiccups

C3,C4,C5 keeps the diaphragm alive

brachial plexus

• Formed by ventral rami of C5–C8 and

• It gives rise to the nerves that innervate the upper limb

• Major nerves from the branches: axillary, musculocutaneous, median, ulnar and radial

brachial plexus injuries

• erb’s injury

• kulmpke’s paralysis

erb’s injury

stretching of upper trunk of brachial plexus

• stuck in internal rotation

klumpke’s paralysis

injury to lower roots of plexus (claw hand)

• hands when baby is delivered

lumbar plexus

• Arises from L1–L4

• Innervates the thigh, abdominal wall, and psoas muscle

• Femoral nerve

• Obturator nerve

Femoral nerve

innervates quadriceps and skin of anterior thigh and medial surface of leg

Obturator nerve

innervate adductor muscles (groin muscles)

• inner thigh

sacral plexus

• Arises from L4–S4

• Serves the buttock, lower limb, pelvic structures, and perineum (lower pelvic floor)

• Sciatic nerve

sciatic nerve

• 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

  • common fibular

sciatica

• pain that travels along the sciatic nerve, often starting in the lower back and going down one leg

• can be caused by

  • spinal stenosis

    • spaces within your spine narrow, putting pressure on the spinal cord and nerves

  • herniated disc

    • punctured jelly filled donut

  • degenerative disc disease

Dorsal roots...
• A. Are a mixture of motor and sensory fibers
• B. Contain afferent fibers only
• C. Innervate skeletal muscles

B. Contain afferent fibers only

Which nerve comes from brachial plexus?
• Musculocutaneous NN
• Sciatic NN
• Phrenic NN
• Obturator NN
• Accessory NN

Musculocutaneous NN

inborn (intrinsic) reflex

a rapid, involuntary, predictable motor response to a stimulus

• splashing hot water from pot on your arm

learned (acquired) reflex

result from practice or repetition

• driving skills

components of a reflex arc (neural path)

• Receptor

  • site of stimulus action

• Sensory neuron

  • transmits afferent impulses to the
    CNS

• Integration center

  • either monosynaptic or polysynaptic region within the CNS

• Motor neuron

  • conducts efferent impulses from the
    integration center to an effector organ

• Effector

  • muscle fiber or gland cell that responds to the efferent impulses by contracting or secreting

spinal somatic reflexes

• Integration center is in the spinal cord

• Effectors are skeletal muscle

• Include: stretch, flexor and crossed-extensor

how stretch reflex works

• Stretch activates the muscle spindle (receptor)

• Sensory neurons synapse directly with alpha motor neurons in the spinal cord

• alpha motor neurons cause the stretched muscle to contract

example: Imagine you're standing on one leg and start to tip over. As your body starts to fall, the stretch reflex kicks in, quickly contracting the muscles in your ankle and leg to help you regain your balance and stay upright.

all stretch reflexes are _____ and _____

monosynaptic (1 synpase)

ipsilateral (same side)

patellar (knee-jerk) reflex

• tapping the patellar ligament excites
  muscle spindles in the quadriceps.

• Afferent impulses (blue) travel to the
  spinal cord, where synapses occur with
  motor neurons and interneurons.

• The motor neurons (red) send
  activating impulses to the quadriceps
  causing it to contract, extending the
  knee.

• The interneurons (green) make
  inhibitory synapses with ventral horn
  neurons (purple) that prevent the
  antagonist muscles (hamstrings) from
  resisting the contraction of the
  quadriceps

abnormal stretch reflexes

• dampened reflex

• abnormal kick

flexor (withdrawal) reflex

• initiated by a painful stimulus

• Causes automatic withdrawal of the
  threatened body part

• Ipsilateral (same side) and polysynaptic (multiple)

• However descending signals from brain can override flexor reflexes. Ie: pin prick

crossed extensor reflex

lower extremities

• 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

plantar reflex (Babinski reflex)

helps diagnosis stroke

• Stimulus: stroking lateral aspect of the sole of the foot

• Normal Response: downward flexion of the toes

  • this goes away as you age, people who experienced a stroke have this reflex again

• Tests for function of corticospinal tracts

Which cranial nerve is the exception and travels
to the thoracic and abdominal cavities?
• Trochlear (4)
• Trigeminal (5)
• Vestibulocochlear (8)
• Vagus (10)

Vagus (10)

Quickly lifting your foot and leg after stepping on
a rock is an example of a(n) ________.
• Learned reflex
• Flexor withdrawal reflex
• Superficial reflex
• Stretch reflex

Flexor withdrawal reflex

CN IV: trochlear

• superior oblique (top muscle at angle)

  • move eye inferior (down) and laterally (out)

CN IV: abducens

• lateral rectus

  • move eye laterally (side)

CN III: oculomotor

• superior rectus

  • superior and medial

• inferior rectus

  • inferior and medial

• medial rectus

  • medial

• inferior oblique

  • superior and lateral