BIOM 2021 - L17 - the PNS

PNS: two divisions:

Sensory (afferent) division

Motor (efferent) division

Sensory (afferent) division

Sensory info from

receptors up to brain

Motor (efferent) division

Motor info from

brain to effectors

Motor (efferent) division Divided into:

1.Somatic nervous system (skeletal muscles)

2.Autonomic nervous system (cardiac & smooth muscles and glands)

•ANS is divided into:

A.Sympathetic

B.Parasympathetic

The PNS is functionally divided into

sensory and motor divisions

Sensory division

•Sensory receptors detect stimuli

Sensory nerves send this information to the

•CNS along sensory pathways

•This info is referred to as sensory input

Motor division

After analyzing the sensory input, CNS initiates actions of

•motor effectors (muscles or glands)

•This info is sent along motor pathways

•This info is referred to as motor output

Sensory Input can be:

•General (touch, pain, pressure etc)

and

•Special (vision, hearing, taste etc)

Motor output can be:

•Somatic (to skeletal muscle) and

•Visceral (to smooth muscle, cardiac muscle and glands)

Motor output can be further subdivided into the

•Parasympathetic division

•Sympathetic division

•General sensory receptors are widely distributed throughout body

Detect stimuli from inside the body

•visceral) eg changes in chemical concentration, taste, stretching or outside the body (somatic) eg touch, pressure, pain, temperature

•Monitor stimuli such as:

•Touch

•Pressure

•Vibration

•Stretch

•Pain

•Temperature

•Proprioception

Proprioceptors

Monitors degree of

stretch in joints/muscles; located in joints

Mechanoreceptors

Respond to mechanical forces eg

•touch, pressure, stretch, vibration, itch; mostly found in skin, also in ear (special sensory)

Baroreceptors

Monitors

blood pressure; located in blood vessels

Thermoreceptors

Responds to

temperature changes; located in skin

Chemoreceptors

Respond to

•chemical changes eg electrolytes, oxygen, carbon dioxide, pH; located in blood vessels

Nociceptors

Responds to

pain; located in skin and organs

Photoreceptors

Respond to

•light, located in the eye (special sensory)

Spinal Nerves, •31 pairs—contain thousands of nerve fibers (axons) bundled together

•Named for where they emerge from the spinal cord

•8 pairs of Cervical nerves (C1-C8)

•12 pairs of Thoracic nerves (T1-T12)

•5 pairs of Lumbar nerves (L1-L5)

•5 pairs of Sacral nerves (S1-S5)

1 pair of Coccygeal nerves (Co1)

Why 8 cervical nerves when there are only 7 cervical vertebrae?

C1 nerve emerges above the C1 vertebrae

Spinal Nerves, Connect to the spinal cord by the

dorsal and ventral roots

Dorsal root—contains

sensory fibers (axons of sensory neurons), carrying sensory input to CNS

Cell bodies—located in the

dorsal root ganglion

Ventral root—contains motor fibers arising from anterior gray column of

spinal cord; carrying motor output to effectors

Spinal nerves branch into a

dorsal ramus and a ventral ramus (plural = rami)

Dorsal and ventral rami contain both

sensory and motor fibers

Dorsal rami innervate*

back muscles in the thoracic area

Ventral rami lead to

•intercostal nerves to supply* intercostal muscles, skin, and abdominal wall in anterior region

Nerve Plexuses, The ventral rami of spinal nerves (except T2-T12) branch and join with one another to form

•four major Nerve Plexuses

•Cervical

•Brachial

•Lumbar*

Sacral*

•Primarily serve the limbs

There is

no thoracic plexus; T1-T12 are known as the intercostal nerves

•Each plexus is a complex interwoven network of nerves that join up then redistribute to a different distribution of nerves into the limbs

•Each end of each plexus contains fibers from several spinal nerves

Why?

So that each limb muscle receives

innervation from more than one spinal nerve; effective 'backup plan' in case of injury

Cervical Plexus, •Spinal nerves C1 to C4

Innervates* muscles attached to

•hyoid bone and neck

•eg phrenic nerve (innervates diaphragm)

Brachial Plexus, •Spinal nerves C5 to T1 Supply nerves to

•upper limb

eg radial nerve, ulnar nerve

Lumbar Plexus, •Spinal nerves L1 to L4

Supply nerves to

•lower limbs

•e.g. sciatic nerve

Sacral Plexus, Often referred together with the lumbar plexus as the

lumbosacral plexus

Sacral Plexus, Spinal nerves L4 to S4

Innervates

buttocks, pelvis, perineum and lower limb (except for anterior & medial thigh)

eg. Tibial nerve

T1-T11 run between two ribs, therefore called

•intercostal nerves

T12 runs just below the last rib, therefore called

•subcostal neve

•(T1 does have fibers that are part of the brachial plexus)

These nerves have ventral and dorsal rami and communicate with various parts of the

chest and abdomen including muscles, deep tissues, skin, and blood vessels

•Dermatomes divide the skin according to sensory nerve distribution

Df: an area of skin innervated by

•cutaneous branches of a single spinal nerve (or CNV); control sensation to that area

Dermatomes, Valuable in detecting, localizing and diagnosing conditions or problems affecting

spine, spinal cord or/or spinal nerves

Upper limb skin is supplied by nerves of the

•brachial plexus

Lower limb: anterior surface supplied by

Lumbar nerves

Lower limb: posterior surface supplied by

Sacral nerves

Cranial Nerves (CN), ____ •pairs of nerves connected to the brain that serve the head and neck

•Categorized by name and number

12

Cranial Nerves (CN), •Primarily serve head and neck structures

The

•vagus nerve (CN X) extends into the abdomen and innervates abdominal organs

•Cranial nerves can be:

•sensory (carries sensory information)

•motor (carries motor information)

•or mixed (carries both sensory and motor)

Sensory

General sensations

eg

•touch, pain, temperature, pressure, tickle, itch proprioception, etc

Sensory: Special sensations

•eg vision, hearing, equilibrium (balance), taste, smell.

•Carried to the brain via cranial nerves

Motor

Somatic motor function-

Innervation of muscles

Visceral motor function-

Innervation of glands or organs

CN I Olfactory, Special sensory—sense of

•smell

•Olfactory receptor cells located in olfactory epithelium of nasal cavity

CN II Optic, Special sensory-

vision

•Originate on the retina of the eye

CN III Oculomotor: •Somatic motor function:

•Innervates four of the six

extrinsic eye muscles

(attached to outside

of eye, allows for

gross eye

movements)

CN III Oculomotor: Visceral motor function (reflexes of

•intrinsic eye muscles)

•Constricts pupil

•Controls shape of lens

CN IV Trochlear: •Somatic motor function:

Innervates one of the

six extrinsic eye muscles

CN V Trigeminal, •Largest of the cranial nerves, three divisions

•Mixed:

•Sensory to face for pain, touch, temperature

•Motor to chewing muscles

CN VI Abducens Nerve, •Somatic motor function:

Innervates one of the

six extrinsic eye muscles

CN VII Facial •Mixed

Special Sensory for

taste to anterior 2/3 of tongue

CN VII Facial

•Mixed

•Special Sensory for taste to anterior 2/3 of tongue

Somatic motor function:

Innervation of facial muscles (five branches)

CN VII Facial, •Visceral motor function: Innervation of

lacrimal glands, salivary glands

CN VIII Vestibulocochlear: Special Sensory nerve of

hearing & equilibrium

Vestibulocochlear, Vestibular branch:

•equilibrium (balance)

Vestibulocochlear, Cochlear branch

hearing

CN IX Glossopharyngeal, •Mixed

Special visceral sensory

for taste on posterior 1/3 of tongue

CN IX Glossopharyngeal, General visceral sensory-

Posterior 1/3 of tongue, pharynx, carotid body and sinus

CN X Vagus, •Mixed

•Sensory and motor to pharynx, larynx, and abdominal organs

'the wanderer"

CN XI Accessory aka spinal accessory, Somatic motor-innervates

•trapezius and sternocleidomastoid (neck and upper back)

•Formed from ventral rootlets of C1-C5, not from the brain stem

CN XII Hypoglossal, Somatic motor function-innervates

the tongue muscles