BIOL 251 - Module 7 Peripheral Nervous System

Peripheral nervous system

Cranial and spinal nerves

Sensory (afferent) nerves

Contain axons of sensory neurons bringing information to the CNS

Motor (efferent) nerves

Carry the axons of motor neurons towards muscle.

somatic nervous system

Contains afferent AND efferent fibers - carrying both sensory and motor information

Ganglia

Cell bodies of neurons grouped together in masses

Epineurium

Outer surface of a nerve

Fascicles

Bundled groups of axons within the nerve

Perineurium

Wraps around each fascicle in a nerve

Endoneurium

Surrounds individual axons

Spinal nerves

31 pairs of nerves arising from the spinal cord

Cervical nerves

8 pairs

Thoracic nerves

12 pairs

Lumbar nerves

5 pairs

Sacral nerves

5 pairs

Coccygeal nerves

1 pair

Dermatome

Region of skin that carries sensory information through a specific pair of spinal nerves to the spinal cord and up to the brain.

Gray matter

Contains the cell bodies of neurons and is where neurons synapse with the interneurons of the CNS

White matter

Contains the axons of neurons

Ventral root

Contains the axons of efferent motor neurons, which conduct impulses away from the cord towards muscle or glands.

Dorsal (posterior) ramus

Contains nerves serving the dorsal portions of the trunk, carrying somatic motor info to the back muscles and sensory information to and from the skin and muscles of the back

Ventral (anterior) ramus

Contains nerves serving the ventral parts of the trunk and the upper and lower limbs carrying visceral motor, somatic motor, and sensory information to and from the body surface, structures in the body wall, and the limbs

Rami communicantes

Branches off of the ventral ramus that communicate with the sympathetic trunk. Can be gray (unmyelinated) or white (myelinated)

Plexus

Network of interconnecting nerves

Meninges

Dura mater, arachnoid mater, pia mater

The connective tissue wrapped around an individual axon is called

Endoneurium

Spinal nerves are mixed, which means

They contain sensory and motor neurons

Which part of the spinal nerve contains afferent fibers?

Dorsal root

Which part of the spinal nerve contains motor fibers?

Ventral root

True or false: A dermatome is the area of skin that provides sensory input to one pair of spinal nerves

True

The motor division of the peripheral nervous system contains:

Sympathetic system, parasympathetic system, autonomic system, somatic system

The _____ carries information from the lateral and ventral sides of the body, somatosensory and proprioceptors from the body surface, body wall, and limbs.

Ventral ramus

True or false: All motor neurons enter the rami communicantes and the sympathetic chain before routing to their effectors.

False

True or false: there are 12 pairs of cervical nerves.

False

Sensation

Biochemical or electrochemical changes at the cellular level in a receptor cell that detect an imbalance in homeostasis or a change in the environment

Perception

Identification, interpretation, and organization of the sensory signal that allows for construction of an appropriate response.

Response

An action or change in behavior that occurs as a result of a stimulus.

Ascending tracts

Carry sensory info from the PNS to the CNS

Descending tracts

Carry output from the brain, to the spinal cord, and out to the periphery

Sensory receptors

Detect a specific stimulus and convert the stimulus into electrochemical signals that are sent to the central nervous system (CNS)

4 main types of sensory receptors

Nociceptors, Thermoreceptors, Mechanoreceptors, Chemoreceptors

Nociceptors

Detect pain

Thermoreceptors

Detect changes in temperature

Mechanoreceptors

Respond to touch, pressure, vibration, sense of sound, balance

Meissner's corpuscles

Detect fine touch and vibration

Lamellar corpuscles (pacinian corpuscles)

Respond to deep pressure

Root hair plexuses

Wrap around a hair follicle, perceiving information when a hair follicle moves

Baroreceptors

Sense changes in pressure within organs. Found in blood vessels and the digestive, urinary, and respiratory tracts.

Proprioceptor

Monitor tension and stretch in muscles to prevent tearing or overstretching

Chemoreceptors

Detect chemical stimuli

Exteroceptor

Detect stimuli coming from the external environment

Telereceptors

Specialized to detect stimuli from a far distance, such as photoreceptors for vision and hair cells for hearing.

Interoceptors

Detect stimuli from internal organs and tissues.

Ex: baroreceptors

Osmoreceptors

Primary present in hypothalamus. Type of intercepter that detects changes in the solute concentrations of blood.

Types of exteroceptors

Somatosensory, chemoreceptors, telereceptors

Types of interoceptors

Baroceptors, chemoreceptors, stretch receptos, osmoreceptors, proprioceptors

A patient's blood has increased sodium (hypernatremia) because their receptors to trigger thirst, which increases blood volume and dilutes the plasma is not occurring.

Osmoreceptor

A patient's sight is deteriorating

Photoreceptors

A patient's heart rate is dysregulated, as the body is not accurately detecting blood pressure changes.

Baroreceptors

Patient has difficulty walking across uneven terrain and is uncoordinated.

Proprioceptors

Patient has pain insensitivity.

Nociceptors

Special sensory nerves

Carry info responsible for sight, smell, hearing, balance

Olfactory (I)

Smell

Optic (II)

Vision

Oculomotor (III)

Eye movement, pupil constriction

Trochlear (IV)

Eye movement

Trigeminal (V)

Facial sensation; mastication

Abducens (VI)

Eye movement

Facial (VII)

Facial expression, taste, saliva, tear secretion

Vestibulocochlear (VIII)

Hearing and balance

Glossopharyngeal (IX)

Taste, swallowing, saliva secretion

Vagus (X)

Parasympathetic control over visceral organs (heart, smooth muscles of GI tract)

Accessory (XI)

Shoulder and neck movement

Hypoglossal (XII)

Tongue movement

Cervical plexus

Composed of ventral rami from spinal nerves c1-c5 and branches into nerves in the posterior neck and head.

Phrenic nerve

Major nerve of the cervical plexus that connects to the diaphragm at the base of the thoracic cavity from spinal nerves c3, c4, c5.

Brachial plexus

C5-T1

Axillary nerve

Supplies deltoid, teres minor, long head of triceps brachia, skin of shoulder, muscles of skin and skin of superior thorax

Radial nerve

Supplies triceps brachii, as well as twelve muscles in the forearm controlling wrist and finger extension.

Median nerve

Supplies flexor muscles of the forearm and the skin of the first three and a half fingers.

Ulnar nerve

Supplies part of the flexor muscles of the forearm, wrist, and hand, as well as the skin of half the ring finger and pinky finger.

Musculocutaneous nerve

Responsible for the flexor muscles of the arm, including the biceps brachii and brachialis

Lumbar plexus

T12-L4. Has an anterior and a posterior division which branch into nerves to supply the pelvis and lower extremities

Major nerves of the lumbar plexus

Ilohypogastric, ilio-inguinal, genitofemoral, femoral, obturator, lateral femoral cutaneous

Femoral nerve

Innervates the hip flexors and knee extensors

Lateral femoral cutaneous nerve

Receives sensory info from the skin of the anterior, lateral, and posterior surfaces of the thigh

Obturator nerve

supplies the adductor muscles of the medial thigh.

Sacral plexus

L4-S4.

Major nerves of the sacral plexus

Sciatic, superior and inferior gluteal

Sciatic nerve

Largest nerve in the human body, supplies the inferior trunk and posterior surface of the thigh to innervate hip extensors and knee flexors. Two main branches - common fibular (peroneal), and tibial

Common fibular (peroneal) nerve

Innervates the lateral aspect of the lower leg and foot

Tibial nerve

Innervates the posterior lower leg and posterior foot

Superior and inferior gluteal nerves

Innervate the gluteal muscles of the hip

Atrophy

Muscles are not stimulated, leading to muscle tissue loss

Entrapment

When a nerve is compressed between two structures

Carpal tunnel syndrome

Compression of the median nerve in the carpal tunnel, leading to decreased sensation in the first three digits and half of the fourth digit. Can lead to atrophy.

Sciatica

Increased pressure on the sciatic nerve from surrounding muscles. Results in pain along the sciatic nerve.

Which nerve is damaged in carpal tunnel syndrome?

Median

The _____ nerve stimulates the diaphragm to contract.

Phrenic

Which nerve plexus does the nerve that stimulates the diaphragm arise from?

Cervical plexus

The largest nerve in the body, the sciatic nerve, arised from which plexus?

Sacral plexus