Overview of the Peripheral Nervous System

What does the Peripheral Nervous System consist of?

Everything outside the Central Nervous System (CNS), including sensory receptors, motor endings, ganglia, and peripheral nerves.

What are the general types of sensory receptors in the Peripheral Nervous System?

Mechanoreceptors, thermoreceptors, photoreceptors, chemoreceptors, and nociceptors.

What are the special senses associated with the Peripheral Nervous System?

Photoreception, gustation, olfaction, audition, vestibular sense, and touch.

What types of fibers can peripheral nerves be classified into?

Sensory (afferent), motor (efferent), and most are mixed.

How many pairs of cranial nerves are there?

12 pairs.

How many pairs of spinal nerves are there, and how are they categorized?

31 pairs: 8 cervical (C1-C8), 12 thoracic (T1-T12), 5 lumbar (L1-L5), 5 sacral (S1-S5), and 1 coccygeal (C0).

What are the two types of ganglia in the Peripheral Nervous System?

Dorsal root ganglia (sensory neurons) and autonomic ganglia (motor neurons).

What is the function of dorsal root ganglia?

They contain sensory neurons that connect receptors with the dorsal horn of the spinal cord.

What is the function of autonomic ganglia?

They contain motor neurons that send axons to effector organs.

What are the three connective tissue sheaths that enclose peripheral nerves?

Epineurium (outer sheath), perineurium (bundles fibers into fascicles), and endoneurium (encloses single axons).

What is the role of Schwann cells in nerve regeneration?

They form regeneration tubes and secrete growth factors that stimulate axons to grow back and produce myelin.

What types of fibers are found in mixed nerves?

Somatic afferent and somatic efferent, visceral afferent and visceral efferent.

What is the function of cranial nerve I (Olfactory)?

Responsible for the sense of smell, processed in the olfactory cortex.

What receptors are associated with cranial nerve II (Optic)?

Photoreceptors (rods and cones) located in the retina.

Where does cranial nerve II exit the eye?

At the optic disc (blind spot).

What is the pathway of olfactory signals from the nasal cavity to the brain?

Odorants bind to olfactory hair cells, triggering action potentials in the olfactory nerve, which travels to the olfactory bulb, then to the olfactory cortex, hypothalamus, amygdala, and limbic system.

What happens if cranial nerve I is damaged?

Loss of the sense of smell.

What is the role of the visual cortex?

It processes visual information received from the optic nerve.

What is the significance of the cribriform plate in relation to cranial nerve I?

It is where the olfactory nerve exits the cranium through the olfactory foramina.

What is the function of the optic canal?

It is the passage through which cranial nerve II (Optic) exits the cranium.

What are the two types of neurons found in the dorsal root ganglia?

Pseudounipolar sensory neurons.

What is the significance of the optic disc?

It is the point where the optic nerve leaves the eye, creating a blind spot.

What is the pathway of light as it enters the eye?

Light enters the cornea, then passes through the Aqueous Humor, Lens, and Vitreous Humor.

What triggers an action potential in the optic nerve?

Photoreceptors in the retina react to light, triggering an action potential that travels along the optic tract.

What is the function of the optic chiasm?

Medial fibers cross over to the other side in the optic chiasm.

Where does the optic nerve exit the eye?

The optic nerve (CN II) exits the eye at the optic disc and leaves the orbit through the optic canal.

What is the role of the oculomotor nerve (CN III)?

It has pure motor fibers that innervate four of the six extrinsic eye muscles and control pupil constriction and lens accommodation.

What happens if the oculomotor nerve is damaged?

If damaged, a person would not be able to open the eyelid.

What muscle does the trochlear nerve (CN IV) innervate?

It innervates the superior oblique muscle of the eye.

What is the consequence of damage to the trochlear nerve?

If damaged, the eye will be held in the upper medial corner.

What are the three branches of the trigeminal nerve (CN V)?

1. Ophthalmic (sensory only) 2. Maxillary (sensory only) 3. Mandibular (sensory & motor) for chewing.

What is the primary function of the abducens nerve (CN VI)?

It innervates the lateral rectus muscle of the eye.

What happens if the abducens nerve is damaged?

The person will not be able to abduct the eye on the ipsilateral side.

What are the functions of the facial nerve (CN VII)?

It has both sensory and motor fibers, innervating facial expression muscles and glands, and supplying taste fibers to the anterior 2/3 of the tongue.

What is the effect of damage to the facial nerve?

Facial muscles will not work on the ipsilateral side, leading to facial nerve palsy (Bell's Palsy).

What type of fibers does the vestibulocochlear nerve (CN VIII) carry?

Mainly sensory fibers for hearing and equilibrium.

What are the two components of the vestibulocochlear nerve?

Vestibular nerve (for balance) and cochlear nerve (for hearing).

What does the glossopharyngeal nerve (CN IX) innervate?

It innervates part of the tongue and pharynx for swallowing and supplies taste fibers to the posterior 1/3 of the tongue.

What is the function of the vagus nerve (CN X)?

It innervates muscles of the pharynx, larynx, esophagus, and palate, as well as the trachea, bronchi, and digestive tract.

What sensory function does the vagus nerve have?

It supplies taste fibers to the posterior 1/3 of the tongue.

What is the significance of the frontal eye field?

It processes motor signals for eye movement.

What is the consequence of damage to the lateral rectus muscle?

The affected eye will not be able to look outward (abduct).

What happens during dental work related to the trigeminal nerve?

The trigeminal nerve is partially deadened to reduce sensation during the procedure.

What cranial nerve supplies taste fibers to the posterior 1/3 of the tongue?

Cranial Nerve X (Vagus Nerve)

What is the primary function of Cranial Nerve XI (Accessory Nerve)?

It contains pure motor fibers and innervates the Trapezius and Sternocleidomastoid muscles.

Where does the Accessory Nerve exit the skull?

Through the Jugular Foramen.

What happens if the Accessory Nerve is damaged?

It can cause dropping of the shoulder and paralysis of the Sternocleidomastoid muscle on the ipsilateral side.

What is the function of Cranial Nerve XII (Hypoglossal Nerve)?

It controls both extrinsic and intrinsic muscles of the tongue.

How many pairs of spinal nerves are there?

31 pairs.

What are the two roots that each spinal nerve connects to the spinal cord?

Dorsal Root (sensory) and Ventral Root (motor).

What type of fibers does the dorsal root contain?

Afferent sensory fibers.

What type of fibers does the ventral root contain?

Efferent motor fibers.

What is the role of the dorsal ramus?

It innervates the back.

What is the role of the ventral ramus?

It innervates the anterolateral thorax and limbs.

What are the four major plexuses formed by the ventral rami?

Cervical, Brachial, Lumbar, and Sacral plexuses.

What is the most important branch of the cervical plexus?

The Phrenic Nerve, composed of C3-C5, which innervates the diaphragm.

What muscles does the Musculocutaneous Nerve innervate?

The Biceps Brachii and Brachialis.

What sensation does the Musculocutaneous Nerve supply?

Sensation along the skin of the lateral forearm.

What reflex tests the integrity of the Musculocutaneous Nerve?

The Biceps Reflex.

What is the consequence of an injury to the Musculocutaneous Nerve?

Difficulty flexing the arm to bring a cup of water to the mouth.

What muscles does the Axillary Nerve innervate?

The Deltoid and Teres Minor.

What sensation does the Axillary Nerve supply?

Sensation along the skin and joint capsule of the shoulder.

What happens if the Axillary Nerve is injured?

Difficulty abducting the arm to reach for something above the head.

What is the primary function of the Radial Nerve?

It innervates muscles in the posterior compartment of the arm and forearm.

What is the significance of the phrase 'C3, 4 & 5 keep you alive'?

It refers to the Phrenic Nerve's innervation of the diaphragm, essential for breathing.

What is the role of Rami Communicantes?

They join to the ventral rami in the thoracic region, forming autonomic pathways.

What muscles does the radial nerve innervate?

All of the posterior arm muscles (Triceps Brachii), extensor muscles of the forearm, the Supinator, and the Brachioradialis.

What sensation does the radial nerve supply?

Sensation along the posterior skin of the upper arm and back of the hand.

What is a consequence of radial nerve injury?

The wrist would flop downward, leading to difficulty in holding the wrist straight.

What does the median nerve innervate?

Most flexors and pronators in the forearm, and some intrinsic muscles of the hand, including the Thenar muscles.

What sensation does the median nerve supply?

Sensation along the lateral palm.

How does the median nerve enter the palm?

Through the Carpal Tunnel.

What are the consequences of median nerve injury?

Carpal tunnel syndrome or atrophy of the thumb area.

What muscles does the ulnar nerve innervate?

Most intrinsic muscles of the hand.

What sensation does the ulnar nerve supply?

Sensation along the medial hand.

What happens when the ulnar nerve is injured?

Striking the 'Funny bone' results in injury of the ulnar nerve.

What is the lumbar plexus formed by?

The ventral rami (roots) of L1-L4.

What areas does the lumbar plexus innervate?

The pelvis and leg.

What are the major nerves of the lumbar plexus?

Femoral Nerve and Obturator Nerve.

What does the femoral nerve innervate?

The Quadriceps.

What sensation does the femoral nerve supply?

Sensation along the anterior thigh and medial lower leg.

What does the obturator nerve innervate?

The adductor muscles.

What sensation does the obturator nerve supply?

Sensation along the medial thigh, hip, and knee.

How does the obturator nerve pass through the body?

It passes through the Obturator Foramen.

What is the sacral plexus formed by?

The ventral rami (roots) of L4-S4.

What area does the sacral plexus innervate?

The leg.

What is the major nerve of the sacral plexus?

The Sciatic Nerve, which is the longest and thickest nerve in the body.

What muscles does the sciatic nerve innervate?

The hamstrings, adductor magnus, and most muscles of the foot.

What are the two branches of the sciatic nerve?

Tibial Nerve and Common Fibular (Peroneal) Nerve.

What does the tibial nerve innervate?

The muscles of the posterior thigh, leg, and foot.

What does the common fibular nerve innervate?

The muscles of the anterior leg.

What is a dermatome?

The area of skin innervated by the cutaneous branches of a single spinal nerve.

What is the significance of dermatomes in relation to spinal nerves?

All spinal nerves except C1 participate in dermatomes, and most dermatomes overlap, meaning destruction of a single spinal nerve will not cause complete numbness.

What are the two basic types of reflexes?

Inborn (Intrinsic) reflexes, which are involuntary, and Learned (Acquired) reflexes, which result from repetition.

What are the five components of a reflex arc?

1. Sensor/Receptor 2. Sensory Neuron (Afferent) 3. Integration Center (Inside the CNS) 4. Motor Neuron (Efferent) 5. Effector (Muscle or gland).

What is the integration center for spinal somatic reflexes?

The spinal cord.

What are Golgi Tendon Organs?

Receptors that measure and inform the brain about the amount of tension in a muscle, leading to muscle relaxation when excessively stretched.

What is the function of muscle spindles?

They measure and inform the CNS of the length of a muscle, leading to muscle contraction when suddenly stretched.

What is an example of a stretch reflex?

The 'Knee Jerk' reflex.

What is the role of motor neurons in spinal reflexes?

They innervate smooth muscles, cardiac muscles, and glands, functioning involuntarily to maintain homeostasis and subconscious control.