Peripheral Nervous System, Special Senses, and Muscle Tissue: Study Guide for ANP College Students

Peripheral Nervous System

Cranial Nerves: Location and Function

The cranial nerves are twelve pairs of nerves that emerge directly from the brain and brainstem, each with specific sensory, motor, or mixed functions. They are identified by Roman numerals and names, and their functions range from smell and vision to facial movement and autonomic control.

• I Olfactory: Sensory; responsible for smell.

• II Optic: Sensory; responsible for vision.

• III Oculomotor: Motor; moves the eye and dilates pupils.

• IV Trochlear: Motor; innervates extrinsic eye muscles.

• V Trigeminal: Both; sensations of head and face, chewing.

• VI Abducens: Motor; abducts the eye.

• VII Facial: Both; taste, secretion of saliva/tears, facial expression.

• VIII Vestibulocochlear: Sensory; hearing and balance.

• IX Glossopharyngeal: Both; tongue sensations, saliva secretion, swallowing.

• X Vagus: Both; sensations from thoracic/abdominal viscera, parasympathetic control, voice production.

• XI Accessory: Motor; shoulder movements, assists in voice production.

• XII Hypoglossal: Motor; tongue movements.

Spinal Nerves and Plexuses

Spinal nerves are mixed nerves that originate from the spinal cord, totaling 31 pairs. They are grouped by region and form plexuses that innervate specific body areas.

• Cervical: 8 pairs

• Thoracic: 12 pairs

• Lumbar: 5 pairs

• Sacral: 5 pairs

• Coccygeal: 1 pair

The anterior and posterior rami of spinal nerves branch to supply motor and sensory innervation to the body.

Cervical Plexus

The cervical plexus is formed by the anterior rami of C1–C5 and innervates the neck, shoulder, and diaphragm. The phrenic nerve is especially important for motor control of the diaphragm.

• Lesser occipital: Sensory to scalp and ear

• Greater auricular: Sensory to skin on ear

• Ansa cervicalis: Motor to geniohyoid and infrahyoid muscles

• Transverse cervical: Sensory to skin on superior chest/shoulder

• Supraclavicular: Sensory to skin on superior chest/shoulder

• Phrenic: Motor to the diaphragm

Brachial Plexus

The brachial plexus is formed by the anterior rami of C5–T1 and innervates the upper limb. Key nerves include the median and musculocutaneous nerves, which control forearm and hand muscles.

• Axillary: C5–C6; posterior cord

• Radial: C5–T1; posterior cord

• Musculocutaneous: C5–C7; lateral cord

• Median: C6–T1; medial/lateral cord fusion

• Ulnar: C8–T1; medial cord

Lumbar Plexus

The lumbar plexus is formed by the anterior rami of L1–L4 and innervates the lower abdomen, anterior thigh, and medial leg.

• Iliohypogastric: L1

• Ilioinguinal: L1

• Genitofemoral: L1–L2

• Femoral: L2–L4; posterior division

• Lateral femoral cutaneous: L2–L3

• Obturator: L2–L4; anterior division

Sacral Plexus

The sacral plexus is formed by the anterior rami of L4–S4 and innervates the pelvis, posterior thigh, and most of the leg and foot. The sciatic nerve is the largest and most important nerve of this plexus.

• Superior gluteal: L4–S1

• Inferior gluteal: L5–S2

• Pudendal: S2–S4

• Posterior femoral cutaneous: S1–S3

• Sciatic: L4–S3; largest nerve, motor/sensory to leg

• Common fibular: L4–S2

• Tibial: L4–S3

The Special Senses

Anatomy of the Ear

The ear is responsible for hearing and balance, consisting of external, middle, and inner regions. Key structures include:

• Cochlea: Spiral organ for hearing

• Eustachian tube: Equalizes pressure

• External acoustic meatus: Canal to tympanic membrane

• Incus, malleus, stapes: Auditory ossicles

• Lobule, pinna (auricle): External ear structures

• Oval window: Entrance to inner ear

• Semicircular canals: Balance

• Tympanic membrane: Eardrum

• Vestibule: Balance

• Vestibulocochlear nerve: Hearing and balance

Anatomy of the Eye

The eye is the organ of vision, composed of several layers and structures for focusing light and processing visual information.

• Choroid: Vascular layer

• Ciliary muscle: Controls lens shape

• Cornea: Transparent front

• Extraocular muscles: Move the eye (inferior/superior oblique, rectus muscles, lateral/medial rectus)

• Iris: Controls pupil size

• Lacrimal sac: Collects tears

• Lens: Focuses light

• Optic nerve: Transmits visual signals

• Pupil: Opening for light

• Retina: Photoreceptors

• Sclera: White of the eye

• Vitreous humor: Gel filling

Muscle Tissue and Physiology

Types of Muscle Tissue

Muscle tissue is classified into three types, each with distinct structure, function, and control mechanisms.

• Skeletal muscle: Voluntary, striated, attached to bones

• Cardiac muscle: Involuntary, striated, found in heart

• Smooth muscle: Involuntary, non-striated, found in walls of hollow organs

Skeletal Muscle Fiber Model

Skeletal muscle fibers are multinucleated cells containing specialized structures for contraction. The model below illustrates key components:

• Mitochondria: Energy production

• Myofibrils: Contractile units

• Nucleus: Genetic control

• Sarcolemma: Cell membrane

• Sarcoplasmic reticulum: Calcium storage

• Terminal cisternae: Enlarged SR regions

• T-tubule: Transmits action potential

• Triad: T-tubule + 2 terminal cisternae

Sarcomere Structure and Muscle Contraction

The sarcomere is the basic contractile unit of muscle, composed of thick and thin filaments. Muscle contraction occurs through the sliding filament mechanism.

• Thick filament: Myosin molecules with heads for binding actin

• Thin filament: Actin, troponin, and tropomyosin

• Z-disc: Boundary of sarcomere

• M line: Center of sarcomere

• H zone: Region with only thick filaments

• I band: Region with only thin filaments

• A band: Region with thick and thin filaments

Order of Muscle Contraction

1. Action potential arrives at neuromuscular junction

2. Acetylcholine released, depolarizes sarcolemma

3. Action potential travels down T-tubules

4. Calcium released from sarcoplasmic reticulum

5. Calcium binds to troponin, moves tropomyosin

6. Myosin binds to actin, power stroke occurs

7. ATP binds to myosin, detachment and reset

Isotonic vs. Isometric Contraction

• Isotonic contraction: Muscle changes length, movement occurs (e.g., lifting weights)

• Isometric contraction: Muscle length does not change, tension increases (e.g., holding a weight steady)

Muscles of the Body

Head, Neck, and Vertebrae Muscles

These muscles control facial expression, mastication, tongue movement, and neck posture.

• Buccinator, masseter, temporalis: Chewing

• Orbicularis oculi, orbicularis oris: Eye and mouth movement

• Sternocleidomastoid, scalene: Neck movement

• Frontalis, occipitalis: Forehead and scalp movement

Abdominal and Pelvic Muscles

These muscles support the trunk, aid in respiration, and control pelvic floor functions.

• Rectus abdominis, external/internal oblique, transversus abdominis: Trunk flexion and rotation

• Diaphragm: Main muscle of respiration

• Levator ani, superficial transverse perineal: Pelvic floor support

Pectoral Girdle and Upper Limb Muscles

These muscles move the shoulder, arm, forearm, and hand.

• Deltoid, pectoralis major/minor, trapezius: Shoulder movement

• Biceps brachii, triceps brachii, brachialis: Arm flexion/extension

• Flexor/extensor carpi, palmaris longus: Wrist movement

Pelvic Girdle and Lower Limb Muscles

These muscles control movement of the hip, thigh, leg, and foot.

• Gluteus maximus/medius/minimus: Hip extension/abduction

• Adductor group, gracilis, sartorius: Thigh movement

• Quadriceps (rectus femoris, vastus group): Knee extension

• Hamstrings (biceps femoris, semimembranosus, semitendinosus): Knee flexion

• Gastrocnemius, soleus, tibialis anterior: Foot movement

Summary Table: Major Nerve Plexuses

The following tables summarize the main nerves, roots, and functions for each plexus:

Cervical Plexus Nerve	Nerve Roots	Structures Innervated
Lesser occipital	C2	Scalp and posterior ear
Greater auricular	C2–C3	Skin on ear
Ansa cervicalis	C1–C3	Geniohyoid and infrahyoid muscles
Transverse cervical	C2–C3	Skin on superior chest/shoulder
Supraclavicular	C3–C4	Skin on superior chest/shoulder
Phrenic	C3–C5	Diaphragm (motor)

Brachial Plexus Nerve	Nerve Roots
Axillary	C5–C6
Radial	C5–T1
Musculocutaneous	C5–C7
Median	C6–T1
Ulnar	C8–T1

Lumbar Plexus Nerve	Nerve Roots
Iliohypogastric	L1
Ilioinguinal	L1
Genitofemoral	L1–L2
Femoral	L2–L4
Lateral femoral cutaneous	L2–L3
Obturator	L2–L4

Sacral Plexus Nerve	Nerve Roots	Structures Innervated
Superior gluteal	L4–S1	Gluteus medius/minimus, tensor fascia latae
Inferior gluteal	L5–S2	Gluteus maximus
Pudendal	S2–S4	Pelvic floor muscles
Posterior femoral cutaneous	S1–S3	Skin of posterior thigh
Sciatic	L4–S3	Leg (motor/sensory)
Common fibular	L4–S2	Leg/foot
Tibial	L4–S3	Leg/foot

Key Muscle Fiber Structures and Functions

• Mitochondria: Provide ATP for contraction

• Myofibrils: Contain sarcomeres

• Nucleus: Controls cell function

• Sarcolemma: Muscle cell membrane

• Sarcoplasmic reticulum: Stores calcium

• Terminal cisternae: Release calcium

• T-tubule: Conducts action potential

• Triad: T-tubule flanked by terminal cisternae

Muscle Contraction Formula

The force generated by muscle contraction can be described by:

$F = n \cdot f_{single}$

Where F is total force, n is the number of contracting fibers, and fsingle is the force per fiber.

Summary

This guide covers the peripheral nervous system, special senses, muscle tissue types, and the anatomy and physiology of muscle contraction, providing a comprehensive overview for ANP college students.