Muscular System

Head and Trunk Muscles

The head and trunk muscles are responsible for facial expressions, mastication, neck movement, respiration, and movements of the vertebral column and thorax.

• Orbicularis oris: Encircles the mouth; enables closing and puckering of the lips.

• Orbicularis oculi: Surrounds the eye; allows blinking and squinting.

• Zygomaticus major: Elevates the corners of the mouth (smiling).

• Risorius: Draws the corner of the mouth laterally.

• Epicranius (occipitofrontalis): Raises eyebrows and wrinkles forehead.

• Platysma: Tenses skin of the neck and depresses mandible.

• Sternocleidomastoid (SCM): Flexes and rotates the head.

• Temporalis: Elevates and retracts mandible (chewing).

• Masseter: Elevates mandible (primary chewing muscle).

• Buccinator: Compresses cheek (whistling, sucking).

• Erector spinae: Extends and laterally flexes the vertebral column.

• External/Internal intercostalis: Muscles between ribs; aid in respiration.

• Diaphragm: Main muscle of inspiration; separates thoracic and abdominal cavities.

• Abdominal Group:

  • Rectus abdominis: Flexes vertebral column, compresses abdomen.

  • External oblique: Rotates and laterally flexes trunk.

  • Internal oblique: Same as external, but deeper layer.

  • Transverse abdominis: Compresses abdominal contents.

• Latissimus dorsi: Extends, adducts, and medially rotates arm.

• Serratus anterior: Protracts scapula; important for arm elevation.

• Trapezius: Elevates, retracts, and rotates scapula.

• Rhomboideus major/minor: Retract scapula.

• Levator scapulae: Elevates scapula.

• Pectoralis major: Flexes, adducts, and medially rotates arm.

Arm and Leg Muscles

These muscles are involved in movement and stabilization of the upper and lower limbs.

• Deltoid: Abducts, flexes, and extends arm at shoulder.

• Rotator Cuff Group:

  • Supraspinatus: Abducts arm.

  • Infraspinatus: Laterally rotates arm.

  • Teres Minor: Laterally rotates arm.

  • Subscapularis: Medially rotates arm.

• Biceps brachii: Flexes elbow and supinates forearm.

• Brachialis: Primary flexor of elbow.

• Brachioradialis: Flexes forearm at elbow.

• Triceps brachii: Extends elbow.

• Flexor carpi radialis: Flexes and abducts wrist.

• Palmaris longus: Flexes wrist.

• Extensor carpi ulnaris: Extends and adducts wrist.

• Extensor digitorum: Extends fingers.

• Opponens pollicis: Opposes thumb.

• Iliacus & Psoas major: Flex hip (together called iliopsoas).

• Sartorius: Flexes, abducts, and laterally rotates thigh; flexes knee.

• Adductor group: Adducts thigh.

• Gracilis: Adducts thigh, flexes knee.

• Quadriceps:

  • Rectus femoris: Extends knee, flexes hip.

  • Vastus lateralis, medialis, intermedius: Extend knee.

• Hamstrings:

  • Biceps femoris, Semitendinosus, Semimembranosus: Flex knee, extend hip.

• Gluteus maximus: Extends and laterally rotates hip.

• Gluteus medius: Abducts and medially rotates hip.

• Tensor fascia latae (TFL): Abducts and medially rotates thigh.

• Gastrocnemius: Plantar flexes foot, flexes knee.

• Soleus: Plantar flexes foot.

• Tibialis anterior: Dorsiflexes and inverts foot.

• Fibularis longus (peroneus): Everts and plantar flexes foot.

Nervous System

Neuron Structure

Neurons are the functional units of the nervous system, specialized for communication.

• Dendrites: Receive signals from other neurons.

• Axon: Transmits electrical impulses away from the cell body.

• Cell body (soma): Contains nucleus and organelles; integrates signals.

• Nucleus of Schwann cell: Contains genetic material of Schwann cell, which forms myelin in PNS.

• Axon hillock: Site where action potentials are initiated.

• Neurilemma: Outer layer of Schwann cell; aids in regeneration.

• Myelin sheath: Insulating layer that increases speed of impulse conduction.

• Node of Ranvier (myelin sheath gap): Gaps in myelin sheath; facilitate saltatory conduction.

Nerve Anatomy

Nerves are bundles of axons in the peripheral nervous system, protected by connective tissue layers.

• Epineurium: Outermost connective tissue covering of a nerve.

• Perineurium: Surrounds each fascicle (bundle of nerve fibers).

• Endoneurium: Surrounds individual nerve fibers (axons).

• Fascicle: Bundle of nerve fibers within a nerve.

• Nerve Fiber: Another term for axon.

• Myelin Sheath: Insulating covering of axons.

• Axon: Long process of a neuron that transmits impulses.

Central Nervous System

Brain Anatomy

The brain is the control center of the nervous system, composed of various regions with specialized functions.

• Corpus callosum: Connects left and right cerebral hemispheres.

• Thalamus: Relay station for sensory information.

• Hypothalamus: Regulates homeostasis, endocrine functions.

• Pituitary gland: Master endocrine gland, controlled by hypothalamus.

• Pons: Relays signals between cerebrum and cerebellum; involved in breathing.

• Medulla oblongata: Controls vital functions (heart rate, breathing).

• Cerebellum: Coordinates movement and balance.

• 3rd and 4th ventricles: Contain cerebrospinal fluid (CSF).

• Cerebral aqueduct: Connects 3rd and 4th ventricles.

• Pineal gland: Secretes melatonin; regulates sleep-wake cycle.

• Optic chiasma: Crossing of optic nerves.

• Lobes of the brain: Frontal, parietal, temporal, occipital (each with specialized functions).

• Central sulcus: Separates frontal and parietal lobes.

• Precentral gyrus: Primary motor cortex.

• Postcentral gyrus: Primary somatosensory cortex.

• Arbor vitae: Tree-like white matter in cerebellum.

• Lateral ventricles (L and R): Largest CSF-filled cavities in cerebrum.

• Longitudinal fissure: Deep groove separating cerebral hemispheres.

Spinal Cord Anatomy

The spinal cord transmits neural signals between the brain and the body and is protected by meninges and vertebrae.

• Dura mater: Tough outer meningeal layer.

• Arachnoid mater: Middle, web-like meningeal layer.

• Pia mater: Delicate inner meningeal layer.

• Spinal nerve: Mixed nerve carrying motor and sensory information.

• Ventral root: Contains motor neuron axons.

• Dorsal root: Contains sensory neuron axons.

• Dorsal root ganglion (DRG): Contains cell bodies of sensory neurons.

• Dorsal/ventral/lateral horn: Gray matter regions for sensory/motor processing.

• Dorsal/ventral/lateral funiculus: White matter columns containing ascending/descending tracts.

Cranial Nerves (I-XII)

Cranial nerves are twelve pairs of nerves that emerge directly from the brain, each with specific sensory, motor, or mixed functions.

Additional info:

• Knowing the location, function, and innervation of each muscle and nerve is essential for lab exams.

• Images and diagrams are commonly used to test identification skills in practical exams.

• Abbreviations (e.g., SCM for sternocleidomastoid) are acceptable in lab settings.