Comprehensive Study Notes: Muscles, Nervous System, and Sensory Anatomy

MUSCLES OF THE HUMAN BODY

Head and Neck Muscles

The head and neck muscles are essential for facial expression, mastication (chewing), and movement of the head and neck. They are categorized based on their primary functions and anatomical locations.

• Scalp Muscles: frontalis, occipitalis

• Facial Expression Muscles: orbicularis oris (closes lips), orbicularis oculi (closes eyelids), zygomaticus (smiling), platysma (tenses neck skin), buccinator (compresses cheek)

• Mastication Muscles: masseter (elevates mandible), temporalis (elevates and retracts mandible)

• Neck Muscles: trapezius (moves scapula), mylohyoid (elevates hyoid), sternocleidomastoid (rotates head), digastricus (depresses mandible)

Example: The sternocleidomastoid is responsible for turning the head to the opposite side and flexing the neck.

Trunk and Shoulder Muscles

These muscles stabilize and move the trunk and shoulders, playing a key role in posture and upper limb movement.

• Pectoralis major: Adducts and flexes the humerus

• Deltoid: Abducts the arm

• Serratus anterior: Protracts scapula

• External/Internal Intercostals: Aid in respiration by moving the rib cage

• Subscapularis: Rotates the humerus medially

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

• Teres major/minor: Assist in arm rotation

• Levator scapulae: Elevates scapula

• Rhomboideus major/minor: Retract scapula

Example: The pectoralis major is used when pushing objects away from the body.

Abdominal Muscles

Abdominal muscles support the trunk, allow movement, and hold organs in place by regulating internal abdominal pressure.

• External oblique: Compresses abdomen, flexes vertebral column

• Internal oblique: Compresses abdomen, rotates trunk

• Transverse abdominus: Compresses abdominal contents

• Rectus abdominus: Flexes vertebral column

Example: The rectus abdominus is commonly known as the "six-pack" muscle and is activated during sit-ups.

Arm Muscles

Arm muscles facilitate movement of the upper limb, including flexion, extension, and rotation.

• Coracobrachialis: Flexes and adducts arm

• Biceps brachii: Flexes elbow, supinates forearm

• Brachialis: Flexes elbow

• Brachioradialis: Flexes forearm

• Triceps brachii: Extends elbow

Hand Movements: Supinator (supinates forearm), Pronator teres (pronates forearm), Flexor carpi radialis (flexes wrist)

Leg Muscles

Leg muscles are responsible for movement and stability of the lower limb, including walking, running, and maintaining posture.

• Gluteus maximus: Extends and laterally rotates hip

• Gluteus medius: Abducts and medially rotates hip

• Hamstrings: Biceps femoris, Semitendinosus, Semimembranosus (flex knee, extend hip)

• Quadriceps femoris: Rectus femoris, Vastus lateralis, Vastus medialis (extend knee)

• Sartorius: Flexes, abducts, and laterally rotates thigh

• Tensor fascia latae: Stabilizes hip and knee

• Gastrocnemius: Plantar flexes foot

• Soleus: Plantar flexes foot

• Tibialis anterior: Dorsiflexes foot

• Flexor digitorum longus: Flexes toes

• Extensor digitorum longus: Extends toes

Example: The gastrocnemius is the main muscle used when standing on tiptoe.

NERVOUS SYSTEM ANATOMY

Histology of Nervous Tissue

Nervous tissue consists of neurons and supporting cells (neuroglia) that transmit and process information throughout the body.

• Satellite cells: Support neurons in peripheral ganglia

• Ependymal cells: Line the central canal of the spinal cord and ventricles of the brain, involved in cerebrospinal fluid production

Example: Ependymal cells help circulate cerebrospinal fluid, which cushions the brain and spinal cord.

Sheep Brain Anatomy

Sheep brain dissection is commonly used to study the gross anatomy of the brain due to its similarity to the human brain.

• External Structures: cerebrum, cerebellum, longitudinal fissure, olfactory bulb, optic nerve, pons, medulla, spinal cord, meninges, corpora quadrigemina

• Internal Structures (Sagittal Section): corpus callosum, lateral ventricles, fornix, third ventricle, fourth ventricle, septum pellucidum, cerebellum, hypophysis (pituitary), cerebral hemispheres, olfactory bulb, pons and medulla, corpora quadrigemina, thalamus (intermediate mass)

Example: The corpus callosum connects the left and right cerebral hemispheres, allowing communication between them.

Human Brain Anatomy

The human brain is divided into several regions, each with specialized functions related to sensation, movement, cognition, and autonomic control.

• Major Structures: longitudinal fissure, central sulcus, cerebellum, arbor vitae, cerebrum, lateral sulcus, frontal lobe, parietal lobe, temporal lobe, occipital lobe, pons, medulla oblongata, precentral gyrus, postcentral gyrus, fornix, thalamus, corpus callosum, cerebral aqueduct, hypothalamus, olfactory bulb, 3rd ventricle, 4th ventricle

Example: The precentral gyrus is the primary motor cortex, responsible for voluntary movement.

SENSORY SYSTEM ANATOMY

Eye Anatomy

The eye is a complex sensory organ responsible for vision. Its anatomy includes structures for focusing light, detecting images, and protecting the eye.

• Optic nerve: Transmits visual information to the brain

• Extraocular muscles: superior rectus, inferior rectus, lateral rectus, medial rectus, superior/inferior oblique (move the eyeball)

• Lacrimal apparatus: lacrimal gland, lacrimal sac, nasolacrimal duct (produces and drains tears)

• Fibrous layer: sclera (white of the eye), cornea (transparent front)

• Vascular layer: choroid, ciliary body, iris (controls pupil size)

• Retina: Contains photoreceptors for vision

• Other structures: pupil, lens, optic disk, tapetum lucidum (reflective layer in some animals)

Example: The lens changes shape to focus light on the retina for clear vision.

Ear Anatomy

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

• External ear: pinna (auricle), lobule, external auditory canal

• Middle ear: tympanic membrane (eardrum), ossicles (malleus, incus, stapes), round window

• Inner ear: cochlea (hearing), vestibule (balance), semicircular canals (balance), oval window, auditory tube

• Nerve: vestibulocochlear nerve (transmits sound and balance information)

Example: The cochlea converts sound waves into electrical signals for the brain to interpret as hearing.

ADDITIONAL INFO

• Muscle Classification: Muscles are classified by location (e.g., head, trunk, limb), function (e.g., flexor, extensor), and structure (e.g., skeletal, smooth, cardiac).

• Brain Regions: Each lobe of the brain has specialized functions: frontal (motor, decision-making), parietal (sensory), temporal (hearing, memory), occipital (vision).

• Eye and Ear Physiology: The eye uses refraction and accommodation to focus light; the ear uses mechanical vibration and fluid movement to detect sound and maintain balance.