pathways

Visual Pathway

• Pathway: Cornea → Aqueous humor of anterior segment → Lens → Vitreous humor of posterior segment → Retina

  • Components of Retina: Photoreceptors → Bipolar cells → Ganglion cells

• Continuation: Optic nerve → Optic chiasm → Optic tract → Thalamus (sensory integration center) → Primary visual cortex (occipital lobe)

Auditory Pathway

• Pathway: Auricle → External auditory meatus (canal) → Tympanic membrane → Malleus → Incus → Stapes → Oval window → Auditory hair cells (in spiral organ of Corti in cochlea)

• Continuation: Cochlear nerve → Medulla → Inferior colliculus (auditory reflex center in midbrain) → Thalamus (sensory integration center) → Primary auditory cortex (temporal lobe)

Olfactory Pathway

• Pathway: Olfactory receptor cells → Olfactory nerve → Olfactory bulb → Olfactory tracts

• Further Pathways:

  1. Thalamus → Olfactory cortex to interpret and identify smells

  2. Hypothalamus, amygdala, limbic system to elicit emotional responses to odors

Gustatory Pathway

• Pathway: Gustatory hair cells → Cranial nerves (facial nerve, glossopharyngeal nerve, vagus nerve) → Medulla oblongata → Thalamus → Gustatory cortex (in insula cortex)

• Emotional Responses: Involvement of hypothalamus, amygdala, limbic system to elicit emotional responses to tastants

Pathway of Blood through the Heart

• Pathway: Superior & Inferior Vena Cavas and coronary sinus → Right atrium → Tricuspid valve → Right ventricle → Pulmonary semilunar valve → Pulmonary trunk → Pulmonary arteries → Lung capillaries → Pulmonary veins → Left atrium → Bicuspid (mitral) valve → Left ventricle → Aortic semilunar valve → Aorta → Systemic arteries → Systemic capillaries → Systemic veins → Superior & Inferior Vena Cavas and coronary sinus

Intrinsic Conduction System of the Heart

• Electrical Pathway: Sinoatrial node (intrinsic pacemaker cells) → Atrioventricular node → Atrioventricular bundle (Bundle of His) → Left and right Bundle branches → Purkinje fibers

Pathway of Air

• Pathway: Nares → Nasal cavity → Nasopharynx → Oropharynx → Laryngopharynx → Larynx → Trachea → Primary Bronchus → Secondary Bronchus → Tertiary Bronchus → Bronchiole → Terminal bronchiole → Respiratory bronchiole → Alveolar duct → Alveolus (alveoli)

• Respiratory Tract Division:

  • Upper respiratory tract: Nasal cavity, pharynx, and larynx

  • Lower respiratory tract: Trachea, bronchi, bronchioles, lungs

Pathway of Food

• Pathway: Oral cavity → Oropharynx → Laryngopharynx → Upper esophageal sphincter → Esophagus → Lower esophageal (cardiac) sphincter → Stomach → Pyloric sphincter → Duodenum → Jejunum → Ileum → Ileocecal valve → Cecum

• Continuation: Ascending colon → Hepatic flexure → Transverse colon → Splenic flexure → Descending colon → Sigmoid colon → Rectum → Anal canal → Anus

• Notes:

  • Common bile duct and pancreatic duct enter the duodenum.

  • Vermiform appendix is attached to the Cecum.

• Small Intestine Components: Duodenum, Jejunum, Ileum

• Large Intestine Components: Cecum, Ascending Colon, Transverse Colon, Descending Colon, Sigmoid Colon, Rectum, Anal Canal

Pathway of Urine Formation

• Pathway: Renal artery → Afferent arteriole → Glomerulus → Bowman’s capsule → Proximal convoluted tubule → Descending limb of Loop of Henle → Ascending limb of Loop of Henle → Distal convoluted tubule → Collecting duct → Minor calyx → Major calyx → Renal pelvis → Ureter → Bladder → Urethra

Pathway of Sperm

• Pathway: Seminiferous tubules → Rete testis → Epididymis → Ductus (vas) deferens → Ejaculatory duct → Urethra → Vagina → Cervix → Uterus → Uterine (Fallopian) tube (oviduct)