Cranial Nerves: Function and Anatomy

Cranial Nerves

• Twelve cranial nerves are listed by Roman numeral and name.
• I (Olfactory nerve) is sensory.
• II (Optic nerve) is sensory.
• III (Oculomotor nerve) is motor.
• IV (Trochlear nerve) is motor.
• V (Trigeminal nerve) is sensory and motor (mixed).
• VI (Abducens nerve) is motor.
• VII (Facial nerve) is sensory and motor (mixed).
• VIII (Vestibulocochlear nerve, or Auditory nerve) is sensory.
• IX (Glossopharyngeal nerve) is sensory and motor (mixed).
• X (Vagus nerve) is sensory and motor (mixed).
• XI (Accessory nerve, or Spinal Accessory nerve) is motor.
• XII (Hypoglossal nerve) is motor.

Sensory Cranial Nerves

• I (Olfactory nerve) is responsible for the sense of smell.
• II (Optic nerve) is responsible for vision.
• VIII (Vestibulocochlear nerve) is responsible for hearing and balance (auditory and vestibular sensations).

Motor Cranial Nerves

• III (Oculomotor nerve) controls most eye movements, pupil constriction, and eyelid elevation.
• IV (Trochlear nerve) controls the superior oblique muscle, which moves the eye downward and laterally.
• VI (Abducens nerve) controls the lateral rectus muscle, moving the eye laterally (abduction).
• XI (Accessory nerve) controls the sternocleidomastoid and trapezius muscles, involved in head and shoulder movements.
• XII (Hypoglossal nerve) controls tongue muscles for speech and swallowing.

Mixed (Sensory and Motor) Cranial Nerves

• V (Trigeminal nerve) has three divisions:
• V1 (ophthalmic nerve): Provides sensory input from the face (touch, pain, temperature).
• V2 (maxillary nerve): Provides sensory to the middle part of the face.
• V3 (mandibular nerve): Controls muscles of mastication (chewing).
• VII (Facial nerve) functions:
• Sensory: Provides taste sensation to the anterior two-thirds of the tongue.
• Motor: Controls muscles of facial expression (e.g., smiling, frowning).
• Parasympathetic: Involved in lacrimal (tear) and salivary glands' function.
• IX (Glossopharyngeal nerve) functions:
• Sensory: Provides taste sensation from the posterior one-third of the tongue and sensations from the pharynx and tonsils.
• Motor: Controls some pharynx muscles (important for swallowing).
• Parasympathetic: Involved in salivation from the parotid gland.
• X (Vagus nerve) functions:
• Sensory: Provides sensory input from the ear, throat, and organs in the chest and abdomen.
• Motor: Controls most muscles of the pharynx and larynx (speaking and swallowing).
• Parasympathetic: Regulates internal organs (heart, lungs, digestive tract).

Cranial Nerves Leaving the Head and Their Functions

• Vagus Nerve (Cranial Nerve X) functions:
• Parasympathetic control: Innervates thoracic and abdominal organs (heart, lungs, digestive system).
• Heart rate regulation: Lowers heart rate via parasympathetic signals.
• Respiratory control: Regulates breathing muscles and smooth muscle of airways.
• Gastrointestinal function: Influences digestion via stomach and intestinal muscles, promoting peristalsis and digestive enzyme secretion.
• Voice and swallowing: Motor functions related to speech and swallowing via innervation of larynx and pharynx muscles.

Cranial Nerves and Parasympathetic Motor Signals

• CN III (Oculomotor nerve): Pupil constriction, lens accommodation.
• CN VII (Facial nerve): Tear production, salivation (submandibular, sublingual glands), nasal secretions.
• CN IX (Glossopharyngeal nerve): Salivation (parotid gland).
• CN X (Vagus nerve): Heart rate, respiratory control, gastrointestinal motility, and secretion.

Cranial Nerves and Their Roles

• Muscles of mastication: Trigeminal nerve (CN V), specifically the mandibular division (V3), controls muscles of mastication (masseter, temporalis, pterygoid muscles).
• Muscles of facial expression: Facial nerve (CN VII) controls muscles of facial expression (Orbicularis oculi, Orbicularis oris, frontalis, and others).
• Visceral muscle control (cardiac and smooth): Vagus nerve (CN X) provides parasympathetic innervation to cardiac muscle and smooth muscle.
• Skeletal muscle control:
• Oculomotor nerve (CN III) controls muscles that move the eyeball (superior, inferior, and medial rectus, inferior oblique) and the levitator palpebrae superioris (raising the eyelid).
• Trochlear nerve (CN IV) controls the superior oblique muscle of the eye.
• Abducens nerve (CN XI) controls the lateral rectus muscle of the eye.
• Accessory nerve (CN XI) controls the sternocleidomastoid and trapezius muscles for head rotation, shoulder elevation, and other neck movements.
• Hypoglossal nerve (CN XII) controls the intrinsic and extrinsic tongue muscles for speech, swallowing, and food manipulation.
• Sense of vision: Optic nerve (CN II) transmits visual information from the retina to the brain allowing for vision.
• Sense of taste:
• Facial nerve (CN VII) provides taste sensation from the anterior two thirds of the tongue.
• Glossopharyngeal nerve (CN IX) provides taste sensation from the posterior one third of the tongue.
• Vagus nerve (CN X) provides taste sensation from the epiglottis and the pharynx.
• Sense of smell: Olfactory nerve (CN I) transmits olfactory information from the nasal cavity to the brain.
• Sense of hearing: Vestibulocochlear nerve (CN VII) transmits sound information from the cochlea to the brain, enabling hearing; the vestibular part is responsible for balance.

Spinal Nerves

• Cervical nerves (C1-C8) innervate the neck, pectoral girdle, and upper limb.
• Thoracic nerves (T1-T12) innervate the viscera.
• Lumbosacral nerves (L1-L5, S1-S5, Co) innervate the pelvic girdle and lower limb.

Specific Spinal Nerves

• C1 (Cervical 1): Known as the suboccipital nerve.
• C2 (Cervical 2): Greater occipital nerve, lesser occipital nerve.
• C3 (Cervical 3): Third occipital nerve, phrenic nerve (from C3-C5, important for diaphragm control).
• C4 (Cervical 4): Phrenic nerve (continues from C3-C5).
• C5 (Cervical 5): Musculocutaneous nerve, axillary nerve, radial nerve.
• C6 (Cervical 6): Radial nerve, musculocutaneous nerve.
• C7 (Cervical 7): Radial nerve, median nerve, ulnar nerve.
• C8 (Cervical 8): Ulnar nerve, median nerve.
• T1 (Thoracic 1): Ulnar nerve, median nerve.
• T2 (Thoracic 2): Intercostal nerves.
• T3 (Thoracic 3): Intercostal nerves.
• T4 (Thoracic 4): Intercostal nerves.
• T5 (Thoracic 5): Intercostal nerves.
• T6 (Thoracic 6): Intercostal nerves.
• T7 (Thoracic 7): Intercostal nerves.
• T8 (Thoracic 8): Intercostal nerves.
• T9 (Thoracic 9): Intercostal nerves.
• T10 (Thoracic 10): Intercostal nerves.
• T11 (Thoracic 11): Intercostal nerves.
• T12 (Thoracic 12): Subcostal nerve.
• L1 (Lumbar 1): Iliohypogastric nerve, ilioinguinal nerve.
• L2 (Lumbar 2): Femoral nerve, obturator nerve.
• L3 (Lumbar 3): Femoral nerve, obturator nerve.
• L4 (Lumbar 4): Femoral nerve, obturator nerve.
• L5 (Lumbar 5): Sciatic nerve, common fibular nerve.
• S1 (Sacral 1): Sciatic nerve, tibial nerve, common fibular nerve.
• S2 (Sacral 2): Sciatic nerve, tibial nerve, common fibular nerve.
• S3 (Sacral 3): Pudendal nerve, pelvic splanchnic nerves.
• S4 (Sacral 4): Pudendal nerve, pelvic splanchnic nerves.
• S5 (Sacral 5): Pudendal nerve, pelvic splanchnic nerves.
• Co1 (Coccygeal nerve 1): Coccygeal nerve (innervates the area around the coccyx).

Spinal Nerve Entry and Exit

• Sensory signals enter the spinal cord through the dorsal root.
• Motor signals leave the spinal cord through the ventral root.
• Combined dorsal and ventral roots form the spinal nerve, which exits the spinal cord and branches.
• Dorsal (posterior) root comprises:
• Sensory (afferent) nerve fibers that carry information from the body to the spinal cord.
• Dorsal root ganglion (DRG), a bulge before entering the spinal cord, contains sensory neuron cell bodies.
• Ventral (anterior) root comprises:
• Motor (efferent) nerve fibers carry signals from the spinal cord to muscles and glands.
• These fibers originate from motor neuron cell bodies in the anterior horn of the spinal cord.
• Spinal Nerve Formation:
• Dorsal and ventral roots join outside the spinal cord.
• The spinal nerve exits the vertebral column via the intervertebral foramen.
• Branching:
• Spinal nerves branch into smaller divisions after exiting the spinal cord.
• Dorsal ramus: supplies the back muscles and skin.
• Ventral ramus: supplies the anterior body and limbs.
• Communicating rami: connect with the autonomic nervous system (sympathetic trunk) in some regions.

Neurons

• Primary (First Order) Neuron
• First neuron in pathway for sensory information from peripheral receptors to the CNS.
• Carries signal from sensory receptors to the spinal cord/brainstem; cell body in dorsal root or sensory ganglion (cranial nerves).
• Secondary (Second Order) Neuron
• Located in the CNS, transmits sensory information from primary neuron to higher processing centers like the thalamus.
• Typically decussates (crosses sides) and ascends to the thalamus/brainstem.
• Tertiary (Third Order) Neuron
• Transmits sensory information from the thalamus to the somatosensory cortex for final processing and perception.
• Completes sensory pathway, transmitting signals from thalamus to cerebral cortex for conscious awareness.
• Upper Motor Neuron
• Originate in motor cortex/brainstem, transmit motor commands from brain to spinal cord, where they synapse with lower motor neurons.
• Regulate voluntary motor activity by sending signals down corticospinal or corticobulbar tracts, involved in planning, initiation, and coordination.
• Lower Motor Neuron
• Final neurons in motor pathway directly innervate skeletal muscles to initiate contraction, receive input from upper motor neurons.
• Execute movements by synapsing directly on muscle fibers, found in spinal cord (limbs/trunk) or brainstem (head/neck).

Reflex Arc

• Reflex arc: pathway controlling a reflex action.
• Receptor: detects a stimulus (various modalities).
• Sensory neuron (afferent): receptor sends signal to spinal cord via sensory neuron.
• Integration center (interneurons): sensory neuron synapses with interneuron in spinal cord, which may directly communicate with motor neuron, bypassing brain for faster response.
• Motor neuron (efferent): motor neuron carries response from the spinal cord to an effector (muscle or gland).
• Effector (muscle/gland): responds by contracting or performing the reflex action.

Dermatomes

• Dermatomes: Regions of skin where efferent signals originate from spinal cord nerves, appearing like slices.

Cervical Plexus

• Cervical plexus (C1-C4) innervates:
• Phrenic nerve: sole innervation of the diaphragm.

Brachial Plexus

• Brachial plexus (C5-T1) innervates:
• Posterior cord nerves:
• Axillary nerve
• Radial nerve
• Lateral and medial cord nerves:
• Musculocutaneous nerve
• Median nerve
• Ulnar nerve

Lumbar Plexus

• Lumbar plexus (L1-4) innervates:
• Iliohypogastric nerve, ilioinguinal nerve, genitofemoral nerve, lateral femoral cutaneous nerve, femoral nerve, obturator nerve, lumbosacral trunk.

Sacral Plexus

• Sacral plexus (L4-S4) innervates:
• Superior gluteal nerve, inferior gluteal nerve, nerve to piriformis, sciatic nerve, posterior femoral cutaneous nerve, pudendal nerve.

Reflexive Behaviors

• Reflexive behaviors (reflexes): Rapid, involuntary responses to stimuli to protect the body from harmful things.

Patellar Tendon Reflex

• Patellar tendon (knee jerk) reflex protects the body from sudden loss of balance or instability during standing.
• Stretching the quadriceps triggers the patellar tendon reflex, causing quadriceps contraction to prevent knee buckling.
• A kick is caused by striking the patellar tendon below the patella, stimulating the L4 and L3 reflex arcs.

Golgi Tendon Organ Reflex

• Golgi tendon organ (GTO) reflex protects muscles from overstretching or tearing.
• Strong muscle contraction is detected by the GTO, which signals the spinal cord to inhibit further contraction of the muscle.
• (1) Muscle contraction increases tension in tendons, detected by Golgi tendon organ.
• (2) Muscle contraction stimulates sensory nerve signals to the CNS.
• (3) Sensory neurons stimulate interneurons in the spinal cord
• (4a) Interneurons inhibit alpha motor neurons to muscle.
• (4b) Interneurons stimulate an alpha motor neuron to antagonist muscles.
• (5a) Muscle relaxes and there is relief of tension on tendon.
• (5b) Muscle contracts (reciprocal activation).

Flexor (Withdrawal) Reflex

• Flexor reflex protects from injury due to pain (heat, cold, sharp objects).
• Touching something hot triggers flexor reflex, causing muscles to contract and pull away to prevent further damage.

Crossed Extensor Reflex

• Crossed extensor reflex helps maintain balance when one limb is withdrawn due to pain or injury.
• Stepping on a sharp object and quickly withdrawing one leg so the crossed extensor reflex causes the opposite leg to extend and stabilize the body.
• Contralateral limb contraction in response to pain sensation.

Sympathetic and Parasympathetic Nervous Systems

Basal Tone

• Basal tone: The constant, low-level activity occurring from both the sympathetic and parasympathetic nervous systems to counteract and "be ready".

Autonomic Reflex

• Autonomic reflex: A reflex from the autonomic nervous system that works automatically
• Heart rate, pupil dilation, stomach stretching, bowel movement, baroreceptor reflex

Autonomic Nervous System Control Center

• Hypothalamus
• Regulates homeostasis, control and integration center for autonomic functions and involved in emotion

Autonomic Nervous System and Basic Drives

• Hunger: Sympathetic system is more prevalent, then switches to parasympathetic system after eating
• Thirst: Sympathetic system is more prevalent, then switches to parasympathetic system after drinking
• Aggression: Sympathetic system is more prevalent
• Sexual Arousal: Parasympathetic system, then sympathetic system for orgasm
• Temperature: Sympathetic if hot and parasympathetic if cold.

Homeostasis and Autonomic Nervous System

• Homeostasis is vital for proper body function.
• The autonomic nervous system (ANS) ensures internal conditions stay balanced, supporting the body's ability to respond and recover from changes in the external environment.
• Without this balance, the body would struggle to maintain health and survival.

Autonomic Nervous System Arms

• SNS (Sympathetic nervous system) excites heart, lungs, and blood vessels while inhibiting digestion during stress ("fight or flight").
• PNS (Parasympathetic nervous system) excites the digestive system while inhibiting the heart, lungs, etc., during resting and digesting.

Cholinergic and Adrenergic Neurons

Pharmaceutical Agents and Autonomic Functioning

• Propranolol: Beta blocker, decreases heart rate and contractility.
• Atropine: Muscarinic antagonist, increases heart rate, reduces secretions; similar effects.
• Phenylephrine: α1 agonist, vasoconstriction occurs, increases blood pressure.
• Sympathomimetic drug: Mimics sympathetic activity.
• Hypothetical (beta?) specific agonist: Stimulates either β1 (heart) or β2 (lungs, vasculature) receptors.

Adrenergic Receptors

• A1 - alpha one:
  • Primary locations and specific actions: almost all effectors of sympathetic division (exceptions include cardiac muscle and bronchioles) cause contraction of most smooth muscle including blood vessels of the skin, blood vessels of GI tract, blood vessels of kidneys, arrector pili, uterus, ureters, internal urethral sphincter, dilator papillae muscle of eye
  • General effect - excitatory.
  • Examples of drugs that interact with receptor – phenylephrine causes vasoconstriction of nasal blood vessels, decreasing nasal secretions.
• A2-alpha two:
  • Primary locations and specific actions – pancreas (inhibit insulin release) CNS (decreases norepinephrine release and thus inhibits sympathetic activity; causes sedation and analgesia) GI sphincters (causes contraction)
  • Primary locations and specific actions - heart (both sinoatrial node and cardiac muscle; increases heart rate and force of contraction). -General effect-excitatory
  • Examples of drugs that interact with receptor - propranolol is a nonselective beta blocker used to treat high blood pressure
• B2beta two:
• Primary locations and specific actions - causes smooth muscle relaxation in blood vessels of the heart wall (coronary arteries), liver, and skeletal muscle; results in vasodilation, smooth muscle relaxation within bronchioles, uterus, GI tract
• General effect – primary inhibitory
• Examples of drugs that interact with receptor – albuterol dilates bronchioles; used to treat asthma, Terbutaline relaxes uterine wall to delay preterm labor
• B3 beta three:
  • Primary locations and specific actions - adipose connective tissue (stimulates lipolysis). urinar bladder (relaxes detrusor muscle)
  • Genral effect - excitatory or inhibitory
  • Examples of drugs that interact with receptor – mirabegron relaxes urinary bladder wall; used to treat overactive bladder

Sensory Receptors

• Proprioceptors: Detect body position, movement, balance, muscle tension.
• Mechanoreceptors: Detect physical pressure, vibration, and sound.
• Thermoreceptors: Detect temperature (heat and cold).
• Nociceptors: Detect pain from tissue damage or harmful stimuli.
• Exteroceptors: Detect external stimuli (touch, sound, light).
• Interoceptors: Detect internal stimuli (organ function, blood pressure).
• Chemoreceptors: Detect chemical changes (smell, taste, blood composition).
• Osmoreceptors: Detect osmotic pressure and regulate fluid balance.

Adaptation in Sensory Receptors

• Adaptation in sensory receptors is when receptors become customed to a stimulus, becoming less responsible to it over time.

Phasic vs. Tonic Receptors

• Phasic Adaptation (Rapid Adaptation):

• Receptors that show rapid adaptation are called phasic receptors.
• These receptors respond quickly to the onset of a stimulus but quickly decrease their firing rate and stop responding to a constant stimulus.
  • Example: Pacinian corpuscles (responsible for detecting pressure and vibration) rapidly adapt when a person sits down. Initially, you feel the pressure of the seat, but after a short time, the sensation fades as the receptor adapts. • Tonic Adaptation (Slow or Minimal Adaptation):
• Receptors that show slow adaptation or minimal adaptation are called tonic receptors.
• These receptors continue to respond to a constant stimulus, though often at a reduced rate. They provide continuous information about the stimulus over time.
  • Example: Nociceptors (pain receptors) typically do not fully adapt, allowing the body to continuously monitor harmful stimuli and alert the brain to ongoing pain.

Acuity

• Acuity refers to how finely a sensory system can detect and interpret stimuli, with higher acuity meaning a greater ability to perceive small, detailed changes or distinctions.

Muscle Spindle Apparatus

• Muscle spindle apparatus monitors muscle stretch and provides feedback to the nervous system about muscle length.
• Length detection: Detects changes in the muscle's length.
• Rate of stretch: Detects how quickly the muscle is being stretched.
• Stretch reflex: Involved in the monosynaptic stretch reflex to resist excessive stretch.
• Proprioception: Contributes to the body's sense of muscle position and movement.
• Muscle tone regulation: Helps maintain appropriate muscle tone and posture.

Golgi Tendon Organ

• Tension detection: The Golgi tendon organ detects tension in the muscle tendon, which correlates with the force generated by the muscle.
• Autogenic inhibition: When tension is too high, the GTO activates a reflex to inhibit the contracting muscle and prevent injury.
• Muscle protection: This inhibition acts as a protective mechanism to prevent overstretching or tearing of muscles and tendons.

Regulation

Fast pain

• A-delta fibers
• Rapid
• Sharp, stabbing, pricking
  • immediate, quick
• Short brief
• superficial
  • actute injury
    • elicit quick withdrawal
    • Sharp cut or burn

Slow pain

• C fiber
• Slow
  • dull, Arching burning, throbbing
    • delayed, slow onset
      • long lasting
      • Deep more diffuse
      • ongoing injury- inflimation
        • distress
          • involve emotional
            • Muscle soreness, visceral pain (e.g., stomach ache)

Innate Analgesic

• Nociceptors detect tissue damage.
• Pain signals travel through the spinal cord to the thalamus and then to the somatosensory cortex for perception.
• The brain activates the periaqueductal gray (PAG) and sends descending signals to the raphe nuclei and locus coeruleus.
• Serotonin and norepinephrine are released from these structures, traveling down to the spinal cord to inhibit pain transmission.
• Endogenous opioids (endorphins, enkephalins) are released to further reduce pain transmission at the spinal cord level.
• The descending pathways block pain transmission, reducing the perception of pain in the brain.

Neuromuscular Junction

• Black widow spider venom causes a huge release of Ach.
• Clostridium botulinum toxin blocks Ach release.
• Curare reversibly binds to Ach receptor sites, blocking Ach receptors.
• Myasthenia gravis antibodies inactivate Ach receptors.
• Neostigmine temporarily inactivates acetylcholinesterase, preventing Ach inactivation.
• Nerve gas (organophosphates) irreversibly inactivates acetylcholinesterase, preventing Ach inactivation.

Specialized Senses

• Vision - photoreceptors
• Olfaction - chemoreceptors
• Gustation - chemoreceptors
• Hearing – mechanoreceptors
• Equilibrium - mechanoreceptors

Cranial Nerves Play In Senses

• a. Optic nerve (II) - carries visual information from the retina to the brain
• b. olfactory nerve (I) - carries sensory info from the nose to the brain
• c. Vestibulocochlear nerve (VIII) - hearing (cochlear branch) and balance (vestibular branch)
• d. Facial nerve (VII) – transmits taste from anterior 2/3 of tongue
• e. Glossopharyngeal nerve (IX) – transmits taste from posterior 1/3 of tongue
• f. Vagus nerve (X)– contributes taste from the epiglottis and pharynx

Sense Of Vision

• Optic nerve (CN II) transmits visual information to the brain.
• Oculomotor nerve (CN III) controls most eye movements (up, down, medial) and pupillary constriction.
• Trochlear nerve (CN IV) controls downward and outward eye movements via the superior oblique muscles.
• Abducens nerve (CN VI) controls lateral eye movement via the lateral rectus muscle.
• Vision:
  • Light becomes signal image
• Refraction of light by the cornea and lens directs it onto the retina
• Phototransduction in photoreceptor cells (rods and cones) converts light into electrical signals
  • Signals are transmitted via bipolar cells to ganglion cells which send info through the optic nerve
    • The visual information reaches the lateral geniculate nucleus in the thalamus and then is processes in the visual cortex of the brain.

Vocabulary Words

• a. Refraction - bending of light as it passes through different media to focus on the retina
• b. Phototransduction - process of converting light into electrical signals in the retina
• c. Myopia - nearsightedness, where light focuses in front of the retina
• d. Opsin- protein in photoreceptors that aids in light detection and phototransduction
• e. Diplopia - double vision caused by misalignment of the eyes or other visual disturbances
• f. Rods - photoreceptor cells responsible for vision in low light and peripheral vision
• G. Astigmatism-Refractive error
• H. Cones-responsible for color vision
• Catract blurring sensation to cataract
• Accommodation adjusts lense

Eye - Autonomic Nervous System

• Sympathetic:
• Dilates pupil
• Elevates upper eyelid
• Reduces tearduct
• Parasympathetic:1
• Constricts pupil
• Contracts ciliary muscles

Steroscopic Vision

• a. Binocular overlap - both eyes see the same object from slightly different angles due to their forward-facing positions.
• b. Retinal disparity / binocular disparity - the brain calculates depth by processing the differences in the images seen by each eye (the greater disparity the closer the object).
• c. Fusion of images - the brain combines the two separate images into a single unified 3D perception.
• d. Cue integration - the brain uses monocular cues (size, texture, motion) and the angle of convergence from further depth info especially for close objects

Sense of Smell

• a. Detection: Odor molecules are detected by olfactory receptors on the sensory neurons in the olfactory epithelium.
• b. Signal Transmission: Action potentials are sent through the olfactory nerve fibers to the olfactory bulb, where they synapse in olfactory glomeruli.
• c. Processing in the Olfactory Bulb: The glomeruli process the signals, and the output neurons (mitral and tufted cells) transmit the information through the olfactory tract.
• d. Higher Brain Processing: The signals reach the olfactory cortex (piriform cortex, amygdala, entorhinal cortex) for recognition, memory, and emotional responses.
• e. Integration: The orbitofrontal cortex integrates the smell with other sensory information for full perception

Olfactory Gomeruli

• they receive input from olfactory sensory neurons that express the same type of odor receptors
• they provide the site for synapses between sensory neurons and output neurons
• they organize and encode info related to specific odors by activating patterns of glomeruli
• glomeruli help sharpen the odor signals, improving the brains' ability to distinguish between similar smells
• they send the processed info to higher brain centers for odor recognition, memory association, and emotional processing.

Mucus's Role

• helps to dissolve the odor molecules so that they can easily bind to the olfactory receptors
• once dissolves the odorants are transported to the olfactory receptors
• protective barrier - helps keep the olfactory epithelium moist

Vocabulary

• When you eat, the scent of the food travels up your nasal cavity

Vocabulary Definition

• Odorant- a chemical substance that stimulates olfactory receptors and has an odor

• Anosmia - the loss or absence of the sense of smell often due to injury, disease, or blockage

Taste

• Nacl salty
• Sucrose and sugar for sweetness
• Plant Derivatives for bitterness
• Acid Proton for sour
• Protein Amino Acid for umami

Saliva

helps dissolve the molecules in food

• helps dissolve triggering signals sent to the brain to interpret flavor
• helping to make the taste receptors detect flavors
• saliva balances the mouths pH and washes away food particles, helping maintain a constant taste experience may also improve sensitivity

Cranieal Roles In eating

• Trigeminal nerve,
• Facial nerve, 7
• Glossophyrangle, 9
• Vaigus Nerve, 10
• Hypoglossla never

Swallowing

• glossophernigmal and vagous in coordination.

Biting

• mandubular is biting.

Hearinf

• pina enters
• external audial tube travels
• the drum virbarates
• The oscilles travel
• and hammer travel/then anvil and sterip then travels to ovel window then to the coochela

Incus (anvil) Incus (anvil) h. Oval Window: The stapes bone pushes on the oval window, a membrane-covered opening to the inner ear, transmitting the vibrations into the fluid-filled inner ear. i. Cochlea: The vibrations travel through the cochlea, a spiral-shaped structure in the inner ear, where they create waves in the fluid. The cochlea contains the hair cells, which are the sensory receptors for sound. Hair Cells (Organ of Corti): Inside the cochlea, the vibrations cause the hair cells in the Organ of Corti to move. This movement triggers electrical signals. k. Auditory Nerve (Cochlear Nerve): The electrical signals from the hair cells are sent to the auditory nerve (also known as the cochlear nerve). Auditory Cortex (Brain): The auditory nerve carries the signals to the brainstem and eventually to the auditory cortex in the brain, where the sound is processed and interpreted as recognizable sound, pitch, and volume.

muleess pick up the ear drum Inces transfer vibations Stirip send vibartions high sound means higher ptich

a. The amplitude increase causes stronger vibrations in the eardrum, more intense stimulation of the cochlea's hair cells, and faster firing of the auditory nerve. -bone deaf -Nerve deaf _pith

j. Tensor tympani/stapedius muscles - muscle attached to the malleus that tightens the tympanic membrane in response to loud sounds to protect from damage. k. Auditory (eustachian) tube - a tube that connects the middle ear to the throat that equalizes pressure in the middle ear with external atmospheric pressure. Also drains fluid from the middle ear to prevent infections. Auricle (pinna)- the outer part of the ear made of cartilage and skin that is visible externally that collects sound waves from the environment and funnels them into the ear canal toward the tympanic membrane. Helps in localizing sound

equilibiram

• The three semicircular canals are arranged perpendicular to each other in three different planes: horizontal, vertical (anterior), and vertical (posterior).
• This positioning allows them to detect rotational movements in all directions, helping the body maintain balance and spatial orientation.

Specialized sensory area within the utricle and saccule that detects changes in head position and linear acceleration. Consists of hair cells embedded in a gelatinous layer containing tiny calcium carbonate crystals (otoliths). i. Sensory structure found in the semicircular canals of the inner ear. Located in the ampullae of the three semicircles canals. Composed of hair cells covered by a gelatinous mass known as cupula. Detects rotational acceleration of the head. When the head moves, the fluid in the canals moves which deflects the cupula and stimulates the hair cells sending signals to the brain.

d. Cupula i. Gelatinous structure that covers the hair cells in the Christa ampullaris. e. Utricle i. Detect horizontal and vertical linear acceleration, respectively.

ii. Detect horizontal and vertical linear acceleration, respectively. g. Otoliths

• Calcium carbonate crystals that help detect changes in position and movement in the macula. h. Kinocilium i. Hair cell structures detect head movements by bending in response to fluid shifts or otolith movement.