PNS Flashcards
Structural Classification of PNS
- Spinal nerves – carry impulses to and from the spinal cord
- Cranial nerves – carry impulses to and from the brain
Functional Classification of PNS
- Somatic – voluntary, consciously controls skeletal muscles
- Autonomic – involuntary, automatically controls smooth and cardiac muscles and glands
PNS Glial Cells
- Schwann cells - Form myelin sheath around nerve fibers in the PNS
- Satellite cells - Protect and cushion neuron cell bodies
Components of Schwann cells
Myelin Sheaths
Neurilemma
Nodes of Ranvier
What are nerves?
Nerves are bundles of neurons found outside the CNS
Connective tissue layers of Nerves
Endoneurium is a connective tissue sheath that surrounds each fiber
▪ Perineurium wraps groups of fibers bound into a fascicle
▪ Epineurium binds groups of fascicles
3 types of nerves
Mixed nerves – contain both sensory and motor fibers, all spinal nerves
Sensory (afferent) nerves – carry impulses toward the CNS
Motor (efferent) nerves – carry impulses away from the CNS
How many cranial nerves are there and what are their names and functions?
12
▪ Oh – Olfactory - smell
▪ Oh – Optic - sight
▪ Oh – Oculomotor – mixed eye movement
▪ To – Trochlear – mixed eye movement
▪ Touch – Trigeminal – mixed facial sensation and jaw movement
▪ And – Abducens - mixed eye movement
▪ Feel – Facial – mixed facial sensation and taste
▪ Very – Vestibulocochlear – sensory hearing
▪ Green – Glossopharyngeal – mixed taste and movement of throat muscle
▪ Vegetables – Vagus – mixed autonomic functions
▪ A – Accessory – nerve movement of neck muscles
▪ H – Hypoglossal – mixed tounge muscle movement
How many spinal nerves are there and what type of nerve are they?
31 Nerves All mixed (afferent and efferent)
What is a ramus?
branch of a spinal nerve; contains both motor and sensory fibers
Duties of Dorsal and Ventral rami
▪ Dorsal rami—serve the skin and muscles of the posterior trunk
▪ Ventral rami (T1–T12) —form the intercostal nerves that supply muscles and skin of the ribs and trunk
▪ Ventral rami (except T1–T12)—form a complex of networks (plexus) for the anterior
What is plexus?
networks of nerves serving motor and sensory needs of the limbs
▪ Form from ventral rami of spinal nerves in the cervical, lumbar, and sacral regions
4 plexuses
- Cervical 2. Brachial 3. Lumbar 4. Sacral
Components of the brachial plexus (5)
Axillary nerve, radial nerve, musculocutaneous nerve, ulnar nerve, median nerve
Components of the Lumbar plexus (5)
Femoral nerve Lateral femoral cutaneous nerve Obturator nerve Anterior femoral cutaneous nerve Saphenous nerve
Components of the Sacral Plexus (9)
Superior Gluteal nerve
Inferior gluteal nerve
Sciatic nerve
What are the two motor subdivisions of PNS
Somatic Nervous System and Autonomic Nervous System
Features of Somatic Nervous system
Motor neuron cell bodies originate inside the CNS
Axons extends to skeletal muscles that are served
Features of Autonomic Nervous System
Chain of two motor neurons
▪ Preganglionic neuron is in the brain or spinal cord
▪ Postganglionic neuron extends to the organ
Has two arms ▪ Sympathetic division ▪ Parasympathetic division
Differences between Parasympathetic and Sympathetic Division
- Control the same organs, but cause opposite effects
- Have varying length of Preganglionic and postganglionic axons
- Type of neurotransmitter chemical they release
2 subdivisions of Autonomic nervous system
Parasympathetic and Sympathetic Division
Anatomy of the Parasympathetic Division
▪ Parasympathetic division is also known as the craniosacral division
▪ Preganglionic neurons originate in: Cranial nerves III, VII, IX, and X ▪ S2 through S4 regions of the spinal cord (control organs of the pelvic cavity), medulla oblongata, midbrain and pons
▪ Preganglionic neurons synapse with terminal ganglia; from there, postganglionic axons extend to organs that are served
Anatomy of the Sympathetic Division
▪ Sympathetic division is also known as the thoracolumbar division
▪ Preganglionic neurons originate from T1 through L2
▪ Axons pass through a ramus communicans to enter a sympathetic trunk ganglion
▪ Sympathetic trunk, or chain, lies near the spinal cord
▪ After synapsing at the ganglion, the axon may synapse with a second neuron at the same or different level
▪ Or, the preganglionic neuron may pass through the ganglion without synapsing and form part of the splanchnic nerves
▪ Splanchnic nerves travel to the collateral ganglion
▪ Collateral ganglia serve the abdominal and pelvic organs
Which organs do not receive fibres from both divisions of autonomic nervous system?
blood vessels, structures of the skin, some glands, and the adrenal medulla
What neurotransmitter are released by preganglionic axons?
acetylcholine
What neurotransmitter are released by parasympathetic axons?
acetylcholine
What neurotransmitter are released by Sympathetic postganglionic (adrenergic) fibers ?
norepinephrine
Sympathetic response
“fight or flight” division ▪ Response to unusual stimulus when emotionally or physically stressed or threatened ▪ Takes over to increase activities ▪ Remember as the “E” division ▪ Exercise ▪ Excitement ▪ Emergency ▪ Embarrassment
Parasympathetic response
“housekeeping” activites ▪ “Rest-and-digest” system ▪ Conserves energy ▪ Maintains daily necessary body functions ▪ Remember as the “D” division ▪ Digestion ▪ Defecation ▪ Diuresis
What are the special senses?
- Smell
- Taste
- Sight
- Hearing
- Equilibrium (ear)
Two special sense receptors
- Large, complex sensory organs (e.g. eyes and ear)
2. Localised clusters of receptors (e.g. taste buds)
Name Accessory structures of the eye
▪ Extrinsic eye muscles ▪ Eyelids ▪ Conjunctiva ▪ Lacrimal apparatus Eyelashes Tears Pupil Iris Eyebrow Lacrimal caruncle Medial and lateral canthus Sclera
Describe the eyelids
Meet at the medial and lateral commissure (canthus)
Describe the eyelashes
▪ Tarsal glands produce an oily secretion that lubricates the eye ▪ Ciliary glands are located between the eyelashes
Describe the conjunctiva
▪ Membrane that lines the eyelids and eyeball ▪ Connects with the transparent cornea ▪ Secretes mucus to lubricate the eye and keep it moist
Describe function and composition of tears
Dilute salt solution ▪ Mucus ▪ Antibodies ▪ Lysozyme (enzyme that destroys bacteria) Function of tears ▪ Cleanse, protect, moisten, lubricate the eye
Describe the Lacrimal Apparatus
= lacrimal gland + ducts ▪ Lacrimal gland—produces lacrimal fluid (tears); situated on lateral end of each eye ▪ Tears drain across the eye into the lacrimal canaliculi, then the lacrimal sac, and into the nasolacrimal duct, which empties into the nasal cavity
What are the 6 extrinsic eye muscles and their actions?
Lateral Rectus - moves eye laterally
Medial rectus - Moves eye medially
Superior Rectus - elevates eye and turns it medially
Inferior rectus - depresses eye and turns it medially
Inferior oblique - Elevates eye and turns it laterally
Superior oblique - Depresses eye and turns it laterally
What are the internal structures (layers) of the eye?
Fibrous, vascular and sensory
Describe the fibrous layer
▪ Fibrous layer = sclera + cornea , outer layer
Sclera ▪ White connective tissue layer ▪ Seen anteriorly as the “white of the eye”
Cornea ▪ Transparent, central anterior portion ▪ Allows for light to pass through ▪ Repairs itself easily ▪ The only human tissue that can be transplanted without fear of rejection
Describe the vascular layer
▪ Choroid is a blood-rich nutritive layer that contains a pigment (prevents light from scattering)
▪ Choroid is modified anteriorly into two smooth muscle structures
▪ Ciliary body ▪ Iris—regulates amount of light entering eye ▪ Pigmented layer that gives eye color ▪ Pupil—rounded opening in the iris, opening to which light passes
Describe the sensory layer
Retina contains two layers
1. Outer pigmented layer absorbs light and prevents it from scattering
2. Inner neural layer contains receptor cells (photoreceptors) ▪ Rods ▪ Cones
Electrical signals pass from photoreceptors via a two neuron chain ▪ Bipolar neurons ▪ Ganglion cells Signals leave the retina toward the brain through the optic nerve
Optic disc (blind spot) is where the optic nerve leaves the eyeball ▪ Cannot see images focused on the optic disc
What are rods
▪ Most are found toward the edges of the retina ▪ Allow vision in dim light and peripheral vision ▪ All perception is in gray tones
What are cones and 3 types of cones
▪ Allow for detailed color vision ▪ Densest in the center of the retina
▪ Fovea centralis–lateral to blind spot ▪ Area of the retina with only cones ▪ Visual acuity (sharpest vision) is here
Three types of cones
Each cone type is sensitive to different wavelengths of visible light (blue, green and a range of green-red/red cones)
Components of the eyeball
▪ Lens - Flexible, biconvex crystal-like structure ▪ Held in place by a suspensory ligament attached to the ciliary body
▪ Lens divides the eye into two chambers
1. Anterior (aqueous) segment ▪ Anterior to the lens ▪ Contains aqueous humor, a clear, watery fluid, maintains intraocular pressure and provide nutrients for the lens and cornea
2. Posterior (vitreous) segment ▪ Posterior to the lens ▪ Contains vitreous humor, a gel-like substance, maintains intraocular pressure
Name 6 visual pathways and fields to the brain
- Optic nerve 2. Optic chiasma 3. Optic tract 4. Thalamus 5. Optic radiation 6. Optic cortex in occipital lobe of brain
Describe the optic nerve
Bundle of axons that exit the back of the eye carrying impulses from the retina
Describe Optic chiasma
▪ Location where the optic nerves cross ▪ Fibers from the medial side of each eye cross over to the opposite side of the brain
Describe optic tracts
▪ Contain fibers from the lateral side of the eye on the same side and the medial side of the opposite eye ▪ Synapse with neurons in the thalamus
Describe optic radiation
Axons from the thalamus run to the occipital lobe ▪ Synapse with cortical cells, and vision interpretation (seeing) occurs
Eye disorders (3) names and causations
Myopia – near-sightedness, ▪ Distant objects appear blurry ▪ Light from those objects fails to reach the retina and are focused in front of it ▪ Results from an eyeball that is too long
Hyperopia - (farsightedness) ▪ Near objects are blurry, whereas distant objects are clear ▪ Distant objects are focused behind the retina ▪ Results from an eyeball that is too short or from a “lazy lens”
Astigmatism - Images are blurry ▪ Results from light focusing as lines, not points, on the retina because of unequal curvatures of the cornea or lens
Two senses of the ear
Hearing and equilibrium
Components of the ear
- External (outer) ear
- Middle ear
- Internal (inner) ear
Explain the external ear
▪ Auricle (pinna)
▪ External acoustic meatus (auditory canal) - Narrow chamber in the temporal bone
▪ Lined with skin and ceruminous (earwax) glands- help clean and lubricate ear
▪ Ends at the tympanic membrane (eardrum)
▪ External ear is involved only in collecting sound waves
Explain the middle ear
- Air-filled, mucosa-lined cavity within the temporal bone
- Hearing
- Located between tympanic membrane and oval window and round window
- separates outer ear to middle ear
Three bones (ossicles)
1. Malleus (hammer) 2. Incus (anvil) 3. Stapes (stirrup)
Functions of the ossicles
▪ Transmit vibrations from tympanic membrane to the fluids of the inner ear
▪ Vibrations travel from the Malleus→ Incus→ Stapes→ oval window of inner ear
Pharyngotympanic tube (auditory tube)
▪ Links middle ear cavity with the throat
▪ Equalizes pressure in the middle ear cavity so the eardrum can vibrate
Internal ear
- Hearing and balance
- Bony labyrinth (osseous labyrinth) consists of: ▪ Cochlea ▪ Vestibule ▪ Semicircular canals
- Bony labyrinth is filled with perilymph
▪ Membranous labyrinth is suspended in perilymph and contains endolymph - Vestibular nerve – carry information about balance to vestibule
Static equilibrium
maintains equilibrium and posture when the head and body is still
Anatomy of the maculae
▪ Hair cells are embedded in the otolithic membrane
▪ Otoliths (tiny stones) float in a gel around hair cells
▪ Movements cause otoliths to roll and bend hair cells
Functions of the maculae
Otoliths fall and pull on otolithic membrane due to gravity when head is tilted
This bends the hair cells
▪ Hair cells signal associate neurons
Impulse is taken to CNS by Vestibular branch of the vestibulocochlear nerve
Results in motor impulses to skeletal muscles which contract to remain balance
Report on the position of the head
▪ Help us keep our head erect
▪ Send information via the vestibular nerve (division of cranial nerve VIII) to the cerebellum of the brain
What is dynamic equilibrium
other organs detect and maintains balance, semi-circular canal receptors
Describe the crista Ampullaris
Crista Ampullaris
Ampullas have ridges which cross the tube and houses sensory organs (Crista Ampullaris)
▪ Responds to angular or rotational movements of the head
▪ Located in the ampulla of each semicircular canal
▪ Tuft of hair cells covered with cupula (gelatinous cap)
Hair cells are connected to dendrites of neurons that make up part of Vestibular branch of vestibulocochlear nerve
▪ If the head moves, the cupula drags against the endolymph
▪ Hair cells are stimulated, and the impulse travels the vestibular nerve to the cerebellum
Anatomy of hearing
Spiral organ of Corti
▪ Located within the cochlear duct
▪ Receptors = hair cells on the basilar membrane
▪ Gel-like tectorial membrane is capable of bending hair cells
▪ Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe
Pathway of vibrations from sound waves
▪ Move by the ossicles from the eardrum to the oval window
▪ Sound is amplified by the ossicles
▪ Pressure waves cause vibrations in the basilar membrane in the spiral organ of Corti
▪ Hair cells of the tectorial membrane are bent when the basilar membrane vibrates against it
▪ An action potential starts in the cochlear nerve (cranial nerve VIII), and the impulse travels to the auditory centres in the temporal lobe
Diseases and issues regarding hearing
High-pitched sounds - disturb the short, stiff fibers of the basilar membrane ▪ Receptor cells close to the oval window are stimulated
Low-pitched sounds- disturb the long, floppy fibers of the basilar membrane ▪ Specific hair cells further along the cochlea are affected
Deafness - refers to any loss of hearing ▪ Results from injury, loud sounds, excessive earwax, scarring of the tympanic membrane
Tinnitus - refers to ringing in the ear ▪ Results from damage to hair cells in the inner ear, randomly moving hair cells
Chemoreceptors
▪ Stimulated by chemicals in solution ▪ Taste has five types of receptors ▪ Smell can differentiate a wider range of chemicals
▪ Both senses complement each other and respond to many of the same stimuli
Olfactory receptors
▪ Olfactory receptors are in roof of nasal cavity
▪ Olfactory receptor cells (neurons) with long cilia known as olfactory hairs detect chemicals
▪ Chemicals must be dissolved in mucus for detection by chemoreceptors called olfactory receptors ▪ Impulses are transmitted via the olfactory filaments to the olfactory nerve (cranial nerve I)
▪ Smells are interpreted in the olfactory cortex
Describe the taste buds
▪ Taste buds house the receptor organs (10,000 approximately)
Locations of taste buds ▪ Most are on the tongue ▪ Soft palate ▪ Superior part of the pharynx ▪ Cheeks ▪ The tongue is covered with projections called papillae that contain taste buds
Gustatory cells
are the taste receptors ▪ Possess gustatory hairs (long microvilli)
▪ Gustatory hairs protrude through a taste pore
▪ Hairs are stimulated by chemicals dissolved in saliva
▪ Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas
▪ Taste buds are replaced frequently by basal cells
5 taste sensations
▪ Sweet receptors respond to sugars, saccharine, some amino acids
▪ Sour receptors respond to H+ ions or acids
▪ Bitter receptors respond to alkaloids
▪ Salty receptors respond to metal ions
▪ Umami receptors respond to the amino acid glutamate or the beefy taste of meat
Disorders of the nose and tongue
▪ Rhinitis is inflammation of the mucous membranes in the nasal passage ▪ Caused by infections, allergies, strong chemical odours and certain drugs
▪ Septum problems
▪ Infections, injuries and abnormal tissue growth affect the tongue
