Peripheral System Flashcards
PNS
All neural structures outside brain and spinal cord
- sensory receptors
- peripheral nerves and associated ganglia
- motor nerves
Sensory receptors
- specialized to respond to changes in their envrionment (stimuli)
- activation results in graded potentials that trigger nerve impulses
- sensation: awareness of stimulus
- perception: interpretation of the meaning of the stimulus that both occur in brain
Receptor classifications
Stimulus type: type of stimulus –> thermoreceptors
- Location: respond to internal/external stimuli
- structural complexity: general senses, simple or special senses, complex (vision/hearing/taste/smell)
Classification by stimulus type
- mechanoreceptors: touch, pressure, vibration, stretch, itch
- thermoreceptors: changes in temp
- photoreceptors: light energy (retina)
- chemoreceptors: chemicals (smell, taste, blood chem)
- nociceptors: pain-causing stimuli (heat, cold, pressure, inflammatory chemicals)
Location classification
- Exteroceptors
- Interoceptors
- Proprioceptors
Sensation to perception
- survival depends upon sensation + perception
- sensation: awareness of changes in internal + external environment, input comes from sensory receptors
- perception: conscious interpretation of that stimuli, occurs in brain
Sensory integration
- Receptor level: sensor receptors
- Circuit level: ascending pathways (spinal cord + brain stem)
- Perceptual level: neuronal circuits in cerebral cortex
Adaptation of sensory receptors
Adaptation: change in sensitivity in the presence of a constant stimulus (bright light)
- Phasic (fast-adapting) receptors: signal beginning/end of stimulus, signals a change
ex: pressure, touch, smell
- Tonic receptors: adapt slow or none
ex: nociceptors + proprioceptor
Nerve
Cordlike organ of PNS
- bundle of myelinated + unmyelinated peripheral axons enclosed by connective tissue
- Endoneurium: loose CT encloses axons + myelin sheaths
- Perineurium: coarse CT that bundles fibers into fascicles
- Epineurium: tough fibrous sheath around nerve
Classification of nerves
Most nerves are mix of afferent + efferent fibers
- somatic afferent/efferent
- visceral afferent/efferent
Peripheral nerves classified cranial/spinal nerves
Ganglia
- collections of cell bodies in PNS
- dorsal root ganglia —> sensory, somatic
- autonomic ganglia –> motor, visceral
Regen of PN fibers
Mature neurons are amitotic
- If soma (cell body) of damaged nerve is intact, axon regenerates
- CNS oligodendrocytes bear growth-inhibiting proteins preventing CNS fiber regen
Cranial nerves
12 pairs of PN with brain
- mixed function (2 sensory)
CN I Olfactory nerve: SMELL
CN II Optic nerve: VISION
CN III: Oculomotor NN (aneurysm)
CN IV: Trochlear NN (congenital trauma)
CN VI: Abducens NN (abducts eye) (cranial pressure)
CN V: trigeminal N –> sensation of face + motor of mastication muscles
CN VII: facial N –> motor face (facial expression), sensory taste
CN VIII: vestibulocochlear N –> hearing/balance
CN IX: Glossopharyngeal N –> tongue/throat, taste/swallowing
CN X: Vagus N –> only cranial nerve leaving head + neck, PNS, regulate heart/lungs/abdominal
CN XI: acessory nerve –> moves head/neck
CN XII: Hypoglossal nerve –> moves tongue
Trigeminal Neuralgia
pain condition characterized by intense, sudden, and stabbing facial pain, often described as an electric shock
Vestibular Nerve Pathology
any condition affecting the vestibular nerve, which is responsible for balance and spatial orientation
Spinal nerves
31 pairs mixed nerves
cervical, thoracic, lumbar, sarcal, coccygeal
Spinal nerve roots
Each spinal nerve connects to spinal cord via 2 roots
ventral roots: contain motor (efferent) fibers from ventral horn motor neurons
- fibers innervate skeletal muscles
dorsal roots: contain sensory (afferent) fibers from sensory neurons in dorsal root ganglia
- impulses from peripheral receptors
- dorsal + ventral roots unite to form spinal nerves
Rami spinal nerves
each spinal nerve branches into mixed rami
- dorsal ramus
- larger ventral ramus
- rami communicantes (autonomic pathways) join to ventral rami in thoracic region
- roots: lie medial to spinal NN either sensory/motor
- rami: lie lateral to spinal NN, mixed
- ALL VENTRAL RAMI except T2-T12 form nerve networks known as plexuses
- Back innervated by dorsal rami
Cervical plexus
formed by ventral rami of C1-C5
- innervates skin + muscles of neck/ear/back of head/shoulders
Phrenic nerve
- major motor + sensory nerve of diaphragm
- irritation of phrenic nerve causes hiccups
Brachial plexus
formed by ventral rami of C5 - C8
- gives rise to nerves that innervate upper limb
- major nerves from branches: axillary, musculocutaneous, median, ulnar + radial
Injury
- Erb’s palsy: stretching of upper trunk of brachial plexus
- klumpke’s paralysis: injury to lower roots of plexus (claw hand)
Lumbar plexus
L1-L4
- innervates the thigh, abdominal wall, and psoas muscle
- femoral nerve: innervates quads and skin of anterior thigh and medial surface of leg
- obturator nerve: innervate adductor muscles (groin)
Sacral plexus
L4-S4
- buttock, lower limb, pelvic structures, and perineum
Sciatic nerve: longest/thickest nerve in body
- innervates hamstring, adductor magnus, and most muscles in leg/foot
- 2 nerves: tibial and common fibular
Sciatica
Sciatica refers to pain that travels along the path of the sciatic nerve. The sciatic nerve travels from the buttocks and down each leg. Sciatica most often happens when a herniated disk or an overgrowth of bone puts pressure on the lumbar spine nerve roots
