The Peripheral Nervous System Flashcards
Nervous System Organization
- Functional
- sensory
- motor
- Anatomical
- central
- peripheral
Anatomical Divisions: Central Nervous System
Brain
Spinal Cord
Overall “command center”, processing and integrating information
Anatomical Divisions: Peripheral Nervous System
Ganglion (ganglia)
Peripheral nerves (axons of neurons)
Receives and projects information to and from the CNS; mediates some reflexes
PNS: Nerve
bundle of fibers
PNS: Satellite cells
Supporting Cells
PNS: Schwann Cells
Myelin Sheath
PNS: Ganglia
Aggregates of Cell Bodies
PNS: Functional Divisions: Sensory
- Some CNS and PNS Components
- includes all axons that transmit impulses from a peripheral structure to the CNS (Afferent)
- Somatic Sensory
- Transmit input skin, fascia, joints, and skeletal
- Visceral Sensory
- Transmits input from stomach and intestines (viscera)
PNS: Functional Divisions: Motor
- Some CNS and PNS components
- includes all axons that transmit impulses from the CNS to a muscle or gland (efferent)
- Somatic motor (Somatic Nervous System)
- Voluntary Control of muscles
- Autonomic Motor (Autonomic Nervous System)
- Involuntary control of smooth muscle, cardiac muscle, and glands
- go through ganglia
Basic Motor Neuron Structure
- Different configurations
- multipolar, bipolar, pseudounipolar
- Same General Structure
- Dendrites
- Cell body
- Axon
Spinal Cord Structure Organization
Nerves Leaving the CNS
- Cranial
- Brain stem/cervical
- Spinal
- Pair at each spinal segment
- Dorsal Root
- Sensory
- Synapse at dorsal root ganglia
- Ventral Root
- Motor
- Somatic - extend axons to periphery
- Autonomic - ganglia in various locations
Signals to/from peripheral nerves
Posterior is sensory neuron roots
Anterior is motor neuron roots
Ganglion
Collection of neuron cell bodies outside the CNS
Will have peripheral nerves and satellite cells
Relay messages from PNS to CNS and vice versa (relay station)
neurons are either pseudounipolar (Sensory, dorsal root ganglia) or Multipolar (Motor)
Ganglion: Peripheral Nerves
may have Schwann Cells
Ganglion: Satellite Cells
small supporting cells
Where are pseudounipolar neurons found?
Sensory (dorsal root ganglia)
Where are multipolar. neurons found?
motor
autonomic
Somatic Sensory Neurons
- Cell bodies of sensory neurons are in the dorsal root ganglia
- trigeminal ganglion for the facial nerves
- Synapse with dorsal spinal neurons in the spinal cord - signal sent to brain
- Provide tactile information
- guide movement
- response to pain (protective)
Dorsal Root Ganglia Anatomy
Looking from posterior side
Dorsal Root Ganglion
- Sensory Neurons are pseudounipolar
- central nuclei
- large perikaryon
- Satellite cells surround each perikaryon
- Visible nerve fibers and CT present
- May Be surrounded by adipose tissue
- Lipofuscin
Lipofuscin
brown crystals
non-digestible remains of old proteins (cell could not digest)
accumulate with age
Dorsal Root Ganglion Histology
Sympathetic ganglion
flight or fight
- part of autonomic nervous system
- physiological/endocrine
- coordinates and integrates visceral functions
- maintenance of homeostasis
- Respond to emergency situations
- Parasympathetic - restful (inhibits stress)
- Connect to adrenal gland
- Parasympathetic are near the organ (intramural)
- Cells are multipolar
- Acentric nucleus
- Smaller Perikaryon
Autonomic Ganglia Anatomy
Sympathetic Ganglion Histology
Dorsal Root v. Sympathetic Ganglia
Relative Size
Location of nucleus
organization of satellite cells
Enteric Ganglia
found in GI Tract
Peripheral Ganglia - Enteric Histology
Special Structure in Birds
- The Glycogen Body
- Found in the lumbosacral region of the spinal cord
- enlargement around central canal and dorsal root
- Consists of:
- Polyhedral vesicular cells
- filled with glycogen (empty on H&E) → energy storage
- Displaced nucleus
- unknown function
PNS: Supporting Cells
Satellite Cells
Schwann Cells
Transmit the signal: Efficient transmission
- Insulation on fibers
- lipid-based wrap (myelin sheath)
- layers of membrane surround an axon
- In CNS, gives white matter its characteristic macroscopic appearance
What is the function of the myelin sheath?
reduces the amount of times the membrane depolarizes
Myelin Sheath: Saltatory Conduction
Signal jumps from node to node→ skipping insulated segments of axon to make more efficient → “skipping over people”
Schwann Cells Histology
Schwann Cell - Cross Section Histology
Myelin Sheath Histology
What is used to stain the myelin sheath?
Osmium Fixation
How does the myelin sheath form?
The fiber wraps around itself
intramembrane proteins regulate winding process
Schmidt-Lanterman Incisure
Channels of cytoplasm
Allow communication between wrapped layers
appear as breaks across the myelin sheath
Schmidt-Lanterman Histology
maintains cytoplasmic continuity
Peripheral Nerve Bundle
Fiber → Fascicle → whole nerve
Epineurium
Encloses the entire nerve → Full Nerve Bundle
Perineurium
encloses each fascicle and consists of neuroepithelial perineurial cells forming the blood-nerve barrier → group of nerve fibers, usually seen on H&E
Endoneurium
surrounds individual nerve fibers or axons
hard to see on H&E
Peripheral Nerve Bundle Histology
Motor Nervous System
- Signal to voluntary muscle
- motor end plate
- forms synapse
Motor Synapse
Motor End plate histology
Sensory Structures
All senses involve 3 steps
- Physical Stimulus
- light, chemical, mechanical
- Transformation
- physical to electrical (transmitter through nerve)
- Response
- Perception
- Conscious Experience
Sensory Receptor Classes
- Mechanical
- Chemical
- Nociceptors
- Thermoreceptors
- Electromagnetic
Sensory Receptor Classes: Mechanical
touch
proprioceptive
hearing
balance
Sensory Receptor Classes: Chemical
Itches
Taste
Smell
Sensory Receptor Classes: Nociceptors
Pain
Sensory Receptor Classes: Thermoreceptors
Heat or cold
Sensory Receptor Classes: Electromagnetic
Photoreceptors
Mechanoreceptors
Distortions, bending, stretching → causes physical displacement of cell
Mechanoreceptors: Tactile
touch, pressure, vibration
- Free nerve endings
- muscle spindles
- receptors in CT capsules
Mechanoreceptors: Baroreceptors
Pressure in walls
Mechanoreceptors: Proprioceptors
Changes in position
Sensory Structures of the Skin: Nonencapsulated
- Free nerve endings in the epidermis
- Touch, pressure, heat, cold, pain
- Associated with Hair Follicles
- Mechanoreceptors
Sensory Structures of the Skin: Encapsulated
Ruffini ending (dermis)
Meissener’s corpuscle (dermal papillae)
Pacinian corpuscle (dermis and hypodermis)
Ruffini Ending
Simplest encapsulated mechanoreceptor
Touch and pressure (stretching)
Groups of nerve terminals surrounded by a thin CT capsule (fluid-filled space)
Axonal endings respond to displacement of collagen fibers
anything that impacts capsule
Meissner’s Corpuscle
- Found in the hairless skin
- apex of the dermal papilla
- endoneurial cells wrapped around a nerve terminal
- Spiral shaped unmyelinated ends of nerve fibers
- Schwann Cells Form
- Lamellae
- Detect Light Touch
Meissner’s Corpuscle: Histology
Pacinian Corpuscle
Deep Pressure and vibrations
Concentric layers of endoneurial cells around myelinated nerve terminal
Myelin is eventually lost
Pacinian Corpuscle Histology
Nonciceptors
- Direct response to stimulus
- Sense chemicals released by damaged tissue
- K+, histamine, proteases, ATP, acidity, bradykinin
Thermoreceptors
Free nerve endings
Separate cold/warm
firing rate changes depending on temperature
Chemoreceptors
Changes in concentrations
