Peripheral Nervous System Flashcards
What are the sites of all neuronal cell bodies in the PNS?
Ganglia
What neurones have their cell bodies in the spinal cord and brain stem?
Motor and preganglionic autonomic neurons
What makes up a nerve?
Bundle of axons, associated glia, myelin sheath and supporting connective tissue
What makes up a nerve fibre?
One axon with its myelin sheath and neuroglial (schwann) cells
What do the small axons function for?
Pain, olfaction and visceral innervation
Where are sensory ganglia present?
Dorsal roots of spinal nerve and on some cranial nerves
What is special about sensory ganglia?
Contain unipolar neurons with axons that bifurcate, with one branch entering the CNS and the other into the PNS
What does skin have sensory nerve endings for?
Touch, temperature, pain
What endings does muscles, tendons and joints contain?
Proprioceptive endings
Where does the motor end plate end?
Striated skeletal muscle
What is the synaptic transmitter that makes the muscle fibres contract?
Acetylcholine
Smooth muscle and glands are innervated by what neurones?
Autonomic ganglia
What do the dorsal root fibres divide into?
Ascending and Descending branches
What is the third class of sensory endings called?
Interoceptors
Where are interoceptors located?
Viscera
What are the two categories of sensory endings?
Somatic afferent and Visceral afferent
What are somatic afferents for?
Skin, bones, muscles and connective tissue
What are visceral afferents for?
Internal organs
What are the two categories of efferent neurones?
Somatic efferent and Visceral efferent
What is another word for somatic efferent neurones?
Motor neurones
Where are somatic efferent neurones located?
In the ventral grey horns of the spinal cord and motor nuclei of cranial nerves
Where do the axons of ventral horn cells terminate?
In motor end plates on skeletal muscle fibres
What is the special feature of visceral efferent neurones?
They have at least two neurones participate in transmission from CNS to smooth muscle, cardiac muscle or secretory cells.
What are the sensory endings supplied by?
Axons that differ in size
Where do cutaneous branches of the spinal and cranial nerves pass through?
Subcutaneous connective tissue into the dermis
What are the three plexuses formed from the spreading of axons in the dermis?
Subcutaneous plexus, dermal plexus and papillary plexus
Where is the subcutaneous plexus?
Loose connective tissue
Where is the dermal plexus?
Within the densely collagenous reticular layer of the dermis
Where is the papillary plexus?
Papillary layer of the dermis beneath the epidermis
Where do free nerve endings occur?
In the subcutaneous tissue and dermis
What are free nerve endings?
They are the terminal branches of group C fibres and the unmyelinated terminal branches of group A fibres.
What are free nerve endings associated with?
Schwann cells
Where are merkel endings found?
Germinal layer of epidermis
How does a merkel cell differ from epidermal cells?
Indented nucleus and electron-dense cytoplasmic granules
Where are merkel cells found?
In glabrous skin and in the outer root sheaths of hairs
What is the Ruffini ending?
An array of terminal branches of a myelinated axon surrounded by capsular cells
What is the Pacinian corpuscle?
Consists of a single axons that loses its myelin sheath and is encapsulated by several layers of flattened cells.
Where do the Meissners tactile corpuscles occur?
Dermal papillary ridges of the finger tips
The types of sensation consciously perceived from the skin are called?
Modalities
What innervates muscles spindles?
Sensory and motor neurones
How many sensory axons supplies the muscle spindle?
Two
What does a motor unit consist of?
One motor neurone and the muscle fibres that innervate it
What do the axonal endings within the end plates contain?
Mitochondria and synaptic vesicles
What are spinal ganglia?
Swellings on the dorsal roots of spinal nerves
Where are spinal ganglia located?
In the intervertebral foramina
What does the spinal ganglia contain?
The cell bodies of primary sensory neurones
Each cell body within the spinal ganglia is invested by a layer of what type of cell?
Satellite cells
What is the entire nerve surrounded by?
Epineurium
What surrounds the bundle fibres of a nerve?
Perineurium
What surrounds an individual fibre?
Endoneurium
What cells do the Epineurium, Perineurium and Endoneurium derive from?
Mesodermal cells
Within the endometrium, the axons are intimately ensheathed by what type of cell?
Schwann cells
What are Schwann cells derived from?
Neural crest
What are the components of Schwann cells?
Neurolemma and myelin sheath
What interrupts the myelin sheath at intervals?
Nodes of Ranvier
Some axons in nerves do not contain?
Myelin sheaths
The thinnest unmyleinated axons are those of?
Olfactory nerves
