PNS Flashcards
what is the PNS
sensory and motor nerves from leaving the spinal cord to endings in skin
are afferents sensory or motor
sensory
are efferents sensory or motor
motor
where are the cell bodies of sensory nerves
dorsal root ganglion
where are the cell bodies of motor nerves
ventral horn
do sensory nerves enter in the dorsal or ventral root
dorsal
do motor nerves exit in the dorsal or ventral root
ventral
what is a spinal nerve
fusion of dorsal and ventral roots
what are Intervertebral foramina
spaces between vertebrae where spinal nerves exit
how are peripheral nerves supplied with blood
Peripheral nerves have arteries within them
what is a plexus
nerves mixing and cross connecting as they leave the intervertebral foramina
what are lower motor neurons
Motor nerve cells that connect with skeletal muscle. Cell bodies in ventral horn, project out of the ventral root. Has a single axon emerging from cell body. Contains many dendrites surrounding cell body.
what are sensory nerve fibres
two sets of dendrite-like processes 🡪 one in PNS and one in the spinal cord. In sensory neurons, the cell body is a T-junction off the axon in the dorsal root ganglion
what is myelin
sheath of fatty insulation wrapped around the neuron
what does a schwann cell do
Maintain the correct pH
buffer electrolytes of action potentials.
After an action potential, it takes up any excess potassium to protect the axons
what is a node of ranvier
gap where 2 sheaths meet
Endoneurium
thin protective membrane that surrounds fibre
contains a small artery and vein
fascicles
groups of functionally related nerve fibres
Perineurium
surrounds each fascicle
Epineurium
surrounds a group of fascicles
which receptor types have a capsule of ct around the nerve ending
sensory receptors
receptor potential
depolarisation of Ending of sensory nerves
where does an action potential form and what triggers it
1st node of ranvier
receptor potentia;
what occurs first - receptor potential or action potential
receptor potential
Conduction Velocity
speed at which action potential travels along a nerve fibre
what effects conduction velocity
myelination
fibre diameter
a-alpha neuron
alpha-motorneuron
la afferent
muscle spindle afferent
lb afferent
golgi tendon afferent
a-beta afferent
gnereal sensory afferent
a-gamma
gamma-motorneuron
a-delta
nociceptor/thermoreceptor
C fibres
nociceptor/thermoreceptor
what fibres are fast pain
a-delta
what is a pain receptor called
nociceptor
2 types of rapidly adapting receptors
Meissner’s Corpuscles
Pacinian Corpuscles
2 types of slowly adapting receptors
Merkel Receptors
Ruffini Corpuscles
what do meissners corpuscles detect
light touch
vibration
what do pacinian corpuscles detect
high frequency vibration
what do merkel receptors detect
light pressure
position
what do ruffini corpuscles detect
heavy pressure
what is the difference between rapidly adapting and slowly adapting receptors
rapidly - rapidly firing, then stops
slowly - fire constantly, slowly
receptive field
area of skin that can activate a single fibre
what does two-point discrimination test measure
measures size/density of RFs
what do free nerve endings detect
movement
chemical changes
temperature
pain
how do peripheral nerve fibres regenerate
Distal part disconnected: degenerates. Schwann cells in this part: unwrap themselves, forma continuous line along endoneurial sheaths.
Proximal ends: axon forms growth cones, which start to grow towards/into distal part guided by chemical factors released from Schwann cells.
As these new nerve fibres extend into the distal part, Schwann cells proliferate, wrap myelin around them. Initially: nerve fibres are thin. They then enlarge but may never reach their original size. The more distal it is, the more likely for it to regenerate.
