PNS Flashcards
How many spinal nerves total + in each region
8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
31 total
How are cervical spinal nerves named
Named after vertebra below them
How are thoracic and lumbar spinal nerves named
After vertebra above them
What and why is a nerve plexus
Nerves serving a specific area originate from several different rami in order to ensure that some impulses arrive even if one ramus is damaged
Nerve plexus only stem from ventral rami
4 nerve plexus
Brachial, lumbar, sacral, cervical
Cervical plexus nerves
C1-C4
Phrenic nerve
Part of cervical plexus, C3-C5, innervates the diaphragm
“3, 4 & 5 keeps them alive”
Brachial plexus spinal nerves
C5-T1
Brachial plexus categories
Roots, trunks, divisions, cords, branches
Really tired drink coffee black
3 trunks of brachial plexus & their spinal nerves
C5 &C6 upper trunk
C7 middle trunk
C8 & T1 lower trunk
2 Brachial plexus divisions
Posterior: goes to muscles on back of arm- triceps, extensors
Anterior: goes to muscles on front of arm-biceps, deltoid, flexors
3 cords of brachial plexus
Posterior cord, behind axillary artery
Medial cord, closer to body than axillary artery
Lateral cord, lateral to axillary artery
5 branches of brachial plexus
Musculocutaneous Median Ulnar Radial Axillary
Brachial plexus Axillary branch function
Lift arm
Musculocutaneous branch function
Bend arm
Median branch function
Flex wrist
Ulnar branch function
Make fist
Radial branch function
Undoes everything
Where do spinal nerves exit spinal column
Intervertebral foramen
Roots vs rami & where do plexus originate
Roots are located within the spinal column, rami are located just outside. When talking about plexus, it’s referring to ventral rami and not roots or dorsal rami
Lumbar plexus spinal nerves
L1-L4
Lumbar plexus important nerves
Femoral nerve: goes to quadriceps, responsible for thigh flexion and knee extension
Obturator nerve: goes to adductors, responsible for opening and closing legs
Sacral plexus spinal nerves
L5-S4
Sacral plexus important nerves
Sciatic nerve: goes to hamstrings, responsible for hip extension&knee flex ion
Tibial nerve: gastrocnemius and soleus (calf)
Gluteal nerve: gluteus max, med, min
Pudential nerve: urination, erection
Word for abnormal sensation-tingling, numbness, etc.
Paresthesia
Dermatomes
Sensory map of spinal nerves
T1-T12 dermatomes
Abdominal and thoracic area front & back
T1 also extends down medial anterior arm
C2-C8 dermatomes
“Hood & cape”:
C2 back of head,
C3, 4, 5 neck,
C6, 7, 8 shoulders, arms, hands
L1-L5 dermatomes
Lower back, hips, anterior, lateral & medial legs, feet
S1-S5 dermatomes
Glutes, posterior legs, genitals
2 types of reflexes
Intrinsic (visceral), acquired (learned)
5 components of a reflex arc
Receptor Sensory neuron Integration Center Motor neuron Effector
Stretch reflex aka
Deep tendon reflex
Proprioceptors
Monitor length and tension of muscles
Muscle spindles
Proprioceptors that measure muscle stretch/length and send information to cerebellum
What does the stretch reflex do
Makes sure that a muscle stays the same length that the brain has commanded it to be. If it begins to lengthen (e.g. your knees buckling) the stretch reflex causes the muscle (quadriceps) to contract w/o having to think about it
Monosynaptic vs polysynaptic
Monosynaptic reflexes involve only a single synapse (stretch reflex is example)
Polysynaptic reflexes involve more than one synapse (the part of stretch reflex that inhibits antagonist muscle is polysynaptic)
Reciprocal inhibition
When a muscle contracts as part of a reflex then its antagonist is automatically inhibited (forced to relax)
Golgi tendon reflex
Opposite of stretch reflex-causes muscle to lengthen to prevent overburdening muscle. Involves reciprocal activation-inhibits agonist, activates antagonist
Flexor reflex
Withdrawal from painful stimuli
Ipsilateral & polysynaptic
Crossed extensor reflex
Extension on the opposite side of the body to where the reflex happens to maintain balance, e.g. extending left leg when right leg pulls away after stepping on something painful
Plantar reflex and babinsky sign
Involves spinal nerves L4-S4. Running something along underside of foot, should cause toes to curve. Babinsky sign means toes splay out instead, this is normal in infants but sign of spinal injury in adults
Abdominal reflex
Involves T8-12. Stroke side of belly button will cause contraction of abdominals
5 types of receptors categorised by stimulus type
1. Mechanoreceptor Thermoreceptor Photoreceptor Chemoreceptors Nociceptor
Mechanoreceptor
a. Deformation
b. Touch, pressure, vibration, stretch, itch
3 types of receptors characterised by location
- Interoceptors
a. Inside body stimuli; blood vessels, internal organs - Exteroceptors
a. Stimulus from outside body; pain, pressure, touch, temperature, smell, taste - Proprioceptors
a. Detect changes and movement in muscle, tendon, ligament, joint cavity
3 levels of sensory organisation
Receptor level
Circuit level
Perceptual level
Receptive field
a. The immediate area around a receptor that it’s responsible for
b. The more sensitive the area, the smaller receptive field each receptor has (feeling two pricks or one)
c. Convergence creates larger receptive fields if multiple primary neurons synapse with the same secondary neuron
Transduction
converting the stimulus energy into a graded potential
Receptor potential
a. When receptor is a separate cell (ass in most special senses) the graded potential is called a receptor potential. It turns into generator potential when it reaches the neuron.
Generator potential
b. When receptor is part of a sensory neuron the graded potential is called a generator potential.
What happens at perceptual level? Where?
- Cerebral cortex
a. Detection (sensation)
b. Magnitude (how loud? How bright?) Frequency of AP determines magnitude
c. Spatial discrimination
d. Quality discrimination of abstract characteristics E.g. how does it smell, look?
e. Pattern recognition
Endoneurium
Wraps each axon
Perineurium
Wraps group of axons to form fascicle
Epineurium
Wraps several fascicles and blood vessels to form nerve
PNS can regenerate if
- Soma/cell body is not damaged
- There is no extensive damage
- Endoneurium is intact
What inhibits nerve regeneration in CNS
Oligodendrocytes
Process of PNS nerve regeneration
iii. Wallerian degeneration: Cut axon ends seal themselves off, area distal to injury on axon will swell and die, but endoneurium is intact
iv. Macrophages come in to clear out debris from dead axon distal to injury
v. Schwann cells form a regeneration tube and release growth factors and cell adhesion molecules (CAMs) that encourage axonal re-growth
vi. Regeneration is very slow, 1-2mm/day
Receptor categorisation based on complexity
- Complex: Special senses
- Simple: most abundant
a. Free nerve endings: throughout body: Receptor comes in direct contact w stimuli
ii. Pain, temperature
iii. Merkel disk (tactile disk)
iv. Hair follicle
b. Encapsulated: Surrounded by connective tissue and never comes in direct contact with stimuli
ii. Detects changes/deformation in tissue surrounding it
