week 6 revision Peripheral Nervous System (PNS) Overview

These flashcards cover the key vocabulary terms related to the peripheral nervous system, including cranial and spinal nerves, their organization, reflex arcs, and plexuses.

Cranial Nerves

there are 12 pairs of cranial nerves presented by roman numerals. They supply all structures of the head neck as well as some of the visceral structures of the thorax and abdomen. Their numbering reflects their sequence of their attachement to the brain

name Cranial Nerves

I.                    olfactory  sensory: nose

II.                  optic sensory: eye

III.                oculomotor  motor: most eye muscles

IV.               trochlear motor: superior oblique muscles

V.                 trigeminal sensory: face, sinuses, teeth/ motor: muscles of mastication

VI.               abducens motor: external rectus muscles

VII.             facial motor: muscles of the face/ sensory: anterior third of the tongue

VIII.           vestibulocochlear motor and sensory inner ear

IX.                glossopharyngeal: motor and sensory

X.                  vagus motor and sensory

XI.                accessory motor  

XII.             hypoglossal motor

PNS:

all the nervous tissue outside the CNS, nerves are categorised as either cranial or spinal nerves (depending on where they exit the CNS) nerves exiting from the brain = cranial nerves, nerves exiting from the spinal cord = spinal nerves

Spinal Nerves

anterior ventral roots contain motor neurons (motor info out). Posterior roots contain sensory neurons (sensory info in). Spinal nerves form where the anterior and posterior roots come together as they exit the spinal cord. Branch into anterior and posterior rami

nerve structure

neuron/ nerve cells wrapped in endoneurium, bundled together to form a fascicle wrapped in perineurium, bundled together to form a nerve wrapped in epineurium

Anterior and posterior rami:

posterior ramus supplies the structures of the back. Anterior ramus supplies the anterior surface of the body and the limbs. Both rami contain sensory and motor neurons

Somatic Nerve Plexus

a limb has many nerves supplying the different tissues and regions of that limb. And these arise from nerve plexus. A nerve plexus serves to redistribute nerve fibres from several anterior and rami into a number of different peripheral nerves in a limb, all rami, except T2-T12 are associated with a nerve plexus

Organisation of a plexus:

many anterior rami combine to form a final peripheral nerve that will enter a limb. This allows a limb to have many nerves supplying different tissue region. Plexus begins with roots i.e the specific anterior rami, that merge into ‘trunks’, then‘divisions’, then ‘cords’, and then finally the peripheral nerve (branches)

Somatic nerve plexus:

-          cervical plexus

-          brachial plexus

-          lumbar plexus

• sacral plexus
  
  

Cervical Plexus

involves anterior rami C1-C5, supplies skin and muscles of the head and neck, and the superior parts of the shoulder and chest. One major peripheral nerve pheric nerve, that supplies to the diaphragm

Brachial Plexus

Formed by anterior rami C5-T1, supplies nerves to the shoulder and upper limb.

Lumbar Plexus

Includes L1-L4, supplies the anterolateral abdominal wall, external genitals, and part of the lower limb.

Sacral Plexus

Includes L4-S4, supplies the buttocks and lower limbs, includes the Sciatic nerve.

Autonomic Nerve Plexus

visceral structures like the heart, lungs and digestive system are also controlled by a nerve plexus. Unlike the ordered somatic plexus, the autonomic plexuses are made up of a tangled network of sympathetic and parasympathetic neurons

the cardiac plexus:

has a sympathetic and a parasympathetic component responsible for taking motor info to the heart and takes sensory info back to CNS

myotomes

a group of muscles that are innervated by one single spinal segment an individual muscle may be a part of multiple myotomes. It is possible to test myotome functionality by checking a patient’s ability to perform specific actions eg. Hip flexion L2, L3

dermatomes

cutaneous (skin) area that receives most sensory innervation from a single spinal segment, similar to myotome. You can test their functionality by the sensation of a specific area of the skin

Reflex Arc

involves a rapid motor response to a stimulus that is entirely mediated by the spina cord, brain is still notified but not involves

reflex arc steps:

1.      sensory receptor: receives stimuli

2.      sensory neuron: either somatic or visceral sends signals to the CNS

3.      Integrating centre: relays  info from sensory to motor neuron

-          Polysynaptic: includes interneuron

-          Monosynaptic: no interneuron

4.      Motor neuron, either somatic or visceral, sends signals to PNS effectors

5. Effector: either muscle or gland that carries out the response

Monosynaptic Reflex

There are a few reflexes that are classified as ‘monosynaptic’, meaning that there are only two neurons involved in the entire
reflex arc E.g. the patellar reflex. Sensory (afferent) neurons detect a stimulus and send a nerve signal into the spinal cord to synapse directly with a motor (efferent) neuron → Motor neuron sends signal to effector muscles. Completely bypass an interneuron

Plantar Reflex

polysynaptic reflex arc is a nociceptive (pain-related) spinal reflex that serves to protect the sole of the foot. Tested by stroking the foot by a sharp object, which produces plantar flexion of the big toe

Stretch Reflex

A monosynaptic reflex arc, The function of a stretch reflex is to ensure
the muscle stays at its desired length. Important for postural muscles, e.g. the quadriceps femoris: If we have a sudden change in the length of that muscle that's
probably because we're falling over, so the body tries to fix that by tightening that
muscle back up (quickly)