Peripheral Nervous System Flashcards
What are the basic units of the Nervous System?
Neurones
What produces the myelin sheath in the PNS?
Schwann cells.
(Oligodendrocytes in the CNS).
Describe a multipolar neuron.
- 2 or more dendrites.
- Majority of CNS neurones.
- All the motor neurons of skeletal muscle and ANS.
- Cell body found in the CNS.
Describe a unipolar neuron.
- Double process.
- Cell body found in the PNS.
- AKA sensory / pseudounipolar.
Another way to describe an Efferent neuron?
Motor neuron.
The impulse of an efferent neuron moves towards?
The body wall, body cavity or organ.
The impulse of an afferent neuron moves towards?
The brain.
Another way to describe an Afferent neuron?
Sensory neuron.
What is a nerve?
Collection of axons surrounded by connective tissue and blood vessels.
Most nerves exist in which modality?
Mixed i.e. somatic motor, somatic sensory and sympathetic.
How many pairs of spinal nerves are there?
31 pairs.
Where are spinal nerves found?
The intervertebral foramina.
Spinal nerves connect structures of the soma via what?
Rami
Spinal nerves connect via rami to what?
Structures of the soma.
Spinal nerves connect with the spinal cord segment of the same number via what?
Roots and rootlets.
Spinal nerves connect via roots and rootlets to what?
The spinal cord segment of the same number.
Describe the posterior rami of spinal nerves.
Small and innervate the posterior body wall.
Describe the anterior rami of spinal nerves.
Large and innervate the anterolateral body wall.
Describe the transmission of sensory axons in relation to the spinal nerves.
ALL sensory axons pass from spinal nerve > posterior root > posterior rootlets > posterior horn of spinal cord.
Where are the cell bodies of primary afferent neurones located?
Dorsal root ganglion.
Describe the transmission of motor axons in relation to the spinal nerves.
ALL motor axons pass from anterior horn of spinal cord > anterior rootlets > anterior root > spinal nerve.
How does segmental innervation of the body wall arise?
Each spinal nerve supplies innervation to a unilateral area of the body.
Each spinal nerve pair supplies all structures in a segment of the body with what?
- General sensory supply to all structures.
Each spinal nerve pair supplies skeletal muscles in a body segment with what?
- Somatic motor supply to skeletal muscles.
Each spinal nerve pair supplies the skin and smooth muscles of arterioles in a body segment with what?
- Sympathetic nerve supply to skin and smooth muscle of arterioles.
What is a dermatome?
Area of skin supplied with sensory innervation from a single spinal nerve.
NB there is overlap by adjacent spinal nerves.
What is a myotome?
Skeletal muscles supplied with motor innervation from single spinal nerve.
NB myotome sometimes deep to dermatome of same spinal nerve, but not always e.g. diaphragm.
Male nipple found in which dermatome?
T4
Umbilicus found in which dermatome?
T10
C2-C4 of the dermatome map cover which areas?
Posterior scalp, neck and shoulder.
C5-T1 of the dermatome map cover which areas?
The upper limb.
L2-Co1 of the dermatome map covers which areas?
The lower limb, gluteal region and perineum.
What spinal nerves contribute to the cervical plexus?
C1-C4
The cervical plexus (C1-C4) supplies what?
- The posterior scalp.
- Neck.
- Diaphragm.
What spinal nerves contribute to the brachial plexus?
C5-T1.
The brachial plexus supplies what?
The upper limb.
What spinal nerves contribute to the lumbar plexus?
L1-L4.
The lumbar plexus supplies what?
The lower limb.
What spinal nerves contribute to the sacral plexus?
L5-S4.
The sacral plexus supplies what?
- The lower limb.
- Gluteal region.
- Perineum.
Where does sympathetic outflow originate from?
Control centres in the brain > then passes down spinal cord.
What segments of the spinal cord have lateral horns for cell bodies?
T1 to L2.
Through which root/rootlets does “presynaptic” sympathetic axons (motor innervation) pass through?
Anterior rootlets/roots.
Where do presynaptic axons destined for the heart synapse?
T1 or cervical PARAverterbral ganglia.
Through what do postsynaptic axons to the SA & AV nodes + the myocardium pass?
Cardiopulmonary splanchnic nerves.
Where do presynaptic axons of the lungs synapse?
In the upper thoracic PARAvertebral ganglia.
Where do postsynaptic axons of the lungs pass to reach the bronchiolar smooth muscle and mucous glands?
Cardiopulmonary splanchnic nerves.
Presynaptic axons of the abdominopelvic organs synapse where?
In one of the PREvertebral ganglia.
Give an example of a PREvertebral ganglia in which presynaptic axons of the abdominopelvic organs synapse?
- Coeliac ganglion of coeliac plexus (foregut).
- Aorticorenal ganglion (kidney).
- Superior mesenteric ganglion of SM plexus (midgut).
- Inferior mesenteric ganglion of IF plexus (hindgut + pelvic/perineal organs).
Presynaptic axons of the adrenal medulla pass through the aorticorenal ganglion to synapse where?
Directly onto the adrenaline/noradrenaline secreting cells of the adrenal medulla.
Presynaptic parasympathetic axons leave the CNS via which cranial nerves?
- CN III.
- CN VII.
- CN IX.
- CN X.
Presynaptic parasympathetic axons leave the CNS via cranial nerves and what other nerves?
Sacral spinal nerves.
Presynaptic parasympathetic axons leave the CNS and reach the eye via what?
The ciliary ganglion and CN III (oculomotor).
Presynaptic parasympathetic axons leave the CNS and reach the lacrimal gland and salivary glands via what?
Parasympathetic ganglia in the head.
Presynaptic parasympathetic axons leave the CNS and reach the organs of the neck, chest, and abdomen (to mid-gut) via what?
CN X - vagus.
Presynaptic parasympathetic axons leave the CNS and reach the hindgut, pelvis and perineum via what?
Sacral spinal nerves.
Name the ipsilateral symptoms of Horner’s Syndrome?
- Miosis.
- Ptosis.
- Anhydrosis.
- Increased warmth and redness.
Impaired innervation to the head and neck of what kind is responsible for Horner’s Syndrome?
Impaired sympathetic innervation.
What may cause compression of the cervical parts of the sympathetic trunk, leading to Horner’s Syndrome?
- Root of neck trauma.
- Carotid dissection.
- Internal jugular vein engorgement.
- Deep cervical node metastases.
- Pancoast tumour (lung apex).
What causes ptosis in Horner’s Syndrome?
A lack of sympathetic innervation of the smooth muscle within levator palpebrae superioris.
What causes miosis in Horner’s syndrome?
A lack of sympathetic innervation to dilator pupillae.
What causes a reduction in sweating in Horner’s syndrome?
Lack of sympathetic innervation to sweat glands of the skin.
What causes increased warmth in Horner’s syndrome?
Dilation of the skin arterioles.
