Somatic Nervous System

List the types of neurons

• Relay

• Motor

• Sensory

Give the breakdown of spinal nerves

31 pairs (8 cervical nerves (7 vertebrae), 12 thoracic vertebra and nerves, 5 lumbar nerves and vertebra, 5 sacral nerves and vertebra)

Where does the spinal cord end on an adult (IMPORTANT)

• spinal cord ends between L1 and L2 vertebra (for children its L3)

What is the role of Glial cells in the PNS

• major scaffolding components of nervous tissue

→Satellite cells support cell body of neuron (glial of PNS)

What are schwann cells

• support axons (wrap around it, saltatory conduction means signal can jump between junctions (aka nodes of ranvier))

What is a fascicle

• a bundle of multiple axons (each with its own endoneurium).

List the Glial cells of the CNS and their role

• Ependymal cells

• Astrocytes 

• Oildogendrocytes

• Microglia

What are the 2 types of nerve damage

• Damage to PNS:

→Crushed nerve can result in regeneration of axon due to intact connection to cell body

Severed nerve usually requires surgical intervention

• Damage to CNS – any growth by injured axons blocked by astrocyte proliferation and thus do not usually recover

Give the dermatome map

• T4= nipple

• T10= umbilical

• L1= ‘hands in pockets’

• L4= knee

What is a dermatome

• unilateral area of skin innervated by sensory fibres of one spinal nerve

Overlap by adjacent spinal nerves

List the areas of the spinal cord and meninges on this cervical vertebra

Lable this typical thoracic spinal section

-Dorsal root: sensory input

-Ventral root: motor input

Draw a basic reflex arc

-Smallest functional unit of NS

-route followed by nerve impulses from receptor to effector

-Reflex testing is a valuable diagnostic aid

What info do cranial and spinal nerves carry

• Cranial: infro to and from brain

• Spinal: to and from spinal cord

Where is motor info transmitted

• From CNS to vol skeletal muscles

• Via somatic nervous system

• and to autonomic nervous system

What are the 2 directions of neurons 

• Afferent: sensroy info towards CNS

• Efferent: motor info away from CNS

What is a nerve plexus

• network of nerve fibres, formed by several individual nerve branches

  from different regions of the CNS fusing together. Plexuses allow multiple nerve fibres (for

  example spinal nerves arising from several spinal cord segmental levels)

What is the spinal cord divided into

outer region called white matter and a central, ‘H’ shaped region, the grey matter with a central canal

What is the denticulate ligament 

• pia mater forms a delicate membrane laterally between the spinal cord and the dura mater

What is the importance of teh subarachnoid space

• contains CSF

Lable these sections

What is the tapered end of the spinal cord called

• Conus medullaris

Give the location and importance of the epidural space

• Between bones of the bertebral canal and dura mater 

• Clinically used for injection of anathetics 

Locate the nerve fibers assoicated with the ventral and dorsal horns

What is the impact of damage to L1

• likely to affect the lower lumbar and sacral spinal cord segments resulting in very serious consequences

How many cranial nerves are there and name them 

List the spinal nerves

• 31 pairs of symmetrically arranged spinal nerves, namely,

→8 cervical, 12 thoracic,5 lumbar, 5 sacral and 1 coccygeal.

=Each spinal nerve contains axons and dendrites which transmit information respectively from or to the spinal cord. They are distributed mainly to the trunk and limbs.

What symptoms may arise if spinal nerves are damaged 

• Tingling of lower legs and arms

• Pain 

• Numbness

What is the epineurium 

• group of fascicles are bound together and surrounded by dense irregular connective tissue

What surrounds fasicles

• surrounded by a sheath of specialised cells that form two to seven layers termed the perineurium

• Within each fascicle the nerve fibers, BV are embedded and surrounded by loose CT (endometrium)

What is the cauda equina

• bundle of spinal nerves at lower end

• a fibrous remnant of pai mater is present (filum terminale)

What cell bodies are located within the dorsal root ganglion 

• Pseudounipolar sensory neurons 

→transmit sensory info e.g. pain

What cell bodies are located within the VENTRAL root ganglion 

• Motor neurons

→carry motor impulses away from CNS to muscles

Where do the majority of spinal nerves emerge from

• intevertebral foraman

• thoracic, lumbar and sacral from below theur numberical vertebrae (cervical are above)

A patient presents with trauma to the back. They have tenderness over the 7th and 8th thoracic spinous processes. The clinician is concerned that the spinal cord may have been damaged. In your group, discuss which segments of the spinal cord may have been affected by the injury.

• T7–T8 vertebral injury affects T9–T10 spinal cord segments (cord lies higher than vertebrae).

• These segments correspond roughly to the umbilical (T10) dermatome.

• Possible effects: motor and sensory loss below the umbilicus.

What area is a lumbar puncture carried out at

• L3-4

• avoids damage to spinal cord as only cauda equina nerve roots and CSF

• Dua and arachoid at risk of puncture

Describe the order of tissues in which the needle goes through to get CSF sample

• Skin

• Subcutaneous tissue (fat and fascia)

• Supraspinous ligament

• Interspinous ligament

• Ligamentum flavum

• Epidural space

• Dura mater

• Arachnoid mater → enters subarachnoid space (CSF)

Define dermatome

• area of skin supplied by single spinal nerve

Define myotome

• a region of skeletal muscle innervated by a single nerve

What types of nerve plexus are there

• Somatic plexuses (supply skin, vol skeletal muscles and joints from ventral rami)

• Autonomic plexus (blood vessels and viscera in thorax, ab and plevis)

What is the cervical plexus 

• ventral rami of cervial spinal nerves C1-4 

• supply skin and muscles of head and neck and shoulder region

What is the brachial plexus

• ventral rami of C5-8 and T1

• supplies skin, muscles of upper limb (via axially, musculocutaneous, radial, ulnar, median)

What is the lumbar plexus

• ventral rami of L1-4

• supply muscles and skin of anterior and medial aspect of thigh via femoral and obturator nerves

What is the sacral plexus 

• ventral rami of L4-5 and S1-4

• posterior aspect of thigh, leg and foot via sciatic nerve 

Explain limb development at week 4

• upper and lower limb appear at week 4 

• ectoderm at tip of bud intro by mesoderm to form apical extodermal ridge 

• this structure directs growth of limb and prolifeartion of mesenchyme 

Explain limb development at week 6

• limb buds form handplates and footplates

• digits formed by cell death allowing seperation

Describe the developmental rotation of limbs and dermatomes

• occurs within weeks 6-8

• upper limbs rotates laterally

• lower limb rotate medially