The Nervous System Part 1 Flashcards
What does the CNS and PNS consist of?
- CNS: brain and spinal cord
- PNS: nerves which pass to and from the CNS (Cranial and spinal nerves)
- Is motor information transmitted to voluntary or involuntary areas and what part of the nervous system transmits it?
- What muscles/organs is motor information carried to?
- To voluntary skeletal muscle via somatic nervous system
- To carciac muscle, glands and involuntary smooth muscle of organs and blood vessels via
What is the neuron structure and what are the 2 types?
- Nucleated cell body with dendrites (cytoplasmic processes) and the axon
1. afferent neurons: carry sensory info to the cns
2. efferent neurons: carry motor info away from cns
Where does the spinal cord end?
Between the 1st and 2nd lumbar vertebrae forming the conus medullaris
What is the grey matter in the spinal cord composed of?
- Cell bodies of neurons (and their glial cells)
Arranged as a - Dorsal (posterior) horn
- Ventral (anterior) horn
What is the white matter in the spinal cord composed of?
- Nerve fibres
- The white colour results from the myelinated axons
Label the transverse section of the spinal cord
What is the bundle of spinal nerves at the end of the spinal cord called?
Cauda equina (from L2-S5)
What is the purpose of the cervical and lumbar enlargements on the spinal cord?
The limbs have a lot of muscles. The more motor neurons, the more cell bodies needed to feed the muscles in the limbs
Where are the brachial plexus and lumbar and sacral plexi found in the spinal cord?
- Brachial plexus: Cervical enlargement between C5-T1
- Lumbar and sacral plexi: Lumbar enlargement between T11 and L1
What does the subarachnoid space contain and what is it located between?
- Cerebrospinal fluid (CSF)
- Between pia and arachnoid mater
What is the lumbar cistern? What’s its clinical significance?
- An area of subarachnoid space which extends from the conus medullaris
- Where a lumbar puncture and spinal anasthesia are administered
What are spinal nerves structure?
Each nerve begins as an anterior (motor) and posterior (sensory) nerve root. These unite at the intervertebral foramina forming a single single spinal nerve
The spinal nerve leaves the vertebral canal via intervertebral foramina and divides into 2.
What are the 2 ramis?
- Posterior rami: supplies nerve fibres to synovial joints of the vertebral column, deep back muscles and overlying skin
- Anterior rami: supplies nerve fibres to much of the remaining area of the body, motor and sensory
What is a nerve plexus?
A network of nerve fibres
What is a ganglion?
A collection of neuronal cell bodies situated outside the CNS.
What is the spinal cord continuous with?
The medulla oblongata
What is the space between the bones of the vertebral canal and the dura mater?
- Epidural space
How many cranial nerves are there and what info do they carry?
Which nerve is the exception?
- 12 pairs of cranial nerves
- Sensory info from and motor info to the head and neck
- Vagus nerve innervates the structures in the thorax and abdomen
How many spinal nerves are there?
- 31 pairs of symettrical spinal nerves
- 8 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
- 1 coccygeal
Whats a fasicle? What connective tissue are they surrounded by?
- Many bundles of nerve fibres
- Dense irregular connective tissue called the epineurium
What is each fascicle surrounded by?
Perineurium (sheath of specialised cells forming 2-7 layers)
Within each fascicle what are the individual nerve fibres and blood vessels surrounded by?
Loose connective tissue the endoneurium
- What do the dorsal roots and roolets transmit?
- What do the ventral roots and ventral rootlets transmit?
- Sensory info towards spinal cord
- Motor info away from the spinal cord
- What neurons are located in the ventral horn of grey mater?
- What neurons are located in the dorsal root ganglion?
- Motor neurons
- Cell bodies of pseudounipolar sensory neurons
In the trunk each thoracic spinal nerve divides into a dorsal (small) and ventral (large) ramus.
- What do the ventral ramus form?
- How is the anterior skin supplied by nerves?
- Intercostal nerves which pass anteriorly in the intercostal space between 2 ribs giving branches to the intercostal muscles
- Skin is also supplied by intercostal nerves via lateral cutaneous branch (lateral chest) and an anterior cutaneous branch (anterior chest)
Can intercostal nerves supply the abdomen?
Yes - the lowest intercostal nerve continues into the abdomen to supply the abdominal wall muscles and overlying skin
Once a sensory axon has entered the spinal cord what 2 things may it do?
- Synapse with a motor neuron whose axon leaves the spinal cord at the same segmental level
- Sensory info may be transmitted upwards. Motor info can then be transmitted down the spinal cord.
What are the sensory nerve endings in the skin called and what do they detect?
- Cutaneous receptors
- Touch, pressure, pain and temperature
the sensory info is transmitted back to the cns in spinal nerves and the pattern of distribution of spinal nerves in the skin is consistent
What is a dermatome?
The area of skin supplied by a single spinal nerve/spinal cord segment
Whats a myotome?
A region of skeletal muscle innervated by a single spinal nerve/spinal cord segment
What are the basic components of a reflex arc?
- Sensory receptor
- Sensory neuron
- Motor neuron
- Skeletal muscle fibres
What are the 2 main types of nerve plexus?
- Somatic plexuses
- Autonomic plexuses
What do somatic plexuses supply?
- Skin, voluntary skeletal muscle and joints
- Formed from ventral rami of spinal nerves
What do autonomic plexuses supply?
- Distribute nerves to blood vessels and viscera
- Found in throax, abdomen and pelvis
Some autonomic plexuses accomany major arteries = perivascular plexuses
What are the 4 somatic plexuses?
- Cervical
- Brachial
- Lumbar
- Sacral
What does the cervical plexus supply?
Ventral rami of cervical spine nerves C1-4 supply:
* Skin
* Muscles of head, neck and shoulder
What does the brachial plexus supply?
Through which nerves does it supply?
Ventral rami C5-C8 and T1 supply:
* Skin and muscles of upper limb
1. Axillary (shoulder region)
2. Musculocutaneous (anterior arm)
3. Radial (posterior arm, forearm, hand)
4. Ulnar (anterior forearm and hand medially)
5. Median (anterior forearm and hand laterally)
- Where do the ventral rami of lumbar spinal nerves and sacral spinal nerves form the sacral plexus?
- What does it supply?
- What nerve innovates?
- L4-L5 and S1-S4
- Skin and muscle of thigh and leg/foot
- Sacral - Sciatic nerve
Lumbar - femoral and obturator nerve
- Where do the ventral rami of lumbar spinal nerves form the lumbar plexus?
- What does it supply?
- What nerves innovate?
- L1-L4
- Muscle and skin of the anterior and medial aspect of the thigh
- Femoral and obturator nerves
Embryology
When does limb development take place?
4th - 8th week of development
* Upper limb buds - day 24
* Lower limb buds - day 28
Embryology
What is the skin of limbs and the skeletomuscular derived from in embryology?
- Limbs: embryonic ectoderm
- Skeletomuscular: mesoderm
Embryology - 4th week of development
- What is the apical ectodermal ridge (AER)?
- Why is it critical for normal development?
- AER is critical structure for normal limb development by mesoderm thickening
- Directs the proximo-distal growth of the limb
Embryology
How does the AER promote formation of cartilage and muscle?
- Promoting proliferation of cells in the underlying mesenchyme (undifferentiated connective tissue)
Embryology - week 6 of development
What forms in week 6 of development after the limbs have grown?
Distal parts of limb buds form
* Handplates
* Footplates
* Digits formed by cell death
Embryology
During 4-5 embryonic weeks, ____ development is sensitive to environmental toxins ( ____ ) such as….
- Limb
- Teratogens
- Thalidomide
Full absence of limb = amelia, partial = meromelia
Label the nerves of the brachial plexus
Label the brachial plexus
- What cells are shown in the image
- What section have the cells been shown in?
- Peripheral nerves
- Transverse (and longitudinal top right)
Blue shows the myelin sheaths
self assessment questions
A) What would be located in the openings A?
B) Identify the structure located in area B
A) Spinal nerves
B) Intervertebral disc
self assessment questions
A) Whats located in area A
B) What would be the consequence of damage to B?
A) Motor neurons
B) Loss of sensation in the corresponding dermatome
self assessment questions
A) Identify structure A
B) Which compartment of the arm would be innervated by the branches of B?
A) Brachial plexus
B) Posterior
self assessment questions
A) Identify precisely part of the spinal cord A
B) What mkaes up the structures of B
A) Dura and arachnoid mater
B) Loss of sensation to the corresponding dermatome
