Anatomy: Nerves Flashcards
What is a group of nerve cell bodies in the CNS called?
A nucleus
What is a group of nerve cell bodies in the PNS called?
A ganglion
What is an axon?
A nerve fibre conveying action potentials
What are bundles of axons travelling together in a) the CNS and b) the PNS called?
a) A tract
b) A peripheral nerve
What is a myelin sheath?
A cover round the nerve which is an electrical insulator. A myelinated nerve conducts faster
What happens at a synapse?
one neurone communicates with another neurone in a ganglion in the PNS or in a nucleus in the CNS. electrical signal (AP) becomes a chemical signal (neurotransmitter) then an electrical signal again
What are the folds in the brain called?
Gyri (single gryus)
What are the spaces in between the gyri called?
Sulci (plural sulcus)
What is the cerebral neocortex/cortex?
the outermost layer of the cerebral hemispheres, consisting of all the gyri and sulci
How many lobes does each cerbral hemisphere consist of?
4
How are the 4 lobes of each cerebral hemisphere named?
approximately according to the bone of the cranial vault they lie deep to: Frontal lobe Parietal lobe Occipital lobe Temporal lobe
What fissure separates the two lobes of the brain sagitally?
The longutidinal fissure
Name the 12 cranial nerves
- CN I the olfactory nerve
- CN II the optic nerve
- CN III the oculomotor nerve
- CN IV the trochlear nerve
- CN V the trigeminal nerve
- CN VI the abducent nerve
- CN VII the facial nerve
- CN VIII the vestibulocochlear nerve
- CN IX the glossopharyngeal nerve
- CN X the vagus nerve
- CN XI the spinal accessory nerve
- CN XII the hypoglossal nerve
What are the indents in the floor of the cranium called?
The anterior, middle and posterior cranial fossae
Name the foraminae for the cranial nerves
Cribriform plate of the ethmoid bone Optic canal Superior orbital fissure Foramen rotundum Foramen ovale Internal acoustic meatus Jugular foramen Hypoglossal canal Foramen magnum
What type of matter is in the cerebral cortex of the brain?
Grey matter- contains cell bodies
What type of matter is deep to the grey matter?
What gives it this appearance?
White matter
It contains many axons which are myelinated
Myelin gives the whiter appearance
What is different about the structure in the spinal cord in terms of the matter?
The white matter is superficial and the grey matter is deep
How does the spinal cord connect with the brain?
It passes through the foramen magnum of the occipital bone
Where does the spinal cord lie?
In The vertebral canal
What are the 4 segments of the spinal cord?
cervical
thoracic
lumbar
sacral/coccygeal
What are the two enlargements (wider parts) of the spinal cord?
cervical enlargement due to all the upper limb nerves
lumbosacral enlargement due to all the lower limb nerves
How many pairs of spinal nerves does the spinal cord connect bilaterally with?
31
Where does the spinal cord end as a solid structure?
At the conus medullaris
At the level of L1/L2 intervertebral disc
What is the cauda equina?
lumbar and sacral spinal nerve ROOTS have to descend in the vertebral canal to their respective intervertebral foraminae
How many pairs of cervical spinal nerves are there?
8
How many pairs of thoracic spinal nerves are there?
12
How many pairs of lumbar spinal nerves are there?
5
How many pairs of sacral spinal nerves are there?
5
How many pairs of coccygeal spinal nerves are there?
1
What is the spinal nerve?
the part that is located within the intervertebral foramen BELOW* the vertebra of the same number (*except cervical region)
What connects the spinal cord to the spinal nerves?
The roots and rootlets
What connects the spinal nerve to the structures of the soma?
The rami
What is a dermatome of a spinal nerve?
the dermatome of the spinal nerve is the area of skin (strip) supplied by both the anterior and the posterior rami
What do the posterior rami supply?
the posterior paramedian strip of the dermatome
What do the anterior rami supply?
the larger anterior rami supply the remainder of the posterior part, the lateral and the anterior parts of the dermatome and ALL of the limb dermatomes (there are no posterior rami in limb dermatomes)
What supplies the limbs?
ONLY anterior rami supply the limbs via plexi
What are nerve plexi?
networks of intertwined anterior rami axons
What is the right cervical plexus and what does it supply?
C1-C4 anterior rami
supplies mainly neck wall
What is the right brachial plexus and what does it supply?
C5-T1 anterior rami
supplies upper limb
What is the right lumbar plexus and what does it supply?
L1-L4 anterior rami
supplies lower limb
What is the right sacral plexus and what does it supply?
L5-S4 anterior rami
supplies pelvis/perineum & lower limb
What is the left musculocutaneous nerve?
a named nerve branch from the brachial plexus
made from axons from both C5 & C6 anterior rami
What are named nerves?
containing axons from more than 1 spinal cord segment/spinal nerve result from a plexus
What are the 5 named nerves that result from the brachial plexus?
What do they supply?
axillary nerve median nerve musculocutaneous nerve radial nerve ulnar nerve They supply the upper limb
Which segments of the spinal cord have lateral horns?
What are they for?
T1 to L2 segments
for cell bodies of the next sympathetic neurones in the chain
Where do sympathetic axons from the brain descend?
In the spinal cord in white matter
Describe the sympathetic supply to the soma
Sympathetic axons travel from autonomic centres in brain
There are connections with T1 to L2 spinal nerves via rami communicans
sympathetic trunks run the full length of vertebral column
sympathetic nerve fibres enter ALL spinal nerves and then ALL anterior and posterior rami
Which cranial nerves contain parasympathetic axons?
What are they for?
cranial nerves III, VII, IX & X
for organs of the head/neck/chest and abdomen as far as the midgut
Apart from some cranial nerves, which other nerves contain parasympathetic axons?
What are they for?
the sacral spinal nerves contain parasympathetic axons for organs of the hindgut/pelvis/perineum
Where do nerves containing parasympathetic axons travel to?
to ONLY the internal organs - not the body wall
How many parasympathetic ganglia are in the head?
4
How is the nervous system subdivided on the basis of function?
The SOMATIC NERVOUS SYSTEM
the body wall senses and responds to the external environment
The AUTONOMIC NERVOUS SYSTEM (ANS)
(also called the visceral motor system)
body organs sense and respond to the internal environment
What are the body wall organs?
What supplies them?
sweat glands in the skin
arrector smooth muscles for hairy skin
arterioles are everywhere
- all supplied by the autonomic NS
What is a) the sensory supply and b) the motor supply of the body wall?
a) Somatic sensory
b) somatic motor
What is a) the sensory supply and b) the motor supply of the body organs?
a) visceral afferent
b) Sympathetic and parasympathetic
What is a) the sensory supply and b) the motor supply of the special sense organs?
a) Special sensory
b) sympathetic and parasympathetic
What is in a peripheral nerve?
nerve fibres (axons), wrapped up in connective tissue, travelling together to/from the same region of the body or structure
Are all of the axons in a peripheral nerve the same type?
They may be, in which case the peripheral nerve would be classified as e.g. a somatic motor nerve a somatic sensory nerve a special sensory nerve a sympathetic nerve a parasympathetic nerve
there is normally a mixture of neuronal types:
a “mixed nerve”
spinal nerves & their branches are usually mixed nerves containing:
somatic sensory, somatic motor & sympathetic axons
How many of the cranial nerves are mixed nerves?
5
Are there sympathetic axons in any cranial nerves?
No
What sensations can our body wall perceive?
coarse touch fine touch vibration position sense (proprioception) temperature – hot & cold thermoreceptors pain – nociceptors
Where does a sensory axon from the left thumb (e.g. in the C6 anterior ramus) join with the spinal cord?
It passes into the posterior root ganglion of the left c6 spinal nerve, then into the posterior root, then into the posterior rootlet, then enters the posterior root horn.
What happens to the sensory action potential in the posterior root horn of spinal nerve 6?
It synapses in the posterior horn spinal cord nucleus onto the second sensory neurone in the chain.
The second sensory neurones axon then crosses the midline onto a spinal cord tract ascending towards the right thalamus then the right side of the cerebral cortex.
sensory AP arrives at the location in the right cerebral cortex specific to the part of the left body wall stimulated
How many neurones are in the somatic sensory pathway for temperature?
3
Where is the right primary somatosensory area?
Where are the sensory action potentials that arrive here from?
In the right parietal lobe.
sensory APs arriving here bring left sided body wall sensations into “consciousness”
Where is the right primary somatomotor area?
In the right frontal lobe
What do motor APs originating here cause to happen?
contractions of left sided skeletal muscles to make a consciously planned movement.
How many neurones are in a somatic motor pathway?
Where do the axons cross over to the other side?
2
In the brainstem
What are the first neurones in a somatic motor pathway called?
The upper motor neurones
How do somatic sensory action potentials travel from the head wall to the brain?
In a cranial nerve
How do somatic motor action potentials travel to skeletal muscle in the head/neck?
In a cranial nerve
What are the second neurones in a somatic motor pathway called?
Lower motor neurones
In a somatic Motor Pathway to the skeletal muscles of the left upper limb, which horn in the brainstem to the upper motor neurone axons descend to?
Left anterior horn
Which spinal nerves are involved in supplying the left upper limb?
C5-T1
What is a reflex?
a reflex is an extremely rapid (missing out the pathway to the brain) involuntary response to a (potentially harmful) stimulus
What is a paralysed muscle?
a muscle without a functioning lower motorneurone
What can a paralysed muscle not do?
a paralysed muscle cannot contract
caused by an injury to the muscle’s motor nerve
How would a paralysed muscle appear on examination?
on examination the muscle would have reduced tone (reduced resistance to stretch – “floppy”)
What is spasticity?
the muscle has an intact and functioning lower motorneurone
the descending controls from the brain are not working
- the muscle is essentially being allowed to “over-contract” continuously
caused by an injury to the descending controls
How would a spastic muscle appear on examination?
the muscle would have increased tone (increased resistance to stretch – “tight”)
What does the ANS do?
senses and responds to the internal environment
What are sensory axons of the organs called?
Visceral afferents
Which organs do the sympathetic and parasympathetic axons supply?
All of them
What is the effect of sympathetic stimulation on the pupils?
They dilate
What is the effect of sympathetic stimulation on the GI tract?
motility is reduced/sphincters close
What is the effect of sympathetic stimulation on arterioles?
In skeletal muscle: dilate
In skin: constrict
What structures in the body wall are supplied by sympathetic axons?
skin sweat glands
skin arrector muscles
ALL arterioles (sympathetic tone)
Do parasympathetic axons supply the body wall organs?
No
Do parasympathetic axons supply arterioles?
No
