Neuroanatomy 2 Flashcards
Organisation of nerves in peripheral nervous system
Nerves in the periphery contain clusters of axons.
Each nerve has bundles of axons.
The nerve is covered in epineurium sheath.
The bundles of axons (fasicles) are covered in perineurium.
The individual axons are covered in endoneurium.
Differentiate the myelin providing glial cells in CNS and PNS
oligodendrocytes and schwann cells
Differentiate the collection of cell bodies in CNS and PNS
Nuclei and ganglia
Define ganglia and glia
Ganglia are collections of nerve cell bodies in PNS
Glia are protective cells found in CNS and PNS as myelin
Differentiate the bundles of axons in CNS and PNS
Tracts (bundles of axons) and nerves
What are the two types of neurons that could compose an axon in a nerve?
Axons of two different types of neurons:
o Neurons that drive tissues to do things (cause muscles
to contract/heart to beat faster/glands to secrete
things) – Motor neurons
o Neurons that are involved in sensing things (the
environment of a tissue/the amount of stretch on a
muscle) – sensory neurons
So, the single axons within that nerve are either going to be motor axons or sensory axons
How is the nerve classified based on where it comes from?
- The nerve is classified based on where it comes from:
o Spinal nerve: originates from spinal cord
o Cranial nerve: originates from brain or brainstem
Differentiate between cell body locations of motor and sensory axons
- Cell bodies of neurons in motor axons are located within the CNS
- Motor neurons are called multipolar neurons as they have dendrites in the axon
- Cell bodies of the neurons of the sensory axons are located in the PNS
- pseudo-unipolar as
their cell bodies sit within the PNS - The cell body gives rise to a single axon that branches – one branch into the periphery to innovate the tissue and the other into the grey box into the CNS to tell the CNS what the periphery has just experienced
- pseudo-unipolar as
If you had a bunch of these sensory neurons together, that would be a group of cell bodies within the PNS, it would called a ganglion
Organisation of spinal cord and spinal nerves
The spinal cord is made of 31 spinal nerves:
- 8 Cervical nerves
- 12 Thoracic nerves
- 5 Lumbar nerves
- 5 Sacral nerves
- 1 Coccegyl nerve
C1-C4 = forms the Cervical Plexus/Phrenic nerve
> Back of head
> neck
> shoulders
> Diaphragm
C5-T1 = Brachial Plexus
> Innervate arm/upper limbs
- Radial nerve
- Ulna nerve
- Median nerve
T2-T12 - nerves that wrap around ribcage
L1-L3 = Lumbar Plexus/Fermoral nerve (lower limb)
> Anterior/medial/lateral thigh
L4-S4 = Sacral Plexus/Sciatic nerve (lower limb)
> Posterior thigh
> Below knee
How are spinal nerves organised and what are efferent and afferent nerves of PNS?
All the motor innervations arise from the ventral side of the spinal cord/anterior side and exit through the ventral/anterior roots
All the sensory information goes to the spinal cord from the back/posterior dorsal sides (called the dorsal roots), they come together to form this mixed spinal nerve that then goes off to innervate the tissue
Peripheral nerve axons can be either efferent (motor) carrying signals from the CNS or afferent (sensory) carrying signals to the CNS
> Separate spinal roots connect efferent and afferent to
the CNS
Efferent and afferent axons segregate at the point just before they contact the CNS (spinal cord or brainstem): sensory axons join the CNS via dorsal (posterior) roots, and motor axons join at a ventral (anterior) root.
The mixed spinal nerve splits into dorsal (posterior) and ventral (anterior) branch/rami (from the spinal cord to the periphery) - (because we need information from back and front parts of the body)
Descibe the structure of a typical spinal segment in somatic nervous system
- Sensory neuron from a sensory receptor (e.g. skin) travels through the dorsal/posterior side of the mixed spinal nerve and the dorsal root ganglion and dorsal root to the dorsal horn passing an interneuron in the gray matter to the motor neuron that passes the ventral horn and root to the effector muscle/organ
Describe segmental innervation
Segmental innervation refers to the specific pattern of nerve supply to different regions of the body based on the spinal segments. Each spinal segment gives rise to a pair of spinal nerves, which innervate a particular area of the body.
o A dermatome is an area of skin that is mainly supplied by a single spinal nerve
o A myotome is the group of muscles that a single spinal nerve innervates
Define nerve plexuses
o A peripheral nerve is often comprised of multiple spinal nerves, ie several segments contribute axons to a single peripheral nerve
o E.g. The Phrenic nerve is responsible for the diaphragm/breathing and is made up of the C3, C4, C5 nerves, so damage to one of these wouldn’t cause paralysis or complete loss of function
List the cranial nerves, their origins and functions and whether they are sensory or motor
- Brain+Brainstem - Cerebral Hemisphere
- Only - Olfactory
- One - Optic (eye) - Midbrain
- Of - Occularmotor (rest of eye muscles)
- The - Trochlear (superior oblique eye muscle) - Pons
- Two - Trigeminal (face, teeth, sinuses) (muscles of mastication/grinding)
- Athletes - Abducent (external eye muscle)
- Felt - Facial (muscles of face)
- Very -Vestibularcocchlear - Medulla
- Good - Glosopharangyeal
- Victorious - vagus
- And - accessory
- Healthy - hypoglossal
Some - Sensory
Say - Sensory
Marry - Motor
Money - Motor
But - Both
My - Motor
Brother - Both
Says - Sensory
Big - Both
Brains - Both
Matter - Motor
Most - Motor
Explain the ANS and its two divisions
Autonomic Nervous System – an effector system in the CNS and PNS mediating unconscious homeostatic control of organ and body physiology.
> Two main divisions:
1. The sympathetic autonomic nervous system: All pre-
ganglionic neurons arise from the thoracic and
lumbar parts of the spinal cord
2. The parasympathetic nervous system: pre-ganglionic
neurons are in the brain stem or in the craniosacral
part of the spinal cord
Thoracolumbar (SNS) - thoracic and upper lumbar regions
Cranionsacral (PNS) - brainstem and sacral region
