Nervous System Flashcards
What is the CNS composed of? Where are these located?
- brain (cranial cavity)
- spinal chord (vertebral canal)
What protects the skull and vertebra? What is it called? How many layers is it composed of?
MENINGES:
- 3 connective tissue membranes
What does the brain and spinal chord ‘float’ in? Where is it located?
cerebrospinal fluid
- occupies the space between the two inner meningeal layers
What is the brain further subdivided into?
cerebrum, cerebellum and the brain stem (connects to the spinal chord)
What is the function of the cerebellum? Where is it located?
- back of head
- movement and balance
What is the ‘gray matter’ of the brain? What does it include? What is its function?
Gray matter=cerebral cortex (outside)
- forms the outermost layer of the brain
- form “nuclei” found in deep portions of the cerebrum and cerebellum
- consists of: nerve cell bodies, axons, dendrites, central glial cells
- site of synapses
What is the brain made up of?
- neurons
- high concentration
What causes the colour of the brain to differ (white vs gray matter)?
- made up of the same thing
- different parts of neurons
What makes the gray matter darker?
- high concentrations of the body’s of neurons
What makes the gray matter darker?
high concentration of neuron processes (dendrites and axons)
What types of cell bodies are found in the gray matter of the brain? What is the collective name for the cell bodies?
- characteristic variety of cell bodies
NEUROPIL - meshwork of axonal, dendritic and glial processes
State the composition of white matter.
- axons of nerve cells (fresh=white)
- associated glial cells and blood vessels
(axons of nerve cells are traveling from one part of the NS to another)
What is the name of the functionally related bundles to which axons are going to or coming from?
tracts
Do tracts stand out as delinated bundles?
no!
What is located in both white and gray matter?
supportive glial cells
What is an additional structure located in white matter?
tracts
Can tracts be seen? How are they formed?
no!
- mostrly hypothetical
- do not have any distinct feautures
- form due to memorization (same action repeated many times)
How many layers is the cerebral cortex divided into?
6 layers
What are the 6 layers of the cerebral cortex?
1) molecular layer
2) external granular layer
3) external pytamidal layer
4) internal granular layer
5) internal pyramidal layer
6) fusiform (multiform) layer
State the composition of the molecular layer of the cerebral cortex.
- neutropil-oriented tangentially
- apical dendrites from pyramidal cells
- terminal branches of superficial cortical afferent fibers
neuropil= no neuron bodies, only their processes
State the composition of the external granular layer of the cerebral cortex.
- SMALL neurons that serve as interneurons (SMALL %)
granular= small neurons (SMALL %)
interneurons= connects molecular&deep
State the composition of the external pyramidal layer of the cerebral cortex.
- small and medium pyramidal neurons
- send axons to adjacent cerebral cortex
pyramidal shape,
State the composition of the internal granular layer of the cerebral cortex.
- small stellate neurons
- recieve specific sensory input
- thick layer in sensory areas of the cortex (eg. primary visual area)
State the composition of the internal pyramidal layer of the cerebral cortex.
- medium to large pyramidal neurons
- send axons to the white matter
- thick layer in the motor area of the cortex
LARGER pyramids
State the composition of the fusiform (multiform) layer of the cerebral cortex.
- many spindle shaped neurons
- send axons into the white matter
- deep to this layer, the cerebral white matter is composed of nerve fibers going to and coming from the cortex.
SPINDLE SHAPED
How many layers is the cerebellar cortex divided into?
3 layers
What are the 3 layers of the cerebral cortex?
1) molecular layer
2) granule cell layer
3) piriform cell layer (purkinje cell layer)
State the composition of the molecular layer of the cerebellar cortex.
- neuropil
- only nerve processes (no neurons)
- most superficial
State the composition of the granule cell layer of the cerebellar cortex.
- adjacent to the white matter
- DENSELY packed granule cells (SMALL NEURONS)
How does the graular cell layer of the cerebellum compare with the cerebrum?
cerebellum= densely packaged= 5x more neurons
State the composition of the piriform cell layer of the cerebellar cortex. What is its other name? Where is it located?
piriform layer= purkinje cell layer
- single layer of LARGE cell bodies
- located at the interface of the molecular and granule cell layers
very small SINGLE layer but BIG cells
How many layers is the brain stem divided into?
- NOT clearly seperated into regions of gray and white matter
What is visible throughout the structure of the brain stem?
Nuclei of cranial nerves:
- appear in islands
- surrounded by distinct tracts of white matter
State the composition of the nuclei of the brain stem.
- contain cell bodies of motor neurons (of cranial nerves)
- morphologic and functional counterparts of the anterior horns of the spinal chord
How are neurons oriented in the lower part of the brain stem?
white matter is oriented:
- transversely
- longitudinally
and is intermixed with gray matter with faintly prominent neurons.
Why is the spinal chord important?
nerves go through the spinal chord
- protects nerves
- provides a distinct tract
What is the spinal chord?
a flattened cylindrical structure that is directly continuous with the brain stem
State the organization of the spinal chord.
- divided into segments
- segments are connected to pairs of spinal nerves
- spinal nerves are connected to its segment of the cord by a number of rootlets grouped as dorsal (posterior) or ventral (anterior) roots.
What are ganglions?
- part of PNS
- bodies of neurons are concenrated in this area
Where are body neurons concentrated?
- CNS: gray matter
- PNS: ganglions
Explain the visual anatomy of the spinal chord.
- opposite arrangement of gray and white matter: gray interior, white exterior
- the gray-matter surrounds the central canal
- the white matter surrounds the gray matter (peripheral substance)
What does the white matter of the spinal chord contain?
tracks of myelinated and unmyelinated axons traveling:
- to and from other parts of the spinal chord
- to and from the brain
What does the gray matter of the spinal chord contain?
- neuronal cell bodies
- neuronal cell dendrites
- neuronal cell axons
- central neuroglia
What are “nuclei”?
Functionally related groups of nerve cell bodies in the gray matter.
- nucleus= cluster/group of neuronal cell bodies, fibers and neuroglia
Compare the nuclei of the CNS and PNS.
nuclei of the CNS are the morphologic and functional equivalents of the ganglia of the PNS.
What only occurs in the gray matter of the spinal chord?
synapses
What is the major difference between the gray matter in the brain and spinal chord?
Spinal chord doesn’t have layers like the molecular, pyramidal or granular layers found in the brain.
How is the spinal cord divided into layers? What are they?
anatomically divided into sections:
- dorsal horn
- intermediate gray
- ventral horn
Where are sensory neuron cell bodies located in the spinal nerve?
In GANGLIA which lie on the dorsal root of the spinal nerve.
State the polarity of sensory neurons in the dorsal root ganglia.
pseudounipolar
Explain the polarity of sensory neurons in the dorsal root ganglia.
psudounipolar:
- single process
- divides into a peripheral segment (brings information from the periphery to the cell body)
- divides into a central segment (brings information from the cell body to the gray matter of the spinal chord)
Where are the cell bodies of motor neurons that innerviate striated muscles located?
In the ventral (anterior) horn of the gray matter.
What are ventral motor neurons? Other name?
- ventral motor neurons = anterior horn cells
- large, basophyllic cells
- easily reorganized in routine histologic preparations
Do motor neurons have direct connection to sensory nerves?
no!
- no direct connection
- connected by interneurons (bipolar neurons- 1 axon, 1 dentrite)
What connective tissue is present in the CNS?
Meninges: connective tissue membranes covering the brain and spinal chord
- dura mater (outermost)
- arachnoid (middle)
- pia mater (directly on the surface if the brain and spinal chord)
What two layers have a very similar developmental patter? What is it? What does this lead to?
- arachnoid and pia mater
- called by 1 name: pia-arachnoid
- single layer of mesenchyme surrounding the developing brain
State the portions in adults of which the pia mater and arachnoid occupy.
pia mater: visceral portion
arachnoid: parietal portion
What is the location of the arachnoid? What structures does it have?
- abuts on the inner surface of the dura mater
- extends delicate arachnoid tubercules to the pia mater (on the surface of teh brain and spinal chord)
What name do the web-like trabeculae of the arachnoid give this layer?
Gr. resembling a spider’s web
‘arachnoid’ structure= ‘spider-web looking’ structure
What are the arachnoid trabeculae composed of?
- loose connective tissue fibers
- containing elongated fibroblasts
What do the arachnoid trabeculae create? What is its name? What is it filled with?
- subarachnoid space (spaced bridge)
- contains: cerebrospinal fluid
What is the location of the pia mater?
lies directly on the surface of the brain and spinal chord
What is the composition of the pia mater? What is it continuous with?
connective tissue layer
- continuous with the perivascular connective tissue sheath of blood vessels of the brain and spinal chord
What are the surfaces of the pia mater and the arachnoid covered with? Which parts?
- arachnoid (both surfaces)
- pia matter (inner surface)
- trabeculae
covered with thin squamous epithelial layer.
What happens to the arachnoid and pia mater as they exit the dura mater? Where does this occur?
- the arachnoid and pia mater fuse
- fuse around the opening for the cranial and spinal nerves
State the differences in thickness between the 3 meninges.
dura mater: thickest
pia mater: thinnest
arachnoid: thin however filled with cerebrospinal fluid making it look large
What 3 spaces exist between the membranes?
- epidural space
- subdural space
- subarachnoid space
Where is the epidural space located? What does it include? What is its function?
- area between the dura mater and the vertebral wall
- contains fat and small blood vessels
- protection from temperature changes and physical impacts (ammortisation)
large
Where is the subdural space located?
- opened seperation between the arachnoid and dura mater
- doesn’t really exist: arachnoid and dura mater are attached very tightly
- space can become larger due to physcial trauma
Where is the subarachnoid space located?
- interval between the arachnoid membrane and the pia mater
largest space
What is the largest and smallest space bewteen the membranes?
largest: subarachnoid space
smallest: subdural space
What does the peripheral nervous system consist of?
- peripheral nerves with specialized nerve endings
- ganglia containing nerve cell bodies (residing outside the CNS)
What are the nerves of the PNS made up of? What are their functions?
- made up of many nerve fibers
- carry sensory and motor (effector) information between the organs and tissues of the body and spinal chord
Where can the cell bodies of peripheral nerves be located?
- within the CNS
- outside the CNS in peripheral ganglia
What do ganglia contain?
- clusters of neuronal cell bodies
- nerve fibers leading to and from cell bodies
What cell bodies belong to sensory neurons?
- dorsal root ganglia cell bodies
- ganglia of cranial nerves
- sensory neurons (somatic afferents and visceral afferents) = autonomic nervous system
What cell bodies belong to the postsynaptic (motor) neurons?
- paravertebral ganglia cell bodies
- prevertebral ganglia cell bodies
- terminal ganglia cell bodies
- motor neurons (visceral efferents)= autonomic nervous system
What is the ganglion? What is it made up of?
- additional small organ
- covered by other organs with a irregular connective tissue capsule
- contains fibers (processes of neurons)
- covered by structures such as myelin
What are the round structures in the ganglion?
bodies of pseudounipolar neurons
