Lecture 1 - Histology of the Nervous System Flashcards
What is the nervous system?
Communication system that relies on chain of cells to physically connect the message source to the message target.
What are the 2 components of the nervous system?
- Organs
- Tissue Cells
What are the organs of the nervous system?
- CNS
- PNS
What makes up the CNS?
Brain and spinal cord
What makes up the PNS?
- Cranial nerves
- Spinal nerves
Are all of the cranial nerves part of the PNS?
All of them except for CN2 (optic)
What are the 4 tissue types and how many are needed to make up an organ?
- Muscular, Nervous, Epithelial, and Connective
- 2
The tissue layer which plays the main role in the function of the organ is referred to as what?
Parenchyma (functional tissue)
The tissue layer which provides support to the organ, such as protecting the parenchyma or providing shape to the organ, is referred to as what?
Stroma (support tissue)
The functional tissue (parenchyma) of the nervous system is involved in what?
Communication
What makes up the support tissue (stroma)?
- glial cells
- blood vessels
- CT
Are neurons considered parenchyma or stroma and why?
Parenchyma because they perform the functional part of the nervous system. They receive and send signals.
What are the 2 tissue cells of the nervous system?
- Neurons
- Glial
What are the directional terms for the brain?
- Rostral (anterior)
- Caudal (posterior)
- Ventral (inferior)
- Dorsal (superior)
NEURONS
NEURONS
Dendrites and Soma recieve what type of input?
afferent (stimuli)
What are the two types of input received by the dendrite and soma?
- Mechanical (sensor/receptor)
- Chemical (neurotransmitter)
The stimuli received by the dendrites and soma open sodium and potassium ion channels on the dendrite and soma to generate a depolarizing change, what is this called?
Graded potential
What is located at the base of the axon and acts as the trigger zone for action potentials?
Axon hillock
What is the mV required for an action potential to occur? How does this occur? What is this called?
- (-55mV)
- This occurs when 2 graded potentials get to the axon hillock at the same time.
- Summation
What are the 2 types of summation and how are they different?
- Temporal summation- this occurs when 2 graded potentials come from the same point on the dendrites.
- Spatial summation- this occurs when 2 graded potentials come from different points on the dendrite.
What part of the neuron carries the AP?
Axon
What type of output is occuring at the axon and where is it going to?
- efferent output
- axon terminal
Conduction at the axon can be either _______ or _________ conduction.
What is the difference?
- Continuous- no myelinization on the axon
- Saltatory- myelin sheath located on the axon
Is continuous or saltatory conduction faster?
saltatory
In saltatory conduction, the AP is traveling between what?
Nodes of Ranvier
What comes after the axon?
axon terminal
Does a single AP reach all axon terminals?
Yes
What happens at the axon terminals?
Voltage gated Ca+ channels open, causing the release of neurotransmitters.
What is the synapse?
Intercellular junction between pre-synaptic membrane (axon terminal) and post-synaptic membrane (target cell)
What is the function of the neurotransmitter?
opens chemical gated channels to generate a depolarization on the postsynaptic membrane
What are the 3 main types of axonal transport?
- Fast anterograde
- Slow anterograde
- Fast retrograde
Both fast and slow anterograde proteins from ______ to _______.
soma to axon terminal
Fast anterograde is considered a ______ microtubule transport while slow anterograde is considered __________ microtubule transport.
- nonstop
- stop and go
What causes the conduction velocity in an axon to be greater?
- fiber diameter
- thickness of myelin
What are the 2 classification to quantify AP velocity?
- conduction velocity
- fiber diameter
What is the scale of conduction velocity and which is the fastest?
- scale goes from A-C
- A is the fastest, C is the slowest
What is the scale of fiber diameter and which is the fastest?
- scale from I-IV
- I is the fastest, IV is the slowest
Where does nocioception (pain) fall on the scale of conduction velocity?
Pain is the slowest in regards to conduction velocity
What is the general direction of signal transmission?
- dendrite
- soma
- axon hillock
- axon
- axon terminal
- synapse
What are the 3 types of neuron functions?
- Sensory
- Motor
- Associative
What is the broad definition of sensory neurons?
Axons in the periphery that carry afferent signals from sensor/receptors to the CNS (brain and spinal cord)
What are the 3 subtypes of sensory neurons?
- Special sensory
- Viscerosensory
- Somatosensory
What nerves are involved in special sensory?
cranial nerves
What are the 5 special senses and what is their exact cranial nerve innervation?
- vision= CN2
- auditory= CN8
- equilibrium= CN8
- olfaction= CN1
- gustatory (taste)= CN7,9,10
What is the difference between viscerosensory and somatosensory?
- Viscerosensory transmits signals from our internal organs to the CNS and are thus unconscious.
- Somatosensory transmits signals from skin or skeletal muscle to the CNS and are thus conscious.
Does viscerosensory or somatosensory maintain homeostasis?
viscerosensory
Is there a single or two neurons involved in the transmission of sensory information?
one single neuron
What is the broad definition of motor neurons?
Axons in the peripheral nerves that carry efferent signals from the CNS to the effectors.
Motor neurons carry signals to muscles as well as what?
Glands
What are the 2 subtypes of motor neurons?
- Somatomotor
- Autonomic motor
What are the main differences between somatomotor and autonomic motor?
- Somatomotor- SINGLE neuron that carries signals from CNS to skeletal muscle (VOLUNTARY)
- Autonomic motor- TWO neuron pathway that carries signals from the CNS to smooth muscle, cardiac muscles, or glands (INVOLUNTARY)
The autonomic nervous system is divided into what 2 parts?
Sympathetic- fight or flight
Parasympathetic- rest and digest
What is an associative (interneuron)?
- Connects sensory and motor neurons
- Consists of the brain and spinal cord
What are the three types of neuron structures?
- Multipolar
- Bipolar
- Pseudo-unipolar
A multipolar neuron is a soma with a _______ axon and _______ dendrite.
Where is this common?
Where is the soma located in this structure?
- single, multiple
- common in the CNS
- at side of dendrite
A bipolar neuron is a soma with a _____ axon and _______ dendrite stalk.
Where is this common?
Where is the soma located in this structure?
- single, single
- special sensory
- in the middle of the axon
A pseudo-unipolar neuron has a ______ axon with a __________ and _______ branch.
Where is this found?
- single, proximal (efferent), distal (afferent)
- sensory neurons of dorsal root ganglion (DRG)
What is the neuronal structure of viscero and somatosensory?
psuedo-unipolar
What are the 3 types of synapses?
- Axosomatic
- Axodendritic
- Axoaxonal
What is the order of the neuron loop?
- sensor/receptor
- sensory neuron
- control center= brain/spinal cord (associative/interneuron)
- motor neuron
- effector (muscle or gland)
What are the 4 types of neuron circuits?
- Diverging
- Converging
- Reverberating
- Parallel after discharge
Describe the structure and function of a diverging circuit.
Structure
-1 neuron splits to 2, which splits into 4
Function
-allows for mass activation of multiple targets
Describe the structure and function of a converging circuit.
Structure
-3 pre-synaptic converge to 1 post-synaptic
Function
-increases stimulation or inhibition of post-synaptic neuron
Describe the structure and function of a reverberating circuit.
Structure
-acts as a loop to act on previous neurons in the chain
Function
-allows perpetuation of a signal
Describe the structure and function of a parallel after discharge circuit.
Structure
-1 neuron splits into parallel portions then converges back to a single neuron distally
Function
-increases the frequency of the output
GLIAL CELLS
GLIAL CELLS
What are the 4 types of glial cells?
- Astrocytes
- Oligodendrocytes
- Microglia
- Ependymal cells
What are the main functions of astrocytes?
- provide support (physical, protective(condition ISF around neurons by removing or adding neurons), nutritional, regulate intracellular Ca+ levels in neurons
- control NT access to neurons
- insulation to isolate neurons electrical activity
- maintain the BBB
- neuronal tissue repair of CNS lesions
What is the function of oligodendrocytes?
Forms myelin sheaths in CNS (white matter)
What is the main function of microglia?
Primary immune defense of CNS (phagocytes)
What are the functions of ependymal cells?
- found in walls of ventricles and facilitate flow and exchange between CSF and ISF of the brain
- tanycytes transfer chemical signals from CSF to CNS (pineal, pituitary, hypothalamus)
- specialized ependymal cells (choroidal epithelial cells) cover capillary tufts of choroid plexus and form a unit withe choroid plexus to produce CSF
What are the 2 glial cells found in the PNS?
- Schwann cells
- Satellite cells
What is the difference between Schwann cells and oligodendrocytes?
- Schwann cells form myelin sheaths in the PNS, while oligodendrocytes form myelin sheath in the CNS (white matter)
- Schwann cells also form individual myelin sheaths while oligodendrocytes form multiple
How do satellite cells function like astrocytes?
They also act to physically support the neurons and condition the ISF
Glial cells wrap around the axon to form what?
Myelin sheath
What seperates myelin sheaths?
Nodes of Ranvier
What is the function of the Nodes of Ranvier?
enable regeneration of AP and salutatory (fast) signal transmission
NERVES
NERVES
What is the difference between a neuron and a nerve?
- A neuron is a single cell in the nervous system that, working with other neurons carries out the electrochemical impulses.
- A nerve is a collection of neurons (typically motor and sensory), organized in parallel that are associated with a common region.
What is the structure order of a nerve from the inside out?
- fiber (single cell)
- endoneurium (connective tissue covering fiber)
- fascicle (bundle of fibers)
- perineurium (connective tissue covering a fascicle)
- whole nerve (bundle of fascicles)
- epineurium (connective tissue covering whole nerve
What are the 2 main parts of spinal nerves?
- roots
- ramus
What do roots connect?
connect spinal nerves to spinal cord
What are the 3 main parts of the spinal roots?
- dorsal (posterior) root
- dorsal root ganglion (DRG)
- ventral (anterior) root
The dorsal (posterior) root contains what neurons?
- somatosensory
- viscerosensory
The DRG is associated with the dorsal root and contains what?
cell bodies of the somatosensory and viscerosensory neurons
The ventral root contains what neurons?
- somatomotor
- autonomic motor
The ventral root connects to what 2 structures?
- ventral horn
- lateral horn
Where in the spinal cord are lateral horns found?
- T1-L2 (sympathetic)
- S2-S4 (parasympathetic)
What do rami connect?
spinal nerves to peripheral structures
Why are rami considered mixed?
They contain axons of both sensory (somato- and viscerosensory) and motor (somato- and autonomic) neurons.
Dorsal rami branch to what structures?
Peripheral nerves to:
- deep back muscles
- vertebral column
- skin of the back
Ventral rami branch to what structures?
Peripheral nerves to:
- anterior and lateral trunk
- upper and lower limbs
Ventral rami fuse to form what?
Nerve plexus
In the _______ region, the ventral rami are unfused to form segmental nerves.
thoracic
What are the 4 plexi and their locations in regards to nerves?
- Cervical plexus-C1-C4
- Brachial plexus-C5-T1
- Lumbar plexus-L1-L4
- Sacral plexus-L4-S4
Rami communicantes connect ventral rami to what?
- Paravertebral ganglia= sympathetic chain ganglia
- Prevertebral ganglia= celiac, superior mesenteric, aorticorenal, and inferior mesenteric sympathetic ganglia
Both viscero and somatosensory signals are carried by a ________ neuron from a sensor/receptor to the spinal cord.
The sensory neuron soma is located in the __________ and reach the dorsal horn via __________.
- single
- dorsal root ganglion (DRG)
- dorsal root
Somatomotor signals are carried by a _______ neuron with its soma in the __________, from spinal cord to ____________.
- single
- ventral horn
- skeletal muscle
Autonomic motor neurons are carried by _____ neuron, a preganglionic neuron with soma in the ________ and a postganglionic with soma in a ganglion from the spinal cord to _______ or _______ muscle and _______.
- two neurons
- lateral horn (T1-L4 or S2-S4)
- smooth, cardiac, glands
Segmentation includes what 2 aspects? What is the difference between the 2?
- dermatomes- region of skin whose somatosensory signals are carried by a particular spinal nerve
- myotome- all muscles innervated by a particular spinal nerve
List the 12 Cranial nerves and their function
CN1= olfactory nerve
-carries olfactory special sensory signals
CN2= optic nerve
-carries visual special sensory signals
CN3= occulomotor nerve
-carries somatomotor signals to eye muscles
CN4= trochlear nerve
-carries somatomotor signals to eye muscles
CN5= trigeminal nerve
-carries somatosensory signals from the head
CN6= abducent nerve
-carries somatomotor signals to eye muscles
CN7= facial nerve
-carries special sensory singal for taste; somatomotor signals to facial muscles
CN8= vestibulocochlear nerve
-carries special sensory signals for both auditory and equilibrium
CN9= glossopharyngeal nerve
-carries special sensory signals for taste
CN10= vagus nerve
-carries parasympathetic signals to organs in thorax
CN11= accessory nerve
-carries somatomotor signals to neck/shoulder muscles
CN12= hypoglossal nerve
-carries somatomotor signals to tongue
What cranial nerves provide parasympathetic innervations?
3, 7, 9, and 10
MENINGES
MENINGES
What are meninges?
The three connective tissue coverings encircling the brain and spinal cord
How are the meninges and their spaces organized?
- tissue
- fluid
- tissue
- fluid
- tissue
What are the 3 tissues called?
- dura mater
- arachnoid mater
- pia mater
What are the parts of the dura mater?
- epidural fat
- subdural space
What space contains CSF?
subarachnoid space
CSF is produced mostly by filtration of blood plasma through specialized capillaries called what? In which ventricles are they located?
- choroid plexuses
- all 4 ventricles
CSF returns to the circulatory system by draining through specialized capillaries called what?
Arachnoid villi
What are the ventricles and where are they located?
- right ventricle- located in right hemisphere in all 4 lobes
- left ventricle- located in left hemisphere in all 4 lobes
- 3rd ventricle- located between hemispheres at level of thalamus/hypothalamus
- 4th ventricle- located brain stem at level of pons/cerebellum and upper medulla
What connects the lateral ventricles to the 3rd ventricle?
interventricular foramen (foramen of Monroe)
What connects the 3rd ventricle to the 4th ventricle?
cerebral aqueduct of Sylvius
What connects the 4th ventricle to the subarachnoid space?
- 2 lateral apertures (foramena of Lushka)
- 1 medial aperture (foramen of Magendie)
What do all 4 ventricles have in common?
They all have choroid plexuses and produce CSF
What is the flow of CSF due to?
pressure gradient
List the flow of CSF.
- lateral ventricles
- interventricular foramen
- 3rd ventricle
- cerebral aqueduct of Sylvius
- 4th ventricle
- lateral and medial apertures
- cerebellomedullary cistern (cistern magna)
- subarachnoid space of spinal cord or brain
- arachnoid villi
- blood
What happens if there is more CSF production than drainage?
Hydrocephalus
What are the functions of the CSF?
- cushion brain
- circulate nutrients and chemicals filtered from the blood
- remove waste products from brain
BLOOD BRAIN BARRIER AND CIRCUMVENTRICULAR ORGANS
BLOOD BRAIN BARRIER AND CIRCUMVENTRICULAR ORGANS
The BBB blocks capillary exchange of what?
hydrophilic substances, does not block hydrophobic substance exchange
What 3 parts does the BBB consist of?
- continuous capillary endothelium with tight junctions
- thick basement membrane
- covering of astrocytes
What are the 3 circumventricular organs?
- hypothalamus
- pituitary
- pineal gland
What is different about circumventricular organs?
They dont have a BBB to monitor the chemical composition of blood
