Lecture 1 Flashcards
Organs
CNS=
PNS= (2 types)
CNS=Brain & Spinal Cord
PNS=Nerves
-cranial nerves and branches
-spinal nerves and branches
Stroma-
Parenchyma-
Stroma - Support tissue in organs (glia, blood vessels, CT)
Parenchyma - Functional tissue in organs (neurons)
What are tissue cells within organs?
- Neurons (parenchyma)
2. Glia (stroma)
Directional Terms for Brain: Rostral- Caudal- Ventral- Dorsal-
Rostral - anterior
Caudal - posterior
Ventral - inferior
Dorsal - superior
Dendrites and Soma: Afferent/Efferent? Mechanical or chemical stimuli? What ion channels? Graded potential (small or large?)
- Receive afferent mechanical and chemical input/stimuli
- Open mechanical (sensor/receptor) and chemical (neurotransmitter) gated Na+ and K+ ion channels on dendrite and soma to generate a depolarizing change in membrane electrical potential (graded potential)
- Small but proportional to intensity of initial mechanical/chemical stimuli
Axon Hillock:
Where/What is it?
How do grade potentials reach?
All or nothing -
- Region at base of axon connected to soma
- Trigger zone for AP
- Graded potentials from dendrite/soma will reach axon if they sum to threshold = -55mV
- Voltage gated sodium and potassium channels open to generate AP which is all or nothing
- All or nothing: always same intensity over entire distance of neuron
Axon:
What is it?
Afferent/efferent?
- Carries AP
- Efferent output to axon terminals
Axon terminals:
How many per axon?
Does AP travel to all terminals?
What occurs once AP reaches terminal?
- Generally many axon terminals associated with a single axon due to collateral and terminal branching
- Single AP generated by axon hillock reaches all axon terminals
- Voltage gated Ca2- channels open (Ca2- travels into presynaptic neuron) to trigger the release of neurotransmitter
Synapse:
Describe the parts
What do the NT do here?
- Intercellular junction between axon terminal (pre-synaptic membrane) and target cell membrane (post synaptic membrane - usually dendrite/some of next neuron in communication chain)
- NT opens chemical gated channels on post synaptic membrane to generate a depolarization
Axonal Transport:
Fast Anterograde -
(nonstop microtubule transports-)
Kinesin or Dynein?
Fast anterograde - Moves proteins associated with vesicle (peptide NT, enzymes, and membrane proteins) from golgi apparatus in soma to synaptic terminals
- Nonstop microtubule transport = fast transport
- Kinesin
Axonal Transport:
Slow Anterograde -
(stop and go microtubule transports = )
Slow Anterograde = axioplasmic flow
- Moves soluble (non membrane bound/associated) cytoskeletal, proteins from soma to axon terminals
- Stop and go microtubule transport = slow transport
Axonal Transport:
Fast retrograde
(nonstop microtubule transport = )
Kinesin or Dynein?
Fast retrograde
- Moves endocytosis vesivles (recycle membrane, chemical messengers, pathogens) from axon terminals to soma
- Nonstop microtubule transport = but slower than fast anterograde
- Dynein
Axon structural variation leads to variation in signal conduction velocity:
- What two variations?
- Classifications -
Variations:
1. Fiber diameter
2. Thickness of myelin
Classifications:
1. Conduction velocity - type A, B, C from fastest to slowest
2. Fiber diameter - Type I, II, III, IV from biggest to smallest
*Look at chart
Direction of signal transmission starting with Dendrite ->
Dendrite -> soma -> axon hillock -> axon -> axon terminal
3 Types of Neurons function:
1. Sensory
Describe
Name 3 types
- Sensory - axons in peripheral nerves carry afferent signals from sensor/receptors to CNS (brain/spinal cord)
- Special
- Viscero
- Somato
1st Type Sensory Neurons
Special Sensory=
Special Sensory=
- Vision: retina to CN 2
- Auditory: Spiral organ corti to CN 8
- Equilibrium: macula (static) and crista ampullaris (dynamic) to CN 8
- Olfaction: olfactory epithelium to CN 1
- Gustatory: taste buds to CN 7, 9, and 10
2nd Type Sensory Neurons
Viscerosensory =
Single neuron from interoreceptors (unconscious) to subcortical CNS
Ex: diffuse temp
3rd Type Sensory Neurons
Somatosensory =
Single neuron from skin, muscle, and joint (conscious) receptors to cortex
ex: Temp, pain, touch
3 Types of Neurons:
2. Motor
Describe
Name 2 types
- Motor - axons in peripheral nerves carry efferent signals to effectors (muscles and glands)
- Somatomotor - single neuron from CNS to skeletal muscle (voluntary)
- Autonomic motor - 2 neuron pathway from CNS to smooth muscles, cardiac muscle, or glands (involuntary) - Sympathetic - activates fight or flight (lateral horn at T1-L2)
- Parasympathetic - activates rest and digest (lateral horn S2, 3, 4
Types of neurons structural: (name where there are usually found)
Multipolar -
Bipolar -
Pseudo-unipolar -
Multipolar - soma with single axon and multiple dendrites (common in CNS)
Bipolar - soma with a single axon and a single dendrite stalk (common in special sensory organs)
Pseudo - unipolar - single axon with a proximal (efferent) and distal branch (afferent) (found in sensory neurons of dorsal root ganglion)
Types of synapses (3):
Name them and describe
- Axosomatic - axon with soma
- Axodendritic - axon with dendrites
- Axoaxonal - axon with axon
(will modulate effect of NT - their bonding or amount)
Neuron Loops:
Describe pathway
-Negative feedback loop (reflex loops)
Sensor/receptor -> sensory neuron -> control center (brain/spinal cord) -> motor neuron -> effector (muscle/gland)
Neuron Circuits (4): 1. Diverging
Diverging - allows amplification of mass activation of many targets
-Can be in same or to multiple pathways
Neuron Circuits (4): 2. Converging
Converging - increase stimulation or inhibition of postsynpatic neuron (stronger signal with stronger output)
-can be from multiple sources or from single source with many axon terminals
Neuron Circuits (4): 3. Reverberating
Reverberating - allows circular, self stimulation perpetuation of signal (creates tone)
Neuron Circuits (4): 4. Parallel after discharge
Parallel after discharge - diverges then converges to increase the frequency of output
Glial Cells:
Parenchyma/stroma?
Describe
- Stroma
- Function as neuron support cells
- Typically 10 glia for every neuron
Glia in CNS =
name 4
Glia in CNS = neuroglia
- Astrocytes
- Oligodendroctyes
- Microglia
- Ependymal Cells
Glia in CNS (4):
- Astrocytes:
- Provide Support
- Control NT access
- Insulation
- BBB
- Tissue repair
Astrocytes - associated with neurons, capillaries, and pia mater of CNS
- Provide support
- Physical
- Protective: condition interstitial fluid around neurons by removing or adding ions
- Nutritional: conduit to deliver nutrients from blood vessles
- Regulate intracellular Ca++ levels in neurons - Control NT access to neurons - barriers to spread NT out of synapse or NT uptake at synapse
- Insulation to isolate electrical activity of adjacent neurons
- Blood Brain Barrier
- Tissue repair on CNS lesions
* most brain tumors develop from astrocytes
Glia in CNS (4):
2. Oligodendrocytes
Form myelin sheaths in CNS (white matter)
-can myelinate more than one axon
Glia in CNS (4):
3. Microglia
Phagocytes
Glia in CNS (4):
4. Ependymal Cells
- Ependymal Cells - line ventricles and central canal facilitating exchange between CSF and interstitial fluid of brain (ciliated to facilitate flow of CSF)
- Tanycytes - transfer substances from CSF to circumventricular organs (pineal, pituitary, and hypothalamus)
- Choroidal epithelial cells - cover capillary tufts of choroid plexus
- Form a unit with endothelial cells of choroid plexus to produce CSF
Glia in PNS (2):
- Schwann Cells
- Satellite Cells
- Schwann Cells - form myelin sheaths in PNS
- All peripheral nerve processes are in contact with Schwann cells even unmyelinated axons - Satellite Cells - found around neurons particularly associated with soma of ganglia where they function like astrocytes in physically supporting neurons and conditioning the interstitial fluid
Myelin Sheath:
Formed by WHAT in the CNS and PNS?
What made out of?
Describe Node of Ranvier & Salutatory conduction
- Formed by oligodendroctyes in CNS
- Formed by Schwann cells in PNS
- Glial cells attach to axons in series and their cell membranes wrap around axon to form the myelin sheath
- Not continuous - between adjacent glial cells, there is gap = node of Ranvier - enable regeneration of AP and salutatory conduction (fast signal transmission)
Nerves: (General description)
Collection of what?
-Collection of neurons (motor/sensory) = parenchyma
and glia = stroma (also blood vessels and CT)
-Organized in parallel
-Associated with a common region
Structure: Fiber - endoneurium - fascicle - perineurium - whole nerve - epineurium -
Fiber - single cell endoneurium - CT covering of a fiber fascicle - bundle of fibers perineurium - CT covering fascicle whole nerve - bundle of fascicles epineurium - CT covering a whole nerve
Spinal Nerves: (describe what you find in each) Roots - Dorsal Root - Dorsal root ganglion - ventral root -
Roots - Connect the spinal nerves to spinal cord
Dorsal Root - (posterior) contains axons of sensory neurons only both somatosensory and viscerosensory neurons
Dorsal root ganglion - associated with the dorsal root; it contains cell bodies of somatosensory and viscerosensory neurons
ventral root - (anterior) contains axons of both somatomotor and autonomic motor neurons
Rami -
Describe
What nerves do they contain?
Rami - connect spinal nerves to peripheral structures
-mixed in that they contain axons of both sensory (somato and viscerosensory) and motor (somato and autonomic) neurons
Dorsal Rami -
Where do they go?
What type of neurons?
- Posterior
- Branch into peripheral nerves to deep back muscles, vertebral column, and skin of the back (mixed sensory/motor)
Ventral Rami -
Where do the go?
Fused vs unfused
- Anterior
- Branch into peripheral nerves to anterior and lateral trunk, and upper and lower limbs
1. Fuse to form nerve plexus
2. Unfused to form segmental nerves (thoracic region)
Ventral Rami that form R/L plexi: Cervical Plexus- Brachial- Lumbar- Sacral-
Cervical Plexus- C1-C5
Brachial- C5-T1
Lumbar- L1-L4
Sacral- L4-S4
Rami communicantes connect ventral rami to:
Paravertebral ganglia -
Prevertebral ganglia -
Paravertebral ganglia - sympathetic chain ganglia
Prevertebral ganglia - celica, superior mesenteric, aorticorenal, and inferior mesenteric sympathetic ganglia
Peripheral sensory pathways: (describe pathway)
# of neurons?
Where soma located?
- Both viscero and somatosensroy carried by a single neuron from sensor/receptor to the spina cord
- Sensory neuron soma is located in the dorsal root ganglion
- Reach spinal cord dorsal horn via dorsal root
Motor pathways: (describe pathway)
# of neurons?
Where soma located?
- Somatomotor signals carried by a single neuron
- Soma in ventral horn
- From spinal cord to skeletal muscle
Autonomic motor pathway: (describe pathway)
# of neurons?
Where soma located?
- Carried by 2 neurons:
1. Preganglionic neuron with soma in lateral horn (T1-L2, S2-S4)
2. Postganglionic neuron with soma in ganglion - From spinal cord to smooth muscle, cardiac muscle or glands
Segmentation:
Dermatome -
Myotome -
Dermatome - region of skin whose somatosensory signals are carried by a particular spinal nerve
Myotome - all muscles innervated by a particular spinal nerve
Cranial nerves (general description)
- 12 pairs nerves connect primarily head structures to brain
- Contain all 3 sensory neuron types and both motor neuron types
CN 1 - CN 2 - CN 3 - CN 4 - CN 5 - CN 6 -
CN 1 - Olfactory: carries olfactory special sensory signals
CN 2 - Optic: visual special sensory signals
CN 3 - Occulomotor: somatomotor signals to eye muscles
CN 4 - Trochlear: somatomotor to eye muscles
CN 5 - Trigeminal: somatosensory from head
CN 6 - Abducent: somatomotor to eye muscles
CN 7 - CN 8 - CN 9 - CN 10 - CN 11 - CN 12 -
CN 7 - Facial: Special sensory for tast; somatomotor to facial muscles
CN 8 - Vestibulocochlear: Special sensory for both auditory and equilibrium
CN 9 - Glossopharyngeal: special sensory for taste
CN 10 - Vagus: Parasymp to organs in thorax and abdomen
CN 11 - Spinal Accessory: somatomotor to neck/shoulder muscles
CN 12 - Hypoglossal: somatomotor to tongue
Which cranial nerves provide parasympathetic innervations?
3, 7, 9, 10
Meninges -
Name layers
Meninges - 3 CT coverings encircling the brain and spinal cord
Dura matter -> subdural space -> arachnoid mater -> subarachnoid space -> pia mater
Meninges:
Dura mater -
Epidural fat -
Subdural space -
Dura mater - outermost layer; dense irregular CT
Epidural fat - protective layer of adipose tissue lying between the vertebral column and the spinal cord not present in cranial cavity
Subdural space - interstitial fluid in a virtual space
Meninges:
Arachnoid mater -
Subarachnoid space -
Arachnoid mater - middle layer; loose CT (delicate, web-like arrangement of collagen ad some elastic fibers)
Subarachnoid space - Cerebrospinal fluid here (CSF)
Meninges:
Pia Matter -
Pia mater - innermost layer, loose CT
-Highly vascularized
Cerebrospinal Fluid (CSF): How produced (mention choroid plexuses, ependymal cells, bbb) ?
- CSF forms a protective cushion and buoys the brain and spinal cord
- Produced mostly by filtration of blood plasma through specialized capillaries called choroid plexuses which have an outer covering of ependymal cells (type of glial cell) that contribute to the bbb (prevent large molecules from leaving blood and entering the ECF of brain tissue)
- Choroid plexi located in all 4 ventricles
CSF:
Arachnoid Villi-
Arachnoid Villi - Project into superior sagittal sinus
- Specialized capillaries that return CSF to circulatory system
- Have one way valves that allow flow only into the superior sagittal sinus
Ventricles: Right - Left - 3rd - 4th -
Right - located in right hemisphere in all 4 lobes
left - left hemisphere in all 4 lobes
3rd - located between hemispheres at level of thalamus/ hypothalamus (diencephalon)
4th - brain stem level of pons/cerebellum and upper medulla
Ventricles are interconnected:
Interventricular foramen (foramen of monroe) - connect lateral ventricles to 3rd
Cerebral aqueduct of sylvius - connects 3rd and 4th
2 Lateral apertures (foramena of Lushka) and 1 Medial aperture (forament of Magendie) - connect 4th ventricle to subarachnoid space
Flow of CSF due to pressure gradient from high to low pressure:
Lateral ventricles (choroid plexus) -> interventricular foramen -> 3rd ventricle (choroid plexus) -> cerebral aqueduct of sylvius -> 4th ventricle (choroid plexus) -> lateral/medial apertures -> cerebellomedullary cistern (cistern magna) ->
- Subarachnoid space brain -> arachnoid villi -> blood
- Subarachnoid space of spinal cord-> subarachnoid space brain-> arachnoid space -> blood
BBB:
What does it do?
What does it consist of?
BBB - blocks capillary exchange of hydrophilic substances
- Does not block hydrophobic substance exchange
Consists of:
1. Continuous capillary endothelium with tight junctions
2. Thick basement membrane
2. Covering astrocytes
Circumventricular organs:
Name 3 main organs
-Have no BBB to monitor the chemical composition of blood 3 Main organs: 1. Hypothalamus 2. Pituitary 3. Pineal Gland
