Exam 1 Flashcards
(221 cards)
1
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Overview of the Nervous System
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- Sensory receptors (the afferent system) and motor neurons/effectors are part of the PNS
- Sensory info feeds into the CNS, where info is processed and sent to the effectors
2
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Cells of the Nervous system
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-Neurons- main cell responsible for integration and relay of messages -Glia- support neurons
3
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Neurons
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-Cell body and dendrites receive input -Axon hillock= summation of APs, integrative -Axon= conductive -Terminal branches= output -Metabolically compartmentalized- proteins made in cell body and dendrites only *Specialized cells that conduct APs over long distances (quickly)
4
Q
How do neurons vary?
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-Number of dendrites -Branching pattern of dendrites -One axon, but vary in # of collaterals
5
Q
What are the two types of neurons?
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-Projection neurons (sensory, motor, tract) -10% pop -Take info from one place to another (large distances) -Largest and best studied -Local Interneurons -90% -Unmyelinated -Modify info within local/small area -Small, difficult to study
6
Q
Pseudounipolar cells
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-One cell body, axon that starts as one and then branches into 2 collaterals -Ex: sensory neurons
7
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Multipolar cells
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-multiple dendrites and an axon -Ex: motor neuron– synapses to muscle
8
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Local Interneuron
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-no myelin -Multipolar
9
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Nissl Stain
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-Shows ribosomes bound to ER and nucleolus (site of RNA synthesis 4 ribosomes -Doesn’t stain axon -Stains proximal dendrites and cell body
10
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Neuronal Cytoskeleton
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-Microtubule- Largest, hollow tube, support axons, laid end to end -Neurofilament- stable, middle size -Microfilament- actin, found in parts of neurons that rapidly change (dendrites)
11
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Axoplasmic Transportation
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-How materials are moved within the cell -Use molecular motors and microtubules -Various rates of transportation -Anterograde- cell body to synapse -Retrograde- synapse to cell body
12
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Features of the synapse
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-Synaptic vesicles/secretory granules present at presynapse–> Hold NTMs -Postsynaptic density- proteins connecting the two synapses -Glia surround the synapse -Mitochondria at synaptic button produce ATP
13
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Dendritic Spines
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-Dendrites have numerous spines to maximize surface area to receive synapses -Neurons receive thousands of synapses which summate to create an AP
14
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Glial Cells
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CNS- -Ependymal cells -Microglia -Astrocytes -Oligodendrocytes PNS -Schwann cells -Satellite cells
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Ependymal cells
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-Line the ventricular system -Fluid-filled part of CNS -Cilia face inward to keep CSF moving
16
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Astrocytes
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-Most numerous -Surround neurons -Protoplasmic in gray matter -Fibrillar in white matter -Control extracellular environment (K+) -Take up NTMs -Break down glucose and pass it down to neurons
17
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Oligodendrocytes
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-Myelinate in CNS only, more than one axon -Each axon requires more than one oligodendrocyte
18
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Microglia
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-Derived from immune system, not nervous system -Phagocytes–> clean up cells -Respond to Injury -Found in resting state
19
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PNS Glia
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-Schwann cells myelinate only 1 axon in PNS —-Need many schwann cells to myelinated the same axon -Satellite cells- Support cells around neurons in ganglia
20
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Grey vs White Matter
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-G: Little myelin, mostly cell bodies and dendrites -W: a lot of myelin and oligodendrocytes
21
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Early Nervous System Development
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-Develops from ectoderm (outermost germ layer) -Begins to form at day 19- ectoderm worlds due to thickening of the neural plate -Neural groove–> neural tube–> CNS cells -Neural folds–> neural crest cells–> PNS
22
Q
Neural Crest Cells
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-Migrate to diff places and make ganglia -Become: —Sensory ganglia (dorsal root ganglia) —Autonomic ganglia (sympathetic, para-) —Enteric ganglia of the digestive system —Arachnoid and Pia covering (CNS) —Schwann cells —Adrenal medulla
23
Q
Ganglia
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-A collection of nerve cell bodies in the PNS -Formed from neural crest cells
24
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Neural Tube
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-Cells become CNS structures —Cerebrum- cerebral cortex and deep nuclei —Diencephalon, Midbrain, Pons, Cerebellum, Medulla —Spinal cord —Glial Cells of CNS
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Neural Tube at week 4
-3 primary brain vesicles form --Forebrain/Prosencephalon (rostral most) --Midbrain/Mesencephalon --Hindbrain/Rhombencephalon (caudal most)
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Neural Tube at week 5
- Forebrain splits to Telencephalon and Diencephalon
- Midbrain/Mesencephalon
-Hindbrain splits to Metencephalon and myelencephalon
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Telencephalon
-Outgrows all other parts of the brain--\> becomes cerebrum ---Expands and fold to increase surface area
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Sulci and Fissures
-Small grooves/valleys= sulci -Larger, deeper grooves= fissures
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Major Lobes in the Adult Brain
-Frontal lobe -Parietal lobe -Temporal lobe -Occipital lobe ----Central sulcus separates frontal and parietal ----Lateral fissure separates temporal from frontal and parietal
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Major Divisions of the Adult Brain
-Cerebrum -Brainstem -Cerebellum -Spinal cord
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Ventricular System of the Adult Brain
-Fluid filled space within vesicles -Choroid plexus-\> produces CSF -Inside= lumen
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Neural Tube Defects
-Occur when neural tube fails to close in development -Spina Bifida--\> failure to fuse at caudal end ---Meningocele--CNS coverings exposed to outside of body ---Meningomyelocele-- Menigies and neural components exposed to outside of body -Anencephaly-Failure of rostral neural tube to develop--\> no brain formation \*\*Caused by folic acid deficiency, high glucose levels, retinoid acid
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Neural tube breakdown
-Prosencephalon--\> Telencephalon + Diencephalon
---Tel--\> Cerebrum, cerebral hemispheres (cortex, white matter, basal nuclei), lateral ventricles
---Diencephalon--\> Thalamus, hypothalamus, epithalamus, 3rd Ventricle
- Mesencephalon- Brain stem, midbrain, cerebral aqueduct
- Rhombencephalon--\> Metencephalon + Myelenchepalon
---Metencephalon- brainstem, pons, cerebellum, part of 4th V
---Myelencephalon- Brainstem, medulla oblongata, 4th V -Spinal cord + central canal
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Cerebrospinal Fluid
-Fluid w/in neural tube -Produced by choroid plexus -Clear fluid; similar to interstitial fluid, but diff from plasma -Potassium, calcium, bicarbonate, and glucose levels tightly regulated--Brain not subject to variations seen in blood -Volume- 150ml; Daily Production= 500ml -Circulates in spaces within brain (ventricular system) and through subarachnoid space around brain
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Choroid Plexus
-Specialized ependymal cells that extract fluid and solutes from plasma and filter it -Located in the Lateral Ventricles
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Ventricular System Flow
Lateral Ventricles--\> Foramen of Monro--\> 3rd V--\> cerebral aqueduct--\> 4th ventricle--\> foramen of Magendie and Luschka (L and R)--\> Superior Sagittal Sinus--\> Arachnoid granulations
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Location of Ventricles
-Lateral Vs-\> under cerebral cortex -3rd-\> midline btwn L and R thalamus -Cerebral aqueduct-\> midline of midbrain -4th-\> btwn pons/upper medulla, cerebellum
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Problems in CSF circulation
-Blockage of circulation -Damage of arachnoid granulations -Overproduction-- rare \*Hydrocephalus--Not as dangerous in children cuz bones haven't fused \*Chiari malformation--\> CSF directed down central canal to spinal cord, compressing spinal cord tissue
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Spinal Taps
-How CSF samples are obtained -Needle inserted through skin btwn L4 and L5 -Test 4 abnormal: pressure, protein, glucose, blood cells, immunoglobulin
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Divisions of the cerebrum
-Cortex: Outermost grey matter; perception, thought, conciousness -Limbic system- white matter structures encircling ventricular system; learning, memory, emotion -Basal ganglia- deep grey matter; motor control
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Association Fibers
-Connect cortical areas on the same side of the brain -White fiber bundle
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Commissural Fibers
-Connect cortical areas on opposite sides of brain -White fiber bundle -Ex: corpus callous
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Projection Fibers
-Connect cortex w subcortical structures and other brain areas -Ex: Internal capsule and corona radiata
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Internal Capsule and Corona Radiata
-Long projection fibers btwn the cortex and inferior structures that make up an array of vertically directed axons-- corona radiata -Internal capsule- fibers from the corona radiata funnel into this compact fiber bundle lateral to the thalamus and caudate nucleus
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Hippocampus
-Temporal Lobe Structure -Related to inferior horn of lateral v's -Involved in learning, memory, spatial localization
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Amygdala
-Temporal lobe structure -Related to inferior horn of lateral v's -Receives info from all sensory systems -Mediates intense emotions such as anger and fear
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Basal Ganglia
-A collection of nuclei -Regulates starting, stopping, and amplitude of activities -Parts- Caudate nucleus, putamen, globes pallidus -Caudate associated w lateral wall of lateral ventricle
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Basal Forebrain area
-Lies anterior and lateral to the hypothalamus on each side -Near front end of corpus callous
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Thalamus
-Gateway to the cortex -Occupies a central position in the brain (btwn brainstem and cerebrum; R and L) \*R and L sometimes (NOT ALWAYS) connected by interthalamic adhesion -On either side of 3rd V
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Thalamic divisions
-Based off of fxn 1. Anterior nuclear group 2. Pulvinar 3. Medial geniculate nucleus 4. Lateral geniculate nucleus \*Each group projects to a diff region of cortex for diff sensations (except smell)
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Hypothalamus
-Central to the limbic system -Homeostasis (body temp, endocrine, behavioral reg) -Group of nuclei -Boundaries: optic chasm, anterior commissure, maxillary body, lamina terminals
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Epithalamus
-Contains pineal gland (melatonin production, regulates circadian rhythms) -Habenula- pain and reward pathways -Posterior commissure (connect L and R sides of the midbrain)
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Subthalamus
-Nucleus -Part of basal ganglia circuitry; internal structure
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Laminar organization of the cortex
-Sheet-like, horizontal organization of the cortex -Difference in thickness of the layers= basis for brodmann areas
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Development of the Cerebral Cortex
-Cells are born in the ventricular zone -cells differentiate into neurons and "climb" radial glia to cerebral surface -Newer cells= top layer, older on bottom -Adult cerebral cortex= 6 layers ----Layer 1= Pia matter
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Vertical Organization of the Cerebral cortex
-The cortical column- built around pyramidal cells ---Columns of cells oriented perpendicular to the surface of the cortex that are individual functional units \*Columns encompassing all 6 layers will fire when receptive field is reached
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Layer 5 of the cortex
-Location of pyramidal cells -Output to subcortical areas -Contains Betz cells -Projection fibers
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Pyramidal cells
-Dictates whether that part of the cortex will send an output -Define boundaries of one cortical column -Long dendrites that extend to layer 1--\> apical dendrites -Basal dendrites extend to bottom of layer 5 -Recurrent collaterals- project into layer 6 -Axon projects into subcortical areas
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Layer 1 of the cortex
-Plexiform/molecular layer -Fibers parallel to the surface
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Layers 2/3 of the cortex
-Small and medium pyramidal layers -Intracortical connections -Short and long association fibers -Commissural fibers ---Stellate and pyramidal neurons with intracortical connections
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Layer 4 of the cortex
-Inner granular layer -Stellate neurons receive INPUT from thalamic nuclei
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Layer 6 of the cortex
-Fusiform/multiform layer -Cortical output to specific thalamic nuclei ----inputs and outputs to thalamus
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Motor areas and sensory areas in regard to cortex layers
- Motor areas have large layer 5, small layer 4 -Sensory areas have large layer 4, small layer 5
- Association ares= in between
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Brodmann's areas
-Defined specific cortical areas based on their histology and functional correlates
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Functional areas of the cerebral cortex
-Primary areas--\> devoted to only 1 function ----Primary visual, auditory, motor, and somatosensory cortices ----Described w maps -Associated areas--\> make sense of info ---Interpretive, integrative, complex processing
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Lateralization of the cerebral cortex
-Processes info related to opposite side of body -L: analytical, precise, organized, literal -R: creative, imaginative, conceptual, intuitive -Dominance: often, one side more strongly controls an activity -Ex: language predominates left side
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Occipital Lobe
-The visual cortex--Brod area 17 ----Map of contralateral retina--points in visual space -Visual association cortex- Brod area 18/19 ---Interpretation
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Dorsal and Ventral Pathways of Visual cortex
-Where= dorsal, what=ventral -Feeds info away from occipital lobe to other brain areas (memory areas) -Damage leads to visual deficits/ "cortical blindness"
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The primary auditory cortex and association area
-Temporal lobe; temporal lobe gyrus inside lateral fissure -Brodmans area 41/42 -Map of tones; sounds mix in both hemispheres -Association area- interprets pattern of sound ----BA 22
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Wernicke's Area
-reading mentally, interpreting speech -Dominant side= left \*Part auditory cortex, part association cortex -Damage--\> sensory aphasia-\> inability to understand speech; fluid nonsensical speech
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Visual Association Cortex
-Temporal Lobe -ID of stimuli we recognize -Agnosias= difficulty recognizing stimuli, naming categories of things \*Ex: prosopagnosia= inability to recognize faces \*Dominant= left
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Primary Somatosensory Cortex and Association area
-Parietal lobe -PSC- Lies on the post central gyrus, BA 3,1,2 ----Map of contralateral body ----Somatic sensation (touch, pain, temp) -AA- Superior parietal lobule (BA 5+7) ----Interprets sensations in space
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Sensory Homunculus
-Neurons of the primary somatosensory cortex are topographically arranged and receive sensory signals from diff parts of the body -Greater area= greater sensory acuity
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Subdivisions of the Frontal Lobe
-Motor region -Prefrontal region
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Motor Region of the Frontal Lobe
-2 final areas: --1. Primary motor cortex= BA 4 ---------precentral gyrus; map of skeletal muscles (primary motor strip) --2. Premotor cortex (rostral to primary motor) --------Designs motor plan; activaion and synchronization of groups of muscles
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Motor Homonculus
-Neurons of the primary motor cortex are topographically arranged and execute commands to skeletal muscles in diff parts of the body
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Broca's area
-Adjacent to speech muscle area of primary motor cortex on DOMINANT SIDE (left) -Damage gives "expressive aphasia" or "non-fluent aphasia"--\> defective grammar/difficulty producing speech
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Parts of the Prefrontal Cortex
-Complex behavioral areas 1. Dorsolateral PFC 2. Orbitofrontal cortex 3. Anterior cingulate
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Dorsolateral PFC
-Working memory --Ex: remembering a phone # -Associative memory--\> learn to associate an action w/ reward -Executive fxn
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Orbitofrontal Cortex
-Involved in social and emotional decision making --Risk vs reward -Damage-- loss of inhibition/ change in behavior \*Last part of the brain to reach maturity
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Anterior cingulate
-Involved in motivation -If damaged--\> Akinetic mutism (not motivated to speak)
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Tasks for executive system impairment
- Alternating sequences task ----Patient asked to draw a circle, then a triangle ---Inability to disengage from stimulus ---Preservation
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Frontal vs. Parietal Association Cortex
-Posterior parietal cortex orients attention toward extra personal world (things around u/ ur body) -Prefrontal association cortex orients attention toward internal mental processes
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Insular Cortex
-Feelings and self-awareness -How feelings are colored onto the body
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4 types of organization w/in the brain
1. Laminar/Horizontal 2.Cortical column/ Vertical 3. Functional (BAs) 4. Topographical (homunculi)
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Peripheral Nerves
-Connect CNS to periphery
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Spinal Nerves
-31 pairs of spinal nerves that connect peripheral structures to the spinal cord -Share similar organization; contain motor and sensory fibers -Cell bodies located in dorsal root ganglia -Mixed nerve--\> sensory and motor mixed together
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Cranial Nerves
-12 pairs that connect brain to periphery -Every cranial nerve is diff from the others -CN II is CNS tissue, formed from neural tube
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Neuron Types in the PNS
-Sensory -Motor
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Sensory Neurons
-carry info from receptor into CNS -Axon= sensory axon or sensory fiber; pseudounipolar -Cell body located in PNS ; joins w others to form ganglion \*No dendrites
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Types of Sensory Neurons
-Somatic sensory- Receive info from skin or skeletal muscle (axons= somatic sensory axons) -Visceral sensory-receive info from receptors in organs (axon visceral sensory axons)
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Motor Neurons
-carry info out of CNS, into PNS -Axon= motor axon or motor fiber; unipolar -Cell body located within gray matter of CNS -Many dendrites; synapse on target cells in periphery
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Types of Motor Neurons
-Somatic Motor- Carry info to skeletal muscle; release NTM onto it so muscle contracts -Autonomic motor/Visceral Motor- go to organs; chain of 2 neurons (1st= preganglionic, 2nd is postganglionic)
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Nerve types in the PNS
-Further classified according to which types axons are mixed within the nerve 1.Motor nerve 2. Cutaneous nerve 3. Splanchnic nerve
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Motor Nerve
-Nerve that enters muscle cells -Contains 2 axon types: ---Somatic motor fibers (axon)= synapses on skeletal muscle cells ---Somatic sensory fibers (axons)= collect info from sensory receptors in muscle and carry it back to the CNS
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Cutaneous Nerve
-Nerve that enters a patch of skin -2 axon types: ---Somatic sensory fibers (axons)- collect info from sensory receptors in skin; carry back to CNS (touch info) ---Autonomic motor fibers (axons)- synapse to smooth muscle or gland cells in skin
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Splanchnic Nerve
-Nerve that enters an organ -2 axon types: --Visceral sensory fibers (axons)- collect info from sensory receptors in organ and carry to CNS --\> info helps CNS adjust conditions of organ --Autonomic motor fibers (axons)- Synapse on cardiac muscle cells, smooth muscle cells, or gland cells in organs to alter organ fan
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Innervate
-When an axon contacts a cell or structure in the body -4 motor axons--\> synapses on skeletal muscles -4 sensory axons--\> synapses
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Axons in the PNS
-Myelinated; produced by Schwann cells -Schwann cells also ensheath axon--\> Hug axons w/o myelinating them
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Thickness of Myelin Sheath and Axon Diameter
-Proportional to each other -Increased myelin or axon diameter increases conduction speed -Diff fxnal classes of peripheral axons conduct APs at diff speeds -Ex: A and B fibers= myelinated, C is unmyelinated (pain, temp, mechanoreception)
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Structure of Peripheral Nerves
-Axons organized by specific connective tissue coverings -----Axons w or w/o myelin arranged into fascicles -Schwann cells -Blood vessels nourish cells \*Axons could be sensory or motor, but look identical -Connective tissue layers --Around each axon= Endoneurium (deepest layer) --Around each fascicle-- Perineurium --Around the entire nerve= Epineurium (tough outer coating)
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Fascicles
-Group of axons bundled together with collagen-rich connective tissue -Have a common fxn \*Only in PNS
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Can one neuron be myelinated by oligodendrocytes and Schwann cells?
-Yes! -Part of axon may be in CNS--\>myelinated by oligo -Part may be in PNS--\> myelinated by Schwann
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Differentiation within the neural tube (Dorsal-Ventral)
-Cells divide into the ventricular zone and migrate from the ventricle within the wall -In SC--\> dorsal alar plate (eventually dorsal root) and ventral basal plate develop (ventral root) -Sulcus limitans= the grove in the lateral wall of the neural tube delineating alar from basal plates
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Differentiation of the neural tube (Medial-Lateral)
-Hollow opening in center= ventricle -Ventricular layer= dividing cells -Mantle layer= neuroblasts ---Cells migrate, differentiate -Marginal layer= axon growth
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Development of the Spinal Cord
-Central grey portion--\> Dorsal and ventral horns -Central canal does not enlarge -White matter surrounds the grey
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Dorsal Root Entry Zone
-Medial DREZ= myelinated axons entering from dorsal root -Lateral DREZ= unmyelinated axons entering from the dorsal root
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Spinal Cord at Diff Levels
-The overall cross-sectional size of the SC decreases from cervical to sacral levels -Volume of white matter decreases from cervical to sacral levels \*\*Shape of grey matter changes at each level ---Greatest volumes of dorsal and ventral horn at limb attachment -Some areas have lateral horns
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Spinal Cord- White Matter
-Carry info up spinal cord (ascending tracts) OR -Down from brainstem or cerebrum--\> descending tracts \*No connective tissue separating tracts -Tracts are only sensory or motor, never both
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Spinal Cord-Grey Matter
-Organized into nuclear cell columns OR Rexed's Laminae
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Rexed's Laminae
1. Marginal Zone 2-3- Substantia Gelatinosa 4- Nucleus Proprius 6-7-Column of Clark 9- Motor neurons \*Different lamina are related to diff functional systems
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Dorsal and Ventral Ramus
-Mixed- sensory and motor -Names refer to location of body they go to ---Dorsal branches to dorsal skin and muscle ---Ventral branches to ventral skin and muscle
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Dorsal Roots and Rootlets
-Only sensory axons
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Ventral roots and rootlets
-Only motor axons
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Spinal Nerves are the first point where...
-First point where sensory and motor axons are bundled together
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Comparison- CNS vs PNS: Terms describing clusters of neuron cell bodies
-CNS: gray matter, nuclei, centers, horns -PNS: Ganglia \*All supported by glia
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Comparison- CNS vs PNS: terms describing groups of axons
-CNS- white matter, tract, funiculi, fasiculi, fiber bundles (ex: corpus callosum) -PNS: Nerves, fascicle
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Meissner's Corpuscles
-Just under skin surface -Sensitive to fine touch -Lead to stimulation of 1st order sensory neurons \*Rapid adapting- fire quickly and stop firing quickly
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Pacinian Corpuscles
-Deep under surface of skin -Sensitive to pressure and vibration -Lead to stimulation of 1st order sensory neurons \*Rapidly adapting- fire quickly and stop firing quickly
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Merkel Cells
-Located just under the surface -Sense of fine discriminative touch -Lead to stimulation of 1st order sensory neurons \*Slow adapting
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Ruffini Endings
-Deep under skin -Provide touch directionality \*Slow adapting
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Free Nerve Endings
-Stimulate 1st order sensory neurons -Sensations of pain and temp \*not a receptor\* -Channels in axon at peripheral terminus change conductance in response to heat or cold/ local chemicals \*Localized in skin, connective tissues, and organs
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Sensory receptors of skeletal muscle
-1a fiber=muscle spindle ---Detect stretch of mucle -1b fiber= tendon ending/ golgi tendon
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Hierarchy in somatosensory pathway
Stimulus--\> receptor--\> 1st order neuron in PNS (dorsal root gang)--\> 2nd order neuron in CNS (SC or brainstem)--\> 3rd order neuron in thalamus--\> neuron in primary sensory cortex--\> conscious perception of stimulus \*reflexes occur at 2nd order neuron
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Divergence
-Ex; Somatosensory system; Muscle afferents -One input in CNS can be sent to many areas simultaneously -Info can be processed in multiple ways in multiple sensory pathways
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3 Major Spinal Somatosensory Pathways
1. Dorsal Spinocerebellar Pathway 2. Dorsal Column/Medial Lemniscal Pathway 3. Anterolateral pathway (spinothalamic)
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Dorsal Spinocerebellar Pathway
-1a, 1b, Abeta afferents -Muscle length -Muscle contraction -Joint contraction \*1st order neuron= Dorsal root gang cell \*2nd= neuron in column of clark -- dorsal spinal cerebellar tract in lateral funiculus (ipsilateral SC)--\> \*3rd: ipsilateral cerebellum
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Column of Clark
-Only present from C8 to L2
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Dorsal Column/ Medial Lemniscal Pathway
-1a, 1b, Abeta afferents -Fine touch, vibration, conscious proprioception -1st order- DRG sensory neuron \*Dorsal column tract in SC\* -2nd order- Gracile or cuneate nucleus (lower medulla) \*\*CROSS THE MIDLINE TO OPPOSITE SIDE OF BRAINSTEM, medial lemniscus pathway in brainstem -3rd order- VPL nuc of thalamus \*Sensory axons in this pathway travel in dorsal funicular of ipsilateral SC (don't relay through dorsal horn nuc)
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Gracile Fasciculus and Cuneate Fasciculus
\*Parts of the dorsal funiculus -Gracile= feet/lower body/ below T6 -Cuneate= arms/ upper body/above T6 T6= bottom of sternum
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VPL
-Relay nucleus of the Medial Lemniscus Pathway -Axons travel trough internal capsule and synapse in layer 4 of the primary somatosensory cortex
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Anterolateral System
-Adelta (sharp pain), C afferents (dull itching or burning) --Pain, temp, itch, crude touch 1. DRG sensory neuron (free nerve endings stimulated) 2. Marginal nucleus or nucleus proprius (dorsal horn of ipsilateral sc) \*\*Cross midline, ascends to brain via anterolateral tract\*\* 3. VPL nucleus of thalamus --\> relays to somatosensory cortex
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Marginal Nucleus
-Alpha Delta fibers carrying sharp pain, some temp -Where dorsal root ganglion neurons synapase in the anterolateral pathway
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Reticular Formation
-Responsible for autonomic and limbic connections of pain ---Arousal ---Emotional component of pain
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Spinal Cord Sensory Pathways
-1st order neurons are DRG cells--\> bring in info from mechanoreceptors and free nerve endings 2nd order neuron= CNS cells which relay to brain -If info is destined for cortex, 3rd order neuron= part of thalamus
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Spinal MOTOR pathways
-DONT USE TERMS 1ST ORDER, 2ND etc -Upper motor neurons and lower motor neurons -Axons form descending tracts traveling in white matter
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Lower Motor Neurons
-Cell bodies in ventral horn -Project to skeletal muscles
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Upper Motor Neurons
-Cell bodies and axons in CNS -Regulate LMNs
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Somatic motor neurons in the ventral horns
1.Alpha Motor Neurons 2.Gamma Motor Neurons -Project through motor nerves -Terminate on skeletal muscle at neuromuscular Jxn \*Only source of skeletal muscle activity Axon damage= cells in motor unit cant contract Nerve damage= whole muscle cant contract
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Alpha Motor Neurons
-Large in diameter -Rapidly conducting cells -Cause skeletal muscle cells to contract
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Gamma Motor Neurons
-Smaller, slower conducting cells -Control tiny muscle cells within muscle spindle receptors -Modulate the sensitivity of MS receptors
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Motor Unit
-One alpha motor neuron and all the muscle cells it innervates --Small: innervates about 10 cells --Large: innervates 1000 cells= less fine control
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How Gamma and Alpha motor neurons work at a muscle spindle
-if only alpha motor neurons were activated, only extramural muscle would contract--\> muscle spindle becomes slack and no APs fire--\> cannot signal further length changes -When alpha and gamma coactivated--\> extrafusal and intrafusal contract--\> tension is maintained in muscle spindle and can signal changes in length
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Choroid plexus
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- Red circle= subthalamus
- Blue circle= epithalamus
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Blue- Dorsolateral PFC
Red-Orbitofrontal PFC
White- Anterior cingulate
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1. Spinocerebellar Pathway
2. Dorsal Column/Medial Lemniscal Pathway
3. Anterolateral Pathway
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The Meninges
- Protective covering of the CNS
1. Dura mater-tough outer membrane
2. Arachnoid mater- Thin, transparent membrane covering superficial blood vessels in the cortex
3. Pia Mater- layer adjacent to brain
- Cannot be removed w/o tearing brain tissue
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Spaces within the Skull
- Epidural space: between skull and dura
- Occurs upon injury- not normally there
- Subdural space: Btwn dura and arachnoid
--Not normally there
-Subarachnoid space- contains CSF
---Location of superior saggital sinus
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Where are blood vessels located within the brain?
- W/in the dura (supply dura only)
- Btwn arachnoid and pia
---Supply blood to brain
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1. Yellow--\> Cerebrum
2. Green--\> brainstem
3. White--\> Cerebellum
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What fissure separates the left and right hemispheres?
-Interhemispheric fissure
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1. Red: Frontal lobe
2. Blue dots= central sulcus
3. Yellow: Parietal lobe
4. White dots= Lateral fissure
5. Black= temporal lobe
6. Green= occipital lobe
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Where can the insular cortex be found?
-At lateral fissure, pull temporal lobe apart from frontal and parietal lobes
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- Back?
- Front/Stomach?
- Coccyx?
- Brain/head?
- Back= dorsal/posterior
- Front= ventral/anterior
- Coccyx= caudal
- Brain/head= rostral
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1. Separating hemispheres?
2. Separating dorsal and ventral planes
3. Vertical separation
4. Separating superior and inferior portions
1. Sagittal (midsaggital if perfect split, parasaggital if unequal)
2. Coronal/Frontal
3. Transverse
4. Horizontal
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- Flax cerebri= btwn cerebral hemispheres
- Tentorium cerebelli= btwn occipital lobe and cerebellum
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What described the 90 degree angle that the brain and brainstem form?
-Mesencephalic Flexure
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1. Red= lateral ventricles
2. Clip= Septum pellucidum--\>membrane separating left and right LVs
3. Yellow- Foramen of monro
4. Blue-\> 3rd V
5. White= cerebral aqueduct
6. Black= 4th Ventricle
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What are the 3 drainage holes from 4th ventricle into subarachnoid space?
1. Foramen of Magendie= midline
2. Two foramen of Lushka- lateral
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1. Superficial Gray matter
2. White matter
3. Deep greymatter
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Caudate, Putamen, and Globus Pallidus= Basal Ganglia \*Grey matter
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Red cross= optic chiasm
Blue= Anterior perforated substance
---Ventral surface where BVs penetrated
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Blue circle- amygdala
Arrows= hippocampus
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- Triangle= hypothalamus
- Blue= Thalamus
- Yellow= epithalamus
- Green= subthalamus
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-interthalamic adhesion
\*only some people have it
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White= pons
Yellow= floor of the hypothalamus
Red= optic chiasm
-Black hole below optic chiasm= pituitary stalk
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1.Parieto-Occipital fissure
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Primary Motor Cortex/ Brodmann's area 4/precentral gyrus
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Motor Homunculus
- Tongue near insula
- Toes/leg near interhemispheric fissure
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-Premotor cortex/BA 6/Part of superior and middle frontal gyri
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- Broca's area: BA 44 and 45
- Motor speech
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-Prefrontal Cortex
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-Primary somatosensory cortex/ BA 3,1,2/post-central gyrus
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Somatosensory Homunculus
- Tongue, pharynx, intrabdominal--\>insula area
- Leg= intrahemispheric fissure
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Red=Somatosensory association cortex (BA 5and7)/ superior parietal lobule
-Blue= intraparietal fissure
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-Inferior parietal lobule
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- Primary visual (blue)- BA 17
- Calcarine fissure (red)
- Visual association cortex- White- BA 18 and 19
-
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- Primary Auditory Cortex (green)- BA 41 and 42
- Auditory association cortex (yellow)- BA 22
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Red= Broca's are- BA 45 and 44
Yellow=Wernicke's area= BA 22
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-Parahippocampal gyrus
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Uncus
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Spinal Cord
- Continuation of the brainstem
- Bones of spine create a protective canal
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- Intervertebral disk-\> cartilage btwn each pair of vertebral bodies
- Vertebral canal= formed by alignment of vertebral foramina
- Intervertebral foramen- formed on each side between every pair of vertebrae
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Organization of the spine
- 7 cervical vertebrae
- 12 thoracic vertebrae
- 5 lumbar vertebrae
- 1 sacrum (fusion of 5 sacral vertebrae)
- 2-4 coccygeal vertebrae--\> coccyx
- Numbered
\*Spines point posteriorly
\*Bodies point anteriorly
-Spinal canal lies within the vertebral canal--\> stops around L1/L2
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Meninges surrounding the spinal cord
- Pia= adheres to SC
- Arachnoid- external to pia, attached by fine fibers
- Dura- surrounds arachnoid, extends out of the intervertebral foramina as dural sleeves
- Epidural, subdural, and subarachnoid spaces similar to brain, but dura not attached to bone
\*Fat gives padding btwn dural sac and bone
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- Space= central canal
- Grey matter is further divided into Rexed Laminae
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- Rootlets merge into roots
- Roots move laterally, run within dural sleeve
- Spinal nerve and rami= mixed
- Ventral ramus= supplies anterior muscles and skin
---Larger than dorsal
-Dorsal ramus= supplies posterior muscles and skin
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1. White matter
2. Grey matter
3. Dorsal root
4. Ventral root
5. DRG
6. Spinal nerve
7. Anterior
8. Posterior
Top arrow= dorsal ramus
Bottom arrow= ventral ramus
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Lumbar Cistern
-Pool of CSF that surrounds the rootlets of the cauda equina in the dural sac
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Why is a spinal tap performed at the L3/L4 or L4/L5 level?
-To reach the lumber cistern, needle isn't likely to damage the cauda equina
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What structures are in the dural sac at the L3/L4/L5 level?
- Cauda equina
- Lumbar cistern
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Why are spinal taps not performed at the T12/L1 level?
S3/S4 level?
-Cannot be performed at T12/L1 cuz could damage the spinal cord
## Footnote
-S3/S4 would not work because dural sac ends b4 then
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What meningeal layers must the needle pass through to collect CSF?
- Dura
- Arachnoid
\*Goes into subarachnoid space
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-Filum terminal= strand of pia mater; attached to bottom of dural sac
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Numbering of the spinal nerves
-Numbered according to the vertebrae where they exit
## Footnote
-Cervical spinal nerves exit above the same numbered vertebrae
----Ex: C3 SN exits between C2 and C3
-Thoracic, Lumbar, and sacral SNs exit below same numbered vertebra
--Ex:T5 exits between T5 and T6
\*C8= exiyd below C7 and above T1
\*\*Spinal nerves= organized topographically
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Which levels of the spinal cord have the largest volume of grey matter? Why?
-Thoracic has the largest volume of grey matter because a lot of cell bodies are located there. Additionally, not as much white matter because not a lot of motor function occurs here.
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Which levels of the spinal cord have the largest amount of white mater? Why?
-Cervical and lumbar because they are important for sensory and motor functions within the arms and legs
\*Overall, WM greatest at cervical and least at sacral
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Spinal Segments
- Give rise to dorsal and ventral rootlets, and spinal nerves
- For every spinal nerve, we can refer to its spinal segment
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Plexus
-A network of nerves undergoing the sorting process
--Nerves branching from the plexus redistribute to muscles and skin
- Brachial plexus= Rostral end, formed from ventral rami C5-T1-- Innervate muscles and skins in upper limbs
- Lumbosacral plexus- Caudal end, formed from L1-S5 ventral rami- innervate muscles and skin of lower limbs and pelvis
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Organization of cell bodies in the ventral horn
- Medial ventral horn= motor neurons for chest and back
- Lateral VH= Motor neurons for arm and hands
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Is there a relationship btwn size of gray matter and the amount of info being processed?
-Increased grey= increased info processed
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Which levels of the SC process the most info? Why?
-L1-S5 and C5-T1 (brachial plexus and lumbosacral plexus) because they are processing touch and moving limbs
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Which two named areas in the dorsal horn have the largest pop. of neurons? What are their Rexed Laminae?
-marginal zone (I) and nucleus proprious (IV)
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Which cell group in the ventral horn has the largest pop of neurons? Rexed Laminae of this group?
-Alpha motor neurons in the ventral horn (XI)
