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The RAS
Reticular activating system - sensory component Alerts
sensory components to reticular activating system Contains
sensory axons projecting to cerebral cortex
Processes visual, auditory and touch stimuli
Uses information to keep us alert
Not active during sleep
TERM 2
What is CSF? How is it made? How is it
circulated? What is its function?
DEFINITION 2
Cerebrospinal fluid. A clear, colourless liquid. Circulates in ventricles and subarachnoid space. Bathes and completely surrounds surfaces of CNS.Formed by choroid plexus. Each ventricle has choroid plexus in it. Has a layer of ependymal cells and blood capillaries (within pia). Produced by secretion from ependymal cells. Originates from blood plasma. Composition somewhat similar to plasma.Circulation: Produced by choroid plexus. Circulates through ventricles - from lateral ventricles to third ventricle, through aqueduct into fourth ventricle. Then enters subarachnoid space - passes into central canal of spinal cord. Flows through subarachnoid space. Excess CSF removed from subarachnoid space - flows into arachnoid villi (fingerlike extensions of arachnoid mater), drains into dural venous sinuses (project through dura into dural venous sinuses) collection termed an arachnoid granulation, conduit for 1-way flow of excess CSF into blood.Functions: Buoyancy - brain floating here, reduces apparent weight by 95% prevents collapse of brain through foramen magnum Protection - Provides liquid cushion, protects delicate neural structures from sudden movements Environmental stability - Transports nutrients and chemical messengers to brain, removes waste products (to venous circulation), and protects tissue from chemical fluctuations
TERM 3
What is the blood brain barrier? What gets in
easily?
DEFINITION 3
BBB - Blood-brain barrier .It strictly regulates which substances enter brains interstitial fluid. Ideally helps prevent neuron exposure to harmful substances (e.g. drugs), blood waste products, variations in levels of normal substances (e.g. ions, hormones). Astrocytes have perivascular feet that surround the capillary. Cells joined by tight junctions. Most capillaries in brain wrapped by perivascular feet astrocyte extensions Endothelial cells and perivascular feet both contributing to BBB Continuous basement membrane of endothelial cells Tight junctions between adjacent endothelial cells reduce capillary permeability Astrocyte gatekeepers controlling materials leaving neurons Barrier not absolute. Selectively allows chemicals in nonpolar molecules not blocked. Lipid-soluble compounds can diffuse across endothelial plasma membranes (Freely pass) e.g., nicotine alcohol some anesthetics Can be damaged by drugs such as cocaine BBB missing or reduced in three locations: Choroid plexus needs to be permeable to produce CSF Hypothalamus and pineal gland produce hormones requiring access to bloodstream TERM 4
Hydrocephalus
DEFINITION 4
Pathologic condition of excessive CSFOften leads to brain
distortionMay result from obstruction in CSF restricting
reabsorptionMay result from intrinsic problem with arachnoid
villiIn a young child, head enlarged with possible neurological
damageMay be treated surgically Implant shunts that brain
CSF to other body regions
TERM 5
CNS vs PNS
DEFINITION 5
Central nervous system
anatomic division of the nervous system
includes brain and spinal cord
brain protected in the skull
spinal cord protected in the vertebral canal
Peripheral nervous system
other anatomic division
includes nerves , bundles of neuron processes
includes ganglia , clusters of neuron cell bodies
Know/understand receptors, stimuli, &
effectors
Receptors detect changes in the stimuli, which is the internal
or external environment. If a response is required, the
response is initiated via nerves to effectors.
TERM 7
Parts of a neuron cell. What are glial cells
(what are all of them and what is their job)?
Where are they found?
DEFINITION 7
Neuron structure: Axon Hillock Cell Body Nucleus Axon Dendrites Nucleolus Nissl Substance Two cell types in nervous tissue Neurons o basic structural unit of the nervous system o excitable cells that transmit electrical signals Glial cells o Non-excitable cells that primarily support and protect neurons o In CNS and PNS o Smaller than neurons o Capable of mitosis o Far outnumber neurons o Half volume of nervous system o Provide physical scaffolding for nervous tissue o Critical for normal function at neural synapses o Types: Astrocytes (CNS) Help form the blood-brain barrier Ependymal cells (CNS) Form choroid plexus with nearby blood capillaries, lines internal cavities of brain and spinal cord Microglia (CNS) Engulf infectious agents; Remove debris from dead or damaged tissue Oligodendrocytes (CNS) Prevent passage of ions through axonal membrane Allow for faster action potential propagation through CNS Satellite cells (PNS) Regulate the exchange of nutrients and waste products Neurolemmocytes (PNS) AKA Schwann cells Ensheathe PNS axons to form myelin sheath Allows for faster action potential propagation
TERM 8
Myelination in the CNS vs. the PNS.
DEFINITION 8
Process by which part of an axon wrapped in myelin o Myelin
insulating covering around axon Consists of repeating layers of
glial cell plasma membrane Has high proportion of lipids Gives
glossy appearance and insulates axon Completed by
neurolemmocytes (PNS) Can myelinate only 1 mm of single axon
Takes many to myelinate entire axon Gaps between
neurolemmocytes neurofibril nodes, or nodes of Ranvier
Completed by oligodendrocytes (CNS) Can myelinate 1 mm of
many axons Extensions wrapping around axons Neurofibril nodes
between adjacent wraps
TERM 9
Can axons regrow? If so in both PNS and CNS?
DEFINITION 9
PNS axons vulnerable to cuts, trauma Regeneration possible if cell
body intact enough neurilemma remains Regeneration success
more likely if amount of damage less extensive smaller distance
between site of damage and structure it innervates CNS axon
regeneration Extremely limited growth-inhibiting molecules
secreted by oligodendrocytes larger number of axons crowded
within the CNS regrowth obstructed by scars from astrocytes and
connective tissue
TERM 10
What is resting membrane potential and how
is it maintained?
DEFINITION 10
Membrane potential in a resting, excitable cell Relative difference in charge across membrane Measured with a voltmeter microelectrodes into neuron and interstitial fluid Negative value, typically -70 mV More positive ions outside a neuron than in it at rest A consequence of the plasma membrane permeability to ions Establishing and maintaining resting potentials: The role of K+ K+ diffusion the most important factor in specific value of RMP Dependent on the electrochemical gradient Outward movement facilitated by steep concentration gradient Leaves relatively more negatively charged structures inside The role of Na+ Typical neuron RMP -70 mV Difference between -90 mV of K+ movement only due to Na+ movement Enters cell through Na+ leak channels Moves down concentration gradient Also pulled by electrical gradient Channels present in limited numbers The role of Na+/K+ Pumps Play relatively small role in establishing RMP Three Na+ pumped out for two K+ pumped in More significant role in maintaining gradients of K+ and Na+ Ions pumped back up concentration gradient by pump Two-thirds of a neurons energy expenditure Requires ATP
Refractory period (what happens or cant
happen).
Refractory period Brief time period after action potential
initiated During absolute refractory period no amount of
stimulus able to generate a second action potential Na+ channels
opened then closed in inactivated state remain closed until
potential almost to resting potential ensures that action potential
moves in one direction only Cell body synapse on end of axon
(preserve signal direction)
TERM 17
What happens at the synaptic knob? (Vessels,
calcium, receptors, etc) What is released by
the vessels? Do all neurons have the same
chemicals in these vessels?
DEFINITION 17
Activity at the synaptic knob Calcium concentration gradient
established by pumps more calcium outside synaptic knob than in
Voltage-gated Ca2+ channels triggered by propagated action
potential movement of calcium ions into synaptic knob Binding of
calcium to proteins of synaptic vesicles Triggers fusion of synaptic
vesicles with neuron plasma membrane Neurotransmitters
released into synaptic cleft by exocytosis
TERM 18
How are neurotransmitters removed from the
cleft? What are neuromodulators?
DEFINITION 18
Removal of neurotransmitters from the synaptic cleft Temporary association between neurotransmitter and receptor Necessary to eliminate molecule after stimulation Can occur by degradation neurotransmitter chemically inactivated in synaptic cleft e.g., breakdown of ACh by acetylcholinesterase Can occur by reuptake neurotransmitter reabsorbed by transport protein in presynaptic neuron recycled into another synaptic vesicle for reuse e.g., drugs, selective serotonin reuptake inhibitors block reuptake of serotonin and used in treatment of depression Neuromodulators Chemical released from cells Locally regulate or alter response of neurons to neurotransmitters Release termed neuromodulation Facilitation occurs when greater response in postsynaptic neuron may increase amount of neurotransmitter in synaptic cleft may increase number of receptors on postsynaptic neurons Inhibition occurs when less response from postsynaptic neuron may decrease amount of neurotransmitter may decrease number of receptors on postsynaptic neuron TERM 19
Parts of the brain and their functions:
cerebellum
DEFINITION 19
Cerebellum Second largest part of the brain Produces fine control over muscular actions Stores memories of movement patterns e.g., playing scales on a piano Cerebellar components Convoluted surface covered by layer of cerebellar cortex Folds termed folia Left and right cerebellar hemispheres Each hemisphere with an anterior and posterior lobe separated by primary fissure Vermis narrow band of cortex lies along midline between left and right lobes Cerebellar components Partitioned into three regions: cerebellar cortex, outer gray matter of cortex internal region of white matter, arbor vitae deepest gray matter layer of cerebellar nuclei TERM 20
Parts of the brain and their functions:
cerebrum
DEFINITION 20
Cerebrum largest part of brain (right and left hemispheres) Center of: Intelligence and reasoning Thought, memory and judgement Voluntary motor, visual and auditory activities Higher order brain functions / thinking Corpus Callosum Provides main method of communication between hemispheres Made of bundles of axons Cerebrum characteristics Usually difficult to assign precise function to specific region Overlapping and indistinct boundaries Some aspects not easily assigned to any single region (e.g. memory) Innervation hemispheres receiving information from opposite side of body hemispheres projecting motor commands to opposite side of body e.g., right cerebral hemisphere controlling the left side of body
Parts of the brain and their functions:
diencephalon
Part of the prosencephalon
Components of diencephalon:
epithalamus, thalamus, and hypothalamus
Provides the relay and switching centers for:
sensory and motor pathways
control of visceral activities
TERM 22
Parts of the brain and their functions: brain
stem
DEFINITION 22
Connects cerebrum, diencephalon, and cerebellum to
spinal cord
Bidirectional passageway
Contains many autonomic centers and reflex centers
Houses nuclei of many cranial nerves
From superior to inferior:
midbrain
pons
medulla oblongata
TERM 23
Cerebrum Lobes and Functions
DEFINITION 23
Cerebrum Frontal lobe deep to frontal bone forms anterior part of cerebral hemisphere ends posteriorly at deep groove, central sulcus ends inferiorly at groove, lateral sulcus Primarily concerned with: Voluntary motor functions Concentration and verbal communication Decision making, planning and personality Cerebrum Parietal lobe Deep to parietal bone forms superoposterior part of cerebral hemisphere terminates anteriorly at central sulcus terminates posteriorly at parieto- occipital sulcus terminates laterally at lateral sulcus postcentral gyrus, mass of nervous tissue posterior to central sulcus primarily concerned with: general sensory functions e.g., evaluating shape and texture of objects Cerebrum Temporal lobe Internal to temporal bone Inferior to lateral sulcus Involved with hearing and smell Cerebrum Occipital lobe Internal to occipital bone Forms posterior part of cerebral hemisphere Responsible for: Processing visual information Storing visual memories Above 4 hemispheres are on the outside and named after the bone they are at Cerebrum Insula lobe Small lobe deep to lateral sulcus Can be observed by laterally pulling aside temporal lobe Involved in: Memory Interpretation of taste Cerebrum functions: Three categories of functional areas: o Motor areas Control voluntary motor function Housed within frontal lobes Primary motor cortex located in precentral gyrus of lobe Control voluntary skeletal muscle activity Project contralaterally (opposite side) within brainstem or spinal cord E.g. left primary motor cortex controlling right-side voluntary muscles
TERM 24
Primary motor cortex distribution
DEFINITION 24
can be diagrammed as motor homunculus displays distorted proportions of the body reflects amount of cortex reflected to each part e.g., hands larger on the homunculus perform detailed, precise movements more motor activity devoted to human hand than in other animals Motor speech area AKA Broca area Controls muscular movement for vocalization Frontal eye field Regulates movements needed for reading and binocular visions o Sensory areas Primary somatosensory cortex Housed within postcentral gyrus of parietal lobes Receives somatic sensory information from: o Proprioceptors, touch, pressure pain, and temperature receptors Primary visual cortex Located within occipital lobe Receives and processes incoming visual information Primary auditory cortex Located within temporal lobe Receives and processes auditory information Primary olfactory cortex Located within temporal lobe Provides conscious awareness of smells Primary gustatory cortex Located within insula Involved in processing taste information o Association areas Connected to adjacent motor and sensory regions Process and interpret data or coordinate motor response Integrate new sensory inputs with memories Premotor cortex Within frontal lobe anterior to precentral gyrus Responsible for coordinating skilled motor activities o E.g. playing the piano Somatosensory association area Within parietal lobe posterior to primary somatosensory complex Integrates sensory information Determines texture, temperature, pressure, and shape of objects Allows us to identify known objections without seeing them Visual association area Within occipital lobe Surrounds primary visual area Helps process visual information Helps us identify things we see o E.g. helps integrate visual information into recognizable face Auditory association area Within temporal lobe, posteroinferior to primary auditory complex Interprets characteristics of sound Stores memories of sound heard in the past Function brain regions Multi-association area between lobes Integrates information from individual association areas Wernicke area, one example Typically located only in left hemisphere Involved in recognizing, understanding and comprehending spoken and written language Works with motor
TERM 25
Meninges -- Composition of layers and order
on brain
DEFINITION 25
Cranial meninges Three connective tissue layers Separate
and support soft tissue of brain Enclose and protect blood
vessels supplying the brain Help contain and circulate
cerebrospinal fluid From deep to superficial: pia mater
arachnoid mater dura mater
