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functional brain systems
- networks of neurons that work together but span wide areas of brain
- example - limbic system
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limbic system
- structures on medial aspects of cerebral hemispheres and diencephalon
- includes parts of diencephalon and some cerebral structures that encircle brain stem
- puts emotional responses to odors (ex: skunks smell bad)most output relayed via hypothalamus
Emotional of affective brain = amygdaloid body: recognizes angry or fearful facial expressions, assesses danger, and elicits fear resonse; cingulate gyrus: role in expressing emotions via gestures, and resolves mental conflict
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limbic system: emotion and cognition
- limbic system interacts with prefrontal lobes (react emotionally to things we consciously understand to be happening; consciously aware of emotional richness in our lives)
- hippocampus and amygdaloid body - play a role in memory
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brain wave patterns and EEG
- brain waves are patterns of neuronal electrical activity generated in the cortex
- each person's brain waves are unique
- can be grouped into four classes based on frequency measured as hertz (Hz): alpha, beta, theta, and delta waves
- EEG = electroencephalogram
- records electrical activity that accompanies brain function (brain waves of the cortex)
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protection of the brain
- bone (skull)
- membranes (meninges)
- watery cushion (cerebrospinal fluid)
- blood brain barrier
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meninges
- cover and protect CNS
- protect blood vessels and enclose venous sinuses
- contain cerebrospinal fluid
- form partitions in skull
3 layers: dura mater; arachnoid mater; pia mater
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dura mater (=tough mother)
- strongest meninx
- two layers of fibrous connective tissue (around brain) separate to form dural venous sinuses
- dural septa limit excessive movement of brain =
- falx cerebri: in longitudinal fissure, attached to crista galli
- falx cerebelli: along vermis of cerebellum
- tentorium cerebelli: horizontal dural fold over cerebellum and in transverse fissure
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arachnoid mater (spider mother)
- middle layer with weblike extensions
- separated from dura mater by subdural space
- subarachnoid space contains CSF and largest blood vessels of brain
- arachnoid villi protrude into superior sagittal sinus and permit CSF reabsorption
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pia mater (=tender mother)
- innermost meninx
- delicate vacularized connective tissue that clings tightly to brain
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cerebrospinal fluid (CSF)
- composition = watery solution formed from blood plasma (less protein and different ion concentrations than plasma); constant volume
- functions = gives buoyancy to CNS structures (reduces weight by 97%); protects CNS from blows and other trauma; nourishes brain and carries chemical signals
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formation, location, and circulation of CSF - fyi
- 1) the choroid plexus of each ventricle produces CSF
- 2) CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures
- 3) CSF flows through the subarachnoid space
- 4) CSF is absorbed into the dural venous sinuses via the arachnoid villi
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choroid plexuses
- hang from roof of each ventricle; produce CSF at constant rate; keep in motion (clusters of capillaries enclosed by pia mater and layer of ependymal cells)
- ependymal cells use ion pumps to control composition of CSF and help cleanse CSF by removing wastes
- normal volume ~ 150ml; replaced every 8 hrs
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hydrocephalus
- obstruction blocks CSF circulation or drainage
- unfused skull bones of newborn allow enlargement of head
- brain damage in adult due to rigid adult skull
- treated by draining with ventricular shunt to abdominal cavity
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blood brain barrier
- helps maintain stable environment for brain
- separates neurons from some bloodbourne substances
- composition: continuous endothelium of capillary walls; thick basal lamina around capillaries; feet of astrocytes (provide signal to endothelium for formation of tight junctions)
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blood brain barrier: functions
selective barrier = allows nutrients to move by facilitated diffusion; denies metabolic wastes, proteins, toxins, most drugs, small nonessential amino acids, K+ entry; allows any fat-soluble substances to pass, including alcohol, nicotine, and anesthetics
absent in some areas, ex: vomiting center and hypothalamus, where necessary to monitor chemical composition of blood
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spinal cord: gross anatomy and protection
- location: begins at the foramen magnum; ends at L1 or L2 vertebra
- Functions: provides two-way communication to and from brain; contains spinal reflex centers
- bone, meninges, and CSF
- epidural space - cushion of fat and network of veins in space between vertebrae and spinal dura mater
- CSF in subarachnoid space
- dural and arachnoid membranes extend to sacrum, beyond end of cord at L1 or L2 (site of lumbar punction or tap)
- terminates in conus medullaris
- filum terminale extends to coccyx (anchors spinal cord; fibrous extension of conus covered w/pia mater)
- denticulate ligaments - extensions of pia mater that secure cord to dura mater
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spinal cord
- spinal nerves (part of PNS) - 31 pairs
- cervical and lumbosacral enlargements - nerves serving upper and lower limbs emerge here
- cauda equina - collection of nerve roots at inferior end of vertebral canal
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gray matter of spinal cord
- dorsal horns - interneurons that receive somatic and visceral sensory input
- ventral horns - somatic motor neurons; axons exit cord via ventral roots; some interneurons
- lateral horns (only in thoracic and superior lumbar regions) - sympathetic neurons
- dorsal roots - sensory input to cord
- dorsal root (spinal) ganglia - cell bodies of sensory neurons
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zones of spinal gray matter
- per relative involvement in innervating somatic and visceral regions of body:
- somatic sensory (SS); visceral sensory (VS); visceral autonomic motor (VM); somatic motor (SM)
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neuronal pathway generalizations
- major spinal tracts part of multineuron pathways
- decussation - pathways cross to other side
- relay - consist of 2 or 3 neurons
- somatotopy - precise spatial relationship
- symmetry - pathways paired symmetrically
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white matter of spinal cord
- myelinated and nonmyelinated nerve fibers allow communication between parts of spinal cord, and spinal cord and brain
- divided into 3 white columns (funiculi) on each side: dorsal; lateral; ventral
- each spinal tract composed of axons with similar destinations and functions
- run in 3 directions:
- -ascending (sensory) = up to higher centers
- -descending (motor) = from brain to cord or below
- -transverse (commissural) = from one side to other
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