Ch 12 - CNS (2)

• networks of neurons that work together but span wide areas of brain
• example - 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

• 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

• 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)

• bone (skull)
• membranes (meninges)
• watery cushion (cerebrospinal fluid)
• blood brain barrier

• 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

• 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

• 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

• innermost meninx
• delicate vacularized connective tissue that clings tightly to brain

• 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

• 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

• 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

• 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

• 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)

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

• 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

• 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

• 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

• per relative involvement in innervating somatic and visceral regions of body: 
• somatic sensory (SS); visceral sensory (VS); visceral autonomic motor (VM); somatic motor (SM)

• 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

• 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