Module 2 Flashcards
outline the organization of the CNS & PNS
CNS: brain & spinal cord; neurons within form complex networks (these allow for: subconscious neuronal regulation of internal environment, emotions, voluntary movement control, perception & higher cognitive function)
- input by afferent neurons (majority lie within PNS)
- interneurons (almost completely within CNS as “connecting” neurons) create circuits for integrating responses
- output to efferent neurons (cell bodies in CNS but relay signals to PNS)
PNS: nerve fibres the carry information between CNS & rest of the body
- afferent division: sensory & visceral stimuli
- efferent division includes somatic (motor neurons > skeletal muscles) & autonomic (sympathetic to smooth muscles/glands & parasympathetic to muscles, cardiac & glands) nervous systems
describe the role of the different types of glial cells & their relation to neurons
a.k.a non-neuronal cells; use chemical signals in CNS & PNS to communicate with one another & neurons
- form connective tissue of brain, primarily supportive and maintain homeostatic control of extracellular environment around neurons
OLIGODENDROCYTES: form myelin sheaths of neuronal axons in CNS; one cell myelinates multiple neurons with it’s extensions
EPENDYMAL CELLS: line fluid-filled areas of the brain (ventricles) & produce CSF; cilia on cells keep CSF flowing through ventricles & central canal
ASTROCYTES: most numerous; form primary connective tissue to hold neurons in proper spatial relationships; induce brain blood vessels to change anatomically/functionally for the blood-brain barrier; help repair brain/spinal cord issues; help halt NT’s; enhance synapse formation & modify transmission; take up excess K+ to maintain environment
MICROGLIA: inactive forms support neurons & glial cells by secreting nerve growth factor; activate in response to pathological change (cytokines, plaques, cell death etc.) & migrate towards affected area to phagocytose foreign particles, reduce inflammation & release cytotoxins (overproduction is implication in several neurodegenerative diseases)
describe the different ways in which the CNS is protected
- bone (SKULL & VERTEBRAE): hard, physical, protective barrier
- MENINGES: DURA MATER (underneath bone & in direct contact except where dural sinuses separate them; venous blood draining from the brain empties into sinuses before returning to the heart); ARACHNOID MATER (delicate & highly vascularized; in regions of dural sinuses arachnoid granulation villi projections penetrate sinuses allowing for transfer of CSF from subarachnoid space to cross villi into sinus blood); PIA MATER (highly vascularized & tightly adhered to brain surface & spinal cord; dips into brain in some regions to bring blood to ependymal cells in ventricles = choroid plexuses)
- CEREBROSPINAL FLUID (CSF); acts as a shock-absorber; suspends brain & location in subarachnoid space; also essential for material transfer between blood & neural tissues; created by choroid plexuses that dip into ependymal cells
- BLOOD-BRAIN BARRIER: endothelial cells of brain capillaries joined by tight junctions to prevent passing materials; regulate movement & protects brain cells from toxins
describe the primary roles of the spinal cord
- a long tube of neurons & glial cells which extend from the brainstem through a hole in the skull to the lumbar region of vertebral column
- acts as a highway for information flow between brain & body
- can independently control reflexes that bypass the brain (simple or acquired)
outline the functional roles of the grey & white matter of the spinal cord
GREY MATTER: consists of nerve cell bodies, short interneurons & glial cells, as well as central canal filled with CSF
- each half is divided into regions/horns: DORSAL HORN (cell bodies of interneurons on which afferent neurons terminate, with cell bodies in dorsal root ganglia of spinal cord); LATERAL HORN (cell bodies of autonomic efferent nerve fibres); VENTRAL HORN (cell bodies of somatic efferent neurons/motor)
WHITE MATTER: consists of bundles of nerve fibres or axons, connecting to a specific region of the brain or periphery (ascending or descending pathways)
- DORSAL ROOT GANGLIA receives information from periphery & relay it to interneurons of dorsal horn; connects to the spinal cord via the dorsal root & ventral root
describe reflexes with an emphasis on the underlying basis of the stretch & withdrawal reflexes
(1) receptors in the skin (sense physical/chemical change) produce AP
(2) afferent neuron transmits AP
(3) interneuron processes signal
(4) efferent neuron transmits response
(5) effector carries out desired response
STRETCH REFLEX: associated with skeletal muscles containing stretch receptors; when muscle is stretched the receptor activates afferent fibre terminating directly on an efferent neuronal which activates muscle contraction
WITHDRAWAL REFLEX: considered protective; (1) pain heat receptors activate thermal pain receptors; (2) action potentials are generated in afferent pathway, propagating impulses to spinal cord; (3) fibre can synapse many interneurons in spinal cord; stimulates excitatory interneurons & inhibitory interneurons on motor neurons, plus interneurons ascending to brain; (4) synapses trigger muscle contraction/relaxation; (5) hand withdraws from heat source
identify structures within the brain stem
MIDBRAIN, PONS, MEDULLA OBLONGATA
describe the primary functions of the brainstem
- provides vital link between spinal cord & higher brain centres; most neuronal synapses occur here before further processing occurs
- majority of the CRANIAL NERVES arise from brainstem for sensory/motor fibres in head/neck for hearing, eye movement, facial sensations, taste, swallowing & face/neck/shoulder/tongue muscles
- controls VEGETATIVE FUNCTIONS of cardiovascular, respiratory (medulla oblongata detects CO2/O2 changes in blood) & digestive systems through clusters of neurons
- muscles reflexes maintain POSTURE & EQUILIBRIUM, providing stability & balance for voluntary activity
- contains the RETICULAR ACTIVATING SYSTEM (RAS), a network of neurons that run throughout brainstem to thalamus & monitors all incoming sensory input acting as a filter for consciously received input; ascending fibres pass information to higher processing centres
- SLEEP is produced by NTs in the brainstem acting on various parts of the brain
describe the functions of the thalamus
located deep within the brain; acts as an INTEGRATING CENTRE for all sensory input before the cortex
- conducts preliminary processing; removes lesser signals & ensures stronger/more important impulses are sent to appropriate cortex regions
- can also amplify/increase importance of some signals
describe the functions of the hypothalamus
an integration centre for HOMEOSTATIC FUNCTIONING
- controls production/secretion of pituitary hormones
- plays a role in the sleep/wake cycle
- acts as autonomic nervous system coordinating centre
- controls uterine contraction & milk ejection
- controls food intake
- urine output & thirst control
- involved in emotion/behaviour
- controls body temperature
describe the structure & function of the cerebral cortex
- composed of GREY MATTER; divided into left & right hemispheres connected by the corpus callous
- 6 defined layers of different cell types; independent but highly interconnected in cortical microcircuits
- 4 lobes: FRONTAL LOBE (responsible for voluntary motor activity, speech, elaboration of thought; contains primary motor cortex which is separated from somatosensory cortex by central sulcus; large pyramidal neurons send axons down spinal cord to synapse on alpha motor neurons of skeletal muscles); PARIETAL LOBE (receives/processes sensory input); OCCIPITAL LOBE (initial processing of visual input); TEMPORAL LOBE (involved in vision & hearing)
describe the mapping of the PNS on the cerebral cortex in terms of somaesthetic & proprioceptive inputs
SOMATOSENSATION: physical sensation is sent to somatosensory cortex in anterior region of parietal lobe; where initial processing of somaesthetic & proprioceptive inputs occurs; each part is equally represented in somatosensory cortex (SENSORY HOMUNCULUS)
- primary motor cortex & premotor cortex also depict movements/relative output to the body in relation to a MOTOR HOMUNCULUS
describe the divisions of the cerebellum & their function
- integrates motor control & sensory perception; contributes to muscle tone, coordination & precise movements
- VESTIBULOCEREBELLUM: important for balance, spatial orientation & eye movement control
- SPINOCEREBELLUM: regulates skilled, voluntary movements; receives proprioceptive input to allow continuous fine-tuning of movement
- CEREBROCEREBELLUM: receives all input from cerebral cortex & is involved in planning of voluntary movement & evaluation of sensory information
describe the structure & functions of the basal ganglia
- consists of several masses of grey matter within cerebral white matter; associated with a variety of motor functions: MOTOR CONTROL, COGNITION, EMOTIONS, LEARNING
- highly connected to other brain regions to form a complex feedback loop between the cerebral cortex, thalamus (to positively reinforce voluntary movement initiated by cortex) & brainstem
- consists of: CAUDATE NUCLEUS, PUTAMEN, GLOBUS PALLIDUS, CLAUSTRUM
describe the basis for motor defects in Parkinson’s disease
- basal ganglia is crucial for inhibiting muscle tone throughout body; balances excitatory/inhibitory inputs while permitting purposeful motor activity; and, helps monitor/coordinate sustained contractions
- symptoms of Parkinson’s: increased muscle tone, involuntary/unwanted movements (i.e. resting tremors) & slowed initiation of movement
- deficient dopamine NT reduces functioning in basal ganglia
