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
identify the components of the limbic system & discuss it’s role in emotions & behaviour
- includes several brain regions interconnected by neural pathways, such as CEREBRAL CORTEX, BASAL GANGLIA, THALAMUS & HYPOTHALAMUS
- associated with emotions, behaviour, motivation & learning
- EMOTIONS: involves feelings/moods, also includes behavioural patterns, expressions & responses varying between individuals; neural mapping has demonstrated the limbic system as a whole being involved in emotions
- BEHAVIOUR: encompasses many actions/mannerisms as individuals interact with their environment; characterized thus by the individual’s response to various stimuli/inputs; conscious or unconscious, & voluntary or involuntary
describe how the cortex & hypothalamus are also involved in behaviour
- hypothalamus governs involuntary internal responses in preparation for appropriate action
- cerebral cortex provides neural mechanism necessary for regulating skeletal muscle responses in behaviour, higher cortical areas can modify, reinforce or suppress responses to refine them based on situational analysis
describe motivation in the context of the reward & punishment centres
- MOTIVATION: the ability to direct behaviour towards specific goals; some are homeostatic in nature, others are not and therefore involve the brain’s reward circuit
- reward circuit includes behaviours that were previously gratifying and may motivate an individual to repeat it
- involves electrical & chemical signals; dopamine neurons release NTs to receptors causing proteins within the receptor to carry on
define & compare the relationship between learning & memory
- LEARNING: the acquisition, modifying or reinforcing of knowledge or skills based on experience &/or instruction; major influences include punishment (decreasing behaviour) & reward/reinforcement (increasing behaviour); either can be positive or negative; learning is therefore a process, building on past experiences
- MEMORY: storage of acquired knowledge for later recall; forms the basis by which individuals can change their behaviour along with learning; neural changes from learning are stored as memory traces which are generally conceptual but reinforced with learning (pattern of signals transmitted across synapses in a vast network)
compare & contrast short term & long term memory
- new information is stored as SHORT TERM MEMORY, with a limited capacity; it is either forgotten or transferred to long term memory through practice or rehearsal
- LONG TERM MEMORY: events, experiences, or facts that occurred or were learned weeks to years ago; recall of knowledge can occur at different rates, as memories involving information/skills used frequency are essentially never forgotten/rapidly accessible while those less used are recalled slower
describe the storage of memory
neurons involved in memory traces are widely distributed throughout the HIPPOCAMPUS, limbic system, CEREBELLUM, PREFRONTAL CORTEX & others
- hippocampus is vital in short term memory; thought to play a role in consolidation and initial storage phase of long term memories before they’re transferred to other cortical sites; also important for declarative memory (“what”)
- cerebellum: role in procedural memories (“how to”) involving motor skills gained through repetitive training; recalled without conscious effort
- prefrontal cortex: key for complex reasoning associated with working memory; in cooperation with brain’s sensory regions, it is responsible for executive functions integrating information for planning, prioritizing, problem solving & organizing activities
compare & contrast habituation & sensitization
HABITUATION: decreased responsiveness to repetitive presentations of an indifferent stimulus that neither rewards or punishes (i.e. Aplysia snail reflexively withdraws gill when syphon is touched; repetitive touching slowly diminishes snail’s response over time)
SENSITIZATION: increased responsiveness to mild stimuli that occurs following a strong/noxious stimulus (i.e. snail pulls in syphon quickly & for longer after a hard hit)
the same neurons are involved in each case, but responses are different (habituation is a depression of synaptic activity)
