Central Nervous System (230 #5) Flashcards
afferent division
(away from the periphery) carries information to the CNS about external environment and provides status reports on internal activities being regulated by the nervous system
efferent division
(entering the periphery) instructions from the CNS are transferred to the effector organs (muscles or glands).
Autonomic Nervous System - fibres that innervated the smooth muscle, cardiac muscle and glands.
Somatic nervous system - fibres of the motor neurons that supply the skeletal muscles.
Sympathetic and Parasympathetic Nervous Systems - innervated most of the organs supplied by the autonomous system.
afferent neuron
1) peripheral ending = sensory receptor
2) cell body = devoid of dendrites and presynaptic inputs, located adjacent to the spinal cord.
3) peripheral axon = afferent fibre, extends from sensor to cell body
4) central axon = from cell body to spinal cord (short). Diverge and synapse with other neurons in the spinal cord.
Lie primarily in the PNS, with small central axons extending into CNS.
efferent neuron
1) cell body = originates in the CNS
2) efferent axon = efferent fibres, leave the CNS to course their way to the muscle or gland they innervate.
Lie primarily in the PNS, with the cell body in the CNS.
interneuron
lie entirely in the CNS. Contain 99% of neurons, with the CNS containing more than 100 billion.
1) Lie between afferent and efferent neurons (as connectors) and are important in integrating peripheral responses to peripheral info.
2) Interconnections are responsible for abstract - thoughts, emotions, memory, etc.
glial cells / neuroglia
do no conduct or initiate nerve impulses. Communicate with neurons and send chemical signals to maintain homeostasis. Serve as the connective tissue of the CNS, maintaining composition of ECF and actively modulate synaptic function.
1) astrocytes
2) oligodendrocytes
3) microglia
4) ependymal cells
Do not lose ability to undergo cell division - brain tumors of glial cells are GLIOMAS.
astrocytes
1) glue - hold neurons together in proper spatial relationships
2) serve as scaffold during fetal dev
3) induce small brain blood vessels to establish blood-brain barrier
4) repair of brain injuries and neural scar formation
5) take up and degrade glutamate and GABA neurotransmitters to halt them.
6) Take up excess K+ from ECF when pump is overwhelmed - if they didn’t, ECF K+ conc would decrease threshold potential of cells and cause hyperexcitability.
7) enhance synapse formation and strengthen synaptic tx via chemical signalling with neurons
microglia
immune cells of the CNS - play a role in the defense of brain as phagocytic scavengers. Derived from bone marrow tissue. Release low levels of nerve growth factor - wispy cells with many long branches.
ependymal cells
1) line internal cavities of brain and spinal cord
2) contribute to formation of CSF
3) serve as neural stem cells with the potential to form new neurons and glial cells.
CILIATED!
ventricles
four interconnected chambers within the interior of the brain, continuous with the narrow, hollow central canal that tunnels though the middle of the spinal cord. Lined by ependymal cells, the beating of their cilia contributes to flow of CSF throughout ventricles.
CNS Injury prevention
1) enclosure in hard bondy structures - cranium and vertebral column
2) three protective and nourishing membranes - meninges
3) brain floats in special cushioning fluid - CSF
4) highly selective blood-brain barrier limits access of blood-borne materials to brain tissue.
meninges
1) Dura Mater (tough mother) - two layers, some regions are separated to blood-filled DURAL sinuses, or VENOUS sinuses.
2) Arachnoid Mater - vascularized cobweb-like. Subarachnoid space is filled with CSF. Protrusions of arachnoid villi in the dural sinuses - CSF is reabsorbed along the surface.
3) Pia Mater - most fragile. Highly vascular and closely adheres to brain and spinal cord. Brings blood supply to ependymal cells lining ventricles.
Cerebrospinal Fluid (CSF)
surrounds and cushions the brain and spinal cord. Shock-absorbing protective fluid. Also helps in exchange between neural cells and brain interstitial fluid. Formed by choroid plexuses - richly vascularized cauliflower-like masses of pia mater tissue. Lower in K+ and higher in Na+ than plasma - specialized for conduction of nerve impulses.
Blood-Brain Barrier
1)anatomical - capillary walls are single layer of cells joined by TIGHT junctions
2) physiological - substances exchanged between blood and brain interstitial fluid (glucose, amino acids and ions) are transported by highly-selective membrane carriers.
Prevents potentially harmful blood-borne substances, hormones that may act as neurotransmitters, limits use of drugs for treatment of brain/SC disorders. Astrocytes surround brain capillaries - tell them to ‘get tight’ and participate in cross-cellular transport of substances like K+
HYPOTHALAMUS is not behind BBB
Nutrients
Brain cannot produce ATP in absence of O2 (anaerobic) - relies on neuroglobin (O2-binding protein) to bring O2 to tissues. Cannot store glucose, but is only fuel source. Brain damage after… O2 = 5 mins, glucose = 15 mins
cognition
the act of process of knowing, including both awareness and judgement.
Brain Stem
Midbrain, pons, medulla -oldest region of brain, continuous with spinal cord.
1) origin of majority of peripheral cranial nerves
2) cardio, resp and digestive control centres (vegetative functions)
3) regulation of muscle reflexes for equilibrium and posture
4) part of ‘reticular formation’ - reception and integration of all synaptic input from spinal cord - activation and arousal of cerebral cortex
5) role in sleep-wake cycle.
Cerebellum
More individual neurons than in rest of brain.
1) Vestibulocerebellum - maintenance of balance – proprioception & controls eye movements.
2) Spinocerebellum - enhancement of muscle tone and coordination of skilled voluntary muscle activity – monitors and adjusts ‘motor plan’ from cortical motor areas.
3) Cerebrocerebellum - planning of skilled voluntary muscle activity (dance routine)
Hypothalamus
1) regulation of many homeostatic functions - temp, thirst, urine output, food intake, uterine contraction, milk ejection.
2) important link btwn nervous and endocrine
3) extensive involvement with emotion and basic behavioural patterns
Thalamus
1)relay station for all synaptic input
2) crude awareness of sensation (can’t distinguish location or intensity)
3) some degree of consciousness
4) role in motor control
Screens out insignificant signals and routes important impulses to areas of somatosensory cortex. Directs attention to stimuli of interest (background noise vs. baby crying).
Basal Nuclei / Basal Ganglia
1) inhibition of muscle tone
2) coordination of slow, sustained movements
3) suppression of useless patterns of movement
Do not directly influence efferent motor neurons, but modify activity in motor pathway.
Cerebral Cortex
1) sensory perception
2) voluntary control of movement
3) language
4) personality traits
5) sophisticated mental events - thinking, memory, decision-making, creativity, and self-conciousness
Organized into six well-defined layers and functional vertical columns and four LOBES (parietal, occipital, frontal and temporal)
Forebrain
Diencephalon (hypothalamus and thalamus) and the Cerebrum (Basal Nuclei and the Cerebral Cortex)
Cerebrum
1) highly convoluted = more developed species. 80% of the total brain weight.
2) Divided into the right and left cerebral hemispheres which are connected by the corpus callosum - a thick band consisting of about 300 million neural axons through which the left & right hemispheres communicate.
3) Grey Matter is made of neural cell bodies & dendrites + glial cells.
4) White Matter is tracts of myelinated nerve fibres (axons).
Parietal Lobe - Cerebral Cortex
Located on the top of the head, to the rear of the central sulcus (deep infolding). Contains the somatosensory cortex - the site for initial cortical processing and perception of somesthetic input as well as proprioceptive input. Locates the source of sensory input (routed from the thalamus) and perceives the level of intensity.
Frontal Lobe - Cerebral Cortex
Activated by the readiness potential (widespread neuronal discharge about 750 msec before any activity in motor area)
1) Contains the primary motor cortex beside the central sulcus. Primarily confers voluntary control over muscles on the the opposite side of the body. Signals from the PMC terminate on the efferent neurons that trigger muscle contraction.
2) Supplementary Motor Area plays a preparatory role in programming movement sequences.
3) Premotor Cortex orients the body and arms to a specific target, guided by posterior parietal cortex.
Together, the 4 motor regions develop a ‘motor program’ for different movement patterns.
use-dependent competition
somatotopic mapping is not set in stone - but is subject to constant subtle modifications based on use. General pattern is genetic/developmental, but individual cortical architecture can be influenced. i.e. modified by experience
