lecture 14: Overview of Nervous System Flashcards
The more interneurons in a pathway…
the greater the ability to integrate and process information
Nervous system contains what pathways
sensory pathways, integrating centers, and output pathways
The Central Nervous system is made up of what pathways/centers?
Integrating centers, made of interneurons
Peripheral nervous system is made up of what pathways?
sensory pathways (sensory receptors) and output pathways (effector organs: ie. muscles and glands)
Most nervous sytesm have three functional divisions
How are Cnidarians the exception?
- 3 divisions: afferent sensory division, integrating centers, and efferent division
- cnidarians have an interconnected web or nerve net, neurons do not specialize into divisions, and are functionally bipolar, able to radiate impulses out from stim.
What two animal groups do not have bilateral symmetry or cephalization
cnidarians and echinoderms
Evolutionary trend of nervous systems
- cephalization, concentrating of sense organs at anterior end,
- and groups of neurons into ganglia and brain
ganglia:
groupings of neuronal cell bodies interconnected by synapses
Nerves:
grouping of axons of afferent and efferent neurons
Brain:
complex integrating center in anterior region made of clusters of ganglia and tras
nuclei
groupins of neuronal cell bodies within the brain
tracts
groupings of axons within the brain
Types of info integration from simple to complex
arc reflexes,
rhyhmic behaviour (pattern generator, breathing, locomotion),
voluntar behaviour (picking things up, fighting, reading),
learning and memory,
creativity,
consciousness
Reflexes can involve as few as
two neurous (monosynaptic) or more (polysynaptic)
Reflexes:
- rapid, automatic, and involuntary responses
- preserve homeostasis and integrity of body through rapid adjustments in function or organs
- little variability, same response each time
Reflexes: classification
by development: -innate (genetic) or acquired/learned
by processing sites: spinal or cranial
by response: somatic (skeletal muscles) or visceral/autonomic (smooth muscle, cardiac, and glands)
by complexity: monosynaptic (afferent directly to efferent; two neurons only) or polysynaptic (seperated by interneurons)
Reflex arcs: Convergence
allows spatial summation
-multiple neurons to one effected site
reflex arcs: divergence
amplify signals and allow the nervous system to engage in parallel processing
-one reflex to multiple effected sites
reflex arcs: partial processing
both convergence and divergence
how can brain influence reflex arcs?
can amplify or inhibit them at interneural integrating sites
CNS vs PNS: aggregation of cell bodies
CNS: nuclei
PNS: ganglia
CNS vs PNS: bundle of myelinated axons
CNS: tracts
PNS: nerves
CNS vs PNS: glial cells that produce myelin
CNS: oligodendrocytes-myelinate several axons at once
PNS: schwann cells-only able to myelinate one axon segment
CNS is protected by
- skull and vertebrae
- meninges: layers of connective tissue
- cerebral spinal fluid: fills space within meninges to act as shock absorber
CNS is isolated by
blood-brain barrier
Meninges
- layers of connective tissue around CNS
- continual with spinal meninges
- 3 layers: dura mater, arachnoid mater, and pia mater
- fish have one, amph, reptiles, and birds have two
CSF
- formed by choroid plexus in roof of each ventricle, then secreted into the ventricles, then central canal of spinal cord, into subarachnoid space around CNS, and into the venous circulation
- secreted by ependymal cells, which also adjust its composition
Blood-brain barrier: isolates the CNS
formed by -network of tight junctions btw endothelial cells of CNS capillaries
- thick basal membrane
- end-foot processes of astrocytes
BBB permeability
- only lipid-soluble compounds (O2, CO2), steroids, alcohols, and prostaglandins diffuse freely into interstitial fluid of brain and spinal cord
- water and ions must pass through channels (tightly controlled
- larger water soluble compounds (glucose and amino acids) cross via facilitated diffusion or active transport
cells controlling BBB
astrocytes: release chemicals controlling permeability of endothelium
pericytes regulate blood flow
3 locations in BBB of greater permeability
- hypothalamus to secrete hormones into blood
- pituitary gland: secrete hormones (ADH, oxytocin, etc) in blood
- pineal glands: pineal secretinos into blood
- thus all permeable sites allow hormone release into body
gray matter
neuronal cell bodies (interneurons)
white matter
bundles of axons and myelin sheaths
different of matter of brain and spinal cord
spinal cord white matter is on surface and gray matter on inside; its opposite for cerebral cortex
spinal cord regions
cervical, thoracic, lumbar, sacral (caudal; not in humans)
spinal cord as an integrating center
- spinal reflexes are involuntary and rapid
- brain receives sensory info as reflex occurs
- cord sends info to brain and receives instruction from brain
the brain is ______, and filled with ____
hollow, filled with cerebral spinal fluid (CSF)
2 major regions of brain
hindbrain=rhombencephalon
midbrain=mesencephalon
forebrain=prosencephalon
hindbrain functions and parts
- supports vital functions like breathing, circulation, and movement
- made of cerebellum, pons, and medulla oblongata
cerebellum
site of sensorimotor integration: integrates sense info from eyes, ears, and muscles
-2 functions: fine tuned motor coordination and maintaining posture/balance; does not INITIATE movement
pons
a relay station between higher and lower brains
- contains tracts that comm btw the two
- controls alertness and initiates sleep and dreaming, and helps regulate breathing
medulla oblongata
- regulates vital functions: breathing , heart rate, diameter of blood vessels, and blood pressure
- controls reflexes and contains pathways between spinal cord and brain
Midbrain:
involved with coordinated behavior (largest in fish and amphibians)
- processes and integrates sensory info
- fine muscle control
- alertness
Tegumentum
part of midbrain
- helps with fine muscle control
- relex response to sensory stimulation
Tectum
part of midbrain
- superior colliculi (eye reflex)
- inferior colliculi (processes auditory signals
Forebrain function and parts:
process and integrate sensory info, and coordinated behaviour
-cerebrum, olfactory bulb, thalamus, epithalamus, hypothalamus, and pituitary gland
cerebrum
- integrates and interprets sensory info and initiates voluntary movements
- in higher vertebrates it takes over many roles of midbrain
thalamus
integrates, filters, and relays info (except olfactory) to primary sensory cortex
epithalamus
contains the pineal gland and involved in circadian rhythms
hypothalamus
controls internal organs, homeostasis, and regulates endocrine system through the pituitary gland
cerebral cortex is folded to…
increase functional complexity, is correlated with intelligence
Cerebrum:
divided into two hemispheres connected by the corpus callosum, tracts of axons linking the two sides
-outer layer is called the cerebral cortex
Cerebral cortex
- initiates voluntary movements
- integrates and interprets sensory information
- in humans, allows concentration, reason, speach, and abstract thinking
inner layer of cerebrum contains
tracks sending info to various parts of brain (corpus callosum)
-basal nuclei involved in subconscious control of skeletal muscle tone and the coordination of learned movement patterns
mammal cerebral cortex is arranged…
in layers, with shape and density of neurons differing among layers
-gives the cortex high computational complexity
lobes of brain
frontal, parietal, temporal, and occipital
two cortexes dividing the frontal and parietal lobes
primary motor cortex and somatosensory cortex
somatosensory and primary motor cortex
govern control of various body parts
limbic system
network of connected structures that lie between cortex and rest of brain
- includes hypothalamus, amygdala, olfactory bulbs, and hippocampus
- influences emotions, motivation, and memory
- limbic system therefore MAKES us want to do things
Peripheral nervous system: nerve structure
parallel bundles of myelinated and unmyelinated axons enclosed in several layers of connective tissue
mixed nerves
contain both afferent and efferent neurons
cranial nerves
exit directly from braincase
spinal nerves
emerge fro the spinal cord
PNS divisions
efferent and afferent (sensory) branch
PNS efferent divisions
autonomic division and somatic motor division
PNS autonomic divisions
sympathetic, parasympathetic, and enteric
somatic motor pathways
control skeletal muscles
“voluntary nervous system”, except for reflexes
neurons of somatic motor pathway
- only one neuron from CNS to skeletal muscles, with its cell body in the CNS
- all neurons of somatic motor division release Acetylcholine as chem messener
- receptors for ACT are all the same in all skeletal muscles cells: nicotinic receptors
autonomic pathways
- control smooth/cardiac muscles, and glands
- usually not conscious control
- ‘involuntary nervous system’
- involved in homeostasis
sympathetic nervous system
- most active during periods of stress or physical activity
- fight or flight response
parasympathetic
- most active during periods of rest
- ‘resting and digesting system’
enteric
independent of sym/parasym
-affects digestion by innervating the GI tract, pancreas, and gall bladder
sym/parasympathetic systems: dual innervation
- together maintain homeostasis
- responses are opposite
- some effectors receive only sympathetic innervations ie, adrenal medulla, most blood vessels
sympathetic and parasympathetic NOT like somatic
-pathways contain neurons in series
-neurons synapse with each other in autonomic ganglia
-one preganglionic neuron may synapse with many postganglionic neurons (divergence- amplification of signal)
sym-10 or more neurons
para-3 or more
