The nervous system is divided into three parts. Name them
CNS, PNS, ANS,
The CNS consists of _____
Structures arising directly from the neural tube. Includes: Brain and spinal cord
The PNS consists of ______
cranial nerves and spinal nerve
The ANS consists of_______
sympathetic and parasympathetic
the CNS consists of unpaired, bilaterally symmetrical structures extending along the longitudinal axis of the midsagittal plane of the body
What is a brain?
Sorts through and properly routes incoming sensory info Initiates controls and coordintes most muscular activity except simple reflexes Site of origin of 12 cranial nerve pairs
What 4 pairs of cranial nerves carry parasympathetic fibers?
III, VII, IX, X
What are the general functional categories of the brain
sensory motor cognitive
Define spinal cord
It is the first CNS structure encountered by most incoming sensory info except sensory fibers in cranial nerves It is the last relay station for most motor information except ANS motor fibers It is the site of coordination of most reflex arcs
Define peripheral nervous system
It is made up of transmission pathways carrying info between the CNS an external/internal environment. Has afferent pathways and efferent pathways
What carries info to the CNS
afferent (sensory) pathways
What carries information FROM CNS
efferent (motor) pathways
How many cranial nerves are included in the PNS?
How many spinal nerves are included in the PNS?
31 of the PNS
PNS has sensory receptors in _____
the skin and wall of the gut tube as well as in tendons and skeletal muscles
PNS motor end plates are between ______
motor neurons and skeletal muscle fibers
ANS may be considered a subdivion of _________
ANS is entirely _________
ANS innervates ______
smooth muscle and glands (viscera)
ANS sympthetic system is also called the ______ and ________
fight or flight also called thoracolumbar
ANS prasympathetic is called _____ and _______
feed and breed also called craniosacral
What is the cell body of a neuron?
It is part of a neruon that encloses the nucleus and other organelles necessary to maintain and repair the neuron Has a trophic unit and perikaryon
What are dendrites of a neuron?
Branches off the cell body that carry information to the cell body: Receptive unit Characteristics: -usually several to many dendrietes per neuron -relatively short, compared to the axon -often branched ***have receptors for neurotransmittors ***conduct local potentials
What is the axon of a neuron?
The conductive unit the neuron that carries info to another neuron or muscle cell
What are axon characteristics?
Usually relatively long Single (one per neuron) Conducts action potentials (nerve impulse) Releases neurotransmitters
What are telodendria?
-Short branched processes at axon ends -They give off endings called terminal boutons
axons may have what type of branches?
what is the cell membrane of the axon called?
what is the cytoplams of the axon called?
what does the axon contain?
mitochondria, neurofilaments, and neurotubules
axon is covered by a __________
neurolemma is made up of _________ and is often________. And the ______ is formed by ___ ____
The neurolemma is made up of Schwann cells and is often myelinated. And the myelin is formed by Schwann cells
What is the ONLY part of the neuron that can be mylinated? Is this part always myelinated?
The Axon Not all axons are myelinated, even though they are covered by schwann cells
What is aggregation of dendrites and nerve cell bodies in CNS called?
What is aggregation of dendrites and nerve cell bodies in PNS called?
What are bundle of fibers (axons) in the PNS called?
What are bundle of fibers (axons) in the CNS called?
What is the tract in the CNS that crosses from one side to the other called?
What are areas of myelinated axons called?
What are areas of unmylenated axons, cell bodies, and dendrites called?
What are two spinal nerve branches (rami)?
dorsal primary rami and ventral primary ramus
Each spinal nerve in the thoracolumbar region, before branching into _______ gives off two small branches called ______ and _______. What are the functions of the two small branches?
1. primary rami 2. White ramus communicans: Carries myelinated preganglionic fibers 3. Gray ramus communicans: Carries unmyelinated postganglionic fibers back to spinal nerve
What is linked together into a long chain on either side of the vertebral column in the thoracolumbar region. Is the site of cell bodies of postganglionic sympathetic nerves And is the site of synapes between preganglionic myelinated sympathetic neurons and postganglionic non myelinated sympathetic neurons?
What is a nerve supplying viscera called
What is typically found anterior to abdonminal aorta And is the site of synapses btw preganglionic myelinated sympathetic neurons and postganglionic non myelinated neurons?
What is a reflex arc?
a pathway that leaves form and returns to the CNS. It consists minimally of a sensory pathway and a motor pathway Extra: can't override consciously, can't fake it
what carries sensations from non-visceral structures such as the skin and skeletal muscle?
Somatic afferent pathways (Sensory)
What carries sensation from viscera?
Visceral (splanchnic) afferent pathways (sensory)
What carries motor signals to skeletal muscles?
somatic efferent pathways
What carries motor signals to smooth or cardiac muscles?
visceral (splanchnic) motor pathway
What are association neurons (interneurons)
-some reflex arcs consist only of an efferent neuron and an afferent neuron but most have intervening neurons, called association neurons or interneurons, in the central nervous system that modulate the interactions btw the afferent and the efferent neurons
What is associated with synaptics vesicles filled with neurotransmitters
What is the synaptic cleft a part of?
part of a synapse
What is associated with receptors for neurotransmitters?
What are pathways consisting only of afferent neurons and efferent neurons and each pathway has a single synapse
What pathways include interneurons as well as afferent and efferent neurons and each pathway has multiple synapses?
Depending on synaptic activity, a neuron may be in one of three physiologic states. What are the three states and explains what is happening in each state?
1. Resting- cell body potential is about -65 mv 2. Excited- cell body potential is more positive; about -45. Typically due to influx of Na ion 3. Inhibited- cell body potential is more negative than at rest;about -70. Typically due to influx of Cl ion or efflux of K ion
What refers to the sequence of structures invloved in the transmission of a sensory signal from the peripheral receptors to higher brain centers
What are components of the somatosensory axis pathway?
peripheral receptors afferent neurons spinal cord or brainstem reticular subatance- medulla, pons, mesencephalon cerebellum thalamus somesthetic areas of cerebral cortex
How are afferent neurons arranged?
In a series of three: primary afferent neurons- synapse in the posterior horns of spinal cord or senrsoy nuclei in the brain secondary afferent neurons- synapse in the thalamus tertiary afferent neruons- synapse in the somesthetic areas of cerebral cortex
the skeletal motor nerve axis refers to _____
the sequence of structures involved in the transmission of an action potential from the higher brain centers to skeletal muscles
skeletal motor nerve axis includes ________
motor cortex of cerebrum efferent pathways effectrors- skeletal muscles
What is made up of upper motor neruons extending form cortical areas to the anterior horns of the spinal cord and its alpha motor neurons (lower motor neruons) are extending to the skeletal muscles?
Skeletal motor nerve axis efferent pathways
What are smooth muscles and glands supplied by?
ANS and have a somewhat different pathway compared to skeletal motor nerve axis
What are the processing areas of the skeletal motor nerve axis?
basal ganglia(nuclei) in telencephalon thalmus in the diencephalon spinal cord relfexes
what is the basal ganglia (nuclei) in the telencephalon made up of?
putamen globus pallidus subthalamic nuclei
Acetylcholine is secreted by what neurons? And are they excitatory, inhibitory, or both?
pyramidal cells (cerebral cortex) some neurons in the basal nuclei alpha motor neurons preganglionic nuerons of ANS postganglionic neurons of the parasympathetic system some postgaglionic neurons of the sympathetic system They are usually excitatory
norepinephrine is secreted by what neurons? And are they excitatory, inhibitory, or both?
many neurons located in brain stem and hypothalamus some neurons located in the pons (i.e., locus ceruleus) most postgaglionic nuerons of the sympathetic system. They can be both
Dopamine is secreted by what neurons? And are they excitatory, inhibitory, or both?
neurons originating in substantia nigra Usually Inhibitory
Glycine is secreted by what? And are they excitatory, inhibitory, or both?
synapses in the spinal cord ALWAYS inhibitory
GABA secreted by ____? And are they excitatory, inhibitory, or both?
many areas in the spinal cord and cerebral cortex Always inhibitory
Glutamate secreted by ______? And are they excitatory, inhibitory, or both?
many sensory pathways entering the CNS many areas of cerebral cortex ALWAYS Excitatory
READ pg 557
what may extend out for a considerable distance?
dendrites... they can receive signals from a large spatial area around a motor neuron
What cannot transmit action potentials?
Dendrites... they use electronic conduction instead
What are long and membranes are thin?
Dendrites... partially permeable to K and Cl ions some potential lost due to leakage
What occurs in a dendrite due to gradual loss of the potential as the depolarization spread from the site of initiation?
decremental conduction The signal becomes weaker as it gets farther away from site of initiation This is in opposition to action potentials which are constantly renewed along the length of the axon and therefore do not decrease in strength
What is direct spread of electrical currect by ion conduction in the dendritic fluids without generating action potential?
What results from electrotonic conduction?
few voltage gated Na channels in dendritic membranes thresholds too high for action potentials to occur
What is defined as the summated degree of excitatory drive to the neuron?
When does the excitatory state occur?
When there is a higher degree of excitation compared to inhibition.
When does the inhibitory state occur?
When there is a higher degree of inhibition compared to excitation.
What is firing rate
as long as the excitatory rate of a neuron remains above the threshold for excitation, the neuron will fire repetitively
The firing rate depends on the
normal excitatory rate and on the changes in the excitatory rate due to superimposition of additional excitatory or inhibitory signals
What refers to the time it takes to transmit a signal form a presynaptic neuron to a postsynaptic neuron?
What does a synaptic delay depend on?
-time it takes to release the neurotransmitter from the presynaptic neuron -time it takes for the neurotransmitter to diffuse across the synaptic cleft -how the neurotransmitter acts on the postsynaptic membrane -the time it takes for the receptor to increase membran permeability -time it takes for the inward diffusion of Na ions
What are the parts of a neuron?
Cell body, dendrites, and axon
What do terminal boutons contain?
Synaptic vesicles filled with neurotransmitters
What will not summate to produce an action potential on a postsynaptic neuron?
Simultaneous firing of only a few synapses
What can cause superimposed action potential on the postsynaptic neuron?
Can be caused by the simultaneous firing of many synapses
What structures are processing areas of the skeletal motor nerve axis?
The basal ganglia (nuclei in the telencephalon Thalamus in the diencephalon Spinal cord reflexes
What are dendritic membranes partially permeable to?
Potassium and chloride ions
what is main cause of lost in dendrite potential?
What are the two sources of blood supply to the brain?
Vertebral arteries and internal carotids
What is the pathway of vertebral arteries?
First branches of the subclavian arteries Ascend through the transverse foramina of CV 1-6 Pass through foramen magnum Unite at caudal border of pons to form basilar artery The basilar artery gives off cerebellar arteries and then divides into two posterior cerebral arteries
What is the pathway of internal carotids?
Terminal branches of the common carotids Enter cranial cavity through carotid canal in temporal bone
What is the Circle of Willis?
A pentagonal-shaped circle of arteries on the ventral surface of the brain that unites the two vertebral and the the two internal carotid arteries
What is an important anastomosis between the two vertebral and two internal carotid arteries?
Circle of Willis
What are the components of the Circle of Willis?
Posterior cerebral arteries Posterior communicating arteries Internal carotids Anterior cerebral arteries Anterior communicating artery (unpaired)
What are the terminal branches of the basilar artery?
Posterior cerebral arteries
What connects the posterior cerebral arteries to the internal carotids?
Posterior communicating arteries
What gives off anterior and middle cerebral arteries?
What branches off internal carotids?
Anterior cerebral arteries
What connects the two anterior cerebral arteries?
Anterior communicating artery (unpaired)