CNS Organization

Question 1

Definition of PNS. Afferent vs efferent pathways

Answer 1

-made up of transmission pathways carrying info between the CNS and external/internal environments

• afferent (sensory) -> carry TO the CNS
• efferent(motor) -> carry AWAY from CNS

Question 2

What does the PNS consist of?

Answer 2

• cranial nerves
• spinal nerves (31 pairs)
• sensory receptors in the skin and wall of the gut tube, tendons, and skeletal muscles
• motor end plates between motor neurons and skeletal muscle fibers

Question 3

What is the ANS?

Answer 3

• subdivision of PNS
• entirely motor
• innervates smooth muscle and glands

Question 4

What are the two divisions of the ANS?

Answer 4

• sympathetic (thoracolumbar)

- -parasympathetic (craniosacral)

Question 5

nucleus vs ganglion

Answer 5

nucleus: aggregation of dendrites and nerve cell bodies in the CNS
ganglion: “ “ in the PNS

Question 6

Nerve vs tract

Answer 6

nerve: bundle of fibers in the PNS
tract: bundle of fibers in the CNS

Question 7

What is a commissure?

Answer 7

-tract in the CNS that crosses from one side to the other

Question 8

What is the trophic, receptive, and the conductive unit in the neuron?

Answer 8

trophic: cell body
receptive: dendrite
conductive: axon

Question 9

What are the two major branches of spinal nerves?

Answer 9

• dorsal primary ramus

- ventral primary ramus

Question 10

What are the two small branches from each spinal nerve before turning into a ramus?

Answer 10

• white ramus communicans: carries myelinated preganglionic fibers
• gray ramus communicans: carries unmyelinated postganglionic fibers back to the spinal nerve

Question 11

What are the paravertebral ganglia?

Answer 11

• linked together into a long chain on either side of the vertebral column in the thoracolumbar region
• site of cell bodies of postganglionic sympathetic nerves
• site of synapses between preganglionic myelinated sympathetic neurons and postganglionic nonmyelinated sympathetic neurons

Question 12

What is a splanchnic nerve?

Answer 12

-a nerve supplying viscera

Question 13

What is a prevertebral ganglion?

Answer 13

• typically found anterior to abdominal aorta

- site of synapses between preganglionic myelinated sympathetic neurons and postganglionic nonmyelinated neurons

Question 14

What are the components of a refl arc?

Answer 14

• afferent pathway
• efferent pathway
• association neurons (interneurons)

Question 15

What is a monosynaptic pathway?

Answer 15

-pathways consisting only of afferent neurons and efferent neurons. Each pathway has a single synapse.

Question 16

What are polysynaptic pathways?

Answer 16

-pathways that include interneurons as well as afferent and efferent neurons. Each pathway has multiple synapses.

Question 17

Resting state cell body voltage

Answer 17

-65mV

Question 18

excited cell body voltage and how does this occur?

Answer 18

• approximately -45mV

- due to influx of Na+

Question 19

inhibited cell body voltage and how does this occur?

Answer 19

• 70mV

- due to influx of Cl- or efflux of K+

Question 20

What are the components of the somatosensory axis?

Answer 20

• peripheral receptors
• afferent neurons
• spinal cord or brainstem
• reticular substance
• cerebellum
• thalamus
• somesthetic areas of cerebral cortex

Question 21

What is the somatosensory axis?

Answer 21

the sequence of structures involved in the transmission of a sensory signal from the peripheral receptors to higher brain centers

Question 22

The somatosensory axis afferent neurons are arranged in a series of 3, what are those three afferent neuron groups?

Answer 22

• primary: synapse in the psterior horns of spinal cord or sensory nuclei in the brain
• secondary: synapse in the thalamus
• tertiary: synapse in the somesthetic areas of cerebral cortex

Question 23

What is the sequence of transmission of AP from higher brain centers to skeletal muscles?

Answer 23

• motor cortex cerebrum
• efferent pathways
• effectors (skeletal muscles)

Question 24

What are the processing areas of the skeletal motor nerve axis?

Answer 24

• basal nuclei in the telencephalon (putamen, globus pallidus, and subthalamic nuclei)
• thalamis in the diencephalon
• spinal cord reflexes

Question 25

ACh is typically excitatory, what is it secreted by?

Answer 25

- pyramidal cells (cerebral cortex) - basal nuclei neurons - alpha motor neurons - preganglionic neurons of ANS - postganglionic neurons of the parasympathetic system - some postganglionic neurons of the sympathetic system

Question 26

What is NE and what secretes it?

Answer 26

-can be either excitatory or inhibitory - neurons located in the brain stem and hypothalamus - neurons in pons - postganglionic neurons of sympathetic system

Question 27

What is dopamine and what secretes it?

Answer 27

- usually inhibitory | - most neurons originating in the substantia nigra

Question 28

What is glycine and what secretes it?

Answer 28

- always inhibitory | - synapses in spinal cord

Question 29

What is GABA and what secretes it?

Answer 29

- always inhibitory | - many areas in the spinal cord and cerebral cortex

Question 30

What is Glu and what secretes it?

Answer 30

-always excitatory - many sensory pathways entering the CNS - many areas of cerebral cortex

Question 31

What are some characteristics of dendrites?

Answer 31

-extend for long distances -cannot transmit AP -> electrotonic conduction instead -partially permeable to K+ and Cl- -potential lost due to leakage -gradual loss of potential as the depolarization spreads from the site of initiation results in decremental conduction +signal is weaker the further from site of initiation

Question 32

What is electrotonic conduction? Why can dendrites do this?

Answer 32

-direct spread of electrical current by ion conduction in the dendritic fluids without generating AP - dendrites have few voltage gated channels - thresholds too high for AP to occur

Question 33

What is the dendritic firing rate dependent on?

Answer 33

- if the neuron remians above the threshold for excitation, the neuron will fire repetitively - 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

Question 34

What is typical synaptic delay?

Answer 34

min time: 0.5sec | -time it takes to transmit a signal from a presynaptic neuron to a postsynaptic neuron

Question 35

Why is there a minimum delay between synaptic surfaces?

Answer 35

- time to release neurotransmitter from the presynaptic neuron - diffuse across synaptic cleft - act on postsynaptic membrane - increase membrane permeability - inward diffusion of Na+

Question 36

What are the two sources of blood to the brain?

Answer 36

- vertebral arteries | - internal carotid

Question 37

What is the name of the anastomosis between the two vertebral arteries and the two internal carotid arteries?

Answer 37

-circle of Willis

Question 38

What are the components of the Circle of Willis?

Answer 38

- posterior cerebral arteries - posterior communicating arteries - internal carotids - anterior cerebral arteries - anterior communicating artery (unpaired)

Question 39

What is the CNS and what belongs in it?

Answer 39

- consists of unpaired, bilaterally symmetrical structures extending along the longitudinal axis of the midsaggital plane of the body - consists of structures arising directly from the neural tube -brain and spinal cord