Nervous System Flashcards
Describe the 3 main functions of the nervous system
- Gather sensory input
- Integration of that sensory input
- Effects a motor output (response)
What is the difference between afferent and efferent systems?
Afferent: input cells/sensory
Efferent: Output cells/motor
Describe the 3 classifications of sensory receptors based on location
1.Exteroceptors: stimulation from outside of the body
2.Interoceptors: stimulation from inside body
3.Proprioceptors: respond to internal stimuli, but located only in skeletal muscle, tendons, joints, and ligaments
Describe the 5 sensory receptor classifications based on receptor type/stimuli detected
1.Mechanorecpetor
2.Chemoreceptor
3.Thermoreceptor
4. Photoreceptor
5.Nociceptors
Describe the 4 types of afferent fibers
1.Aalpha: are types of proprioceptors
2. A beta: are the non noxious mechanoreceptors
3. A delta: are the noxious mechanoreceptors for quick intense pain
4.C fibers are the classic pain receptors
What is the only afferent fiber not myelinated?
C fibers
Describe the two types of efferent motor neruons
-Upper motor neurons (UMN): motor cortex, Brain stem,
-Lower motor neurons (LMN): final common pathway, project to muscles
Where are the pre and post ganglion located for the ANS?
-Pre ganglion is located in CNS and post ganglion is located in PNS
What are the 3 neuron types?
-Multipolar neuron
-Unipolar neuron
-Bipolar neuron
Describe Multipolar neurons and where they are located in the nervous system
- dendrites extend from body
-only one axon, but multiple collaterals
-most common
-can be UMN or LMN, ex: alpha motor neurons in spinal cord, or pyramidal neurons in the cerebral cortex
Describe bipolar neurons and where they are located in the nervous system
-Two processes extending from cell body
-Dendrites receive information from sensory cell then signal is transmitted centrally via the axon
-Found in retina, olfactory epithelium and vestibulocochlear nerve
Describe unipolar neurons and where they are located in the nervous system
-Have two axons rather than dendrites and an axon
-one axon extends from sensory receptors in the periphery and the other extends centrally toward the spinal cord
-Only exists in the dorsal root ganglion
Describe the roles of glial cells
-provide mechanical and physical support
-provide nutrients to neurons
-remove cellular debris including rapid uptake of toxic substances (ie synaptic glutamate)
-provide electrical insulation (myelination)
What are the 6 main glia cells and their functions
-Schwann cell(PNS): myelinate peripheral axons, one schwann cell per segment of axon. involved in axonal regeneration
-Satellite cells (PNS): support cells, envelop PNS neuronal cell bodies and serve to regulate the chemical environment
-Microglia (CNS): super small. Responsible for immuno surveillance and immuno-regulation, phagocytic activity following cell death or injury. Produce inflammatory mediators that can ultimately result in neuronal damage
-Oligodendrocytes (CNS): Myelination of CNS axons. Can myelinate multiple sections of axon.
-Astrocytes: role in blood brain barrier. Critical role in synthesis and metabolism of major excitatory and inhibitory NT. Critical in clearance of synaptic excitatory NT. Maintain structural integrity of CNS following injury (scar)
-Ependymal cells: involved in the production of cerebrospinal fluid. clia important for CSF flow
Describe CSF production and purpose
-produced by the choroid plexus within the ventricles of the brain
-purpose: removes waste from brain and spinal cord, bring nutrients, and serve as a cushion
What are the 3 main meninges and their purpose
- Dura Matar:
-seperate the cranial cavity into compartments
-protect the brain from displacement
2.Arachnoid:
-middle layer filler with CSF
-projects into sinuses formed by dura mater to transfer CSF back into the bloodstream
-all blood vessels entering the brain as well as cranial nerves pass through this space
3.Pia:
-innermost layer that adheres closely to brain
-it fuses with the lining of the ventricles (ependymal) to for choroid plexus
What is the primary energy sources of the brain?
glucose
True/False: conditions that alter glucose levels or oxygenation quickly impact neurological processes
True
Describe the basic internal structure of the spinal cord
organized into grey and white matter. Grey matter surrounds the central canal and consists of dendrites, axon terminals, and interneurons. The white matter consists of myelinated axons passing to and from the brain or different segments of the spinal cord.
Describe the organization of spinal cord grey matter
3 horns:
1. Dorsal: neurons that receive somatosensory information
2. Ventral: motor neurons exiting the spinal cord to innervate muscle
3. Lateral: only in thoracic/lumbar region: contains neurons that innervate visceral and pelvic organs as part of the ANS
True/False: spinal nerves are mixed nerves, i.e they carry both motor and sensory neurons
true
List the general segmental divisions of spinal nerves in mammals (6)
-cervical (C1-C5)
-Cervicothoracic (C6-T2)
-Thoracolumbar (T3-L3)
-Lumbosacral (L4-S3)
-Cauda equina: caudally streaming spinal roots
-Filum terminale: an extension of the pia mater that is attached to the coccygeal segments
Describe the structures that support and protect the spinal cord
-Encased within the vertebral column of the vertebrae
-Supported by spinal meninges: dura mater, arachnoid, pia
Explain the function of muscle spindles
Muscles spindles are proprioceptors within muscle bellies that provide information about the length (stretch) and speed of movement. Innervated by both afferent and efferent axons. Efferent contracts intrafusal fibers to match length of extrafusal fiber. Afferent sends info to CNS.
What is the role of gamma motor neurons in muscle spindle activity?
They maintain the intrafusal sensitivity by having the contractile part contract to then be able to fire again.
Describe the stretch reflex
primary afferent inputs from muscle spindles are activated by muscle stretch, they enter the spinal cord via the dorsal root ganglion, they then synapse an efferent neuron in the ventral horn and this excitatory reflex increases muscle contraction in response to muscle elongation.
What is the role of interneurons in the stretch reflex?
1a afferents possess branches to synapse inhibitory interneurons, these interneurons will then synapse on antagonistic alpha-motorneurons, which then inhibits the antagonist muscle
Explain the function of golgi tendon organs
located in the tendon, and innervated by a single myelinated afferent. muscle contraction straitens the collagen fibers around the golgi tendon organ, compressing the sensory ending, which results in depolarization. They sense changes in muscle tension and force.
Describe tendon reflexes
golgi tendon organ senses excessive tension on the muscle, action potential generated in the 1b fiber, synapses on inhibitory interneuron, the inhibitory neuron inhibits the alpha motor neurons to relax the muscle under tension and at the same time an excitatory interneuron stimulates the contraction of the antagonist muscle.
Describe withdrawal and crossed extensor reflexes
-Activated by painful stimulus
-Activates cutaneous nociceptor
-Travels to spinal cord via dorsal root ganglion, synapses multiple interneurons, 2 excitatory and 2 inhibitory, to withdraw from the painful stimulus and extend the supporting limb, the crossed extension reflex is what enhances postural support during withdrawal of the affected limb from the painful stimulus
What are the two efferent pathways?
-Somatic
-Autonomic
The ANS is regulated by inputs from where?
the hypothalamus and brain stem
Why is the ANS referred to as a two neuron system?
Because as opposed to the one neuron system of the somatic system, the ANS has a pre and post ganglion neuron
What are the two divisions of the ANS? and what are their general functions?
-Parasympathetic: controls autonomic function in the resting, unstressed animal
-Sympathetic: involved in autonomic response to stressful external stimuli
What are the neurotransmitters and receptors for the two divisions of the ANS
- All preganglionic neurons release acetylcholine (cholinergic) on nicotinic receptors
-Postganglionic neurons of the parasympathetic division release acetylcholine on muscarinic receptors
-postganglionic fibers of the sympathetic division releases norepinephrine (noradreneric) which can act on both norepinephrine or dopamine receptors
-sweat glands are an exception, they are part of the sympathetic division but the postganglionic fibers release acetylcholine on muscarinic receptors in the sweat gland
Where are pre and post ganglionic cell bodies located in the sympathetic division?
Pre- are located in the lateral horn of the thoracolumbar spinal subdivision
Post- are located in either the sympathetic chain or prevertebral ganglia
Where are the pre and post ganglionic cell bodies located in the parasympathetic division?
pre- are located in the brainstem or sacral spinal cord
post are very short and usually located near or in the organs being innervated
What is spreading activation?
the fact that a single preganglionic sympathetic neuron can synapse with many postganglionic neurons up and down the sympathetic chain. This results in a rapid and diffuse sympathetic activation
Describe sympathetic innervation of the head
Provided by the cranial cervial ganglia ONLY. the signal travels via the vagosympathetic trunk. Innervates smooth muscle of the orbit, superior eyelid, and the dilator muscle.
-Activation=dilated pupil, eyes wide open, protruding slightly.
-Damage leads to horner’s
Describe the parasympathetic innervation of the head
Most cranial parasympathetic innervation is involved in glandular activation. The two cranial nerves mainly responsible are the facial (VII) and the glossopharyngeal (IX)
-The oculormotor (III) is the origin to the parasympathetics for pupillary constriction and the ciliary muscle for the lens
Is the viscera considered part of the ANS?
no
What role does the viscera have in ANS regulation?
visceral afferents can stimulate local reflex function (ie local pacemakers in the intestinal wall), inputs from the tongue, carotid sinus, aortic arch, etch can send projections to the brainstem for reflexive activation or the somatosensory cortex for conscious perception
What roles does the brainstem have in ANS regulation?
-The respiratory and cardiovasular centers are located in the caudal medulla and pons, these regions have UMN that regulate the function of both alpha motor neurons going to respiratory muscles and autonomic neurons that innervate cardiac and vascular smooth muscle.
What brain region is the only one to have direct influence over both the parasympathetic and sympathetic outflow?
the paraventricular nucleus in the hypothamalus
What brain region is the primary integrator of autonomic signaling?
the paraventricular nucleus in the hypothalamus
