Exam 1 Flashcards
Somatic Nervous System
voluntary skeletal muscle
Visceral Nervous System
nerve supply of organs
Motor
efferent
Sensory
afferent
Ganglia
cluster of nerve cell bodies located outside the CNS
Nuclei
Cluster of nerve cell bodies located within the CNS
Tracts
bundles of axons carrying similar information, axons with same origin and common insertion (lemniscus, fasciculus, pedunc;e, column, capsule)
Sensation
awareness of stimuli
Perception
interpretation of stimuli into meaningful information
Unipolar
only one projection off the cell body (projection is considered an axon), most peripheral sensory neurons
Bipolar
have two processes coming off. Found in retina, vestibular nerve, cochlear nerve
Multipolar
many processes of the cell body. Most motor and CNS interneurons
How many axons do unipolar, bipolar and multi polar neurons have respectively?
They all have one!
Autograde transport
Flow of NT/NMs, nutrients, proteins etc from the cell body to the terminus
Retrograde transport
Flow of substances from the terminus to the cell body (Toxins (tetanus) and viruses (herpes, polio, rabies), tracing dyes & nerve growth factor are transported into the CNS via this route)
Paresis
Partial loss of voluntary contraction (weakness)
Paralysis
Complete loss of voluntary contraction
Plegia
means paralysis
Myoclonus
Involuntary contractions (hiccups, eye twitches)
Hypotonia
Abnormally low resistance to passive stretch
Flaccidity
Lack of resistance to passive stretch
Neurons
release the neurotransmitters and neuromodulators across a synaptic gap. REsting membrane potential of -70 mV (compared to outside of the neuron)
How is the resting membrane potential maintained by the neuron?
Passive: sodium (+) higher concentration outside the neuron, chloride(-) is higher outside so goes inside. Potassium (+) higher cnocentration inside so goes out making the cell more negative.
Active: Sodium potassium pump in the membrane, 3 positive Na out and 2 positive K(+) in (net negative) Needs ATP to function, which you need oxygen for ATP
Also, negatively charged ions/proteins are trapped (they are large and can’t get out)
Neuroglia
can divide and multiply, 10 x more glial cells than neurons. (astrocytes, oligodendrocytes, schwann cells, microglia, ependymal cells)
Astrocytes
Good: Add structure, BBB, maintain K+ levels, guide migrating neurons
Bad: Scar up in CNS injury (why theres trouble healing from CNS injury)
They actually transmit information:
Transmit Ca2+ to other astrocytes
2 way communication with neurons(neurons stimulate astrocytes, and astrocytes release glutamate into neurons via gap junctions.
2 types: protoplasmic (gray matter) and fibrous (white matter)
susceptible to forming neoplasms (astrocytoma)
Oligodendrocytes
Myelinate axons in the CNS, antibodies attack these in multiple sclerosis (MS), 1 segment of multiple axons in CNS
Schwann Cells
Myelinate axons in the PNS, antibodies attack these in guillan-barre, myelinate 1 segment of 1 axon in PNS
Microglia
phagocytes, over-activated in Alzheimers and AIDS
Ependymal Cells
Line the ventricles and central canal, Ependymomas (tumors)
Saltatory Conduction
Action potential appears to jump from one node of ranvier to the next, there are few Na+ channels in the myelin covered axolemma.
Cell body of neurons
Contains organelles (nucleus, golgi apparatus, ER, ribosomes, etc) Manufactures NT/NM, membrane proteins etc.
Axon of neurons
Only 1 per neuron, but can have many branches
Each branch has a nerve terminal for release of NT/NM
Dendrites
1º receptive area, Most neurons have many dendrites; each dendrite branches multiple times
Chemical Synapses
Presynaptic membrane, synaptic gap, post synaptic membrane
Types of synapses
- Axo-dendritic (most numerous; usually excitatory)
- Axo-somatic (usually inhibitory)
- Axo-axonic (presynaptic inhibition or facilitation; either reduces or increases Ca2+ influx)
- Dendro-dendritic
Excitatory Post-synaptic Potentials (EPSPs)
- Binding of neurotransmitters opens voltage-gated Na+ channels → causes influx of Na+ and/or Ca2+
- RMP rises from -70 to -55
- Na+ channels open at the axon hillock in motor and interneurons → APs travel down the axon – Ca2+ channels open at terminus – Ca2+ enters – causes fusion of NT/NM vesicles to fuse to membrane – release by exocytosis
- In sensory neurons, Na+ channels near the receptor open (trigger zone) – APs travel up the axon toward the cell body.
IPSP’s
Binding of NT/NM to a receptor on a neuron causes:
- Efflux of K+ or influx of Cl-
- Lowers RMP from -70 to a more (-) value
What could block the voltage-gated Na+ channels?
The voltage-gated Na+ channels are blocked by procaine (novocaine) and lidocaine to reduce pain transmission of sensory nerves
Leak channels
Allow diffusion of ions in a slow continuous manner, Important in maintaining osmotic gradients and membrane potentials
Modality-Gated channels
Channels that open in response to stretch, temperature, pressure, Found in receptors
Ligand-gated channels
a.ka. ionotropic - Function as receptors for NT’s/NM’s, rapid, short term effect
Voltage gated channels
Respond to changes in membrane potentials (Ca2+ channels at the synapse, Na+ channels at the axon hillock and trigger zone)
Repolarization
Voltage-gated Na+ channels close (refractory period), also prevents AP’s from going in a retro-directed (toward the cell body), Voltage-gated K+ channels open
Whats the difference between a Nerotransmitters & neuromodulators?
NT is a short-term quick effect, NM long-term/delayed effect (not immediate response). Some chemicals can function as both.
Glutamate
the major excitatory NT in CNS! Chemical that produces the most EPSP’s.
GABA
The major inhibitory NT in CNS! most IPSP’s
GABA-a & GABA-c: ↑ Cl- influx
GABA-b: ↑ K+ efflux (Baclofen)
Diazepam (Vallium) binds to GABA receptors and potentiates GABA’s effect
Norepinephrine
Released from post-ganglionic sympathetics, can be inhibitory or excitatory depending on receptor it binds to, Implicated in post-traumatic stress disorder and panic disorders
Dopamine
Involved in motor control (Parkinson’s disease), Associated with feelings of pleasure/reward, Cocaine and amphetamines inhibit re-uptake
Serotonin
Produced by neurons in the brainstem, Low levels associated with depression, anxiety, OCD, Prozac, Paxil & Zoloft decrease its reuptake/removal
Acetylcholine (ACH)
PNS – cause muscle contraction, Botox; ↓ spasticity by impairing vesicle fusion to the membrane (causing muscle to relax)
ANS – released from pre-ganglionic sympathetic and parasympathetic neurons; released from post-ganglionic parasympathetic neurons
CNS – released from neurons at the base of the cortex (these neurons degenerate in Alzheimer’s disease) & from the pedunculopontine nucleus (these neurons degenerate in Parkinson’s disease)
Substance P
Released by sensory neurons transmitting pain
Endorphins and enkephalins
Inhibit neurons involved in perception of pain
Glycine
Prominent inhibitory neurotransmitter in the spinal cord
Where in the brain is Serotonin produced?
The raphe nuclei of the brainstem –> axons from these neurons project to the spinal cord, telencephalon & diencephalon
Where in the brain is Dopamine produced?
the substantia nigra and ventral tegmental area of the midbrain. Axons project to the basal ganglis (motor control), frontal cortex, amygdala, and hippocampus.
G-protein gated ion channel
something binds to a receptor, which causes a messenger to come off and bind to a channel and opens it. More delayed effect.
G-protein gated 2nd messenger complex
Receptor complex, part of it is removed, and that part bonds to enzyme which catalyzes something and starts a chain reaction. Very delayed. Can stimulate protein synthesis.
Myasthenia Gravis
Auto-antibodies to Ach receptors in muscle cell membranes, Ach cant find receptor to bind to, characterized by weakness/fatigue
Signs/sxs:
Weakness of levator palpebrae superioris, EOMs and limb muscles which becomes worse with exercise
Sxs improve with anti-cholinesterase drugs
Increases the [Ach] in the synaptic gap (Endrophonium (tensilon) is an anti-cholinesterase drug that blocks the action of acetylcholinesterase ↑Ach ↓sxs, Neostigmine; a drug that blocks the acetylcholinesterase enzyme and used to treat MG )
Tensilon test - give the drug to see if symptoms improve or not. Sxs would not improve with this test in Eaton-Lambert syndrome
Eaton-Lambert Syndrome (Myasthenic Syndrome)
Auto-antibodies to calcium channels, they are blocked, characterized by weakness/fatigue
In Eaton Lambert there is NO AcH released! Improve with exercise because it stimulate Ach to be released.
More information on slide 58
Botulism�
Botulinum toxin is a protease that cleaves “SNARE” proteins in the vesicles and presynaptic membrane, SNARE proteins direct the vesicle to the membrane, Ach not released
Tetanus toxin
A protease that cleaves “SNARE” proteins in inhibitory interneurons (so the neurons can’t inhibit actions) – results in tetanic contractions
Types of Myasthenia Gravis
I) ocular: Confined mostly to eye muscles
II) generalized: Mostly affects eye, face and proximal limb muscles
III) severe generalized
IV) “crisis”: Affects respiratory muscles
Dorsal Primary Rami
do not merge to form plexi. Motor innervate deep back muscles, sensory innervate joint capsules/ligaments
Ventral Primary Rami
merge to form plexi, but stay segmental in the thoracic region.
Peripheral Nerves
contains thousands of afferent and efferent fibers
Membranes Surrounding Afferent/Efferent Fibers
Axolemma –> myelin – neurilemma –> endoneurium (contains blood vessels that supply O2 and nutrients)
Endoneurium
surrounds individual nerve fibers
Perineurium
surrounds bundles of nerve fibers
Epineurium
surrounds entire nerve
What would result in paresthesias?
compression of any of the peripheral nerves - means abnormal sensory sensations
Skin receptors
Pacinian, Ruffini, free nerve endings, Meissner corpuscles, Merkel’s discs, hair follicles, Krause end bulbs
Joint receptors
Ruffini, Golgi ligament endings, free nerve endings
Muscle Receptors
Muscle spindles, Golgi tendon organs
Superficial sensations (exteroreceptors)
Responsible for pain, temperature, and fine touch.
Deep Receptors (proprioceptors)
Responsible for joint position, kinesthetic awareness, vibration, muscle length and muscle tension, skin movements, deep pressure. (Muscle spindles, Golgi tendon organs, Ruffini corpuscles, Golgi ligament endings, Pacinian corpuscles)
Free nerve endings
Detect pain, touch/tickle/itch, temperature.
The axon reflex: superficial heat stimulates temperature receptors in skin –> a branch of the peripheral process synapses on cutaneous blood vessels –> dilation
Ruffini Endings
detect joint angles at end range, continuous stretch of skin (encapsulated collagen fibers which are interconnected with collagen in dermis)
Hair follicle receptor organs
Combination of hair follicle and nerve fiber, Responsible for superficial touch
Krause End Bulb
Responsible for touch, light pressure and cold temperature sensations
Meissner’s corpuscles
detect moving 2 point discrimination, low frequency vibration (~30)
Pacinian corpuscles
detect pressure, high frequency vibration(~250)
Merkels Discs
detect texture, localized touch (Semmes-Weinstein filament), static 2 point discrimination
What is a receptor field?
An area of skin innervated by a SINGLE afferent neuron, Tend to be smaller distally d/t smaller receptive fields
Babinski Reflex
Stroking along the heel → along the 5th metatarsal → across the metatarsal heads
Skin receptors stimulate motor neurons of S1 that innervate flexor hallucis longus (motor neurons of extensor hallucis longus are inhibited from higher centers)
Oppenheim reflex
Stoking down the medial side of the tibia causes 1st toe extension
Abnormal in adult (suggests UMN disease)
Chaddock Reflex
Stroke along lateral ankle/lateral aspect of foot causes 1st digit extension
Abnormal in adult (suggests UMN disease)
Types of joint receptors (mechanoreceptors)
Type I: Ruffini endings (static end-range position; speed/direction of active/passive movement; continuous stretch)
Type II: Detect sudden movement
Type III: Golgi ligament endings (ligament receptors)
Type IV: Free nerve endings
What is the neuron doctrine?
Ramon y Cajal proposed that the nervous system was made up of individual neurons, was confirmed in the 1950’s with the electron microscope
What is the telencephalon composed of?
cerebral cortex, subcortical white matter, basal ganglion
What is the diencephalon composed of?
thalamus, subthalamus, hypothalamus, epithalamus, metathalamus
What is the brainstem composed of?
midbrain, pons, medulla
