Final! Flashcards
Synaptic relationships between neurons
- Communication of one neuron with another at a synapse
- Also communication with another cell- neuromuscular junction
- One spinal motor neuron can have 10,000 synaptic knobs from other neurons on it
- one cerebellum neuron can have as many as 100,000
Synapses
- can be many synapses on a some- if enough of them “fire” on a soma a local potential
- two types of synapses
- • chemical and electrical
Acetylcholine
- Found in the neuromuscular junctions, most synapses of autonomic nervous system, retina, and many parts of the brain
- Excites skeletal muscles, inhibits cardiac muscle, and has excitatory or inhibitory effects on smooth muscle and glads depending on location
Glutamate (glutamic acid)
Found in cerebral cortex and brainstem;retina
Accounts for about 75% of all excitatory synaptic transmission in the brain; involved in learning and memory
Aspartate (aspartic acid)
Found in spinal cord
Effects similar to those of glutamate
Glycine
Found in inhibitory neurons of the brain, spinal cord, and retina
Most common inhibitory neurotransmitter in spinal cord
GABA
- Found in thalamus, hypothalamus, cerebellum, occipital lobes of cerebrum, and retina
- most common inhibitory neurotransmitter in the brains
Norepinephrine
- Found in sympathetic nervous system, cerebral cortex, hypothalamus, brainstem, cerebellum, and spinal cord
- involved in dreaming, waking, and mood
- excites cardiac muscle
- can excite or inhibit smooth muscle and glands depending on location
Epinephrine
- found in hypothalamus, thalamus, spinal cord, and adrenal medulla
- effects similar to those of norepinephrine
Dopamine
- found in hypothalamus, limbic system, cerebral cortex, and retina
- highly concentrated in substantia nigra of midbrain
- involved in elevation of mood and control of skeletal muscles
Serotonin
- found in hypothalamus, limbic system, cerebellum, retina, and spinal cord
- also secreted by blood platelets and intestinal cells
- involved in sleepiness, alertness, thermoregulation, and mood
Histamine
- found in hypothalamus
- also a potent vasodilator released by mast cells of connective tissue and basophils of the blood
Substance P
Found in basal nuclei, midbrain, hypothalamus, cerebral cortex, small intestines, and pain-receptor neurons
Mediates pain transmission
Enkephalins
- found in hypothalamus, limbic system, pituitary, pain pathways of spinal cord, and nerve endings of digestive tract
- acts as analgesics (pain-relieved) by inhibiting substance P
- inhibit intestinal mortals
- secretion increases sharply in women in labor
Beta endorphins
- found in digestive tract, spinal cord, and many parts of the brain
- also secreted as a hormone by the pituitary
- suppresses pain
- reduces perception of fatigue and many produce “runner’s high” in athletes
Cholecystokinin
Found in cerebral cortex and small intestines
Suppresses appetite
An exciting cholinergic synapse
Cholinergic
Postsynaptic potential
An inhibitory GABA-ergic synapse
GABA
Works the same as stimulators cholinergic synapses
But- this GABA receptor is a Cl- channel
-inhibits the neuron
An andrenergic Synapse
Enzyme amplification
Source of norepinephrine can be in the synapse or bloodstream
Cessation of the signal
Diffusion- neurotransmitter diffuses away, astrocytes pick it up and return it to the neurons
Reuptake- synaptic knob reabsorbs neurotransmitter and break them down with monoamine oxidase, MAOI (monoamine oxidase inhibitors are powerful antidepressants)
Degradation in the synaptic cleft- acetylcholinesterase (for example),reabsorbed by synaptic knob
Neural integration
This is where “though@, memory and all the good stuff related to processing come in to play
Most neurons have many input axons articulating with it
This network of nerves and synapses is what we are going to talk about
Postsynaptic potentials
Can be exciting or inhibitory
Increase/decrease the rate at which a neuron fires because neurons all depolarize are a certain background rate
Summation, facilitation and inhibition
EPSPs and IPSPs reach a postsynaptic neuron and depending on the balance the neuron fires-this is how we process
Summation- adding up PSPs giving a net effect in the trigger zone
- temporal summation- EPSPs are generated at a high rate, there is no time for the signal to decay between signals
- spatial summation- EPSPs from several synapses add up to the threshold at the hillock
Facilitation and presynaptic inhibition
Facilitation- where more than one neuron cooperates to stimulate the postsynaptic neuron
Presynaptic inhibition- when on neuron inhibits and counteracts the effects of other neurons
Memory and synaptic plasticity
Memory is not individual cells it is a pathways called a memory trace (engram)
- pre-existing pathways are modified in response to experience (synaptic plasticity)
- takes 1-2 hours
- when you learn something you form and reform a pathway until it gets easier and more efficient- called synaptic potentiation
Immediate, short, and long-term memory
Immediate memory
You need to be able to hold on to some thoughts to be able to function
- example reading- you have to remember the earlier words in the sentence to function
Seems to be based on reverberating circuits
-keeps it active long enough to use it later
Short-term memory
Lasts for a few second to a few hours
Easy to forget things in STM
- probably carried out mainly by reverberating circuits
- longer-lasting memories seem to be made by making a neuron hyper-sensitive by stimulating it over and over- it fires more easily and stronger
-• you try hard to program something in, and it is “jogged” very easily and comes back strong
Long-term memory
Declarative - having to do with language Procedural - retention of motor skills Physical remodeling of synapses Experienced synapses get easier and easier to remodel and better and better at what they remember the more you use the information
The spinal cord functions
Conduction - sensory info to the brain - motor commands reach the effectors Routing of input around the cord Locomotion - simple repetitive muscle contractions, like in walking, are controlled from the spinal cord -• central pattern generators Reflexes - involuntary responses to certain stimuli that are always the same
Anatomy
Cord and 31 ours of spinal nerves
C, T, L, and S regions
Cervical enlargement- where nerves of upper limbs originate
Lumbar enlargement- where nerves of the pelvic region and lower limbs originate
Medullary cone-> cauda equina
Spinal cord meninges
Meninges- three fibrous membrane layers that cover brain and spinal cord
Separation and protection
Spina bifida
When one or more vertebrae fail to form a complete vertebral arch
Meninges and even parts of the spinal cord can exist outside of the spinal canal
This is why women should take folic acid during the earliest part of pregnancy
Cross-sectional anatomy
Gray matter- proximal parts of axons and neurons- little myelin - dorsal horns -ventral horns - gray commissure -central canal - lateral horn White matter- bundles of axon (tracts)- lots of myelin - columns, funiculi -tracts, fasciculi
Spinal tracts
White matter- bundles of axons
Ascending and descending
Each had different functions
Important for understanding spinal cord injuries
Poliomyelitis and amyotrophic lateral sclerosis
Motor neurons
Polio- nerves of the brainstem and central horn of the spinal cord
- anything from paralysis to cessation of breathing (a brainstem function)
ALS= Lou Gehrig disease- degeneration of motor neurons and sclerosis of lateral portions of the spinal cord
- astrocytes fail to reabsorb glutamate (it becomes toxic)
-sensory and intellectual functions remain
Afferent fibers
Carry sensory signals from receptors to the CNS
Efferent fibers
Carry motor signals from the CNS to effectors
Somatic fibers
Inner age skin, skeletal muscles, bones, and joints
Visceral fibers
Inner are widespread organs such as muscles, skin, glands, viscera, and blood vessels