1st exam Flashcards
Cell body
aka soma
- nucleus
- cytoplasm (watery substance)
nerve cell structure
- cell body
- axon
- dendrites
- synapse
axon
- usually 1
- transmit nerve impulses away from cell
- covered in myelin
- ends in branches with endfeet/endplates/boutons
dendrites
- usually more than 1
- usually short
- transmit nerve impulses toward the cell
- may be covered with projections called spines
synapse
- space between the axon end terminal of one (presynaptic) cell and another (postsynaptic) cell
types of synaptic communication
- electrical - current flows between
- chemical - neurotransmitter
types of synaptic communication
- axodendritic- axon to dendrite
- axosomatic- axon to cell body
- axoaxonic- axon to axon
- neuromuscular junction- nerve to muscle
Action potentials
- way to speed up transmission of info over long distances.
- regenerative (don’t have to continue stimulating, it will go the whole way)
- very brief
- All or Nothing
sequence of events in an action potential
- stimulation of neuron depolarizes membrane potential.
- if depolarization reaches threshold voltage -> action pot. occurs.
- depolarization is very brief
- quick return to resting state
- brief period when cell is unresponsive to stimulation (refractory)
Myelination
- purpose
- increases efficiency
- speeds conduction/traveling
- saltatory propagation - propagates only at nodes of Ranvier
Neurotransmitter synthesis and storage
- aka making and storing of neurotransmitters
- different types are synthesized in different ways
- usually synthesized in axon terminals and packaged in synaptic vesicles
neurotransmitter release and removal
- action potential arrives at axon terminal of presynaptic cell
- stimulates synaptic vesicle fusion with membrane of axon end terminal
- contents of vesicle emptied into synaptic cleft
- neurotransmitter binds with receptor proteins on post-synaptic cell, then unbinds
- neurotransmitter removed from cleft or broken down then product removed
how drugs and toxins affect neurotransmission
- promote release of NT
- prevent release of NT
- mimic action of NT
- stimulate receptors on post-synaptic cells
- block receptors on post-synaptic cells
- prevent removal (reuptake) from synaptic cleft or breakdown of transmitter
Major neurotransmitters
- acetylcholine (ACh)
- GABA
- Serotonin
- glutamate
- dopamine
ACh
- acetylcholine
- excitatory (makes post-synaptic cell create an action potential)
- found at neuromuscular junction, basal ganglia, brainstem
- degraded in synaptic cleft by acetylchonlinesterase (AChE)
- nerve gas blocks AChE -> does not allow breakdown of ACh and muscle is continuously contracted.
Glutamate
- Major excitatory NT
- used by > 50% of CNS cells
- synthesized in terminals
- removed by transport to glial cells, then back to neuron.
- too much (eg occlusive stroke) is toxic (excitotoxicity)
GABA
- Major inhibitory NT
- found throughout the CNS
- synthesized from glutamate in the terminals
- removal by reuptake to glia and presynaptic terminals
- Baclofen is a GABA agonist (mimics the effects of GABA)
Seratonin
- mainly excitatory
- found in brainstem and limbic system
- serotonergenic NT have wide projections to the forebrain
- involved in regulating sleep, mood, and emotional behavior
- removed by reuptake or degraded by MAO
- some antidepressants prevent reuptake
Dopamine
- excitatory
- found in basal ganglia and other brain regions
- involved in movement, motivation, reward, and reinforcement
- removed by reuptake, degraded by MAO, COMT
- reuptake blocked by cocaine
Post-synaptic responses
- excitatory postsynaptic potential (EPSP)
- inhibitory postsynaptic potential (IPSP)
Excitatory Postsynaptic Potential (EPSP)
- depolarizes membrane potential so it exceeds threshold
- postsynaptic cell more likely to fire an action potential
Inhibitory Postsynaptic Potential (IPSP)
- acts to keep the membrane potential more negative then threshold
- cell is less likely to fire an action potential
Components of typical reflex arc
- sensory receptor (afferent arm)- detects stimulus
- interneuron - inbetween two neurons
- motor neuron (efferent arm)- produces muscle contraction, motor response.
interneuron actions
- receives input from afferent
- acts on motor neuron (inhibition, excitation)
- not present in monosynaptic reflex
Deep Reflex
- ex. tap knee -> leg kicks
- sensor is deep to the skin
- stretch (myotatic) reflex
Superficial Reflex
- elicited by scraping of the skin
- example - plantar reflex: scrape bottom of foot -> curl toes in.
descending neurons ________ relexes
modulate
Brainstem LMNs
- somatic motor branches of cranial nerves
- cell bodies in motor nuclei of cranial nerves
- trigeminal nerve (V)
LMN damage
- signs and symptoms
- muscle weakness (paresis)
- Paralysis (all input to a muscle is destroyed)
- muscle atrophy
- fasiculations
- fibrilations
What is a sign
- subjective complaint
what is a symptom
- objective
- measurable
Fasciulations
- LMN damage
- spontaneous contractions of small groups of muscle fibers
- visible
- may or may not be a sign of pathology
fibrillation
- LMN damage
- individual muscle fiber contractions
- sign of pathology
- not visible
- electromyography used for diagnosis
LMN arise from …? where?
spinal cord or brain stem
LMNs innervate what?
- striate muscles of head and body
UMN
- location of cell bodies
- in the cerebral cortex or brainstem
UMN act on …?
act on LMN system (LMN or local circuit neurons)
Functions of brainstem UMNs
- maintain balance
- govern posture
- orient gaze
location of cell bodies in brainstem UMNs
- in vestibular nuclei
- reticular nuclei
- superior colliculus
Cortical UMNs
- cell body location
- cell bodies reside in several cortical regions
cortical UMNs
- pathway
- axons descend in the corona radiata
- then through internal capsule
- then through cerebral peduncle to brainstem and spinal cord
cortical UMN
- function
- plan and initiate complex, voluntary movements
UMNs from primary motor cortex
- portions of the corticospinal and corticobulbar tracts originate here
- cell bodies located in pyramidal cells in layer V.
corticobulbar tract
- axon exit tract in brain stem
- synapse on appropriate cranial nerve nuclei
- innervate ipsilateral and contralateral brainstem LMNs with 2 exceptions (VIIth lower face, only contralateral and XIIth only contralateral)
- terminates in brainstem
Corticospinal tract
- forms medullary pyramids on ventral medulla
- at caudal medulla, most axons (~90%) cross to the opposite side (decussate) -> form lateral corticospinal tract
- remaining ~10% continue to cord.
- Terminates in spinal cord.
most corticospinal axons synapse on __________ __________ _________
- local circuit neurons
a few corticospinal axons synapse ________ onto ________ _______ ________
directly
alpha motor neurons
** direct synapse only for alpha motor neurons innervating muscles of hand and forearm
Cortical UMNs
- premotor cortex
- PMC, BA 6,8, & 44/45
- PMC receives extensive input from parietal cortex (multisensory info), and prefrontal cortex (info regarding motivation and intention)
- some corticospinal (~30%) and corticobulbar neurons originate in PMC
- some PMC neurons project to and influence M1
- PMC neurons involved in selection of movement
Signs and Symptoms of UMN damage
- paralysis or paresis
- spasticity -> too much tension/tone
- hyperreflexia
- clonus -involuntary muscle contraction and relaxation
- Babinski reflex- toes fan when bottom of foot stroked
UMNs originate in the _____ and ______
Brainstem
Cerebral cortex
UMNs influence the actions of _______
LMNs
all cranial nerves are innervated by the ______________ tract
corticobulbar
all spinal nerves are innervated by the _______________ tract
corticospinal tract
Basal Ganglia
- a collection of cell bodies inside CNS
nuclei of the basal ganglia
- corpus striatum -> caudate and putamen
- globus pallidus -> internal segment (GPi) & external segment (GPe)
- substantia nigra -> pars compacta (SNc) & pars reticulata (SNr)
- subthalamic nucleus (STN)
Basal Ganglia circuits
- input
- from all cortical regions except V1, A1
- to corpus striatum (corticostriatal pathways)
- excitatory -> neurotransmitter: glutamate
Basal Ganglia circuits
- output
- inhibitory -> neurotransmitter: GABA
- projects to thalamus
- arises from substantia nigra reticula and globus pallidus
- normal function requires balance between 2 pathways: direct and indirect.
Basal Ganglia Circuit
- output -> direct pathway
- increases cortical activation
Basal Ganglia circuit
- output -> indirect pathway
- decreases cortical activation
