NAS W2 - SOMATIC & SYNAPSE Flashcards
AFFERENT
- sensory - to brain
- carry sensory info from surface of body to the brain
EFFERENT
- motor - to effectors
- convey commands from brain (SNS) to skeletal muscles (lead to contraction)
- has dendrites around the cell body & connects to axon BUT afferent has a naked cell body (no dendrites)
PNS
connects CNS to target organs & connects sensory organs to CNS
INITIATION SEGMENT
where AP is generated
GLIAL CELLS
produce myelin (for myelin sheath - to protect axon)
SNS CHARACTERISTICS
- bi-stable state (always either active or inactive)
- effector organ is skeletal muscle & is responsible for muscle tone of body (tensing)
CRANIAL NERVES
transfer info to/from brain in relation to head & neck
FEATURES/JOB OF DENDRITES OF SOMATIC EFFERENTS
- outside ones are thin & dendrite gets thicker as you get closer to cell body
- increase SA of membrane cell body (for dendrite to receive signal)
DIF. IN INITIATION OF EFFERENT & AFFERENT IMPULSES
efferent - impulses generated in cell body to axons to muscles
afferent - peripheral end of axon creates impulse & passes it to side of axon which is in brain (cell body only used for metabolism & to make nutrients for cell)(not used to initiate any signals in afferent)
HOW TO TELL IF NEURONE IS HEALTHY
if nucleus in centre of body
SOMATIC MOTOR NEURONES
- in ventral horn of spinal cord or cranial nerve motor of brain
- heavily myelinated as very quick impulse transmission
STRIATED MUSCLE
- all fibres travel in one direction & has sarcomere (skeletal & cardiac)
NON-STRIATED MUSCLE
fibres flow in opp. directions (smooth)
DISEASES THAT DEMYELINATE AXON
multiple sclerosis, diabetes, Guillain barre
MYELINATION IN PNS
- 1 schwann cell myelinates each axon (insulated to speed up impulse conduction)
- satellite cells support support the neurones
- microglia used for immune & inflammatory functions
MYELINATION IN CNS
- one single oligodendrocyte myelinates several axons at once
- damage to oligodendrocyte cell way more dangerous than PNS damage as once cell myelinates all axons not one cell per axon
CHROMATOLYSIS
nucleus pushed to side of cell (indicates injured neurone)
MEMBRANE ENVELOPE OF NERVES (IN TO OUT)
ENDONEURIUM - encases a single cells axon
PERINEURIUM - encases nerve fascicle (collection of axons)
EPINEURIUM - encases entire nerve & has interfascicular bands attaching adjacent nerve fascicles (perineuriums)
SPINAL NERVES
transmit info to & from spinal cord in relation to rest of body
PRIMARY SENSORY NEURONES
- cell bodies have no dendrites
- cell bodies appear as ganglia (round clumps)
- detect environment signals & convert them to electrical messages conducted to CNS neurones for processing
NORMAL NEURONES (W/DENDRITES)
- have cell bodies in CNS & involved in receiving signals from other cells via dendrites
AXON STRUCTURE
- has axon hillock (membranes of cell body that lead to axon (start as bulge))
- has initiation segment where AP are initiated
GREY MATTER
- made of cell bodies of NS (more cell bodies = more grey)
TYPES OF GLIAL CELLS
- ependymal - secrete CSF
- astrocytes - link neurones to blood supply
- microglial cell - phagocyte pathogens
- Schwann/oligodendrocyte - myelinate neurones
GAP JUNCTION (ELECTRICAL SYNAPSE)
- fastest & easiest means of communication between cells
- common between glia-neuron or glia-glia
CHEMICAL SYNAPSE
- uni-directional (pre synaptic to post)
- neurotransmitter in vesicles bind with membrane & release neurotransmitter (exocytosis) which diffuses across synaptic cleft & goes to post-synaptic receptors
RAPID TERMINATION OF SIGNAL (FOR EFFICIENCY)
- by enzyme breakdown (enzymes around synapse breakdown neurotransmitter)(AcH esterase hydrolyses AcH into choline + acetate in post-synaptic & choline up-taken by choline carriers in pre-synaptic to form AcH)
- by re-uptake of neurotransmitter (re-uptake proteins reuptake any neurotransmitter back into pre-synaptic to be broken down by enzyme)
IONOTROPIC RECEPTOR
- transmitter binds = structrural change = channel opens = ion movement (fast but slow lasting)
- e.g. Ach nicotinic receptor
- e.g. AP where channel opens & NA+ released
METABOTROPIC RECEPTOR (GPCR)
- transmitter binds = activates G-protein = activates effector = indirect effects on excitability (slower but last long)
- activated GPCR can open/close ion channels or stimulate/inhibit enzymes
- e.g. ACH muscarinic
HOW SYNAPTIC INPUT LOCATION IMPACTS INFLUENCE
Synaptic input closer to cell body/axon hillock = more influence
EPSP
small excitatory post synaptic potential (not big enough for threshold)
SPATIAL SUMMATION
summing of post synaptic potentials generated at separate synapses (many small EPSP = more NA+ influx = reaches threshold)
TEMPORAL SUMMATION
summary of rapid succession of post synaptic potential but from ONE synapse
