L13 - Neurons Flashcards
what are the functions of the nervous system
Homeostasis!
- Heart, lungs , blood vessels, kidneys, GI, pancreas, liver, skin, muscles
- body fluid composition, nutrient intake, waste removal, movements, sensations, memory, reproduction, thoughts, feelings, emotions, behaviour
describe the organisation of the nervous system
CNS
- brain
- brain stem
- spinal cord
PNS
- peripheral nerves and ganglia
- afferent division - sensory
- efferent division - motor
- somatic
- autonomic nervous system (ANS) - sympathetic, parasympathetic, enteric
describe what nerves are
bundles of many, many axons surrounded by connective tissue in the peripheral nervous system
contains afferent and efferent axons
some myelinated, some not
have lots of blood supply to them
describe the zones in neurons
Input zone (dendrites): receives chemical signals from other neurons
Summation zone: summation of inputs
Conduction zone (axon): axon can be very long, carries electrical signals between neurons or from neuron to effector
Output zone (terminals): contact with other neurons or effectors, release neurotransmitter
what are glia and what are the four different types
Glia are supporting cells/the glue
- astrocytes: supply nutrients, ensheathe capillaries
- ependymal cells: line fluid-filled spaces in brain and spinal cord, produce CSF and have cilia that help move that fluid around the brain
- cells which form myelin: oligodendrocytes (CNS) and Schwann cells (PNS)
- microglia: immune cells of the CNS
describe the different types of synapses (use diagrams from lecture slides)
Electrical:
- very fast
- connexin (subunits) -> connexon (subunits together) -> gap junction (two connexons together)
- ions flow from cell to cell
Chemical:
- slower (but still ms)
- more complex series of events
- synapse strength modifiable
- including neuromuscular junctions
- “nerve agents” - prevent activity of enterases which get rid of the ACh in the cleft once don’t need that signal anymore. leaving ACh there results in decreased breathing rate and then death
Neurotransmitters:
- many different
- some excite, some inhibit
- require specific receptors
describe neural networks
Convergence: many cells to one
Divergence: one cell to many
Networks: complex connections
Information is encoded as changes in membrane potential
- subthreshold = EPSP or IPSP - hyper polarises the cell so harder to reach threshold for APs and get one going
- supra threshold = APs
how is the brain organised?
functions are separated by area (list)
- basal nuclei (3) are important for motor control and learning, relay stations that talk to each other and check information they are getting from motor cortex. checking system o make sure commands will result in successful movement
- then also list what major sections of brain do (look up answers)
describe the major fibre tracts in the brain
information flows between brain regions mainly via bundles of axons, called tracts of fasciculi
- bundles of axons that cross between the two sides of the CNS are commissural tracts eg. corpus callosum
- bundles of axons that connect brain regions on the same side are association tracts eg. superior and inferior longitudinal fasciculi
- bundles of axons that connect cerebrum with other CNA regions are projection tracts eg. corticospinal tract
describe the primary motor cortex
Spatial arrangement:
- mapped at any individual point in time
- somewhat plastic across time
Finer movement = larger area of cortex
Representation of the body (a “homunculus”) in the primary motor cortex
- contains all the neurons that are involved in voluntary control of the body
describe the somatosensory cortex
Spatial arrangement:
- similar to (but not identical to) primary motor cortex with regards to both mapping and plasticity
- information arrived into somatosensory cortex with a specific ‘map’ of the body
Higher receptor density = larger area of the cortex
Homunculus of somatosensory cortex
Describe information flow (look at diagram/draw out diagram from slides)
All information is a combination of synapses and changes in membrane potential
Afferent neurons (into)
- sensory receptor, cell body usually in DRG, transmit information from periphery to CNS
Interneurons
- entirely within the CNS, integrators and modifiers, ~99% if neurons
- integrate information and after a response is selected they will send out information of what do to with efferent neuron
Efferent neurons (out of)
- cell body usually in CNS, transmit information from CNS to periphery
describe the autonomic nervous system (refer to diagram on slides)
Subconscious functions for homeostasis eg. BP, HR, breathing, body temp, GIT activity. so we can continue to operate when environment changes
Modulate organ function based on external stimuli eg. pupil diameter w/ change of light
Influences endocrine system
3 divisions:
- parasympathetic (mostly use ACh), nerves exit from brainstem and sacral region of spinal cord
- sympathetic (mostly use adrenaline), nerves exit from thoracic area of spinal cord (sympathetic chain ganglia)
- enteric
describe ANS neurotransmitters (refer to diagram in slides for visual)
Acetylcholine (ACh) is released at the first synapse outside of the CNS:
- Nicotinic (ion channel) receptors (nAChR) in PSNS, SNS ganglions and in adrenal medulla
- muscarinic (GPCR) receptors (mAChR) at postganglionic synapses
Noradrenaline (NA): receptor expression can lead to opposing responses (eg. alpha vs. beta receptors on blood vessels)
Adrenaline = epinephrine
Noradrenaline = norepinephrine
describe the enteric nervous system (diagram on slides)
“brain of the gut”
- ~500M neurons
- more neurons than spinal cord
Has own pacemaker cells: activity modulated by ANS
Embedded in layers of gut:
- submucosal plexus: sensory and motor neurons, innervates epithelia and muscularis mucosa
- myenteric plexus: chemoreceptors and mechanoreceptors, innervated GO smooth muscle
Controls muscles for propelling and mixing food
Regulates GI hormones
Uses many neurotransmitters
