Introduction to Nervous System Flashcards
What are the 2 parts of the CNS?
brain, spinal cord
What constitutes the PNS?
nerves in body, cranial nerves
Divisions of PNS?
Sensory division (somatic and autonomic) (5 senses, pressure sensing in brain, chemoreceptors, thermoreceptors)
Motor division = somatic division (spinal nerve/cranial nerves) or autonomic division (sympathetic - spinal nerves only) and (parasympathetic division - spinal and cranial nerves)
What does the somatic PNS do?
control motor and sensory function for body wall (skin, skeletal muscles)
What does the autonomic PNS do?
aka visceral PNS
regulates function of viscera (internal organs, smooth muscle, pupils, sweating, blood vessels, bladder, intestine, glands, heart contraction)
What is the sympathetic NS?
fight or flight response
increase HR, dilate pupils, increase blood flow to muscles, inhibit digestion
What is the parasympathetic NS?
rest and digest response
can counteract sympathetic (decrease HR, stimulate digestion)
more discrete anatomy largely controlled by cranial nerves
Two directions of impulse flow?
sensory = afferent motor = efferent
EFFERENT = EXIT
What is the importance of afferent/efferent flow?
understand flow of information through brain
E.g. body responds to changing BP by changing vascular tone
baroreceptors in aorta sense pressure in vessel, sends afferent impulse to hypothalamus that sends an efferent motor response
Frontal lobe?
from front of brain to central sulcus
personality/conscious decision making
Parietal lobe?
behind frontal lobe
contains somatosensory cortex
sensory info from somatic PNS comes here
Occipital lobe?
at back of brain
vision
Temporal lobe?
one either side of brain
primary auditory cortex
personality (fear, anxiety, food behaviour at amygdala)
Cerebellum?
fine motor skills
Brain stem?
centres vital for life here
What is the function of cortex folds?
to pack neurones into confines of skull (high SA)
sulcus - valley
gyrus - ridge, folds
Corpus callosum?
fibrous tract that allows communication between two hemispheres of the brain
What are the 12 cranial nerves?
control face and neck
vagus nerve has both afferent and efferent pathways
O O O To Touch And Feel Very Good Velvet Such Heaven
Olfactory I Optic II Oculomotor III Trochlear IV Trigeminal V Abducens VI Facial VII Vestibulocochlear VIII Glossopharyngeal IX Vagus X Accessory XI Hypoglossal XII
What 3 layers protect the brain?
meninges - connective tissue layers to protect and supply of blood vessels dura mater (outer and inner) arachnoid pia mater (superficially to deeply)
What two PNS roots emerge from the spinal cord?
ventral horn - efferent (from spinal cord to body)
dorsal horn - afferent (from peripheries and reflex at spinal cord or to brain)
Where does the CNS end?
at the margins of the spinal cord
How to distinguish between ventral and dorsal root?
dorsal root ganglia (collection of sensory neurone cell bodies)
What is the structure of a nerve?
Spinal nerves contain afferent and efferent axons bundled into fascicles surrounded by perineurium
whole nerve in tough epineurium capsule
individual axons myelinated and wrapped in endoneurium (or if no myelin = nociceptive (pain) )
What is resting membrane potential for neurone?
-70mV
Process of action potential
Release of NT cause depolarisation - influx of Na+
via VCSCs
At +40mV, VGPC open and K+ moves out - repolarisation
Hyperpolarisation - rebalance two ions
Diameter of synaptic cleft
10nm
Synaptic transmission?
Action potential causes release of NT filled vesicles across synaptic cleft
NT bind to receptors on post-synaptic neurone
How to tell if it is a presynaptic neurone?
lots of NT filled vesicles
What other cells are in the brain?
glia cells (50% of all cells in brain) - astrocytes form blood brain barrier, wrap podocytes around blood vessels to form junctions to seal blood brain barrier, mop up NT from synapse, sense chemicals in blood and move to synapse
microglia - phagocytes of brain (immune cells)
oligodendrocytes - myelin producing cells of CNS
What are myelin producing cells of PNS?
Schwann cells
Difference in regenerative capacity between CNS and PNS?
PNS axons can regenerate after injury
- injury stimulates phagocytes to remove debris inhibiting regrowth
- not complete regeneration
CNS axons are limited
- glia inhibit regeneration
- glial scars form in place of injured brain tissue
- absence of guidance cues to stimulate axon growth
How is PNS axon regeneration compromised?
by abnormal axons sprouting and non-specific target reinnervation
this may cause neuropathic pain
First pathway in involved in sensory perception?
What type specifically?
dorsal column/mediated lemniscus pathway
fine touch, vibration, two-point discrimination
How does sensory pathway work for stubbed toe?
- nociceptors in toe enter spinal cord grey matter
- axons of these neurones travel up spinal cord to brainstem (medulla)
- here side of control switches (to contralateral side, not ipsilateral) and second axon sent to thalamus then to primary somatosensory cortex
What is the primary somatosensory cortex?
receives all sensory information from body
What sensory pathway conveys pain and temperature sensation?
spinothalamic pathway
What does damage to dorsal column do?
still feel pain and temp in affected limb if spinothalamic pathway intact
Difference between both pathways?
- dorsal column pathway enters spinal column on same side and switched at brainstem
- spinothalamic pathway immediately goes to other side of body
What is the first motor pathway?
Lateral corticospinal tract
Where do motor pathways originate from?
pre central gyrus (motor cortex) and go down via brain steam and jump to other side and go down spinal column
What is the second motor pathways for orientation and balance?
Vestibulospinal tract
Ipsilateral
If one side of body is working what is likely to be the case?
Damage not to entire somatosensory cortex
What tells if an injury is not peripheral?
if reflex activity intact and arm and leg affected
Why would a injury be unlikely to be spinal cord injury?
only one side affected
