nervous system (theory) Flashcards
CNS
the central nervous system
this is associated with the brain and spinal cord
PNS
the peripheral nervous system
associated with tissues innervated outside of the CNS
ex… upper and lower limbs
CNS breakdown
brain and spinal cord
PNS break down
CNS input and output
the CNS can integrate, process and coordinate sensory input and motor output
the CNS is the seat for intelligence, memory, learning and emotion
CNS sensory input
sensory input travels along the spinothalamic tract (ascending)
sensation –> up the tract –> thalamus –> post central gyrus (parietal lobe)
CNS motor output
motor output travels down the corticospinal tract (descending)
cortex –> pre central gyrus (pre frontal lobe)
pre
front
post
back
PNS function
provide sensory information to the CNS and receive motor commands from the CNS
afferent and efferent signalling
afferent
sending sensory information to the brain
efferent
carries out motor commands
“efferent escapes the CNS”
dorsal horn of the grey matter
receives sensory information from the PNS
ventral and lateral horns of the grey matter
receives motor commands from the CNS
smooth muscle
autonomic control
skeletal muscle
somatic control
PNS cranial nerves
there are 12 cranial nerves
PNS spinal nerves
there are 31 spinal nerves
8x cervical
12x thoracic
5x lumbar
5x sacral
1x coccygeal
afferent breakdown
the PNS can send sensory information from the visceral organs OR the muscles to the CNS
visceral organs = visceral
muscles = somatic
efferent breakdown
the PNS can receive motor commands from the CNS for either skeletal muscle or visceral organ movement
skeletal muscle = somatic nerves
visceral organs = autonomic nerves
visceral
afferent signaling from the PNS to the CNS about visceral organ sensation
monitors smooth muscle, cardiac muscle and other visceral organs
somatic
afferent signaling from the PNS to the CNS about muscle sensation
monitors skeletal muscles and the joints
autonomic nerves
efferent signaling from the CNS to the PNS to affect visceral organs
controls visceral organ activities
somatic nerves
efferent signaling from the CNS to the PNS to affect skeletal muscle
controls skeletal muscle contraction
autonomic nerve subdivision
sympathetic and parasympathetic nerves
the effects of either system often counter act the other
sympathetic nerves
pupil dilation, increase heart rate, relaxes bladder
parasympathetic nerves
pupil constriction, decrease heart rate, tenses bladder
neurons
consists of the soma, axons, and dendrites
these cells transfer electrical signals to target tissue for nervous system to organ tissue coordination
neuroglia
AKA glial cells
these cells form a supporting framework for the neurons and offer protection
the number of neuroglia outnumber the number of actual neurons
there are 4 types of neuroglia in the CNS and 2 types in the PNS
4 neuroglia cells of the CNS
- astrocytes
- microglia
- oligodendrocytes
- ependymal cells
2 neuroglia cells of the PNS
- satellite cells
- schwann cells
Nissl bodies
analogous to the rough ER of the cell
axon hillock
funnels the action potential signaling received by the dendrites before continuing onto the axon
grey matter myelination
no myelination here
white matter myelination
yes, there is myelination
astrocytes
star shaped, axo-axonic cell
- provides structural support
- forms scar tissue after injury
- maintains the CSF
- recycles NTs
oligodendrocytes
- myelinate the CNS’s axons
- provides structural framework
microglia
- act as phagocytes
ependymal cells
- some secrete CSF
- lines the central canal of the spinal cord
- lines the ventricles of the brain
satellite cells
- surrounds the neuron cell bodies in the ganglia
- regulates O2 and CO2
- recycles NTs
- regulates cell body and environment exchange
schwann cells
- myelinates the PNS’s axons
- helps repair damaged PNS axons
BBB
blood brain barrier, maintained by the astrocytes
saltatory conduction
node to node AP conduction
helps increase the speed of the AP down the axon
why can’t we repair a damaged soma
neuron cells lack centrosomes so they can’t reproduce, however damaged axons may be fixed
neuron classification
neurons can be classified by their structure and function
structural classification
- anaxonic
- bipolar
- pseudounipolar
- multipolar
anaxonic
a neuron who’s axons and dendrites can’t be easily distinguished
ex… astrocytes
bipolar
the soma lies between the dendrite and the axon
no myelination of the axon
pseudounipolar
similar to bipolar structure, but the cell body is offset
almost all sensory neurons are pseudounipolar neurons
multipolar
has a single axon + many dendrites
most common CNS neuron type
synapse types
- synapsing with another neuron
- neuromuscular junctions
- neuroglandular synapses
functional classification
- sensory (somatic sensory or visceral sensory)
- motor (somatic nerves or autonomic nerves)
- interneurons
interneurons
connect sensory and motor neurons
they are located within the CNS (grey matter only)
can be excitatory and inhibitory
reflexes like the knee jerk can be done without interneurons (monosynaptic)
receptor types (3x)
- exteroceptors –> external environment
- proprioceptors –> body position and body movement
- interoceptors –> internal organ activity
effectors of skeletal muscle vs effectors of smooth, cardiac, glandular, adipose tissue
efferent neurons on skeletal muscle don’t require ganglia
the latter requires pre and post ganglionic fibers
neural regeneration
the ability to repair a damaged/severed axon is limited
- schwann cells grow in the cut area (forms a cord)
- axon sends buds into the schwann cell network
- axons begin to grow into schwann cells
- hopefully a repaired axon
AP speed of impulse
how fast an AP can be sent down an axon
fast impulses = myelination + large diameter
slow impulses = no myelin + smaller diameter
5 types of vesicle synapses
- axodendritic
- axosomic
- axoaxonic
- neuromuscular
- neuroglandular
nonvesicular synapses
normal vesicular synapses are unidirectional
nonvesicular synapses are electrical synapses due to the flow of ions and can propagate bidirectionally and doesn’t need a synaptic cleft
these are found in the CNS and PNS, but are rare
nonvesicular synapse events:
1. presynaptic and postsynaptic membranes are tightly bound together allowing for the passage of ions
neuron organization (5x)
there are 5 types of neuronal pools
- divergence
- convergence
- serial processing
- parallel processing
- reverberation
divergence
information from one neuron can easily spread to multiple neurons and cover a great distance
ex… sensation received by the special senses going to the brain (vision, smell, hearing)
convergence
information from multiple neurons going to one neuron
ex… voluntary movement of the diaphragm
serial processing
sequential transfer of information from one neuron to the next (a conga line of neurons)
ex… information that needs to hop between different parts of the brain
better ex… smelling food in the kitchen and imagining what that food might be (olfaction to auditory)
parallel processing
the same information that’s being processed at the same time by other neurons
NOT like divergence bc it doesn’t spread exponential
ex… stepping on a nail results in multiple actions that happen at the same time
reverberation
information is sent back to the impulse’s origin via a collateral axon to enhance / continue the impulse
“running it back”
ex… maintaining consciousness when scared
nervous system anatomical organization
- grey matter
- white matter
grey matter
- cell bodies of neurons contained here
- neural cortex (outer layer of the brain)
white matter
bundles on CNS axons arranged in descending and ascending columns
grey-white matter junction
pyramidal cells
contralateral crossing
happens either in the medulla or the spinal cord
sensory information from one side of the body is integrated by the other side
