general Flashcards
what are the functions of the nervous system?
communication
regulating internal events (very well defined events compared to endocrine)
organising behaviours (external)
information storage (memory: pre-empt neuronal cell to do a certain response as all neuronal cells can preform all roles and accept signals from anywhere in the body)
sensations, perceptions & emotions
neurons
excitable cells
generation and transmission of signals
synaptic processing e.g. memory etc
various types - structure related to function
glia cells
more numerous than neurons
supportive, nutritive role - very specialised cells
types: astrocytes microglia ependymal cells oligodendrocytes Schwann cells
afferents
neurons going towards the CNS (arrival)
not all sensorial afferents will reach the brain - action can occur before (reflex)
efferents
neurons going away from CNS (exit)
somatic neurons
transmit information between the skin or skeletal muscle to CNS
viceral neurons
transmit information between the internal organs to the CNS
e.g. visceral efferent response is a change in HR
2 sub-organisations of the nervous system
central nervous system CNS
peripheral nervous system PNS
CNS subdivisons
spinal nerves
cranial nerves
how many spinal nerves are there?
31 pairs emerge along the length of the spinal cord
8 Cervical 12 Thoracic 5 Lumbar 5 Sacral 1 Coccygeal
what fibres are in the spinal nerves?
can contain sensory and/or motor axons
what do spinal nerves supply?
structures in a well defined part of the body and innervate sensorial response
sensory neurons - dermatomes
motor neurons - myotomes (muscle blocks)
run in parallel to each other
how can dermatomes and myotomes be used to check for damage to spinal cord?
as spinal nerves innervate specific regions
can check for no or hyper response
spinal nerve ventral root
anterior of cord
spinal nerve dorsal root
posterior of cord
how many cranial nerves are there?
12 pairs of cranial nerves connect to the brain (esp. brainstem)
what do cranial nerves do? (generally)
supple sensory and motor to the head & neck structures
what does the peripheral nervous system do?
carries information to and away from the CNS
what are the 2 types of peripheral nerves?
afferent nerves (sensory) efferent nerves (motor)
What is the role of afferent nerves?
carry sensory information to CNS from periphery
somatic or visceral signals
what do somatic afferent signals give rise to?
give rise to sensation and perceptions
what do visceral afferent signals give rise to?
not usually sensations
related to internal unconscious activity instead
What is the role of efferent nerves?
carry motor information away from CNS
cause actions e.g. muscle contractions
what do somatic efferent nerves control?
voluntary muscle contractions
what do visceral efferent motor nerves make up?
the Autonomic Nervous System
- control smooth and cardiac muscle
endoneurium
coats individual nerve fibres coated in myelin
perineurium
coats fasciculi of nerve fibres
fasciculi of nerve fibres
bundles of nerve fibres
epineurium
coats large bundles of nerve fasciculi
also contains fat, lymph, arteries and veins
what influences local anaesthetic action on nerves?
other structures in the epinerium bundle (e.g. fat, lymph spaces) - affects how it dilutes onto nerve
3 points to remember for local anaesthetic application
want local anaesthetic in sensorial nerves not motor nerves
want local anaesthetic to be present as short a time possible - pain revealed in absence can show complication unaware of at appointment
least volume of chemical injected - in case of side effects
what are nerve plexuses?
nerves grouped together for part and branch off at other parts (sensorial and motor responses)
if tracts of nerves get too close together for too large an area can cause confused or no response as clash signal
what is anastomosis?
overlap of innervation
i.e. dermatome overlap
what do variations in neuronal structure allow?
basic neuronal structure can be altered to perform different functions
e.g. cell body shifted
(primary sensory neuron has cell body relatively far away from dendrites)
basic components of a neuron
dendrites
cell body
axon
(myelin sheath)
what effects propagation of action potential?
diameter of axon
degree of myelination
role and characteristics of A-beta fibre
largest diameter
myelinated
sensory neurones only
mechanorecptors in skin
role and characteristics of A-alpha fibre
smaller diameter than A-beta
myelinated
sensory and motor neurons
proprioceptors of skeletal muscle
role and characteristics of A-gamma fibre
myelinated
special form of motor neuron
role and characteristics of A-delta fibre
myelinated
sensory neurons only
pain, temperature
role and characteristics of C fibre
smallest diameter
unmyelinated
sensory neurons and some autonomic nerves e.g. pulp
pain, temperature, itch
paradoxical effect
body will induce a compensatory paradoxical effect to try and reverse single control effect only sympathetic autonomic nervous system innervated organs
unexpected but natural response
somatic nervous system (SNS) - motor divison role
carries information to somatic effectors - skeletal muscles
somatic nervous system (SNS) - sensory divison role
carries feedback information to somatic integration centres in the CNS
autonomic nervous system (ANS) - efferent division role
carries information to the autonomic or visceral effectors
- smooth or cardiac muscle, glands, adipose and other tissues
role of sympathetic division of ANS
prepares the body to deal with the immediate threats to the internal environment
flight/fight/fright
role of parasympathetic division of ANS
coordinate the body normal resting activities
rest and repair
what are neurons?
wiring that connects structures need for homeostasis
what are sensory neurons role?
receptors that detect changes in external and internal environments
responsible for responding to more than just stimuli
capable of learning, memory, thought generation etc
what are neurotransmitters in the bloodstream?
hormones e.g. adrenaline
what are the functional regions of neurons?
INPUT ZONE - dendrites and cell body
SUMMATION ZONE- axon hillock
CONDUCTION ZONE - axon
OUTPUT ZONE - synaptic knobs of axon
how are neurons classified?
by number of processes extending from cell body
mutipolar neurons
one axon many dendrites
bipolar neuron
one axon and one dendrite
least common
unipolar/pseudounipolar neuron
one process comes off neuron cell body but divides almost immediately into 2 fibres
what are functional classifications of neurons?
AFFERENT SENSORY NEURONS
conduct impulses to spinal cord or brainstem
EFFERENT MOTOR NEURONS
conduct impulses away from spinal cord or brainstem towards muscles or glandular tissue
INTERNEUONS
reflex only
what is a reflex arc?
a single conduction route to and from the CNS with electrical signal beginning in receptors and ending in effectors
3 neurons arc most common
- afferent neuron, interneuron, effent neuron
what are bundles on nerve fibres called in the CNS?
tracts
rather than nerves
what is endoneurium composed of?
delicate layer of connective tissue
surrounds each nerve fibre
what is perineurium composed of?
connective tissue holding fascicles together
what is epineurium composed of?
fibrous coat surrounding numerous fascicles and blood vessels to form a complete nerve
white matter in the CNS is composed of
myelinated tracts
white matter in the PNS is composed of
myelinated nerves
grey matter is composed of
cell bodies and unmyelinated fibres
CNS - nuclei
PNS - ganglia
can mature nerve fibres divide?
NO, mature nerve fibres are uncapable of cell divison
damage can be permanent for nerve tissue
if not extensive damage (cell body & neurilemma are intact and scarring not occurred) nerve fibre can be repaired
what are local potentials?
slight shift away from the RMP in a specific region of the plasma membrane
graded potentials as the maginitude o deviation from the RMP is proportional to the stimulus
what is excitation?
when stimulus triggers the opening of additional sodium channels
allowing the membrane potentials to move towards 0
depolarisation
upstroke
what is inhibition?
when stimulus triggers the opening of additional potassium channels
increasing the membrane potential
hyperpolarisation
downstroke
what is a synapse?
where nerve signals are transmitted from one neuron to another
what are the 2 types of synapse?
electrical
chemical
what are electrical synapse?
occur where cells joined by gap junction
allow AP to simply continue along along postsynaptic membrane
what are chemical synapses?
located at the junction of a synaptic knob one neuron and the dendrites/cell of another
occurs when presynaptic cells release a chemical neurotransmitter across a tiny gap to postsynaptic cells
possibly inducing AP there
synaptic knob
tiny bulge at the end of terminal branch of the presynaptic neuron axon that contain vesicles housing neurotransmitters
synaptic cleft
spaces between the presynaptic knob and the plasma membrane of the postsynaptic neuron
plasma membrane of postsynaptic neuron
has protein molecules that serve as receptors for the neurotransmitters
when bind either cause:
excitatory postsynaptic potential (EPSP)
inhibitory postsynaptic patents (IPSP)
how is neurotransmitter action terminated?
quickly
neurotransmitter molecules transported back into synaptic knob (reuptake)
and/or metabolised into inactive compounds by enzymes
and/or diffused and taken up by nearby glia
spatial summation
adding together effects of the several knobs being activated simultaneously and stimulating different locations of the postsynaptic membrane
produce AP
temporal summation
synaptic knobs stimulate a postsynaptic neuron in rapid succession
effects summate over a brief time period
produce AP
how are memories stored?
by facilitating (or inhibiting) synaptic transmission
short term memories (secs/mins) may result from the axoaxonic facilitation /inhibition of presynaptic terminal
long term memory (mins/weeks) happens when serotonin backs potassium channels in presynaptic terminal
- prolonging AP
- increasing amount of neurotransmitter released
requires structural changes to synapse (more vesicles, release sites etc)
how are neurotransmitters classified by function?
by postsynaptic receptor
also if receptors directly open a channel or instead use a second messenger mechanism involving G protein and intracellular signals
what are the 2 major functional classification of neurotransmitter?
excitatory neurotransmitters
inhibitory neurotransmitters
how are neurotransmitters classified by chemical structure?
mechanism by which neurotransmitters cause a change
4 main classes
usually neurotransmitter are classified by chemical structure since the function of specific neurotransmitters varies by location
3 types of small molecule neurotransmitters
acetylcholine ACh
amines
amino acids
acetylcholine
small molecule neurotransmitter
ACh
unique chemical structure
deactivated by acetylcholinesterase
present at many locations
either excitatory or inhibitory
amines
small molecule neurotransmitter
2 categories:
- monoamines
- catecholemaines
found in various regions of the brain
amino acids
small molecule neurotransmitters
one of the most common in CNS
in PNS stored in synaptic vesicles
neuropeptides
large molecule neurotransmitter
made of 2 or more amino acids
-neutrophins:
nerve growth factors
stimulate neuron development but act as neuromodulators
nervous system cells Cycle of Life
nerve tissue development begins in ectoderm
nerve cells organise into body network
formation of new synapse and stretching or elimination of old synapse stimulation learning and memory
age causes degeneration of the nervous system which may lead to senility
