nervous system Flashcards
what are the two original theories for the composition of the nervous system ?
. reticular theory - composed of a network of structures
. cell theory - composed of discrete cells
who is camillo golgi ?
stained the CNS tissue and showed many discrete cells, different shapes and sizes
1873
who is ramon y cajal ?
from 1888
use Golgis stain on the CNS and PNS tissues to draw and classify the different cell types and the contacts between them
what is the nervous system composed of ?
the nervous system is made of million of individual cells called neurons
what is the function of the nervous system ?
the nervous system is a way of sending electrical signals very rapidly through out the body
describe the path of a reflex arc ?
1 . stimulus - e.g. change in body PH - stimulus must be converted into electrical signal via the receptor
- receptor - convert stimulus to electrical signals - (transduction ) and then sends electrical signals to the CNS via sensory neuron
- sensory / afferent - PNS - send electrical signals to interneurons
- interneurons- CNS
- motor / efferent - PNS - send electrical signals to effector
- effector - muscle / gland
- response
what is an example of a behaviour controlled by a reflex arc ?
myotatic reflex
what is myotatic reflex ?
muscle contraction in response to stretching within the muscle
what happens in a KNEE JERK REFLEX ?
- stretching a muscle by hitting tendon with a hammer
- this activates a muscle stretch receptor ( the muscle spindle ) and causes nervous activity in a 1 a sensory motor neuron
- the sensory neuron synapses with an alpha motor neuron in the spinal cord which causes muscle to contract and legs to jerk
what are the 3 different types of muscle ?
skeletal - attached to skeleton - striated - forceful - voluntary
cardiac - found in heart - striated - forceful - involuntary
smooth - hollow organs/glands - unstriated - weak - involuntary
where do afferent ( sensory ) neurons carry signals from ?
afferent neurons carry sensory signals from body toCNS
where do efferent motor neurons carry signals from? .
efferent neurons carry signals away from the CNS to the body
what are the two types of efferent motor system ?
. somatic ( voluntary ) - innervates skeletal muscle
. autonomic ( involuntary ) - innervates smooth and cardiac muscle and glands
what are the two types of autonomic efferent motor system ?
. sympathetic - flight , fright and fight
increases respiration and decreases digestion
. parasympathetic - resting and digestion
slows heart rate and respiration
. these 2 subdivisions usually have opposite effects
how many nerves connect CNS to rest of body ?
. 43 pairs of nerves connect the CNS to the rest of body
. 12 pairs of cranial nerves exit the brain
. a further 31 pairs exit at various levels of the spinal cord
what are the two cells of the nervous system ?
- neuron or nerve cell
2. supporting cells ( neuroglia )
what are neurons or nerve cell ?
. number 10^11
. found in adult CNS and PNS
. generate and transmit electrical signals
. have same structure as other cells what makes them unique is their function with it to conduct electricity
what are supporting cells ( neuroglia ) ?
. number 10^12
. supporting roles in nerve cell functions
what is the generalised neuron structure ?
. several dendrites
. a cell body ( soma ) which contains the nucleus
. a long axon
. synaptic region ( axon terminal )
what structure do neurons have ?
. polar structure - information comes in one end and leaves in another
. dendrites to synapses
. a single neuron can receive input from many others
what is the function of dendrites ?
. receive incoming electrical information
. each cell in body is connected to dendrite to form electrical signal
what is the structure of dendrites ?
. their branching increase surface area - this allows them to gather information from neurons coming into them
. spines on dendrites increase surface area
what is axondendritic ?
most input is on to dendrites
incoming neurons connect to dendrites
what is axosomatic ?
incoming neurons connect to the cell body
what is axoaxonic ?
incoming neurons connect to axons
what is the function of cell body ( soma ) ?
sums electrical signals coming from dendrites
what is the structure of cell body ( soma ) ?
contains the usual organelles including prominent nucleus and nucleolus and rough ER ( known nissl substance )
what is the function of axon ?
takes electrical signals away from the cell body
what is the structure of axon ?
. varies in length «1mm to >1m
. usually unbranched but may have collaterals
. the axoplasm is surrounded by a phospholipid bilayer membrane embedded with proteins
. possession of a myelin sheath
. contains microfilaments ( actin ) , microtubules and intermediate filaments
where does axon join the soma ?
join soma at axon hillock ( where signal is generated )
where do axons end ?
ends in synaptic terminals where it contacts other neuron
how do substances move within axon ?
movement of substances via axonal transport and axoplasmic flow
what is axoplasmic flow ?
anterograde transport from cell body to synapse
transport protein to the synaptic region maintain+repair flow
.involves intermediate filaments and is slow(1-5 mm day)
one direction
Slow
involves intermediate filaments
what is axonal transport ?
.anterograde and retrograde
. mediated via microtubules and neurofilaments which are faster(400-2000mm day)
.goes both ways
fast
e.g chemical towards synapse and waste products back from synapse to cell body
where do axons terminate ?
axons terminate in a series of synapses ( axon terminals )
what happens in synapses ( axon terminals ) ?
. this is where electrical signals are transferred to other neurons or muscles
. this usually occurs through release of a chemical neurotransmitter
. neuron has a synaptic region this contains vesicles containing neurotransmitters ,where neurotransmitters are released
what are the types of neural supporting cells in the PNS ?
. over 50% of the cells in the nervous system are neural supporting cells
. schwann cells
. satellite cells
what are the types of neural supporting cells in the CNS ?
. oligodendrocytes
. microglia
. ependymal cells
. astrocytes
what is the function of schwann cells ?
. produce myelin in the PNS that covers most axons in most neurons ( in the process of myelinisation )
. the schwann cell membrane repeatedly wraps itself around an axon
. a single schwann cell provides myelin for only one neuron
. a single neuron receives its myelin from several schwann cells
what is myelin ?
mixture of proteins and phospholipids forming an insulating sheath around neurons ( membrane of schwann cells )
where are the gaps in the myelin sheath formed ?
gaps in the myelin sheath are formed between the bits of myelin provided by individual schwann cells
what are nodes of ranvier ?
this is where the electrical signal is regenerated
what is the structure of small axons ?
small axons remain umyelinated and rather than being wrapped in schwann cell cytoplasm, simply lie in a groove on the surface of such a cell
what are oligodendrocytes ?
. produce myelin in the CNS
. wrap themselves around a neuron
. a single oligodendrocyte provides myelin for several neuron
what is the structure of astrocytes ?
. star-shaped with ‘feet’ covering blood vessel
what is the function of astrocytes ?
. important for blood:brain barrier
. have a role in damage repair ( proliferate and form scar tissue )
. control what comes out of capillary and into neuron
. store nutrients ( glucose )
. isolates synapses
. astrocytes replicate - main source of CNS tumours
what is the function of the ependymal cells ?
. line ventricles of brain and central canal of spinal cord
. involved in secretion of CSF which has protective function
what is the function of microglia ?
. normally dormant but involved in CNS injury / inflammation
. move to damage site
. phagocytose derbis and pathogens
. release cytokines to attract other immune cells e.g. lymphocytes
what are the 4 basic morphological types of nerve cells/neurons?
- anaxonic
- unipolar
- bipolar
- multipolar
what are anaxonic nerve cells ?
no axon
e.g. retinal amacrine cell
what are unipolar nerve cells ?
only one neurite emanating from the cell body
e.g. some sensory neuron
what are bipolar nerve cells ?
one dendritic process and one axon leave the cell body
e.g. retina
what are multipolar nerve cells ?
many neurites emanating from the cell body
e.g. most CNS neurons
what is the organisation of a nerve ?
. never confuse a nerve with a neuron
. a nerve is an organ which is collection of neurons
. it contains both afferent and efferent fibres
. individual fibres are separated by a connective tissue sheath - endoneurium
. the perinurium splits nerves into fascicles
. the epineurium forms an outer coat
what are individual neurons separated by ?
. individual neurons are separated by a connective tissue sheath - endoneurium
what does perinurium split nerves into ?
the perinurium splits nerves into fascicles
what forms the outer coat of a nerve ?
epineurium
