the nervous system Flashcards
what are the components of the reflex arc
1) Stimulus
2) Sensor/integrator neuron
3) relay neurones
4) muscle or other effector neurone
5 ) response
what features led to the evolution of centralization and cephalization
centralization= the local concentration of neurones
cephalisation= development of brain like tissues from increasing concentrations of nervous tissues
1) Nerve nets are the most simple nervous system= just a network of cells
2) simple ganglia and nerve rings evolved for more complex behaviour such as in radial symmetric animals like starfish
3) a true CNS evolved with bilateral symmetry= centralisation began with longitudinal nerve cords coordinating nervous activity
4) True brains evolved at the anterior end of complex animals= the anterior end of the CNS was larger and contained sizable clusters of neurones aka the brain
why are complex ganglionic nervous systems characteristic of advances non-verterbrates
how does the expensive tissue hypothesis explain relative brain size
the metabolic cost of neural tissue is comparatively high due to energy needed to maintain the membrane potential across axonal membranes = very energy intensive
therefore the larger the brain the greater energy expenditure
this means animals increased brains size cant be achieved without a increase in quality of diet seen in carnivores and herbivores- carnivores have bigger brains as they have better diets
compare the regulatory systems known as nervous control and hormonal control
Nervous= CNS & PNS, electrochemical signalling, nerve impulses and neurotransmitters, Rapid short term responses, localised effect, target effectors
hormonal= secretory cells, chemical signalling, hormones in blood stream, wide spread effect, many cells
what is a membrane potential
a separated unbalanced charge across the membrane
resting potential in all cells is at -70mv
what causes changes in membrane potenital
triggering events which alter the membrane ion permeability of gated ion channels which are sensitive to changes in voltage and when there is one they open allowing passive movement of ions down conc gradient into the cell
what are the different types of potential
1) Graded = generated from sensory input causing a change in the conductance of the membrane cell and are localised to active areas, they decay very rapidly
2) Action= a result of large and rapid changes in membrane potential when a graded potential reaches threshold (-30mv) causing it to be propagated without decay due to positive feedback mechanisms causing rapid influx of ions
outline how an action potential is generated
1) Resting potential= all channels are closed
2) threshold is met and Na+ channels open resulting in depolarisation and positive feedback
3) rapid influx of Na+ into cell and at peak inactivation gate closes causing K+ channels to open for repolarisation
4) Na+ channels conformation resets
5) hyperpolarisation occurs
6) K+ channels shut returning to resting potential where Na+/K+ ATPase channels restore resting potential
what part of the axon do graded and action potentials occur
Dendrites = only graded potentials can occur but if they reach threshold they trigger action potentials in the axon hillock
axon= automatic conduction of action potential towards axon terminals
What are the different types of synapse
1) Electrical= gap junctions in which transmission jumps to next neurone causing rapid transmission
2) Chemical synapses= use of neurotransmitters allowing different messages to be sent in one direction, occurs more slowly than electrical
what is a refactory period
A refractory period is a period of time during which an excitable membrane is incapable of repeating an action potential. It occurs after an action potential is generated and until the resting potential is re-established
ensures one way flow and limits number of action potentials
outline of a message is sent across chemical synpases
1) Action potential reaches axon terminal of presynaptic neurone
2) Calcium enters synaptic knob causing release of neurotransmitter into synaptic cleft by exocytosis
3) NT binds to receptors on chemically gated channels on subsynaptic membrane of postsynaptic neurone
4) Binding of NT to receptor opens specific channel causing another action potential to be generated
what is the difference between afferent neurons and efferent neurons and interneurons
A = transmits signals from sensory receptors to the CNS
E= transmit information from CNS to effectors
I= transmits information between afferent and efferent neurones
what is the autonomic nervous system
responsible for regulating involuntary physiological processes
