Nerves and Synapses Flashcards
how does nervous control compare to hormone action
nervous control is faster, more precise and shorter
hormone is slower but longer lasting
what does nervous control usually involve
receptors (eyes,ear,nose) and effectors (muscles) and an interlinking coordinator
what do receptors respond to
a particular type of stimulus
eg. something we see, hear, touch or smell
what do effectors do
parts of the body that produce the response eg mammalian muscle
what is the CNS
central nervous system which comprises the brain and spinal cord
what are the three types of neurones
motor - carry impulse from CNS to effector
sensory- carry impulse from receptors to CNS
connector/association - connects neurones with CNS
what does axon do
a nerve fibre that transmits impulses away from the cell body
what is the difference between dendron and dendrite
dendrites are very small and numerous extensions that conduct impulses to the dendron
dendron is a part of the fibre carrying impulses to the cell body
what are nodes of ranvier
small gaps along the nerve fibre, in the absence of schwann cells
what organelles does the cell body usually contain
nucleus, mitochondria, RER, golgi, nissls granules etc
what does resting potential mean
at rest the neurone is -70mv inside relative to the outside. the membrane is polarised
what is action potential
when rapid depolarisation occurs, causes a change to +40mv inside relative to outside (the action potential occurs)
define the all or nothing law
the principle that once the threshold stimulus is reached, the action potential results ie. the action potential either occurs or it does not (only occurs above the critical level
what is the threshold stimulus
the level of stimulus a neurone requires before an action potential is produced
how is a nerve impulse propagated
as one part of the membrane becomes depolarised, it sets up local (electrical) circuits with the areas immediately adjacent on each side, +ve ions from the depolarised zone pass along the inside of the membrane towards the polarised zone immediately infront.
similarly on the outside +ve ions move back from the still polarised zone into the depolarised zone
it is these processes occurring that cause a wave of depolarisation that moves rapidly along neurone
similar circuits enable resting potential to be restored directly behind action potential
what factors increase the speed of nerve impulses
-presents of myelin sheath(acts as an insulator, as it prevents depolarisation)
-thicker diameter of axon - thicker the axon faster the impulse( there is proportionally less leakage of ions in a neurone with a larger diameter making it easier to maintain potential gradients
what is saltatory conduction
a term which describes how action potentials ‘jump’ from node of ranvier to node of ranvier
what is a synapse
junction between axon of one neurone and the dendrite of an adjacent neurone
what are neurotransmitters
a chemical which diffuses across the synapse, carrying information
how do they pass into the synapse
through synaptic vesicles
what is an EPSP
an excitatory post-synaptic potential
occurs when positive ions fuse in, making membrane +40 mv, leading to formation of an action potential
why are there many mitochondria in the pre synaptic neurone
-they are important in manufacturing neurotransmitters
-atp produced by mitochondria is required to allow acetylcholines breakdown products to diffuse out and be resynthesised
explain the 4 advantages of synapses
1.enable the continuous nature of nerve communication from neurone to neurone throughout the body
2.ensure unidirectionality - neurotransmitters is ONLY made in the presynaptic neurone and neurotransmitters receptors are only in the post synaptic membrane
3. prevents over stimulation of effectors. too many impulses in a short period will exhaust the supply of neurotransmitters- leading to their fatigue
4. provide integration. synapses provide flexibility without them, nervous activity would be little more than a series of reflexes
what is summation ***
it is important in providing complexity and flexibility that synapses show
eg.
