nerves Flashcards
outline the role of sensory receptors in mammals in converting different forms of energy into nerve impulses
A sensory receptor is a cell in which a change in the internal or external environment produces nerve impulse or action potential. some receptors are scattered in appropriate body tissues- e.g. sin or the lining of airways. or concentrated in eyes or ears.
why are receptors called biological transducers
because one form of energy, the stimulus energy, to converted into another form- always electrical.
receptors in mammals adapted to respond to different aspects of the environment such as:?
light intensity and wavelength sound touch and pressure temperature chemicals
describe with the aid of diagrams, the structure and functions of sensory neurones
sensory neurones:
- long processes on either side of the side body
- a process, the dendron, carrying nerve impulses towards the cell body from a receptor
- an axon carrying nerve impulses away from the cell body, this time to the central nervous system
describe with the aid of diagrams the struture and function of motor neurones
- a cell body (centron) with a large nucleus and large quantities of rough ER and golgi bodies
- many short dendrites that carry nerve impulses toward the cell body
- a very long axon that carries impulses away from the cell body to an effector
relay neurones
- many shorter processes around their cell bodies
- carry impulses from sensory neurones to motor neurones
what are schwann cells
axons with mylineated sheaths
what are the gaps between individual schwann cells called?
the nodes of ranvier
what’s the purpose of the mylinated sheath
helps to speed up the transmission of a nerve impulse from about 4ms-1 to 100ms-1
describe and explain how resting potential is established and maintained
- when not conducting a nerve impulse, there’s a potential difference across the plasma membrane, such that the inside has a negative charge of -70 mV compared to the outside
- sodium-potassium pumps in the plasma membrane actively transprt K+ ion into the cell and Na+ out
- three Na+ ions are actively transported out for every 2 K+ ions in
- the axon contains organic anion to which the membrane is impermeable
- this, and a slight loss of K+ ions through the permeable membrane, accounts for the resting potential
- the membrane is effectively impermeable to Na+
descrive and explain how an action potential is generated
when the membrane is depolarised and the PD across the membrane reaches about -40 mV (the threshold to fire) the voltage gated sodium ion channel proteinsin the memrbane suddenly open (example of positive feedback)
Na+ are in high conc outside the cell and low inside cell, so Na+ flood into the cell making it positive with respect to the outside and changing the PD to +40 mV inside the cell.
the sodium ion channels now close. Voltage gated potassium ion channels open and potassium ions diffuse out of the cell. the PD becomes negative inside the cell again, falling to about -75 to -90 mV. the membrane is hyper polarised.
more of the potassium ion channels close, and the sodium potassium pump restores resting potential.
this sequence of events is an action potential. transmission of an action potential along an axon forms a nerve impulse.
descrive and explain how action potential is transmitted in a myelinated neurone, with ref to roles of voltage-gated sodium ion and potassium ion channels
the action potential travels along the plasma membrane. caused by the movement of sodium ions, both indside and outside the axon, towards a negatively charged region.
this intern begins to depolarise the membrane ahead of the action potential. when the depolarisation reaches the threshold to fire, the sodium channels open, giving an action potential.
when the membrane is hyper polarised, depolarisation will not reach the threshold to fire, the sodium channels open, giving an action potential.
