what are the components of the peripheral nervous system
Cranial nerves (12 pairs)
I. nose, smell – sensory
II. eye, vision – sensory
III. upper eyelid and eyeball, motor
IV. movement of eyeball, motor
V. touch, pain, chewing – sensory/motor
VI. eyeball movement - motor
what is the difference, between afferent nerves and efferent nerves
afferent nerves
- sensory neurones
- impulses from receptors to CNS
efferent nerves
- motor neurones
- impulses from CNS to effectors.
describe the myotatic/ stretch reflex
- Stetch sensed by M - spindles
- Afferent signal to spinal cord
- Sensory neurons transmit signal -> motor neurons, interneurons
- Motor neurons send efferent impulse, to agonist muscle, to contract
Interneurons block motor neurons, signalling antagonist muscle to contract
why do we need myelination
- increase speed of transmission of impulses
- transmit of signal at speed as high as 100m/s
describe a motor unit
describe an action potential
- resting potential - 70mv
- once the firing threshold of -55mv has been reached full firing occurs
- membrane potential - the difference in the amount of charge inside and outside the cell.
describe the resting membrane potential
concentration of ions inside and outside
- extracellular
- NA+ and cl-
cytosol
- K+, organic phosphates (-) and amino acids (-)
membrane permeability
- 50-100 times greater for K+
inward flow of Na+ can’t match the flow of K+
- leak channels
- Na+/K+ pump removes Na+ as fast as it leaks in.
describe the four different transport channels
- Voltage gated channels - opens (transiently) in response to change in the membrane potential.
- Ligand - gated channels - opens (closes) in response to a specific extracellular neurotransmitter.
- Single gate channels - open (close) in repones to specific intracellular molecule.
- Mechanical gated channel (mechanoreceptor) - when the neuron is mechanically deformed, the mechanoreceptor protein changes shape which opens a channel.
describe the process of depolarisation
- occurs when sufficient stimulus, depolarises the cell
- voltage gated sodium channels (Na+) open (-55mv) and sodium floods in
describe the two types of summation and the differences between the two
- spatial summation - summation of effects of neurotransmitters released from several end bulbs, onto one neuron
- temporal summation - summation of effect, of neurotransmitters released from 2 or more in rapid succession.
describe the depolarisation process
- return to resting membrane potential
- Na + channels close
- K+ leaves the cell
- voltaged gate K+ channels (-30mv)
describe the hyperpolarisation process
- delay in closing of voltage gate K+ channels
- membrane potential overshoots, the resting potential of -70mv, to ensure that membrane has been depolarised back to resting potential
what is the refractory period, and its purpose
- the period of time, where polarisation of the membrane is unable to occur
- allows for the excitable membrane, to recover
