neural communication

• dendrons- transmit impulses towards cell body

  axons- transmit impulses away from cell body
• sensory neurones

  • one dendron
  • one axon
  • sensory receptor- relay neurone
• relay neurone

  • many short axons
  • many short dendrons
  • sensory neurone- motor neurone
• motor neurones

  • one axon
  • many dendrites
  • relay neurone- effector
• myelinated neurone

  • shwann cells produce myelin sheath layers by growing around the axon many times
  • conduct electrical impulses faster than unmyelinated neurones as impulse jumps from node to node
• generator potential- stimulus converted to nerve impulse
• pacinian corpuscle

  • the neurone ending in a pacinian corpuscle has a specialised sodium ion channels called stretch mediated sodium ion channels
• creating a generator potential

  1. the pacinian corpuscle has resting potential. stretch mediated sodium ion channels are too narrow to allow sodium ions to pass through them
  2. when pressure is applied, the corpuscle changes shape, causing the membrane surrounding the neurone to stretch
  3. sodium ion channels widen and sodium ions can diffuse into the neurone
  4. influx of sodium ions depolarises the membrane creating a generator potential
  5. generator potential creates an action potential
• creating a resting potential

  1. 3NA+ transported out the axon and 2K+actively transported into the axon
  2. more charged ions outside the axon causes a resting potential of -70mV
• creating an action potential

  1. resting potential, some K+ channels are open and NA+ channels are closed
  2. stimulus triggers NA+ channels open and NA+ diffuse into axon down electromagnetic gradient
  3. more NA+ channels open so more NA+ diffuse into axon (positive feedback)
  4. when potential difference reaches +40mV, NA+ channels close and K+ channels open
  5. K+ diffuse out the axon down down electromagnetic gradient
  6. too many K+ diffuse out of axon (hyperpolarisation). K+ channels close, NA-K pump causes NA+ to move out and K+ in so the axon is repolarised
• all or nothing law

  • if the threshold is reached, an action potential will be generated
• synapse

  -the junction between two neurones
• excitatory neurotransmitter

  • action potential triggered
  • results in depolarisation of postsynaptic neurone
  • acetylcholine
• inhibitory neurotransmitter

  • prevents action potential
  • results in depolarisation of postsynaptic neurone
  • GABBA
• transmission across cholingeric synapse (1)

  1. action potential reaches end of presynaptic neurone
  2. calcium ion channels open and calcium enters the synaptic knob
  3. synaptic vesicles fuse with presynaptic membrane, releasing acetylcholine into the synaptic cleft
  4. acetylcholine molecules fuse with receptor sites on the postsynaptic neurone
  5. this causes sodium ion channels to open allowing sodium ions to diffuse into the postsynaptic neurone
  6. this generates an action potential in the postsynaptic neurone
• transmission across cholingeric synapse (2)

  7. acetylcholinsterase hydrolyses acetylcholine into acetyl and choline

  8. these diffuse back across the synaptic cleft into presynaptic neurone (recycling)

  9. breakdown of acetylcholine prevents it from continuously genrating a new action potential in the post synaptic neurone

  10.ATP released by mitochondria is used to recombine acetyl and choline. This is stored in synaptic vesicles for future use

  11. sodium ion channels close in the absence of acetyl and choline in receptor sites
• spatial summation

  • a number of presynaptic neurones connect to one postsynaptic neurone
  • each releases neurotransmitter which builds to a high enough level to trigger an action potential
• temporal summation

  • single presynaptic neurone releases neurotransmitter several times over a short period of time
  • builds up in the synapse until the quantity is sufficient to trigger an action potential
• reflex arc

  1. stimulus
  2. receptor
  3. sensory neurone
  4. relay neurone
  5. motor neurone
  6. effector
  7. response
• peripheral nervous system- consists of neurones
• central nervous system- consists of brain and spinal cord
• somatic nervous system- conscious control, when you decide to do something
• autonomic nervous system- works constantly under subconscious control (no decisions made)
• sympathetic nervous system- increases activity
• parasympathetic nervous system- decreases activity
• cerebrum

  • controls voluntary actions and conscious thought
  • split into cerebral hemispheres
  • outer layer called cerebral cortex
• medulla oblongata

  • used in autonomic control
  • heart rate
  • breathing rate
• hypothalamus

  • regulatory center for water balance and temperature
  • produces hormone (ADH)
• cerebellum

  • controls unconcious functions and non voluntary movement
  • body posture/balance
• pituitary gland

  • stores and releases hormones
  • anterior pituitary- FSH
  • posterior pituitary- ADH
• knee jerk reflex

  1. stimulus causes extensor muscle on top of the thigh to contract
  2. simultaneously a relay neurone inhibits the motor neurone of the flexor muscle causing it to relax
  3. this causes the leg to kick
• blinking reflex

  1. sensory neurone carries impulse from cornea
  2. impulse passes through relay neurone in the lower brain stem
  3. motor neurone carries impulses to facial muscles
  4. causes eyelids to blink
• survival importance of reflexes

  • involuntary responses
  • not learnt
  • extremely fast
  • maintain everyday actions
• blinking reflex

  • can be overidden
  • cranial reflex
  • sensory-relay-motor
  • prevents damage from foreign bodies
• knee jerk reflex

  • cant be overidden
  • spinal reflex
  • sensory-motor
  • maintain posture-balance
• actin- thinner filament
• myosin- thicker filament
• I bands- no overlap
• A bands- overlap
• sacromere- distance between Z lines