9. 7 The Synapse Synapse junction between two communicating neurons



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9.7 The Synapse


Synapse – junction between two communicating neurons


Nerve pathway – nerve impulse travels from neuron to neuron
Synaptic Transmission

Dendrite  cell body  along axon  synapse (gap)


To complete the signal, a NEUROTRANSMITTER is released at the gap to signal the next neuron
Excitatory – increase membrane permeability, increases chance for threshold to be achieved
Inhibitory – decrease membrane permeability, decrease chance for threshold to be achieved
Types of Neurotransmitters
Acetylcholine – stimulates muscle contraction

Monoamines – Norepinephrine & Dopamine (sense of feeling good, low levels = depression)

Serotonin (sleepiness)

Endorphins (reduce pain, inhibit receptors)



Synapses are highly susceptible to drugs and fatigue

  • Curare (poison used by S. American Indians) and atropine stops Acetylcholine from depolarising the post-synaptic membrane, i.e. become paralysed.

  • Strychnine and some nerve gases inhibit or destroy acetylcholinesterase formation. Prolongs and enhances any stimulus, i.e. leads to convulsions, contraction of muscles upon the slightest stimulus.

  • Cocaine, morphine, alcohol, ether and chloroform anaesthetise nerve fibers. (inhibitory)

  • Mescaline and LSD produce their hallucinatory effect by interfering with nor-adrenaline & serotonin

9.8 Impulse Processing
Neuronal pool – groups of neurons that make hundreds of synaptic connections and work together to perform a common function
9.9 Types of Nerves
Sensory Nerves – conduct impulses into the brain or spinal cord
Motor Nerves – carry impulses to muscles of glands
Mixed Nerves - contain both sensory and motor nerves


9.10 Nerve Pathways
Reflex arc – simple pathway, includes only a few neurons (reflexes)
Reflex Behavior – automatic, subconscious responses to stimulu

Knee-jerk reflex (patellar tendon reflex)


stimulus knee  sensory nerve  spinal cord  motor nerve

Withdrawal reflex – occurs when you touch something painful




9.11 Meninges = membranes located between bone and soft tissues of the nervous system
Dura mater = outmost layer, blood vessels, nerves

Arachnoid mater = no blood vessels, located between



Pia mater = contains many nerves and blood vessels to nourish cells of brain and spinal cord
*Cerebrospinal fluid = between arachnoid and pia maters




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