Animal Science – study notes Revision: Cranial Nerves exercise Withdrawal Reflex Cranial nerves video: Michelle explaining the key concepts and setting out the topic https://youtu.be/-wHfHuaVsMY?fbclid=IwAR07sMDJ-2IYP5-h0ZcYZpNMfUWnLt_o3VnPV0nzRAy5XTTXCSB5Sx7zq8 To aid your understanding of the cranial nerves, structure, function and pathways. Try the following activity: Design a poster or mindmap depicting a diagram of the nerve activity that occurs when a dog stands on a sharp thorn. Add the following labels: afferent [motor] nerve pathway efferent [sensory] nerve pathway dorsal root of spinal nerve ventral root of spinal nerve intercalated neuron Use large labels and bold colours, when it is complete, stick it somewhere you will regularly read it. CRANIAL NERVES PPT MINDMAP MNEMONIC TO REMEMBER THE CRANIAL NERVES: https://youtu.be/6ENCJkXJvio Activity p. 66 in Bowden,2009. What happens? Sensory nerve pathway is stimulated and spinal reflex is initiated, reflex causes stimulation of the motor pathway directly from spinal cord and dog withdraws foot. Meanwhile sensory information reaches the brain and the dog becomes aware of injury. (Bowden, 2009) - - Spinal reflex: Involve the PNS and the spinal cord, the signal does travel to the brain to be processed and to make the animal aware of the injury, the lifting of the foot happens earlier Reflex Arc : fixed involuntary response to certain stimuli pedal reflex Dorsal root: sensory fibres towards the spinal cord Ventral root: motor fibres away from spinal cord Intercalated neuron: neurons that are not motor nor sensory? , also called interneurons, so the signal travels sideways rather than up or down the nervous system, so to speak. Use of more than one synapse – the intercalated neurons transmit the signal to another pathway.. Most generally any neurons which are not motor or sensory. Interneurons may also refer to neurons whose axons remain within a particular brain region as contrasted with projection neurons which have axons projecting to other brain regions. – XMRI.com Kelly Budé 1 Animal Science – study notes - Polysynaptic reflex: eg. Withdrawal reflex Involves one or more intercalated neurons and several synapses within the grey matter. Instructing the antagonist muscle not to restrict the motion? Type Polysynaptic reflex Mechanism 1. Noxious stimulus -> excites the sensory nociceptor 2. Signal travels through a primary sensory neuron -> enters the dorsal horn of the spinal cord 3. The neuron synapses with an interneuron 4. The interneuron synapses with an alpha motor neuron 5. The motor command leaves via the ventral horn -> excites the ipsilateral (same side) flexor muscle group 6. In parallel, motor neurons that supply the ipsilateral extensor compartment receive signals from inhibitory neurons and supply the antagonist muscles -> reciprocal inhibition Table 1: Key facts about the withdrawal reflex https://www.kenhub.com/en/library/anatomy/the-withdrawal-reflex Crossed Extensor reflex on the other side of the spinal cord - separate reflex arc - Polysynaptic - Multisegmented Stabilising the animal by stimulating the opposite leg to extend WITHDRAWL REFLEX : https://youtu.be/RLe9koPfVoo CROSSED EXTENSOR REFLEX: https://youtu.be/iaXVUtS8Y4I WITHDRAWL REFLEX: https://youtu.be/ZuK0LGiDszY Mindmap: Thorn in foot Stimulates somatic receptor cells afferent / sensory nerve pathway dorsal root of spinal nerve grey matter of the spinal cord – Reflex Arc triggered = unconditional, pedal reflex (the signal travels up to the brain (through white matter of the spinal cord) to alert of injury = conscious perception) + synapses with intercalated neuron (interneuron) ventral root of spinal nerve efferent/ motor nerve pathway flexor muscle group excited + extensor muscle group relaxed (reciprocal inhibition) pulls foot away Kelly Budé 2 Animal Science – study notes Kelly Budé 3
