Anatomy and Physiology Answer Key

Reflexes page 77 1 higher reasoning is not a

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Unformatted text preview: hdrawal (polysynaptic). A cranial reflex involves integration within the brain stem (e.g. pupil reflex). 3. A monosynaptic reflex arc involves just two neurons and one synapse (e.g. knee jerk reflex) and a polysynaptic reflex arc involves two synapses through a relay or interneuron, e.g. pain withdrawal. 4. (a) Newborn reflexes equip them with the appropriate survival behaviour in their otherwise helpless state: the rooting reflex helps them to locate a nipple, the suckling reflex insures feeding, the startle reflex induces crying, invoking a parental care response, the grasp reflex ensures they keep contact with (usually) the mother. (b) The presence of these reflexes indicates appropriate development. An absence of reflex behaviours in newborns may indicate neural damage or developmental impairment. 5. Cranial reflexes are protective and reduce the risk that the brain or associated sensory structures will be damaged by a sudden stimulus. The Cells of Nervous Tissue (page 75) 1. (a) Any one of: • Motor neurons have many short dendrites and a single (usually long) axon. • In sensory neurons, the branch (process) from the cell body divides into a dendrite and an axon (carries impulses away from the cell body). The axon is usually short. • A sensory neuron has a sense organ at the ‘receptor’ end or it synapses with a sense organ (as in the retina of the eye). In a motor neuron the dendrites receive their stimuli from other neurons. (b) Any one of: Motor neuron transmits impulses from CNS to muscles or glands (effectors) • Relay neuron transmits impulses from sensory to motor neurons. 2. (a) Oligodenrocytes produce insulating myelin sheaths around the axons of neurons in the CNS. They are highly extensible and can wrap around up to 50 axons. (b) Ependymal cells line the ventricles of the brain and the central canal of the spinal cord and circulate and absorb the CSF. They have cilia and microvilli to facilitate this. (c) Microglia have a role in defense of the central nervous tissue. Phagocytic so they can recogn...
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