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(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
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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- Winter '13