Question

Differentiate between:

(a) Myelinated and non-myelinated axons

(b) Dendrites and axons

(c) Rods and cones

(d) Thalamus and hypothalamus

(e) Cerebrum and cerebellum

Answer 1

(a) A myelinated neuron is a neuron whose axon is covered by the myelin sheath (myelin means white). The conduction of nerve impulse is faster in this neuron than non-myelinated neuron due to the presence of myelin sheath over the axon. Myelin sheath avoids the loss of impulse during conduction.

Whereas non-myelinated neuron is the neuron whose axon is not covered by the myelin sheath. The conduction of nerve impulse in this neuron is slow than myelinated neuron due to the absence of myelin sheath. There are more chances of loss of impulse during conduction.

(b) Axon is a single long, thick neurite structure in the neuron. It contains neurofibrils. It is the efferent component of the impulse. Whereas dendrites are multiple short and thick neurites in the neuron. It is the branched structure which contains both neurofibrils and Nissl's granules. It is the afferent components of the neurons.

(c) Rods are the photoreceptor cells of the retina that are sensitive to dim light. They have the visual purple pigment called as rhodopsin.

Whereas cones are the photoreceptor cells of the retina that are sensitive to bright light. They have the visual violet pigment called as iodopsin.

(d) Thalamus and hypothalamus are both names of structures in the brain. While the hypothalamus is cone-shaped, the thalamus consists of two connected lobes, one located in each hemisphere. The hypothalamus regulates the body's vital metabolic processes, affecting temperature, blood pressure, hunger, thirst and sleep. It controls the endocrine system by affecting the pituitary gland's production of hormones. The thalamus takes information from a number of different areas of the brain and relays it to the cerebral cortex, the outer layer of gray matter where higher level brain functions take place.

(e) The cerebrum is the part of the forebrain that controls voluntary functions. It is the place where intelligence, will power, memory, etc., reside. It is the largest part of the brain, forming four fifths of its weight. Whereas cerebellum is the part of the hindbrain that controls voluntary functions and controls the equilibrium. It is the second largest part of the brain, forming one eight of its mass.