Questions & explanations
1. Which of the following correctly describes the sequence of events in the process of hearing?
- Waves in the fluid cause the basilar membrane to vibrate, bending hair cells against the tectorial membrane, generating nerve impulses transmitted by afferent fibres via the auditory nerve to the auditory cortex.
- Waves in the fluid cause the tectorial membrane to vibrate, bending hair cells against the basilar membrane, generating nerve impulses transmitted by efferent fibres via the auditory nerve to the auditory cortex.
- Waves in the fluid cause the basilar membrane to vibrate, bending hair cells against the tectorial membrane, generating nerve impulses transmitted by afferent fibres via the vestibular nerve to the auditory cortex.
- Waves in the fluid cause the basilar membrane to vibrate, bending hair cells against the tectorial membrane, generating nerve impulses transmitted by afferent fibres via the auditory nerve to the cerebellum.
Answer: Waves in the fluid cause the basilar membrane to vibrate, bending hair cells against the tectorial membrane, generating nerve impulses transmitted by afferent fibres via the auditory nerve to the auditory cortex.
The correct sequence is that fluid waves cause basilar membrane vibration, which bends hair cells against the tectorial membrane. This generates nerve impulses that travel via afferent fibres through the auditory nerve to the auditory cortex. Option B is wrong because the tectorial membrane does not vibrate; it is stationary. Option C is wrong because the nerve is the auditory nerve, not the vestibular nerve. Option D is wrong because impulses go to the auditory cortex, not the cerebellum.
2. Which of the following correctly distinguishes between myelinated and non-myelinated axons?
- Myelinated axons are found only in the brain, while non-myelinated axons are found in spinal nerves.
- Myelinated axons have a myelin sheath formed by Schwann cells, whereas non-myelinated axons lack a myelin sheath.
- Non-myelinated axons conduct impulses faster than myelinated axons.
- Myelinated axons are not surrounded by Schwann cells.
Answer: Myelinated axons have a myelin sheath formed by Schwann cells, whereas non-myelinated axons lack a myelin sheath.
Myelinated nerve fibres are enveloped by Schwann cells that form a myelin sheath, while unmyelinated nerve fibres are enclosed by Schwann cells that do not form a myelin sheath. The other options are incorrect: myelinated axons are found in both spinal and cranial nerves, not just the brain; myelinated axons conduct impulses faster due to saltatory conduction; and myelinated axons are indeed surrounded by Schwann cells that form the myelin sheath.
3. Neurons are considered excitable cells because their membranes are:
- In a depolarised state at rest
- In a polarised state at rest
- Impermeable to all ions
- Always conducting impulses
Answer: In a polarised state at rest
Neurons are excitable because their resting membrane is polarised (negative inside relative to outside), allowing them to generate action potentials in response to stimuli. Depolarisation occurs during an action potential, not at rest. The membrane is selectively permeable, not impermeable to all ions, and neurons do not always conduct impulses.
4. What is the role of Schwann cells in myelinated nerve fibres?
- They form the myelin sheath around the axon.
- They produce neurotransmitters.
- They generate action potentials.
- They remove debris from the synapse.
Answer: They form the myelin sheath around the axon.
Schwann cells wrap around the axon to form the myelin sheath, which insulates the axon and speeds up impulse conduction. The other options are incorrect: neurotransmitters are produced by neurons, action potentials are generated by the axon membrane, and debris removal is primarily done by microglia in the CNS.
5. The autonomic neural system is divided into two main divisions. Which of the following correctly identifies these divisions?
- Somatic and visceral nervous systems
- Sympathetic and parasympathetic nervous systems
- Central and peripheral nervous systems
- Afferent and efferent nervous systems
Answer: Sympathetic and parasympathetic nervous systems
The autonomic neural system is specifically classified into the sympathetic and parasympathetic divisions, which control involuntary functions. The somatic system is voluntary, central/peripheral is a broader classification, and afferent/efferent refer to direction of impulse flow, not autonomic divisions.
6. The gaps between adjacent myelin sheaths on a myelinated axon are called:
- Synaptic clefts
- Nodes of Ranvier
- Axon hillocks
- Schwann cell bodies
Answer: Nodes of Ranvier
Nodes of Ranvier are the unmyelinated gaps between adjacent myelin sheaths where ion exchange occurs, facilitating saltatory conduction. Synaptic clefts are gaps between neurons at synapses, axon hillocks are the initial segments of axons, and Schwann cell bodies are the nucleated parts of Schwann cells.
7. Which of the following is true regarding the axonal membrane at rest?
- It is permeable to negatively charged proteins in the axoplasm.
- It is impermeable to negatively charged proteins in the axoplasm.
- It actively transports proteins out of the axon.
- It allows free diffusion of all intracellular molecules.
Answer: It is impermeable to negatively charged proteins in the axoplasm.
The axonal membrane is impermeable to negatively charged proteins, which remain inside the axon and contribute to the negative resting potential. The membrane does not allow free diffusion of proteins, nor does it actively transport them out; proteins are large and cannot cross the lipid bilayer.
8. During the resting state of a neuron, the axonal membrane is:
- More permeable to sodium ions than to potassium ions
- Equally permeable to sodium and potassium ions
- More permeable to potassium ions and nearly impermeable to sodium ions
- Impermeable to both sodium and potassium ions
Answer: More permeable to potassium ions and nearly impermeable to sodium ions
At rest, the axonal membrane is more permeable to K+ due to leak channels, and nearly impermeable to Na+. This differential permeability establishes the resting membrane potential. The other options are incorrect: Na+ permeability is low at rest, and the membrane is not impermeable to both ions.
9. Which of the following statements about color vision in humans is correct?
- There are three types of cones, each containing a photopigment sensitive to red, green, or blue light, and color perception results from their combined stimulation.
- There are four types of cones, each sensitive to a primary color, and all colors are perceived by equal stimulation of all cones.
- Rods are responsible for color vision and contain three different photopigments.
- Color vision is solely due to the activity of rods, which respond to red, green, and blue light.
Answer: There are three types of cones, each containing a photopigment sensitive to red, green, or blue light, and color perception results from their combined stimulation.
The human retina contains three types of cone cells, each with a specific photopigment that absorbs light maximally at different wavelengths (red, green, blue). Color vision is based on the relative activation of these cones, as described by the trichromatic theory.
10. The afferent neuron in a reflex arc transmits impulses from the sensory organ into the CNS via the:
- Ventral nerve root
- Dorsal nerve root
- Sympathetic ganglion
- White matter of the spinal cord
Answer: Dorsal nerve root
Afferent (sensory) neurons enter the spinal cord through the dorsal nerve root. The ventral root carries efferent (motor) signals. Sympathetic ganglia are part of the autonomic system, and white matter contains tracts but is not the entry point for sensory fibers.
11. Which of the following is a transparent jelly-like substance that fills the space between the lens and the retina?
- Aqueous humour
- Vitreous humour
- Rhodopsin
- Ciliary body
Answer: Vitreous humour
Vitreous humour is a transparent, jelly-like substance that occupies the posterior cavity between the lens and the retina. Aqueous humour is a watery fluid in the anterior chamber, rhodopsin is a pigment in rods, and the ciliary body is a muscular structure.
12. Which of the following best describes the function of the neural system?
- It provides a network of point-to-point connections for quick coordination among organ systems.
- It secretes hormones that regulate long-term changes in the body.
- It filters blood and removes waste products.
- It transports oxygen and nutrients to tissues.
Answer: It provides a network of point-to-point connections for quick coordination among organ systems.
The neural system is specialized for rapid coordination via point-to-point connections, unlike the endocrine system which uses hormones for slower, widespread effects. The other options describe functions of the excretory, circulatory, or endocrine systems.