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Biology · Unit 5

Coordination & Control: MDCAT Notes and MCQs

Receptors — biological transducers

Receptors convert stimulus energy (light, heat, pressure, chemicals) into electrical nerve impulses.

  • Chemoreceptors — taste, smell, blood CO2/pH. Mechanoreceptors — touch, pressure (Pacinian corpuscles), hearing, balance. Thermoreceptors — heat/cold. Photoreceptors — rods & cones. Nociceptors — pain.

Neuron

  • Cell body (cyton): nucleus + Nissl's granules (rough ER/ribosomes). Dendrites carry impulses towards the cell body. Axon carries impulses away.
  • Myelin sheath — formed by Schwann cells (PNS) / oligodendrocytes (CNS); gaps = nodes of Ranvier → saltatory conduction (much faster).
  • Types: sensory (afferent), motor (efferent), interneurons / associative (within CNS).

Nerve impulse

  • A wave of electrochemical change (action potential) travelling along a neuron.
  • Resting membrane potential ≈ −70 mV (inside negative) maintained by the Na+/K+ pump (3 Na+ out, 2 K+ in).
  • Depolarization: Na+ rushes in (to ≈ +50 mV); repolarization: K+ moves out. Follows the "all-or-none" law.
  • At a synapse, neurotransmitters (acetylcholine, adrenaline/noradrenaline) carry the signal across the cleft.

Reflexes

  • Reflex = rapid, automatic, involuntary response. Reflex arc: receptor → sensory neuron → interneuron (in spinal cord/brain) → motor neuron → effector (muscle/gland).
  • Classification: spinal (knee jerk, withdrawal) vs cranial (blinking, pupil reflex); unconditioned/inborn vs conditioned/acquired (Pavlov's dog); monosynaptic (knee jerk) vs polysynaptic.

Brain

PartKey functions
Cerebrum (largest; 2 hemispheres joined by corpus callosum)Intelligence, memory, learning, voluntary movement, speech, sensory perception (cortex lobes: frontal, parietal, temporal, occipital)
ThalamusRelay centre for sensory impulses to cerebrum
HypothalamusBody temperature, hunger, thirst, water balance, controls pituitary
MidbrainVisual and auditory reflexes
PonsBridge; assists breathing regulation
Medulla oblongataBreathing, heart rate, blood pressure, swallowing, coughing, vomiting
CerebellumMuscle coordination, posture, balance

Brain stem = midbrain + pons + medulla oblongata.

PMDC learning outcomes for this unit
  • Receptors: 5.1 Recognize receptors as transducers sensitive to various stimuli.
  • Neurons: 5.2 Explain the structure of a typical neuron (cell body, dendrites, axon and myelin sheath)
  • Neurons: 5.3 Define nerve impulse
  • Neurons: 5.4 Classify reflexes
  • Neurons: 5.5 Briefly explain the functions of components of a reflex arc
  • Brain: 5.6 Discuss the main parts of the brain (e.g. components of brain stem, mid brain, cerebellum, cerebrum)
  • Brain: 5.7 Describe the functions of each part.

Coordination & Control MCQs with answers

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Q1
Receptors are called transducers because they:
AAmplify impulses
BProduce hormones
CStore energy
DConvert stimulus energy into nerve impulses
Show answer
Answer: D (Convert stimulus energy into nerve impulses). Receptors change one form of energy (light, heat, pressure) into electrical impulses.
Q2
Pacinian corpuscles in the skin are sensitive to:
APain
BDeep pressure
CHeat
DCold
Show answer
Answer: B (Deep pressure). Pacinian corpuscles are mechanoreceptors for deep pressure.
Q3
Myelin sheath in peripheral nerves is formed by:
AMicroglia
BAstrocytes
CNissl's granules
DSchwann cells
Show answer
Answer: D (Schwann cells). Schwann cells wrap around axons forming myelin in the PNS.
Q4
Saltatory conduction occurs because of:
ANodes of Ranvier
BDendrites
CSynaptic vesicles
DNissl's granules
Show answer
Answer: A (Nodes of Ranvier). The impulse jumps from node to node in myelinated fibres, making conduction faster.
Q5
The resting membrane potential of a neuron is about:
A−70 mV
B+70 mV
C0 mV
D+30 mV
Show answer
Answer: A (−70 mV). At rest the inside is negative (≈ −70 mV) relative to outside.
Q6
During depolarization of a neuron, which ions move into the axon?
ANa+
BK+
CCa2+ out
DCl−
Show answer
Answer: A (Na+). Opening of Na+ gates lets Na+ rush in, making the inside positive.
Q7
Knee-jerk reflex is an example of:
AVoluntary action
BConditioned reflex
CMonosynaptic spinal reflex
DCranial reflex
Show answer
Answer: C (Monosynaptic spinal reflex). It involves one synapse between sensory and motor neurons in the spinal cord.
Q8
Which part of the brain controls body temperature, hunger and thirst?
AHypothalamus
BMedulla
CThalamus
DCerebellum
Show answer
Answer: A (Hypothalamus). The hypothalamus is the homeostatic control centre and regulates the pituitary.
Q9
Balance and coordination of muscular activity are controlled by:
ACerebellum
BPons
CThalamus
DCerebrum
Show answer
Answer: A (Cerebellum). The cerebellum coordinates movement, posture and balance.
Q10
The brain stem consists of:
AMidbrain, pons, medulla oblongata
BThalamus and medulla
CCerebellum and pons only
DCerebrum, thalamus, hypothalamus
Show answer
Answer: A (Midbrain, pons, medulla oblongata). Brain stem = midbrain + pons + medulla oblongata.
Q11
The centre for breathing and heartbeat is located in:
AThalamus
BCerebrum
CMedulla oblongata
DCerebellum
Show answer
Answer: C (Medulla oblongata). The medulla contains cardiovascular and respiratory centres.
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