AFNS Academic Test Biology Nervous system

Good morning, class. Please take your seats. Today, we are exploring the body’s most sophisticated communication network: The Nervous System. For those of you preparing for clinical practice and the AFNS Initial Test, this chapter is foundational. You must understand how the body detects stimuli, processes information, and coordinates lightning-fast responses—often in mere milliseconds—which is significantly faster than the endocrine system’s hormonal responses.

I. Divisions of the Nervous System

The nervous system is divided into two primary sections:

1. Central Nervous System (CNS): Comprising the Brain and Spinal Cord, this is the command center where all integration and processing occur.
2. Peripheral Nervous System (PNS): This includes the cranial nerves (12 pairs) and spinal nerves (31 pairs). It is further subdivided into the Somatic NS (voluntary control of skeletal muscles) and the Autonomic NS (involuntary control of smooth muscle and glands).

The Autonomic Nervous System is particularly important for nursing assessments:

• Sympathetic Division: The ‘Fight or Flight’ system. It increases heart rate, blood pressure, and breathing while releasing adrenaline to prepare for emergencies.
• Parasympathetic Division: The ‘Rest and Digest’ system. It restores the body to normal by slowing the heart rate and stimulating digestion.

II. The Functional Unit: The Neuron

The basic unit of the nervous system is the Neuron. Each of the 100 billion neurons in your brain consists of three main parts:

• Cell Body (Soma): The metabolic center containing the nucleus.
• Dendrites: Short extensions that receive signals and bring impulses TOWARD the cell body.
• Axon: A single long fiber that carries impulses AWAY from the cell body to the next neuron or effector.

Many axons are insulated by a fatty white Myelin sheath, which allows for saltatory conduction—where the impulse “jumps” between gaps called Nodes of Ranvier. This significantly increases the speed of conduction, reaching up to 120 m/s. When myelin is destroyed, as in Multiple Sclerosis, nerve conduction is slowed or blocked.

Types of Neurons to Remember:

• Sensory (Afferent): Carry signals TOWARD the CNS (Arrive = Afferent).
• Motor (Efferent): Carry commands AWAY from the CNS to muscles or glands (Exit = Efferent).
• Interneurons: Located entirely within the CNS, these are the most numerous and act as connectors.

III. The Nerve Impulse and Action Potential

At rest, a neuron maintains a Resting Membrane Potential of −70 mV, meaning the inside is more negative than the outside. This is actively maintained by the Na⁺/K⁺ ATPase pump, which moves 3 Na⁺ out for every 2 K⁺ moved in.

When a stimulus reaches a threshold of −55 mV, an Action Potential is triggered. This is an “All-or-Nothing” event—if the threshold isn’t met, nothing happens; if it is, the pulse fires at full magnitude.

1. Depolarisation: Na⁺ channels open and Na⁺ rushes IN, reversing the potential to +30 mV.
2. Repolarisation: Na⁺ channels close and K⁺ rushes OUT, returning the cell toward its negative state.
3. Hyperpolarisation: Briefly, too much K⁺ leaves, making the cell more negative than resting before the pump restores balance.

IV. The Synapse and Neurotransmitters

The junction between two neurons is the Synapse. Signals travel only one-way across the synaptic cleft via chemical messengers called Neurotransmitters.

• Mechanism: An action potential arrives, causing Ca²⁺ to enter the axon terminal, which triggers the exocytosis of neurotransmitters into the cleft.
• Key Neurotransmitters:
  • Acetylcholine (ACh): Essential for muscle contraction; a deficiency is linked to Alzheimer’s.
  • Dopamine: Controls movement and reward; a deficiency causes Parkinson’s disease.
  • GABA: The main inhibitory neurotransmitter in the CNS; it has a calming effect.
  • Glutamate: The main excitatory neurotransmitter, vital for learning.
  • Endorphins: The body’s natural pain relievers.

V. Brain Structure and Functions

The brain is protected by the skull, the three meninges (Dura, Arachnoid, and Pia mater), and Cerebrospinal Fluid (CSF).

• Forebrain: Includes the Cerebrum (conscious thought) and the Hypothalamus (homeostasis/pituitary control).
• Hindbrain: Includes the Cerebellum (balance and coordination) and the Medulla Oblongata (vital centers for heart rate and breathing).

The Cerebral Cortex Lobes:

1. Frontal: Motor control, personality, and Broca’s area (speech production).
2. Temporal: Hearing and Wernicke’s area (language comprehension).
3. Parietal: Processing touch, pain, and spatial awareness.
4. Occipital: Vision.

⭐ REMEMBER FOR AFNS TEST:

• Medulla oblongata = Vital centers for heart rate and breathing.
• Cerebellum = Balance and coordination (not conscious movement).
• Hypothalamus = Homeostasis and master endocrine control.
• Hippocampus = Formation of long-term memories.

VI. The Spinal Cord and Reflex Arc

The spinal cord acts as both a conduction pathway and a reflex center. It contains 31 pairs of spinal nerves. Remember the Bell-Magendie Law: the Dorsal root is sensory (afferent), while the Ventral root is motor (efferent).

A Reflex is a rapid, automatic response that often bypasses the brain for the initial reaction. A Reflex Arc consists of 5 parts: Receptor → Sensory Neuron → Interneuron → Motor Neuron → Effector. The Knee-jerk (patellar) reflex is unique because it is monosynaptic, meaning it lacks an interneuron.

VII. Neurological Disorders: Nursing Relevance

As nurses, you must recognize these critical pathologies:

• Stroke (CVA): Use the FAST assessment (Face, Arm, Speech, Time). Ischemic strokes may be treated with thrombolytics within 4.5 hours.
• Meningitis: Recognized by the classic triad: severe headache, fever, and nuchal rigidity (neck stiffness). This is a medical emergency.
• Parkinson’s Disease: Characterized by a dopamine deficiency, leading to resting tremors (pill-rolling), rigidity, and bradykinesia.
• Alzheimer’s Disease: Involves an ACh deficiency and damage to the hippocampus, leading to the inability to form new memories.
• Epilepsy: Abnormal electrical discharges. During a seizure, do not restrain the patient; simply protect them from injury.
• Spinal Cord Injury (SCI): Injuries above C4 require a ventilator for breathing. Autonomic dysreflexia is a concern for injuries above T6.

Study these clinical signs and the “AFNS” highlights carefully. Class dismissed.

1. The brain cortex is divided into how many lobes?
2. A) 2
3. B) 3
4. C) 4
5. D) 5

✔ Answer: C) 4

2. The lobe of the brain responsible for vision is the:
3. A) Frontal lobe
4. B) Parietal lobe
5. C) Temporal lobe
6. D) Occipital lobe

✔ Answer: D) Occipital lobe

3. The basic functional unit of the nervous system is the:
4. A) Axon
5. B) Neuron
6. C) Synapse
7. D) Dendrite

✔ Answer: B) Neuron

4. The gap between two neurons is called a:
5. A) Node of Ranvier
6. B) Myelin sheath
7. C) Synapse
8. D) Dendrite

✔ Answer: C) Synapse

5. The part of the neuron that carries impulses TOWARD the cell body is the:
6. A) Axon
7. B) Myelin sheath
8. C) Dendrite
9. D) Terminal button

✔ Answer: C) Dendrite

6. The part of the neuron that carries impulses AWAY from the cell body is the:
7. A) Dendrite
8. B) Axon
9. C) Nucleus
10. D) Synapse

✔ Answer: B) Axon

7. The cerebellum controls:
8. A) Memory
9. B) Balance and coordination
10. C) Breathing only
11. D) Vision

✔ Answer: B) Balance and coordination

8. The frontal lobe of the brain is associated with:
9. A) Vision
10. B) Hearing
11. C) Personality and decision-making
12. D) Smell

✔ Answer: C) Personality and decision-making

9. The parietal lobe processes:
10. A) Vision
11. B) Smell
12. C) Sensory information (touch, pain)
13. D) Language only

✔ Answer: C) Sensory information (touch, pain)

10. The temporal lobe is mainly associated with:
11. A) Touch
12. B) Vision
13. C) Hearing and memory
14. D) Balance

✔ Answer: C) Hearing and memory

11. Which part of the brain regulates body temperature and hunger?
12. A) Cerebellum
13. B) Hypothalamus
14. C) Medulla
15. D) Thalamus

✔ Answer: B) Hypothalamus

12. The medulla oblongata controls:
13. A) Thinking
14. B) Involuntary actions like heartbeat and breathing
15. C) Voluntary movement
16. D) Vision

✔ Answer: B) Involuntary actions like heartbeat and breathing

13. The myelin sheath around a nerve fiber is produced by:
14. A) Neurons
15. B) Schwann cells
16. C) Dendrites
17. D) Axon terminals

✔ Answer: B) Schwann cells

14. The neurotransmitter at the neuromuscular junction is:
15. A) Dopamine
16. B) Serotonin
17. C) Acetylcholine
18. D) Epinephrine

✔ Answer: C) Acetylcholine

15. Reflex actions are controlled by the:
16. A) Brain
17. B) Spinal cord
18. C) Cerebellum
19. D) Hypothalamus

✔ Answer: B) Spinal cord

16. Which nervous system controls “fight or flight” responses?
17. A) Parasympathetic
18. B) Somatic
19. C) Sympathetic
20. D) Enteric

✔ Answer: C) Sympathetic

17. The parasympathetic nervous system promotes:
18. A) Fight or flight
19. B) Rest and digest
20. C) Adrenaline release
21. D) Increased heart rate

✔ Answer: B) Rest and digest

18. The central nervous system consists of:
19. A) Brain and spinal nerves
20. B) Brain and spinal cord
21. C) Spinal cord and peripheral nerves
22. D) All nerves in the body

✔ Answer: B) Brain and spinal cord

19. The largest part of the human brain is the:
20. A) Cerebellum
21. B) Medulla
22. C) Cerebrum
23. D) Hypothalamus

✔ Answer: C) Cerebrum

20. Which of the following is a sensory neuron?
21. A) Motor neuron
22. B) Interneuron
23. C) Afferent neuron
24. D) Efferent neuron

✔ Answer: C) Afferent neuron

21. Nodes of Ranvier are found on:
22. A) Dendrites
23. B) Myelinated axons
24. C) Synapses
25. D) Cell body

✔ Answer: B) Myelinated axons

22. The chemical released into the synapse is called a:
23. A) Hormone
24. B) Enzyme
25. C) Neurotransmitter
26. D) Receptor

✔ Answer: C) Neurotransmitter

23. Multiple sclerosis is caused by damage to the:
24. A) Synapse
25. B) Myelin sheath
26. C) Dendrites
27. D) Axon terminals

✔ Answer: B) Myelin sheath

24. The spinal cord passes through the:
25. A) Cranium
26. B) Vertebral column
27. C) Sternum
28. D) Femur

✔ Answer: B) Vertebral column

25. An action potential is:
26. A) A chemical signal
27. B) A hormonal signal
28. C) An electrical nerve impulse
29. D) A muscular contraction

✔ Answer: C) An electrical nerve impulse